Posted by: oikosasa | October 22, 2013

Safer with close neighbors

Does new-density increase or decrease predation rate? Find out in the new Early View paper “Adaptive nest clustering and density-dependent nest survival in dabbling ducks” by Kevin M. Ringelman and co-workers. Here’s Kevin’s summary of the paper:

IMG_0421Many wildlife populations are regulated by density dependence: when populations become very large, survival and recruitment rates tend to decline.  In North American waterfowl, density dependence is often observed at continental scales, and nest predation has long been implicated as a key factor driving this pattern.  Predators may aggregate in areas of high nest density, and can reduce nest success to the point where it limits population growth.  However, despite extensive research on this topic, it remains unclear if and how nest density influences predation rates.  Part of this confusion may have arisen because previous studies have examined density-dependent predation at relatively large spatial and temporal scales.  To address this, we used three years of data on nest survival of two species of waterfowl, Mallards and Gadwall, to more fully explore the relationship between small-scale patterns of nest clustering and nest survival. 

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Throughout the season, we found that the distribution of nests was consistently clustered at small spatial scales (~50 – 400 m), especially for Mallard nests, and that this pattern was robust to yearly variation in nest density and the intensity of predation.  We also showed that nests within a cluster had lower predation rates, which runs counter to the general assumption that predators are attracted to areas of high nest density.  Because the predators at our study site probably only depredate duck nests incidentally, nesting a group could effectively dilute predation risk from predators that are “just passing through.”

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