Tuesday, August 5, 2008
Exhibit Hall CD, Midwest Airlines Center
Background/Question/Methods Spatial matching between resource and consumer organisms at different scales conditions reciprocal demographic effects in food webs. In plant-animal networks, ecological outcomes depend on how mobile animals track for sessile, but spatially heterogeneous, plant resources, and also on the effect of habitat structure on this resource tracking. We evaluated the spatial matching at different scales between plants and animals in two different interactions; seed dispersal by frugivorous birds and postdispersal seed predation by rodents. The role of habitat structure on resource-consumer matching was also investigated. Three structurally similar plant-bird-rodent systems were compared; in the Cantabrian mountain forests of northern Spain , the Mediterranean mountain shrublands of southern Spain, and the temperate forests of southern Argentina . In a single fruiting year, we sampled tree and shrub cover, fruit availability, abundance of dispersed seeds, abundance of frugivorous birds and seed predation rate along 1,500 m transects subdivided into 100 sampling units. By means of principal coordinates analysis of neighbor matrices analyses, we dissected the spatial variance of bird abundance and seed predation rate at three progressively finer spatial scales. We used path analyses to evaluate the relationships between habitat structure, plant resource availability, and frugivory and seed predation, at different spatial scales.
Results/Conclusions Both frugivore abundance and seed predation varied significantly in space at different scales. In frugivore abundance, the spatial variance was distributed between the broad and the intermediate scales in all sites, suggesting a hierarchically nested structure of patchiness along the transects. On the other hand, the broad scale accounted for almost all the predictable spatial variability in seed predation in all sites, indicating large-scale, landscape patchiness. Frugivorous birds tracked fruit resources at different spatial scales. The scale of fruit tracking by birds, and the consistency of tracking across scales, varied among sites. In those sites with a more complex habitat structure, habitat features accounted for the majority of spatial variability in frugivore abundance at the broad scale, diluting fruit resource tracking. Conversely, seed resource tracking by predatory rodents was rare at any spatial scale, and the large-scale spatial patterns of seed predation were mostly related to habitat features. Our study suggests that different plant-animal interactions acting through the regeneration cycle of a plant operate at different spatial scales. This spatial scale depends on the ability of animals to track for plant resources but also on the effect of habitat features.
Results/Conclusions Both frugivore abundance and seed predation varied significantly in space at different scales. In frugivore abundance, the spatial variance was distributed between the broad and the intermediate scales in all sites, suggesting a hierarchically nested structure of patchiness along the transects. On the other hand, the broad scale accounted for almost all the predictable spatial variability in seed predation in all sites, indicating large-scale, landscape patchiness. Frugivorous birds tracked fruit resources at different spatial scales. The scale of fruit tracking by birds, and the consistency of tracking across scales, varied among sites. In those sites with a more complex habitat structure, habitat features accounted for the majority of spatial variability in frugivore abundance at the broad scale, diluting fruit resource tracking. Conversely, seed resource tracking by predatory rodents was rare at any spatial scale, and the large-scale spatial patterns of seed predation were mostly related to habitat features. Our study suggests that different plant-animal interactions acting through the regeneration cycle of a plant operate at different spatial scales. This spatial scale depends on the ability of animals to track for plant resources but also on the effect of habitat features.
