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)