Category: Classics from the Literature Page 2 of 4

Anolis armouri basking on a rock.

Our era of human-mediated climate change has brought startling new realities that we must face – ocean acidification, desertification, and receding ice caps, among others. For those of us who study lizards, one message is pervasive and clear – many species are being pushed to their thermal limit, and it is likely that many lizards, especially those that prefer cooler temperatures, won’t be able to take the heat. But, how do we know this? One of the main methods used to determine how reptiles will respond to climate change is to compare their preferred temperature (i.e., where lizards would like to keep their body temperature, given the option) to a random sampling of the thermal environment.

From a lizard’s eye view, though, the thermal environment is more complex than just air temperature. Lizards have volume, shape, and color, all of which affect their core temperature. Essentially, the operative temperature (Te) describes a lizard’s thermal environment as the sum total of many different interactions, such as radiation and convection, among others. Because it describes how temperature is shaped by everything except behavior and physiology, the operative temperature essentially describes how a perfect thermoconformer instantaneously perceives the environment. As such, it has been used as the null hypothesis for behavioral thermoregulation – if we can describe the thermal environment by recording Te, then we can use field-measured body temperature to determine the degree to which animals are thermoregulating. Here on the Anole Annals I’ve considered how devices have evolved to capture the operative temperature. The earliest prototype was a water-filled beer can, and we now have copper models painted to match the organism’s reflectance and HOBO devices.

Copper models of Anolis cybotes in the making.

But just where did these devices come from? I’ve been in Terre Haute, Indiana working with Dr. George Bakken at Indiana State University for the past two weeks making copper models of Anolis cybotes for my field research in the Dominican Republic. Dr. Bakken, along with Dr. David Gates, operationalized the term “operative temperature” for the ecological community in a seminal 1975 paper. I sat down with Dr. Bakken for an interview to learn how the intellectual climate promoted this and other important foundational works for biophysical ecology and reptilian thermobiology.

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Lineage accumulation curves (Fig. 2, Rabosky and Glor 2010) showing that Hispaniola (blue), Jamaica (purple), and Puerto Rico (orange) have reached speciation-extinction equilibrium. Cuba (red) is still gaining species.

Losos, J.B., and D. Schluter. 2000. Analysis of an evolutionary species-area relationship. Nature 408: 847-850.

Rabosky, D.L, and R.E. Glor. 2010. Equilibrium speciation dynamics in a model adaptive radiation of island lizards. Proc. Nat. Acad. Sci. 107: 22178-22183.

Losos and Schluter (2000) return to Caribbean anoles to test three hypotheses about the species-area relationship: (1) that there is an area threshold above which speciation surpasses immigration as a source of new species; (2) above the threshold size, speciation events per unit time should increase with island area; and (3) the slope of the species-area relationship should become steeper above the area threshold. Qualitatively similar to Losos (1996), this paper was novel in that a newly available, nearly complete, mt-DNA phylogeny allowed Losos and Schluter to reconstruct immigration and speciation events and to model whether species number has reached speciation-extinction equilibrium.

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Losos, J.B. 1996. Ecological and evolutionary determinants of the species-area relation in Caribbean anoline lizards. Philosophical Transactions of the Royal Society of London B 351: 847-854.

As alluded to previously,  MacArthur and Wilson (1967) did consider evolutionary processes when they developed their Theory of Island Biogeography. Specifically, in situ evolutionary diversification (i.e. speciation) may contribute substantially to the species diversity of an island and should be considered in any general attempt to model species-area relationships on islands. Building on Rand’s 1969 paper studying the ecological determinants of species richness in Caribbean anoles, Losos (1996) incorporates an evolutionary perspective into the Caribbean Anolis species-area story.

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This is the first of a series of posts that will review a number of papers that examined species richness patterns in anoles, starting with Rand’s 1969 paper described below and moving towards the present day understanding. Read on!

Species richness predictions from the Theory of Island Biogeography

 Rand, A.S. 1969. Competitive exclusion among anoles (Sauria: Iguanidae) on small islands in the West Indies. Breviora 319: 1-16.

The empirically observed species-area relationship (SAR) is one of the closest things to a law that we have in evolutionary ecology. All else equal, the larger the area, the more species will be in it. In a paper in 1963, and a book in 1967, MacArthur and Wilson (M&W) put forward the Theory of Island Biogeography (TIB) to explain the species-area relationship on islands. They observed that the number of species that inhabit an island scales positively with island area and negatively with distance of an island from the mainland species source. M&W argued that the SAR is governed by two ecological processes: colonization and extinction. Colonization probability increases with the size of an island and decreases with island distance from the mainland. Extinction probability increases as island size decreases because small islands support smaller population sizes and leave species are more vulnerable to fluctuations in abiotic and biotic environmental factors. Thus, the TIB predicts that large islands close to the mainland will be species rich, while small islands far from the mainland will be species poor. The TIB inspired thousands of papers: according to Google Scholar, the 1967 book has been cited 11,148 times and the 1963 paper has been cited 1,416 times.

