As ecologists are being called upon to predict the consequences of human
perturbations to natural communities, an important goal is to understand what factors
drive variability or consistency in nature.
In the rocky intertidal of San Juan Island, Washington, a comparative
experimental approach was used to investigate spatial and temporal variation in
community organization. The effect of predation on B. glandula varied dramatically over
small spatial scales between microhabitats but was remarkably consistent over time
withing a given microhabitat. The effects of predation on S. cariosus varied over time
within the same microhabitat. By repeating previous landmark experiments at our study
site, and replicating these experiments across microhabitats, the domain of applicability
of previous experimental information was greatly expanded.
In an early successional assemblage on the Oregon coast, I tested the hypothesis
that, when the direct effect of one species on another increases in relative strength, its
total effect (direct + indirect) is less variable or conditional than if the link between those
species is weak. The effect of strong predation by whelks was less sensitive to the
presence of additional species and more consistently dampened natural variation between
experimental starting dates and between individual replicates within a given experiment.
In contrast, the outcome of weak predation was more spatially and temporally variable in
sign, and whether it magnified or dampened differences between individual replicates
varied between experiments. Consequently the mean total effect of weak predation
generally did not differ significantly from zero. However, in some cases, the range of
variation (both within and between experiments) in the effect of weak predation exceeded
the magnitude of the strongest total effect observed.
Longer term results of the experiments on the Oregon coast examined the role of
historic factors in influencing the degree to which successional paths are canalized and
repeatable or contingent and variable. Succession in mid-intertidal patches in the mussel
bed displayed complex patterns of historic effects that varied between species and
between different stages of succession. Despite its potential complexity, this system
exhibited some consistent and repeatable patterns of succession. Some important
canalizing, or noise-dampening forces in this system included: 1) physiological and life-history
constraints, 2) compensatory responses of functionally redundant species, and 3)
strong interactions between species. / Graduation date: 1996
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/34584 |
| Date | 09 June 1995 |
| Creators | Berlow, Eric Layani |
| Contributors | Menge, Bruce A., Lubchenco, Jane |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
Page generated in 0.0027 seconds