The Dawn and Dusk of the Age of Mammals

In Beasts Before Us, paleontologist, Elsa Panciroli, traces the evolutionary history of the mammal class of the animal kingdom, of which humans are members, to its origins about 300 million years ago.  It’s a tedious recitation of multitudes of now extinct species from their earliest ancestors up to the dawn of the age of mammals that began 66 million years ago after the abrupt end of the age of dinosaurs. But it’s also a rewarding read because it reminds us of our close relationships with other animals as well as the ways in which we are different.  Those differences predict which mammals will survive the forthcoming sixth great extinction that humans have inflicted on life on Earth.

Mammals living today have in common only one characteristic that distinguishes them from other classes of close relatives.  The subdivisions of mammals alive today have mammary glands that produce milk to feed their young.  The three subdivisions of mammals are monotremes, marsupials, and placentals.  Monotreme species alive today are platypus and echidna whose young are hatched from eggs, but are milk fed by their mothers.  Marsupials are born at an undeveloped stage and carried to term in their mothers’ pouch.  By far the largest group, placentals carry their developing offspring inside the mothers’ abdomen until birth. 

The earliest ancestors of mammals were four-legged vertebrates called amniotes. Amniotes were named for the membrane that lined the hard shells of their eggs, protecting the embryo.  The development of the amniotic membrane provided protection needed to lay and hatch eggs on land rather than the ocean where earlier forms of life lived.  This evolutionary development was associated with the transition of life from the ocean to the land.  The earliest amniotes diverged to take two different evolutionary paths, one as reptiles and dinosaurs (sauropsids) and the other as mammals (synapsids).  Pause here briefly to contemplate our close relationships with other animals. 

The Science of Paleontology

Beasts Before Us is also interesting as a history of paleontology, the branch of science that studies fossils of plants and animals to determine the evolutionary history of life.  Beasts focuses on advances in modern paleontology, but this article takes readers further back in time to appreciate how recently we learned about the scale of past extinctions that predict future extinctions.

Prior to the 19th century, an understanding of extinction was inconsistent with prevailing Western belief that the world was created by God as complete, perfect, and unchangeable.  In the late 17th century fossils of extinct animals were discovered that appeared to be unlike any living species.  Inquiring minds began the search for an explanation for what happened to these unknown species. 

George Cuvier is credited with establishing the modern concept of extinction in a lecture to the French Institute in 1796.  Cuvier is sometimes called the “founding father of paleontology.”  He rejected the theories of evolution, believing instead that extinctions could be explained by “cyclical creations” and catastrophic natural events such as floods. 

The fossil record is limited in what it can tell us about life in deep time because it does not preserve the remains of extinct species with equal reliability.  Bones survive to tell the tale with greater accuracy than soft tissues and plants.  Paleontology is developing techniques to compensate for gaps in the fossil record, drawing from other scientific disciplines, such as botany, biochemistry, mathematics, and engineering. 

Since more than 99% of all species that ever lived on Earth—more than five billion species–are now extinct, we can only imagine the difficulty of the task of piecing together the complete phylogenetic tree of life.  Beasts Before Us gives us a current view of what has been accomplished to date.  Clearly it is not the end of the story and much of the story is still speculative. 

Divergent Evolution

The 300-million year journey from the first ancestors of mammals to modern mammals of today is a story of divergent evolution, the accumulation of differences between closely related populations within species that lead to new species. Tracing that long process was until recently dependent upon the fossil record and was therefore focused on changes in bone structure, particularly teeth, jaws, and skulls for which the fossil record is more intact. 

Evolutionary tree of mammals. Wikimedia Commons

These bone structures are important clues about the diet of animals. The teeth of herbivores, insectivores, and carnivores are different.  “Mammal fossils can be distinguished and named based on their teeth alone.” (1) Nearly half of all mammal species are rodents, a name that comes from the Latin word for gnaw.  Their long front teeth grow continuously as they are ground down by gnawing on tough plant material such as tree bark in the case of beavers or the wooden shingles on my home in the case of squirrels.

The digestive systems of mammals also diverged to accommodate their different diets (or vice versa).  Carnivores typically have a short intestinal track where digestion is accomplished with enzymes and resident microbial communities.  Herbivores have a longer digestive system in which plant material is fermented in a series of separate chambers in the case of ruminants (cows, sheep, deer, etc.). 

Divergent evolution creates diverse species with diverse abilities to exploit different ecological niches while reducing competition between species.  Shortly after the divergence of mammal and reptile lineages, the characteristic most consequential to the fate of those lineages was endothermy (warm-bloodedness) in mammals and ectothermy (cold-bloodedness) in reptiles. The divergence of this characteristic occurred about 250 million years ago, shortly after the divergence of mammal and reptile lineages. 

Only mammals and birds are generally capable of generating their body heat internally.  Over millions of years they also evolved insulation that conserves body heat with fur, feathers, and blubber in the case of marine mammals. A diet high in sugar and fat also helps to maintain body heat. Cold blooded animals depend on external heat sources such as sunlight to be active.  These crucial differences in mammals and reptiles relegate them to different ecological niches to which they are suited, for example:

  • Mammals and birds can survive in colder climates than reptiles.
  • Mammals and birds can be more active at night when it is cooler.
  • Mammals and birds can be more active for longer periods of time than reptiles.
  • Mammals and birds can live below ground where it is colder in summer and warmer in winter than above-ground temperatures.
  • On the other hand, mammals and birds must eat more and more frequently than reptiles. 

These significant differences are partly responsible for the sudden transition from the age of dinosaurs to the age of mammals 66 million years ago.  During the age of dinosaurs, mammals were small, lived below ground, and ate primarily insects.  This lifestyle avoided competition with huge dinosaurs that dominated the land. 

Scale diagram comparing a human and the largest-known dinosaurs of five major clades Creative Commons Attribution-Share Alike 4.0 International license.

When the asteroid hit the Earth 66 million years ago, the climate was suddenly and drastically transformed from a tropical climate to a cool, partly sunless climate.  Vegetation adapted to a tropical climate quickly died, depriving dinosaurs of their food if they weren’t killed outright by the impact. 

Beasts paints a vivid and dire picture of the cataclysmic event that ended the age of dinosaurs.  The asteroid created a crater almost 100 miles in diameter and 12 miles deep.  “An earthquake larger than any recorded in human history would have made the Earth reverberate like a bell.  The thermal shockwave would have flash-fried all life for hundreds of miles.  The blast of air probably flattened forests as much as 1,000 kilometers away…[the impact] created a mega-tsunami at least 330 feet in height…[that] mounted the coasts of North American and barreled inland like a liquid steam-roller…The dust in the atmosphere swirled its way around the planet until it enclosed all life in its smothering grip.  The sun rose, but as little as half of its light could penetrate the dust in the atmosphere.  The sulphur in the dust combined with water droplets to rain sulphuric acid on the land, burning away the green vegetation…Few animals bigger than a Labrador dog survived the extinction event.”  (1; not verbatim)

The fifth extinction predicts the consequences of the sixth extinction

Small mammals were safely below ground and they didn’t require the great quantities of plant food required by dinosaurs.  Mammals inherited the Earth and over millions of years they evolved into some 5,500 mammal species today of which 90% are still small bodied, most of them rodents.

The final chapter of Beasts uses the consequences of the fifth extinction that ended the age of dinosaurs to predict the consequences of the anticipated sixth extinction because “Humans are replicating many of the conditions of previous mass extinctions.” (1)

  • Animals are likely to become more active at night, when temperatures are cooler.
  • Animals are likely to find some respite by living below ground where temperatures are more moderate in winter and summer. 
  • Animals will move to more temperate regions if they can.

The animals that are most likely to survive will be small generalists, who need less food, are not fussy about what they eat, and are more capable of tolerating heat. Think rats. Beasts advises, “If I were you, I’d say goodbye to any wild animal bigger than a pig—zoos are likely to be the only refuges for them in the future we are creating.”

Birds were the only descendants of dinosaurs to survive the fifth great extinction.  They are expected to fare better in the sixth extinction for much the same reason:  they can be active at night; they eat insects as well as plants; they are more mobile than most classes of animals.  We often hear dire predictions of the fate of birds, but in fact they are less threatened than other classes of animals.  A recent study reported that 21% of reptiles are threatened with extinction, a higher risk than birds (of which about 13 percent of species are threatened with extinction) and slightly less than mammals (25 percent). Amphibian species are at highest risk with about 40 percent of species in danger of extinction.  We hear more about birds because their popularity motivates greater media coverage about them.

