Predicting occupancy and abundance by niche position, niche breadth and body size in stream organisms

Abstract

The regional occupancy and local abundance of species are thought to be strongly correlated to their body size, niche breadth and niche position. The strength of the relationships among these variables can also differ between different organismal groups. Here, we analyzed data on stream diatoms and insects from a high-latitude drainage basin to investigate these relationships. To generate measures of niche position and niche breadth for each species, we used sets of local environmental and catchment variables separately, applying the outlying mean index analysis. Beta regression and negative binomial generalized linear models were run to predict regional occupancy and mean local abundance, respectively. We found a positive occupancy-abundance relationship in both diatoms and insects, and that niche-based variables were the main predictors of variation in regional occupancy and local abundance. This finding was mainly due to local environmental niche position, whereas the effects of niche breadth on regional occupancy and local abundance were less important. We also found a relationship between body size and local abundance or regional occupancy of diatoms. Our results thus add to current macroecological research by emphasizing the strong importance of niche position rather than niche breadth and body size for regional occupancy and local abundance in rarely studied organisms (e.g., diatoms and insects) and ecosystems (i.e., wilderness streams).

Using traits to explain interspecific variation in diatom occupancy and abundance across lakes and streams

“…Hydrological connectivity has indeed been shown to affect biodiversity through dispersal (Heino et al., ; Lopes et al., ). Overall, the positive relationship between occupancy and abundance for both lakes and streams is in line with earlier observations on various freshwater organism groups (Heino & Tolonen, ; Passy, ; Rocha et al., ; Verberk et al., ).…”

“…First of all, we found rather clear indications that the size of the species is tied to its occupancy and abundance, with smaller species showing larger abundances and occupancies than larger species. The effect of cell size on diatom occupancy and abundance has been reported in earlier studies as well (Passy, ; Rocha et al., ), and the interpretation of the observed size‐related pattern is the same in this study: for diatom species, the smaller the better, regarding prospects for local survival (cf. abundance) and regional dispersal (cf.…”

“…Species’ pH preferences were variably associated with occupancy in lakes and streams, but in general, different environmental preferences of species were not clearly related to their occupancy and abundance. This finding is partly contradictory to earlier studies showing that species’ ‘true’ niche parameters can greatly affect interspecific variation in occupancy and/or abundance of freshwater organisms (Heino & de Mendoza, ; Heino & Tolonen, ; Rocha et al., ; Tales et al., ; Verberk et al., ; Vilmi et al., ). The difference between these earlier investigations and our current study is that we used existing literature knowledge on species’ pH and trophic preferences, while ‘true’ niche parameters are calculated based on actually measured environmental variables.…”

“…Although the total explained deviances in the models were not very high, species with similar traits tended to show similar levels of occupancy and abundance, irrespective of the type of aquatic system. Earlier studies have also observed that biological traits can affect occupancy and/or abundance of freshwater species (Heino & Grönroos, ; Passy, ; Rocha et al., ; Verberk et al., ). First of all, we found rather clear indications that the size of the species is tied to its occupancy and abundance, with smaller species showing larger abundances and occupancies than larger species.…”

“…When trying to reveal mechanisms behind the positive occupancy–abundance relationship, researchers have studied if and how species characteristics (e.g. biological traits, ecological preferences and phylogeny) are associated with variation in abundances and distributions of species (Heino & Tolonen, ; Passy, ; Rocha et al., ; Verberk, van Noordwijk, & Hildrew, ; Verberk et al., ; White, Ernest, Kerkhoff, & Enquist, ). The connections among species characteristics, abundances and distributions have traditionally been addressed using sites as data points and observing how these variables vary in space, that is, in a community ecology perspective (Heino & Tolonen, ; Verberk et al., ).…”