Reptiles and their role in the web of life – what if they disappeared?

by Theresa Peluso, with valuable input from Dr. Fred Schueler*

What class of animal has existed for more than 310 million years, but is now considered endangered in most areas of the world?  You guessed it — reptiles.  What exactly are reptiles, and why do they matter?

The oldest known reptile ancestor, Hylonomus, a 30-cm-long, lizard-like animal, lived in the steaming swamps of the late Carboniferous period, in an area known today as Nova Scotia.

Northern watersnake on the Ottawa River (Brent Eades photo)

The Collins English Dictionary defines “reptile” as “any of the cold-blooded vertebrates constituting the class  Reptilia, characterized by lungs, an outer covering of horny scales or plates, and young produced in amniotic eggs. The class today includes the tortoises, turtles, snakeslizards, and crocodiles; in Mesozoic times it was the dominant group, containing the dinosaurs and related forms”.

The word “reptile” is a problem for experts because of how animals are classified, whether according to taxonomy (in groups based on shared characteristics), or in groups (or clades) based on their shared ancestors. Reptilia used to be a taxonomic category, a class, along with birds (Aves) and mammals (Mammalia), but since these classes are descended from reptilian ancestors, in the new cladistic understanding (that taxa can’t exclude some descendants of the common ancestor), ”reptiles” is just an informal ecological grouping of what may be described as ”cold-blooded amniotes”. (Amniotes differ from modern amphibians, in having dry, waterproof skin and shelled (amniotic) eggs, internal fertilization, and more advanced circulatory, respiratory, excretory and nervous systems.)

In Ontario we have two reptilian lineages: shelled turtles and scaly squamates (mostly snakes, but one lizard, the five-lined skink). In the tropics, the closer-to-birds crocodylians are also classed as reptiles.  In New Zealand, the superficially lizard-like tuatara which is the only surviving member of the rhynchocephalia, is also classed as a reptile.  Biologists have recently analyzed the genomes of turtles and their closest relatives, and have concluded that turtles are most closely related to crocodilians and birds rather than to lizards, snakes, and tuataras.

Because they depend on external warmth to keep their metabolisms active, reptiles are generally diurnal, and maintain their body temperatures by relying on external sources, such as basking in the sun to warm up, or hiding in burrows or water to cool down. Egg-laying species need to find warm places to lay their eggs, and live-bearing species (of snakes) must bask to promote fetal development. During the cold months reptiles go into dormancy: squamates in terrestrial hibernacula, and turtles submerged in water.

Although reptiles comprise a very tiny fraction of the global biomass, they vary in levels of complexity and in size and shape (from 17 mm long (the Jaragua dwarf ghecko) to 6 metres long (the Indo-Pacific crocodile).  As of July 2018, according to the Canadian Herpetological Society, the total number of reptile species identified (as of July 2018) was 10,793.  Australia has the most reptile species (1,038), followed by Mexico (916 species), Brazil (807 species) and Indonesia (728 species).  In all of Canada, there are only 42 native species of reptiles, and in Ontario, there are 29.  In Nova Scotia, where the oldest known reptile was found, there are only 12, of which 3 are endangered. The most numerous reptiles are thought to be the viviparous lizard, found in Europe and Asia, and the dozen or so species of garter snakes found in most of North America.

Modern reptiles are predominantly carnivorous, although some are herbivorous.  Because herbivorous reptiles such as tortoises lack teeth, many species swallow rocks and pebbles – just like birds do – to help grind up the plant matter they eat when it reaches their stomach. Carnivorous or insectivorous reptiles have fairly short digestive tracts, and take a long time to digest their food, which explains why large reptiles like crocodiles and large constrictors can live on a single large meal for months.

Although reptiles are considered less intelligent than mammals and birds, larger reptiles such as the monitor lizard, crocodile and komodo dragon, exhibit complex behaviour.  Some tortoises and turtles, such as the red-footed tortoise and the North American wood turtle, are also quite intelligent.  One study found that wood turtles were better than white rats at learning to navigate mazes!

Reptiles play an important role in the food webs in most ecosystems, both as predators and prey.  Different species provide different functions.  A few function as important seed dispersers and pollinators in some habitats.  Others, such as crocodiles, are considered keystone species, both as predators and prey.  Crocodiles keep the populations of certain insects, fish, birds, crabs, and small mammals in check.  Some crocodiles dig large holes in the mud that retain water during the dry season, which are vital in enabling many littoral animals to survive dry spells.  The young also do their part in providing sustenance for herons, egrets and eagles – a kind of tit for tat on the birds’ part!

Farmers in some countries value snakes for the role they play in controlling rat populations.  The eastern milk snake, found in southern Ontario, is a voracious rodent eater, as is the appropriately named black rat snake and the garter snake, which also includes insects, snails, slugs and leeches in its diet. Although venomous snakes are to be feared, Ontario has only  one venomous snake, the endangered eastern massassauga rattler, which is quite timid.  (To avoid being bitten, it is recommended to wear closed-toe footwear and to use a flashlight if walking around at night.)  Snake venom (perhaps a way for snakes to compensate for their venimousness) has proven beneficial to humans in its use for diabetes and heart-disease medicines, as well as treatments for autoimmune diseases, cancer and pain – and also anti-venom for snake bites!

First, just how endangered are these fascinating reptiles, which have survived the past 310 million years, and which are now, in many cases, being threatened with extinction?

The International Union for Conservation of Nature, which publishes an annual global roster of threatened and endangered species called the Red List, identifies about 669 species of reptiles as endangered or facing extinction, 406 species as near threatened, and 467 species as vulnerable.  There is insufficient data to assess the status of 1,018 species.  These declines appear similar in many respects to the decline in amphibian species.  As a whole, only about 35 percent of identified species have been evaluated, not always systematically, and so it is hard to assess the extent of species loss.  See this link for more information.

