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Untangling the complexity of nearshore ecosystems : examining issues of scaling and variability in benthic communitiesSchoch, G. Carl 12 May 1999 (has links)
The objective of this research was to improve our understanding of how
changes in the environment affect ecological processes. Change detection is often
confounded by the large variation found in ecological data due to the difficulty of
finding replicates in nature. Intertidal communities were chosen for studies of biophysical
interactions because the physical gradients are very strong, thus creating
complex systems within spatial scales that are easily sampled. The selection of
replicate beach habitats was the first step in designing a sampling protocol for
comparative analyses of nearshore community structure. A high resolution shoreline
partitioning model was developed to quantify the physical attributes of homogeneous
shoreline segments and to statistically cluster replicate segments. This model was
applied at 3 locations in Washington State. A portion of the south shore of San Juan
Island was partitioned and the physical attributes quantified. Three groups of rocky
segments differing only in slope angle were selected for biological sampling. The
objective was to test the fidelity of macroalgal and invertebrate populations to replicate
bedrock shore segments. The results showed that community structure and population
abundances were more similar within groups of replicate segments (similar slopes)
than among groups (different slopes). In South Puget Sound, community structure was
compared to test for a deterministic organization of communities among replicate soft
sediment beaches in an estuary. The results showed that replicate beach segments
support similar communities, that communities become less similar as the distance
between replicates increases, and that replicates within or among nearshore cells with
similar temperature and salinity support communities that are more similar than
replicates among cells with different water properties regardless of distance. On the
outer Olympic coast, community comparisons were made among 9 sand beaches over
a shoreline distance of 250 km. The results show that these communities are similar
within segments and within nearshore cells, but because of population abundance
fluctuations, the communities were different among cells and among years. This study
shows that processes determining patterns in nearshore habitats can be quantified,
which is a significant contribution to studies of habitat distribution and the siting of
marine preserves. / Graduation date: 2000
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Patterns and dynamics of context-dependency in the marine rocky intertidalBerlow, Eric Layani 09 June 1995 (has links)
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
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