Refuting Jake Sigg: No, 90% of Insects Do Not Eat Only Native Plants

Jake Sigg, considered the doyen of San Francisco’s native plant activists, has an influential newsletter. Recently, it said: “Did you know that 90 percent of insects can only eat the native plant species with which they’ve co-evolved?” It included a link to a video from the California Native Plant Society (CNPS) … which provided no evidence for the statement at all. Nor was there any data to substantiate the claim – which is false. In fact, as Professor Art Shapiro points out, insects easily adapt to using other plants than the ones  they “co-evolved” with. He notes, “… the urban-suburban California butterfly fauna is now overwhelmingly dependent on non-native plants.

FIRST, THE NATIVE PLANT SOCIETY VIDEO

Here’s the link to the video:  Plants are the Foundation. https://www.facebook.com/YerbaBuenaCNPS/videos/459268941549309/

Not only did the video from not contain any reference to 90% of insects, it was in itself an interesting piece of sleight-of-hand. It made the fair point that plants were the foundation of the web of life.

Then, I suppose because it was from CNPS, it said: “None of us can live without them, especially native plants” and “Native plants support local wildlife”… the video shows a Western Tiger Swallowtail butterfly fluttering in. They’re native butterflies, but they don’t need native plants. In San Francisco, they breed on (non-native) London Plane Trees that are found on Market Street and other urban streets, which means their caterpillars readily eat those non-native leaves.

The video continues...”and ecosystems. The web of life depends on them For habitat

And it illustrates this with a photograph of a great horned owl, which nests on large tall trees, usually non-native eucalyptus, as in this photograph below.

Bumblebee on oxalis flower

Bumble bee on wild radish flower

 

“for food”

Then it shows a bumblebee on a Western thistle (native)… except that bumblebees happily nectar on a vast number of non-native plants, including wild radish and the yellow oxalis that Jake Sigg loves to hate.

Then it adds a picture of a Monarch butterfly… which does indeed depend on milkweed as its nursery plant (though it nectars on non-native ivy flowers as well as eucalyptus blossoms). But it readily breeds on non-native milkweed as well as native milkweed (and contrary to some native species activists, non-native milkweed does not spread disease or reduce breeding success). More to the point, the western migration of the Monarch butterfly relies heavily on (non-native) eucalyptus trees to over-winter in. Without the eucalyptus, the western migration will probably die out.

It argues that habitat is shrinking (with a picture of a highway in LA), which is perhaps reasonable (though farming is more likely the culprit than urban sprawl). And goes on to suggest planting native plant gardens. That’s not objectionable in itself, of course, but it’s planting a mix of various kinds of plants that will benefit the most species.

So though the video certainly shows the need for plants as the basis of an ecosystem, it emphatically does not make the case for native plants.

NO, 90% OF INSECTS DO NOT DEPEND ON NATIVE PLANTS

We reprint, with permission and minor changes, a thorough refutation of the statement from Professor Art Shapiro, published on the Million Trees blog. In sum, Professor Shapiro challenges the statement, and points out that “ecological fitting” – which allows species that didn’t “co-evolve” to interact – is very common. He cites examples from all over the world.

ERADICATING NON-NATIVE PLANTS DOES NOT BENEFIT INSECTS

We briefly reactivate the Million Trees blog to publish an interesting and important debate between Jake Sigg and Professor Art Shapiro about the relationship between insects and native plants.  Their debate was initiated by this statement published in Jake Sigg’s Nature News on April 26, 2019:

“Did you know that 90 percent of insects can only eat the native plant species with which they’ve co-evolved?”

Jake Sigg has been the acknowledged leader of the native plant movement in the San Francisco Bay Area for 30 years.  He is a retired gardener for the Recreation and Parks Department in San Francisco. Art Shapiro is Distinguished Professor of Ecology and Evolution at UC Davis.  He has studied the butterflies of Central California for 50 years.

