Tag: evolution

The Monkey’s Voyage: How plants and animals are dispersed throughout our planet

The Monkey’s Voyage (1) is as much a history of the science of evolution and ecology as it is a report of the prevailing scientific opinion of the means by which plants and animals were dispersed around the world.  Just as life has evolved, so too has the science that studies it.

In the beginning….

The story begins with Charles Darwin, the author of the first publications that identified natural selection as the mechanism that drives the evolution of life on the Earth.  These ideas came to him as the result of a five-year voyage around the world in 1831-1836:  down the coast of Africa, across the Atlantic, down the coast of South America, around the horn, to the Pacific Ocean to many islands—most famously the Galapagos—to New Zealand, Australia, islands in the Indian Ocean, round the horn of Africa to home.

Voyage of the HMS Beagle, 1831-1836. Creative Commons - Share Alide
Voyage of the HMS Beagle, 1831-1836. Creative Commons – Share Alike

He spent 3-1/2 of the 5 years on land, collecting plant and animal specimens, including many fossils.  The fossils suggested to him the existence of animals no longer occupying the land.  He also observed many similar plants and animals with slightly different forms around the world.  The classic example of closely related, but widely dispersed animals is a family of large, flightless birds:  the ratite family.

Family of ratite birds
Family of ratite birds

These similarities suggested a common ancestry to Darwin.  Yet, their dispersal across oceans was puzzling to him because at that time the continents were considered fixed in place both going back in time and going forward into the future.  Nothing was known at the time about the constant movement of continents, known as continental drift, because the movement was too slow to be observed by humans.

Darwin’s theory about the similarities he found in widely dispersed plants and animals was consistent with his perception of the fixed nature of the geography in which they were found.  He theorized that the common ancestors of the similar plants and animals had been dispersed by wind, ocean currents, carried by birds, or other means of transportation. 

He conducted experiments to determine how long seeds could survive in sea water to test his theory and he examined migrating birds for evidence of seeds and small animals in their feet and feathers.  What he found supported his theory that it was physically possible for plants and animals to be dispersed across oceans to new ranges where subsequent evolution in a different environment would eventually result in alterations of form.  When plants and animals are moved from their home ranges and are physically isolated, their genetic compositions diverge.  Over time they are sufficiently genetically and morphologically distinct to be considered different species. 

Continental Drift

Around the turn of the 20th century, scientists began to theorize that Africa and South America may have been merged at one time because maps revealed that they fit together like pieces of a puzzle.  Alfred Wegener is best known for his pursuit of this theory.  He visited both sides of the Atlantic and observed that seams of rock and sediments lined up on the two shores, suggesting their past connections.  Although Wegener’s theory gained considerable traction, he did not propose an equally compelling theory about the physical mechanism that would be capable of moving the continents apart.

The mechanism that moves the continents was identified about 50 years later when the ocean floor was studied as a result of developments in radar and sonar.  These analytical tools eventually identified seams running the length of the oceans that separate the tectonic plates on which continents ride.  Beneath the crust of the earth magma of molten material moves in a current, emerging through the seams of the Earth’s crust as volcanic activity.  As molten material emerges from this seam between the tectonic plates, it cools on the ocean floor to form new sea floor.  The expansion of the sea floor moves the plates away from the seams, which moves the continents.   This is the engine that drives continental drift.

Tectonic Plates - USGS
Tectonic Plates – USGS

By the late 1960s there was scientific consensus about plate tectonics and consequent continental drift. That knowledge led to an understanding of the history of the continental configuations.  About 300 million years ago, all continents were fused into one, called Pangaea.  Pangaea began to break up about 100 million years later.  However, South America, Africa, Madagascar, Australia, New Zealand, and Antarctica remained fused in a continent called Gondwana until about 100 million years ago.

Pangea0001
Pangaea

 

“The history of life is the history of the earth.”

This new understanding of the history of the earth’s geology resulted in a paradigm shift in scientific theories regarding dispersal of life forms.  Very quickly, scientific consensus formed around the theory that life moved as a result of movements in the continents.  This theory was succinctly expressed as “The history of life is the history of the earth.”  That is, where life is found depends upon changes in the geology of the earth.  For example, scientists assumed that life found on Madagascar originated in Africa before Madagascar separated from the African continent.  Similarly, scientists assumed that life found in New Zealand originated in Australia before New Zealand separated from the Australian continent.  In other words, life migrated from the continent along with the land, like Noah’s ark carrying the animal kingdom.   Previous theories about trans-oceanic voyages of plants and animals were quickly abandoned in favor of this new, elegant theory which seemed so much more plausible than its predecessor.

DNA analysis trumps elegant theory

Although scientists were comfortable with their new theory of how life was dispersed, the inexorable forward movement of human knowledge intervened to disrupt their complacency.  The new analytical tool that overturned this theory was DNA analysis which enabled scientists to study the genetic composition of life forms. 

When there are two morphologically similar species in physically isolated locations, their common ancestry can now be determined by DNA analysis.  And the genetic distance between the species can help scientists determine when those species became physically separated.  When populations become separated their genetic pools become progressively more distant from one generation to another.  This rate of genetic change is called the “molecular clock” and it can be used to determine when the physical separation occurred if the rate of change is known.  Unfortunately, the molecular clock varies from one lineage to another, so first scientists must calibrate the clock and when they do they can estimate the arrival of a specific plant or animal in a new territory that is physically isolated from its former range and therefore its ancestors.

Genetic analysis has overturned former theories of how life was dispersed on the earth.  In most cases, plants and animals arrived in their present locations long after the continents separated into their present configuration. Plants are more likely to have been dispersed by wind and ocean currents than animals.  New ranges of plants are often on the receiving end of ocean currents and plumes from big rivers.

Also, new understanding (1980s) of the most recent mass extinction approximately 65 million years ago—when dinosaurs disappeared from the earth—would predict the same result.  The mass extinction at the end of the Cretaceous period occurred after the separation of the continents.  Therefore, most life forms that moved along with the separating continents were wiped out by the mass extinction about 65 million years ago.  Life forms found now are more likely to have arrived after present continental configurations formed and therefore are more likely to have arrived by long-distance dispersal. 

Evolutionary science comes full circle

Olive baboon, Old World monkey by Mohammad Mahdi Karim
Olive baboon, Old World Monkey by Mohammad Mahdi Karim

There are some die-hard scientists that have not made the transition from the “life-moves-with-the earth” theory.  However, the molecular evidence that life has dispersed across vast expanses of ocean is mounting and most scientists have accepted the reality of the evidence.  Science has come full circle, to return to Darwin’s original theory.  As improbable as it may seem, monkeys made the voyage from Africa to South America, across the Atlantic Ocean.

