We conducted an experiment to determine the effects of cage aquaculture on the functional properties of a lake. We installed a commercial aquaculture operation into a lake located within a pristine headwater region of the boreal shield. We used a before-after control-impact design to evaluate the weight of evidence for causal effects. We quantified sinks, sources and exchanges of carbon, nitrogen and phosphorus to the lake and presented this information in a budget format. We then calculated retention rates for these chemicals and compared them to integral amounts of carbon, nitrogen and phosphorus accumulating in the water column. We also measured removal rates (sedimentation) of these elements from the water column and transformation rates (primary production) within the water column. We found that the amounts of nitrogen and phosphorus retained in the lake increased dramatically during farm operation. With the exception of an increase in particulate carbon, we did not observe an accumulation of these chemicals in the water column. We did however observe lake wide increases in carbon and nitrogen sedimentation. Primary production increased significantly in the aquaculture-impacted lake and the period of peak productivity shifted to later in the summer. We discuss our results in the context of consequences to aquatic life and source water and we provide some recommendations for management.

Methylmercury (MeHg) is a toxic heavy metal and a health threat to wildlife and humans, however nothing is known about its effects on amphibians. MeHg is produced from inorganic Hg in the aquatic environment, and bioaccumulates in the food chain. This exposes tadpoles to elevated levels of MeHg in their diet, and may pose a risk to development. Tadpoles of the North American species Bufo americanus and Rana pipiens as well as the African frog model species Xenopus tropicalis were subchronically exposed to dietary McHg ranging in concentration from 1ng/g to 1000 ng/g to determine LC50s and species sensitivity differences. A developmental differences study was also performed with B. americanus. The 33-day LC50 estimates indicate that Gosner stage 25 tadpoles of both B. americanus and R. pipiens were the most sensitive, and they exhibited a similar sensitivity to McHg toxicity. The X. tropicales LC50 estimate is significantly higher (p=0.05) than those calculated for B. americanus and R. pipiens Gosner stage 25, and the developmentally advanced B. americanus Gosner stage 27-30 LC50 estimate is also significantly higher (p=0.05) than the B. americanus Gosner stage 25 LC50. (Abstract shortened by UMI.)

Selection-cutting is the preferred method of logging in northern hardwood forests, because it is thought to favor the regeneration of valuable, shade-tolerant trees, maximize long-term productivity, and increase the health, quality and economic value of residual trees. Claims have also been made for the ecological sustainability of selection cutting, in particular that it: (a) preserves soil fertility; (b) maintains natural canopy composition; (c) protects plant and animal habitat. I evaluated these claims by studying the effects of selection-cutting on several measures of soil fertility (Ca, Al, Ca/Al molar ratios, pH), canopy composition and tree regeneration, herbaceous layer composition, and structural features related to habitat quality (cavity trees, snags, coarse woody debris) in 55 stands ranging from newly cut to old-growth (not all data overlaps). I found that forest growth after selection-cutting depletes soil solution calcium and lowers soil solution Ca/Al molar ratios, posing a threat to long-term forest health and productivity, particularly at higher elevations and in sites on siliceous bedrock. I found that selection-cut stands dominated by red oak (Quercus rubra) are converting to sugar maple (Acer saccharum) stands, posing a threat to both canopy and herbaceous layer diversity. I found no lasting effects of selection-cutting on herbaceous layer composition, diversity or quality, but I found indirect threats from the conversion of red oak stands to sugar maple and from depletion of soil solution calcium. Finally, I found that current selection-cutting practices generally do not meet published targets for large trees, cavity trees, snags and coarse woody debris, but that they probably could meet those targets with minor changes to cutting practices. I conclude by discussing the implications of these results for the management of northern hardwood forests.