Jake and Art are both passionately committed to the preservation of nature, but their divergent viewpoints reflect their different experiences.  Jake’s viewpoint is based on his personal interpretation of his observations.  As a gardener, his top priority is the preservation of plants rather than the animals that need plants.  As a scientist, Art’s viewpoint is based on empirical data, in particular, his records of plant and butterfly interactions over a period of 47 years as he walked his research transects about 250 days per year. The survival of butterflies is Art’s top priority.

Although their discussion is informative, it does not resolve the questions it raises because Jake and Art “agree to disagree.”  Therefore, Million Trees will step into the vacuum their discussion creates to state definitively that it is patently false to say that “90% of insects can only eat native plants.” That statement grossly exaggerates the degree of specialization of insects and underestimates the speed of adaptation and evolution.

There are several reasons why insects do not benefit from the eradication of non-native plants:

  • Insects use both native and non-native plants.
  • Pesticides used to eradicate non-native plants are harmful to both plants and insects as well as the entire environment.
  • There is no evidence that insects are being harmed by the existence of non-native plants.

INSECTS USE BOTH NATIVE AND NON-NATIVE PLANTS

This statement was recently made in an article published by Bay Nature magazine about Jake Sigg:  “More than 90 percent of all insects sampled associate with just one or two plant families.”  (7,500 insect species were sampled by the cited study.  There are millions of insect species and their food preferences are largely unknown.)  This exaggerated description of specialization of insects seems the likely origin of the subsequent, inappropriate extrapolation to the statement that specialized insects require native plants.

Anise Swallowtail butterfly in non-native fennel. Courtesy urbanwildness.org

There are over 600 plant families and thousands of plant species within those families.  Most plant families include both native and non-native plant species.  An insect that uses one or two plant families, is therefore capable of using both native and non-native plant species.

We will use the Oxalidaceae plant family to illustrate that insects can and do use both native and non-native plants.  Oxalidaceae is a small family of about 5 genera and 600 plant species.  We choose that family as an example because Jake Sigg’s highest priority for eradication is a member of that plant family, Oxalis pes-caprae (Bermuda buttercup is the usual common name)In a recent Nature News (April 9, 2019), Jake explained why:  Oxalis is not just another weed; this bugger has a great impact on the present and it will determine the future of the landscapes it invades.”

Five members of the Oxalis genus in the Oxalidaceae family are California natives. An insect that uses native oxalis can probably also use the hated Bermuda buttercup oxalis because they are chemically similar. 

Honeybee on oxalis flower, another non-native plant being eradicated with herbicide

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THE CONSEQUENCES OF ERADICATING NON-NATIVE PLANTS

Partly because of Jake’s commitment to eradicating non-native oxalis, San Francisco’s Recreation and Parks Department has been spraying it with herbicide for 20 years Garlon (triclopyr) is the herbicide that is used for that purpose because it is a selective herbicide that does not kill grasses in which oxalis usually grows.  Garlon is one of the most toxic herbicides available on the market.  More is known about Round Up (glyphosate) because it is the most widely used of all herbicides.  However, according to a survey of land managers conducted by California Invasive Plant Council in 2014, Garlon is the second-most commonly used herbicide to eradicate non-native plants.

Garlon is toxic to bees, birds, and fish.  It is an endocrine-disrupter that poses reproductive and developmental risks to female applicators.  It damages the soil by killing mycorrhizal fungi that are essential to plant health by facilitating the transfer of nutrients and moisture from the soil to plant roots. 

A recent article in the quarterly newsletter of Beyond Pesticides explains that insecticides are not the only killers of insects: “Insecticides kill insects, often indiscriminately and with devastating consequences for biodiversity, ecosystem stability, and critical ecosystem services. Herbicides and chemical fertilizers extinguish invaluable habitat and forage critical to insect survival. Taken together, insecticides, fungicides, herbicides and chemical fertilizers make large and growing swaths of land unlivable for vast numbers of insect species and the plants and animals they sustain.” The loss of insects where herbicides are used to kill non-native plants are undoubtedly contributing to the failure of attempts to “restore” native plants which require pollinators and insect predator control as much as non-native plants.

