| dc.description.abstract | The North Mountain of the Annapolis Valley, NS, in eastern Canada, is a ~200
km basalt ridge drained by many small first or second order streams in independent
catchments. The area is fairly uniform geologically, presenting an opportunity to compare
streams of similar chemistry, slope and aspect, that vary in other respects, such as
invertebrate community structure. In this thesis, I examine two macroinvertebrate
functional groups to determine key factors influencing their abundance, composition and
diversity across catchments.
Chapters 2 and 3 are concerned with the predatory invertebrate guild in eight of
the streams, in two groups separated by ~65 km. In Chapter 2, I assessed factors
influencing composition of the predator guild using similarity matrices. Similarity in
predator composition declined with distance, and streams that were more similar in
disturbance (spates) were more similar in predator composition. Similarity within one
family, Rhyacophilidae, was related to similarity in fish population. Chapter 3 reports the
results of laboratory experiments involving two widespread species. Field data suggested
an asymmetric interaction between Sweltsa onkos (Plecoptera: Chloroperlidae) and
Rhyacophila vibox (Trichoptera: Rhyacophilidae); behavioural observations in artificial
streams supported this. In the presence of R. vibox, S. onkos had higher mortality and
injury rates, and grew less. The results of these chapters suggest that, although
disturbance is important in shaping community structure, the results of interspecific
interactions can be detected at large scales. S. onkos can only attain high numbers in
streams where fish predation reduces the abundance of R. vibox.
Chapter 4 examines biodiversity patterns in the macroinvertebrate detritivore
guild in 25 streams encompassing ~80 km of the ridge. Using density and richness of the
detritivore community, detrital resource quantity, and top predator abundance, I looked
for evidence in support of several mechanisms that can lead to positive species-energy
relationships. Patterns conformed to expectations of the ‘More Individuals Hypothesis’. It
appears that taxonomic richness of the detritivore guild increases with detrital resource
availability because more taxa can attain their minimum viable population size where
more resources are available. | en_US |
