Spatial patterns in macroinvertebrate assemblages of tropical insular streams (Gorgona Island, Tropical Eastern Pacific): Do relevant scales change seasonally?

Spatial patterns of stream macroinvertebrate assemblages are unknown in the Tropical Eastern Pacific. We tested for spatial patterns from regions to microhabitats in Gorgona Island (Colombia) during dry and rainy seasons. Assemblage composition was consistently different between the island’s regions, and among streams during both seasons. Different assemblages were observed between reaches within streams, and between riffles and pools during the dry season but did not during the rainy season. Differences between gravel and cobble patches were only significant during the rainy season. Watershed geology and water conductivity were consistently the most important drivers of macroinvertebrate assemblages during both seasons. pH and mean water depth were additional drivers during the dry season. <i>Thraulodes</i>, Chironominae, <i>Leptonema</i> and <i>Anacroneuria</i> exhibited deterministic distributions during the dry season; <i>Thraulodes</i>, <i>Anchytarsus</i>, <i>Microcylloepus</i> and <i>Farrodes</i> did it during the rainy season. <i>Potimirin</i> shrimps exhibited a deterministic distribution but it was correlated to pH only during the dry season. <i>Thraulodes</i> distribution was predicted by water depth, conductivity, geology and type of habitat; Chironominae was predicted by geology and pH. During the rainy season only <i>Microcylloepus</i> was predicted by region. We highlight the importance of multiscale drivers on spatial distributions insects and diadromous shrimps in tropical islands.