In other words, eradicating non-native oxalis is damaging the environment and the animals that live in the environment.  Furthermore, after twenty years of trying to eradicate it, Jake Sigg admits that there is more of it now than there was when this crusade began:  “Maybe you’ve noticed that there’s more and more of it every year, and fewer and fewer other plants.  That is unlikely to reverse.”  (Nature News, April 9, 2019).

Coyote in oxalis field. Copyright Janet Kessler

In fact, local failure of eradication efforts mirrors global failures of similar attempts:  “…despite international policies aimed at mitigating biological invasions, the implementation of national- and regional-scale measures to prevent or control alien species has done little to slow the increase in extent of invasions and the magnitude of impacts.” 

[Ref: “A four-component classification of uncertainties in biological invasions: implications for management,” G. LATOMBE , S. CANAVAN, H. HIRSCH,1 C. HUI, S. KUMSCHICK,1,3 M. M. NSIKANI, L. J. POTGIETER, T. B. ROBINSON, W.-C. SAUL, S. C. TURNER, J. R. U. WILSON, F. A. YANNELLI, AND D. M. RICHARDSON, Ecosphere, April 2019.]

DO INSECTS BENEFIT FROM ERADICATING NON-NATIVE PLANTS?

There is no question that insects are essential members of every ecosystem.  They are the primary food of birds and other members of wildland communities.  They perform many vital functions in the environment, such as consuming much of our waste that would otherwise accumulate.

The Economist magazine has reported the considerable evidence of declining populations of insects in many places all over the world.  (However, the Economist points out that the evidence does not include large regions where insect populations have not been studied. The Economist is therefore unwilling to conclude that the “insect apocalypse” is a global phenomenon.) The report includes the meta-analysis of 73 individual studies that describe declines of 50% and more over decades. The meta-analysis concluded that there are four primary reasons for those declines, in order of their importance:  habitat loss, intensive farming, pesticide use, and spread of diseases and parasites.  The existence of non-native plants is conspicuously absent from this list of threats to insect populations.

In other words, although the preservation of insects is extremely important, there is no evidence that the eradication of non-native plants would benefit insects.  In fact, eradication efforts are detrimental to insects because of the toxic chemicals that are used and the loss of the food the plants are providing to insects.

JAKE SIGG AND PROFESSOR SHAPIRO DISCUSS INSECTS AND NATIVE PLANTS

The discussion begins on April 26, 2019, with this statement published in Jake’s Nature News:

“Did you know that 90 percent of insects can only eat the native plant species with which they’ve co-evolved?”

On April 26, 2019, Arthur Shapiro wrote:

“No, I didn’t know 90% of insects can only eat the native plants with which they’ve co-evolved. I’ve only been studying insect-plant relationships and teaching about them for 50 years and that’s news to me, especially since on a global basis we don’t know what the vast majority of insects species eat, period! That’s even true for butterflies and moths, which are probably the best-studied group. And it’s even true here in California, one of the best-studied places on the planet (though way behind the U.K. and Japan). Where on earth did that bit of non-information come from?”

Jake Sigg responds:

“Art, I did my best to run down source for that statement.  As I suspected, it may lack academic precision.  That kind of precision is hard come by, and what exists is not entirely relevant.  Most of the information comes from Doug Tallamy.  But the statement is not accurate; it should have read “…90 percent of plant-eating insects eat only the native plants they evolved with”.  Whether that is true or not I don’t know, but it accords with my understanding and I am willing to go along with it, even if proof is lacking.  If you wait for scientific proof on everything you may wait a long time and lose a lot of biodiversity.  I have had too much field experience to think that exotic plants can provide the sustenance that natives do.

I expect you will be unhappy with this response.”

