Effects of plant litter diversity, species, origin and traits on larval toad performance

Decreased plant diversity is expected to reduce ecosystem function. Although many studies have examined eff ects of plant species on trophic interactions, information regarding eff ects of native or non-native plant diversity on performance of individuals of higher trophic levels is limited. We reared larval American toad Anaxyrus americanus tadpoles in outdoor mesocosms containing litter of 1, 3, 6 or 12 plant species drawn randomly from a pool of 24 (15 native, 9 nonnative) species. Tadpole performance varied signifi cantly among litter types in single litter treatments and pH and litter C:N were signifi cant predictors of tadpole performance. Metamorphs were larger in mixtures than expected based on performance in single species treatments, suggesting a non-additive eff ect of diversity. Litter diversity did not aff ect probability of survival or probability of metamorphosis. Plant origin (native or non-native) had no signifi cant eff ect on amphibian performance. Our study suggests some benefi ts to tadpole development at low levels of plant diversity, but questions assumed benefi ts of increased plant diversity and assumed detrimental eff ects of nonnative plant species for a common larval amphibian. Presence of specifi c plant species with strong negative eff ects on tadpole performance may outweigh diversity benefi ts in brown food webs.