Studies in tropical regions have shown that trees and grasses respond differently to fire, grazing and browsing. In African savannas, the responses to fire, grazing and browsing are different, determined by negative or positive correlations. Browsing may have other consequences than grazing because instead of increasing woody biomass it reduces it, causing increase in grass growth, leading to increase in fuel that results in more intense fires and decrease in woody biomass. Fire and herbivory are an important interactive disturbance factors affecting vegetation succession and the tree-grass dynamics in savanna environment. Several of the fire-herbivory interactions are landscape level effects, which is shown in 2 models. My hypothesis is that the tree-grass balances are determined by interactions of both grazing and fire. There have come new scientific data about fire and herbivory and the interaction effects on tree-grass dynamic and succession in the savanna. By analyzing my hypothesis through a comparison between hypotheses, Intermediate disturbance hypothesis, Janzen-Connell hypothesis and the Huston hypothesis, I propose several scenarios of the savanna tree-grass dynamics in East Africa, as a result of this comparison.

Hydrilla (Hydrilla verticillata) is an invasive aquatic plant that grows quickly across shallow freshwater habitats. It is a problem for recreational users of lakes and landowners. Grass carp (Ctenopharynogodon idella) is an effective biological control agent that preferentially consumes and can control the spread of hydrilla. However, grass carp also will consume other vegetation, which influences aquatic communities via direct and indirect interactions that can change food and habitat availability and use by various species. Aquatic plants influence habitat and types of prey used by sunfish (Centrarchidae), which must also avoid their own predators. Prey use among sunfish species depends on density and taxonomic identity of both prey and vegetation. This was a one-year analysis of stomach contents from three common species of invertivorous sunfish: bluegill (Lepomis macrochirus), longear sunfish (Lepomis megalotis), and redear sunfish (Lepomis microlophus). Thirteen sampling stations were randomly selected using ArcGIS software. Percentage of water surface covered by vegetation was recorded at each station. A five-minute electrofishing sample was performed within the littoral zone early morning in late September. The stomach contents of all targeted sunfish (N=489) showed high percentages of diet overlap pre- (0.77-0.92) and post- (0.83-0.88) introduction of grass carp. Multivariate analysis showed total explained variation (15.5%) in sunfish diet composition was (P < 0.05) correlated significantly with sunfish species (6.67%), percent surface vegetation coverage (3.97%), and sampling periods pre- versus post-introduction of grass carp (2.13%). Prey-specific abundance showed that all sunfishes displayed a generalized feeding strategy in both sampling periods. Diets of each sunfish species showed differences in abundance (by volume) and occurrence (among individual fish) of prey items between sampling periods. Levin?s standardized index of diet breadth for all sunfish species decreased from pre- (0.12) to post-introduction (0.05). Results imply that vegetation control by grass carp influenced the diets and feeding strategies of three cohabitating sunfish species. These findings may help fisheries biologists to plan future management actions that influence assemblages of aquatic plants and macroinvertebrates, herbivorous fish, invertivorous prey-fish, and piscivorous game fish, to promote a healthy and balanced ecosystem for Lake Conroe stakeholders.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 84-89). Also available on the World Wide Web.

Grass-fed cattle ranching is growing in popularity, but the characteristics and motivations of the ranchers, however, remain undefined. Based in Texas and using a mail survey and interviews with three grass-fed, three organic, and three conventional ranchers to identify some of their distinctive characteristics, this study achieved similar results to those comparing organic and conventional farmers. Grass-fed cattle ranchers tend to have high levels of education, approach ranching as a second career, and possess outside income sources. Motivated as much by ethics as economics, they embrace grass-fed methods primarily because they believe them to be healthiest for animals, humans, and the land. They eschew organic certification primarily because they perceive government regulations to be influenced by large conventional competitors, and they market their beef directly, often locally. Although many hope to expand their herd, most grass-fed cattle ranchers believe they are resisting “conventionalization” and say that they feel more self-sufficient and satisfied thanks to their choices. / text

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