I will also presume to give my readers some advice. 

  • Quibbling about whether native plants are superior to non-native plants is like arguing about the color of the lifeboat. It really doesn’t matter.  Soon enough we will be glad to have ANY vegetation that is capable of living in the climate we have created. The universe is indifferent to the survival of any specific species of life.
  • You can do more for the environment and the animals that live in it by stopping the use of pesticides than by planting native plants. 
  • Be humble about what you think you know.  Many important scientific concepts such as evolution and extinction are less than 200 years old and the cause of the extinction of dinosaurs was discovered less than 50 years ago.  What you learned 50 years ago may need to be reconsidered and revised.  A rapidly changing situation requires that we keep an open mind to new information.
  • Set meaningful prioritiesClimate change is an existential threat to all life on Earth.  Ask yourself how we can justify the destruction of healthy trees that sequester the carbon that contributes to climate change? 

  1. Elsa Panciroli, Beasts Before Us: The Untold Story of Mammal Origins and Evolution, Bloomsbury Sigma, 2021

History of Earth predicts its future

My interest in the native plant movement began about 25 years ago when my neighborhood park was designated as a “natural area” by San Francisco’s Recreation and Park Department.  My park was only one of 33 parks in San Francisco that were designated as a “natural area.” 

What did it mean to be a “natural area?”  As I studied the plans, my reaction was primarily to the proposed destruction of non-native plants and trees.  Later I realized that the eradication of non-native plants and trees would be accomplished with herbicides. 

Stern Grove Park in San Francisco was my neighborhood park where I began my long journey to understand why anyone would want to destroy trees in a treeless neighborhood. 

How could the creation of native plant gardens justify the destruction of our urban forest using herbicides?  I have spent the last 25 years trying to answer that question.  There are many useful lines of inquiry in the search for the answer, but the approach that has been most helpful to my understanding of the futility of the undertaking has been the study of the physical and biological forces that created Earth and its inhabitants.  Today, I will take you on an abbreviated journey of the past 4.6 billion years of events on Earth that have resulted in present-day nature, drawing from A Brief History of Earth by Andrew Knoll, Professor of Natural History at Harvard University. (1)

Gravity “created” the Earth

“Gravity is the architect of our universe.”  Gravity is the attraction of objects to one another in proportion to their mass and proximity that over billions of years accumulated the elements dispersed in Earth’s universe.  As these dispersed objects coalesced into stars, planets, moons, and asteroids, Earth was formed about 4.6 billion years ago.

Cross-section of Earth. Source: USGS

“Earth is a rocky ball.”  Its inner core is solid, composed mostly of iron.  Earth’s molten outer core moves by convection as hotter, denser material near the base rises and cooler, less dense matter toward the top sinks.  This circular motion generates electrical current that creates the Earth’s magnetic field.  The mantle is composed of the molten magma that emerges on the surface crust of Earth where tectonic plates are separating and when volcanoes erupt where tectonic plates submerge into the mantle. The crust of Earth that is visible to us is only 1% of Earth’s mass.

Physical Earth

Simplified map of Earth’s principal tectonic plates, which were mapped in the second half of the 20th century (red arrows indicate direction of movement at plate boundaries).  Source:  USGS

The crust of Earth is composed of plates that are moved on the surface of the Earth by the convection current of the mantle.  Some of the plates are moving away from one another where they meet.  As the plates separate, molten magma from the mantle is pushed through the crust, forming new crust.  The North American and Eurasian plates are moving apart in the middle of the Atlantic Ocean at the rate of about 1 inch per year. 

Since the Earth is not getting bigger, the expanding crust collides with adjacent plates.  In some places, the collision of the plates pushes up the crust into mountain ranges.  The Himalayan mountain range is the result of the collision of the Indo-Australian and the Eurasian Plates, a process that continues today.

Map of subducted slabs, contoured by depth, for most active subduction zones around the globe. Source:  USGS

In other places, the expanding crust is pushed below the adjacent plate in subduction zones, where the crust dives below the crust into the mantle.  Earthquakes are common in subduction zones and the subducting plate triggers volcanic eruptions in the overriding plate.  Earthquakes are also common where adjacent plates are grinding against one another in opposite directions, as is the case on the coast of California.

Pangea super-continent

The movement of tectonic plates has assembled and reassembled the Earth’s continents many times. The entire history of the configuration of continents is not known to us because of the cycle of the crust emerging from the mantle only to return to the mantle about 180 million years later.  We know that all continents were fused into a single continent, named Pangea, about 350 million years ago and began to break up 200 million years ago.  Much of life as we know it evolved on Earth while the continents were fused, which is one of the reasons why all life on Earth is related.  Geographic isolation of species results in more biodiversity as genetic drift and different environments result in greater speciation.  Geologists believe such continental mergers are likely in the distant future.  

Earth’s oceans and atmosphere were formed within the first 100 million years of its birth.  Continents were visible above oceans, but small compared to their present size.  The absence of oxygen in the air at that early stage was the most significant difference between present and early Earth.

Biological Earth

Life, as presently defined, requires growth and reproduction, metabolism, and evolution. (I say, “presently defined” because debate continues about defining viruses as life since they do not meet all criteria.)  The chemical components required to perform the functions of life and the natural processes to combine them (such as heat and lightning) were available on Earth for millions of years before they combined to perform the functions of life.  Precisely how and when that happened on Earth is studied intensely, but not conclusively known, although Professor Knoll describes theoretical possibilities. 

The geological record suggests that “Earth has been a biological planet for most of its long history.” Microbes may have been living on Earth 4 billion years ago.  Climate on Earth was warm at that time for the same reason the climate is warming today.  The atmosphere was composed primarily of carbon dioxide (the greenhouse gas that traps heat on the surface of the Earth) and nitrogen:  “…life emerged on an Earth barely recognizable to the modern eye—lots of water and not much land, lots of carbon dioxide but little or no oxygen…”

Oxygen Earth

Phylogenetic tree of life based on Carl Woese et al. rRNA analysis. The vertical line at bottom represents the last universal common ancestor.

Two of the three domains of life were capable of living without oxygen:  archaea and bacteria.  Archaea are single-cells without nuclei.  We are all too familiar with bacteria, as they are as much a part of our bodies as our own cells.  Oxygen was the prerequisite for the evolution of the third domain of life, eukarya.  The kingdoms of eukarya most familiar to us are plants, animals, and fungi. 

Oxygen arrived on Earth when early life forms evolved the ability to photosynthesize, the process by which plants (and some other organisms) use sunlight to synthesize food from carbon dioxide and water, generating oxygen as a byproduct.  This transition occurred about 2.4 billion years ago, as measured by the absence of iron on the seafloor after that time. 

Photosynthesis alone could not have accomplished the transformation of Earth’s atmosphere to the balance of carbon dioxide and oxygen needed to support complex life on our planet because photosynthesis also requires nutrients as well as sunlight and water.  Phosphorous weathers from rocks, a process that was initially limited by the small amount of land above sea level.  As the planet matured, more land emerged from the sea, making more phosphorous available to photosynthesizing organisms.  Photosynthesis was also enhanced when some bacteria and archaea evolved the ability to convert nitrogen gas into biologically usable molecules, a process called nitrogen-fixing.  Many plants in the legume family are capable of nitrogen-fixing today.

Extinctions of the past predict extinctions of the future

There have been five major extinction events in the past 500 million years that changed the course of evolution of life on Earth and at least 20 mass extinctions in total (2).  The first representatives of all modern animal phyla (a taxonomic classification between kingdom and class) evolved during the Cambrian Period (541-486 million years ago).  All extinction events were associated with radical changes in the climate.  Many of the changes in the climate were caused by changes in the balance of carbon dioxide and oxygen in the atmosphere.  All these catastrophic events were natural events, not caused by the activities of humans because they all occurred long before the advent of human evolution. 

The third and biggest extinction event occurred 252 million years ago at the end of the Permian geologic period, when more than 90% of marine animals and 70% of terrestrial species disappeared.  At that time, continents were fused into the single supercontinent of Pangea.  The extinction of most life on Earth was caused by the sudden and catastrophic change in the atmosphere–and therefore the climate–by an episode of volcanism in Siberia “a million times greater than any volcanism ever witnessed by humans” or our primate ancestors.  Gases emitted by volcanism at the end of the Permian period rapidly increased the carbon dioxide content of the atmosphere and oceans by several times greater than before that event.  “It would take 10 million years for life to reassemble into something approaching the complexity of the ecosystems that preceded it. The world that emerged from the volcanic dust was unlike anything that came before.” (2) The current increase of carbon dioxide in the atmosphere caused by the burning of fossil fuels by human activities is comparable to this event and is expected to cause the sixth great extinction on Earth.  

