Of mice and mallards: positive indirect effects of coexisting prey on waterfowl nest success

Abstract

Ackerman, J. T. 2002. Of mice and mallards: positive indirect effects of coexisting prey on waterfowl nest success. -Oikos 99: 469-480.Coexisting prey species interact indirectly via their shared predators when one prey type influences predation rates of the second prey type. In a temperate system where the predominant shared predator is a generalist, I studied the indirect effects of rodent populations on waterfowl nest success, both within the nesting season among sites and among years. Among six to ten upland fields (14 to 27 ha), mallard (Anas platyrhynchos) nest success was positively correlated with rodent abundance in all three years of the study. After removing year effects, mallard nest success remained positively correlated with the relative abundance of rodents. Of the rodent species present, California voles (Microtus californicus) were the most important coexisting prey type influencing nest success. Among years, mallard nest success was positively correlated with vole abundance; the asymptotic relationship suggests a threshold response to vole abundance, beyond which predators become satiated and additional voles do little to affect nest success. I tested and rejected three alternative explanations for the observed positive correlation between mallard nest success and rodent abundance that do not involve an indirect effect of coexisting prey populations. The influences of dense nesting cover, nesting density, and predator activity did not explain the observed patterns of nest success. These results suggest that rodent populations buffer predation on waterfowl nests, both within and among years, via the behavioral responses of shared predators to coexisting prey.

Density-dependent nest predation in waterfowl: the relative importance of nest density versus nest dispersion

“…and thistle (family Asteraceae) have become increasingly common during the past 10 years. Over the past two decades, striped skunks (Mephitis mephitis) have been the major nest predator in this area (McLandress et al 1996;Ackerman 2002), although the skunk population appears to have declined in recent years while predators such as raccoons (Procyon lotor) and common ravens (Corvus corax) have become more numerous (K.M. Ringelman, personal observation).…”

Prey Behavior, Age‐Dependent Vulnerability, and Predation Rates

“…If coyotes live in an area with a preferred prey species that is readily available in winter (e.g., snowshoe hares [Lepus americanus]), we would expect coyotes to reduce the time spent hunting ungulates in winter, which should benefit mule deer. As with other forms of alternative prey (Patterson et al 1998;Cooper et al 1999;Ackerman 2002;Prugh 2005;Miller et al 2006), the presence of the second deer species would be likely to influence predation on the first (Robinson et al 2002) and should be considered in future models.…”

“…However, prey vulnerability is not the only source of temporal variation that affects predation rates. The size and hunting tactics of a predator can affect the size or age of prey it captures (Paquet 1992;Pierce et al 2000;Downes 2002;Essington and Hansson 2004), and seasonal variation in alternative prey can affect the time of year when a predator hunts any particular species (Patterson et al 1998;Cooper et al 1999;Ackerman 2002;Miller et al 2006). A prey species will presumably suffer the greatest impact from predators that target the animal at the time of year when it is most vulnerable.…”

High predation on small populations: avian predation on imperiled salmonids

“…In some cases, small prey populations may be relatively buffered from predation when refuges are available or if predators switch to target more abundant prey (Holling 1959, Ackerman 2002, Twardochleb et al 2012. Furthermore, if predators are specialists, their populations may decline following the decline of their prey, thereby reducing predation rates (Elton andNicholson 1942, Hanski et al 2001).…”