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I previously characterized Albert Schwartz as one of the five kings of Greater Antillean anole taxonomy for having described eight new species from the region.  Although Schwartz described the fewest species among the five kings, focusing on new species masks Schwartz’s even more important contributions to cataloguing geographic variation within species.  Schwartz’s career-spanning interest in biogeography and geographic variation resulted in a prolific history of describing subspecies in anoles and other taxa.  Anyone who’s looked at Schwartz and Henderson’s classic book on West Indian reptiles and amphibians is familiar with the irregular blobs that designate subspecies boundaries on the range maps for many of the region’s most geographically widespread species.  Many of these blobs were the result of Schwartz’s own efforts.  The pinnacle of Schwartz’s work on geographic variation may be his 1968 monograph on geographic variation in Anolis distichus.

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The last of the five kings described more new anoles than any of the others: Orlando Garrido.  Garrido is unique among the five in two ways.  First, he’s still alive, still active, and still making contributions to our understanding of anole diversity.  Second, he’s actually a citizen of a Greater Antillean country: Cuba.

Garrido is often recognized as Cuba’s greatest naturalist.  In addition to his impressive body of work with reptiles, he has made many other important contributions to our understanding of Cuban nature, including the spectacular “Field Guide to the Birds of Cuba.”  His successes  are a testament to how far science has come since Barbour’s time, when practicing science in the West Indies required a wealthy North American pedigree.  I’ve credited Garrido with a whopping 24 species, all from his native Cuba.

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I’ve credited the fourth king of Greater Antillean anole taxonomy – Albert Schwartz – with describing eight Greater Antillean anole species.  The period during which Schwartz’s career overlapped with Williams’s and that of the fifth yet-t0-be-revealed king were the glory years of Greater Antillean anole taxonomy.  Over a little more than a decade in the late 1960s through the 1970s, these three figures described over 10 species, including some of the last new species discovered on Hispaniola and Jamaica.  The activities of these three key figures were highly synergistic; Schwartz and Williams often contributed to one another’s work and divvied up projects to mutual benefit (even though they never described an anole species together) and Schwartz was a junior coauthor with the fifth king on several species descriptions.

After graduating with a PhD from the University of Michigan, Schwartz spent the majority of his academic career at Miami Dade Community College, an institution known more for its massive enrollment than for its faculty’s contributions to systematics.  Early in his career, Schwartz worked primarily in Cuba, resulting in the description of three species, including two locally restricted species related to the Cuban crown-giant anole Anolis equestris (baracoae and smallwoodi) and a widespread trunk-ground species (jubar) that is the xeric forest counterpart to another widespread Cuban trunk-ground anole found primarily in mesic environments (homolechis).  Schwartz would later devote his attention to Hispaniola, ultimately describing five species from both Haiti and the Dominican Republic.  As was the case with Williams, many of the Hispaniola taxa that Schwartz described were unusual montane endemics (rimarum, fowleri, sheplani, and eugenegrahami).

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Following Barbour’s work, nearly a quarter century would pass before another Harvard man picked up the mantle of describing new anoles.  Among his many other contributions, Ernest Williams named 12 species of anoles from Jamaica, Cuba, and Hispaniola between 1959 and 1975.  By the time Williams came along, most of the abundant and widely-distributed anoles had already been described.  Many of the species Williams described are montane endemics (A. reconditus, A. christophei, A. etheridgei, A. dolicocephalus, A. occultus, A. singularis, A. insolitus) that might have been more difficult to access during previous generations of herpetological exploration in the West Indies.  The last Greater Antillean species he described – Anolis marcanoi – was among the first “cryptic” anole species to be recognized with the aid of molecular markers.  Even after his work describing new Greater Antillean anoles came to an end, Williams continued to describe new species of anoles from the mainland through the 1980s.  In his last publication in 1999 (published after his death in 1998), Williams called an end to the era of discovery in anoles.  For more on Williams, you can read the memorial published in the Harvard Gazette in 2009 by A. W. Crompton, Karel Liem and Jonathan Losos.

I previously introduced my mission to recognize the five anole systematists responsible for describing the majority of the anole species found in the Greater Antilles.  The first king of Greater Antillean anole taxonomy was the prolific E. D. Cope.  Cope was the last in a line of authors who described anole species that he’d never actually spent time with in the field (see also Duméril and Bibron).  The next king on my list, by contrast, was an avid field biologist and conducted field work in the West Indies throughout his career.

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