Editor

Raul E. Diaz

University of Kansas, USA

Craig Hassapakis

Berkeley, California, USA

Associate Editors

EIoward O. Clark, Jr. Erik R. Wild

Garcia and Associates, USA University of Wisconsin-Stevens Point, USA

Assistant Editors

Alison R. Davis

University of California, Berkeley, USA

Daniel D. Fogell

Southeastern Community College, USA

Editorial Review Board

David C. Blackburn

California Academy of Sciences, USA

Bill Branch

Port Elizabeth Museum, SOUTH AFRICA

Jelka Crnobrnja-Isailovc

IBISS University of Belgrade, SERBIA

C. Kenneth Dodd, Jr.

University of Florida, USA

Lee A. Fitzgerald

Texas A&M University, USA

Adel A. Ibrahim

Ha’il University, SAUDIA ARABIA

Harvey B. Lillywhite

University of Florida, USA

Julian C. Lee

Taos, New Mexico, USA

Rafaqat Masroor

Pakistan Museum of Natural History, PAKISTAN

Peter V. Lindeman

Edinboro University of Pennsylvania, USA

Henry R. Mushinsky

University of South Florida, USA

Elnaz Najafimajd

Ege University, TURKEY

Jaime E. Pefaur

Universidad de Los Andes, VENEZUELA

Rohan Pethiyagoda

Australian Museum, AUSTRALIA

Nasrullah Rastegar-Pouyani

Razi University, IRAN

Jodi J. L. Rowley

Australian Museum, AUSTRALIA

Peter Uetz

Virginia Commonwealth University, USA

Larry David Wilson

Instituto Regional de Biodiversidad, USA

Allison C. Alberts

Zoological Society of San Diego, USA

Michael B. Eisen

Public Library of Science, USA

Russell A. Mittermeier

Conservation International, USA

Advisory Board

Aaron M. Bauer

Villanova University, USA

James Hanken

Harvard University, USA

Robert W. Murphy

Royal Ontario Museum, CANADA

Walter R. Erdelen

UNESCO, FRANCE

Roy W. McDiarmid

USGS Patuxent Wildlife Research Center, USA

Eric R. Pianka

University of Texas, Austin, USA

Antonio W. Salas

Environment and Sustainable Development, PERU

Dawn S. Wilson

AMNH Southwestern Research Station, USA

Honorary Members

Carl C. Gans Joseph T. Collins

( 1923 - 2009 ) ( 1939 - 2012 )

Cover :

This painting shows a young Dumeril’s Monitor ( Varanus dumerilii) creeping through the foliage on the floor of a Bornean Kerangas forest. This

interesting community is characterized by heavily leached soils, a density of small trees and a flora that is homogeneous by tropical standards.

Among the plant groups commonly represented are the orchids and pitcher plants. Dumeril’s Monitors occur near rivers in various types of forest

from southern Burma through the Malaysian Peninsula, Borneo and Sumatra. The hatchlings, like the one shown, are well-known for their strik-

ing coloration. It has been suggested that the colors, which begin to fade at the age of six weeks, mimic the dangerously venomous Red-headed

Krait ( Bungarus flaviceps), which shares its range. Dumeril’s Monitors are of modest size, usually not attaining a length much more than four

feet. They feed on crabs, snails, and other animals. Cover art work Carel Brest van Kempen.

Amphibian & Reptile Conservation — Worldwide Community-Supported Herpetological Conservation (ISSN: 1083-446X; elSSN: 1525-9153) is

published by Craig Hassapakis /Amphibian & Reptile Conservation as full issues at least twice yearly (semi-annually or more often depending on

needs) and papers are immediately released as they are finished on our website; http://amphibian-reptile-conservation.org; email:

arc.publisher@gmail.com

Amphibian & Reptile Conservation is published as an open access journal. Please visit the official journal website at:

http://amphibian-reptile-conservation.org

Instructions to Authors : Amphibian & Reptile Conservation accepts manuscripts on the biology of amphibians and reptiles, with emphasis on

conservation, sustainable management, and biodiversity. Topics in these areas can include: taxonomy and phylogeny, species inventories, distri-

bution, conservation, species profiles, ecology, natural history, sustainable management, conservation breeding, citizen science, social network-

ing, and any other topic that lends to the conservation of amphibians and reptiles worldwide. Prior consultation with editors is suggested and

important if you have any questions and/or concerns about submissions. Further details on the submission of a manuscript can best be obtained

by consulting a current published paper from the journal and/or by accessing Instructions for Authors at the Amphibian and Reptile Conservation

website: http://amphibian-reptile-conservation.org/submissions.html

* ~

amphibian-reptile-conservation.org

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Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the

original author and source are credited.

Amphibian & Reptile Conservation 6(1): 1-24.

POINT OF VIEW

Can humans share spaceship earth?

Eric R. Pianka

Section of Integrative Biology* C0930, University of Texas at Austin, Austin, Texas, USA

Abstract . — Earth was a pretty durable spaceship, but we have managed to trash its life support

systems, the atmosphere, and the oceans. Humans have also destroyed vast areas of habitats and

fragmented many others. We have modified the atmosphere and in doing so have increased the

greenhouse effect, which has changed the climate to produce ever increasing maximum tempera-

tures. Increased temperatures threaten some lizard species in highly biodiverse tropical and sub-

tropical regions. Many lizards are also threatened by habitat loss and over-harvesting. Although

lizards are ectotherms and might therefore be expected to be resilient to global warming, evidence

strongly suggests that many species could be threatened by warming. Some, such as fossorial or

nocturnal species or those in cold temperate regions, may be little affected by climate warming but

many others such as thermoconformer species in tropical forests and live bearers appear to be

particularly vulnerable. The 2011 IUCN Red List of Threatened Species lists 12 lizard species as ex-

tinct and another 462 species as Critically Endangered, Endangered, or Vulnerable. Together, these

constitute at least 8.4%, probably more, of all described lizard species. The highly biodiverse lizard

fauna of Madagascar is especially threatened mostly due to habitat loss from extensive deforesta-

tion by humans. Three of the IUCN listed species are monitor lizards. Most varanids are top preda-

tors, generally have large territories, and have low population densities, which make them particu-

larly vulnerable to habitat loss, habitat fragmentation, and over-harvesting. All monitor lizards are

listed by CITES as Endangered, and five species are officially listed as “threatened with extinction.”

Others, including the sister taxon to varanids, the Earless monitor Lanthanotus from Borneo, and

several island endemic Varanus species from biodiversity hot spots in SE Asia should be added to

these lists. The future survival of all lizards including varanids will depend on our ability to manage

the global environment. Sustainable management will require controlling the runaway population

growth of humans, as well as major changes in our use of resources. To maintain lizard biodiversity,

anthropogenic climate change and habitat destruction must be addressed.

Key words. Biodiversity, climate change, conservation biology, deforestation, extinction, global wanning, Lantha-

notus, lizards, Madagascar, Milankovitch cycles, overpopulation, threatened species, Varanus, wildlife management

Citation: Pianka ER. 2012. Can humans share spaceship earth? Amphibian & Reptile Conservation 6(1):1-24(e49).

