Reptile diversity study findings are less scary than a snake in your boot

Mainstream reportage focused on the bad news,  but reptiles remain likely to outlive us

WASHINGTON D.C.––All dinosaurs except birds,  all ichthyosaurs,  and all pterosaurs are  confirmed extinct.

Dragons,  griffins,  and Godzilla are alive and well in human imagination,  the only habitat they ever actually occupied.

Among the other 10,196 reptile species for whom population and habitat assessments are available,  “at least 1,829 (21%) are threatened,”  according to International Union for the Conservation of Nature scientists Neil Cox,  Bruce E. Young,  and a battalion of co-authors.

Nine hundred sixty-one colleagues had input altogether.

Godzilla of biodiversity studies

The Cox/Young study,  “A global reptile assessment highlights shared conservation needs of tetrapods,”  appeared in the April 27,  2022 edition of the peer-reviewed journal Nature.

A tetrapod is any animal who evolved to have four limbs.

Snakes are included because snakes started out as four-legged lizards.

During the Late Cretaceous period,  82 to 66 million years ago,  the ancestral snakes’ legs evolved into the flippers that propelled the giant ichthyosaur-eating mosasaurs.

Their legs then disappeared altogether after those ancestral snake species who survived the extinction of the ichthyosaurs,  pterosaurs,  and dinosaurs slithered up on land.

From slithering they evolved to climb trees,  eventually tempting Eve to eat an apple in the Garden of Eden.

Or so the story goes.

“Even the king cobra is ‘vulnerable.’”

The Cox/Young study,  based on seven years of research,  inspired anxious headlines suggesting more-or-less that the end is near.

Wrote Erik Stokstad of Science,  “One in five reptile species is at risk of extinction
Turtles and crocodiles are particularly threatened, new global survey finds.”

Offered Associated Press science writer Christina Larson,  “Even the king cobra is ‘vulnerable.’”

But the Cox/Young study assessed reptile species diversity,  not overall reptile abundance.

Which reptiles are not at risk

Rattlesnakes in the U.S. southwest,  western fence lizards throughout the U.S. west,  alligators in the swampy South,  and allegedly invasive Florida pythons and iguanas,  among at least 8,367 reptile species,  are all apparently abundant as ever,  in no danger of disappearing.

Even brown tree snakes are not at risk,  despite intense ongoing efforts by USDA Wildlife Services to eradicate them from Guam.

Turtles excepted,  most familiar reptiles are––as broad classes of animal––likely to outlive humanity.

The odds favor many turtles too.  Here before the dinosaurs,  turtles have long outlasted the vast majority of all the tetrapods who ever existed,  including human-like species.

Gharials & marine iguanas

The scary part of the Cox/Young study pertains to the least abundant,  least well-known,  most narrowly distributed,  most specialized and most seldom seen reptiles.

The long-snouted gharials of the upper Ganges river and other southeast Asian habitats,  the marine iguanas of the Galapagos islands,  and more than 1,800 species whose names almost no one recognizes are indeed in trouble.

Yet the good news from the Cox/Young study is that reptile species diversity remains relatively healthy.

Reptiles doing twice as well as amphibians

Wrote Cox and Young,  “Global assessments reveal that, among tetrapods,  40.7% of amphibians,  25.4% of mammals and 13.6% of birds are threatened with extinction.”

In other words,  reptiles are doing twice as well,  as a category,  as toads,  frogs,  and salamanders  and a little better than mammals.

To further put the numbers in context,  mathematical odds alone would suggest that at any given time,  a third of all species are increasing,  a third are neither increasing nor decreasing,  and a third are decreasing.

This indicates that while an accelerating decline rate in any one species is of concern,  and an accelerating decline rate in any category of species would be of far more concern relative to overall biodiversity,  only amphibians are currently in serious danger as a class.

Reptiles v. birds

Only bird diversity is healthier than reptile diversity,  probably for the same reason that bird diversity survived the comet strike that killed the dinosaurs and practically every other non-avian species that then lived on land:  birds,  tremendously diverse to begin with,  are mostly able to fly from one habitat to another.

And most birds are migratory,  routinely relocating thousands of miles across vast bodies of water twice a year,  while most land animals must grow thicker fur,  hibernate,  or freeze.

The 1,829 reptile species who are in danger,  Cox,  Young,  and colleagues point out,  represent “15.6 billion years of phylogenetic diversity.”

This is a fancy way of saying evolution to fill unique habitat niches.

“Threat posed by climate change remains uncertain”

But,  Cox,  Young et al found  “Reptiles are threatened by the same major factors that threaten other tetrapods—agriculture,  logging,  urban development and invasive species—although the threat posed by climate change remains uncertain.”

Note:  the allegedly “invasive” species most threatening to endangered reptiles turn out to be other reptile species who are better suited to changing habitats.

