Disturbance, biological legacies and community development in stream mesocosms

Abstract

Disturbances reduce the biota in stream ecosystems, and leave biological legacies, including remnant species, which potentially influence post-disturbance community development but are poorly understood. We investigated whether three remnant species, the snail Radix peregra, the mayfly Serratella ignita and the freshwater shrimp Gammarus pulex, affected community development in mesocosms that mimicked disturbed habitat patches in streams. Following 21 days of colonisation, we found that the occurrence of legacy effects depended on the identity of the remnant species. Radix had the strongest effect. By bulldozing epilithon, the snails acted as ecological engineers that promoted settlement of filter feeders (Simuliidae) and invertebrate predators (especially Pentaneura and Aphelocheirus) and strongly deterred settlement of non-predatory chironomids (e.g. Heterotrissocladius and Microtendipes). Gammarus increased in density (by 665%) where remnant, probably through rapid reproduction. Baetis and Pentaneura were scarce, and Asellus absent, in remnant Gammarus treatments, as a consequence of interference and/or predation by the amphipods. In contrast, Serratella tolerated the colonisation of immigrant species and did not affect the structure of the developing benthic community. Despite the observed effects on the presence and abundance of benthos, remnant fauna had no significant effect on assemblage taxon richness, or that of any specific trophic group. The contrasting effects of remnant species on immigrant colonisation echoed differences in their life-history traits and foraging behaviours. Our results indicate that biota can generate spatial patchiness of epilithon and benthic invertebrates in stream ecosystems.

Extreme Climatic Events Alter Aquatic Food Webs

“…Nevertheless, a shift from algal crusts to filaments may have shaped macroinvertebrate assemblages indirectly, by modifying benthic habitat architecture. We have shown in a related study that filamentous diatom mats provide habitat for large populations of midge larvae (Ledger et al, 2006) and it could be that their proliferation under drought is partly driven by the resilience of key producers to drought. s0090 4.2.…”

“…4, Table 6). In a related research (Ledger et al, 2006(Ledger et al, , 2008, we observed that under perennial flow, mat-forming diatoms rapidly colonised and exploited empty space to form filamentous mats, but were subsequently displaced by relatively slow-growing but longerlived colonies of G. incrustans and associated epiphytes, which formed hard, calcified crusts that covered stone surfaces. Under drought, dewatering bleached the crusts, which disintegrated, whereas mat diatoms were more resilient (Ledger et al, 2008).…”

“…In particular, during the recovery phase one hypothesis is that there may be a time lag or hysteresis in its trajectory, as community closure or ecological inertia may retard the ability of K-selected species to reassert their dominance. Priority or legacy effects become important here, as demonstrated by Ledger et al (2006). Analogous arguments have been put forward for the seemingly tardy and patchy biological recovery of previously acidified systems, which contrast with their much smoother, progressive and more monotonic chemical recovery (Layer et al, 2010(Layer et al, , 2011.…”

Mesocosm Experiments as a Tool for Ecological Climate-Change Research

“…food-chain length, species richness) are far more sensitive ( Fig. 11C and D; Ledger et al, 2006Ledger et al, , 2008Ledger et al, , 2013a. Impacts on ecosystem processes (e.g.…”

Experimental evidence that predator range expansion modifies alpine stream community structure

“…Before initiating the experiment, flow in the channels was established for 3 d with the inflow 150 pipe covered by 100-µm mesh, to inhibit colonization by drifting invertebrates while 151 allowing algal colonization (Ledger et al 2006). 152…”