The introduction of Sitka black-tailed deer, Odocoileus hemionus sitkensis Merriam, to Haida Gwaii (Queen Charlotte Islands, B.C., Canada) in the late 19th century provides a valuable opportunity to understand the long-term effects of deer populations on the vegetation of the North American temperate rain forest. We conducted two island-based experiments to investigate the effect of Sitka black-tailed deer on the forest understorey vegetation of this archipelago. In the first experiment we used a set of seven small islands (<15 ha) with different browsing histories (more than 50 years of deer presence, less than 20 years of deer presence, and no evidence of any deer presence) to test the effects of deer on plant cover, species richness and community composition. Browsing history was inversely proportional to both vegetation cover and plant species richness. Modification of the forest understorey plant communities followed a series of steps towards a greatly simplified community of plants possessing mechanisms to keep developing plant tissue inaccessible to deer. In the second experiment we utilized the cull of Sitka black-tailed deer from two large islands (295 ha and 170 ha) to investigate the release of forest plant communities from deer browsing. Using a paired-island approach, deer were culled on two experimental islands but remained on three adjacent control islands. Clear increases in species richness and cover as well as changes in the community composition of the forest understorey of experimental islands in the five years following the initiation of culls suggested a quick return to the forest understorey communities thought to exist before deer modification. However, failure of key shrub species to establish, coupled with the development of closed canopy stands of Sitka spruce, Picea sitchensis, suggests possible alternate stable-states for some communities.

It has long been recognized that climate can influence the diversity and dynamics of communities and regional assemblages. Within this thesis, I ask three questions: (1) which processes are most important in mediating climate-species richness relationships; (2) are predictions of spatial climate-richness models temporally consistent, and (3) is local community structure determined primarily by regional or local processes. Metabolic theory proposes that climate-richness relationships arise due to the temperature dependence of metabolic rate. I tested the theory's predictions for six taxa in North America. Contrary to the theory's predictions, temperature-richness relationships were curvilinear and their slopes deviated from the predicted value. This suggests that the mechanism proposed by metabolic theory does not underlie climate-richness relationships. If climate determines species richness, then climate should predict how species richness will change over time. To test this, I compared alternative methods (regression and niche modelling) of forecasting shifts in species richness given global climate change. Models were trained on butterfly richness data from the early 20th century and their predictions were compared to observed changes throughout the 20th century. Overall, regression-based approaches that incorporated spatial autocorrelation outperformed other methods. Broad-scale richness gradients could arise from climatic niche conservatism. I tested this hypothesis for treefrogs (Hylidae) by combining data on species' distributions and phylogeny. I found that while niches were conserved with respect to cold tolerance, species richness was determined by precipitation, not temperature. This suggests that the processes determining regional species composition and richness are controlled by fundamentally different climatic components. I evaluated the relative importance of regional and local processes and how there were affected by climatic gradients by examining patterns of body size dispersion at local and regional scales for hylid frogs. On average, communities were over-dispersed, but there was no increased signature of competition in the tropics. Dispersion of regional assemblages decreased in cold areas, but this was not due to an elevated tropical rate of body size evolution. Overall, regional processes explained twice as much variance in body size dispersion than did local processes. This thesis rejected several hypotheses for the link between climate and macroevolutionary patterns. In doing so, it provided new insight to the role of ecological and evolutionary processes along broad-climatic gradients.

No description available.

Master of Science / Department of Biology / Kimberly A. With / Organisms exist within complex landscapes, and landscape features may influence multiple aspects of a species’ distribution within the landscape, including patch occupancy, abundance within patches, and population genetic diversity at a local or regional scale. We took two approaches to identify the relative importance of landscape context for populations of the Eastern Collared Lizard (Crotaphytus collaris collaris) in the northern Flint Hills of Kansas. First, we conducted surveys at limestone outcrops in experimental watersheds managed under different burning and grazing practices. Habitat occupancy and lizard abundance were estimated by constructing models that incorporated aspects of the environment at multiple scales. Both abundance and occupancy were higher on rock ledges that had more crevices, greater complexity in vegetation, covered a larger area, and were more prominent than available habitat. Abundance and occupancy were also higher in watersheds that were burned frequently (1–2 year intervals), but grazing only had a significant effect in less frequently burned (four–year burn interval) watersheds. Our second approach was to measure genetic diversity and population genetic differentiation and relate these measures to differences in landscape context. We sampled collared lizard DNA at four locations (sample sites < 45 km apart) and analyzed trends in 10 polymorphic microsatellite loci. We found evidence for low genetic variability and moderate population differentiation among our sample sites relative to estimates reported in the literature at the core of the species’ range. Differences in migration rates and ancestry among sampling locations also appear to correspond to differences in landscape resistance based on land cover and rock availability. Thus, it appears that habitat management may influence the suitability of habitat patches at the local scale, and that differences in land cover and rock availability may influence the connectivity of populations at the landscape scale.

