How does climate influence the interactions between insects and their host plants over large evolutionary time scales? The effects of temperature and precipitation on herbivory have been well documented in modern ecosystems, and new information is emerging from fossil ecosystems as well. An increase in temperature should correspond with an increase in the types and levels of herbivore damage on leaves. Precipitation has been found to affect herbivory in modern ecosystems, but its effects in fossil ecosystems have not been well established. This study begins to examine how climate has affected herbivory over time by focusing on the effects of temperature, precipitation and elevation on herbivory in modern oak species. One goal of this study is to establish baseline predictions that can be tested using fossil oak floras from the last 30 million years.
To study modern oak-herbivore interactions, leaf samples from four co-occurring oak species, including two evergreen and two deciduous species, were collected from over a 1.8 km elevation gradient. Leaves were sampled from the leaf litter beneath each tree and 10-16 trees were sampled per species. Herbivorous insect damage types were quantified for 60 leaves per tree to identify feeding guilds of herbivores, the percentage of leaves with insect damage and the average leaf area removed per tree. These measures of herbivory were compared to measured elevation and estimated temperature and precipitation levels.
Results/Conclusions
Preliminary results suggest that while each species had a slightly different relationship between herbivory, elevation and climate, the overall trend for all species was the same. First, overall levels of insect damage did not appear to be correlated with temperature or precipitation. That is, neither the number of leaves eaten nor the amount of leaf tissue removed from individual leaves were correlated with climate or elevation variables. However, all species had an increase in the number of leaves displaying specialized damage, correlated with an increase in precipitation levels. This relationship was especially strong for leaf mining damage. Both evergreen and deciduous species responded similarly to the overall pattern of variation in elevation, temperature and precipitation.