The fifth and most recent massive extinction event occurred 66 million years ago, bringing 170 million years of dinosaur evolution to an abrupt end. The entire environment of the planet was radically and suddenly altered by the impact of an asteroid 7 miles in diameter that landed on what is now the Yucatan peninsula in Mexico.  The impact engulfed Earth in a dust cloud that precipitated the equivalent of a nuclear winterkilling most vegetation and animals adapted to a much warmer climate.  As with all massive extinctions, it took millions of years for plants and animals to slowly evolve adaptations to the new environment.  Dinosaurs did not evolve again, a reminder that evolution does not necessarily repeat itself (although birds evolved from dinosaurs).  Although there were small mammals during the dinosaur age, the disappearance of dinosaurs and corresponding changes in the climate introduced the age of mammals, including the human lineage about 300,000 years ago.  When multiple animal groups disappear it creates opportunities by reducing competition between groups.

What can we learn from the history of Earth?

If a native plant advocate were reading this abbreviated history of Earth, these are the lessons I would hope they might learn from it:


  1. Andrew H. Knoll, A Brief History of Earth, 2021.  All quotes in this article are from this excellent book unless otherwise indicated.
  2. Elsa Panciroli, Beasts Before Us: The Untold Story of Mammal Origins and Evolution, Bloomsbury Sigma, 2021.

Weeds are making a comeback!

While the native plant movement remains strong in California and locally in the San Francisco Bay Area, some communities are waking up to the fact that weeds make valuable contributions to our gardens and the wildlife that lives in them.  The British have always been ahead of us in welcoming plants from all over the world in their gardens.  The British have been enthusiastic importers of plants from all over the world for hundreds of years.  They had one of the biggest empires in the world, spanning the globe from India to Africa, Australia, New Zealand, and America, which put them in a unique position to sample the botanical riches of the world.

The English garden, where plants from all over the world are welcome

In a recent article in The Guardian, an English gardener describes her journey from fighting the weeds in her garden to her new relationship with them:  “I remember writing, many years ago, about my fight to get rid of these dandelions. Clearly, I didn’t win. Now, when I am greeted by them, I am glad I lost the battle. These days, I truly consider them friends…they are welcome in my garden, because I know they do more good than harm.”

The English gardener reminds us that the war on weeds began only recently.  Going deep into agricultural history, weeds were natural forage that were a part of our diet. Weeds fed our domesticated animals, stuffed our mattresses and made twine and rope. Many have medicinal properties, but most have marketable substitutes now. They were tolerated on the edges of agricultural fields and in our gardens.

The typical American lawn, maintained with pesticides and fertilizer is not habitat for pollinators or other insects. Source: Pristine Lawn Care Plus

The war on weeds began after World War II, when chemicals were introduced to agriculture.  Pesticides were considered benign for decades.  We have learned only recently of the dangers of some pesticides. The promotion of pesticides changed the aesthetics of gardening, initiating an era in which weeds were banished from our agricultural fields and our gardens.  

Note the drone hovering over the children in a strawberry field. Drones are the latest development in chemical warfare. They are used to spot non-native plants in open space as well as to aerial spray pesticides. They are cheaper than other methods of application and for that reason are likely to increase the use of pesticides.

Do not underestimate the power of propaganda to promote the use of pesticides:  “A publishing company linked to the most powerful agricultural lobby group in the U.S. is releasing children’s books extolling the benefits of pesticides and nitrogen fertilizers.”  Industrial agriculture begins the indoctrination of the public at childhood. 

Bumblebee in clover. Source: buzzaboutbees.net

Weeds made their way back into our gardens partly by evolving resistance to the pesticides we used for decades to kill them.  There is growing awareness of the impact of pesticides on insects and wildlife.  As populations of pollinators decline, we are more willing to indulge their preference for weeds such as dandelions and clover.  Weeds are often the first to arrive in the spring garden, as native bees are emerging from their winter hibernation in ground nests.  Weeds prolong the blooming season in our gardens, providing nectar and pollen before cultivated plants are blooming. 

“No Mow May” comes to America!

“No Mow May” originated in Britain out of concern for declining populations of bees.  Communities make a commitment to stop mowing their lawns in May to let the weeds dominate their lawns.  Weeds such as dandelions and clover give the bees an early boost in the spring that studies show increases bee populations.  Lawns maintained with pesticides and fertilizers provide poor habitat for bees. 

Two professors in the Midwest of the US introduced “No Mow May” to their community in Wisconsin in 2020.  They signed up 435 residences to participate in “No Mow May” and studied the impact:  “They found that No Mow May lawns had five times the number of bees and three times the bee species than did mown parks. Armed with this information, they asked other communities to participate.”  According to the New York Times, “By 2021, a dozen communities across Wisconsin had adopted No Mow May. It also spread to communities in Iowa, Minnesota, Illinois and Montana.”

Farmers climb on board

Hedgerows are the backbone of the English countryside.  They are a complex bramble of woody and herbaceous plants that traditionally served as fences, separating roads from agricultural fields and confining domesticated animals.  They nearly disappeared when industrial agriculture dictated that fields be cultivated from edge to edge. They are making a comeback in the English countryside as farmers realize that their loss contributed to the loss of wildlife.  The concept of hedgerows as vital habitat is slowly making its way to America.

US Department of Agriculture reports improvements in agricultural practices in the past 10 years:  more no-till farming that reduces fossil fuel use and carbon loss from the soil; more efficient irrigation methods; broader field borders for pollinators and wildlife; more crop rotations that reduce disease and insect pests; reduction of nitrogen and phosphorous run-off; reduction in diesel fuel use, etc.  These are all well-known methods of reducing environmental damage from industrial agriculture, but there is now evidence that farmers are actually adopting them. 

Nativists are late to the game

We see progress being made to reduce pesticide use and provide more diverse habitat for wildlife, but nativists drag their feet.  They continue to use pesticide to eradicate non-native plants and they deny the value of non-native plants to insects and wildlife, despite overwhelming evidence to the contrary. 

In a recent comment posted on Conservation Sense and Nonsense, a nativist explains the justification for using herbicides to eradicate non-native plants:  “No one likes herbicides, but in the absence of a labor force willing to abandon its modern conveniences to do very hard work, they are important tools in restoration ecology, and methods are improving as a result of careful science to determine how the least amount of them could be used to gain the greatest amount of benefits to the maximum amount of species. Throwing those tools away is about like tossing chemotherapy or vaccinations because of that “all-or-nothing” black or white point of view that native plant supporters are being (unjustly) accused of.”

For nativists, the harm done by non-native plants is greater than the harm done by pesticides.  This equation does not take into consideration the benefits of many non-native plants to wildlife and it underestimates the damage caused by pesticides to the environment and its inhabitants.   

Argentine Ants: An “invasion” that wasn’t

Bay Nature article about Argentine ants

Bay Nature published an article about Argentine ants with an alarming title and disturbing accusations, such as:

  • “…from its home range around the Paraná River region in Northern Argentina, this ant has spread to six continents and numerous islands, including Hawaii. In numbers, it is probably the most successful invasive nonhuman creature in California.”  
  • “Argentine ants have been documented aggressively going after other, bigger species of ants.”
  • “…most native ants cannot resist well and are wiped out by the Argentine ants.”
  • When native ants are displaced, it can disrupt whole ecosystems and reduce the diversity of other arthropods in the region.”

After establishing the Argentine ant’s credentials as a dangerous “invasive species,” the article abruptly changes directions by contradicting itself.  According to a 30-year monitoring survey of Argentine ant populations at the 1,200 acre Jasper Ridge Biological Reserve, “…the ants had, counter to expectations, actually retreated from some areas they had occupied in previous years at Jasper Ridge…”  Early survey data showed the Argentine ants spreading rapidly in the preserve.  They reached a stable distribution around 2001, and have since declined. 

The monitoring survey at Jasper Ridge speculates that the decline in Argentine ant populations was caused by drought.  However, that theory is not consistent with similar declines in Argentine ant populations elsewhere, where and when there was no drought. 

Jasper Ridge is just one of many places that have reported declining populations of Argentine ants over many years.  In 2011, Scientists in New Zealand reported the disappearance of the Argentine ant from 40% of sites they populated in the past and their populations have shrunk significantly where they are still found.  Native ants have “reinvaded” the areas vacated by the Argentine ant.  The scientists reporting this finding “concluded the species naturally collapses after 10 to 20 years.”

