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Risk-Disturbance Overrides Density Dependence in a Hunted Colonial Rodent, the Black-Tailed Prairie Dog Cynomys ludovicianus
Jonathan N. Pauli and Steven W. Buskirk
Journal of Applied Ecology
Vol. 44, No. 6 (Dec., 2007), pp. 1219-1230
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/4539345
Page Count: 12
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1. Traditional understanding of how hunting affects vertebrate populations emphasizes competitive release and density dependence of vital rates, but more recent thinking has proposed complex non-lethal responses to hunting disturbance and predation risk. Colonial species have been proposed to be more vulnerable than dispersed, solitary species to disturbance and perceived risk from hunting. However, empirical comparisons of density dependence vs. risk disturbance in hunted species are few. 2. To compare density dependence with risk-disturbance effects of hunting on individuals and populations of a colonial species, we tested the response of black-tailed prairie dogs Cynomys ludovicianus to shooting in a before-after, treatment-control experiment. We subjected five colonies to a pulse of shooting, and compared individual and colony attributes to those of five control colonies, protected from shooting. 3. Surviving prairie dogs increased alert behaviours eightfold and reduced both above-ground activity and time spent foraging by 66%. Changes in behaviour lowered the body condition of surviving adults by 35%. Survivors of shooting, especially juveniles, exhibited elevated stress levels; faecal corticosterone concentrations increased by 80% among juveniles. Unexpectedly, overwinter survival rates did not increase in response to reduced prairie dog density. Colonies subjected to shooting experienced reproductive near-collapse the summer after shooting; pregnancy rates declined by 50% and reproductive output fell by 82%. 4. Risk-disturbance overwhelmed any possible density-dependent effects of shooting in prairie dogs, which exhibited additive mortality in response to hunting, and reproductive failure 1 year after shooting. Risk-disturbance was the predominant mechanism whereby individuals and colonies were affected by hunting. 5. Synthesis and applications. Because of their coloniality, prairie dogs possess certain life-history traits that predisposed them to be particularly susceptible to hunting-associated disturbances, which had cascading effects on population-level processes. Our findings contradict the general belief that small-bodied mammals quickly rebound from hunting exploitation via compensatory mortality and reproduction. Managers should consider measures to reduce recreational shooting intensity and duration in regions where black-tailed prairie dog colony growth and persistence is desired, yet allow shooting in areas where colonies conflict with landowner interests.
Journal of Applied Ecology © 2007 British Ecological Society