 

Brown spider monkey, New World monkey. Creative Commons - Share Alike
Brown spider monkey, New World monkey. Creative Commons – Share Alike

But is that voyage really so improbable?  Within the past decade, we have witnessed two massive earthquakes that caused massive tsunamis.  In December 2004, a tsunami following an earthquake in Asia killed approximately 200,000 people.  A few survivors tell harrowing stories of clinging to rafts of debris at sea to arrive many days later on a foreign shore.  And less than 10 years later, in March 2011, an earthquake and tsunami in Japan killed tens of thousands of people.  Over a year later, huge rafts of debris washed ashore on the West Coast of America, encrusted with sea life that accumulated on that long trip.  They were called “invasive species” when they arrived.  But were they really?  After all they arrived as the result of a natural occurrence with no assistance from humans.

These may seem rare events to us because of our short time perspective.  Multiply those two catastrophic disasters by the millions of years of life on earth to arrive at the conclusion that these events are routine when put into the context of the lifespan of the earth rather than the lifespan of humans. 

Bringing it home

What we learn from The Monkey’s Voyage is relevant to the concerns of Million Trees:

  • Life is constantly in motion whether we are capable of perceiving it or not.  To choose some specific landscape that existed in the distant past as an ideal to be re-created is to deny the reality of nature.  The concept of “native plants” is meaningless.  Native to where?  Native to when?
  • Change in nature is random and therefore unpredictable.  Cataclysmic events render humans impotent to manipulate complex ecosystems.  Human attempts to “manage” nature are arrogant at best and harmful at worst.  For example, when we kill one animal based on a belief that it will benefit another animal, we haven’t sufficient knowledge to predict the outcome with certainty.
  • Science is constantly evolving, just as nature is evolving.  Invasion biology is stuck in a cul-de-sac that is contradicted by the reality of the dynamism and complexity of nature.  There is little scientific evidence that supports the assumptions of invasion biology.

(1)    Alan de Queiroz, The Monkey’s Voyage:  The improbable journeys that shared the history of life, Basic Books, New York, 2014

A Book Review: The Signature of All Things

Organisms classified as mosses. 72nd plate from Ernst Haeckel's "Kunstformen der Natur" (1904, public domain)
Organisms classified as mosses. 72nd plate from Ernst Haeckel’s “Kunstformen der Natur” (1904, public domain)

We have read little fiction in the past few years, as we struggle to keep pace with the scientific literature that is revising conservation biology.  Happily, we were recently given the opportunity to read a charming work of fiction that is firmly in the center of our interest in botanical issues.

The Signature of All Things was written by Elizabeth Gilbert.  Its title refers to a botanical myth about which we have published an article that is available here.  The Doctrine of Signatures seemed a logical botanical belief at a time when plants were one of man’s few medicinal tools and religion was a powerful influence in human society.  The Doctrine of Signatures, which was actively promoted by the church in 17th century Europe, was based on a belief that God had “signed” plants with certain suggestive shapes and colors to inform humans of their medicinal properties.  For example, a heart-shaped leaf was considered God’s message to us that a particular plant would be beneficial to the human heart and this message was strengthened by a flesh-colored flower. Every plant was believed to be useful in some way if man could only discern its purpose.  Else why would they have been created, since the Garden of Eden was created for the benefit of man?  The church encouraged man’s study of plants as a way to worship God’s creation.

After reading a rave review by one of our favorite authors, Barbara Kingsolver, we were unable to resist the diversion to this story that is inspired by botanical history.  Kingsolver concludes, “The Signature of All Things is a bracing homage to the many natures of genius and the inevitable progress of ideas, in a world that reveals its best truths to the uncommonly patient minds.”

Signature begins in Kew Garden in London during the 18th Century reign of one of our great horticultural heroes, Joseph Banks.  We featured Banks in an article about the English garden.  He began his career as an intrepid collector of exotic plants when he joined one of Captain Cook’s voyages into the Pacific.  He returned with thousands of plants from all over the world and they became the core of Kew Gardens, one of the greatest horticultural collections in the world.

The hero of Signature is sent by Banks on expeditions to collect valuable plants and his adventures are an historical account of early explorations of the New World.  We learned from Richard Henry Dana’s Two Years Before the Mast that the physical hardships of these voyages are not exaggerated by Signature’s fictional account.  The hero of Signature eventually makes his home in Pennsylvania and his extensive garden there is reminiscent of the garden of John Bartram, the Early American collector of plants about whom we have also written.

So you see, Signature covers familiar ground for us and we enjoyed revisiting it in the company of an extraordinary heroine, Alma Whittaker.  She is gifted with a remarkable mind and her equally intelligent parents provided her with the education and tools needed to make life-long good use of her talents.  She “discovered” her own version of evolutionary theory based on a deep understanding of mosses, which model the mechanics of natural selection.

We don’t wish to give away too much of the plot because we hope you will be intrigued to read it.  Readers will have the privilege of eavesdropping on a fascinating (fictional) conversation with Alfred Russel Wallace, a contemporary of Darwin.  Although Darwin and Wallace shared a belief in evolution, they diverged on a variety of other topics.  Wallace’s busy mind strayed into spiritualism, hypnotism, and mesmerism as well as left-wing politics.  Wallace was as eccentric as Darwin was sensible and cautious.

Alfred Russel Wallace
Alfred Russel Wallace

Our heroine, Alma, confides to Wallace that despite a tortuous path in life, she considers herself lucky: “I am fortunate because I have been able to spend my life in study of the world…This life is a mystery, yes, and it is often a trial, but if one can find some facts within it, one should always do so—for knowledge is the most precious of all commodities.” 

Alma’s confession was a welcome reminder of why we persist in our effort to inform the public of the destruction of our public lands by native plant “restorations.”  Although we make little visible progress, we have learned a great deal about nature.  That is our reward.  Thank you, Alma, for the reminder of our mission to understand and inform and to Elizabeth Gilbert for the very pleasant entertainment of The Signature of All Things.

The Endangered Species Act is based on outdated science

We have reported to our readers many times about the changes in scientific opinion regarding invasion biology in the past fifty years, since the inception of the theories that originally supported that discipline.  Now we see an acknowledgement of the changed scientific viewpoint in a critique of the Endangered Species Act by the legal profession.

Holly Doremus is Professor of Law at Boalt Law School at the University of California, Berkeley.  Her critique of the Endangered Species Act (ESA) was published by the Journal of Law & Policy in 2010.  She previews her theme in her introduction:

“I am interested in why the ESA came to assume an unrealistically static vision of nature.  First, the Act’s static structure is typical of law in general, which has traditionally embodied the human search for stability.  Second, the Act is inevitably, a product of the political times in which it was drafted and of a rapid and chaotic legislative process, which did not encourage thoughtful examination of the complex contours of the conservation problem.  Third, it followed in part from incorrect but widely shared assumptions about the nature of the problem and potential solutions.  Fourth, scientific understanding was itself in transition as the law was being crafted, moving from a focus on the tendency of ecological systems to approach equilibrium to one on the ongoing dynamics of many systems.” (1)

We will focus on the fourth issue, i.e., how the ESA is in conflict with the reality of constantly changing ecosystems.

