Biotic interactions enhance survival and fitness in the caddisfly Micropterna sequax (Trichoptera: Limnephilidae)

Hydrobiologia, Jan 2018

Patches of coarse particulate organic matter in lowland streams are inhabited by many different macroinvertebrate species, yet knowledge of interactions among the members of these assemblages is scarce. In a mesocosm experiment we aimed to determine the effect of interspecific interactions on species survival and fitness of two caddisfly species. It was hypothesized that, as a result of positive interactions, mixed species populations would yield higher survival and fitness than single species populations. Larvae of two caddisfly species, Micropterna sequax and Potamophylax rotundipennis, were reared in single species and mixed species populations. Emergence rate was recorded and adult fitness was measured in terms of wingspan and biomass. We found that in mixed populations, emergence rate, wing length and biomass of M. sequax were higher than in single species populations. P. rotundipennis was only significantly, yet negatively, affected in terms of biomass of the male individuals. This study showed that occurring together with other species holds advantages for M. sequax, and emphasizes the importance of species diversity in streams. Furthermore, the observed positive effects on survival and fecundity might influence population sizes of the interacting species, in turn affecting macroinvertebrate-mediated ecosystem processes such as leaf litter decomposition.

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Biotic interactions enhance survival and fitness in the caddisfly Micropterna sequax (Trichoptera: Limnephilidae)

Biotic interactions enhance survival and fitness in the caddisfly Micropterna sequax (Trichoptera: Limnephilidae) Judith J. Westveer 0 1 . Piet F. M. Verdonschot . Ralf C. M. Verdonschot 0 1 0 P. F. M. Verdonschot R. C. M. Verdonschot Wageningen Environmental Research, Wageningen UR , P.O. Box 47, 6700 AA Wageningen , The Netherlands 1 J. J. Westveer (&) P. F. M. Verdonschot Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam , P.O. Box 94248, 1090 GE Amsterdam , The Netherlands Patches of coarse particulate organic matter in lowland streams are inhabited by many different macroinvertebrate species, yet knowledge of interactions among the members of these assemblages is scarce. In a mesocosm experiment we aimed to determine the effect of interspecific interactions on species survival and fitness of two caddisfly species. It was hypothesized that, as a result of positive interactions, mixed species populations would yield higher survival and fitness than single species populations. Larvae of two caddisfly species, Micropterna sequax and Potamophylax rotundipennis, were reared in single species and mixed species populations. Emergence rate was recorded and adult fitness was measured in terms of wingspan and biomass. We found that in mixed populations, emergence rate, wing length and biomass of M. sequax were higher than in single species populations. P. rotundipennis was only significantly, yet negatively, affected in terms of biomass of the male individuals. This study showed that occurring together with other species holds advantages for M. sequax, and emphasizes the importance of species diversity in streams. Furthermore, the observed positive effects on survival and fecundity might influence population sizes of the interacting species, in turn affecting macroinvertebrate-mediated ecosystem processes such as leaf litter decomposition. Macroinvertebrates; Interspecific facilitation; Niche complementarity; Ecosystem functioning; Biodiversity Introduction High-flow-induced within-stream habitat fragmentation results in isolated patches of preferred substrate for many macroinvertebrate species (Tolkamp, 1980; Lake, 2000; Ja¨hnig et al., 2009; Schro¨ der et al., 2013) . In lowland streams these patches consist of coarse particulate organic material (leaves, leaf fragments, twigs) embedded in a matrix of sand, and are an important resource in terms of, amongst others, food and shelter (Egglishaw, 1964; Lancaster & Hildrew, 1993) . As consumers of leaf material aggregated in these patches, shredders play an important role in the decomposition process (Anderson et al., 1978; Malmqvist & Oberle, 1995; Mermillod-Blondin et al., 2002) . With many different species inhabiting these patches, intra- and interspecific interactions are expected to be frequent. Nonetheless, knowledge on biotic interactions among macroinvertebrates performing the same functional role is scarce. Biotic interactions can be positive (mutualism and commensalism; Milbrink, 1993; Tokeshi, 1993) and/ or negative (competition, parasitism, amensalism; Burkholder, 1952; Connel, 1983; Didham et al., 1996) for one or both species. The positive effect of an interaction, also known as facilitation, is seen as a key mechanism in which species diversity positively affects ecosystem processes and functioning (Mulder et al., 2001; Stachowicz & Byrnes, 2006; Bulleri et al., 2016) . A study by Cardinale et al. (2002) showed that multiple species from the same functional feeding guild (aquatic suspension-feeders) enhanced each other’s feeding success by decelerating the flow from upstream to downstream neighbours. This example shows that it is well possible that changes in species assemblages alter the likelihood of positive species interactions. While Cardinale et al.’s study is valuable for a better understanding of biotic interactions and resource partitioning, it remains unknown how biotic interactions affect species survival and development, and with that the long-term effect on future populations. Species belonging to the same functional guild within a community could hypothetically become functionally redundant, with several species occupying the same ecological niche and consequently competing for resources (Walker, 1992; Duffy et al., 2001; Dole´dec & Bonada, 2013) . However, studies across terrestrial, marine and freshwater ecosystems suggest that species within the same functional guild often have niches that do not overlap, causing functional complementarity instead of redundancy (Fargione et al., 2007; Rudolf et al., 2014; Kelly et al., 2016) . Functional or niche complementarity results in greater resource uptake efficiency and faster ecosystem process rates (Loreau, 2000; Loreau & Hector, 2001; Fox, 2005; Leibold et al., 2016) . Considering the organic patches as rather isolated streambed microhabitats, inhabited by a set of species with similar feeding strategies, it is probable that these speci (...truncated)


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Judith J. Westveer, Piet F. M. Verdonschot, Ralf C. M. Verdonschot. Biotic interactions enhance survival and fitness in the caddisfly Micropterna sequax (Trichoptera: Limnephilidae), Hydrobiologia, 2018, pp. 1-11, DOI: 10.1007/s10750-017-3493-8