Predicting the ecological effects of climate change is complicated by differential responses of species and the potential for complex alterations in both direct and indirect effects of species interactions. Such issues may be especially important within communities characterized by strong top-down effects exerted by ectothermic predators. Recent research has demonstrated that the terrestrial plethodontid salamander, Plethodon cinereus, plays an important role in the regulation of species composition of forest-floor invertebrate communities. P. cinereus exerts both direct, trophic effects as well indirect effects through suppression of intermediate predators and through regulation of competitive interactions among microbi-detritivores. Here, I report on a study that tested for the effects of temperature on these dynamics. Invertebrate densities within litter bags were compared among temperature (10, 16.5, and 23 oC) and salamander presence/absence treatments in a 3-month long, factorial experiment using forest-floor microcosms. The overall response of the invertebrate community was assessed by multivariate analysis of covariance (MANCOVA), followed by univariate analyses of covariance for individual invertebrate taxa.
Results/Conclusions
P. cinereus had a significant effect on the composition of the invertebrate community (MANCOVA, P = 0.033). Overall densities were 15% greater in the presence of salamanders in comparison to controls. However, individual taxa differed in response to salamander and temperature treatments. Hypogasturid Collembola declined in density in the presence of salamanders but were unchanged within controls (P = 0.044); the strength of this response was greatest at 23 oC. In contrast, isotomid Collembola increased in the presence of salamanders (P = 0.037), and the strength of this response increased with temperature. Isotomid densities within microcosms with P. cinereus increased as much as 14-fold at 16.5oC and 2-3-fold at 23 oC in comparison to controls. Upon completion of the experiment, invertebrate communities within control microcosms were dominated by oribatid mites at all temperatures, whereas communities within salamander microcosms were dominated by isotomids at the warm temperatures, especially 16.5 oC, but were essentially identical to controls at 10 oC. P. cinereus is a common and often abundant resident of the floor of temperate forests of eastern North America. The results of the current study indicate that P. cinereus may play a significant role in the response of forest-floor communities to predicted changes in environmental temperature.