Introduction

Amphibian and Reptile Conservation invited me to write

an essay for this special issue on the conservation biology

of monitor lizards. As I began to write, I quickly realized

that I wanted to address the much larger issue of the enor-

mous impact we humans have had on the entire planet

(our one and only “spaceship” Boulding 1966) as well

as on all of our fellow Earthlings. Although the subjects

of anthropogenic climate change and habitat loss are far

too broad to be fully addressed here, I offer a synopsis

and attempt to illustrate selected global-scale issues with

examples drawn from lizards, monitors where possible.

Correspondence. Email: erp@austin.utexas.edu

I ask readers to indulge me and permit some opinions

and editorializing.

The incomplete fossil record shows that lizards first

appeared 150 million years ago — since then many clades

have appeared and some have gone extinct (Evans 2003).

The oldest varanoid fossils date from about 90 million

years ago (mya) but the clade is older than that (Molnar

2004). Throughout this long evolutionary history, lizards

have survived many extreme climate changes. The planet

has undergone numerous ice ages as well as some ex-

tremely warm episodes. However, the exploding human

population combined with increased energy use per per-

son has resulted in ongoing increases in global tempera-

tures. Will lizards be able to survive?

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Anthropogenic extinction events

Hundreds of species, especially megafauna, in many

different taxa went extinct during the transition from

the Pleistocene to the present day. Possible causes of

this “Quaternary extinction event” (Koch and Bamosky

2006, http://en.wikipedia.org/wiki/Quatemary_extinc-

tion_event) include climate change and overkill by hu-

man hunters as people migrated to many previously un-

inhabited regions in the New World and Australia during

the late Pleistocene and Holocene. Humans first reached

Australia about 50,000 years ago but did not get to the

Americas until about 13,000 + years ago. Massive ex-

tinctions followed soon thereafter on both continents,

strongly suggesting that anthropogenic activities were in-

volved. Fossil records show that Pleistocene extinctions

following human invasions were extensive and among

others included many large mammals, such as mam-

moths, mastodons, chalicotheres, gomphotheres, pampa-

theres, glyptodonts, many ungulates, saber-toothed cats,

cave lions, cave bears, diprotodons, several marsupial

carnivores, lemurs, as well as various apes including

other humans. Some birds that perished include giant

South American Adzebills and huge Australian emu-like

Dromomithids.

A more recent wave of extinctions followed human

colonization of many islands, including the Caribbean

and Galapagos Archipelagos, Indian Ocean islands, Ha-

waii, New Caledonia and other Pacific islands, Mada-

gascar, islands of the Mediterranean, and New Zealand.

Many flightless island birds, including Dodos and Moas,

went extinct (Steadman 2006), as did other island en-

demics such as land tortoises. Of course, little evidence

is available for how people might have affected smaller

species such as most lizards, but at least one gigantic

Australian monitor lizard is known to have gone extinct

during the Pleistocene following human colonization. A

potentially greater anthropogenic extinction event is cur-

rently underway.

History of global warming

Together, the atmosphere and the oceans control cli-

mate. Ocean currents act as conveyor belts moving heat

away from the equator. Changes in ocean currents due to

tectonic events like the rise of the Panamanian isthmus

3-5 mya, or the ongoing constriction of the Indonesian

through flow by the northward movement of the Austra-

lian plate have had drastic impacts on past climates and

are likely to do so again in the future. However, we now

face a dramatic and rapid anthropogenic change in global

climate — humans have broken the life support systems

of spaceship Earth. When coupled with massive habitat

loss and fragmentation due to human overpopulation, all

denizens of planet Earth are potentially imperiled.

With the advent of human agriculture and city states

about 10,000 years ago, humans began large scale de-

forestation. Human activities, primarily deforestation,

began to alter atmospheric carbon dioxide and methane

levels many centuries ago, long before the industrial rev-

olution (Ruddiman 2003, 2005). Oxygen isotopes in air

samples from ice cores from the Antarctic and Greenland

dating back for more than 400,000 years have allowed

inference of temperature changes over most of the last

half a million years. Four prolonged ice ages are evident.

These changes are caused largely by periodic fluctua-

tions in Earth’s orbit and the inclination of its axis known

as the Milankovitch cycles. Four spikes in temperature

were spaced approximately every 100,000 + years. Earth

is presently in a warm interglacial phase, and through

burning of fossil fuels, deforestation, and loss of soil and

peat carbon, C0 2 levels have increased to well above any

that have occurred over the last 400,000 years. The last

thermal spike has been prolonged for considerably longer

than the three preceding ones. Earth should be entering a

colder glacial period but has stayed warm for roughly the

last 10,000 years (“the long summer” Fagan 2004). An

ice age seems overdue (Ruddiman 2003).

This extended warm period corresponds to the inven-

tion of agriculture and the resulting surge in human popu-

lation and, based on current evidence, is almost certainly

due to anthropogenic activities, especially deforestation

and burning of fossil fuels. The rate of global warming is

accelerating because long frozen reserves of methane are

now being released into the atmosphere (in terms of the

greenhouse effect, each molecule of methane is equiva-

lent to 25 molecules of carbon dioxide). When a mol-

ecule of methane burns, it gives off heat and is oxidized

into two molecules of water and one of carbon dioxide,

both of which are powerful greenhouse gases. Long fro-

zen fossil methane is being released from rapidly thaw-

ing permafrost and from the deep oceans at an ever accel-

erating rate. As temperatures rise, more methane bubbles

up to the surface, further raising temperatures in an ever-

increasing positive feedback loop. A tipping point has

probably already been reached at which climate cannot

return to pre-industrial conditions. Eventually, of course,

the Milankovitch cycles will generate another ice age,

but that could be many millennia from now.

Human activities, especially the enhanced greenhouse

effect, but also including burning of fossil fuels and even

the waste heat produced by nuclear reactors, have added

greatly to our already overheated spaceship. Glaciers are

melting, and sea levels have risen by a foot since 1 900

and are rising by over three mm per year (Kemp et al.

2009). The high specific heat of water has helped to mod-

erate this increased heat load to some extent, resulting

in the world’s oceans warming by nearly a frill degree

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Varanus baritji (above) and V. doreanus (below). Photos by JeffLemm (above) and Robert Sprackland (below).

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Celsius over the past half century. The oceans also ab-

sorb carbon dioxide, forming carbonic acid, which leads

to acidification and the bleaching of coral reefs.

Despite frequent outcries that global warming is some

sort of hoax, the vast majority of experts are convinced

that it is a real and enduring threat. If current trends con-

tinue, the planet will be at least 1-2 °C warmer by 2050

(IPPC 2007, NOAA 2012). Moreover, the rate of climate

change seems to be ever increasing and appears to be ir-

reversible.

Until the advent of agriculture, humans were hunter

gatherers — many fewer of us existed. Food supplies lead

population — populations tend to increase to the level

that foods will allow. Agriculture has been called “the

worst mistake in the history of the human race” (Dia-

mond 1987) because it allowed us to increase in popu-

lation density to unsustainable levels, ultimately leading

to the present day overpopulation crisis (Catton 1982).

We could never have reached seven billion without fos-

sil fuels. Just as supplies of bird and bat guano began

to be exhausted, the Haber-Bosch process rescued ag-

riculture by using methane to fix atmospheric nitrogen

and produce virtually unlimited amounts of ammonium

nitrate (Smil 2001, http://en.wikipedia.org/wiki/Haber_

process), which is an explosive as well as a fertilizer.

