Tadpole co-occurrence in ponds: when do guilds and time matter?

Abstract

An extensive meta-analysis study suggested that co-occurrence in communities composed mostly of ectotherm species would not be segregated in space. However, there is some evidence of segregated occurrence for ectotherms when guilds were considered in the analysis. Therefore the apparent randomness found in co-occurrence analyses may be a consequence of the pooling of heterogeneous groups. We tested the following hypotheses for tadpole pond communities: i) an analysis including all species will indicate random co-occurrence, ii) co-occurrence will differ between seasons, and iii) analysis of co-occurrence within guilds will reveal a segregated pattern. We sampled tadpoles in Caçapava do Sul, southern Brazil, in two seasons (spring, summer). Species co-occurrence patterns were analyzed using the C-score index and three null models. We collected 10,852 tadpoles of 21 species, which belonged to four guilds: benthics, nektonics, suspension-raspers, and suspension-filterers. The last two guilds contained only a single species each, and therefore the analyses were restricted to the benthic and nektonic guilds. We obtained contrasting results depending on the null model. We used results only from non-degenerate simulated matrices. The co-occurrence of all species analyzed together was random in both seasons. Benthic tadpoles showed a tendency to segregated co-occurrence in spring, and random co-occurrence in summer. Nektonic tadpoles showed random co-occurrence for the total and the spring matrices, and segregated co-occurrence in summer. Our results indicate that the strength of negative co-occurrence may depend on season and guild. We conclude that apparent random cooccurrences of ectotherm communities may actually result in a segregated structure when restricted to a single guild, which is in concordance with other studies where guilds were considered, and supports the hypothesis that an apparent lack of negative associations might be related to the study of heterogeneous groups.