Anole Annals

Andrew Battles presents his work on Anolis cristatellus and A. sagrei at SICB 2016.

Greetings from SICB! Sessions are off to a roaring start here in Portland. At Monday’s poster session, Andrew Battles presented his work on the thermal ecology of urban anoles. Andrew, a Ph.D. student working with Jason Kolbe at the University of Rhode Island, presented his work in the poster session for the prestigious Huey award.

Around the world, many natural habitats are being replaced with artificial, heat-absorbing structures, such as concrete and metal. This is a really big deal for the animals that perch on these substrates, particularly ectotherms, which derive their heat from external sources. Andrew examined environmental temperatures and canopy openness at a variety of urban and natural sites in (and around) Miami, Florida. What he found was that urban perches (posts, building walls, etc) were considerably warmer and more exposed than natural perches.

He then examined body temperatures for the lizards Anolis cristatellus and A. sagrei that are commonly found in those habitats. On average, A. sagrei had higher body temperatures than A. cristatellus. Both species benefitted from warmer urban structures early in the morning, as they were able to reach temperatures in their preferred range sooner than in the cooler natural sites. In light of these results, Andrew’s next work will examine patterns of physiological divergence in urban and natural habitats. Congratulations to Andrew for being a finalist (and the sole Anolis ambassador) in this year’s Huey Award Symposium.

Anolis onca basking. Photo by Gabriel Ugueto.

The ecological niche is one of the most controversial concepts in ecology with a long history of debate about its definition and scope. Some authors have suggested that this concept should be abandoned (see for example McInerny & Etienne, 2012a,b,c), while others, including me, consider that this controversial history, and a plethora of definitions, should not preclude its use. However, it needs to be explicitly defined to known exactly we are talking about.

The ecological niche is understood as the set of environmental factors that allow a local population to persist without immigration from others sources (Hutchinson 1959). Some evolutionary ecologists have envisioned the ecological niche as a phenotypic extension of a species and therefore subject to natural selection and other evolutionary process. Based on this, in my doctoral dissertation, I evaluated whether the ecological niche (or more precisely, the climatic niche), as a population-level trait, can promote species diversification in Anolis lizards. Although there are several studies linking organismal and species’ level traits with speciation, there are few exploring this association in Anolis lizards.

Our study exploring this was recently published in the Journal of Biogeography (Velasco et al. 2016). Explicitly, we adopt  Hutchinson’s niche definition using only coarse-grain variables (or the Grinnellian niche dimension; see Soberón 2007). To do this, we compiled an extensive occurrence database for 328 species with help of several colleagues. Using climatic layers from WorldClim database, we calculated a set of niche metrics for species and clades, including mean niche position (based on PCA analyses), niche breadth (based on Mahalanobis distances) and occupied niche space (as a proxy of climatic niche diversity).

We compared how climatic niche breadth and occupied niche space differ among regions (insular vs. mainland) and clades (Fig. 1 & 2). Mainland species and clades tend to exhibit larger niches than Caribbean clades and species (Fig. 1).

These differences were maintained after controlling for range size differences. We suggest that these differences are directly related to the available climatic space in each region. For instance,  Caribbean islands exhibit a limited climatic space in comparison with  mainland regions and therefore insular clades occupy all available climatic conditions in each island (Fig. 2). By contrast, mainland clades are more restricted to climatic conditions and therefore occupy only a portion of all available climatic conditions (Fig. 2).

We correlated these niche metrics with species diversification using a calibrated time tree. We found that anole clades occupying warmer and drier areas diversified more than clades occupying very humid and colder areas. In addition, anole clades with narrow niches tend to speciate more than clades with widespread niches (Fig. 3). Our findings suggest that climatic specialization has played a strong role in anole diversification with differences among insular and mainland settings.

It would be interesting to evaluate whether other traits (e.g., body size, geographical range size, or other Eltonian niche dimensions) also play a similar role on cladogenesis in Anolis lizards and evaluate their relative importance in diversification dynamics.

References

Hutchinson, G.E. (1957) Concluding remarks. Cold Spring Harbor Symposia on Quantitative Biology, 22, 415-427.

McInerny, G.J. & Etienne, R.S. (2012a) Ditch the niche ? is the niche a useful concept in ecology or species distribution modelling? J. Biogeogr., 39, 2096-2102.

McInerny, G.J. & Etienne, R.S. (2012b) Stitch the niche ? a practical philosophy and visual schematic for the niche concept. J. Biogeogr., 39, 2103-2111.

McInerny, G.J. & Etienne, R.S. (2012c) Pitch the niche ? taking responsibility for the concepts we use in ecology and species distribution modelling. J. Biogeogr, 39, 2112-2118.

Soberón, J. (2007) Grinnellian and Eltonian niches and geographic distributions of species. Ecology Letters, 10, 1115-1123.