A Static Vision of Nature

The ESA is based on assumptions about nature that were the conventional wisdom at the time the law was passed in 1973:

  • Evolution was considered a series of events that occurred in the distant past and is no longer actively changing plant and animal species.  Theoretically evolution does not end, but at the time the ESA was passed in 1973, it was not believed to occur within a time frame that would be observable by man.  Plant and animal species were therefore viewed as being distinct and unchanging.
  • This view of evolution was consistent with the prevailing public opinion in the United States, which does not believe in evolution.  Many Americans believe that species have not changed since they were created by God.
  • Nature was perceived as reaching an “equilibrium state” that was stable over long periods of time.
  • Early conservation efforts were therefore based on the assumption that once achieved, an equilibrium state could be sustained if left undisturbed in nature preserves.

    Darwin's finches are an example of rapid evolution
    Darwin’s finches are an example of rapid evolution

We now know that these assumptions were mistaken.  Evolution can occur very rapidly, particularly amongst plants and animals with short life spans and frequent generations.   And ecosystems are constantly changing, particularly at a time of a rapidly changing climate and associated environmental conditions such as atmospheric conditions.

Professor Doremus tells us that ecological scientists played no role in the writing of the ESA and took little notice of the law when it was passed.  The press also ignored the new law, which may have been a factor in its being unnoticed by the scientists who may have been in a position to raise the questions that should have been asked.  “It seems that conservation scientists, like the general-interest press, and most legislators, did not consider the ESA groundbreaking, or even particularly important.” (1) In any case, the problems that have arisen in the implementation of the law were not foreseen by the politicians who passed it, nearly unanimously in 1973.

How does the ESA define “species?”

As its name implies, the heart of the law is how “species” are defined.  In fact, if the law had stopped at providing legal protection for “species,” we would not be experiencing nearly as much difficulty with the implementation of the law.  Unfortunately, the ESA’s “…definition of ‘species’ [is] broad, but not a model of clarity, ‘The term “species” includes any subspecies of fish or wildlife or plants, and any distinct population segment of any species of vertebrate fish or wildlife which interbreeds when mature.”  (1)

Splitting species into sub-species and “distinct population segments” has proved problematic because taxonomy (the classification of organisms) has always been inherently subjective and will probably continue to be.  The taxonomic system that was popular at the time the ESA was passed was Mayr’s biological species concept which identifies as a species any group that interbreeds within the group but not with outsiders.  This definition is not useful for a species that hybridizes freely, such as the manzanitas of which six species have been designated as endangered.  Professor Doremus tells us that US Fish & Wildlife Service now evaluates the legal consequences of hybridization on a case-by-case basis.

Since the ESA was passed, many competing definitions of “species” have been proposed by scientists.  There were 22 different definitions of species in the modern literature as recently as ten years ago.  These competing definitions reflect disagreement about appropriate criteria for identifying species—morphology, interbreeding, or genetic divergence, as well as the degree of difference needed to define the boundary between species.   We see these scientific controversies played out repeatedly in the law suits that are interpreting the ESA. 

The identification of “distinct population segments” amongst vertebrates has proved to be even more problematic.  Legal challenges to the determination of distinct population segments have reversed the rulings of the US Fish & Wildlife Service for many species that were considered genetically identical such as the sage grouse (eastern vs, western?) and the Preble’s meadow jumping mouse (found in different meadows in the Rocky Mountains).  In some cases, these rulings were reversed several times, and perhaps will be again!  These reversals reflect the ambiguity of the law, as well as the science of taxonomy.  The fact that the ESA specifically allows “citizen suits” has pushed the regulating agencies to implement the law more aggressively than  politics alone would have predicted.

Species can and do move

In addition to considering species immutable and unchanging, the ESA also takes a static view of where they live.  The concept of “distinct population segments” depends somewhat on the assumption that species of animals don’t radically alter their ranges in the short-term.  The assumption is also consistent with the underlying conservation policies that tend to preserve specific places in order to protect rare species within those places.

We now understand that some ecosystems are internally dynamic.  We recently told our readers of the need for the sand dunes near Antioch, California to move freely in the wind to sustain that fragile ecosystem.  Professor Doremus also tells us about the constantly changing courses of braided rivers in Nebraska that are essential to the sustainability of that unique ecosystem.

Platte River in Nebraska is a braided river. Creative Commons
Platte River in Nebraska is a braided river. Creative Commons

In a rapidly changing climate, the preservation of a species may require changing ranges.  If the climate becomes too cold, too hot, too wet, or too dry for a species of plant or animal, its immediate survival may require that it move to higher or lower altitudes or latitudes.  Moving may be a more effective strategy than the adaptation that may be slower than necessary to survive.  Freezing species into their historic ranges does not ensure their survival at a time of rapidly changing climate.  In some cases, a species has become plentiful in the new territory it has freely chosen to inhabit and simultaneously rare in its historic range where it has been designated as an endangered “distinct population.”  Draconian measures have been taken to restore a species in its historic range, where it is no longer adapted to current conditions.

We leave you with Professor Doremus’ observation about the ESA:  “The ESA’s static view of species, landscapes, and conservation obligations, while entirely understandable, has become a hindrance to effective conservation.  The ESA’s lofty goals of conserving species and the ecosystems upon which they depend cannot be achieved without a more realistic vision of the dynamic qualities of nature and the ability to respond to the changes that are inevitable in dynamic systems.”

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(1)    Holly Doremus, “The Endangered Species Act:  Static Law Meets Dynamic World,” Journal of Law & Policy, Vol. 32: 175-235, 2010.

Wily weeds win the war

Farmers have been battling with weeds since the advent of agriculture, about 6,000 years ago.  Most of the weapons used against weeds were mechanical until the last century or so when herbicides became the primary weapon.  At the same time that the weapon became more lethal, farming techniques changed to give weeds the advantage.  Farms became huge monocultures and crop rotations were abandoned in favor of the most profitable crop. 

Cornfield
Cornfield

When weeds evolved defenses against the herbicides, farmers responded by increasing doses and manufacturers created new products to which weeds hadn’t yet evolved resistance.  Finally, the use of herbicides skyrocketed when crop seeds were invented that weren’t killed by the herbicides, so that huge amounts of herbicides can be used without killing the crop. 

When Roundup with the active ingredient glyphosate went on the market in the 1970s, its manufacturer, Monsanto, claimed that weeds would not be able to evolve resistance to it.  And apparently that was initially true until Roundup was used on a huge scale when herbicide-resistant seeds were put on the market in the 1980s.   Norman Ellstrand of UC Riverside explains why:  “He argues that the reason was that farmers applied glyphosate to relatively little farmland.  As they applied it to more and more acreage, they raised the evolutionary reward for mutations that allowed weeds to resist glyphosate.  ‘That ups the selection pressure tremendously,’ he said.” *

There are now 24 species of weeds that are resistant to glyphosate and they are rapidly expanding their range in agricultural areas all over the world.  In 2012, an agricultural consulting firm reported that 34% of farms in the US had glyphosate-resistant weeds.  In the first half of 2013, half of all farms in the US are reporting glyphosate-resistant weeds.