In an unpublished communication in 2011 with an entomologist at UC Davis, I learned that Argentine ant populations in Davis were declining. 

In 2008, a study of ants in San Francisco’s “natural areas” in city parks reported that the existence of non-native Argentine ants does not have a negative impact on populations of native ants. (1) They report that Argentine ants occupy the perimeter of the “natural areas” where native ants generally are not found.  This observation contradicts the usual nativist claims that non-native plant and animal species have negative impacts on native species.

The “invasion” curve

Introduced species are often accused of being invasive and there is a range of explanations, including the bias against non-native species that assumes every non-native species will eventually becoming invasive.  In some cases, a new species spreads aggressively because it is better adapted to disturbed conditions to which it has been introduced.  The initial success of an introduced species is sometimes enabled by the absence of its predators in its new home.  This is called “predator release,” which does not confer permanent protection to a new species that will eventually encounter new predators.  These and likely other factors are probably operating simultaneously. 

Like most so-called “invasions,” introduced plants and animals may briefly expand, but eventually most find their niche in the ecosystem without causing permanent harm to their neighbors.  The assumption that introduced plants and animals threaten native species is usually unsupported by empirical evidence 

Journalistic due diligence

If the author of the Bay Nature article about Argentine ants had searched research literature about Argentine ants, she could have learned that the negative tone of the article and its hyperbolic title were not justified.  In the author’s defense, the demonization of non-native plants and animals is routine in mainstream media.  The bad news about introduced species always precedes their eventual participation in ecosystems and the record is seldom corrected when they do, as in the case of Argentine ants. The reader can compensate for this journalistic bias by reserving judgment about non-native species until more is known about their fate. 


  • Kevin M. Clarke, et. al., “The influence of urban park characteristics on ant communities,” Urban Ecosyst, 11:317-334, 2008

A Natural History of the Future

“The way out of the depression and grief and guilt of the carbon cul-de-sac we have driven down is to contemplate the world without us. To know that the Earth, that life, will continue its evolutionary journey in all its mystery and wonder.” Ben Rawlence in The Treeline

Using what he calls the laws of biological nature, academic ecologist Rob Dunn predicts the future of life on Earth. (1)  His book is based on the premise that by 2080, climate change will require that hundreds of millions of plant and animal species—in fact, most species–will need to migrate to new regions and even new continents to survive.  In the past, conservation biologists were focused on conserving species in particular places.  Now they are focused on getting species from where they are now to where they need to go to survive.

In Dunn’s description of ecology in the future, the native plant movement is irrelevant, even an anachronism.  Instead of trying to restore native plants to places where they haven’t existed for over 100 years, we are creating wildlife corridors to bypass the obstacles humans have created that confine plants and animals to their historical ranges considered “native.” 

The past is the best predictor of the future. Therefore, Dunn starts his story with a quick review of the history of the science that has framed our understanding of ecology.  Carl Linnaeus was the first to create a widely accepted method of classifying plants and animals in the 18th century.  Ironically, he lived in Sweden, one of the places on the planet with the least plant diversity.  Colombia, near the equator, is twice the size of Sweden but has roughly 20 times the number of plant species because biodiversity is greatest where it is hot and wet.

Global Diversity of Vascular Plants. Source: Wilhelm Barthlott, et. al., “Global Centers of Vascular Plant Diversity,” Nova Acta Leopoldina, 2005

 

Humans always have paid more attention to the plants that surround us and the animals most like us.  Dunn calls this the law of anthropocentrism.  We are the center of our own human universe.  Consequently, our awareness of the population of insects that vastly outnumber us came late to our attention in the 20th century.  In the 21st century we learned that all other forms of life are outnumbered by the microbial life of bacteria, viruses, and fungi that preceded us by many millions of years.  Our knowledge of that vast realm of life remains limited although it is far more important to the future of the planet than we realize because those forms of life will outlast our species and many others like us.

Tropical regions are expanding into temperate regions

The diversity and abundance of life in hot and wet tropical climates give us important clues about the future of our warming climate.  We tend to think of diversity as a positive feature of ecosystems, but we should not overlook that tropical regions are also the home of many diseases, such as malaria, dengue fever, zika, and yellow fever that are carried by insects that prey on animal hosts, including humans.  In the past, the range of these disease-carrying insects was restricted to tropical regions, but the warming climate will enable them to move into temperate regions as they warm. The warming climate will also enable the movement of insects that are predators of our crops and our forests into temperate regions.  For example, over 180 million native conifers in California have been killed in the past 10 years by a combination of drought and native bark beetles that were killed during cold winters in the past, but no longer are.  Ticks are plaguing wild animals and spreading disease to humans in the Northeast where they did not live in the cooler past. 

Human populations are densest in temperate regions“The ‘ideal’ average annual temperature for ancient human populations, at least from the perspective of density, appears to have been about 55.4⁰F, roughly the mean annual temperature of San Francisco…” (1) This is where humans are most comfortable, free of tropical diseases, and where our food crops grow best.  As tropical regions expand into temperate regions, humans will experience these issues or they will migrate to cooler climates if they can.

Our ability to cope with the warming climate is greatly complicated by the extreme variability of the climate that is an equally important feature of climate change.  It’s not just a question of staying cool.  We must also be prepared for episodic extreme cold and floods alternating with droughts. Animals stressed by warmer temperatures are more easily wiped out by the whiplash of sudden floods or drought.

Diversity results in resiliency

Diversity can be insurance against such variability.  If one type of crop is vulnerable to an insect predator, but another is not, growing both crops simultaneously increases resiliency.  That principle applies equally to crops that are sensitive to heat, cold, drought, or floods. 

Agricultural biodiversity. Source: Number of harvested crops per hectar combining 175 different crops. Source: Monfreda et al. 2008. “Farming the planet: Geographic distribution of crop areas, yields, physiological types, and net primary production in the year 2000”. Global Biogeochemical Cycles, Vol. 22.

Historically, cultures that grew diverse crops were less likely to experience famine than those that cultivated monocultures.  The Irish potato famine of the mid-19th century is a case in point.  The Irish were dependent upon potatoes partly because other crops were exported to Britain by land owners. When the potato crop was killed by blight, more than one million people died in Ireland and another million left Ireland.  The population dropped about 20-25% due to death and emigration.  The diversity of crops in the United States (where corn is the commodity crop) and Brazil (where soy is the commodity crop) is very low, compared to other countries.  This lack of diversity makes us more vulnerable to crop failure and famine, particularly in an unpredictable climate.

Change in total use of herbicides, antibiotics, transgenic pesticide producing crops, glyphosate, and insecticides globally since 1990. Source: A Natural History of the Future

Instead of increasing crop diversity, we have elected to conduct chemical warfare on the predators of our crops by using biocides, such as pesticides for agricultural weeds and insects and antibiotics for domesticated animals.  The scale of our chemical warfare has increased in response to growing threats to our food supply.  This is a losing strategy because as we increase the use of biocides we accelerate evolution that creates resistance to our biocides. We are breeding superweeds, insects, and bacteria that cannot be killed by our chemicals.  This strategy is ultimately a dead end.

Evolution determines winners and losers

Inevitably, evolution will separate the survivors of climate change from its victims. Dunn reminds us that “The average longevity of animal species appears to be around two million years…” for extinct taxonomic groups that have been studied.  In the short run, Dunn bets on the animals that are most adaptable, just as Darwin did 160 years ago.  The animals most capable of inventing new strategies to cope with change and unpredictability will be more capable of surviving.  In the bird world, that’s corvids (crows, ravens, jays, etc.) and parrots.  In the animal world that’s humans and coyotes.  We aren’t helping adaptable animals survive because we are killing abundant animals based on a belief it will benefit rare animals.  Even in our urban setting, the East Bay Regional Park District contracts Federal Wildlife Services to kill animals it considers “over-abundant,” including gulls, coyotes, free-roaming cats, non-native foxes, and other urban wildlife throughout the Park District.  We are betting on evolutionary losers.

 

If and when humans create the conditions that cause our extinction, many of our predators are likely to disappear with us.  Bed bugs and thousands of other human parasites are unlikely to survive without us.  Many domestic animals will go extinct too, including our dogs.  On the bright side, Dunn predicts that cats and goats are capable of surviving without us.             

