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No description available.

No description available.

No description available.

Urbanization is an intensive form of habitat disturbance associated with detrimental effects on biodiversity. However, few studies have investigated its effects on the number, identity and structure of species interactions while considering seasonal fluctuations in communities. Avian seed dispersal is a vital ecosystem service, and the interplay of urbanization and seasonality may impact seed dispersal in ways not predicted by either factor alone. In this study, we evaluate the effects of urbanization and season on avian seed dispersal networks in the southern Appalachians. We found that the number and richness of interactions was unaffected, but the identity of interacting bird species differed based on landscape type. We also found that species strength was impacted by urbanization and season, but other network metrics were unaffected. These results suggest that species identity should be considered when making comparisons of seed dispersal networks, as it may reveal differences between networks with implications for dispersal quality and future plant communities.

Whether species interactions are static or change over time has wide-reaching ecological and evolutionary consequences. However, species interaction networks are typically constructed from temporally aggregated interaction data, thereby implicitly assuming that interactions are fixed. This approach has advanced our understanding of communities, but it obscures the timescale at which interactions form (or dissolve) and the drivers and consequences of such dynamics. We address this knowledge gap by quantifying the within-season turnover of plant-pollinator interactions from weekly censuses across 3years in a subalpine ecosystem. Week-to-week turnover of interactions (1) was high, (2) followed a consistent seasonal progression in all years of study and (3) was dominated by interaction rewiring (the reassembly of interactions among species). Simulation models revealed that species' phenologies and relative abundances constrained both total interaction turnover and rewiring. Our findings reveal the diversity of species interactions that may be missed when the temporal dynamics of networks are ignored.

The Bonneville Basin encompasses an area that was covered by ancient Lake Bonneville and which today lies within the Great Basin province. The Bonneville Basin is distinguished geologically by its characteristic parallel north-south mountain ranges that are separated by broad, alluviated desert basins and valleys. Benches and other shoreline features of ancient Lake Bonneville prominently mark the steep, gravelly slopes of these ranges. Numerous artesian desert springs are present at the base of the mountains and in the valley floors that form various sizes of both isolated wetlands and wetland complexes. Many these wetlands are some of the most unique and currently some of the most threatened wetlands in the United States. Several aquatic species and communities have maintained an existence as relict populations and communities in these wetlands since the receding of Lake Bonneville over 10,000 years ago. For example, Hershler has described 58 previously undescribed species of hydrobiid snails, 22 of which are endemic to single locations. Like hydrobiid snails, numerous other species, such as the least chub, Iotichthys phlegethontis and the Columbia spotted frog, Rana luteioventris, depend on these wetlands for their continued existence, many of which are already imperiled. The continued decline and loss of these wetlands would further push many of these species toward endangerment and/or extinction. Several factors have already eliminated or altered many of these habitats including capping and filling,water depletions, agricultural practices, livestock grazing, and introduction of nonnative species. In recent years, the significant loss and degradation of wetlands resulting in sensitive species designations have provided impetus for resource agencies to develop and implement management plans to conserve and protect these vital ecosystems. One problem facing appropriate management is the lack of biological information for determining which wetlands should receive protection priorities based on the presence of viable, functioning characteristics. The purpose of this dissertation project was to obtain biological information needed to support defensible decisions concerning conservation, protection, acquisition, restoration, and mitigation of the artesian springs in the Bonneville Basin. The primary objectives of this project were to 1) Develop bioassessment procedures for artesian wetlands of the Bonneville Basin using macroinvertebrates and 2) Determine patterns of community composition and diversity for macroinvertebrates and metaphyton algae at multiple scales in Bonneville Basin artesian wetlands.

Global climate models predict that the current trend of warming in the Arctic will continue over the next century. The productivity of arctic plants is often limited by short growing seasons with relatively low temperatures such that a warmer climate could have large impacts on plants and plant communities. This study characterised alpine plant responses to changes in temperature at an alpine tundra site near Whitehorse, Yukon, Canada. I examined relationships between plant productivity and natural temperature variations and assessed responses of plants exposed to an experimental warming treatment. Non-destructive measurements of reproductive and growth characteristics of four target species (Dryas octopetala, Lupinus arcticus, Polygonum viviparum, and Salix arctica) were taken annually from 1999 to 2008. There was no significant effect of the warming treatment (OTCs) on average daily mean temperatures as midday warming of up to 1.4 °C was largely offset by night time cooling in the OTCs. Vegetative measurements of target species showed no significant responses to OTC treatments. However, peduncles of D. octopetala and sections of P. viviparum inflorescences that produced bulbils were an average of 34.6 % and 64.7 % longer in OTCs than in controls, respectively. These treatment responses were likely due to plants responding to a factor other than temperature that was modified by the chamber. One vegetative and five reproductive characteristics were significantly related to annual variation in temperature. The summer of 2004 was exceptionally hot, and some species that did not respond to smaller fluctuations in temperature showed large changes in growth or reproduction in this year, perhaps indicating a non-linear response to temperature. Among the larger responses to the warm summer of 2004 was a shift in P. viviparum allocation from predominantly asexual to sexual means of reproduction. Measurements of plant community composition assessed at five-year intervals showed no differences in community composition between experimental plots and controls, and changes in composition over the study period were not uni-directional. In general, both individual plants and community composition were highly resilient to observed variation in summer temperatures. Other factors, such as nutrient availability, may be more important in determining plant responses to environmental change at this site than the direct effects of summer temperature variation.

