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Causes of vertical stratification in the density of Cameraria hamadryadella
Author(s) -
BROWN JESSI,
VARGO STEVE,
CONNOR EDWARD,
NUCKOLS MICHAEL
Publication year - 1997
Publication title -
ecological entomology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.865
H-Index - 81
eISSN - 1365-2311
pISSN - 0307-6946
DOI - 10.1046/j.1365-2311.1997.00046.x
Subject(s) - biology , crown (dentistry) , interspecific competition , stratification (seeds) , overwintering , competition (biology) , juvenile , ecology , abundance (ecology) , botany , horticulture , germination , medicine , seed dormancy , dentistry , dormancy
1. The density of Cameraria hamadryadella , a leaf‐mining moth, is vertically stratified within the crown of oak trees. It occurs at higher densities on foliage in the lower crown. 2. Oviposition preference tests indicate that females display no preference to oviposit on foliage from the lower tree crown over foliage from the upper tree crown. 3. Experiments in which potted trees were placed at various heights indicate that foliage nearest ground level receives more oviposition, and that the higher rates of oviposition on foliage near the ground is not caused by differences in quality between foliage from low or high in the tree crown. 4. Host‐plant‐ and natural‐enemy‐mediated juvenile mortality and the abundance of parasitoids did not differ between the upper and lower crown. 5. Vertical differences in the timing of leaf production within the tree crown are unlikely to account for the observed gradient in the abundance of C. hamadryadella . Furthermore, the mean date of leaf fall does not differ among heights within the tree crown. 6. It is argued that microclimatic gradients and interspecific competition are also unlikely to account for the observed gradients in the density of C. hamadryadella within the tree crown. 7. Because of the absence of effects of other potentially causal factors, the most likely explanation for the gradient in density of C. hamadryadella is a lack of movement by females into the upper tree crown from overwintering, emergence, or resting sites located in the lower tree crown, combined with egg depletion by females as they move from the lower to the upper tree crown. 8. It is suggested that the lack of movement and egg depletion hypothesis should serve as the null hypothesis in studies of vertical stratification of tree‐feeding insects. In the absence of evidence of an effect of foliage quality, natural enemies, plant phenology, interspecific competition, or microclimate, the movement and egg depletion hypothesis is the most reasonable.