Timeline of the evolution of life. Source: CK-12 Foundation

However, in the long run Dunn bets on microbial life to outlast humans and the plants and animals with which we have shared Earth.  Humans are late to the game, having evolved from earlier hominoids only 300,000 years ago, or so.  The plants and animals that would be recognizable to us preceded us by some 500 million years, or so.  But microbial life that is largely invisible to us goes back much further in time and will undoubtedly outlast us.  Dunn says microbial life will give a big, metaphorical sigh of relief to see us gone and our environmental pollutants with us.  Then microbial life will begin again the long process of rebuilding more complex life with their genetic building blocks and the tools of evolution. 

Some may consider it a sad story.  I consider it a hopeful story, because it tells me that no matter what we do to our planet, we cannot kill it.  For the moment, it seems clear that even if we are not capable of saving ourselves at least we can’t kill all life on Earth.  New life will evolve, but its features are unfathomable because evolution moves only forward, not back and it does not necessarily repeat itself. 


  1. A Natural History of the Future, Rob Dunn, Basic Books, 2021

Beyond the War on Invasive Species: Interview with Tao Orion

I am republishing with permission a portion of Kollibri terre Sonnenblume’s interview of Tao Orion.  Kollibri is a writer, photographer, tree hugger, animal lover, and cultural dissident. Kollibri was born and raised in Nebraska, earned a Bachelor of Arts in Writing at the St. Olaf Paracollege, and lived in the Twin Cities and Boston before moving to Portland in 2001. Since 2011, Kollibri has lived predominantly in rural areas in the Western US, working in agriculture and exploring wildtending. Kollibri has published several books, including The Troubles of ‘Invasive’ Plants (with Nicole Patrice Hill), originally a zine and soon to be published as a book.  Kollibri has also recorded interviews available as podcasts, “Voices for Nature & Peace,” which can be found at radiofreesunroot.com.

Conservation Sense and Nonsense


Tao Orion, author of “Beyond the War on Invasive Species”

Tao Orion is the author of “Beyond the War on Invasive Species: A Permaculture Approach to Ecosystem Restoration.” She is a permaculture designer, teacher, homesteader, and mother living in the southern Willamette Valley of Oregon. I interviewed her on May 18, 2020, for my podcast, “Voices for Nature & Peace.” What follows is a partial transcript of that conversation, edited for clarity. [Listen to the entire interview here]

Kollibri terre Sonnenblume, macska moksha press

K: A lot of people have heard the term, “invasive species” and most of them of course are assuming it’s something bad, but when it comes right down to it, it’s actually very difficult to define the term and we could even say that there isn’t one definition of that term.

T: Yes, that’s something that I found really interesting as I was researching my book, because I was really trying to find out if there was a clear, objective description of what an invasive species is, and I found that even the National Invasive Species Council—which in the US is the federal government level board that looks at invasive species issues—spent years on deliberating on the definition and even so, they weren’t able to come up with something that I felt was purely an objective description that could be [applied] in all contexts. It seemed to vary from place to place and time to time.

K: Monsanto was one of the companies involved in setting [that council] up.

T: That’s another disturbing element about how the big frenzy around invasive species and the purported damage that they do came to be so popular; a lot of that was informed and funded by pesticide interests to spur the sale of products, herbicides in particular, to deal with species invasions.

K: I think that most people are probably not aware of the fact that the use of pesticides and herbicides has been rising over the last 20 years, not falling. I think people hear about organic agriculture and they think we must be on the right path. But due in part to the war on invasives and also due to genetically modifying crops to be Round-up Ready so they can survive the use of pesticides—these two things seem to have driven an increase in the use of pesticides over the last 20 years.

T: Yes, it’s definitely alarming. My background is in organic agriculture. I was immersed in that world. Even before writing this book, I was under the impression that herbicides were somewhat less toxic in the realm of pesticide toxicity [as opposed to insecticides or fungicides, for example]. In researching herbicides more for invasive species management and agriculture in general, I learned a lot more about their toxicity and insidious toxicity to insects and mammals and other lifeforms that I don’t think gets talked about enough. People assume they’re more ecologically benign, but really they’re not, and that’s important to bring to the table.

K: One thing you mentioned in your book that I hadn’t thought about much before is that it’s not only the active ingredient in a pesticide, but also the adjuvants—the things that they add to the active ingredient to help it stick to plants or to help make it soluble in water, etc.

T: Yeah, that was a big realization for me too. We talk about these two different terms: “Round Up” is the trade name of the herbicide, of which “glyphosate” is considered the active ingredient. Glyphosate is the ingredient that’s tested for pesticide registration purposes, but that might be only ten percent of a mixture that’s sold in the bottle. The rest of that solution is made up of other ingredients that help the herbicide stay on the plant if it rains or if its windy, or help the herbicide active ingredient penetrate the cells of the plant. A lot of these are trade secrets so they’re not tested and the manufacturers don’t have to say what’s in there. But one compound that has been pulled out and studied by independent researchers is POEA [polyoxyethyleneamine], which has been shown to make glyphosate penetrate human placental cells. So even if you come into contact with glyphosate itself, that wouldn’t necessarily happen, but if you come into contact with Round Up, which contains this adjuvant, POEA, it can actually then allow the glyphosate to enter into the cell. Because that’s what it’s in there to do.

K: The reason we’ve been talking about pesticides because herbicides are such a big part of getting rid of “invasive” species… But your book tries to turn things on its head and to question the concept of whether we should be trying to eradicate them.

T: Yes. I was shocked when I started working in the field of ecological restoration, coming from a background in organic agriculture. I had heard of “invasive species” before but when I got into this context, I was around people who did this professionally, it was just assumed that I was going to use herbicides and I would be totally fine with that, because that’s just what everybody did. The whole context was, “we have to get rid of these plants at all costs, and if we do, everything will be okay.” [Laughs.] That’s the the framework in which we’re approaching ecosystem restoration, and to me, I was amazed because from a more holistic perspective, I could see right off the bat that in every case where invasive species were thriving, there were other things going on in the ecosystem that pesticides weren’t going to address.

It’s the same in conventional agriculture. If you’re having, quote, pest pressure issues, the issue isn’t the pest, the issue is the soil or the plant stress or drought stress. There’s all these different things playing into the manifestation of pest pressure in the ecosystem. So, taking that knowledge a few steps further to ecosystem restoration I think is really necessary. A lot of people involved in these contexts are really highly trained ecologists and it’s still hard for me to square that with the belief that herbicides, pesticides are the only solution. These are often people who are shopping at organic food markets, and only buy organic food, and believe really strongly in that framework for food production, and yet are making decisions about ecosystem restoration outside of agricultural contexts that rely on pesticides and I just think that really needs to be questioned.

I had some very interesting discussions over the years and maybe the needle is starting to shift a little bit, although as you mention, sometimes these discussions flare up online where people are really quite defensive about their position and belief around this.

K: The issue tends to infect any discussion around plants. I’ve been using a couple of plant ID groups on Facebook because I’m in a new area and I’m seeing things coming up and I’m like, “What is this?” Of course if you’re in a native plant group, that’s definitely going to be someplace where [the invasive framework] is strong. You know, a native-plants-equals-good, non-native-plants-equals-bad, black and white paradigm. Which brings us around to looking at the invasive plant not being a problem in and of itself but of being a symptom of something going on.

T: That’s a huge part of the conversation that a lot of folks really aren’t willing to easily engage in, but the design of our livelihood system has really degraded ecosystems to a place where native flora and fauna aren’t thriving. You know, to really sit with that, and acknowledge it, think about how we might approach things differently as a basis for our understanding is challenging. It’s a lot easier to blame the messenger. Also I think one of the things that’s really missing from the discussion of native plants is the fact that native ecosystems were or are managed by indigenous people. They don’t just exist in a vacuum, free from people’s influence and the whole idea of this “pristine” wilderness is very much a western, colonial thought pattern that definitely needs to be disrupted.

K: What you’re referring to in part is that when people are designating a plant as invasive or non-native, there’s a point in time they’re referring to, and that might be different from place to place, but it’s generally accepted in the United States that anything anything that showed up after 1492 is not native. There are people who are willing to describe most non-native plants as “invasive” or throw them in that bin as soon as possible, and then the poisons come out, so this is an important issue.

T: Yes, but we don’t really know the social, ecological, economic context that was going on at that point in time that led to a particular assemblage of plants. There’s no doubt that the floral and faunal assemblies were different, but we should think really hard about why they’ve changed. Draining the wetlands of the Sacramento and San Joaquin valleys in California has major ecological implications. Damming the Colorado River for hydro-power and irrigation capacity has major ecological implications. These bigger scale things that we do—that we support—are going to change the surrounding ecosystem. If we can acknowledge that and observe what’s happening because of those major shifts, I think we’ll be in a better position to understand so called “invasions” from a more holistic perspective.

