Fewer crocodiles and turtles, more snakes and lizards

Monika Böhm

Snakes and lizards deserve a greater share of the research limelight, according to new study (published in the Journal of Herpetology) led by the Indicators and Assessments Unit at ZSL’s Institute of Zoology.

Let's take a look at what the results of this new research  means for the wider herpetology community, and why the globe’s reptiles have been found to be suffering a decline of more than 50 per cent on average​.

Things really are hotting up in the world of reptiles – and for once we are not talking about the impacts of changing climate on our scaly friends, but about the increase conservation research focus this previously understudied group of species is now enjoying. Following hot on the heels of last year’s publication – for the first time – of global reptile distributions and this year’s high-profile launch of ZSL’s EDGE Reptiles List, we are now working hard on filling the next knowledge gap: population trends of reptiles.
Previously overshadowed by conservation research on mammals and birds, over the past few years we have learned a lot more about reptiles, specifically:

In short, from a conservation perspective, things are looking up for reptiles and they are finally starting to get the attention they deserve (and need). However, our work is never done, and is reminiscent of the proverbial opening of cans of worms (or lizards in this case). Specifically, we wondered if reptiles were adequately represented in one of our headline biodiversity indicators, the Living Planet Index (LPI). The LPI – published every two years in partnership with WWF - uses time series data for vertebrate populations, gathering information from around the world to track changes over time. The most recent publication of the index revealed a 58 per cent decline in vertebrate populations between 1970 and 2012, based on more than 14,000 populations representing more than 3,700 species. We have been continually adding data since (including reptiles!), so now the database that underpins the LPI contains population trends for over 4,000 vertebrate species.

Ganas Komodo Dragon
But what about reptiles? In our latest paper, published this week, we investigated the coverage of reptiles within the Living Planet Index and estimated population trends globally from all available data. The first thing that struck us was how comparatively little data on reptile populations is currently out there: our Living Planet Database currently only holds information for 549 reptile populations, representing 194 species. Given that there are currently nearly 11,000 reptile species described, this shows how little we still know about this species group.

We also found that our existing data are biased towards the more ‘charismatic’ reptiles, such as crocodiles, turtles and tortoises – when overall, these actually make up only around 3-4 per cent of the reptile species we find globally. In fact, the majority of reptiles are lizards and snakes: at present, there are 6,451 lizard and 3,691 snake species described according to The Reptile Database. Yet in our Living Planet database, only 1 per cent of lizard species and 2 per cent of snake species were represented, compared with 64 per cent of crocodiles and 12 per cent of turtles and tortoises.

Despite this lack of data, we estimated a global decline in reptile populations of on average 54–55% between 1970 and 2012, a number closely mirroring our overall vertebrate LPI estimate. This is the first in-depth analysis of global trends and representation for a major taxonomic group using the LPI. A 55% decline is a staggering number, but we clearly require more population data to fill not only taxonomic but also geographic bias within our very small dataset: most of our population time series data for reptiles was located in North America, with sparse data for Africa and Southeast Asia. The latter in particular has been found to be a hotspot for threatened reptile species in previous studies.

Of course, we can’t ourselves go out and monitor reptile populations across the globe – even if it sounds rather tempting! Instead, we rely on the global community of reptile experts (or herpetologists, that’s people studying reptiles and amphibians) to provide the data that the Living Planet Index relies upon. What we do here in London is network with experts and people carrying out species monitoring programmes, but most of the time, we trawl through the existing literature to find data on population trends for species. This is what we did for this present study, and as a result, we also examined what types of publication our population data originated from. For crocodiles, turtles and tortoises, which have been the focus of conservation action for decades, data generally stemmed from literature on conservation management. But for lizards and snakes, the majority of reptiles, these conservation studies are still very much lacking and most of our data originated from research focussing on specific ecological questions. This is not very surprising since lizards, for example, have been used as study systems in ecology for a long time.

However, this may also bias our time series data towards shorter time series lengths, because ecological research is often time-bound to limited project durations

So in reality, while there may be a lot of data in researcher’s notebooks, on computers and hard drives, in reality it is a matter of getting to the raw population data to make use of it for the LPI. Open-access publication and sharing of datasets are vital to improving knowledge of reptile status and trends, but of course also put the onus on us to properly store and curate data and use and share data responsibly. We are working hard to keep the Living Planet database up to speed with the latest developments and latest information, so it can continue to be used to track trends in populations over time, including those of reptiles.

Read the paper in the Journal of Herpetology

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