Document: ROB-3-48-16

The role of spatial autocorrelation in the detection and interpretation of patterns of tree seed and seedling predation by rodents in old-fields.

MANSON, R.H.*

Instituto de Ecología, A.C., Xalapa, Veracruz, Mexico ¹

Abstract:
Spatial autocorrelation is present in all ecological systems. However, consideration of this phenomena in seed and seedling depredation studies has been limited, perhaps explaining some of the variation observed between studies and the difficulty in generalizing about the impacts of herbivores on successionary processes. I examined the patterns and prevalence of spatial autocorrelation in the survival of neighboring tree seeds and seedlings experimentally placed into old-fields located in New York state, U.S.A. All experiments were conducted within enclosures in which it was possible to manipulate the density of meadow voles (Microtus pennsylvanicus) while simultaneously allowing entry by competitively inferior white-footed mice (Peromyscus leucopus). White-footed mice and meadow voles are the dominant consumers of tree seeds and seedlings in old-fields of the northeastern United States, respectively. Spatial autocorrelation was present in approximately 50% of all predation trials conducted. Furthermore, the frequency of spatial autocorrelation increased under low vole density conditions and in study sites with greater heterogeneity in vegetation cover. Survival of neighboring tree propagules was generally positively autocorrelated, suggesting that mouse and vole foraging should generate clumped patterns of tree propagule survival. A review of 24 published predation studies found that only 13% attempted to test or control for spatial autocorrelation and that the minimum average spacing used between replicates was well below the average autocorrelation distance of 8.1 m observed in the current study. Patterns of autocorrelation appear predictable based on knowledge of the ecology of mice and voles and to provide insights into the factors influencing their foraging decisions and potential impacts on old-field succession.

Keywords: spatial autocorrelation, seed predation, seedling predation, white-footed mice, Peromyscus leucopus, meadow voles, Microtus pennsylvanicus, tree invasion, old-field succession

This abstract is being presented at: 10:15 AM in session:
Oral Session #21: Small Mammal Population Ecology.