Without this technological “advance,” neither Germany

nor Japan could ever have gone to war — moreover, hu-

mans would have been limited by food supplies at much

lower population densities. Basically, humans exploited

these one-time fossil energy reserves to demolish many

of Earth’s natural ecosystems and turn them into arable

land and crops to feed increasing numbers of people. We

turned the tall grass prairies of North America into fields

of corn and wheat and replaced bison herds with cattle,

ultimately into masses of humanity. Of course, without

agriculture and fossil fuels, we could never have built

cities, let alone developed our civilization and human

knowledge. However, in many ways our cities are little

more than giant but fragile feed lots supporting unsus-

tainably dense aggregations of people. Without a steady

inflow of food, water, and power and a continual outflow

of garbage and sewage, cities will collapse. We missed

our chance to live in a sustainable world.

Human populations have grown exponentially over

the past century, doubling each generation. Our eco-

nomic system, based on runaway greed and the principle

of a chain letter — growth, growth, and more growth, is

fundamentally flawed. Ponzi schemes like this only work

briefly, until the cost of recruiting resources needed to

sustain them exceeds the value they represent. We are

far overextended in terms of local resource bases already,

and approaching limits in things transported from afar,

such as quality timber, larger fishes and some minerals.

As transport costs rise, bulky and heavy items (such as

metal ores) will become regionally scarce, until eventu-

ally transport becomes a limiting factor. The prevalent

attitude that no limits exist in a finite world is obviously

insane, but somehow it has become politically incorrect

even to allude to overpopulation. Not wanting to face

reality, people are locked in denial that such a problem

could even exist. And yet, population pressures clearly

underlie and drive almost all of the many challenges we

face, from energy and food shortages to political unrest

and climate change. Some are convinced that technology

will come to our rescue, but so far it has only led us far-

ther out on t hin ice.

Many think that the solution to the energy crisis is

access to more energy, but that will only exacerbate the

planet’s heat load and accelerate the rate of global wann-

ing.

Why lizards?

When I was about six years old in the mid- 1940s, our

family drove east from our hometown, in far northern

California, across the U.S. to visit our paternal grandpar-

ents. Somewhere along Route 66, we stopped at a road-

side park for a picnic lunch. There I saw my first lizard,

a gorgeous, green, sleek, long-tailed arboreal creature

(later I determined that this must have been an Anolis

carolinensis ) climbing around in some vines. We did our

utmost to catch that lizard, but all we were able to get

was its tail. I stood there, looking up at the sassy tailless

lizard, wishing intensely that I was holding it instead of

just its tail.

About a year later back in California, I caught my

first garter snake, which I tried to keep as a pet. Alas, it

soon escaped. Then in the third grade, I discovered that

the classroom next door had a captive baby alligator. I

was transfixed by that alligator and stood by its aquarium

for hours on end, reveling in its eveiy move. As a little

boy, I was obviously destined to become a biologist, long

before I had any inkling about what science was. Years

later, in graduate school, I discovered the rich layers of

the biological cake (Figure 1), and eventually I went on

to earn a Ph.D., and, later, my D. Sc. as an ecologist.

Figure 1 . Biological “cake” showing the intersection of taxon-

based sciences (slices) and concept-based sciences (layers) —

neither is complete without the other. Rather than specialize

on just one taxonomic unit, ecologists study the interactions

between organisms and their environments across all taxa.

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Varanus glauerti (above) and V keithornei (below). Photos by Stephen Zozaya (above) and JeffLemm (below).

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People sometimes ask me why I study lizards. Or

worse, some say “what good are lizards?” to which I

respond with “what good are YOU?” Those who would

think, let alone ask, such a narrow-minded question seem

to me to be hopelessly anthropocentric. Lizards are spec-

tacular and beautiful fellow Earthlings that deserve our

full respect and care. They were here long before us and

deserve to exist on this spaceship, too.

When my co-author Laurie Vitt and I received the

advance copy of our coffee-table book “Lizards: Win-

dows to the Evolution of Diversity,” we sat side-by-side

thumbing through its pages. Laurie said “if there’s a copy

of this 50 years from now, people will be looking at these

photos and saying ‘were these things really here?’” Lor

us, and for many others, a world without lizards would

not be a world worth living on. That said, let us explore

future prospects for all lizards including monitors. Gib-

bons et al. (2000) reviewed the global decline of all rep-

tiles, comparing it to the loss of amphibians, especially

frogs. They identified many threats, including habitat

loss and degradation, introduced invasive species, pol-

lution, disease, unsustainable land use, and of course

global climate change.

Minimum Viable Populations and Extinction

Vortices

Conservation biologists have formulated concepts of

“minimum viable population size” and “extinction vor-

tices.” Together, these can capture an endangered species

and inexorably drive its population to extinction (Gilpin

and Soule 1986; Pianka 2006; Traill et al. 2007), as fol-

lows. Habitat destruction, degradation, and fragmenta-

tion lead to reduced population density or even rarity,

at which stage a species’ survival becomes precarious.

Small populations lose genetic variation, which limits

their ability to adapt to changing environments. They

also experience elevated demographic stochasticity,

which can lead to extinction by a random walk process if

deaths exceed births. When exposed to added insults of

climate change, pollution, disease, and competition and

predation by invasive species, a threatened target species

can become doomed to extinction.

Because they are aquatic and long-lived, pollution and

disease are important threats to crocodilians and turtles,

but these two agents are less likely to impact most liz-

ards. However, studies of pollutant contamination of

aquatic African nile monitors living near abandoned

chemical stockpiles in West Africa showed that pesticide

and heavy metal contamination levels in tissues differ

between the sexes, but are not high enough to have no-

ticeable detrimental effects (Ciliberti et al. 2011, 2012).

Nevertheless, Campbell and Campbell (2005) suggest

that lizards could be useful as sentinel species to detect

and monitor low levels of pollution through bioaccumu-

lation.

Lor many lizard species, habitat loss and climate

change are the two major factors that have had strong

negative impacts and both will almost certainly continue

to increase well into the foreseeable future.

Habitat destruction and species loss:

Modern day fossils

When I first began studying desert lizards just half a cen-

tury ago, North American deserts were largely unfenced

and pristine. Permits were not required to conduct field

research, and lizards were very abundant at a dozen study

areas I worked from southern Idaho to Sonora. I have

since returned to several of these former study sites only

to find that they no longer support any lizards: one is now

part of the city of Mojave, California, another at Twen-

tynine Palms has been developed, and a third outside

Casa Grande, Arizona, is now a trailer park. Two sites in

northern Mexico have succumbed to agriculture (Google

Earth). Specimens collected a mere 50 years ago, safely

ensconced in major museums, now represent fossil re-

cords of what was once there before humans usurped the

habitat (Pianka 1994). Human populations have more

than doubled during the past half century — we already

use over half of the planet’s land surface and more than

half of its freshwater. Our voracious appetite for land and

other resources continually encroaches on the habitats of

all our fellow Earthlings, including lizards.

Many people embrace the anthropocentric attitude that

Earth and all its resources exist solely for human benefit

and consumption. Organized religions teach mastery of

nature and by setting people above all else, they have led

to many of the worst ecological abuses. For example, the

Bible says “be fruitful, and multiply, and have domin-

ion over the fish of the sea, and over the fowl of the air,

and over every living thing that moveth upon the earth”

(Genesis I, 28), but it also says “and replenish the earth.”

