PARENT SESSION
Oral Session # 53: Herbivory IV: Communities, Populations, and Genetics.
Presiding: JA Rudgers
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 103.
Synergistic abiotic factors and host plant quality: Trophic consequences of variable nitrogen and elevation.
Yarnes, Christopher*,1, Boecklen, William1, 1 New Mexico State University, Las Cruces, NM
ABSTRACT- Theory surrounding the structure and dynamics of trophic relationships in terrestrial ecosystems has emphasized the need for empirical studies that describe and quantify the function of biotic and abiotic heterogeneity. Abiotic heterogeneity can have significant consequences for natural populations both directly and indirectly through the production of biotic heterogeneity. Plant species are known to exhibit heterogeneity in host quality for insect herbivores across multiple spatial and temporal scales, from within-leaf and intraplant variation to population and intraspecific variation. This heterogeneity may serve as a defense strategy per se for plants with long generation times by serving as a means to contend with a multitude of rapidly-evolving insect herbivores exhibiting rapid generation times. To date, relatively few empirical studies have examined the synergistic effects of multiple sources of abiotic heterogeneity on spatio-temporal host quality variation and the effect on the relative roles of bottom-up and top-down control on herbivore populations. We examined preference-performance relationships and mortality of two species of leaf-mining Lepidoptera, Phyllonorycter sp. and Camareria sp. (Lepidoptera: Gracillariidae and Nepticulidae), associated with host-quality of Quercus gambelii (Nutt.) along an elevation gradient under two nitrogen amendment levels in the San Mateo mountain range of west-central New Mexico, U.S.A. during 2001 and 2002. Foliar nitrogen was heterogeneous at multiple spatial and temporal scales and was significantly related to elevation, nitrogen availability and ambient environmental parameters. Elevation and seasonal variation in foliar nitrogen had significant effects on herbivore densities. Herbivore emergence and parasitoid success was significantly related to nitrogen treatment. Herbivore performance and parasitism rates appear to be related to the magnitude of within-tree spatio-temporal heterogeneity in foliar nitrogen. Extreme drought during the 2002 growing season contributed to massive levels of unexplained mortality and will be discussed.
Key words: elevation, nitrogen, heterogeneity, trophic