- The study examined how competitive interactions with salamander larvae and abiotic habitat variables determine macroinvertebrate species richness in ephemeral ponds. - Experimental sites varied in canopy cover (open or closed) and presence/absence of salamander larvae. Species richness was highest in open sites and was best predicted by abiotic habitat variables like hydroperiod rather than biotic interactions. - Competition from salamander larvae appeared to have little impact on species richness, possibly due to the highly disturbed nature of ephemeral ponds and low larval densities.