Our numbers have increased vastly, and we have over-

fished the world’s oceans and decimated many birds, but

we have not abided by the latter command. Instead we

have raped and pillaged the planet for anything and ev-

erything it can offer. Millions of other denizens of space-

ship Earth evolved here just as we did and are integral

functional components of natural ecosystems. All life on

Earth requires space to live — other organisms have as

much right to exist on this planet as people do. We need

to embrace bioethics and we must learn to share.

Climate change

At present, because of the effects of elevated levels of

greenhouse gasses, Earth cannot even dissipate the inci-

dent solar radiation it receives from the Sun fast enough

to stay in thermal balance (Hansen et al. 2005). Climate

change includes not only temperature but also has dra-

matic effects on the amount and periodicity of precipi-

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Can humans share spaceship earth?

Trend in Annual Total Rainfall i

1970-2011 (mm/lOyrs)

Australian Gwtnmtnl

liurcau DfltklEWDlnp

S CiKiiiin^nin^l'i Of ftj&YriJiu LS'ltl. fVAtmliiiii EVmhul itf Miilai^ufagp

50.0

40.0

30.0

20.0

15.0

10.0

5.0

0.0

-5.0

- 10.0

-150

- 20.0

-30.0

-40.0

-50.0

issued . wihi ii^is

Figure 2. Trends in annual total rainfall in Australia over the past four decades ( Reprinted with permission from the Australian

Bureau of Meteorology).

tation, producing both droughts and floods locally. The

atmosphere and oceans are commons (Hardin 1968) that

must be shared by all, but sadly they have been much

abused.

Because of the vastness and isolation of the Austra-

lian deserts, I used to think that Australian desert lizards,

including varanids, would be able to persist long after

humans had gone extinct (Pianka 1986), but I am no lon-

ger so sanguine. Global climate change is having a mas-

sive impact upon the Australian continent. A map from

the Australian Meteorological Bureau (Figure 2) shows

long-term trends in rainfall over the past four decades.

The eastern 2/3 rds of the continent has become much

drier, whereas rainfall has increased dramatically in the

westernmost top end and interior of Western Australia.

Historically, interior Western Australia had a low

and stochastic annual rainfall of about 150-250 mm and

might thus be particularly vulnerable to the 20-30% per

decade increase in precipitation. After being away from

my long-term study site for only five years, I drove right

past it because the vegetation has changed so much I

didn’t even recognize it. Shrubs are encroaching and spi-

nifex is declining. These floral changes are having an im-

pact on the fauna, including insects and other arthropods,

and abundances and diversity of their predators, birds

and lizards, have declined.

Lizard thermal biology and behavior

Lizards are often described as “cold blooded,” how-

ever, this loose term is a confusing misnomer — many

lizards maintain active body temperatures as high as

mammals and nearly as high as those of birds. Whereas

birds and mammals are endothenns that generate body

heat metabolically to maintain their thermal optima,

lizards are ectotherms that rely mainly on the external

environment to regulate their body temperature via be-

havioral adjustments. Nocturnal lizards including most

geckos are passive thermoconfonners, maintaining body

temperatures close to external ambient temperatures

when active at night. In contrast, many diurnal lizards

are heliothenns that regulate their body temperature be-

haviorally by choosing to be active during times when

environmental temperatures are most favorable and by

selecting appropriate microhabitats such as basking sites.

During early morning hours, when environmental tem-

peratures are cold, these lizards bask in warmer sunnier

spots and achieve body temperatures well above ambi-

ent conditions. As the day progresses and temperatures

climb, they then exploit a narrow thennal window during

which they can move around freely, foraging, and mating

along with other daily activities (Figure 3). Later in the

day, as air and substrate temperatures rise above thermal

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Varanus prasinus (above) and V rudicollis (below). Photos by JeffLemm.

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optima, they select cooler microhabitats such as shady

areas or avoid high temperatures altogether by becoming

inactive and going underground. Even within geographi-

cally widespread species, populations from colder high

latitude regions compensate for cooler temperatures by

being active at slightly lower body temperatures and by

activity later in the day when ambient temperatures are

higher (Pianka 1970).

Consequently, diurnal lizards living in cold temperate

regions should be able to accommodate to climate warm-

ing by becoming active earlier on a daily and seasonal ba-

sis (Kearney et al. 2009). However, many shade-seeking

tropical forest lizards are remarkably sensitive to high

temperatures and have few behavioral ways of escaping

from higher ambient air temperatures (Huey et al. 2009;

Huey and Tewksbuiy 2009). Such thermoconfonner spe-

cies are exceptionally vulnerable to extinction because

even modest elevations of forest temperatures may in-

duce heat stress. Higher air temperatures in the shade of

their forest microhabitats may lead to their decline and

possible extinction. Moreover, not only will warmer for-

est temperatures depress the physiological performance

of shade-dwelling forest species during summer, but it

may also enable warm-adapted, open-habitat competitors

and predators to invade tropical forests and replace these

shade species through increased competition and preda-

tion (Huey et al. 2009).

Climate change imperils lizards in other ways as well

(Huey, Losos, and Moritz 2010; Sinervo et al. 2010).

Sinervo et al. (2010) documented extinctions in 24 out

of 200 populations of 48 species of Sceloporus lizards

in Mexico. They suggested that when hours of restric-

tion in thermal refuges exceed four hours, the resulting

shortened thermally acceptable periods for activity of fe-

male lizards in spring were probably responsible because

females could not acquire resources adequate for repro-

duction. Figure 3 shows how the already narrow thermal

window for activity is further shortened by global warm-

ing. Live bearing species at low latitudes and elevations

are particularly prone to extinction, presumably because

embryonic development is compromised by higher ma-

ternal body temperatures. Sinervo et al. (2010) modeled

possible global extinction trends and suggested that, if

current warming trends continue, 58% of Mexican Scelo-

porus species and 20% of the world’s lizard species could

go extinct by 2080. For varanids, they estimate local ex-

tinction levels by 2080 of 17.8% and a species extinc-

tion level of 16.2%. Using similar climate niche mod-

els, Araujo et al. (2006) suggested that many European

reptiles could benefit from global warming by expanding

their geographic ranges. However, because such model-

ing efforts do not include consideration of many critical

biotic niche dimensions, particularly habitats, microhabi-

tats, and foods, they may not be very reliable predictors.

More sophisticated studies of this sort are badly needed.

Threatened lizards

A recent review of the conservation status of reptiles

found that 21% of the world’s lizard species are threat-

ened (Bohm et al. 2012). The IUCN (International Union

for the Conservation of Nature) Red List of Threatened

Species, based on just over half of the known lizard

species, lists 12 species as already extinct, 75 species

as Critically Endangered, 173 others as Endangered,

and 214 more as Vulnerable (IUCN 2011). These four

lists sum to 462 species (an underestimate, as a couple

thousand other species were not included), representing

nearly 8.4% of the 5,634 named lizard species (Reptile

Database 2012). The actual percentage of threatened

species would presumably be higher if all lizard species

were included. Island species are particularly prone to

Before warming

4 )

4»

After warming

Too hot

Minimum

operative

temperature

►

Acceptable for activity

Too cold

Time of day Time of day

Figure 3. Global warming will shorten activity times for lizards, thus reducing energy gains from feeding below minimum levels

needed for reproduction, potentially leading to failed reproduction and extinction ( Reprinted in modified form with permission from

Huey et al. 2010, Science 328:833).

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Table 1 . Critically Endangered lizards by families, genus, number of species, and localities.

