Wolves, ungulate carcasses, and ecological heterogeneity: Testing the spatial structure of carrion-derived soil respiration
Understanding how migration and predation influence carrion dynamics is necessary for predicting contingent outcomes in nature and for maintaining mosaics of resource heterogeneity that help support microbial, plant, and scavenger diversity. Ungulate carrion can result in biogeochemical hotspots, which alter nutrient cycling rates and elemental composition of vegetation, and modify animal activity, especially that of facultative scavengers. Whether migration events and/or predators facilitate heterogeneity or homogeneity in nutrient cycling and biological activity through their influence on carrion resource distribution is unknown because carrion studies have not adequately assessed carrion-derived biogeochemical effects relative to existing spatial variance caused by other mechanisms that influence biogeochemistry. We assessed soil community respiration rate – an important ecosystem process – at and around experimental and wolf-killed ungulate carcasses using a cyclical sampling technique and spatial variance analyses that allowed us to 1) determine whether or not ungulate carcasses generate spatial heterogeneity in soil respiration and 2) examine such a determination at multiple scales. This allowed us to test the potential importance of predation and ungulate carcasses relative to other mechanisms that enhance or diminish heterogeneity in soil respiration.
Mean soil community respiration rates at wolf-killed moose sites were significantly higher at carcass centers compared to the edge of carcass sites and off-site references. Soil respiration was also elevated at experimental white-tailed deer carcass sites compared to reference locations for at least a month, but pretreatment soil measurements were not significantly different from reference measurements throughout the experiment. We also detected differences in soil respiration between 9-year old white-tailed deer carcass sites and current reference sites. Semivariance modeling indicated soil community respiration rate was spatial independent at separation distances greater than ~1.5-3.0 meters. Soil respiration was spatial autocorrelated at locations separated by less than ~1.5 meters. We found that ungulate carcasses both elevate soil respiration rates compared to existing background levels influenced by multiple other mechanisms and enhance the spatial heterogeneity of soil respiration rates at scales relevant to the maintenance of microbial, plant, and scavenger diversity. Our results suggest that migration and predators can significantly modulate spatial structure in soil respiration by influencing carcass distribution.