Global Assessment of Reptile Distributions
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Between a rock and a hard place – unique rare species face grave dangers due to human action

24/11/2021

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In a recent paper published in the journal Science Advances Gopal explored drivers of phylogenetically endemic land vertebrates. He also looked at conservation attributes of regions with high phylogenetically endemic species.

We live in the age of the ‘sixth mass extinction’. Our daily activities are causing hundreds and thousands of species to be lost forever. To turn the tide on the biodiversity crisis we have to identify those regions and species that are most in need of our conservation efforts. However, the characteristics of regions or species most in need of protection are not always clear. In this work we focus on those species that have two distinct features that make especially good candidates for conservation efforts. First – they are confined to only small and distinct location on the globe – what are known as endemic species and face greater risk of extinction. Second – they are evolutionary unique - they do not have close relatives on the ‘tree of life’ and their loss will represent a loss of millions of years of evolution. Species that poses both of these attributes (phylogenetic endemics) are therefore of great conservation importance as they represent unique and threatened components of biodiversity. To explore these species, we collected data regarding the evolutionary relationships and geographic distribution of almost all land vertebrate species (~30,000 species of amphibians, birds, mammals, and reptiles). We set out to map global ‘hotpots’ of such species, understand what are the unique conditions that support them, and evaluate their current protection and threats.
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Some of the range-restricted evolutionary unique species. The Red ruffed lemur (photo credit: Charles J Sharp), Madagascar fish eagle (photo credit: Anjajavy le Lodge), Hula painted frog (photo credit: Gopal Murali - own image), and Chinese Crocodile Lizard (photo credit: Holger Krisp). Images from Wikimedia Commons (apart from the painted frog).

We found that hotspots of phylogenetically endemic species mostly occur in the tropics and in the southern hemisphere along mountain ranges and in islands. Altogether, these hotspots, when combining the hotspots for all of the four above-mentioned groups, they occupy 22% of the total landmass. Hotspots that were important for all of the four groups are located in the Caribbean islands, Central America, along the Andes, eastern Madagascar, Sri Lanka, southern Western Ghats in India, and New Guinea. Although some of these regions have been previously prioritized for conservation actions, our study also found hotspots outside well-known biodiversity centres. For instance, we found the Asir mountains in Saudi Arabia to be important for such unique birds and Morocco to harbour phylogenetically endemic reptiles. Globally, these regions are mostly defined as mountainous tropical regions. This finding supports the notion that tropical mountains have an important role in the generation and maintenance of biodiversity.

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Global map of Phylogenetic endemism hotspots for all land vertebrates corrected for species richness

We next quantified how human activities and climate change are threatening these hotspots. Alarmingly, we found human activities such as buildings, roads, land-use, population density, and rate of climate change to be disproportionately higher in these hotspots (when compared to regions outside them). Consequently, our study highlights that many uniquely rare species, which probably perform important roles in the ecosystem, will be the first to be lost due to global change. Furthermore, we found most of the hotspots are not adequately protected. About 70% of the hotspots regions have less than 10% overlap with protected areas. Some of these regions which require urgent conservation action are the southern Andes, Horn of Africa, Southern Africa, and the Solomon Islands.
 
To-date most conservation strategies still focus on species-rich regions or flagship species, which may miss out on regions with uniquely rare species we identified. Overall, our study emphasizes on the need for strategic conservation policy and management to safeguard the persistence of thousands of small-ranged species that represent millions of years of unique evolutionary history.

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Infographic representing this work. Press to download in high resolution
Author: Gopal Murali
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No evidence of shorter lifespans for tetrapods with higher metabolism

