Thermal gradients across broad distances account for biodiversity at large spatial scales. Ecologists know all about this. On the other hand, even though they may be just as important, we don't know much about the biology of thermal gradients at very fine spatial scales -- just mere millimeters. These gradients may explain much of the variance in alpha and beta diversity in the leaf litter of tropical rainforests. In a Costa Rican tropical wet forest, we manipulated the depth of leaf litter, and used dataloggers to measure changes of ambient temperature in the litter in a vertical transects at 2cm intervals. Second, we measured temperature along vertical transects in unmanipulated ambient litter. Third, we sampled the colonies of ants nesting within leaf litter, measuring the depth of the litter above and below each colony, and tested whether colony size and functional composition of the community varied predictably with the thermal environment.
Results/Conclusions:
We found that deeper leaf litter provides a greater thermal buffer, staying cooler in the daytime and warmer in the evening. We found that differences in the where ants choose to nest in the litter that varied with species and colony size, with interactions among both variables. We conclude that the thermal properties of leaf litter are highly predictive of the species richness and functional composition of the community. It is only reasonable to surmise that these effects on ants are recapitulated by other animals that cohabit this environment.