Habitat associations of riverine odonates near La Fortuna, Costa Rica: effects of stream size and landscape context

The dragonflies (Insecta: Odonata) of Costa Rica are well-described, providing a solid foundation for studies in community ecology. We described the effects of stream size and habitat matrix (forest vs. pasture/development) on several indices of odonate community structure: abundance, species richness, diversity, and composition. We sampled adults in eight 100 × 5 m plots on six waterways near La Fortuna, Alajuela Province, Costa Rica. Four plots were on waterways in secondary forest: single plots were on large rivers (Río Caño Negro and Río Caliente), and two plots were on a small unnamed stream. Four plots were on smaller waterways in agricultural areas: two on the Río Chachagua and single plots on the Río Chachagüita and a small creek. Plots were surveyed seven times from January–March 2023. The composition of the communities exploiting rivers, the forested stream, and agricultural streams were significantly different using NMDS and PERMANOVA. Plots on the forested stream had significantly fewer individuals, fewer species, and lower diversity than the waterways in agricultural areas, and large rivers were intermediate (GLM and Tukey post-hoc mean comparison tests). Communities exhibited significant nested-subset structure (NODF), with species in forested stream plots nested within river communities that were nested within communities in agricultural areas. These patterns are not explained by differences in mean light levels, which were greatest in rivers. This suggests that evaluating the effect of anthropogenic riparian canopy removal during land transformations may be complicated by initial differences in community composition related to stream/river size.