20/3/2020

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It has long been thought that animals that ‘live slowly’, having a slow rate of metabolism, live longer than those that live their lives at a fast rate: having high metabolic rates. The notion is based on the assumption that animals with fast metabolic rates are more active, more exposed to predators, have higher rates of potentially harmful somatic mutations and produce more harmful metabolic by products such as free radicals. This tradeoff between metabolism and lifespan is commonly referred to as the ‘rate-of-living’ theory.
In a recent publication in the Journal Global Ecology and biogeography, we (Gavin Stark; Daniel Pincheira donoso and Shai Meiri) showed that the assumption under the “rate of living” theory which have been around for almost a century is unsupported by the results of our largest scale study (4,100 land vertebrate species: 2,214 endotherms & 1,886 ectotherms) to date of this theory. We could not find any connection between animal metabolic rate and longevity, either when we tested all land vertebrates (i.e. Mammals, Birds, Reptiles and Amphibians) or when we tested each group separately. In contrast, we did find other factor that did affect the lifespan of ectotherms (Reptiles and Amphibians), and it is ambient temperature. In colder regions around the world we expect species of reptiles and amphibians to live longer than other ectotherms living in warmer environments. The link between ectothermic (amphibians and reptiles) lifespan and ambient temperatures could mean that they are especially vulnerable to the unprecedented global warming that the planet is currently experiencing. Indeed, if increasing ambient temperatures reduces longevity, it may make ectothermic species more prone to go extinct as the climate warms. Our findings add a previously overlooked layer to the range of factors that are commonly thought to imperil species in the Anthropocene.
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The relationship between longevity (y axis of all panels, log10 transformed) and (a–d) body mass (in g, log10 transformed) of amphibians (red circles), reptiles (black circles), birds (green triangles) and mammals (inverted blue triangles). (e–h) Mean annual temperature (regression lines only shown for amphibians and reptiles for which the relationship is significant), (i) basal metabolic rate (in ml O2/hr, log10 transformed), according to the color codes depicted in the top plots and (j) field metabolic rate (kJ/day, log10 transformed)
Author: Gavin Stark
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Long lived reptiles: What causes reptiles to have longer lifespans?

29/10/2018

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In a recent publication in Biological Journal of the Linnean Society, we present a comparative analysis exploring patterns and drivers of longevity of 1320 reptile species, spanning all orders.
In recent years, there have been many studies focusing on the effect of different ecological variables and life-history traits on the variation in longevity of specific taxonomic groups, focusing mostly on birds and mammals (with the only large- scale ectothermic study done on squamates by Scharf et al. 2015). In order to expand our knowledge on the effect of environmental and life-history variables on the variation in longevity of animals, we tested the effect of ecological variables (through various hypotheses) related to extrinsic mortality (e.g. predation) on the variation in longevity among and within lizards, snakes, turtles and crocodiles. We found that species living on islands, and in colder and more seasonal environments, live longer. Moreover, sampling more individuals increases the chances of finding older specimens, and should be corrected for when studying maximum longevity.

We hope these analyses will enable us to better understand the drivers of longevity in reptiles (and other taxa). We hope this paper will facilitate more large-scale comparative studies on the causes of the variation in longevity of tetrapods in general.
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Species representing long lived reptiles (from each order) I studied in my research, in the top: right, Sphenodon punctatus, left, Aldabrachelys gigantea, in the bottom: right, Gavialis gangeticus, left, Cyclura lewisi.
Author: Gavin Stark
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The latitudinal diversity gradient and interspecific competition: no global relationship between lizard dietary niche breadth and species richness

27/1/2017

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In a 2017 publication in Global Ecology and Biogeography, we collated a novel quantitative volumetric dietary dataset for 308 lizard species worldwide from the field and literature. This novel dataset enabled us to test seven competing hypotheses posited to explain dietary niche breadth, focusing on those that are thought to either cause, or be influenced by, the latitudinal diversity gradient.
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Notomabuya frenata (photo Alison Gainsbury)
A species’ niche breadth is defined as the suite of environments or resources that the species can inhabit or use. Niche breadth is often invoked to explain the latitudinal diversity gradient. The latitudinal diversity gradient is the increase in species richness or biodiversity that occurs from the poles to the tropics. Despite this pattern having been recognized for over 200 years, the processes that drive and maintain the latitudinal diversity gradient remain unclear. We investigated which processes are important drivers of global lizard dietary niche breadth patterns, focusing on the relationship between niche breadth and species richness.
A major tenant explaining greater species richness in the tropics is interspecific competition. Dietary niche breadth has long been hypothesized to decrease from the poles toward the tropics, as the numbers of competitors increase. Geographical variation in niche breadth is also hypothesized to be linked to high ambient energy levels, water availability, productivity and climate stability – reflecting an increased number of available prey taxa. Range size and body size are also hypothesized to be strongly and positively associated with niche breadth. We sought to determine which of these factors is associated with geographical variation in niche breadth across broad spatial scales and thus potentially drive the latitudinal diversity gradient.
Overall, our findings are consistent with the notion that climate is an important predictor of dietary specialization, with both less rainfall and more stable temperatures associated with narrower dietary niches. Trophic interactions between lizard species and their arthropod prey are sensitive to climate. It is likely that climatic conditions not only affect these interactions but also alter the functional role of other vertebrate predators in terrestrial ecosystems. The sensitivity of dietary niche breadth to climate has important implications for essential ecosystem functions that maintain increased species richness in the tropics, such as food web stability and energy flow.
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Norops meridionalis (photo: Alison Gainsbury)
The synergistic effects of a narrow dietary niche and small range size augments the vulnerability of species to habitat loss and climate change. Based on our findings, the ‘competitionist’s paradigm’ seems to be the exception rather than the rule in explaining the latitudinal diversity gradient.
Author: Alison Gainsbury
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Patterns of species richness, endemism and environmental gradients of African reptiles