Family

Genus

No. species

Localities

Agamidae

Cophotis

Sri Lanka

Agamidae

Phrynocephalus

Turkmenistan; Armenia; Azerbaijan; Turkey

Anguidae

Abronia

El Salvador, Honduras

Anguidae

Celestus

Hispaniola (Haiti and Dominican Republic)

Anguidae

Diploglossus

Montserrat

Carphodactylidae

Phyllurus

Queensland, Australia

Chamaeleonidae

Brookesia

Madagascar

Chamaeleonidae

Calumma

Madagascar

Chamaeleonidae

Furcifer

Madagascar

Diplodactylidae

Eurydactyloides

New Caledonia

Gekkonidae

Cnemaspis

Western Ghats, India

Gekkonidae

Dierogekko

New Caledonia

Gekkonidae

Hemidactylus

Socotra Island, Yemen

Gekkonidae

Lygodactylus

Madagascar

Gekkonidae

Manoatoa

Madagascar

Gekkonidae

Oedodera

New Caledonia

Gekkonidae

Paroedura

Madagascar

Geldconidae

Phelsuma

Madagascar

Iguanidae

Brachylophus

Fiji

Iguanidae

Cyclura

Bahamas; Jamaica, Cayman Islands, Virgin Islands, Dominican

Republic

Iguanidae

Ctenosaura

Oaxaca, Mexico, Honduras

Lacertidae

Acanthodactylus

Israel, Turkey, Tunisia, Algeria

Lacertidae

Darevskia

Georgia; Turkey

Lacertidae

Eremias

Armenia, Azerbaijan, Iran and Turkey

Lacertidae

Gallotia

Canary Islands, Spain

Lacertidae

Iberolacerta

Sierra de Francia, Salamanca, Spain

Lacertidae

Philochortus

Egypt; Libya

Lacertidae

Podarcis

Vulcano Island, Italy

Phrynosomatidae

Sceloporus

Pena Blanca, Queretaro, Mexico.

Polychrotidae

Anolis

Cuba; Culebra, Puerto Rico

Pygopodidae

Aprasia

Victoria, Australia

Scincidae

Afroablepharus

Annobon Island, Equatorial Guinea

Scincidae

Brachymeles

Cebu Island, Philippines

Scincidae

Chalcides

Morocco

Scincidae

Emoia

Christmas Island

Scincidae

Geoscincus

New Caledonia

Scincidae

Lerista

Queensland, Australia

Scincidae

Lioscincus

New Caledonia

Scincidae

Marmorosphax

New Caledonia

Scincidae

Nannoscincus

New Caledonia.

Scincidae

Paracontias

Madagascar

Scincidae

Plestiodon

Bermuda

Scincidae

Psendoacontias

Madagascar

Sphaeroddactylidae

Gonatodes

Saint Vincent and the Grenadines

Sphaeroddactylidae

Sphaerodactylus

Haiti

Teiidae

Ameiva

Saint Croix; Cochabamba, Bolivia

Tropiduridae

Stenocercus

Provincia Bolivar, Ecuador

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Varanus salvadorii (above) and V doreanus (below). Photos by JeffLemm.

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extinction due to invasive species increasing competi-

tion or predation, almost total vegetation clearance, or to

over-harvesting.

Two of the extinct species were teiids ( Ameiva ) from

the islands of Guadeloupe and Martinique. Two others

were tropidurids in the genus Leiocephalus (one known

only from Martinique has not been seen since the 1830s

and the other was last seen around 1900). The Navassa

rhinoceros iguana, Cyclura onchiopsis, once found only

on Navassa Island off Puerto Rico, has not been seen

since the middle of the 19 th century. The New Zealand

endemic diplodactyline gecko, Hoplodactylus delcourti,

also went extinct in the mid 19 th Century. Last recorded in

1840, the Giant galliwasp, an anguid, Celestus occiduus,

from Jamaica, was probably driven extinct by introduced

mongoose predators. The skink, Leiolopisma mauritiana,

known only from Mauritius, went extinct around 1600

also due to introduction of predators. The Cape Verde gi-

ant skink, Macroscincus coctei , died out early in the 20 th

century due to hunting pressures and prolonged drought

on its island habitats. The Giant day gecko, Phelsuma gi-

gas, known only from Rodrigues, Mauritius, disappeared

around the end of the 19 th century. The Tonga ground

skink, Tachygyia microlepis, is thought to have gone ex-

tinct in 1994. Tetradactylus eastwoodae, a small limb-

reduced gerrhosaurid known only from two specimens

collected at the type locality Limpopo, South Africa, has

not been seen since it was originally described in 1913

and seems to have succumbed to its habitat being trans-

formed into pine plantations.

One of the places where lizards have been hardest hit

is the large island of Madagascar. Deforestation there

has been extensive. Some 220 + species occur there, and

almost half of these (105 species in 21 genera belong-

ing to four families) are classified by the IUCN as either

Critically Endangered (14 species), Endangered (42 spe-

cies), or Vulnerable (49 species). In Madagascar nature

reserves, 21% of lizards have gone extinct (Sinervo et al.

2010). Madagascar allows massive exports of its char-

ismatic and highly sought after lizards, and its geckos

{Phelsuma and Uroplatus ) and chameleons ( Brookesia ,

Calumma, and Furcifer ) are especially marketable in the

herpetoculture trade.

The IUCN Red List of Threatened Species includes

75 lizard species in 47 genera from 15 families classified

as “Critically Endangered” (Table 1).

Ten species of habitat-specialized arboreal anguids in

the genus Abronia from montane cloud forests that have

been extensively deforested by humans for agriculture

and cattle ranching in Mexico and central America are

on the IUCN Red List of Threatened Species. One spe-

cies Abronia montecristoi listed as “Critically Endan-

gered” has not been seen in El Salvador for half a Cen-

tury (Campbell and Frost 1993) but may still occur on a

couple of isolated mountains in Copan Honduras (J. R.

McCranie, pers. comm.). Six Mexican Abronia species

Figure 4. A prime candidate for imminent extinction, the very rare Guatemalan A bronia frosti. Photo courtesy of Jonathan Camp-

bell.

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Figure 5. The rare Earless monitor lizard, Lanthanotus borneensis, from Borneo. Photo by Alain Compost.

are Endangered, and three are Vulnerable. Three highly

Vulnerable Guatemalan species are A. frosti , A. mel-

edona, and A. campbelli (J. A. Campbell, pers. comm.).

Because of their small population sizes and limited geo-

graphic ranges in areas heavily overpopulated with hu-

mans, many Abronia are essentially “dead man walking”

species that will go extinct during our lifetimes (Camp-

bell and Frost 1993; J. A. Campbell, pers. comm.). Sadly,

some species of Abronia likely went extinct in southern

Guatemala and adjacent El Salvador due to habitat de-

struction even before they were officially described by

biologists (Campbell and Frost 1993). Rare and endan-

gered species of Abronia are also threatened by illegal

collection for the pet trade.