Velasco, J. A., Martínez-Meyer, E., Flores-Villela, O., García A., Algar, A. C., Köhler, G. and Daza, J. M. (2016), Climatic niche attributes and diversification in Anolis lizards. J. Biogeogr., 43: 134-144. doi:10.1111/jbi.12627

As 2015 comes to an end, now is a good time to reflect on the year in Anole Annals. Fortunately, our good friends at WordPress have provided us with a nice summary.

For all the details on how things went down on Anole Annals in 2015, check out WordPress’s full report.

Recently, Jackson Weaver, Danielle Losos, and I spent two weeks researching both Anolis lineatus and Anolis bonairensis in the Netherland Antilles, specifically on the islands of Curacao and Bonaire. Working alongside Dr. Losos, Dr. Herrel, and Dr. Fabre, we observed the various activities of the lizards, filming them for periods of up to thirty minutes to analyze the behavioral characteristics of both species. Furthermore, we investigated the mystery of the asymmetrical dewlap of Anolis lineatus–why does one side of its dewlap exhibit a lighter shade than the other? This short video documents our research process and explores our intriguing results. We are currently in the process of writing papers on these subjects, and are releasing this video to give background knowledge on the topics of our studies.

We hope you enjoy this short film about our excursion!

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At last we’ve found a place in the Caribbean that Anolis sagrei hasn’t invaded: Cuba! Because, of course, A. sagrei is native there, as well as 63 other species of anoles. In fact, there are no introduced anoles on Cuba, which is quite unusual. There are, however, a number of other herps that have invaded there, as a recent paper in Herpetological Conservation and Biology by Borroto-Páez discusses. Here’s the abstract:

The number of introductions and resulting established populations of amphibians and reptiles in Caribbean islands is alarming. Through an extensive review of information on Cuban herpetofauna, including protected area management plans, we present the first comprehensive inventory of introduced amphibians and reptiles in the Cuban archipelago. We classify species as Invasive, Established Non-invasive, Not Established, and Transported. We document the arrival of 26 species, five amphibians and 21 reptiles, in more than 35 different introduction events. Of the 26 species, we identify 11 species (42.3%), one amphibian and 10 reptiles, as established, with nine of them being invasive: Lithobates catesbeianus, Caiman crocodilus, Hemidactylus mabouia, H. angulatus, H. frenatus, Gonatodes albogularis, Sphaerodactylus argus, Gymnophthalmus underwoodi, and Indotyphlops braminus. We present the introduced range of each of the 26 species in the Cuban archipelago as well as the other Caribbean islands and document historical records, the population sources, dispersal pathways, introduction events, current status of distribution, and impacts. We compare the situation of introduced herpetofauna in Cuba with that in other Caribbean islands. We also document impacts, areas of missing information, and possible directions for future research. The paper contributes a systematic review as well as new knowledge for national and international agencies and databases. This information is critical for use in conservation, management, and eradication. Additionally, it alerts management authorities as to specific pathways of introduction for proactive action, which may be used to avoid potential introductions.

A typical PCA table that I trawled from the internet.

This post isn’t really very anole-specific, but because lots of studies of anoles use principal component analyses, I think it’s at least tangentially relevant.

PCA is a way of to reduce the variation in a data set to a few dimensions by constructing new variables that combine variables that are highly correlated with each other into a smaller number of variables called PC axes. I won’t go into the details of the method here, because Ambika Kamath explains all in a post she wrote on her blog a while back.

What I want to mention here is how we interpret these new statistical axes. Back in my day, computer programs spit out a matrix of numbers like the one above, which we called “loadings.” These values represented how strongly an individual’s value for each variable was correlated with the individual’s score on the new axes. So, for example, in the table above, values on PCA axis one correlate most strongly with an individual’s values for the top four variables (sodium, calcium, magnesium and chloride concentrations) and most weakly with melt percentage and some other variables.

Now, everyone uses the computer program R to conduct PCAs, and R, too, spits out “loadings.” But those are not your father’s loadings (or my loadings). Rather, those values are the coefficients of the new equation that defines the PCA axis (a PCA axis is a linear regression of all the variables). Thus, in the example above, individuals that scored high on PCA 1 would have the largest largest concentrations of the top four variables; an individuals melt percentage would have little impact on an individual’s score on PC I. Back in the day, we could also access those values, but we called them “coefficients.”

Does this really matter? Only to the extent that what much of the literature used to call “coefficients” is now called “loadings” and what used to be called “loadings” apparently isn’t routinely spit out by R. And, more importantly, most R users are completely unaware of the switcheroo.

Ambika did a very preliminary analysis to see whether the values of coefficients (new “loadings”) and correlations (old “loadings”) are very different. Her tentative conclusion is that they aren’t, so maybe this doesn’t matter much, but it might be worth looking into more.