The conservation status of the world’s reptiles

Monika Böhm

Determining the status and trends of the world's species is important to track success of conservation policy, but it's no mean feat. ZSL, with a multitude of collaborators, has been working hard over the years to determine which species are threatened and which species aren't. Here's the story from the reptile perspective.

Rough nose horned lizard_credit Anslem de Silva
Rough nose horned lizard

When I first started working in the Institute of Zoology in the spring of 2009, I was given a dataset of 1,500 reptile species with IUCN Red List assessments in various states of completeness. “Finish these, and write up the results” were the instructions (though I may be paraphrasing a bit).

The idea behind this: the IUCN Red List estimates extinction risk of species, using a scale of increasing extinction risk from low risk (Least Concern category) to Extinct, via the threatened categories of Vulnerable, Endangered and Critically Endangered. Since the 1,500 reptiles species had been drawn randomly from the full species list of all reptiles (at the time around 8,800 species long), carrying out status assessments for each species in the sample should give us a broad overview of the extinction risk of the group as a whole. This is referred to as the Sampled Red List approach and is used as a biodiversity indicator (the Sampled Red List Index) to track trends in extinction risk over time.

Being a bright eyed and bushy tailed post doc at the time, I commenced on doing as I was told. It became evident quickly, however, that the simple instruction I was given translated into something much more work involved. Something which would never have been achieved without the help of: (1) a huge number of species experts giving their time voluntarily to help push the IUCN Red List assessments to completion; (2) a huge number of volunteer research assistants helping with data collection and processing, and distribution mapping; (3) an exceptionally large number of cups of tea.

And so during the course of 2010 and early 2011, our 1,500 reptiles started trickling, or rather scuttling and slithering, onto the IUCN Red List. Two years later, the write up of this Herculean effort was finally published. Why Herculean? Because of the important contribution of our species experts – reflected in the fact that the resulting paper lists 245 co-authors. Consider herding cats as being easy in comparison - though a lot less rewarding!

Our efforts showed that around one-fifth of reptile species are threatened with extinction, with threat levels being highest in freshwater environments, tropical regions, and amongst turtles and tortoises.

Atheris ceratophora: Photo credit Michele Menegon
The Usambara eyelash viper is listed as Vulnerable on the IUCN Red List of Threatened Species due to restricted range in the montane rainforests of Tanzania, an area affected by high rates of degradation and deforestation.

By the time of the publication, we had already embarked on project Reptile 2.0. So far we had managed to assess the status of reptiles. But what about trends? Should we wait ten years for a reassessment, then go through the same time-consuming process again? Well, maybe. But in the meantime, we wanted to find ways to predict extinction risk in a more time-efficient way. Maybe we can predict extinction risk of a species from certain traits intrinsic to a species (such as reproductive output, or body size) or from data relating to pressures acting on species (for example spatial data on human population density, or spatial maps of threat processes).

We decided to start by examining factors correlating with extinction risk in our sampled species set. Sounds easy, right? Think again – we now had extinction risk for 1,500 species (or to be precise, for 1,199 species, excluding species listed as Data Deficient). Now we needed the trait data. Three Masters projects later (a big thank you for all your hard work!), and through collaboration with colleagues at Stony Brook University/NatureServe and Universidad Nacional Autónoma de México, we now have assembled a dataset of life history traits and environmental factors for our reptiles. 

This week our first output from “Reptile 2.0” was published, examining the correlates of extinction risk in reptiles. So what are the factors that correlate with extinction risk? Unsurprisingly, range size of a species is the main predictor of extinction risk. Why is this unsurprising? Because the vast majority of our species were assessed under the IUCN Red List criterion B, which uses restricted range size as a symptom of extinction risk.

However, in addition to species with a smaller range size having a higher risk of extinction, we found that at smaller range sizes, other factors become important predictors of extinction risk. Specifically, accessibility of a species range to humans appeared as a significant factor across a number of our models. How could this help the lengthy assessment process though? Well, even when we assess a species under the IUCN Red List criterion B, a restricted range alone does not equate to high extinction risk. In addition, we also need evidence of the species being restricted to a few locations within the range or the population to be severely fragmented, or for there to be a continuing decline in population size or range size etc.

Our current study suggests that there may be a way to predict extinction risk based on range size coupled with other key factors, such as measures of accessibility of a species’ range to humans (or measures of other anthropogenic influences). In simple terms, a model may be used to discriminate between range-restricted species alone and range-restricted species that have anthropogenic pressures within their range and are hence threatened. It’s early days yet, of course. However, we are also in the process of using our data to examine the true fate of Data Deficient species using more complex “models” – in effect we are training a computer to discriminate between threatened and non-threatened species by deriving decisions based on the trait data we provide and training the computer on a data set where the outcomes (threatened or not-threatened) are known.

Echis pyramidum: Photo credit: Michele Menegon
Echis pyramidum, the Egyptian saw-scaled viper, is listed as Least Concern on the IUCN Red List. This is because it is a common species south of the Sahara, although some populations, for example in Egypt, are in decline.

With these current developments in place, and us also running a retrospective assessment of our 1,500 species – i.e. we are trying to estimate their extinction risk for specified time points in the past – a trend over time in the extinction risk of our reptile species is hopefully just around the corner. One thing is for sure though: reptiles have well and truly entered the conservation arena, with a multitude of global assessments and increased interest in incorporating them into the conservation agenda.

We sincerely hope that the stunning lyre head lizard on the cover of this journal issue, photographed by our collaborator Ruchira Somaweera (one of the many reptile experts I collectively refer to as “superheroes”), will only help to inspire more people to shine a spotlight on the plight of the world’s reptiles.

Here’s to project Reptile 3.0!

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