Understanding the dynamics of open marine populations is difficult.
Ecological processes may vary with the spatial structure of the habitat, and this
variation may subsequently affect demographic rates. In a series of observational
and experimental studies in the Bahamas, I examined the roles of emigration,
mortality, and predation in the local population dynamics of juvenile coral-reef
fishes. First, I documented mortality and emigration rates in populations of
bluehead and yellowhead wrasse. Assuming that all losses were due solely to
mortality would have significantly underestimated survivorship for both species on
patch reefs, and for yellowheads on continuous reefs. Mortality differed between
species, but emigration did not differ between species or reef types. Mortality of
blueheads was density-dependent with respect to both conspecific density and total
wrasse density on continuous reefs. In contrast, mortality of yellowheads varied
inversely with the density of blueheads on patch reefs. Emigration rates varied
inversely with distance to the nearest reef inhabited by conspecifics. In subsequent
experiments, I manipulated densities of yellowhead wrasse and beaugregory
damselfish, and determined that the relationship between density and mortality
varied with reef spatial structure. On natural reefs, mortality rates of the wrasse
were highly variable among reefs. On artificial reefs, mortality rates of both
species were density-dependent on spatially isolated reefs, yet high and density-independent
on aggregated reefs. Heterogeneity in the spatial structure of natural
reefs likely caused variation in predation risk that resulted in high variability in
mortality rates compared to artificial reefs. A final experiment demonstrated that a
single resident predator caused substantial mortality of the damselfish, regardless of
reef spacing. Patterns suggested that resident predators caused density-dependent
mortality in their prey through a type 3 functional response on all reefs, but on
aggregated reefs this density dependence was overwhelmed by high, density-independent
mortality caused by transient predators. These results (1) suggest
post-settlement movement should be better documented in reef-fish experiments,
(2) demonstrate that the role of early post-settlement processes, such as predation,
can be modified by the spatial structure of the habitat, and (3) have ramifications
for the implementation of marine reserves. / Graduation date: 2004
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/30593 |
| Date | 09 June 2003 |
| Creators | Overholtzer-McLeod, Karen L. |
| Contributors | Hixon, Mark A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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