Spider venoms are complex mixtures of chemicals whose primary function is to immobilize prey. The chemical composition of venoms and the role of venoms in prey immobilization vary widely among spiders. Yet, little is known about patterns of venom diversity and evolutionary processes that influence venom diversification. I used a comparative approach to (1) investigate phenotypic and evolutionary plasticity in whole venom chemical composition by comparing venoms among taxa that differ in time since divergence; and (2) determine whether evolutionary changes in venom are predictable based on changes in behavior or ecology. Non-genetic variation in venoms of a funnel-web spider, Agelenopsis aperta, was investigated by determining the effect on adult venom expression that results from rearing broodmates on different diets. This analysis provided no evidence of an effect of rearing diet on the chemical composition of adult venoms. Variation within species in venoms among sexes and populations was investigated in two spider groups. Tegenaria agrestis, a species suspected of interpopulational differences in venom pharmacology, had limited differences in venom composition and potency between same-sex individuals from isolated populations. However, within populations, sexes differed in concentrations of shared components, and female venoms were more potent on insects. Similarly, venom sexual dimorphism was detected in species of Tetragnatha. Male venoms had large concentrations of high molecular weight proteins that were absent in females. The dimorphism in Tetragnatha is likely not a function of sexual niche differences. Finally, ecological and behavioral correlates of differences in venom chemistry among clades of spiders that differ in feeding behavior were investigated in Hawaiian Tetragnatha. Associated with loss of web-use in prey capture in a lineage of this genus, was a reduction in the concentration of low molecular weight components, and an increase in the concentration of components between 35 and 80 kDa. Coincident with this change was an increase in the taxonomic range of prey and a decrease in the rate of onset of paralysis in prey after bites. However, there were no detectable differences in the role of venom in prey immobilization, and the general physiological effects of bites on prey.

Data were collected on woody vegetation for 10 years in 6 undisturbed plant communities including slash pine forest, wet prairie, hardwood hammock, edge and interior old-growth cypress forests, and freshwater marsh at National Audubon Society's Corkscrew Swamp Sancturary in South Florida. Forested communities all showed a trend toward greater successional maturity. Numbers and total basal areas generally decreased over the 10 year period for early successional species and tropical species affected by the 1982 freeze in hammock and edge cypress communities. Otherwise, total basal areas steadily increased for all species in the forested communities. Initially the slash pine forest contained only canopy pine, but hardwoods entered the sites 3-4 years after fire and continued to increase in number throughout the study. Woody vegetation in the two marsh communities were less stable, partially due to fire. Fire and hydrologic conditions had measureable impacts on community structure and growth patterns.

Fire-scarred cross-sections from coast redwood (Sequoia sempervirens) at two sites were dendrochronologically dated and used to develop a fire history. Redwood offers a challenge for dendrochronological study due to ring wedging and complacency. Crossdating was successful in 12 of 24 trees. The fire history was developed by comparison of fire scars and fire-associated ring characteristics (resin ducts, double latewood, growth releases, and ring separations) recorded in ring series. Using only dates of fire scars from the first fire in 1714 to the last in 1962, the mean fire interval (MFI) was 9.9 years. MFI for the best represented presettlement segment 1714-1881 was 8.0 years. Using all fire-associated ring features, MFI 1714-1962 was 7.0 years and 1714-1881, 6.0 years. Use of all fire-associated ring characteristics is argued to be a more accurate representation of past fire frequency. MFIs determined are less than others reported for coast redwood and suggest fire frequency in redwood may have been underestimated in past studies.