Models indicate that increases in air and water temperature will alter the structure and function of ecosystems at both global and local scales. Communities are structured by a variety of abiotic (e.g., temperature) and biotic (e.g., competition) factors. In freshwater ecosystems, hydrologic characteristics (e.g, hydroperiod, magnitude, & timing) are central factors that influence community composition and abundance. Although warming experiments are not uncommon among research on freshwater ecosystems, little information is known on how warming will affect temporary aquatic systems that are dependent on annual temperature and hydroregime intervals. The purpose of this study is to examine the aquatic community composition of temporary ponds in response to increases in water temperature and a shift in the timing of inundation. To accomplish this, I manipulated water temperature (warm, ambient) and inundation timing (early, late). Each treatment was replicated 5 times. Mesocosms lined with 2.0 cm of California vernal pool soil were established on the CSU, Sacramento campus on January 15, 2017. Measurements on invertebrate richness and densities and water quality will be sampled for 5 months. ANOVA, linear regression, NMDS, and SIMPER will be used to test for treatment effects on community composition.
Warm treatments were +2.07℃ above ambient temperatures. During the early inundation cycle, warming had a signifcant effect on species density but not on species richness. The opposite is observed in the late inundation treatments where species richness but not density was positively effected by warming. Conductivity and D.O measurments were negatively correlated to species richness and density, while turbidity was positively correlated. These finding suggest that water temperature, aside from the initial inundation event, is another important environmental cue which initiates the emergence of passive disperser species. These findings also suggest that warmer temperatures can increase the metabolic demands of organisms by increasing growth and feeding rates. A strong temperature and timing effect for late inundation treatments was observed. The timing of passive disperser emergence was at least one week earlier than early treatments. Culicid larvae abundances were high in warm-late treatments, while almost entirely absent in both warm/control early and control-late treatments. The presence of mosquito larvae likely suppressed the abundance of endemic macroinvertebrates through exploitative competition. With models forecasting a +2-3 °C increase in mean air temperature in California by the year 2069, understanding how these changes affect community structure will be essential for the management of the few remaining vernal pools in the state.