Global climate models predict that the current trend of warming in the Arctic will continue over the next century. The productivity of arctic plants is often limited by short growing seasons with relatively low temperatures such that a warmer climate could have large impacts on plants and plant communities. This study characterised alpine plant responses to changes in temperature at an alpine tundra site near Whitehorse, Yukon, Canada. I examined relationships between plant productivity and natural temperature variations and assessed responses of plants exposed to an experimental warming treatment. Non-destructive measurements of reproductive and growth characteristics of four target species (Dryas octopetala, Lupinus arcticus, Polygonum viviparum, and Salix arctica) were taken annually from 1999 to 2008. There was no significant effect of the warming treatment (OTCs) on average daily mean temperatures as midday warming of up to 1.4 °C was largely offset by night time cooling in the OTCs. Vegetative measurements of target species showed no significant responses to OTC treatments. However, peduncles of D. octopetala and sections of P. viviparum inflorescences that produced bulbils were an average of 34.6 % and 64.7 % longer in OTCs than in controls, respectively. These treatment responses were likely due to plants responding to a factor other than temperature that was modified by the chamber. One vegetative and five reproductive characteristics were significantly related to annual variation in temperature. The summer of 2004 was exceptionally hot, and some species that did not respond to smaller fluctuations in temperature showed large changes in growth or reproduction in this year, perhaps indicating a non-linear response to temperature. Among the larger responses to the warm summer of 2004 was a shift in P. viviparum allocation from predominantly asexual to sexual means of reproduction. Measurements of plant community composition assessed at five-year intervals showed no differences in community composition between experimental plots and controls, and changes in composition over the study period were not uni-directional. In general, both individual plants and community composition were highly resilient to observed variation in summer temperatures. Other factors, such as nutrient availability, may be more important in determining plant responses to environmental change at this site than the direct effects of summer temperature variation.

In the southern Great Plains, the encroachment of grassland ecosystems by mesquite (Prosopis glandulosa), is widespread, and prescribed fire is commonly used in its control. Despite this, substantial quantitative information concerning their influences on the community composition, functional dynamics, and soil organic carbon (SOC) storage potential of grassland ecosystems is lacking. The objectives of this study were to: a) quantify the effects of seasonal prescribed fire treatments and mesquite encroachment on aboveground net primary productivity (ANPP) and herbaceous community composition; b) characterize SOC pool sizes, turnover, and storage potential relative to vegetation type and fire treatment; c) evaluate the structure and diversity of soil microbial communities relative to vegetation type; and d) characterize the functional diversity of these same microbes using the GeoChip functional gene microarray. Repeated winter and summer fires led to increased ANPP rates (average, 434 and 313 g m-2 y-1, respectively), relative to unburned controls (average, 238 g m-2 y-1), altered herbaceous community composition, and increased the storage of resistant forms of SOC, but did not affect overall SOC storage. Herbaceous ANPP rates did not differ significantly as a result of mesquite encroachment, but herbaceous community composition and SOC storage did. Mesquite soils contained significantly more total, slow-turnover, and resistant forms of SOC than those that occurred beneath C3 or C4 grasses. Similarity among the soil bacterial and fungal communities associated with the major vegetation types in this system was low to moderate. Significant differences were detected among soil fungi, with the mesquite-associated fungi harboring significant differences in community structure relative to the fungal communities associated with each of the other vegetation types examined. Despite this result, few significant differences were detected with respect to the functional diversity of these communities, suggesting either a high degree of functional redundancy, or that the functional differences harbored by these communities are beyond the scope of the GeoChip. The results of this study demonstrate that both fire and mesquite encroachment have the potential to alter ecosystem components and processes significantly, providing new insight regarding the effects of these widespread land use and land cover changes on ecosystem structure and function.