Experimentally disentangling the influence of dispersal and habitat filtering on benthic invertebrate community structure

Abstract

Abstract1. Ecological communities are structured by a combination of local processes like habitat filtering and species interactions, and regional forces driven by the dispersal of organisms between localities on a landscape. Previous studies suggest that the position of local communities within a dispersal network can greatly influence the relative influence of these two sets of processes on community assembly. However, the majority of previous investigations have used models or inferences based on observational data to investigate these hypotheses, while experiments directly addressing this question have been rare. 2.We experimentally investigated the relative influence of local and regional processes in structuring benthic invertebrate communities using artificial streams.We manipulated three factors-source pool for the macroinvertebrate community (headwater vs. mainstem) as a surrogate of network location, habitat complexity (high vs. low) in the flume, and dispersal (high vs. low)-and followed changes in macroinvertebrate community structure for 8 weeks.3. Previous research suggests that because headwater (HW) streams are isolated within river networks, HWs are less influenced by regional processes relative to more well-connected mainstems (MSs). We therefore predicted (i) that flumes colonised from a HW source community would respond more strongly to our dispersal treatment than those colonised by MS communities because MS were already largely structured through dispersal-driven processes, and (ii) that both HW and MS communities would respond to manipulations of local habitat, indicating that responses to the dispersal treatment were a direct result of dispersal driven dynamics rather than specific affinity for conditions in the flumes.4. Both of our predictions were strongly supported by the results of the experiment. For flumes with HW source pools, the high dispersal treatment had significantly higher diversity than low dispersal flumes. However, this difference only occurred in flumes with HW source pools and did not occur in flumes with MS sources. There was also strong evidence of community composition in HW flumes shifting significantly towards the macroinvertebrate composition in our experimental dispersal treatment. The major effect of experimental dispersal was to introduce new species in fairly low abundances as would be expected from dispersal via drift over a relatively short time. Both MS and HW colonised flumes showed highly significant signals of habitat filtering, though the influence of specific habitat differed between the source types.

Colonisation, emigration and equilibrium of stream invertebrates in patchy habitats

“…However, population sizes within a riffle may thus be constrained by limited dispersal, but also by limited recruitment within the riffle due to microhabitat constraints , although possibly only in the short term (Patrick & Swan, 2011). Because of the prevalence of these within-riffle processes, and given the scale of our experiments, it is likely that our results apply across whole riffles, indicating the importance of dispersal in structuring assemblages of small streams, in keeping with larger scale studies (e.g., Brown et al, 2018;Sarremejane, Mykra, Bonada, Aroviita, & Muotka, 2017).…”

“…Understanding the links between ecosystem functioning, species' traits and the mechanisms that determine species diversity gradients requires description of ecological processes at small scales (Baird et al, 2007;Willig, Kaufman, & Stevens, 2003). In streams, local biotic diversity is influenced by many factors, including both niche and neutral processes (Brown, Wahl, & Swan, 2018;Thompson & Townsend, 2006; Valente-Neto, Durães, Siqueira, & Roque, 2018) such as habitat characteristics, species' traits and interactions, disturbance and dispersal (Astorga, Heino, Luoto, & Muotka, 2011;Pearson et al, 2017;Rosser & Pearson, 2018). An ecological issue that is unresolved generally is the nature of the link between diversity and productivity (Grace et al, 2016;Gross, 2016;Pierce, 2014), which, in streams, is frequently enhanced by anthropogenic nutrient inputs that alter biotic assemblages (Connolly & Pearson, 2013;Dudgeon et al, 2006;Malmqvist & Rundle, 2002).…”

The role of dispersal in river network metacommunities: Patterns, processes, and pathways

“…Well‐designed manipulative field experiments allow direct insight into the processes structuring communities (Brown, Wahl, & Swan, ). However, these can be time and cost prohibitive and not easily replicated, and are thus not often used in riverine metacommunity studies.…”

Metacommunity detectives: Confronting models based on niche and stochastic assembly scenarios with empirical data from a tropical stream network

“…This is a complementary approach, because the position of patches in the network may influence metacommunity processes (Brown & Swan, 2010). For example, headwater insect communities may be more prone to species sorting and mainstem | 91 rivers by mass effects (Brown & Swan, 2010;Brown, Wahl, & Swan, 2017). This may affect the overall model prediction (given by regression models), but model predictions may exactly estimate observed richness for specific patches (e.g.…”