28/7/2016

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In our recent publication in the Journal of Biogeography, we assembled a comprehensive distribution map of all reptiles in Africa in order to quantify their geographical overlap with the other vertebrate groups, and to assess the environmental correlates underlying these patterns.
The latitudinal gradient of increasing biological diversity towards the equator is one of the best recognized patterns in biogeography, and has been acknowledged for some time. The naturalist, Alexander von Humboldt wrote of his travels over 200 hundred years ago, that as we approach the tropics, "the greater the variety of structure, form, colour, youth and vigor of organic life." A number of well-known hypotheses explaining this pervasive pattern of the increasing number of different species towards the equator have since proliferated. These include elevated ambient energy and precipitation, the number of different habitats or niches, higher plant productivity, and many more.
Until now reptile diversity gradients have remained largely unmapped and the least studied of the terrestrial vertebrates, especially in Africa. This is an important distinction because reptiles are an extremely diverse class of terrestrial vertebrates (over 10,000 species and counting), and as ectotherms, which often thrive in arid regions, their diversity patterns are thought to differ from the classic latitudinal gradient of the other land vertebrates (amphibians, birds, and mammals). In addition, the distinct reptile lineages - amphisbaenians, crocodiles, lizards, snakes, and turtles are likely to respond differently to environmental variables.

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Vipera palaestinae (photo: Uri Roll)
To create our geographic distribution map of reptiles in Africa, we obtained data from a variety of field-guides and atlases, museum databases, the primary literature, IUCN assessments, and maps based on expert knowledge of reptile species and the habitats they occupy. A challenging aspect of the project was to ensure that our maps remained current with respect to new species discoveries and taxonomic name changes (which are constantly being revised), and we also had to confirm the validity of type specimen identifications and localities, especially those referenced from obscure sources and archaic museum specimens. We used GIS software to digitize and overlay the maps of each individual African reptile species (1,601 species in total!) one on top of the other, which allowed us to count the number of species present in a given area - which we call “species richness”.
Here is the product of all of that hard work - the first comprehensive richness map of all reptile species in Africa. The colour codes correspond to the number of species from low (blue) to high (red). It shows that the reptile richness map is largely congruent with previously mapped amphibian, bird, and mammal richness showing the classic species latitudinal gradient, including high richness in the arid regions not seen in the other vertebrates. But when you look at the reptile groups distinctly you see that while the overall reptile richness map mostly resembles snakes, lizards in particular are qualitatively very different. Lizard richness hotspots are widely dispersed with high diversity in tropical regions, as well as arid and mountainous areas, where the distribution of the other reptile and non-reptile groups is relatively low.

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When we looked at which environmental predictors best explained these species richness maps we found that net primary productivity (the amount of photosynthetic activity by plants) and precipitation explain most of the variation in reptile and other vertebrates. This explains the clear latitudinal pattern seen in their respective maps, which reflects a strong correlation with plant productivity and rainfall as you move closer to the equator. But again, lizards are unique in that none of these environmental correlates explain their distributions. This is because lizards are well adapted to a wide range of habitats including the tropics as well as the harsh conditions of the desert where plant productivity and rainfall are low. We also showed that individual lizard species on average occupy smaller geographic distributions, reflecting their ability to occupy diverse niches.
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Our findings that the distribution of lizard species in Africa is unique when compared to the other vertebrate groups now confirms a pattern that has been seen elsewhere in previous studies (i.e. Australia) and most recently by our paper on the global distribution of reptiles. This shows the importance of studying the diverse reptile groups distinctly instead of lumping them all together, and will have bearing on large-scale conservation efforts that do not represent all reptile groups.
Author: Amir Lewin
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