Abstract
Whether anthropogenic mortality is additive or compensatory to natural mortality in animal populations has long been a question of theoretical and practical importance. Theoretically, under density-dependent conditions populations compensate for anthropogenic mortality through decreases in natural mortality and/or increases in productivity, but recent studies of large carnivores suggest that anthropogenic mortality can be fully additive to natural mortality and thereby constrain annual survival and population growth rate. Nevertheless, mechanisms underlying either compensatory or additive effects continue to be poorly understood. Using long-term data on a reintroduced population of the red wolf, we tested for evidence of additive vs. compensatory effects of anthropogenic mortality on annual survival and population growth rates, and the preservation and reproductive success of breeding pairs. We found that anthropogenic mortality had a strong additive effect on annual survival and population growth rate at low population density, though there was evidence for compensation in population growth at high density. When involving the death of a breeder, anthropogenic mortality was also additive to natural rates of breeding pair dissolution, resulting in a net decrease in the annual preservation of existing breeding pairs. However, though the disbanding of a pack following death of a breeder resulted in fewer recruits per litter relative to stable packs, there was no relationship between natural rates of pair dissolution and population growth rate at either high or low density. Thus we propose that short-term additive effects of anthropogenic mortality on population growth in the red wolf population at low density were primarily a result of direct mortality of adults rather than indirect socially-mediated effects resulting in reduced recruitment. Finally, we also demonstrate that per capita recruitment and the proportion of adults that became reproductive declined steeply with increasing population density, suggesting that there is potential for density-dependent compensation of anthropogenically-mediated population regulation.
Highlights
The effects of human-caused mortality on the population dynamics of wild species has long been a topic of both theoretical and management interest, and continues to be relevant for protection of small and recovering populations and establishment of sustainable targets for harvest
Anthropogenic Effects on Annual Rates We found strong evidence that anthropogenic mortality is additive to natural mortality in the reintroduced red wolf population, with higher adult anthropogenic mortality resulting in lower annual adult survivorship (Table 1; Fig. 1A)
We found evidence that anthropogenic mortality had an additive effect on the annual preservation of pair bonds, with higher levels of anthropogenic mate loss resulting in lower annual preservation of existing breeding pairs (Table 1; Fig. 1B)
Summary
The effects of human-caused mortality on the population dynamics of wild species has long been a topic of both theoretical and management interest, and continues to be relevant for protection of small and recovering populations and establishment of sustainable targets for harvest. A major debate has centered on whether anthropogenic mortality is additive to natural mortality, resulting in a net reduction in total survival rates, or whether increased anthropogenic mortality is compensated for by a reduction in natural mortality, leaving the total survival rate unchanged [1]. In the latter scenario, compensation should be manifest through density-dependent mechanisms, where anthropogenic mortality triggers a release of limited resources that can enhance survival and recruitment in the remaining population, thereby buffering any negative effects on population growth. Rather than benefiting from a general reduction in population density, productivity of breeding groups may suffer from loss of adult members, in species with prolonged juvenile dependency
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