K: Because the entry of an invasive plant or animal into a landscape is in virtually all cases preceded by a human-caused disturbance of some kind.

T: It’s interesting. When I was writing, [I wondered if I] should I put forward the idea of reclaiming a different name because “invasive species” has kind of this negative connotation, but the more I looked into evolutionary biology and some of the ways—in the deep time perspective—how systems have changed, “invasion” is one of these processes and it’s not unnatural. Taking that longer term perspective is important as well. That’s how plants came to be on land. There were marine beds of algae hanging out in the shallow seas a couple billion years ago and eventually, speciation happened because of changing conditions and the land was “invaded” by those plants. You just see that change over time leading to the type of biodiversity that we have now, punctuated by other kinds of events of course, but it’s not something that’s “outside the realm of nature,” which is how invasive species are situated in a lot of discussions.

Words Matter: “Die-Off” vs. “Die-Back”

California has been in severe drought conditions for over 10 years.  Climate change is the underlying reason for the extremity of the drought.  Maintaining our carbon sinks that sequester greenhouse gases causing climate change is one of our most important defenses against climate change and forests are one of our primary carbon sinks.  Unfortunately, California’s forests are dying of drought and associated insect infestations. You might think that given these conditions, we would try to preserve our forests. 

In fact, the drought has accelerated the war on our non-native urban forest in the San Francisco Bay Area.  All trees and plants have suffered during our prolonged drought.  Where trees are not irrigated in our parks and open spaces, signs of drought stress are visible.  Today, I am publishing my letter to the IPM Director and Fire Chief of East Bay Regional Park District about the need to make a distinction between dead trees and trees that are not dead, but showing symptoms of prolonged drought. My letter explains why we must distinguish between dead (described as “die-off”) and living trees (described as “die-back”) when making commitments to destroy trees that we desperately need during this climate crisis.

Links are provided to email addresses of recipients of my letter.  Please consider writing a letter of your own.


To:   Pam Beitz, Aileen Theile

CC:  Natural and Cultural Resources Committee, Matteo Garbelotto

As you know, the Park District hired the Garbelotto Lab at UC Berkeley to evaluate two species of trees in the parks, acacia and eucalyptus.  The reports of the Garbelotto Lab were recently published on the Lab’s website.  I am writing to ask that responsible staff read those reports and make adjustments in plans to remove trees as needed, based on those reports. 

Source: Report of Garbelotto Laboratory
Acacia die-off in Leona Canyon, East Bay Regional Park District. Source: US Forest Service

The diagnoses for acacia and eucalyptus are entirely different.  The pathogens are different in the two tree species.  The pathogens killing acacia are new and they are lethal.  The pathogens found in eucalyptus are not new.  They have been latent and asymptomatic in eucalyptus for decades and have only become symptomatic because of the stress of drought. The pathogens found in eucalyptus disfigure leaves and twigs, but are not fatal. 

Much like the microbes (bacteria, viruses, fungi, parasites) in our bodies that outnumber human cells, every tree is inhabited by microbes that are usually asymptomatic.  If similar tests were done on other tree species in the Bay Area, similar results would be found where trees are not irrigated.  The pathogens are always there.  Drought has made them visible.  If we were obligated to destroy every tree in the parks showing signs of drought stress, we would be required to remove most trees in the parks. 

There are significant disadvantages to destroying living trees:

  • A dead tree is not capable of resprouting, but a living tree is capable of resprouting unless it is a species that is not capable of resprouting. Eucalyptus, acacia, redwoods (not candidates for removal, but dying of drought nonetheless) and bay laurels are all vigorous resprouters.  The stumps of these living tree species will require herbicide applications to prevent them from resprouting. 
  • The herbicides used to prevent resprouting travel through the roots of the tree to kill the roots. Herbicides used to prevent resprouting damage the roots of neighboring plants and trees connected by their mycelium networks. 
  • The trees that are destroyed release their stored carbon into the atmosphere contributing to the greenhouse gasses causing climate change. In the absence of those trees, less carbon dioxide is removed from the atmosphere in the future.  Since the underlying cause of increased frequency and intensity of wildfires is the warmer/drier climate, removing living trees increases wildfire risks in the future.
  • As more trees die, wood debris has accumulated to the point that there isn’t sufficient disposal capacity. When roadsides in the Berkeley hills were clearcut over one year ago, it took 9 nine months to dispose of the wood debris.  Huge piles of wood debris were stacked on roadsides, creating a fire hazard.  The more trees that are destroyed, the more wood debris is created.
One of many piles of logs, Claremont Ave, November 2020. Photo by Doug Prose, courtesy Hills Conservation Network.

I am therefore concerned about the Park District’s plans to remove one million trees from parks in the East Bay, according to press coverage: “In consultation with academics and state experts, they’ve identified a mass die-off of trees in the parks as a result of stress from drought, climate change and a proliferation of non-native species. Now they estimate they need to remove more than 1 million trees on their land, at a cost of $20 million to $30 million in one park alone. One area of the die-off, located between Mt. Diablo and communities in Oakland and Berkeley, is particularly concerning to Fire Chief Aileen Theile.”  

In an earlier media interview Fire Chief Theile included eucalyptus in the list of dead trees: “The die-off, first noticed last October, has mostly hit eucalyptus, acacias, pines and bay laurels and has expanded this summer amid an exceptional drought.”  Oaks are strangely absent from that list of dead trees, although it is well known that there are thousands of dead oaks in the Park District that have not been removed.

In summary, I ask for your reconsideration of Park District plans and public communications regarding tree removals in the parks:

  • The Park District should confine plans for tree removals to dead trees. Dead trees are public safety risks that should be mitigated. Drought stressed trees that may be unsightly are not a priority for removal.  Given our heavy rains in December, it is still possible that many will recover.
  • Park District communications with the public should make a distinction between “die-off” and “die-back.” Acacias are accurately described as experiencing a die-off.  Eucalyptus are accurately described as experiencing a die-back.

Thank you for your consideration.

“When the Killing’s Done” Maybe never.

I have few opportunities to read fiction because most of my time is spent trying to keep up with rapidly evolving ecological science.  I was grateful for the chance to read the fictional account of island eradications on the Channel Islands because it closely relates to my interest in the planned eradication of mice on the Farallon Islands, which is still pending and as controversial as similar projects on the Channel Islands.  TC Boyle’s book foretells the Farallones project as he sends a member of the fictional project team to the Farallon Islands after completion of the project on the Channel Islands.

When the Killing’s Done by TC Boyle is not entirely fictional. (1)  It is impressively accurate in its description of the eradication projects themselves, but Boyle weaves a tight fictional plot around the key players who implemented the project and those who fought like hell to prevent it from happening.  Like other books by Boyle that I have read, When the Killing’s Done creates intense suspense that moves the reader along at top speed.  His characters are vivid and complex. 

Boyle lives in Montecito, near Santa Barbara, close to the Channel Islands.  No doubt he followed the projects closely as they were debated and resisted by opponents, who were primarily animal rights activists according to Boyle’s account.  In interviews after the publication of the book in 2011, Boyle claimed not to have a personal opinion of the projects:  “I’m not an activist in any way. With certain exceptions, I don’t think politics and art mix very well.”  He sees value in both sides of the debate and the characters in his story have much in common.  The antagonists are vegetarians who value nature and care deeply about the environment and the animals who live in it.  I believe this common ground is also true of the adversaries in the debate about the Farallones project and others like it.

However, the ending of the book suggests that Boyle doubts the ability of humans to control nature.  Although the projects on the Channel Islands were completed to the satisfaction of the land managers–National Park Service and The Nature Conservancy—the final image in Boyle’s story is of animals considered non-native on the Islands making their way to the shore of the Island.  The implication is that maybe the killing is never done and that is the crux of the problem with island eradications in general and the planned mice eradication on the Farallon Islands in particular.

Rat eradication on Anacapa Island

The aerial application of rodenticide to kill rats on Anacapa Island in 2001-2002 was the first of its kind in North America.  The project was also unique because it was complicated by the need to spare a population of endemic native mice on Anacapa.  Over 1,000 native mice were captured before the aerial application of rodenticide and released back on the island after the poison was no longer effective. 

