Ecosystems with harsh abiotic conditions tend to have fewer species than more temperate systems, and the species that persist in these harsh environments have evolved to tolerate their conditions. Biotic interactions (e.g. competition, herbivory, mutualisms) also tend to be very specific, and can be both directly and indirectly affected by perturbations to abiotic conditions. The ecosystem of the eastern Sierra Nevada is shaped by limited precipitation, predominantly in the form of snow. Great Basin sagebrush, Artemisia tridentata, a dominant shrub in this ecosystem, is host to many species of gall-forming insects and other arthropods. Artemisia-dwelling insects represent a large portion of the insect biodiversity in this system. The suitability of A. tridentata as a host for these insects will likely change under future climate scenarios if the abiotic conditions are different than those conditions under which these interactions evolved. Snow precipitation is one condition that is predicted to change in the future. Host suitability may depend on the water status of the plant, so future snow conditions could change the number, diversity or community composition of insects utilizing A. tridentata.
To determine the effects of increased or decreased snow on insects, we surveyed the galling and herbivory patterns on A. tridentata in areas with experimentally increased or decreased snow. We found surprisingly high diversity of gall morphotypes (> than 20), as well as several species of aphid herbivores that were tended by ants. The degree of galling and diversity of galling insects increased with decreased snow. With any manipulation of snow depth, leaf damage from homopteran herbivores increased, and leaf litter volume also increased. Additionally, the aphid-ant mutualism appears to break down with any change to snow regime. These patterns suggest that insects are sensitive to plant responses to changes in the snow regime. Ongoing research to determine the underlying mechanism of this indirect effect includes studying how plant defense chemistry is affected by snow conditions. These results suggest that direct effects of climate change on this plant community will likely alter and shape the herbivore, arthropod community, and changes to plant-herbivore interactions may alter the leaf litter from A. tridentata, which may alter the fire regime.
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