Let’s take another approach

Obviously, we are losing the war against weeds.  So, let’s examine the strategy we have been using and try another approach.  Weed ecologists are now studying the strategies that weeds have used to cope with the weapons we have been using against them.  Here are a few of those strategies:

  • Some weeds have changed color so that they are indistinguishable from the crop they are hiding in.
  • Weeds that grew in dry ground, evolved to thrive in wet ground in rice fields that are flooded much of the crop season.
  • Some weeds became shorter to escape the mowing and harvesting of the agricultural crop.
  • Some weeds drop their seeds and go dormant before the crop is harvested and create seed banks that can sprout when conditions are more favorable for them.
  • Parasitic weeds wrap around their host and steal nutrients from them.

Some weed ecologists believe that a better understanding of the mechanisms used by weeds to foil our attempts to control them will enable us to devise better weapons against them.  They believe that developing new herbicides and/or using more of them will always be a short-term solution. 

Darwin2

For example, David Mortensen of Penn State is “investigating controlling weeds by planting crops like winter rye that can kill weeds by blocking sunlight and releasing toxins.  ‘You want to spread the selection pressure across a number of things that you’re doing so that the selection pressure is not riding on one tactic,’ he said.”*

Regardless of what method is used to control weeds in the future, let’s consider the toxicity of the method the most important criterion for judging their effectiveness.  Even if it kills fewer weeds, the least toxic alternative is the best alternative in our opinion.

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*Carl Zimmer, “Looking for Ways to Beat the Weeds,” New York Times, July 15, 2013.

Professor Arthur Shapiro’s Review of Emma Marris’ Rambunctious Garden

Rambunctious GardenProfessor Arthur Shapiro is Distinguished Professor of Evolution and Ecology at University of California Davis and a renowned expert on the butterflies of California.  His public comment on the Draft Environmental Impact Report for the Natural Areas Program is one of the most popular articles on Million Trees.

Professor Shapiro has written a review of Emma Marris’ Rambunctious Garden and given us permission to reprint it here.  We share his high opinion of Ms. Marris’ book and we urge you to give it the careful read it deserves.

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Rambunctious Garden: Saving Nature in a Post-Wild World by Emma Marris

Review by: Arthur M. Shapiro
The Quarterly Review of Biology, Vol. 88, No. 1 (March 2013), p. 45
Published by: The University of Chicago Press
Stable URL: http://www.jstor.org/stable/10.1086/669328

“Several years ago, I attended a seminar on the psychology of the animal-liberation movement. The speaker observed that although very few animal-lib activists were actually religious, most such people scored very highly on the “religiosity” scale in personality inventories. He suggested that animal liberation served the same functions for such people as religion did for many more: it gave life meaning and conferred a group identity centered on shared moral superiority over others. After years of interacting with “weed warriors”—people who spend their free time trying to eradicate “invasive species” from parks and public lands—I would advance the same hypothesis about most of them. They tend to be absolutely convinced of the righteousness of their cause and highly resistant to any suggestion that naturalized exotics might not be all bad. They also tend to be oblivious to the disconcerting degree to which their rhetoric converges to that of racists and xenophobes, and highly defensive if you point that out to them. After all, they are on the “green” side, right?

In the face of such popular enthusiasm for the alarmist viewpoint on exotics, Emma Marris, a professional science writer, has produced an eminently reasonable, well-researched, and engagingly written defense of the notion that human beings have changed the world and the most sensible way to deal with that is to manage it for the greatest good. She demonstrates very convincingly that communities and ecosystems have always been in flux as the physical world changes around them. The idea of freezing them at some arbitrary moment in time is as wrongheaded as it is impractical. Some naturalized exotics present serious threats to human beings or their support systems: we call them pests, pathogens, and vectors, and they are not what is at issue. Some are such radical ecological gamechangers that they need to be assessed with an eye to the full scope of their impacts (think cheatgrass in the desert and its impact on fire ecology). Most, however, are trivial, and in a world of limiting resources where we must assign priorities to our actions, they do not merit serious attention. But it is not merely a matter of using our management resources effectively. Much of our “invasive species” discourse simply ignores the evolutionary creativity consequent on community reorganization.

Yet we know both in theory and from the fossil record that precisely such creativity is essential for long-term survival in a changing physical context. Ecotypes or ecological races arise in response to novel challenges, both biotic and abiotic. The future of endangered species is likely to depend on such processes. Failure to appreciate this is the single biggest flaw in the “climatic envelope” or “niche modeling” approach to conservation biology. Much of California’s lowland butterfly fauna is now dependent on nonnative larval host plants. When I tell garden clubs—or public land managers—that successful eradication of invasive “weeds” would drive their beloved backyard butterflies to extinction, they stare at me in disbelief. But it is true and emblematic of the larger problem explored very well in this volume.

Shortly after Marris’s book appeared there was a flurry of articles in the professional literature advancing precisely the same ideas. Among the best are by Carroll (2011. Evolutionary Applications 4:184–199) and Thomas (2011. Trends in Ecology and Evolution 26:216 –221). But Marris got there first, and with luck her wise words will be read and acted upon far and wide.”

Arthur M. Shapiro, Center for Population Biology, University of California, Davis, California

Hybridization is an adaptive strategy for species survival

Large ground finch. Linda Hall Library

We introduced Darwin’s finches to our readers in our previous post.  We told you about the research of Rosemary and Peter Grant on the Galápagos Islands that documented the rapid adaptation of the finches to radical changes in their food sources resulting from extreme weather events.  In this post we will continue the story by telling you about another of the amazing discoveries of the scientists studying the finches over a period of nearly 30 years.

Natural selection resulted in the survival of finches with body sizes and shapes that were best suited to the availability and type of food.  Sexual selection enhanced those physical characteristics during periods in which females had more choice because they were greatly outnumbered by males.  In addition to these adaptations, the birds increased their cross-breeding with other species and the resulting hybrids actually had a survival and breeding advantage over their species “pure” parents.*

In the first five years of the research study, there was little evidence of different finch species interbreeding, known as hybridizing.  On those rare occasions when species interbred, the resulting generation was not as successful as their parents, with respect to finding a mate and raising another generation.

Such lack of success of hybrids is considered the norm in nature.  In fact, many hybrids are sterile, incapable of reproducing.  Think of the sure-footed but sterile mule—the offspring of a horse and a donkey—as the classic example of a hybrid.

After the severe drought of 1977 and the flood of 1983, the Grants began to notice an increasing number of cross-breeding birds.  It seemed that the resulting hybrids were having more breeding success than the pre-drought hybrids and the data confirmed their observation.

