Density-related predation by the Carolina chickadee, Poecile carolinensis,on the leaf-mining moth, Cameraria hamadryadella at three spatial scales

Citation
Ef. Conner et al., Density-related predation by the Carolina chickadee, Poecile carolinensis,on the leaf-mining moth, Cameraria hamadryadella at three spatial scales, OIKOS, 87(1), 1999, pp. 105-112
Citations number
43
Categorie Soggetti
Environment/Ecology
Journal title
OIKOS
ISSN journal
00301299 → ACNP
Volume
87
Issue
1
Year of publication
1999
Pages
105 - 112
Database
ISI
SICI code
0030-1299(199910)87:1<105:DPBTCC>2.0.ZU;2-H
Abstract
The impact of predation by the Carolina chickadee, Poecile carolinensis, on populations of the leaf-mining moth Cameraria hamadryadella, was inversely spatially density-dependent at each of three spatial scales: among woodlan ds, among trees, and among leaves. P. carolinensis exhibited an aggregative response to the density of C. hamadryadella at the scale of woodlands, but did not preferentially forage in trees or on leaves with high densities of leaf mines. P. carolinensis exhibits no numerical response to the abundanc e of C. hamadryadella. The functional response of P. carolinensis suggests that per capita foragin g efficiency is actually lower in high-density populations of C. hamadryade lla. This may arise because of predator confusion and because of mechanical limitations to foraging behavior. Human subjects, used as surrogates for c hickadees, took more time to discover and discovered fewer leaf-miner larva e on leaves with higher proportions of the leaf-area mined. Chickadees hang "upside down" to attack leaf-miner larvae and this posture may limit the d uration of foraging bouts. Either predator confusion or mechanical limitati on, alone or in combination, could account for the observed inversely densi ty-dependent impact of predation at the leaf scale. In outbreak populations of C. hamadryadella where P. carolinensis is a common predator, the invers ely density-dependent attack by P. carolinensis on C. hamadryadella complem ents the strongly density-dependent mortality caused by intra-specific comp etition. Therefore, the pattern of predation by P. carolinensis contributes more to suppression of C. hamadryadella than would occur if P. carolinensi s foraged in a density-dependent manner. Birds in the family Paridae appear to be the dominant avian predators of le af-mining insects. We suggest that their altered leg musculature permits th em to use a hanging "upside down" posture more frequently and pre-adapts th em for foraging on leaf-mining insects feeding on broad-leafed plants.