Hypsilurus papuensis from Mt. Victoria, PNG Throughout the years, scientists have formulated various ecological "rules" describing how body size evolves as an adaptation to various climatic factors – the first and most famous of these being Bergmann's Rule which posits animals increase in size in cold habitats as an adaptation to minimize heat loss.
In our recent paper published in Global Ecology and Biogeography, we examined trends in body size of squamates, utilizing GARD's massive dataset of distributions and body sizes. We examined these trends both at the assemblage level (how median size of squamate assemblages changes from one area to the next, and how it's correlated with climatic conditions in those areas) and at the species level (how body size changes from one species to the next, and how it's correlated with the climatic conditions experienced by each species).
In our recent paper published in Global Ecology and Biogeography, we examined trends in body size of squamates, utilizing GARD's massive dataset of distributions and body sizes. We examined these trends both at the assemblage level (how median size of squamate assemblages changes from one area to the next, and how it's correlated with climatic conditions in those areas) and at the species level (how body size changes from one species to the next, and how it's correlated with the climatic conditions experienced by each species).
Cerastes gasperetti from the Arava Our most basic prediction was that if the proposed mechanisms behind these rules work, we'd see the expected correlations in most cases. What do we mean by that? If, for instance, Bergmann's Rule works, in most cases (squamates on different continents, or in different families, etc.) we'd see a negative relationship between size and temperature.
What we found is, for lack of a better term, a huge mess - the spatial patterns for squamates differ from the spatial patterns for lizards and snakes separately, and from continent to continent, and between different families. For each of the climatic variables we examined, we found positive relationships with size in roughly a third of the cases, negative relationships in roughly a third of the cases, and no relationships in about a third of the cases.
Varanus mertensi from Litchfield National Park, NT
When we examined patterns at the species-level we found an extremely strong phylogenetic signal, which makes sense (geckos and skinks are typically all small, varanids and pythons are typically all large, etc.), and we found that climatic variables explain about 1-2% of the interspecific variation in body size, a fraction so small as to be almost negligible.
To sum it all up, our conclusion was that the effect of climate on size evolution in squamates is negligible at best, at least at the interspecific level. Of course, climate can be very important – it can serve as an ecological filter for dispersal and colonization of different groups, which can create spatial patterns in body size when these groups differ in size, as we indeed find (for instance – most squamates in Australia are skinks, and most skinks are very small). In any case there doesn't seem to be some general "rule" we can formulate on how climate affects body size evolution, and we think such evolutionary relationships, if they exist, are highly species-specific and should be examined on a case-by-case basis.
To sum it all up, our conclusion was that the effect of climate on size evolution in squamates is negligible at best, at least at the interspecific level. Of course, climate can be very important – it can serve as an ecological filter for dispersal and colonization of different groups, which can create spatial patterns in body size when these groups differ in size, as we indeed find (for instance – most squamates in Australia are skinks, and most skinks are very small). In any case there doesn't seem to be some general "rule" we can formulate on how climate affects body size evolution, and we think such evolutionary relationships, if they exist, are highly species-specific and should be examined on a case-by-case basis.
The global distribution of median log species component of mass
Author & photographer: Alex Slavenko
RSS Feed
