Effects of litter diversity on macroinvertebrate communities in Neotropical water-filled tree holes

Background/Question/Methods

The quality and quantity of resource inputs from terrestrial habitats to aquatic habitats is important for structuring aquatic communities. Water-filled tree holes contain obligate and preferential residents highly affected by leaf litter input. Considering the loss of tree diversity and replacement of native species with exotic timber species occurring in tropical habitats, we investigated the effects of leaf litter diversity on communities in artificial tree holes. We used leaves from two native timber-producing species and one common, non-native timber species to test the effects of leaf litter species and richness on invertebrate aquatic communities in Gamboa, Panama

We used all combinations of three species resulting in seven treatments with three levels of leaf litter richness at equal initial dry mass. Cups were open to colonization in a common garden plot for three weeks. After the colonization period we quantified macroinvertbrate richness and abundance as well as leaf litter breakdown and dissolved carbon to nitrogen ratios (C:N). We hypothesized that higher diversity treatments would have higher levels of decomposition and nutrients and would support higher abundance and species richness.

Results/Conclusions

Litter types differed in breakdown and nutrient quality. All three species had significantly different rates of leaf litter breakdown ranging from one species losing 25% to another species losing 50% of their initial mass. While the two native species did not differ in dissolved C:N ratios, the exotic timber species had much lower dissolved C:N. Litter types also resulted in different macroinvertebrate abundance. There was no difference in abundance between the native tree species; however, the exotic species supported one third the number of invertebrates. Eleven different taxa colonized our experimental treeholes, including eight species of mosquito, some of which are important disease vectors and one of which is predacious. However, there were no differences in species richness among the 3 monocultures all litter types had only 1-2 species on average. Litter richness had important effects on resources and community responses. Litter breakdown did not differ among levels of litter species richness; however, C:N ratios declined with increasing diversity, suggesting high resource quality in treeholes with more litter species. Similarly, both macroinvertebrate abundance and richness increased with increasing litter species level. Our results highlight the importance of a diverse allochthonous resource base in structuring aquatic treehole communities.