“Reptiles inhabiting forests,  where these threats [from agriculture,  logging,  urban development and invasive species] are strongest,  are more threatened than those in arid habitats,”  Cox,  Young,  et al discovered.

Protecting habitat for other species helps reptiles too

“Although some reptiles—including most species of crocodiles and turtles—require urgent, targeted action to prevent extinctions,”  Cox,  Young et al assessed,  “efforts to protect other tetrapods,  such as habitat preservation and control of trade and invasive species,  will probably also benefit many reptiles.”

In other words,  saving the Everglades on behalf of migratory birds and/or saving the Sonoran desert on behalf of pronghorn will also save much critical reptile habitat.

(See Sonoran desert pronghorn: safer on a bombing range than in a refuge.)

Even if the public tends to have little sympathy for snakes and lizards,  saving the species the public does like will tend to conserve endangered reptile species too.

But many threatened species have no protected habitat

Currently,  however,  at least 227 threatened bird species,  194 threatened mammal species, 607 amphibian species,  and 474 reptile species range “completely outside formally protected areas,”  Cox,  Young et al mentioned.

“Concentrations of threatened reptiles are mostly in regions in which other tetrapods are also threatened,”  Cox,  Young et al observed.

“Threatened reptiles are concentrated in southeastern Asia,  West Africa,  northern Madagascar,  the northern Andes and the Caribbean,”  Cox,  Young et al found.

Snow belt species

Conversely,  few reptiles are at risk in “Australian drylands;  the Kalahari,  Karoo,  and Sahara deserts;  northern Eurasia;  and the Rocky Mountains and northern North America.”

To be sure,  not many reptile species occur north of the snow belt.  But most reptiles who survive annual snows,  including garter snakes and timber rattlers,  are doing quite well.

Pond and box turtles are an exception partly due to poaching,  probably mostly because they are at frequent risk of being road-killed while seeking mates.

Human threats “increasing extinction risk in reptiles,”  Cox,  Young et al emphasized,  “are mainly habitat destruction from agricultural expansion,  urban development and logging.  Other important threats are invasive species [again mostly other reptiles] and hunting,  which includes commercial harvest and trade.

Relative risk

“Among reptile groups,”   Cox,  Young et al noted,  “crocodiles and turtles are most frequently affected by hunting and less by agriculture,  whereas squamates,”  the reptile category including snakes and lizards,   “are most frequently threatened by agriculture.

“The major threats are broadly similar across tetrapods,”  Cox,  Young et al pointed out.

“For all tetrapod groups,  agriculture threatens the most species,  logging is the second or third most prevalent threat,  and invasive species and disease are the fourth or fifth most prevalent threat.

Hunting

“Threats causing habitat destruction (complete removal of habitat) affect proportionately more species than those causing habitat change (degradation of habitat).

“The largest differences in relative threat prevalence,”  Cox,  Young et al found,  “are for hunting,  which threatens mammals much more than the other tetrapods,  and urban development,  which affects amphibians,  reptiles,  and mammals more than birds.”

Nonetheless,  “Intentional use of reptiles (local consumption and trade) is an important threat to reptiles,”  Cox,  Young et al agreed,  “and was found to threaten 329 species (3.2%),  especially turtles (30.8% of all turtle species).

What about global warming?

Since reptiles are cold-blooded,  an overall warmer climate will mean more habitat congenial to reptiles––but not necessarily to all reptiles.

“Climate change is a looming threat to reptiles,”  Cox,  Young et al reported,  “for example, by reducing thermally viable windows for foraging,  skewing offspring sex ratios in species that have temperature-dependent sex determination,”  a category which includes sea turtles,  “and contracting ranges.”

But evidence that global warming is actually harming reptiles right now is sparse,  possibly because relatively little relevant research has been done.

Summarized Cox,  Young et al,  “Researchers have predicted that reptiles are particularly vulnerable to climate change in tropical biomes as well as freshwater and arid habitats, although so far no clear geographical signal in reptile declines due to climate change has been detected.”

Disease

Disease seldom entirely wipes out a species,  since the infected species tends to decline to the point that isolated survivors are no longer able to infect each other.

But disease does often reduce populations of mammals and birds to the point that they become vulnerable to other threats.

Reptiles,  though often carriers of bacterial diseases when handled by humans,  turn out to be relatively resistant to infectious disease.

“Disease is documented as a threat for only 11  species of reptiles,”  Cox,  Young et al mentioned with evident surprise.

The Cox/Young study closed input in December 2020,  to focus on analysis.

“As of December 2020,”  the authors noted,  “1,145  reptile species,  primarily snakes and lizards,  were omitted from the present study,  including the phylogenetic diversity analyses,  because they were [scientifically] described [only] recently,  after previous comprehensive assessments from the region.  Geographically,”   Cox,  Young et al said,  “they are primarily from tropical regions (as are assessed reptiles),  with an underrepresentation of African species.”

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