Among anoles, West Indian ecomorphs are the best known microhabitat specialists, but they are not the only ones. Semiaquatic anoles, of which there are 11 described species, live exclusively near streams and will sometimes enter water to feed or to escape a threat. The Central American species Anolis aquaticus appears to be specialized for climbing on rocks, particularly relative to other Central American semiaquatic anoles (Muñoz et al. 2015). Recent posts on A. aquaticus have addressed sleep site fidelity, dewlaps and trait scaling, and underwater foraging.
During a field ecology course with the Organization for Tropical Studies last winter, I compared patterns of substrate use between A. aquaticus and another Central American semiaquatic anole, Anolis oxylophus. Unlike A. aquaticus, A. oxylophus perches predominantly on woody and leafy substrates (Table 1). I wondered what was driving the differences in substrate use between these two species that appear broadly similar in morphology and lifestyle. Some Caribbean anoles alter their behavior to use only a narrow subset of available substrates in their habitat, whereas others have a greater breadth of substrate use that more closely reflects habitat-wide availability (Irschick and Losos, 1999; Mattingly and Jayne, 2004; Johnson et al., 2006). To evaluate whether substrate use differences between A. aquaticus and A. oxylophus are driven by substrate availability, species-specific selectivity, or both, I simultaneously quantified lizard substrate use and substrate availability within their streamside habitats.
On a surface area basis, ground was the most abundant substrate available to both species (Figure 1). Yet in accordance with the tendency of most anoles to occupy elevated perches, neither species was observed frequently on the ground, suggesting that both are selective in their substrate use. Substrate availability also contributes to patterns of substrate use in these species. The largest difference between streams was in the availability of rocky substrates. Streams with A. oxylophus have almost no rocks, whereas rocks were the most abundant non-ground substrate in streams with A. aquaticus. This pattern of rock availability between streams matches the difference in rock use between species.
In summary, both substrate selectivity and availability contribute to patterns of microhabitat use in A. aquaticus and A. oxylophus. Both species are biased toward using elevated perches within their streamside habitats, yet the elevated substrates available to each species are different. One lingering question is what drives the substrate selection biases observed in these species. Is their use of elevated substrates driven by an aversion to perching on the ground or an affinity for perching on something else? Although controlled substrate choice trials might provide a more definitive answer, some simulations I ran suggest that the former is more likely. You can check out the details here!
- Irschick, D. J., and J. B. Losos. 1999. Do lizards avoid habitats in which performance is submaximal? The relationship between sprinting capabilities and structural habitat use in Caribbean anoles. The American Naturalist 154: 293–305.
- Johnson, M. A., R. Kirby, S. Wang, and J. B. Losos. 2006. What drives variation in habitat use by Anolis lizards: habitat availability or selectivity? Canadian Journal of Zoology 84: 877–886.
- Mattingly, W. B., and B. C. Jayne. 2004. Resource use in arboreal habitats: structure affects locomotion of four ecomorphs of Anolis lizards. Ecology 85: 1111– 1124.
- Muñoz, M. M., K. E. Crandell, S. C. Campbell-Staton, K. Fenstermacher, H. K. Frank, P. Van Middlesworth, M. Sasa, J. B. Losos., and A. Herrel. 2015. Multiple paths to aquatic specialisation in four species of Central American Anolis lizards. Journal of Natural History 49: 1717–1730.
- Vitt, L. J., P. A. Zani, and R. D. Durtsche. 1995. Ecology of the lizard Norops oxylophus (Polychrotidae) in lowland forest of southeastern Nicaragua. Canadian Journal of Zoology 73: 1918–1927.