Appendix E. Effects of fish on mayflies and other benthic macroinvertebrates.
While fish had an adverse effect on the density of Ephemeroptera and Corixidae, no effect was detected for the other invertebrate taxa. Although the lack of a fish effect on some of these taxa is in contrast to other studies (e.g., McPeek 1990, Knapp et al. 2001), there are several possible explanations. Our finding may be a consequence of having combined certain taxa above the species level prior to analysis (i.e., Trichoptera, Corixidae). Another explanation is that unpalatable invertebrate species such as dytiscid beetles and burrowing species such as midges and alderflies may be less vulnerable to predation than palatable species that cling to the substrate (e.g., mayflies) or swim in the water column such as water boatmen (Scrimshaw and Kerfoot 1987, Knapp et al. 2001). The cases built by caddisflies may help protect this group from fish predation (but see Knapp et al. 2001). Finally, the differences in damselfly density between lake types may be inconclusive because they were only detected in 4 of the 24 lakes (1 fish-containing lake and 3 fishless lakes). Furthermore, in this study, elevation, not fish presence, may exert the strongest control on damselfly distribution.
FIG. E1. Taxonomic composition of benthic macroinvertebrates/m2 in the littoral zone of fishless and fish-containing lakes, from samples collected with D-nets in 2006. Bars indicate ± 1 standard error from mean. Asterices indicate results of Wilcoxon-Mann-Whitney two-sample test adjusted with a Bonferroni correction (***: P < 0.0001; *: P < 0.007; NS: P > 0.05 prior to the Bonferroni adjustment).
FIG. E2. Estimate of current (fish present) and historic (fish entirely absent) annual production of total individual mayflies (± 1 SE) in the four headwater lake basins sampled in 2006. Estimates were based on the density of mayfly nymphs/m2 in the littoral zone of lakes, sampled with D-nets.
Knapp, R. A., K. R. Matthews, and O. Sarnelle. 2001. Resistance and resilience of alpine lake fauna to fish introductions. Ecological Monographs 71:401421.
McPeek, M. A. 1990. Behavioral differences between Enallagma species (Odonata) influencing differential vulnerability to predators. Ecology 71:17141726.
Scrimshaw, S., and W. C. Kerfoot. 1987. Chemical defenses of aquatic organisms: beetles and bugs. Pages 240262 in Kerfoot, W. C., and A. Sih, editors. Predation: direct and indirect impacts on aquatic communities. University of New Hampshire Press, New Hampshire, USA.