Wed, Aug 04, 2021:On Demand
Background/Question/Methods
Targeted removal of problem wildlife may fail to measurably reduce populations because of compensation via enhanced reproduction, reduced mortality, reduced emigration, and/or enhanced immigration. Following a human fatality attributed to coyotes (Canis latrans) in Nova Scotia, Canada in 2009, the provincial government implemented an incentive program to reduce coyote populations, and although the program ended in 2015, high pelt values continued to drive sustained harvest through 2018. Critics argued that reproductive compensation would outpace harvest; we tested this by quantifying coyote placental scars over time as a measure of reproductive output. We also tested indirectly for other mechanisms of compensation by evaluating changes in population age-sex structure. Finally, we tested for changes in mass and morphology during the harvest.
Results/Conclusions Placental scars per female remained essentially constant over time. Similarly, there were no marked changes in proportions of coyotes breeding or in population age-sex structure. Subadult females were smaller at the end of the study, whereas condition (mass corrected for size) increased significantly for all age-sex categories, consistent with reduced intraspecific competition following sustained harvest. However, effect sizes for each of these results were small, and other factors, such as natural fluctuations in food supply, may have been responsible for changes in condition. Reproductive compensation is entrenched in the literature and other forms of compensation are often suggested, but formal tests are frequently not undertaken. A literature review on terrestrial carnivores found that few tests found evidence of reproductive compensation. Significant problems with many published tests are small sample sizes and open populations in which immigration likely overwhelms even sustained harvests so that there is no selection for reproductive compensation. Our study had the advantage of large sample sizes (4000 animals) and a population with limited immigration because of an inhospitable isthmus that joins Nova Scotia to mainland North America. Our results suggest limited proximate control of reproductive output in coyotes, and other terrestrial carnivores. We conclude that reproductive compensation is not as common as is frequently assumed.
Results/Conclusions Placental scars per female remained essentially constant over time. Similarly, there were no marked changes in proportions of coyotes breeding or in population age-sex structure. Subadult females were smaller at the end of the study, whereas condition (mass corrected for size) increased significantly for all age-sex categories, consistent with reduced intraspecific competition following sustained harvest. However, effect sizes for each of these results were small, and other factors, such as natural fluctuations in food supply, may have been responsible for changes in condition. Reproductive compensation is entrenched in the literature and other forms of compensation are often suggested, but formal tests are frequently not undertaken. A literature review on terrestrial carnivores found that few tests found evidence of reproductive compensation. Significant problems with many published tests are small sample sizes and open populations in which immigration likely overwhelms even sustained harvests so that there is no selection for reproductive compensation. Our study had the advantage of large sample sizes (4000 animals) and a population with limited immigration because of an inhospitable isthmus that joins Nova Scotia to mainland North America. Our results suggest limited proximate control of reproductive output in coyotes, and other terrestrial carnivores. We conclude that reproductive compensation is not as common as is frequently assumed.