LEASE, HM; Univ. of New Mexico, Albuquerque: Temporal Patterns in a Chihuahuan Desert Grassland: an Investigation using a Higher-order Insect Predator
Several species of robber flies (Family Asilidae) were sampled from Chihuahuan Desert grasslands and shrublands at the Sevilleta LTER site, in central New Mexico, to investigate their isotopic carbon signature. Asilids are opportunistic ambush predators. Prey type and prey size varies among Asilid species, but is predominantly composed of plant-feeding insects. Little is currently known about the diet specificity of the Asilid fauna in this particular region, though most are probably generalists. The Chihuahuan Desert ecosystem is characterized by bimodal rainfall patterns (i.e., winter and summer monsoonal rains), which drive seasonal patterns of resource availability. The summer monsoons drive a shift in the isotopic signature of the dominant vegetation from C3 to C4 plants, and there is evidence that tissues of some secondary consumers in this ecosystem (e.g., lizards) show a shift from C3 to C4 derived signatures. While acknowledging that the diet composition of a generalist predator is a function of prey availability, I hypothesized that the carbon isotope signature of potential insect prey assemblages for Asilids will generally exhibit temporal variation with the monsoonal rains�and will subsequently be reflected in body tissues of the Asilids. Specifically, that species of Asilids emergent in late spring/early summer will reflect the isotopic signature associated with winter rains (C3 plant growth) and species of Asilids emergent in late summer will reflect the isotopic signature associated with summer rains (C4 plant growth). To test this, I present carbon isotope data from 10 different species of Asilids that occur sympatrically on the Sevilleta LTER site, collected over a 5 month sampling period. My results show that Asilid body tissue reflects the derived source of carbon of their prey items, and demonstrates how seasonal changes in plant resources can cascade up through food webs.
