Functional strategies drive community assembly of stream fishes along environmental gradients and across spatial scales

Abstract

Trade-offs among functional traits produce multi-trait strategies that shape species' interactions with the environment and drive the assembly of local communities from regional species pools. Stream fish communities vary along stream size gradients and among hierarchically structured habitat patches, but little is known about how the dispersion of strategies varies along environmental gradients and across spatial scales. We used null models to quantify the dispersion of reproductive life history, feeding, and locomotion strategies in communities sampled at three spatial scales in a prairie stream network in Kansas, USA. Strategies were generally underdispersed at all spatial scales, corroborating the longstanding notion of abiotic filtering in stream fish communities. We tested for variation in strategy dispersion along a gradient of stream size and between headwater streams draining different ecoregions. Reproductive life history strategies became increasingly underdispersed moving from downstream to upstream, suggesting that abiotic filtering is stronger in headwaters. This pattern was stronger among reaches compared to mesohabitats, supporting the premise that differences in hydrologic regime among reaches filter reproductive life history strategies. Feeding strategies became increasingly underdispersed moving from upstream to downstream, indicating that environmental filters associated with stream size affect the dispersion of feeding and reproductive life history in opposing ways. Weak differences in strategy dispersion were detected between ecoregions, suggesting that different abiotic filters or strategies drive community differences between ecoregions. Given the pervasiveness of multi-trait strategies in plant and animal communities, we conclude that the assessment of strategy dispersion offers a comprehensive approach for elucidating mechanisms of community assembly.

Environment and predation govern fish community assembly in temperate streams

“…By contrast, fish predators did not affect microhabitat use by potential prey species in a North Carolina stream; however, the low abundance of predators might explain the lack of an observed effect of predator-prey interaction (Grossman et al, 1998). predators and herbivores) not competitors provided biotic resistance to freshwater invaders, and they support previous studies that inferred weak or absent competitive effects in aquatic communities from the lack of community saturation (Moyle & Light, 1996;Troia & Gido, 2015). In the single final model that contained COMP, the relationship between competition strength and species segregation was opposite to what would be expected if competition was indeed important in structuring communities.…”

Integrating systematics and biogeography to disentangle the roles of history and ecology in biotic assembly

“…HAA also places assemblages in historical context, and would allow for comparative studies (e.g. Liu et al, 2013;Troia & Gido, 2015) to be conducted at large extents and with explicit consideration of specific historical areas.…”

Fish assemblage convergence along stream environmental gradients: an intercontinental analysis

“…Although evolution plays a major role in establishing trait distributions in species assemblages (Webb et al 2002, Cavender‐Bares et al ), contemporary ecological processes also have a significant influence, especially at local scales (Lebrija‐Trejos et al 2010, Kraft et al ). For example, habitat template theory posits that spatial and temporal variation of habitat features selects for certain traits and, therefore, influences the structure of local communities (Southwood 1977, Poff 1997).…”