In Ontario , of the 29 species (10 turtles, 19 snakes and 1 lizard), 19 of these are endangered (8 species of turtles, 10 species of snakes, and the 1 and only lizard).

What exactly are the threats? These include intensive agriculture practices, deforestation, wetland destruction, urban development, and natural system modification (such as damming and fire-suppression strategies), which all result in habitat loss.

Another significant threat is reptile capture and persecution. Throughout history, reptiles have been hunted and traded for use as food, medicine, clothing, jewelry and decoration.  Most of this hunting is illegal.  Some species have been hunted out of fear.  Truth be told, some species of snakes, like the black mamba in sub-Saharan Africa, sound downright scary, and several species of crocodiles must be given a wide berth.  But – most reptiles are harmless, and needlessly persecuted by humans. In Ontario and elsewhere, car drivers have been known to target not only snakes, but also turtles – by swerving out of their way – to deliberately kill them!  Yet another problem is overcollecting of reptile species for the pet trade.

And there are yet more threats:  pollution, increased UV radiation, invasive species, and diseases such as snake fungal disease and ranavirus (which affects fish, turtles, and amphibians).  Climate change also affects reptiles, by altering their traditional habitats, triggering extreme weather events, and in more subtle ways.  Although warmer temperatures may be a bonus for more northern reptiles, excess heat can lead to changes in the sex of the emerging reptiles (in some species sex is determined by incubation temperature), distorting sex ratios and population growth.

Many animals are inadvertently hurt or killed every day by cars and trucks. Turtle populations are especially affected, because the death of even a small number of adult turtles can have a huge negative impact on the survival of their species as whole.  This is because so few of them hatch, let alone grow to adulthood.  Less than 1 in 100 turtle eggs hatch and result in a mature adult (in 8 to 25 years, depending on the species).  Turtle nests, which are abandoned after the mother lays her eggs and covers them up, are easily found and destroyed by predators, including feral cats.  Any babies that hatch are at risk of being eaten by racoons, skunks and cats, fish, birds, frogs, and even other turtles.

The odds of an adult turtle living to a ripe old age (before the era of combustion engines) were 99 in 100, because the turtle had no natural predators.  During a female turtle’s adult life (anywhere from 30 to 100 years, depending on the species) she could lay a clutch of eggs every spring, right up until the end of her life.

Now it is the adult female that is most at risk of being hit by a vehicle because she travels long distances (half a kilometre or more), often crossing roads (built through wetland areas) to get to an appropriate nesting site.  This is made more difficult by the fact that many of the bogs, fens, and marshes that turtles once called home have disappeared or been altered. Hence, the tragic decline in turtle numbers.

This all sounds very discouraging, but many organizations and individuals are working hard to stem this decline.  Some communities in Canada, including the Kawarthas in Ontario, operate turtle conservation centres to treat, rehabilitate, and release injured turtles; conduct research; encourage conservation initiatives; and run education and outreach programs.  The Ontario Turtle Conservation Centre also collects eggs from injured females, incubates, hatches and releases them back to the turtle’s home wetland.

Public education is key.  Many nature organizations are only too happy to provide information on everything from how to avoid harming turtles, to moving turtles on the road safely, to protecting turtle nests.  By joining reptile conservation groups and programs such as Ontario Nature, we can help conserve threatened species and habitats.

We can also encourage our community to erect road signs near turtle crossings and nesting areas, and to build ecopassages, such as under-road culverts and appropriate fencing.  This is already being done in several nature parks in Ontario. We can also get together every spring to identify turtle nests and protect them from predation by covering them with wire-mesh frames.

As for snakes, people in this province need to learn to overcome their instinctive fear of them   – because, as already mentioned, only one of the 19 snakes found in Ontario, the massassauga rattler, is venomous, but it’s also timid and only bites if it feels threatened.  You can help by learning about the snake species in your area, and providing suitable nesting and hibernation sites for them.

More needs to be done at higher levels of government.  Our federal and provincial governments need to produce and coordinate a comprehensive, regularly updated inventory of reptile observations to better identify, conserve and manage species at risk; produce an atlas of reptiles; improve public awareness of the threats to these species, and provide conservation solutions. Individuals can assist in this objective by submitting reptile sightings as part of Ontario Nature’s atlas project.  More information on how to do this can be found on this link:

https://ontarionature.org/programs/citizen-science/reptile-amphibian-atlas/

Many of the suggestions already made in my columns on this Web of Life series about wildlife conservation, apply to reptiles as well.  Protect wetlands, natural shorelines, provide unmowed buffer zones around ponds and along streams and natural rock and log piles on your property, discourage the use of pesticides and excessive amounts of fertilizer, adopt a local reptile species as the “official” one for our community, and support our county’s stewardship council, local field naturalist clubs, and other conservation organizations.  Take advantage of lectures, workshops, daycamps, outings, books, films, etc., to learn more about these creatures.  Persuade your municipality to build roads and barriers that work in harmony with nature.  Don’t use motorized vehicles and watercraft in sensitive habitats.  Watch out for turtles and snakes when driving, and if feasible, help them cross the road in the direction they’re already headed.  Don’t pester or capture native reptiles, or release non-native pets or plants into the wild.  Keep your dogs and cats under control and out of natural areas.  And do what you can to reduce pollution and your carbon footprint.  We don’t want to be responsible for contributing to the extinction of these 310-million-year-old remarkable creatures!

*   When starting to research this topic, I suspected that the traditional definition of reptiles, which I learned at school long ago and which is still widely employed in popular works, was not being employed in modern systems of classification.  For this reason, I am grateful to Dr. Fred Schueler for coming to my assistance in explaining how “reptiles” are properly classified.