Seasonal fluctuations in the environment frequently lead to important modifications in the distribution of all kinds of resources in all sorts of ecosystems. Consequently, environmental seasonality has long been known to determine the biology, ecology and behavior of animals. Less known, however, is whether and how seasonality differentially affects populations of the same species inhabiting mainland and island areas.
By conducting field observations on Anolis nebulosus from a mainland and a nearby island population in the Jalisco coast (Western Mexico), Siliceo-Cantero & Garcia (2015) investigated i) if anoles from these populations experienced similar degrees of seasonality and ii) whether they responded similarly to these seasonal changes. At each of the study sites, the authors conducted a series of transects at three different time blocks of the day within the normal activity range of the species. They collected information on each of the observed anoles including sex, perch height, temperature and humidity. Behavioral information was obtained for males by conducting focal observations in which researchers quantified movement rates, perch height and width, as well as the type of movements (i.e. dedicated to thermoregulation, socialization, and feeding).
Results showed several differences in substrate use and behavior between sexes, sites, and seasons. Overall, females perched lower than males (see Figure below), which could be a strategy of females to minimize competition with males. Interestingly, both sexes tended to perch lower on the mainland site. The authors suggest this could be a way of decreasing niche overlap with the larger lizard Sceloporus melanorhinus, a species that is not present on the island site. The reason why females perched lower during the rainy season whereas males did not remains unclear.
In general, males showed higher movement rates and covered longer distances on the San Agustin island site, maybe due to reduced environmental fluctuation on the island. The explanation for this is that, on the mainland, lizards may have to spend more energy to keep an appropriate body temperature so the costs of being active are higher that the potential benefits. Daily patterns of activity seem to be mainly determined by seasonal fluctuations in temperature and relative humidity (see Figure). The bimodal daily pattern of activity found during the dry season is possibly the consequence of an increased risk of overheating by direct solar irradiation, since the trees have lost their leaves during this time of the year. The lack of such bimodal pattern of activity on the island is compatible with possibility that this environment has less harsh weather conditions (e.g. lower temperatures due to regular wind currents), allowing anoles to be active with a lower risk of overheating.
Perch height differed among sexes, seasons and sites (means and 95% CI shown). Box shows significant differences among groups. Males (M), females (H), from island (I) and continent (C) during dry (S) and rainy (LI) seasons. (Figure 2 from Siliceo-Cantero & Garcia 2015)
In summary, the behavior of anoles is affected by seasonal fluctuations in their environment, but these effects seem to be the consequence of a complex interaction between several geographic and biotic factors. For instance, an increased seasonality in the environmental conditions of mainland may cause anoles to show a bimodal pattern of activity that does not exist on islands. In addition, the presence of a larger lizard is suggested to influence perch height in mainland anoles. Finally, increased intraspecific competition on islands could explain both increased activity of males (e.g. to defend their territories) as well as increased resource partition on perch height between males and females.