Anacapa Island is the usual success story cited by supporters of the Farallones project where non-native mice are the target for eradication.  Native mice on Anacapa were not considered a threat to birds, but non-native mice on the Farallones are, although there is no evidence that mice actually harm birds on the Farallones either.  The operative word here is “native.”  The mice on the Farallones are targets only because they aren’t native.  The mice on Anacapa undoubtedly eat vegetation too, but that’s not considered a problem so long as they are native.   The mice on Anacapa are probably an important source of food for birds, just as they on the Farallones. 

If mice are not harmful to birds, there is no legitimate reason to poison them, along with untold numbers of non-target animals.  The mice on the Farallones are targets only because they aren’t native. 

Killing of non-target animals

Rodenticides are indiscriminate killers of warm blooded animals, including birds.  An animal who eats rodenticide slowly bleeds to death.  The grisly process of dying takes about 10-20 days.  If poisoned mice are eaten by other animals that animal is also poisoned.  It is therefore inevitable that non-target birds who are predators of mice will be killed by widespread dispersal of rodenticide pellets on the ground that can also be directly eaten by birds and other animals.  This deadly sequence of events has been demonstrated many times by island eradications using rodenticides all over the world and the project on Anacapa Island is no exception. 

Billboard sponsored by Raptors Are The Solution (RATS)

Raptors are the main predators of mice.  Therefore, 63% of raptors on Anacapa Island (37 of 59 individual birds) were captured and either relocated or kept in captivity until the project was done, according to the first study of the project published in 2005. According to that study, “The fate of the remaining birds of prey on the island is unclear. There is evidence that some birds survived the bait application… However, three barn owls, six burrowing owls and an American kestrel either died while in captivity or were found dead on the island. The American kestrel and a burrowing owl that were captured in 2001, after the bait application, likely died from brodifacoum poisoning.” The analysis of the project considers these deaths “negligible.”

A total of 94 seed-eating birds were also found dead after the poison drop.  Most were song birds, but an additional 6 birds were too decomposed to identify the species.  The study notes that these collateral kills were consistent with other similar projects.

Western Gull on Channel Islands. NPS photo

The study makes no mention of gulls that were undoubtedly killed by the project.  Gulls are omnivorous scavengers for whom dead and dying mice are ideal food, preferable to dive bombing for French fries on your picnic table.  According to the National Park Service, “Western gulls are the most abundant breeding seabird in the Channel Islands National Park, with a population estimated at more than 15,000.” Shortly after the poison drop, dead seabirds washed up on the shore near the Santa Barbara harbor.  UC Santa Barbara’s daily newspaper said, “…a strong correlation exists between the National Park Service’s most recent airdrop of pesticide on Anacapa Island and the dead birds.”

In other words, those who implemented the eradication project on Anacapa are probably not telling the full story about the death of non-target birds.  The death of hundreds of gulls is anticipated by the promoters of the project on the Farallones.  If the organization that implements the project is the same organization that monitors and reports on the project (as was the case for the projects on the Channel Islands), we may never know the actual impact on the birds living on the Farallones.

Those who promote these poisonous projects justify the death of non-target birds by saying they are “incidental” and have no lasting impact on the species population.  They will apply for and receive “incidental take permits” in advance of the Farallones project that will satisfy legal requirements of the Migratory Bird Treaty Act and the Endangered Species Act.  The lawsuit that was filed to prevent the Anacapa project was overturned on those grounds.

The killing is never done

Rat eradication on Anacapa and pig eradication on Santa Cruz (where over 5,000 pigs were shot by sharpshooters and 54 Golden Eagles were removed because they were predators of endemic foxes) are the focus of TC Boyle’s masterful book.  Both were implemented and considered successful by the organizations that implemented the projects.  Although land managers are no longer killing animals (to our knowledge) in the Channel Islands they are waging a continuous war on non-native plants by spraying them with herbicide.  When we visited Santa Cruz Island in 2010, we witnessed the application of Garlon on non-native fennel.

Roundup (glyphosate) has been used on the Farallon Islands every year since 1988.  Between 2001-2005, an average of 226 gallons of herbicide were used annually (5.4 gallons per acre per year), according to the annual report of the Farallon National Wildlife Refuge.  Given that these islands are not far from the California coast and are visited by thousands of migratory birds every year, we must expect that the arrival of new plants to the islands will be continuous: seeds are eaten and carried by birds; seeds are carried by birds in their feathers and feet; wind and storms carry seeds to the islands, etc.

The Environmental Protection Agency recently published a Biological Evaluation of glyphosate products.   EPA reports that glyphosate is “likely to adversely affect” 93% of legally protected endangered and threatened plants and animals. That finding applies equally to all plants and animals, whether they are legally protected or not because the physiological processes of species in the same order are similar.

The Environmental Impact Statement for the Farallones project accuses mice of eating vegetation, although far more vegetation is probably killed by herbicides.  Non-native vegetation arrives on the Farallones partly because birds eat it and carry it to the Farallones.  Animals do not care if edible vegetation is native.  Nativism is a human prejudice not shared by animals who seek food and shelter wherever they can find it.

The constant poisoning of plants is perhaps a trivial consideration in comparison to the futility of trying to eradicate mice.  Although rats have been successfully (leaving aside the death of non-target animals) eradicated by some projects, attempts to eradicate mice have been significantly less successful. 

A study of 139 attempted eradications on 107 Mediterranean islands in eight countries, with Greece, Italy, and Spain accounting for the highest number found that eradication projects targeted 13 mammal species. The black rat was the target of over 75% of the known attempted eradications in the Mediterranean Basin; other species targeted were feral goat, house mouse, European rabbit, and domestic cat. The most widely used technique was poisoning (77% of all eradications), followed by trapping (15%) and hunting (4%).  Techniques were largely target-specific.

The average failure rate of the projects was about 11%, but success was defined only as the death of animals living on the islands at the time of the project. However, this percentage varied according to species. The failure rate of house mouse eradication was 75%. Reinvasion occurred after 15% of eradications considered initially successful. 

Farallon Islands, NOAA

The proposed project on the Farallon Islands is a dead end in many ways.  It will kill many non-target animals. It will probably not be successful in the short run or the long run.  Every time it is repeated it will kill more animals. Furthermore, it is pointless because mice do not harm birds on the Farallon islands. 


  • T.C. Boyle, When the Killing’s Done, Viking, 2011.

Open Letter to California Native Plant Society

A diverse garden of native and non-native plants will be the most resilient to climate change. Photo credit Marianne Willburn, Garden Rant

In a recent edition of Nature News, Jake Sigg published an announcement of a new publication and a brief description of it that was apparently written by Susan Karasoff, Outreach Chair of the Yerba Buena Chapter of the California Native Plant Society:

San Francisco Estuary Institute (SFEI) developed Making Nature’s City: A Science-based Framework for Building Urban Biodiversity, which summarizes the key indicators supporting urban biodiversity. Local native vegetation is the base of the food web for our wildlife, including our local native pollinators, our native bees, butterflies and hummingbirds.

Biodiversity is biosecurity. Biodiversity only applies to locally native plants and wildlife. Introduced, invasive and non-local native plants contribute to landscape diversity, not to biodiversity. Our pollinators eat local native plants and pollen as caterpillar food. Introduced plant leaves feed few, if any, caterpillar species. Caterpillar species feed the rest of our local food web. Healthy urban ecosystems are measured by the health of contributors to their biodiverse food web and habitat.

Native plants planted in plant communities are resilient to climate change. Introduced and non-local native plants and trees are not resilient to climate change. San Francisco benefits from native plants planted in plant communities. San Francisco Estuary Institute (SFEI)’s Hidden Nature project, done in conjunction with the Exploratorium, maps the locations of plant communities in San Francisco prior to European arrival.

Jake Sigg’s Nature News, February 18, 2022

I compared the description to the SFEI document because the description contains several counterintuitive statements.  Although the SFEI document reflects a clear preference for native plants, it does not corroborate these specific statements:

  • “Biodiversity only applies to locally native plants and wildlife. Introduced, invasive and non-local native plants contribute to landscape diversity, not to biodiversity.”
  • “Introduced plant leaves feed few, if any, caterpillar species.”
  • “Native plants planted in plant communities are resilient to climate change. Introduced and non-local native plants and trees are not resilient to climate change.”

Here are a few studies, references, and public policies that explicitly contradict these counterfactual statements.

Biodiversity is not confined to native plants

“Biodiversity is the biological variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic, species, and ecosystem level.” (Wikipedia)  The Simpson index and the Shannon-Wiener index are the two most commonly used measures of biodiversity by ecological scientists.   Neither index makes a distinction between native and non-native species.  In fact, such a distinction is difficult to make and is often hotly debated. 