This counter-intuitive conclusion required some careful consideration and the conclusion is a valuable lesson in our rapidly changing environment.  The environment on the islands was radically transformed by the severe drought and subsequent flood.  The cactus was overwhelmed by a vine that smothered it.  The plants with big, hard seeds were attacked by a fungus that decimated the population.  The small seeded plants thrived and became the dominant food source.

The rapidly changing environment was causing more rapid evolution and the genetic variability of hybrids was giving them an advantage.  If the environment is changing rapidly in unpredictable ways, the birds could increase the odds of finding a winning strategy by increasing the variability of their genes, sometimes resulting in novel traits.

We cannot and should not, however, anthropomorphize the birds by imputing motives to the selection of a mate of another species.  The starving cactus finch probably observes that a male of another species—a seed-eating ground finch, for example—appears to be more fit than a male of her own species.  She is not thinking of the odds of increasing genetic variability.  Natural selection operates without the conscious effort of species.

The implications of hybridization

We are experiencing a period of rapid change because of the anthropogenic (caused by humans) impacts on the environment, most notably climate change, but surely many other impacts which we don’t necessarily understand.  These would seem the ideal conditions for the hybridization of species which speeds up evolution by increasing genetic variability. 

Unfortunately, one of many strategies of the native plant movement and nativism in the animal kingdom is to prevent hybridization because it is perceived as a threat to native plants and animals.  We have reported to our readers some examples of such attempts to prevent hybridization and there are many more in the literature:

The variety of California poppy being eradicated from the Presidio in San Francisco.

Are efforts to prevent hybridization depriving plant and animal species of opportunities to adapt to the rapidly changing environment?  We don’t know the answer to that question, but we find it a provocative line of inquiry.

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*This information is drawn from:   Jonathan Weiner, The Beak of the Finch, Vintage Books, 1994

Darwin’s Finches: An opportunity to observe evolution in action

The finches on the Galápagos Islands are called Darwin’s finches because of the important role they played in the development of his theory of natural selection and evolution of species.

Galapagos Islands, satellite photo. Daphne Major is too small to be visible.

Charles Darwin spent five weeks on the Galápagos Islands in 1835, near the end of a five year expedition.  Although he noticed the similarity of the birds on the different islands, he didn’t realize they were all related to one common ancestor until he returned home.  Fortunately, he collected many specimens of the birds to bring home for study.  It wasn’t until those specimens were examined by an ornithologist that he learned they were 13 species of finches, distinguished primarily by variations in the size of the bird and its beak size and shape.

Unfortunately, he hadn’t recorded which islands the specimens were from, so the implications of their differences were somewhat of a mystery.  He lamented in Voyage of the Beagle, “It is the fate of every voyager, when he has just discovered what object in any place is most particularly worthy of his attention, to be hurried from it.”

But Darwin was no dummy, so despite lacking the data necessary to prove his point, he speculated in his memoir, “…in the thirteen species of ground-finches, a nearly perfect gradation may be traced from a beak extraordinarily thick, to one so fine, that it may be compared to that of a warbler.  I very much suspect that certain members of the series are confined to different islands…”

Such development of new species from a common ancestor in response to varying environmental conditions is called adaptive radiation.  Species also diverge from one another to reduce competition by specializing in a particular food forage type or technique.  Nearly 200 years later, science has proven Darwin’s hunch, but just as he had no way of knowing how long this process of speciation took, modern science still cannot answer that question.

Darwin’s finches continue to change in response to changing conditions

Large ground finch (Geospiza magnirostris). Linda Hall Library

Rosemary and Peter Grant have studied the finches on two Galápagos Islands (Daphne Major & Genovesa) for about thirty years.  Nearly every year they visited the finches, weighing and measuring every appendage of the birds, especially their beaks.  They banded the birds so they could follow their breeding success. They also measured their food:  how much food but more importantly how accessible the food is to the birds such as the difficulty of opening seeds.

The availability and type of food is what determines the shape and size of the birds’ beaks.  In a year in which there is plenty of rain, there is usually plenty of food which is relatively easy for the birds to eat.  When it doesn’t rain, the birds are reduced to the difficult task of trying to crack open a large, hard seed pod.  That’s when a big bird with a big beak has an advantage.   

Extreme weather is therefore a “selection event,” a time when not every bird is equipped to survive.  And the birds that survive are best equipped for those extreme conditions.  When the conditions improve, the bird that survived the hard time is not necessarily best equipped for the good times.

These are the principles of natural selection, but they were largely theoretical until the Grants spent many years watching the birds and how they survived such selection events.  They had the good fortune to witness two such events in the first twelve years of their study.

The drought

In the fifth year of the Grants’ study, 1977, there was a severe drought.  After one short storm in early January, there was no more rain for the remainder of the year.  In January, there were 1,300 finches on the island they studied that year.  At the end of the year, there were less than 300 finches left on the island.

The Grants measured and weighed the birds that survived the drought.  Then they returned to their lab at Princeton University to study their data:

  • Not a single finch was born and survived on the island in 1977
  • The surviving birds were 5-6% larger than the dead birds
  • The average beak size of the birds that survived was 11.07 mm long and 9.96 mm deep.  The average beak size of the birds that did not survive was 10.68 mm long and 9.42 mm deep.  These critical differences were too small to see with the naked eye, but became evident when the measurements were analyzed by computer.  This makes a strong case for scientific measurement verses anecdotal observation, which passes for “evidence” amongst native plant advocates.
  • Few female birds survived the drought, presumably because male birds are larger than females.

In the years following that drought, sexual selection played an important role in maintaining the population of larger birds with larger beaks.  Because the female birds were scarce, they could be very selective in their mates.  Who did they choose?  Of course, they chose the males with the traits that allowed the birds to survive the drought year.  When the ratio of males to females is more even, sexual selection plays a less important role in natural selection in monogamous species such as the finches.

The flood

Here on the West Coast, we are familiar with the weather phenomenon of El Niño, the nickname given to a heavy rain year resulting from an unusually warm ocean current.  In 1983, we experienced the strongest El Niño on record, as did the Galápagos Islands. 

In 1983, the Grants witnessed the reversal of the results of the 1977 drought:  “Natural selection had swung around against the birds from the other side.  Big birds with big beaks were dying.  Small birds with small beaks were flourishing.  Selection has flipped.” *

Lessons learned

Darwin’s finches give us reason for optimism about the future.  Nature can and will respond to changes in the environment.  Natural selection is not just an historical process that stopped when The Origin of Species was written nearly 200 years ago.  Natural selection is operating at all times, whether we notice it or not. 

However, the loss of nearly 80% of the birds on a Galápagos Island during a severe drought is not cause for celebration.  Although the species survived, hundreds of individual birds did not.  So, we are quick to add that our confidence in the adaptive abilities of nature is not an argument for abusing the environment.

Climate change has caused extreme weather events which are undoubtedly selection events for many species of plants and animals.  Unless we take action to reduce greenhouse gas emissions we can predict more of such events.  Destroying millions of trees solely because they are not native is irresponsible given the contribution their destruction makes to the greenhouse gases causing climate change.

