This thesis describes the ecology of invertebrate predators (Plecoptera and Trichoptera) across steams, some without fish. Focusing primarily on stoneflies of the families Perlidae and Perlodidae, I studied the density and diversity of predators and the invertebrate prey, predator diet, size-mass relationships and microhabitat use. The abundance of invertebrate predators varied across streams and seasons but numbers of predatory invertebrates did not differ with fish presence. Only the smallest species of invertebrate predator was more abundant in substrate complexes in streams with fish. Overall biomass of invertebrate predators was lower in streams with fish, because the size-class distributions of some species were biased towards small individuals. The size-mass relationships and pre-emergent weights of all predators, except the Perlidae, varied across sites, but there was no clear relationship between condition and fish presence/absence. Invertebrate predators were mainly carnivorous in fishless sites, but in some species diet broadened with fish presence to include more algae. I hypothesise that the fixed nocturnal habit of Perlidae, permitted by their slower growth, accounted for the similarity in abundance, size, condition and diet across streams. Nocturnal activity and the coarse stony substrate which provided abundant refugia, minimised any effect of fish. By contrast, Perlodidae and other predators have shorter life cycles, forage by day and night, and have greater growth requirements, accounting for the greater variability in size and condition across streams. Though these species should incur greater exposure to fish, the coarse substrate may provide foraging space free from predation risk, thus minimising any effects of fish. For stream invertebrate predators, direct predation effects of fish appear to be minimal and principal effects may be sublethal, indirect, and prey mediated.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:649899 |
| Date | January 2005 |
| Creators | Edwards, Francois K. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14773 |
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