Effects of Culling on Mesopredator Population Dynamics

Abstract

Anthropogenic changes in land use and the extirpation of apex predators have facilitated explosive growth of mesopredator populations. Consequently, many species have been subjected to extensive control throughout portions of their range due to their integral role as generalist predators and reservoirs of zoonotic disease. Yet, few studies have monitored the effects of landscape composition or configuration on the demographic or behavioral response of mesopredators to population manipulation. During 2007 we removed 382 raccoons (Procyon lotor) from 30 forest patches throughout a fragmented agricultural ecosystem to test hypotheses regarding the effects of habitat isolation on population recovery and role of range expansion and dispersal in patch colonization of mesopredators in heterogeneous landscapes. Patches were allowed to recolonize naturally and demographic restructuring of patches was monitored from 2008–2010 using mark-recapture. An additional 25 control patches were monitored as a baseline measure of demography. After 3 years only 40% of experimental patches had returned to pre-removal densities. This stagnant recovery was driven by low colonization rates of females, resulting in little to no within-patch recruitment. Colonizing raccoons were predominantly young males, suggesting that dispersal, rather than range expansion, was the primary mechanism driving population recovery. Contrary to our prediction, neither landscape connectivity nor measured local habitat attributes influenced colonization rates, likely due to the high dispersal capability of raccoons and limited role of range expansion in patch colonization. Although culling is commonly used to control local populations of many mesopredators, we demonstrate that such practices create severe disruptions in population demography that may be counterproductive to disease management in fragmented landscapes due to an influx of dispersing males into depopulated areas. However, given the slow repopulation rates observed in our study, localized depopulation may be effective at reducing negative ecological impacts of mesopredators in fragmented landscapes at limited spatial and temporal scales.

Melding kin structure and demography to elucidate source and sink habitats in fragmented landscapes

“…Therefore, we are confident that the majority of adult females not captured in subsequent years were more likely to have died than to have emigrated to surrounding habitat patches. This expectation is further supported by the limited colonization of vacant patches by adult female raccoons observed in our study area following a depopulation experiment (Beasley et al 2013).…”

“…This finding, in combination with strong evidence for a high degree of site fidelity of female raccoons to their natal patch (Gehrt and Fritzell 1998, Ratnayeke et al 2002, Cullingham et al 2008, Dharmarajan et a. 2009, Beasley et al 2013, led (Dharmarajan et al 2014) to hypothesize that significant spatial variation in vital rates exists for raccoons inhabiting fragmented agricultural ecosystems, consistent with expectations of a sourcesink population structure.…”

Raccoon Social Networks and the Potential for Disease Transmission

“…This result may indicate that when infected individuals die, the subsequent social networks may not lose a great deal of their connectivity. These results may also be applicable to raccoons living in lower density populations (also see [47]). We posit that further studies of raccoon social network connectivity should be conducted across a broad range of population densities to better address the effect of population density on the potential for disease transfer.…”

Effect of compensatory immigration on the genetic structure of coyotes

“…Similarly, reproductive output of the remaining animals will increase, which is consistent with the somewhat greater litter sizes of adults and the greater frequency of juveniles breeding following trapping (Kilgo et al ). Both increased immigration and younger ages of breeding are common responses to trapping in other trapped species (Beasley et al , Robinson et al , Lieury et al , Minnie et al ). Like previously studied mesocarnivores, the greater number of animals breeding combined with high immigration rates ensure that coyotes will likely recover quickly, which could easily undermine control efforts within the southeastern United States.…”