Linking precipitation and C_3-C_4 plant production to resource dynamics in higher-trophic-level consumers

摘要

In many ecosystems, seasonal shifts in temperature and precipitation induce pulses of primary productivity that vary in phenology, abundance, and nutritional quality. Variation in these resource pulses could strongly influence community composition and ecosystem function, because these pervasive bottom-up forces play a primary role in determining the biomass, life cycles, and interactions of organisms across trophic levels. The focus of this research is to understand how consumers across trophic levels alter resource use and assimilation over seasonal and interannual timescales in response to climatically driven changes in pulses of primary productivity. We measured the carbon isotope ratios (δ~(13)C) of plant, arthropod, and lizard tissues in the northern Chihuahuan Desert to quantify the relative importance of primary production from plants using C_3 and C_4 photosynthesis for consumers. Summer monsoonal rains on the Sevilleta Long Term Ecological Research (LTER) site in New Mexico support a pulse of C_4 plant production that has tissue δ~(13)C values distinct from C_3 plants. During a year when precipitation patterns were relatively normal, δ~13C measurements showed that consumers used and assimilated significantly more C_4-derived carbon over the course of a summer, tracking the seasonal increase in abundance of C_4 plants. In the following spring, after a failure in winter precipitation and the associated failure of spring C_3 plant growth, consumers showed elevated assimilation of C_4-derived carbon relative to a normal rainfall regime. These findings provide insight into how climate, pulsed resources, and temporal trophic dynamics may interact to shape semiarid grasslands such as the Chihuahuan Desert in the present and future.