COS 114-2
Hydroregime, litter, and nutrient interactions alter species composition in California vernal pools
Communities are structured by numerous abiotic (e.g., nutrients) and biotic (e.g., food web interactions) factors. In many freshwater ecosystems, hydroperiod (length of inundation) is a dominating factor that can also interact with other factors to affect species composition and abundance. Few studies, however, have experimentally investigated the importance of abiotic and biotic interactions under different hydroregimes on species composition. The purpose of this study was to examine the aquatic and subsequent terrestrial community structure of seasonal ponds in response to hydroregime (inundation length and timing), nutrient addition, and leaf litter. I used a fully factorial experiment that included hydroperiod length (long, short), nutrients (none, added N and P), and leaf litter (none, exotic, and native plants), and each of the 12 treatments was replicated 4 times. Mesocosms lined with California vernal pool soil were established on the CSU Sacramento campus. Invertebrate and plant species richness and abundance and water quality were sampled for 5 months; ANOVA, linear regression, NMDS, and SIMPER were used to assess treatment effects on richness, density, and species composition.
Results/Conclusions
Passive and active dispersers were present over the course of the experiment. Similar to previous studies, species richness and densities exhibited unimodal relationships with hydroperiod. Nutrient addition interacted with litter addition in affecting chlorophyll-a, which translated into increased densities for some invertebrate species. Hydroperiod effects, along with increasing macrophyte and invertebrate abundance, altered chlorophyll-a density over time. Litter addition reduced passive disperser richness and densities of most of the large branchiopods, including the 2 endangered species present in this study. Hydroperiod interacted with litter and nutrients to alter invertebrate species richness and composition over time. This extended to the passive and active dispersal groups, which responded differently to treatments. Following desiccation, plant cover and richness was negatively affected by litter addition. These results highlight how habitat characteristics (i.e. hydroperiod) can interact in complex ways with the local community to influence species composition of the wet and dry phases. Nutrient pollution and invasive plant disturbances are major issues with seasonal wetlands worldwide and these results highlight potential negative effects in this ecosystem. With California’s variable climate, understanding how temperature and precipitation variation affects community structure and endangered species’ responses will be important for management of California vernal pools.