The role of niche measures in explaining the abundance–distribution relationship in tropical lotic chironomids

The positive relationship between species regional distribution and local abundance is one of the most ubiquitous patterns in ecology. Among the hypotheses proposed to explain the relationship, the niche breadth and the niche position (or habitat availability) hypothesis are the most investigated. An unappreciated issue, but that is likely to be important for the understanding the relationship is the nature of variables used to estimate niche measures. Here, we analyzed the form of this relationship in lotic chironomid genera and tested whether niche measures estimated from local and landscape variables explain the observed pattern. Analyses were based in 47 forested streams within Southeastern Brazil. From our data set, we randomly partitioned the data in two non-overlapping sets to estimate taxa distribution and abundance (Distribution Data; n = 23 sites) and to generate niche measures (Niche Data; n = 24). We repeated that process 1,000 times, and for each one, we generated niche breadth and position measures using in-stream and landscape variables and estimated abundance and distribution for each taxa. With these, we estimated the relationship between both abundance and distribution and niche measures using ordinary least-squares regressions. We found no relationship between niche position estimated from local variables and local abundance nor regional distribution. There was a negative relationship between niche position estimated from landscape and local abundance, and regional distribution. We found a positive relationship between niche breadth (local and landscape) and both local abundance and regional distribution. When the relationship was significant, both niche position and niche breadth explained less than a half of total variation in abundance and distribution. This suggests that not only niche-based processes, but also other mechanisms may be responsible for the abundance–distribution relationship in lotic chironomids. A novel finding of this study was that although there was much unexplained variability around the relationships, niche breadth was a better predictor of abundance and distribution than niche position. We suggest that future studies should investigate if spatial processes, like dispersal, together with environmental processes affect interspecific abundance–distribution relationships.