Distribution and dispersal of desert mistletoe is scale-dependent, hierarchically nested

Authors

  • Juliann Eve Aukema


J. E. Aukema (jeaukema@ncsu.edu), Dept of Ecology and Evolutionary Biology, Univ. of Arizona, Tucson, AZ 85721-0033, USA (present address: International Institute of Tropical Forestry, Jardín Botánico Sur, 1201 Calle Ceiba, Río Piedres, PR 00926-1119 Puerto Rico).

Abstract

Spatial patterns are important to many ecological processes, and scale is a critical component of both patterns and processes. I examined the pattern and scale of the spatial distribution of infection of host plants by the desert mistletoe, Phoradendron californicum, in a landscape that spans several square kilometers. I also studied the relationship between mistletoe infection and seed dispersal. I found elevated seed rain in areas with a high prevalence of mistletoes and I found that a greater proportion of trees receive seeds than are infected, suggesting that mistletoes will be aggregated in space. Using nested analysis of variance and variograms, I found that mistletoe infections were distributed in hierarchical patches. Mistletoes were aggregated within trees and mistletoe prevalence was correlated at scales of <1500 m, and at scales >4000 m. Patterns at the largest scales were correlated with elevation: sites at higher elevations showed reduced mistletoe infection compared to those at lower elevations. I propose that at small scales, mistletoe distributions are primarily the result of aggregation of seed-dispersing birds, and that the elevational effect could reflect the recent colonization of higher elevations by the mistletoes' mesquite hosts or the limits of the mistletoes' physiological tolerance to freezing-induced cavitation.

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