Modeling the effects of predation, prey cycling, and. time averaging on relative abundance in raptor-generated small mammal death assemblages

摘要

Raptors concentrate the remains of their small mammal prey in pellets rich in skeletal material. Stratified pellet deposits beneath long-term roost sites should, therefore, represent valuable archives of Holocene faunal change. Accurate paleoecological reconstruction from such deposits, however, requires a complete assessment of factors that may bias the ecological information that such records preserve. Three factors that could bias or obscure the community structure of a small mammal death assemblage relative to the living community include: (1) short-term transient dynamics of prey populations; (2) feeding activity of the raptors; and (3) extent of time averaging represented in individual stratigraphic horizons. Here I model (1) how much summed time is necessary for a raptor-derived small mammal death assemblage to capture a long-term (centennial to millennial) signal of relative abundance; and (2) the accuracy of the relative abundance information preserved in such death assemblages given short-term (decadal) cycling of small mammal prey populations. Results generated from an empirically parameterized model of prey dynamics assuming a multi-species type III functional response of raptors to fluctuations in density of two prey species suggest that the maximum extent of time averaging necessary to capture a stable relative abundance signal in a death assemblage is similar to 140 years. This estimate is highly conservative, yet still remains fine enough to analyze phenomena operating at the centennial to millennial time scales critical for addressing long-term community response to habitat transitions through the Holocene. Results also suggest that the mismatch between relative abundance information in the living community and the death assemblage is generally low (< 1%), except for a few specific parameter combinations that result in the population dynamics of the prey species being extremely similar to one another.