Eight species of Sceloporus are on the IUCN Red List:

one is Critically Endangered (S. exsnl, Mexico), three are

Endangered, and four are Vulnerable. The Dunes sage-

brush lizard, S. arenicolus, is endemic to small areas of

sandy habitats, occurring in localized populations chiefly

on the Mescalero Sands in southeastern New Mexico and

the Monahan Sandhills in adjacent Texas. Large-scale

habitat destruction and activities associated with oil and

gas extraction constitute the major threat to the continued

existence of S. arenicolus. Widespread use of herbicide

for control of Shinnery oak is causing significant reduc-

tions in Sand dune lizard populations due to develop-

ment of unsuitable grassland habitat. Increased habitat

fragmentation results in increased probability of extinc-

tion of individual populations. Other activities, including

off road vehicle use, livestock grazing, and fire may also

contribute to habitat destruction (L. A. Fitzgerald, pers.

comm.).

The region with the highest density of threatened

species is Southeast Asia, a recognized hot spot of bio-

diversity. Sister to monitor lizards, the Earless monitor

Lanthanotus, known only from Sarawak on Borneo, is a

threatened species: this elusive rare lizard may also oc-

cur in West Kalimantan, also on Borneo (Iskandar and

Erdelen 2006). Only about 100 Lanthanotus have ever

been collected and virtually nothing is known about the

natural history or biology of this living fossil (Pianka

2004a). Lanthanotus is not listed by either the IUCN or

CITES but it should be considered potentially threatened.

Monitor lizards

Of all the lizard families, monitor lizards (Varanidae) are

among the most endangered. Monitor lizards have long

been greatly admired by their many aficionados. Accord-

ing to Mertens (1942), Werner (1904) called them the

“proudest, best-proportioned, mightiest and most intel-

ligent” of lizards. Monitors appear curious, can count,

have memories, have shown map knowledge, and plan

ahead (Sweet and Pianka 2003). They have greater aer-

obic capacity, metabolic scope, and stamina than other

lizards. Because of their size, some large monitors can

retain body heat in their nocturnal retreats allowing them

to emerge the next morning with body temperatures well

above ambient air temperatures. Their mass thus confers

a sort of “inertial homeothenny” on them (McNab and

Auffenberg 1976).

Many monitors are top predators that live in a wide

variety of habitats, ranging from mangrove swamps to

dense forests to savannas to arid deserts. Some species

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are aquatic, some semi-aquatic, others terrestrial, while

still others are saxicolous or semi-arboreal or truly arbo-

real. The varanid lizard body plan is thus versatile and

has been exceedingly successful as it has been around

since the late Cretaceous, 80-90 million years ago, but

now, many are threatened due to human activities.

Varanus are morphologically conservative, but vary

widely in size, ranging from the diminutive Australian

pygmy monitor Varanus brevicauda (about 17-20 cm in

total length and 8-20 g in mass, Pianka et al. 2004) to the

largest living varanid, the Indonesian Komodo dragons

( Varanus komodoensis ), which attain lengths of three m

and weights of 150 kg. During the Pleistocene, pygmy

elephants are thought to have been their major prey

(Auffenberg 1981). Luckily for varanophiles, when these

small elephants went extinct, Komodo dragons were able

to survive by switching to smaller prey. However, these

big lizards are themselves dwarfed by the largest known

terrestrial lizard, a closely-related gigantic varanid,

Megalania prisca , originally placed in the genus Vara-

nus. Megalania is a Pleistocene fossil (19,000-26,000

years BP) from Australia, estimated to have reached six

m in total length and to have weighed as much as 600 kg

(Hecht 1975; Auffenberg 1981).

These spectacular creatures must have been as for-

midable as modem-day saltwater crocodiles. The major

prey of these gigantic monitor lizards is thought to have

been large diprotodont marsupials (rhinoceros-sized

beasts, now extinct, that were relatives of wombats and

koalas). Being contemporary with aboriginal humans in

Australia, Megalania very likely ate Homo sapiens as

well. Its teeth were over two cm long, curved, with the

rear edge serrated for cutting and tearing the skin and

flesh of its prey as these powerful predators pulled back

on their bite. Many other species of Varanus also possess

such teeth. Varanus komodoensis routinely kill deer and

pigs (recently introduced by humans) in this way — one

Komodo monitor actually eviscerated a water buffalo

(Auffenberg 1981). Varanus komodoensis and Megala-

nia prisca are/were ecological equivalents of large saber-

toothed cats (Akersten 1985; Auffenberg 1981).

Endangered varanids

Many of Earth’s 70-odd described species of monitor liz-

ards (Varanidae) are potentially Endangered. Five vara-

nid species, Varanus komodoensis , V bengalensis , V.fla-

vescens, V. griseus , and V nebulosus, are officially listed

under the CITES (Convention on International Trade in

Endangered Species of Wild Fauna and Flora) on their

Appendix I protected list (http://www.cites.org/eng/re-

sources/trade.shtml), which means these species are clas-

sified as Threatened with extinction. Komodo dragons are

considered Vulnerable by the International Union for the

Conservation of Nature and Natural Resources (IUCN

2011). Only a few thousand Varanus komodoensis now

exist in the wild, and these populations are restricted to

the Indonesian island of Flores and a few nearby smaller

offshore islands. Komodos were first successfully bred

in captivity at the Smithsonian National Zoo in Wash-

ington, D.C. in 1992, and they have since been bred in

several other major zoos. Juveniles have been sold to

many other zoos around the world where these giant liz-

ards have become centerpieces of reptile exhibits. Funds

from these sales were earmarked to sponsor studies of

Komodo dragons in the wild. Resulting studies have doc-

umented low population sizes and reduced genetic varia-

tion and suggest that genetic bottlenecks have occurred

(Ciofi 2002; Ciofi et al. 2002). These data on population

genetics should be useful in conservation efforts.

All other species of monitor lizards are classified by

CITES under Appendix II, loosely defined as “species

that are not necessarily threatened with immediate ex-

tinction, but may become so unless trade in such spe-

cies is subject to strict regulation to avoid utilization

incompatible with survival of the species in the wild.”

The IUCN lists two of the three Philippine frugivorous

species, V mabitang and V olivaceus, as Endangered

and Vulnerable, respectively (IUCN 2011). The third, re-

cently described V. bitatawa, should also be considered

Endangered (Welton et al. 2010). All three of these Phil-

ippine species have restricted geographic ranges and live

in areas with high densities of humans, and should be

added to the CITES Appendix I list. In 1997, the Europe-

an Union wisely imposed import restrictions from Indo-

nesia of live animals and their products for four species

of monitor lizards, V dumerilii, V. jobiensis, V. beccarri,

and V salvadorii (Engler and Parry-Jones 2007). Island

endemic species, such as the handsome Yellow monitor

V melinus (also known as the Quince monitor) from SE

Asia are much sought after and bring high prices in the

herpetoculture trade — V. melinus has been proposed to

be added to CITES Appendix I. However, it may be pre-

mature to declare V melinus as Threatened because it oc-

cupies an area on Mangole and Taliabu as large as Long

Island and this species thrives in coconut plantations and

second growth — a similar argument can be made for V

beccarri from the large, impenetrable and uninhabited

Aru Islands (S. S. Sweet, pers. comm.).

Hunting pressures on some species of varanids for the

skin trade are extremely high with estimates of over two

million being killed annually (De Buffrenil and Hemery

2007; Jenkins and Broad 1994; Pemetta 2009). Huge

numbers of African V niloticus are captured inhumane-

ly using baited treble hooks. Shine et al. (1996, 1998)

claim that populations of some monitor lizards, espe-

cially Asian V. salvator, may be able to withstand such

intensive pressure by virtue of their ecological flexibility

and high reproductive rate. However, because these high

harvesting rates target pre-reproductive and early repro-

ductive animals, they may well prove to be unsustainable

over the long term (De Buffrenil and Hemery 2007).