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*Jonathan Weiner, The Beak of the Finch, Vintage Books, 1994

Doug Tallamy refutes his own theory without changing his ideology

In our debates with native plant advocates, the scientist who is most often quoted to support their beliefs is Doug Tallamy who wrote an influential book, Bringing Nature Home:  How Native Plants Sustain Wildlife in our Gardens.    Professor Tallamy is an entomologist at the University of Delaware.

Professor Tallamy’s hypothesis is that native insects require native plants because they have evolved together “over thousands of generations.”  Because insects are an essential ingredient in the food web, he speculates that the absence of native plants would ultimately result in “ecological collapse” as other animals in the food web are starved by the loss of insects. (1)

Professor Tallamy freely admits that his theory is based on his anecdotal observations in his own garden, not on scientific evidence:  “How do we know the actual extent to which our native insect generalists are eating alien plants?  We don’t until we go into the field and see exactly what is eating what.  Unfortunately, this important but simple task has been all but ignored so far.”  (1)

This research has now been done to Professor Tallamy’s satisfaction by a Master’s Degree student under his direction.  The report of that study does not substantiate Professor Tallamy’s belief that insects eat only native plants.  In his own words, Professor Tallamy now tells us:

“Erin [Reed] compared the amount of damage sucking and chewing insects made on the ornamental plants at six suburban properties landscaped primarily with species native to the area and six properties landscaped traditionally.  After two years of measurements Erin found that only a tiny percentage of leaves were damaged on either set of properties at the end of the season….Erin’s most important result, however, was that there was no statistical difference in the amount of damage on either landscape type.” (2)

Corroborating Evidence

This finding that insects are equally likely to eat native and non-native plants may be new to Professor Tallamy, but it isn’t new to the readers of Million Trees.  We have reported many studies which are consistent with this finding.

Anise Swallowtail butterfly in non-native fennel
The English garden, where plants from all over the world are welcome

Specialists vs. Generalists

When debating with native plant advocates, one quickly learns that the debate isn’t ended by putting facts such as these on the table.  In this case, the comeback is, “The insects using non-native plants are generalists.  Insects that are specialists will not make that transition.”  Generalists are insects that eat a wide variety of plants, while specialists are limited to only one plant or plants in the same family which are chemically similar.

Professor Tallamy offers in support of this contention that only “…about 10 percent of the insect herbivores in a given ecosystem [are not specialists],” implying that few insects are capable of making a transition to another host plant.

However, categorizing insects as specialists or generalists is not a dichotomy.  At one extreme, there are some insects that choose a single species of plant as its host or its meal.  At the other extreme, there are insects that feed on more than three different plant families.  It is only that extreme category which has been estimated at only 10% of all phytophagous (plant-eating) insects.  The majority of insects are in the middle of the continuum.  They are generally confined to a single plant family in which the plants are chemically similar.

Putting that definition of “specialist” as confined to one plant family into perspective, let us consider the size of plant families.  For example, there are 20,000 plant members of the Asteraceae family, including the native sagebrush (Artemisia) and the non-native African daisy.  In other words, the insect that confines its diet to one family of plants is not very specialized. 

Soapberry bug on balloon vine. Scott Carroll. UC Davis

Professor Tallamy offers his readers an explanation for why specialist insects cannot make the transition from native to non-native plants.  He claims that many non-native plants are chemically unique and therefore insects are unable to adapt to them.  He offers examples of non-native plants and trees which “are not related to any lineage of plants in North America.”  One of his examples is the goldenrain tree (Koelreuteria paniculata).  This is the member of the soapberry (Sapindaceae) family to which the soapberry bug has made a transition from a native plant in the soapberry family in less than 100 generations over a period of 20 to 50 years.  Professor Tallamy’s other examples of unique non-native plant species are also members of large plant families which probably contain native members.  Professor Tallamy is apparently mistaken in his assumption that most or all non-native plants are unique, with no native relatives. 

The pace of evolution

Even if insects are “specialists” we should not assume that their dependence on a native plant is incapable of changing over time.  Professor Tallamy’s hypothesis about the mutually exclusive relationships between native animals and native plants is based on an outdated notion of the slow pace of evolution.  The assumption amongst native plant advocates is that these relationships are nearly immutable.

In fact, evolution continues today and is sometimes even visible within the lifetime of observers.  Professor Tallamy provides his readers with examples of non-native insects that made quick transitions to native plants:

  • The hemlock wooly adelgids from Asia have had a devastating effect on native hemlock forests in the eastern United States.
  • The Japanese beetle introduced to the United States is now eating the foliage of over 400 plants (according to Professor Tallamy), some of which are native (according to the USDA invasive species website).

These insects apparently made transitions to chemically similar native plants without evolutionary adaptation. If non-native insects quickly adapt to new hosts, doesn’t it seem likely that native insects are capable of doing the same?  That is both logical and consistent with our experience.    For example, the native soapberry bug mentioned above has undergone rapid evolution of its beak length to adapt to a new host.

Although Professor Tallamy tells us that the relationship between insects and plants evolved over “thousands of generations,” he acknowledges much faster changes in plants when he explains why non-native plants become invasive decades after their arrival:  “Japanese honeysuckle, for example, was planted as an ornamental for 80 years before it escaped cultivation.  No one is sure why this lag time occurs.  Perhaps during the lag period, the plant is changing genetically through natural selection to better fit its new environment.”  Does it make sense that the evolution of plants would be much more rapid than the evolution of insects?  Since the lifetime of most insects is not substantially longer than the lifetime of most plants, we don’t see the logic in this assumption.

Beliefs die hard

Although Professor Tallamy now concedes that there is no evidence that insects are dependent upon native plants, he continues to believe that the absence of native plants will cause “ecological collapse.”  In the same book in which he reports the study of his graduate student, Professor Tallamy repeats his mantra:  “…our wholesale replacement of native plant communities with disparate collections of plants from other parts of the world is pushing our local animals to the brink of extinction—and the ecosystems that sustain human societies to the edge of collapse.”

This alarmist conclusion is offered without providing examples of any animals being “pushed to the brink of extinction.”  In fact, available scientific evidence contradicts this alarmist conclusion. (3)

Here are more articles about the mistaken theories of Doug Tallamy:

  • Doug Tallamy claims that non-native plants are “ecological traps for birds.”  HERE is an article that disputes that theory.
  • Doug Tallamy claims that native and non-native plants in the same genus are not equally useful to wildlife, but he is wrong about that.  Story is HERE.
  • Doug Tallamy advocates for the eradication of butterfly bush (Buddleia) because it is not native.  He claims it is not useful to butterflies, but he is wrong about that.  Story is HERE.
  • Doug Tallamy publishes a laboratory study that he believes contradicts field studies, but he is wrong about that.  Story is HERE.
  • Doug Tallamy speaks to Smithsonian Magazine, Art Shapiro responds, Million Trees fills in the gaps:  HERE
  • Doug Tallamy’s Nature’s Best Hope perpetuates the myth that berry-producing non-native plants must be eradicated because they are less nutritious than the berries of native plants.  Available HERE. 
  • Doug Tallamy believes we must prevent hybridization.  Hybridization is a natural process that increases biodiversity and enables plants and animals to adapt to changes in the environment.  Available HERE.
  • There is NO evidence to support Doug Tallamy’s claim that insect populations are declining because of the existence of non-native plants.  Available HERE.