On May 2, 2019, Art Shapiro replies:

“If Tallamy said “90% of the plant-eating insects that I have studied…”  or “90% of the plant-eating insects that have been studied in Delaware…” or some such formulation I might take him more seriously. The phenomenon of “ecological fitting,” as described by Dan Janzen, is widespread if not ubiquitous. “Ecological fitting” occurs when two species with no history of coevolution or even sympatry (co-occurrence) are thrown together and “click.”  A.J.Thorsteinson summed up some 60 years ago what is needed for an insect to switch onto a new host plant: the new plant must be nutritionally adequate, possess the requisite chemical signals to trigger egg-laying and feeding, not possess any repellents or antifeedants and not be toxic.

That set of circumstances is met very frequently. To those of us who study it, it seems to happen every other Tuesday.  As we showed, the urban-suburban California butterfly fauna is now overwhelmingly dependent on non-native plants. The weedy mallows (Malva) and annual vetches (Vicia) are fed upon by multiple native butterfly species and are overall the most important butterfly hosts in urban lowland California. . Within the past decade, our Variable Checkerspot has begun breeding spontaneously and successfully on Butterfly Bush (Buddleia davidii). The chemical bridge allowing this is iridoid glycosides. When I was still back East I published that the Wild Indigo Dusky Wing skipper, Erynnis baptisiae, had switched onto the naturalized European crown vetch (Coronilla varia) which had converted it from a scarce and local pine-barrens endemic to a widespread and common species breeding on freeway embankments. And the hitherto obscure skipper Poanes viator, the Broad-Winged Skipper, went from being a rare and local wetland species best collected from a boat to becoming the most abundant early-summer butterfly in the New York metropolitan area by switching from emergent aquatic grasses and sedges to the naturalized Mesopotamian strain of Common Reed, Phragmites australis. I can go on, and on, and on. If you find a sponsor for me to give a lecture about this in the Bay Area, I’ll gladly do it. If you promise to come!

I won’t snow you under with pdfs. Here’s just one, a serendipitous one that resulted from my walking near Ohlone Park in Berkeley. And one from the high Andes in Argentina. That paper cites one of mine in Spanish demonstrating that the southernmost butterfly fauna in the world, in Tierra del Fuego and on the mainland shore of the Straits of Magellan, is breeding successfully on exotic weeds.-! Copy on request.”

On May 2, 2019, Jake Sigg published his last reply:

“I believe many of your statements, Art, and many of these cases I am familiar with.  A conspicuous local example is the native Anise Swallowtail butterfly that still lays eggs on native members of the Umbelliferae, the parsley family, but which also breeds on the exotic fennel, which is an extremely aggressive weed that in only a few years can transform a healthy and diverse grassland supporting much wildlife into a plant monoculture—that, btw, won’t even support the butterfly, which shuns laying eggs where its larval food plant is too numerous and easy target for a predator, like yellow jackets.

What puzzles me is why you can keep your equanimity at the prospect of losing acres of very diverse habitat to a monoculture of fennel.  You live in the heart of the world’s breadbasket where for hundreds of miles both north and south there are almost no native plants except those planted by humans.  That would tend to distort one’s view.  I don’t mean to be flip, but it is not normal for even an academic to be indifferent about a loss of this magnitude.  I have worked hands-on on the land (I was raised on a ranch) all my life and still work every Wednesday maintaining our natural habitat in San Francisco—a task that hundreds of citizens pitch in on because they value the quality and diversity of the areas.  And why do you remain indifferent, are you just a contrarian?  You cite examples to bolster your view, but the examples are too small a percentage to be meaningful and wouldn’t stand up against a representative presentation.

I got my view from life.  I type this in my second-floor sunroom, which looks into a coast live oak growing from an acorn I planted in the late 1960s, about 50 years ago and which is immediately on the other side of the window.  It is alive with birds of many different species—flocks of bushtits, chickadees, juncos every day (plus individuals of other species), which species-number balloons in the migratory season.  What I can’t figure out is how the tree can be so productive as to stand up to this constant raiding.  I will take instances of this sort as my guide rather than the product of academic lucubrations.  And I will throw in Doug Tallamy; the world he portrays is one I recognize and love.

