Quantity Counts: Amount of Litter Determines Tadpole Performance in Experimental Microcosms

Terrestrial plant litter is an important subsidy to freshwater ecosystems, where it serves as a basal resource in benthic food webs. Litter quantity and decomposition rate strongly influence energy flow through these food webs. Litter quantity often increases following nonnative plant invasions, but the impact this additional litter has on aquatic consumers is largely unknown. We conducted an experiment in outdoor microcosms containing plant litter, microbes, algae, and tadpoles. Many tadpoles feed on biofilms (bacteria, fungi, and algae) that develop during decomposition; as such, they are ideal organisms to test bottom-up effects of litter subsidies. We used a related pair of native and nonnative wetland grasses to investigate whether litter quantity affects tadpole performance. Tadpole performance metrics (developmental stage, size, and survival) showed significant positive responses to increased litter quantity but were mostly unaffected by plant species. Therefore, litter quantity was the primary determinant of tadpole performance in our experimental community. We suggest that changes to litter quantity can have important impacts on larval amphibians.