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(1)    Tallamy, Doug, Bringing Nature Home, Timber Press, 2007

(2)    Tallamy, Doug, “Flipping the Paradigm:  Landscapes that Welcome Wildlife,” chapter in Christopher, Thomas, The New American Landscape, Timber Press, 2011

(3)    Erle C. Ellis, et. al., “All Is Not Loss:  Plant Biodiversity in the Anthropocene,” http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0030535

California Academy of Sciences: “Evolution in the Park”

In 2003, when the great debate with native plant advocates about the future of San Francisco’s public parks reached a fever pitch, the California Academy of Sciences stepped into the fray by publishing this article in their quarterly publication, California Wild.  This article was written by Gordy Slack, free lance science writer and former editor of California Wild. 

Golden Gate Park in 1880. The trees are about 10 years old. In the distance, looking south, we see the sand dunes of the Sunset District. That’s what most of Golden Gate Park looked like before the trees were planted.

As you will see, “Evolution in the Park”  (1) urges the public to consider that the parks of San Francisco have been transformed over the past 150 years from predominantly barren sand dunes to green oases of non-native trees and plants.  Using Golden Gate Park as an example, Mr. Slack reminds us that the non-native trees provided the windbreak needed to protect the entire landscape which we admire today.  The park has changed and it will continue to change, because nature is dynamic.  The forces of evolution are stronger than human desires to freeze-frame our world.

At the time, we were deeply grateful to Mr. Slack and to the Academy of Sciences for taking a position on the controversy.  We remember thinking that the opinion of this prestigious institution would surely settle the controversy.  But we were mistaken, because native plant advocates would not even read this article, let alone heed its message.

As the Environmental Impact Report for the Natural Areas Program undergoes revision and the controversy heats up again, we reprint “Evolution in the Park.”  We can only hope that someday reason will prevail.

Tree ferns from New Zealand are one of many species of non-native trees that make Golden Gate Park the beautiful place it is today. Creative Commons

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“When San Francisco officials asked the great nineteenth-century landscape architect Frederick Law Olmstead how to turn the wind-scoured dunes of the western half of the city into a green, rambling park, he was happy to offer advice: Don’t bother, he said, it’ll never work.

They went ahead anyhow, establishing three-mile-long, 1,107-acre Golden Gate Park on April 4, 1870. The decades that followed saw an almost unbelievable transformation under the strong hand of the park’s first superintendent, William Hammond Hall. He shaped glades and grew forests, dug lakes and planted lawns, until people nearly forgot that under the acres of grass and trees and shrubs lay mountains of sand.

The invention of Golden Gate Park was an amazing engineering and horticultural accomplishment, but it was not an environmental one—at least not in the sense of conserving native natural resources. If the California Native Plant Society (CNPS) had existed then, it would never have allowed Hall to spread tons of exotic barley seed over the dunes as part of his plan to “reclaim” them. The barley achieved what Hall wanted—to create favorable conditions for the thousands of alien trees and shrubs he would soon plant. And yet the CNPS now meets in Strybing Arboretum and botanists love the park. Everyone does. It would seem as silly to criticize the park’s blue gum trees for being out-of-towners as it would be to criticize most of us for being exotics. The park is as much an urban invention as the parking lot or the shopping mall, only much better. There is nothing wild about it…except what goes on there.

Nancy de Stefanis is the Director of San Francisco Nature Education, a group that leads nature studies in Golden Gate Park. She is perhaps best known for her discovery in 1993 that great blue herons were nesting in the park’s Stow Lake, and for her efforts to protect those nests from raccoons and other threats (California Wild, Summer 2002). A few days ago, on an early morning walk in the park, she saw a great blue plucking endangered red-legged frogs out of a pond. She saw feral cats, gray squirrels, and a three-foot-long box turtle. All this, and she had intended to look for birds! She saw those, too: an albino robin, varied thrushes, ravens, white- and gold-crowned sparrows, and a courting pair of red-tail hawks doing loopty-loops and dives. She saw a bevy of seven California quail running through Strybing Arboretum, the only population of quail left in the park. “It was incredible,” she said. “We saw 25 bird species easy.”

Anyone who’s spent much time in Golden Gate Park has wild stories to tell. My own favorite took place a few years ago, after I’d pulled an all-nighter at the magazine and was tired enough to sleep dangling off of Half Dome. Half Dome was too far away, so I walked a few hundred yards east on Middle Drive and up a tiny path back to Lily Pond. I walked the perimeter looking for a place to sleep. The pond had steep vegetated banks all around except for a small, reasonably sloped patch of dirt on the east side. I kicked away some guano, put a newspaper under my head, and fell asleep.

I woke up half an hour later; something soft was tickling my arm. I raised my head slowly to find myself surrounded by mallards. There must have been 20 and they filled every inch of the dirt patch around me. One nestled comfortably between my outstretched arm and my torso.

Each duck had its head swiveled and tucked into the feathers on its back. When I lifted my own head, the birds next to me raised and turned theirs as well, and a couple of them stirred, causing a chain reaction of awakenings in the ultimate morning-after surprise. No one lost his or her cool, though. I tiptoed out of their realm and headed back to work, downy feathers clinging to my sweater and my hair. That was how I became the Man Who Sleeps with Ducks.

Raymond Bandar, a field associate in the Academy’s Department of Ornithology and Mammalogy, grew up in Golden Gate Park and has a thousand wild stories to tell. He says that in the 1940s, when he was a boy, it was a “biologist’s paradise.” He spent long summer days hunting for garter snakes, alligator and fence lizards, bush rabbits, Pacific pond turtles, weasels, and red-legged frogs. Peacocks roamed free in the park, and there Bandar courted his wife, Alkmene. They took long, moonlit walks from the beach to the park’s entrance on Stanyan, stopping to spoon in the Valley of the Moon.

Most old-timers like Bandar long for the good old days, when the park was “less manicured.” It’s hard to tell if this is because the park used to be wilder, or because the old-timers were. But there’s no doubt that the park refuses to cooperate by holding still. As Heracleitus said, “You can’t step into the same river twice.” (Or as Cratylus, Heracleitus’s follower, trumped, ‘You can’t step into the same river once.’)