I think our battle lines are drawn.  This discussion could go on, as we have not even scratched the surface of a deep and complex subject.  But will either of us change our minds?  No.”

“Jake Sigg:  N.B.  Art responded with another long epistle, not for posting.  It clarified some of the points that were contentious and seemed to divide us.  We differ, but not as much as would appear from the above discussion.”


On a personal note, we’d like to point out that one of the writers of this article has a (non-native) red wattle tree outside their window – which also attracts bushtits, juncos, and chickadees, not to mention hummingbirds (both Anna’s and Allens), house finches, white-crowned sparrows, and a bunch of other species. Oak trees are certainly good habitat – but so are a lot of other plant and tree species, where ever they originate.

 

The Logic of Ecological Change – Prof Art Shapiro

Recently, UC Davis Professor Art Shapiro gave a talk at the Commonwealth Club.  It was a tour-de-force. He described it as a very quick resume of a course he’s been teaching for 40 years at UC Davis.

The takeaway: The conventional wisdom about ecology is often wrong.

[You can listen to the one-hour audio recording of his talk HERE.]

SPECIES THROWN TOGETHER

eco-jigsaw2Nativists idealize an ecosystem as a community of plants, animals, fungi, and other organisms that have evolved together over many thousands of years in a particular place so that they fit like a complicated jigsaw – the balance of Nature. (We’ve heard them use phrases such as “lock and key” to describe the effect of this co-evolution.) When non-native and invasive species enter, nativists believe, they destroy this intricate mechanism, resulting in an impoverished and simplified ecosystem with fewer species and no natural balance – and even the dire possibility of ecosystem collapse. They talk in terms of plants and animals that “shouldn’t be there” – usually, immigrant species brought in by humans.

But it’s not often true. What the scientific data show is that “communities” of that interdependent kind are unusual. Instead, most ecosystems are groups of plants and animals that happen to be in a place where they can thrive. When they interact, it’s usually because of “ecological fitting” – they can use the other plants and animals in that area to help them survive. Depending on how ancient they are, communities may include tightly co-evolved mutually interdependent multispecies systems. But these make up only a fraction of the community as a whole.

Anise swallowtail butterfly breeds on fennel

Anise swallowtail butterfly breeds on fennel

Here’s the evidence against the concept of tight-knit interdependent “communities”:

1. There’s no functional difference between a heritage ecosystem and one with exotic species. If there was, scientists should be able to tell an undisturbed “community” from an invaded one without knowing its history. In fact, they can’t. There are no consistent  functional differences once an “invading” species has been established. Some ‘invaders’ can drastically transform the systems they enter – an example is cheatgrass in the Western deserts, which greatly amplified fire risk there. But most do nothing of the sort.

2. Species recolonize open land at different rates.Species move, communities don’t.” If a landscape is wiped clean – say by glaciers or a volcanic eruption – nature begins to move back in almost immediately. The pollen record allows scientists to understand which species of trees arrived at which time. It shows that tree-species move individually, not as communities.

3. Species that now don’t exist in the same place did so in the past, which would not be true if plants and animals normally lived in fixed communities. One example: the wood turtle and the southern toad are not found in the same areas now – but the fossil record shows that in the past, the ranges did overlap. This couldn’t have happened if they needed to be part of different communities. Vast areas were occupied in the past by “no-analogue” communities – ones that simply don’t exist anywhere at all today.

He ended by pointing out that we – humans – are an invasive species. So are most things, at least at one time.

Read on for detailed notes from Professor Shapiro’s talk at the Commonwealth Club.

Again, you can listen to an audio-recording of the whole talk HERE (on the Commonwealth Club website).