According to Pemetta (2009), based on a review of

CITES records over the 30-year period from 1975 and

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Juvenile Varanus salvator. Photo by JeffLemm.

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2005, over 1.3 million live varanids representing some

42 species were harvested worldwide during these three

decades. Over one million (90.6% of the total) of these

belong to just three heavily exploited species: V exan-

thematicus, V. niloticus, and V salvator. Over a million

live specimens of these three species were exported from

Benin, Ghana, and Togo, mostly to the USA. According

to CITES records, proportions of lizards reported as wild

caught have fallen since 1996-98, as putatively “ranched

and fanned” animals have risen to 50% ( V. exanthemati-

cus ) and 75% (V niloticus) of the total harvest taken in

2005. As of 2005, all V salvator were still being reported

as wild caught. For all remaining varanid species, num-

bers reported as “ranched and fanned” or captive bred

have increased steadily since 1998, totaling over 50% by

2005.

Commercial trade in live monitor lizards of other

species is dwarfed by the vast numbers killed for their

skins over the decade from 1995 to 2005, about 20 mil-

lion lizards were bmtally killed for their skins. During

the same decade, annual numbers of live lizards traded

fluctuated around 80,000 to 90,000 and peaked with of

over 120,000 in 2002. Almost 100,000 live monitors of

39 other much less abundant smaller species were ex-

ported from Indonesia, Malaysia, Philippines, Tanzania,

and Thailand. Legal exports from Thailand and the Phil-

ippines were stopped in 1992 and 1994, respectively.

However, uncommon endemic species are still being ex-

ported from Indonesia and Malaysia. Smuggling and ille-

gal trade continues along with legal exportation (Christy

2008; Pemetta 2009; Schlaepfer et al. 2005; Yuwono

1998).

Africa, Asia, and Australia compared

Almost half of the 70 known species of monitor lizards

are found in Australia, whereas species richness is con-

siderably lower in Africa and mainland Asia. Varanid

diversity is also high in tropical SE Asia, where many is-

land endemics occur. African and mainland Asian moni-

tors are large and include terrestrial and aquatic species.

Small size has evolved independently twice: Once in a

clade of monitor lizards from the humid tropics of SE

Asia east of Wallace’s Line and again in Australia, which

hosts its own large clade of pygmy monitors in the sub-

genus Odatria (Pianka 2004b).

Because human population densities are much higher

in Africa and Asia than in Australia, African, and Asian

monitor lizards face greater threats from humans than do

those in Australia. Among the monitor species most heav-

ily exploited for the skin trade, two are African (the ter-

restrial V exanthematicus and aquatic V niloticus) while

the third most exploited species is the widespread aquatic

SE Asian species V salvator. Populations of three other

terrestrial Asian species ( V bengalensis, V. flavescens,

and V nebulosus) have been decimated and all three are

listed as Endangered on the CITES Appendix I list. Habi-

Figure 6. Number of species of living varanids traded over the

30 year period from 1975 to 2005, based on CITES data (from

Pemetta 2009).

tat destruction in semiarid African and Asian habitats has

been extensive. Desertification has claimed much of the

Sahara and is spreading southwards in the Sahel.

In contrast, much of the landscape in Australia remains

comparatively semi-pristine. Although native aboriginals

do hunt monitor lizards for food, most Australian moni-

tors cannot be considered threatened. Australia has never

permitted legal exports of its fauna, except among zoos.

The large clade of pygmy monitors (subgenus Odatria)

includes many charismatic species much sought after by

herpetoculturists. Some of these, including V. acanthur-

us, V. gilleni, V. glauerti, V. pilbarensis , V storri, and V.

tristis have leaked out of Australia illegally and are now

being bred in captivity and are available for sale. Several

larger Australian monitors, including V. gouldii flaviru-

fus, V. mertensi, and V varius are also bred in captivity

and available for sale. Captive breeding programs reduce

demand for wild caught lizards, hence promoting con-

servation. However, an animal in a cage is out of context

and can never substitute for a wild one living in its natu-

ral habitat where it evolved, to which it is adapted, and

where it makes profound ecological sense (Pianka 2006).

Unfortunately, captive animals in zoos will never replace

those living in the wild because habitat destruction is

typically irreversible, so re-introduction of captives back

into natural habitats is unlikely.

Cane toads and varanids

South American cane toads, Bufo marinus, were intro-

duced as a biological control agent into sugar cane fields

in Queensland in 1935 (Ujvari and Madsen 2009). These

toads are toxic, even as eggs or tiny tadpoles (Shine

2012). Cane toads have become an Australian ecoca-

tastrophe, recently expanding their range northwards

and westwards, where they have reached Arnhem Land

and the Kimberley during the last decade (Urban et al.

2007). Many invertebrates, some marsupials, crows, rap-

tors, freshwater crocodiles, turtles, snakes, and lizards.

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Figure 7. The arboreal Australian pygmy monitor Varanus gilleni. Photo by Eric R. Pianka.

including at least eight species of monitor lizards ( Vara-

nus acanthurus, V. glauerti, V. glebopalma, V. gouldii, V.

mitchelli, V. mertensi, V. panoptes, and V semiremex ) that

eat Cane toads have been negatively affected (Doody et

al. 2006, 2007, 2009; Shine 2012; Ujvari and Madsen

2009). An effort has been made to breed the Mangrove

monitor V semiremex in captivity for release back into

the wild (S. Irwin, pers. comm.). Monitors have been

found dead with Cane toads in their mouths and/or stom-

achs. Limited anecdotal evidence suggests that some

monitors have adapted to Cane toads either by refusing

to eat them or not eating their toxic parts.

Shine (2010) reviewed the impact of Cane toads on

Australia’s native fauna, including monitor lizard popula-

tions. Varanid populations declined in Cape York follow-

ing the arrival of Cane toads (Burnett 1997). Over a 6-7

year period before and after toad invasion, large declines

in population densities of three species of monitors, Vara-

nus panoptes (83-96%), V mertensi (87-93%), and V

mitchelli (71-97%) were reported by Doody et al. (2009).

Following toad arrival in the Darwin area, occupancy of

water holes by V mertensi fell from 95% to 14% over an

18-month period (Griffiths and McKay 2007). In Kakadu

National Park, radio-tracked V panoptes suffered 50-

Figure 8. Spread of cane toads across Australia.

70% mortality due to toad invasion (Holland 2004). In a

second radio-tracking study on the Adelaide River flood-

plain, at least 90% of adult male V panoptes were killed

by toad ingestion (Ujvari and Madsen 2009). Evidence

is overwhelming that invasion of Cane toads has had se-

rious impacts on many Australian varanid populations.

Invasive species of lizards (and snakes)

An unfortunate flip side to threatened and endangered

species exists: Some lizard species have invaded habitats

where they do not belong, sometimes with adverse ef-

fects on native species.