The park’s “ecosystems” are a moving target, changing with park administrations and larger cycles of growth and death. In recent years, the Parks Department has cleared away much of the undergrowth that had been protecting ground-nesting birds—and homeless humans. Other forces originate outside the park but have an influence by increasing, diminishing, or eliminating the animals that live within. If there are no peregrines anywhere else in California, there aren’t going to be any in Golden Gate Park either.

Late Academy ornithologist Luis Baptista used to talk about the 1980s in the park. California quail were common then, running here and there on urgent business. Native bush rabbits lived here, too. The rabbits are now gone and the quail nearly so. I’ve heard speculation that the rabbit population may have collapsed partly under predation by humans, too. But both are most likely victims of the park’s shifting food web.

Raptors returned when their populations rebounded from the DDT poisoning that largely ended four decades ago. Recently, red-tailed, red-shouldered, and Cooper’s hawks have moved in, according to Douglas Bell, a biology professor at California State University in Sacramento. The park is now “probably a sink for white-crowns” he says. “It draws them in, but because of the intense predation, their survivorship is very low.” But even bigger players in the songbird and quail equation are the park’s resident feral cats. According to Baptista and Bell, white-crowned sparrow deaths in the park are probably due mostly to cats.

In addition to feral cats and other predators, floral changes affect park wildlife as well. Many of the Park’s trees are reaching climax now, says Peter Dallman, who is writing a natural history guide to Strybing Arboretum. The big trees are falling or are being cut down in anticipation of their natural collapse. The pygmy nuthatch, a bird that nests in the park’s climax Monterey pine forest, will likely flee the park when those trees come down.

Today, raccoons are plentiful. So are ravens, though Bell remembers that not long ago no ravens nested here. Exotic cowbirds have arrived, too; they lay their eggs in the nests of other birds, which then raise ravenous cowbird chicks, often at the expense of their own young. Squirrels are multiplying out of control, says Dallman.

Cat populations are strong, but not as strong as their political lobby. The bison herd, introduced to the park in 1894, remains stable at eleven. But the reintroduced grizzly bears (Bandar remembers when there were at least two sad grizzlies in cages in the park’s southeast corner) are long gone. The last Golden Gate grizzly, Monarch, is now stuffed and on exhibit in the Academy’s Wild California Hall.

These changes and conflicts raise some uncomfortable questions about the park and its mission. By what standard can the costs or benefits of these changes be measured? Should we be trying to restore Golden Gate Park systems and populations that are at bottom artificial? Should we simply maintain the species we prefer, and get rid of, or let slip away, the unpopular ones? Should “maximum diversity” be the goal, and mandate mediations of conflicts that arise between incompatible species, such as cat and quail?

To maintain quail in the park for the long term, for instance, would require “intensive and sustained human intervention,” says Bell. “We’d have to rely on the full range of wildlife management techniques.” Predation would have to be monitored and protective habitat cultivated. New quail stocks would have to be introduced, and electrically charged wire cages (through which the quail could fit, but not cats or ravens or raptors) could be built around nesting areas. But without heroic and constant human support, the quails’ days in the park are numbered.

Like its creation, the park’s future will be shaped by human invention, its progression determined by our priorities.”

Golden Gate Park, aerial view. Gnu Free Documentation

(1) Gordy Slack, “Evolution in the Park,” California Wild, Spring 2003 [reprinted with permission of author]

Nature is resilient, animals can adapt to change

We are always puzzled by the widespread belief amongst native plant advocates that native animals are dependent upon native plants and the corollary argument that non-native plants are invasive because they have no predators.  We suspect that one of many reasons for this assumption is a lack of understanding about evolution.  That is, if you believe that animals are unable to adapt to new plant species, then you probably assume that the new plant species are not useful nor are they prey to native animals.  

The Gallup Poll tracks the opinions of Americans regarding evolution.  In 2010 a surprisingly small percentage of Americans (16%) believed in the evolution of man unguided by God.  Even amongst those who believe in evolution, it is often seen as an historical process that moves too slowly to be perceived.  Science has only recently found living examples of on-going evolution:

“A growing appreciation that organic evolution, like mountain building, is an ongoing rather than simply historical process has stimulated an infusion of evolutionary thinking into mainstream ecology.”(1)

The Soapberry Bug

Soapberry bug on balloon vine. Scott Carroll, UC Davis

The soapberry bug (Jadera haematoloma) is an example of a native insect that has changed genetically in less than 100 generations over a period of 20 to 50 years in response to a new non-native plant host. 

The soapberry bug is named for the plant upon which it depends for both food and reproduction, the Sapindaceae family (‘Soapberry’ family).  In southern Florida, the native host plant of the soapberry bug was the balloon vine (Cardiospermum corindum).  As its name suggests, its seed is large and round.  The soapberry bug that feeds on that seed has a large jaw–up to about 70% of its body length–that enables it to get the seed into its mouth. 

In the 1950s a new member of the Sapindaceae family of plants was introduced to southern Florida, the Chinese flametree (Koelrueleria elegans) as an ornamental.  Its seed is much smaller than the seed of the balloon vine.  The soapberry bug quickly made a transition to its new host and over time it evolved several adaptations to it.  The jaw of the soapberry bug that feeds on the flametree is much smaller, as little as 50% of its body length. 

The life cycle of the soapberry bug has also changed and is better suited to the brief, simultaneous availability of seeds of its new host, the flametree:  “The flametree-specialized race [of soapberry bug] has a briefer development time (and thus an earlier age at first reproduction), greater fecundity, and exhibits greater expenditure of effort towards reproduction than the balloon vine race of J. haematoloma from which they originated.”(2)

In south Florida, the soapberry bug now has two genetically distinct races that are suited to their specific hosts–one native, one not.  The original race has not changed where its host is the native balloon vine.  The soapberry bug is not very mobile, so these two populations are physically separated.  This is an example of increased genetic biodiversity in response to an introduced plant. 

There are 400 genera and 1,500 species of plants in the Sapindaceae family all over the world(3), so we should not be surprised to find many other examples in the scientific literature of insect hosts that are adapted to them, whether they are native or introduced plants, as well as differences in those insects that are suited to the specific plants and/or their locations.  The soapberry bug isn’t an isolated example of an insect that has rapidly evolved to adapt to new hosts.  On the other hand, science cautions us against generalizing to all insects. 

We offer our readers three sources of information, depending upon their scientific knowledge.  The National Public Radio story about soapberry bug evolution is addressed to the layman.  At the opposite extreme, the citation in our footnotes is addressed to scientists with expertise in genetics.  The middle ground, from which we drew most heavily, is a website about soapberry bugs. 

Cheerful conclusion

As we often do, we conclude cheerfully that nature is remarkably resilient.  Although nature is less fragile than native plant advocates believe it to be, we don’t take that as an invitation to abuse it.  We treat nature with respect, and that includes taking care of what is here, whether it is native or non-native.  

(1) Carroll, Scott P., et. al., “Genetic architecture of adaptive differentiation in evolving host races of the soapberry bug, Jadera haematoloma,” Genetica, 112-113: 257-272, 2001