title: Density-dependent nest predation in waterfowl: the relative importance of nest density versus nest dispersion.
abstract: When nest predation levels are very high or very low, the absolute range of observable nest success is constrained (a floor/ceiling effect), and it may be more difficult to detect density-dependent nest predation. Density-dependent nest predation may be more detectable in years with moderate predation rates, simply because there can be a greater absolute difference in nest success between sites. To test this, we replicated a predation experiment 10 years after the original study, using both natural and artificial nests, comparing a year when overall rates of nest predation were high (2000) to a year with moderate nest predation (2010). We found no evidence for density-dependent predation on artificial nests in either year, indicating that nest predation is not density-dependent at the spatial scale of our experimental replicates (1-ha patches). Using nearest-neighbor distances as a measure of nest dispersion, we also found little evidence for "dispersion-dependent" predation on artificial nests. However, when we tested for dispersion-dependent predation using natural nests, we found that nest survival increased with shorter nearest-neighbor distances, and that neighboring nests were more likely to share the same nest fate than non-adjacent nests. Thus, at small spatial scales, density-dependence appears to operate in the opposite direction as predicted: closer nearest neighbors are more likely to be successful. We suggest that local nest dispersion, rather than larger-scale measures of nest density per se, may play a more important role in density-dependent nest predation.
authors.affiliation: Department of Wildlife, Fish, and Conservation Biology, University of California, One Shields Ave., Davis, CA 95616, USA. kmringelman@ucdavis.edu
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Ringelman
authors.forename: John M
authors.initials: JM
authors.lastname: Eadie
authors.forename: Joshua T
authors.initials: JT
authors.lastname: Ackerman
mesh_terms: D000818:Animals; D046368:Crows; D004372:Ducks; D012889:Mephitidae / Q000502:physiology*; D009425:Nesting Behavior; D010063:Ovum; D011156:Population Density; D011235:Predatory Behavior; D011821:Raccoons / Q000502:physiology*