A Few Meters Matter: Local Habitats Drive Reproductive Cycles in a Tropical Lizard.

Reproductive phenology often varies geographically within species, driven by environmental gradients that alter growth and reproduction. However, environments can differ between adjacent habitats at single localities. In lowland Puerto Rico, both open (sunny, warm) and forested (shady, cool) habitats may be only meters apart. The lizard Anolis cristatellus lives in both habitats: it thermoregulates carefully in the open but is a thermoconformer in the forest. To determine whether reproduction differs between habitats, we compared reproductive cycles of females in open versus forest habitats at two localities for over 2 years. Open females were more likely than forest females to be reproductive throughout the year, probably because open females were able to bask and thereby achieve warmer body temperatures. These between-habitat differences in reproduction were especially marked in cool months and are equivalent in magnitude to those between populations separated by elevation. Thus, environmental differences (even on a microlandscape scale) matter to reproduction and probably to demography.

Population density and energetics of lizards on a tropical island.

1. Population density, biomass, thermal relations and energetics of three common species of lizards (Anolis bonairensis, Cnemidophorus murinus, Gonatodes antillensis) were measured in a thornscrub community on the arid Caribbean island of Bonaire. 2. Population density and biomass estimates of these populations were 1318, 561, and 4200 individuals/ha and 4.2, 15.4, and 3.5 kg/ha, respectively. Although these densities are not exceptional for other Carribbean islands, they greatly exceed lizard densities reported for mainland communities. 3. Mean diurnal body temperatures are 33.4° C for Anolis, 40.4° C for Cnemidophorus, and 34.5° C for Gonatodes. Nocturnal temperatures average 27° C for all species. 4. Resting rates of oxygen consumption for all species were measured at naturally experienced diurnal and nocturnal temperatures. The values were used to calculate Minimal and more realistic Field Active estimates of the respiratory energy utilization of these lizard populations. 5. Minimal estimates of energy expenditure are 326, 950, and 268 kJ/(haxday) for Anolis, Cnemidophorus, and Gonatodes, and Field Active estimates are 693, 2510, and 379 kJ/(haxday), respectively. 6. These estimates greatly exceed values previously reported for other lizard populations. They also exceed reported values for the respiratory metabolism of populations of small mammals in temperate regions. 7. These values are probably not atypical of other tropical insular lizard populations, and the significance of these animals to energy flow in these communities has not generally been appreciated.