In San Francisco, home of the Yerba Buena Chapter of the California Native Plant Society, public policy explicitly acknowledges that non-native species contribute to local biodiversity:  “Parks and open spaces in San Francisco include both native and non-native species, both of which can contribute to local biodiversity.” (Policy 4.1, Recreation and Open Space of San Francisco General Plan)

 Non-native plants are host to many butterflies in the Bay Area

Butterflies lay their eggs on plants called their host plants. The eggs develop through several larvae stages into caterpillars that feed on the host plant that is often confined to a particular plant genus or family.  Few butterflies are confined to a single plant species. For example, plants in the milkweed genus are the host of monarch butterflies.  There are many species within the milkweed genus and many are not native to the San Francisco Bay Area.  An introduced milkweed species, tropical milkweed, is a particular favorite of monarchs and it has the advantage of being available throughout the year, unlike native milkweed species that are dormant during winter months. Some have attributed the recent comeback of the California monarch migration to the widespread planting of tropical milkweed in residential gardens.

This article from the UC Davis Bug Squad says they plant tropical milkweed and two species of native milkweed in their experimental garden. Monarchs show a strong preference for tropical milkweed in their experimental garden: “In July, we collected 11 caterpillars from the narrowleaf [native] milkweed; we rear them to adulthood and release them into the neighborhood. But in the numbers game, the tropical milkweed [A. curassavica] won. From July through today, we have collected a whopping 43 eggs or caterpillars from A. curassavica. How many from [native] A. speciosa? Sadly, none.”

Anise swallowtail butterfly is another common butterfly species in the Bay Area that is dependent upon a non-native host plant.  Before non-native fennel was introduced to California, anise swallowtail bred only once each year. Now it is able to breed year around on non-native fennel and is therefore more plentiful than it was in pre-settlement California.

These butterfly species in the San Francisco Bay Area are not unique with respect to their need for non-native plants:  “California butterflies, for better or worse are heavily invested in the anthropic landscape [altered by humans].  About a third of all California butterfly species have been recorded either ovipositing [laying eggs] or feeding on nonnative plants.  Roughly half of the Central Valley and inland Bay Area fauna is now using nonnative host plants heavily or even exclusively.  Our urban and suburban multivoltine [multiple generations in one year] butterfly fauna is basically dependent on ‘weeds.’  We have one species, the Gulf Fritillary that can exist here only on introduced hosts.  Perhaps the commonest urban butterfly in San Francisco and the East Bay, the Red Admiral is overwhelmingly dependent on an exotic host, pellitory.  And that’s the way it is.” (1)

During the butterfly phase of life, butterflies eat pollen and nectar of many different plants, not just its host plant.  When native plant advocates eradicate important sources of food for butterflies, they aren’t helping butterflies.  For example, butterfly bush (buddleia) is as popular with butterflies as they are unpopular with native plant advocates because they aren’t native.  Butterflies don’t care if they are native because they are an important source of food. 

Butterfly bush is the host plant of Variable checkerspot butterflies. It is also an important source of nectar for butterflies and bees. It is being eradicated on public land because it is not a native plant. butterflybush.com

Native plants are NOT more resilient to climate change

The most dangerous of the counter-factual statements by the spokesperson for the California Native Plant Society is the claim that native plants are resilient to climate change, but non-native plants are not.  That claim defies reality and it prevents us from responding effectively to climate change. 

Here are a few samples from scientific literature that contradict this inaccurate claim about native plants.  There are many others, just Google “Are native plants more resilient to climate change.” 

  • “As spring advances across the Midwest, a new study looking at blooming flowers suggests that non-native plants might outlast native plants in the region due to climate change.”
  • “Warming temperatures affect native and non-native flowering plants differently, which could change the look of local landscapes over time, according to new research.”
  • ”Whether in natural areas or in our gardens, climate change is affecting native plants. According to the Maryland Climate Summary, our temperatures are expected to increase 5⁰ F to 11⁰ F by 2100.
    1. “Higher temperatures cause native plants to experience more heat-related stress. Heat stress causes higher water demand, a situation made worse by longer droughts.
    2. “Higher atmospheric carbon dioxide (CO2) levels preferentially promote the growth of invasive plant species, decreasing the space needed to support natural areas.
    3. “Elongated growing seasons cause earlier leaf out and bloom times, which in turn affects the animal species synchronized to the life cycles of native plants, especially pollinators.”

An appeal to native plant advocates

I am publishing this article today as an open letter to the California Native Plant Society as an appeal to their leadership to make a new commitment to accuracy.  CNPS and native plant advocates enjoy a vast reservoir of positive public opinion.  However, they put their reputation in jeopardy by advocating for policies that are not consistent with reality, with science, or with public policy.  CNPS can’t distance itself from the Yerba Buena Chapter of CNPS because Susan Karasoff has made several presentations for CNPS that are available on its website.  Native plant advocates can best promote their agenda by providing accurate information.


Where do squirrels live? Wherever they can.

We have always had a big population of squirrels in our neighborhood, probably because we have many big trees, including our coast live oak.  Oaks in California had a big mast year in 2021, which means they produced many more acorns than usual.  The population of squirrels increased significantly, which is typical of mast years.

Some of the big trees in our neighborhood before they were pruned or removed. Google Earth

In the fall of 2021, several of our neighbors radically pruned their trees, presumably because they wanted more light in their yards and their homes. They also cut down several trees including a big, old tree behind us and several fruit-bearing trees down the street from us.   

Same trees after pruning.

We didn’t give it a lot of thought when that happened.  We respect the rights of our neighbors to do what they think is best on their property. I remember thinking it wasn’t nesting season for the birds, but I also should have given some thought to the squirrels. (California Department of Fish and Wildlife biologists have defined the nesting season as February 1st through August 15th.) Even if I had, I doubt that I would have objected because it wouldn’t have been neighborly.  I have always confined my activism on behalf of trees and wildlife to public land that belongs to everyone (although I have also tried to help property owners to save their trees at their request).  

Fox Squirrel, the species in our neighborhood. Source: University of Utah, Natural History Museum

 We didn’t realize that our neighbors’ trees were the homes of many of the squirrels who are now searching for new homes.  Squirrels have gnawed holes into the eaves of our roof and the wood shingled siding of our home.  They are living in the walls of our home.  If we can’t move them on to new homes, they will soon have their babies inside our home. 

We have found a service that uses humane methods to coax the squirrels out of one-way doors and seal their holes behind them. If you have a similar problem, I recommend the Wildlife Detectives in San Rafael. 

I had not predicted the impact of tree pruning and removal in my neighborhood.  As we try to deny squirrels access inside our home, it only recently occurred to me why the squirrels are seeking refuge inside our home and our neighbor’s home after 15 years of living in peace with them. 

This has been a humbling experience because I considered myself fairly knowledgeable about both trees and wildlife.  Apparently I’m not.  Humans aren’t very good at anticipating the consequences of the choices we make in nature and our choices rarely take wildlife into consideration because our understanding of their needs is limited.  That’s one reason why I often advocate for the “leave it alone” approach to land management.

The Big Picture

The squirrels looking for new homes in our neighborhood are a reminder to keep wildlife in mind when making changes in our gardens and homes.  Our gardens are food and habitat for wildlife. 

But protecting wildlife goes far beyond our own homes because the activities of humans have an impact on wildlife on a population level.  Here are a few examples of projects that have kept wildlife in mind…or NOT!

  • The federal infrastructure bill includes $350 million to construct wildlife road crossings.  Such road crossings help to prevent serious accidents caused by cars hitting animals and save animal’s lives.  California is building a wildlife bridge over the 101 freeway to connect split portions of the Santa Monica Mountain National Recreation Area.  A vegetation bridge is also being built over the Ventura freeway in California.  These wildlife corridors benefit wildlife populations by preventing genetic isolation that can weaken the species. The California Governor’s budget for 2022-2023 includes funding to build more wildlife corridors. 
  • Scientists have learned it is possible to relocate burrowing owls before their underground burrows are destroyed to build new developments.  The owls are enticed into their new homes by surrounding them with the poop of other burrowing owls.  The owls are more willing to stay in their new homes if they believe other owls are living there.  Just like people, they want to live among friends.
  • We must convince native plant advocates to quit destroying important food and habitat for wildlife.  The birds don’t care if Himalayan blackberries are not native.  It is a primary food source that is more productive than its native relative.  When Himalayan blackberries are sprayed with herbicides—as they are regularly in San Francisco—the birds are being poisoned as well.   

There are many more opportunities to take wildlife into consideration in everything we do.  Please write a comment to add more examples.