Being tropical, Florida is particularly prone to inva-

sions and hosts a long list of introduced exotics, most by

way of the pet trade (Krysko et al. 2011). At least eight

species of Anolis (A. chlorocyanus, A. cristatellus, A. cy-

botes, A. distichus, A. equestris, A. garmani, A. porcatus,

and A. sagrei ) have been introduced in southern Florida,

where A. sagrei appears to be displacing the more arbore-

al native A. carolinensis. Both species coexist in other ar-

eas with greater vegetation structure. Basilisks and igua-

nas, both Ctenosaura and Iguana , have also invaded. The

Curly tail lizard, Leiocephalus carinatus, native to the

Bahamas, was introduced to Florida in the 1940s to com-

bat sugar cane pests. The Hispaniolan curly tail L. sch-

reibersii has invaded more recently. Texas homed lizards

( Phrynosoma cornutum ) have long had well-established

populations in Florida — ironically, these lizards have

gone extinct over large parts of their original geographic

range in Texas. Three exotic species of agamids {Agama

agama, Calotes versicolor, and Leiolepis belliana) and

three teiids {Ameiva ameiva, Aspidocelis sexlineatus,

and Cnemidophorus lemniscatus) have populations in

Florida. Mediterranean geckos ( Hemidactylus turcicus )

have been introduced into many southern states, includ-

ing Florida, Louisiana, and Texas. Four other species

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of Hemidactylus ( H . frenatus, H. garnoti, H. mabouia,

and H. platyurus ) are also found in south Florida and the

Florida Keys. The gecko, Sphaerodactylus elegans , has

established itself in the Florida Keys. The large Asian

tokay gecko, Gekko gecko, and Madagascar day geckos

Phelsuma grandis, also have established populations in

Florida. Several of these Florida invasive lizard species

( Anolis sagrei, Phrynosoma cornutum, Hemidactylus

turcicus , and H. garnoti) have also managed to establish

themselves in South Carolina and Georgia.

Even one varanid species has successfully invaded

southwestern Florida. The large African aquatic moni-

tor V niloticus has been introduced into the wild around

the Cape Coral region, where a feral breeding population

has become established. These voracious predators are

preying on many native North American species, includ-

ing waterbirds, Burrowing owls {Athene cunicularia),

eggs of sea turtles, and other native wildlife (Enge et al.

2004). Efforts to eradicate this invasive monitor popu-

lation have failed and V niloticus appear to be expand-

ing their geographic range in Florida. Snakes, of course,

are merely one (albeit rather successful) clade of legless

lizards. Three species of large constrictors have now es-

tablished breeding populations in Florida. These include

Boa constrictors and two species of pythons, the largest

being Burmese pythons ( Python molurus) (http://www.

wired.com/wiredscience/2009/ 1 0/giant- snakes/).

Four species of Old World lacertids have established

themselves in the New World. Populations of the Euro-

pean wall lizard Podarcis muralis thrive in Garden City,

Long Island, New York, and in Cincinnati, Ohio. Podar-

cis muralis and the green lacertid ( Lacerta viridis) have

been introduced in the United Kingdom. Lacerta viridis

has been introduced in Kansas. The Italian wall lizard

Podarcis sicula was also introduced to Long Island, New

York, about 1966-67. Lacerta melisellensis fiumana was

first reported from Philadephia in 1 93 1 and was still ex-

tant in 1959.

Three exotic lizards have been introduced on the is-

land of Mauritius, the Asian agamid, Calotes versicolor,

the Madagascar panther chameleon, Furcifer pardalis,

and the Madagascar day gecko, Phelsuma grandis.

Jackson’s chameleons ( Chamaeleo jacksonii), natives

of Kenya and Tanzania, were released in the Hawaiian

Islands in 1972 and have spread to several islands where

they are now well established. They give birth to living

young and feed largely on native insects and snails, at

least one of which is itself endangered. Males sport three

rhinoceros like horns on their snouts and can reach to-

tal lengths of nearly 25 cm about half of which consists

of a strongly prehensile tail. Many people like these at-

tractive chameleons, which are exported from Hawaii

to the mainland USA where they are sold as pets. More

recently, the much larger (up to two feet long) Veiled cha-

meleon {Chamaeleo calyptratus ), native to Yemen and

Saudi Arabia, has been illegally introduced to Hawaii.

Veiled chameleons lay very large clutches of eggs and

are primarily insectivorous but they also feed on leaves,

flowers, and buds, as well as an occasional bird or small

mammal. Concerned about these invasive chameleons,

Hawaiian officials have attempted to restrict movements

of chameleons between islands.

The Brown tree snake {Boiga irregularis), a native of

Australia, Indonesia, and Papua New Guinea, was acci-

dentally introduced on the island of Guam in the 1950s

with disastrous effects on native endemic lizard and bird

species (Pimm 1987; United States Department of De-

fense 2008 ).

Future prospects?

Maintenance of the existing diversity of varanids, as well

as clade diversity of all other extant lizards, will depend

increasingly on our ability to manage and share belea-

guered spaceship Earth. Current and expanding levels of

human populations are unsustainable and are direct and

indirect causes of habitat loss. They also contribute to

escalating rates of climate change. To address anthropo-

genic habitat loss and climate change, we will have to

make major changes in our resource use.

Sadly, “wildlife management” is somewhat of a farce:

Currently we are failing to adequately conserve species

or habitats — we humans do not even have the will to lim-

it our own population! Humans have now dramatically

altered the ecology of over half of the land surface of this

our one and only spaceship planet Earth. Conservation

biology is a man-made emergency discipline rather like

surgery is to physiology or war is in political science.

Wild animals could and would flourish if people could

manage to share the planet and leave them large enough

undisturbed areas of habitat. However, even if we could

somehow designate and maintain large nature reserves,

the menace of irreversible global warming seems des-

tined to take a heavy toll on all Earthlings. Hopefully,

with new approaches and increased global efforts, liz-

ards, including varanids, will be among the survivors of

this current massive anthropogenic extinction event.

Acknowledgments . — I thank Craig Hassapakis for

inviting me to write this essay. I am grateful to Robert

Browne, Ray Huey, Mitchell Leslie, Sam Sweet, and

Laurie Vitt, all of whom suggested many ways to im-

prove this effort. Of course, all opinions expressed herein

are my own and none of these people are responsible for

any of them. Thanks to Jonathan Campbell for allowing

us to use his photograph of Abronia frosti, Stephen Zo-

zaya for allowing us to use his photograph of Varanus

glauerti, and to Jeff Lemm who generously shared his

outstanding photographs of varanids.

‘United States Department of Defense. 2008. Report to the

Congress. Control of the Brown Tree Snake.

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Varanus semiremex. Photo by JeffLemm.

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Pianka

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Received: 05 March 2012

Accepted: 09 May 2012

Published: 08 August 2012

ERIC R. PIANKA earned a B.A. from Carleton College in 1960, a Ph.D. from the University of Wash-

ington in Seattle in 1965, and the D.Sc. degree on his collected works in 1990 from the University of

Western Australia. He was a postdoctoral student with Robert H. MacArthur at Princeton University dur-

ing 1966-68. He is currently the Denton A. Cooley Centennial Professor of Zoology at the University of

Texas in Austin, where he has taught evolutionary ecology since 1968. Pianka has presented hundreds of

invited lectures at most of the world’s major academic institutions as well as several important plenary

lectures. During his 45 year academic career, Eric Pianka sponsored 20 graduate students and published

well over a hundred scientific papers, four of which became “Citation Classics,” as well as dozens of

invited articles, book chapters, and 1 8 books including an autobiography. His classic textbook Evolution-

ary Ecology , first published in 1974 went through seven editions, and has been translated into Greek,

Japanese, Polish, Russian, and Spanish, and is now available as an eBook.

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