Ecological niche features override biological traits and taxonomic relatedness as predictors of occupancy and abundance in lake littoral macroinvertebrates

The degree to which species ecological and biological traits determine their distribution and abundance has intrigued ecologists for a long time, and it has seen a revival in recent years. This topic is important because it provides information about the determinants of species rarity and their conservation implications. We examined the effects of niche breadth, niche position, biological traits and taxonomic relatedness on the interspecific occupancy–abundance relationship, as well as on occupancy and abundance, in lake littoral macroinvertebrates. We sampled 48 lakes in a boreal lake district, found altogether 155 species, and calculated regional occupancy (as the proportion of sites occupied) and local abundance (as mean abundance at occupied sites) for each species. We determined niche position and niche breadth for each species using the outlying mean index analysis. Also, we calculated trait vectors and taxonomic vectors describing species trait similarity and taxonomic relatedness, respectively, using principal coordinates analysis. We found a strong positive occupancy–abundance relationship that was mostly explained by among‐species variation in niche position, followed by niche breadth. Instead, trait vectors and taxonomic vectors tended to be less important in affecting occupancy and abundance than the niche features. Our results strongly suggest that niche position, a measure of habitat availability for littoral macroinvertebrates, is the chief determinant of their occupancy and abundance. This finding has important implications for ecology and conservation of species, as species with marginal niche position, a reflection of low habitat availability, are both regionally rare and locally uncommon. Such species may face double jeopardy if environmental conditions change and affect their preferred marginal habitat types.