————————————————————————

NOTES FROM ART SHAPIRO’S TALK:

ECOLOGICAL COMMUNITIES AND THE MARCH OF TIME

(The talk was dedicated to Prof Shapiro’s late neighbor, Steven Warnock.)

commonwealth club motto

Commonwealth Club motto

The talk was in three parts: The first laid out the historic context for two opposing schools of thought about ecology. The second examined the data, and concluded that the evidence supports Gleason. The third part looked at the future, which includes climate change.

ECOLOGICAL “COMMUNITIES” OR “ASSEMBLAGES” ?

Here’s the conventional wisdom about ecology, associated with Frederic Clements: Plants, animals, insects, fungi and microscopic creatures form interdependent groups, or “communities.” The process by which this happens is “co-evolution” (sometimes described as evolving a “lock and key”), leading to an ecology where all the species fit together like a jigsaw puzzle. (“Co-evolution” is associated with Peter Raven and Paul Ehrlich, who described it in butterflies and plants that evolved together.) If an area is disturbed, it will go through a predictable process of “natural succession” that will lead to a stable “climax” situation, with all its species again interacting as a community.

This stable ecosystem is sometimes called “the balance of nature.” Tamper with  it, this theory says,  and you could destabilize the whole community, even leading to ecological collapse.

assemblageThe opposing view, associated with Henry Gleason, is that plants and animals do not necessarily form ecological communities. Instead, groupings or “assemblages” of plants and animals occur mainly by accident. They happen to arrive in that space at that time, and find conditions that allow them to survive and thrive. The species in such an assemblage will interact, not because they co-evolved, but because they find an opportunity to do so.

These theories about how species fit within an ecosystem were quantified when several ecologists – including the famous Robert McArthur – introduced mathematical models that looked at populations of plants and animals and their interactions. They used these models to look at Species Packing – i.e., how many different species of plants and animals could live in a particular ecosystem.  Assembly rules says that the distribution of plant and animals species in a given area isn’t random: both competition and cooperation between plants and animals affect what you find. Competing species can’t all live in the same area, but their niches can overlap. Where they do overlap, the two species may evolve more differences (“character displacement“) so they compete less. These mathematical models assumed a condition of equilibrium, i.e. stability. Opponents have argued that ecological niches are seldom stable because the physical environment is not stable for very long.

R.H. Whittaker introduced the idea that the levels of dependency could vary within communities. For any two species, you could assign a number: +1 meant that the species needed each other to survive; -1 meant that they could not live in the same space.  He speculated  that these relationships tended to be distributed in a bell curve – meaning that most species in a group didn’t depend on the presence or absence of another species. But some subsets of the community were tightly integrated.

How adaptable are living things? They can evolve, but only in certain ways.  Niche conservatism is the idea that most species cannot change very much or very fast in response to changes in their ecological niches.

The idea of co-evolution was fine-tuned with John Thompson’s concept of Geographic Mosaics. Co-evolution between two species can happen differently in different  geographic areas. So, for example, a plant in one place might depend totally on one insect for pollination, but elsewhere, the same species of plant might find alternative pollinators available. Such Fine-Tuning is the opposite of Niche Conservatism – and both occur in Nature.

TESTING THESE IDEAS

Cladistics (i.e., the system of showing how related species evolved from common ancestors) provided a way to test the Ehrlich-Raven co-evolution hypothesis. If one kind of animal or plant developed into a separate species (“speciation”) then did the plants and animals depending on it also co-evolve into a separate species? There was no evidence that this happened. Co-evolution was a lot sloppier and more unpredictable than that!

Every time you see two organisms working together, it doesn’t necessarily mean they are co-evolved. Dan Janzen, a great tropical ecologis, pointed out that organisms could be taking advantage of niches and resources that appear through  Ecological fitting, with no history of coevolution at all. We see this happen when introduced pests attack native plants, and native insects attack introduced plants, forming brand-new associations. It happens all the time.

pacific reed grass under eucalyptus

Pacific reed grass thrives in eucalyptus fog drip

Is there really a difference between “intact” ecosystems and ones that are disturbed or invaded? Mark Sagoff pointed out that if there really is a functional difference between “invaded” and “co-evolved” ecosystems, then scientists should be able to tell them apart without knowing their history.

