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

• Published in: Ecography (Copenhagen) 2004-04, Vol.27 (2), p.137-144
• Main Author: Aukema, Juliann Eve
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Birds; Deserts; Disease models; Fundamental and applied biological sciences. Psychology; General aspects; Infections; Landscape ecology; Metapopulation ecology; Parasite hosts; Phoradendron; Population ecology; Spatial distribution; Wetland ecology
• ISSN: 0906-7590; 1600-0587
• DOI: 10.1111/j.0906-7590.2004.03640.x

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.