“The theory that evolutionary processes structure ecosystems and endow them with a mathematical organization (e.g., rule-governed patterns that ecologists can study) has the following implication….scientists should be able to tell by observation whether a given ecosystem is heavily invaded or remains in mint condition…

“In fact, once non-native species have become established, which may take only a short time, ecologists are unable by observing a system to tell whether or not a given site has been heavily invaded. Invaded and heirloom systems do not differ in pattern or process, structure or function, in any general ways.”

There’s more evidence against the idea of stable interdependent communities as the norm in nature. For example: pollen core data shows that trees recolonizing lands after glaciation don’t move in “communities.” The tree species migrate at different rates. Only those species that have mutualistic relationships move together (for example, mycorrhizae and trees).

WoodTurtle public domain Ltshears sm“Communities” are like still shots from a movie. They show a set of relationships at a particular point in time. That doesn’t mean the relationships are stable or unchanging. Many species show different sets of relationships in the past. For instance: at present, the wood turtle and the southern toad have completely different ranges – but in the past, those ranges overlapped in places. In the UK, workers building Hadrian’s Wall nearly 2000 years ago left middens that have remains of beetles of species now found only in Lapland.  When an event that wipes out an ecosystem and recolonization starts, it takes trees 50-100 years to leave a pollen signature. Bufo_terrestris public domain Norman Benton smBeetles that can fly get there in  months to a few years.

If communities were stable groupings of interdependent co-evolved species, then we would expect to see the same communities repeated in similar conditions. But in fact, we often see different groupings in similar conditions.

THE FUTURE

Decisions about what ecosystems should look like are subject to human preferences. For most people, what they grew up with is “normal.” But the world has changed. The climate is changing.  The pool of available species has increased enormously. In terms of trying to “restore” an earlier ecosystem – there’s no going back.

What is Biodiversity?

There’s been a lot of talk of ‘biodiversity’ in San Francisco recently. The city’s ‘Recreation and Open Space Element’ (ROSE) mentions it without clearly defining it. The Natural Areas Program claims to preserve it. There’s a new position, the Director of Biodiversity Coordinator (currently Peter Brastow, formerly of Nature in the City) within San Francisco’s Department of the Environment.

One of our readers, puzzled by all the discussion, asked a simple question of UC Davis Professor Arthur Shapiro, who gave a talk at the Commonwealth Club a few days ago. Instead of the two-line answer they expected,  he sent this detailed response — which he kindly permitted us to publish.

Mt Davidson woodland path

WHAT IS BIODIVERSITY? BY ARTHUR M. SHAPIRO

A buzzword.
Biodiversity means whatever you want it to mean. I hate the word. Here’s why.

The following is from the introductory biology textbook we use at U.C. Davis, Life: The Science of Biology, (10th edition, Sadava et al., p.1229 — yes, I said p. 1229!):

“…the term BIODIVERSITY, a contraction of ‘biological diversity,’ has multiple definitions. We may speak of biodiversity as the degree of genetic variation within a species….Biodiversity can also be defined in terms of species richness in a particular community.  At a larger scale, biodiversity also embraces ecosystem diversity—particularly the complex interactions within and between ecosystems….One conspicuous manifestation of biodiversity loss is species extinction…”

Got that?

The glossary at the back of the book defines “biodiversity hot spot” (itself ambiguous, conflating numbers of species and degree of endemism), but NOT biodiversity itself. One can see why.

Where did this verbal monstrosity come from?

Anise swallowtail butterfly breeds on fennelThe raw number of species in a defined area or system – what many of us call “species richness”—is a useful number. There are more species of butterflies in Brazil than in California, and more in California than in Alaska. That is true even if we pro-rate species number by area, and it is not trivial to ask why.

But there is more to biodiversity than mere numbers of species. Ecologists are also interested in how individuals are divided among species, that is, the distribution of commonness and rarity among species. You can have a “community” consisting of exactly two species.  It could have, say, 50 individuals of each species, or it could have 99 of one and 1 of the other—or any ratio in between. Does this matter? Why? What can those numbers tell us?

QUANTIFYING DIVERSITY – A DIVERSITY INDEX

A century ago a Danish plant ecologist named Christen Raunkiaer observed that there was a statistical regularity to this; he called it the “law of frequency.” In subsequent years it was found to hold for bird censuses and moths collected at lights, as well as for old-field plants.  A whole series of mathematical models developed over the years attempted to account for this regularity by means of assumptions about how species interacted—competing for resources, for example. These exercises were at the core of community ecology for several decades, and were seen as immensely important.

During World War II an applied mathematician named Claude Shannon, working on war-related communications problems at Bell Labs, developed a formula that concisely expressed the information content of a message. Ecologists discovered the Shannon formula in the 1960s and realized it could easily be adapted to give a single number that combined the number of species in a community and their relative abundances.

Thus whole communities could be compared efficiently, a potentially informative and useful tactic in trying to understand how multispecies systems worked. The number generated by the Shannon formula came to be called diversity, and the formula became the first and most widely-used of several diversity indices. I learned it in high school and I still use it in teaching. Diversity had two components, then:

  • Species richness and
  • “Equitability,” (the difference between a 50:50 and a 99:1 community).

And we were off and running. Now everything could be quantified with a diversity index: “foliage height diversity” in a forest canopy, or “aspect diversity” in moth faunas (how many wing shape-pattern themes could be recognized?). The number of uses and abuses of the term multiplied like rabbits. By 1971 things had gotten so bad that a paper was published caustically titled “The nonconcept of species diversity.” It was widely applauded for its candor. Unfortunately, the author ended up inventing his own new measure of diversity—one he thought was better than the old ones.

MORE LEVELS OF ‘BIODIVERSITY’

But things could get worse. And they did. With the passage of the Endangered Species Act, which opened the door to protection of endangered subspecies (keep in mind that there is no concept of the subspecies; a subspecies is whatever some taxonomist says it is) and even “distinct population segments” (no one knows what that means), genetics got in on the diversity game. Now we would not be content with diversity at the species level; we needed to get inside species.

In the scramble to define what might be protectable, a search was launched for “evolutionarily significant units.” With modern molecular-genetic tools, we quickly learned that taxonomic subspecies may be genomically nearly identical, while organisms indistinguishable by the naked eye may be wildly different. Defining diversity at the genetic level is still, well, challenging.

One very useful dimension of biodiversity is known as alpha, beta and gamma diversity:

  • Alpha diversity is species richness at the local level.
  • Beta diversity is a measure of how much the biota of different localities within a region differ among themselves—that is, how quickly species composition “turns over” in space [i.e. when you have many different little ecosystems next to each other].
  • Gamma diversity is at a large spatial scale.

The Bay Area has phenomenally high beta diversity in almost everything.

THE BOTTOM LINE

So what is biodiversity? It’s species richness, plus the distribution of abundance and rarity, plus the geography of all that, plus the amount of genetic variation in selected species of interest, plus whatever you please.

Somehow or other concepts of “quality” have gotten mixed in, too. When you clear-cut a redwood forest (which has very low species richness), the early-successional communities that develop on the site, which may be dominated by “invasive weeds,” will have both much higher species numbers and a richer distribution of species abundances than the forest they replaced. But early-successional communities don’t get any respect despite being more diverse and despite the supposition that biodiversity is good. Because they’re made up of the ‘wrong’ species—whatever that means.

Because biodiversity, after all, is only a buzzword.

tony holiday glen canyon 7881491_orig