The study of species diversity patterns and their causes remains a central theme of ecology. Work conducted over the last few decades has shown that both historical and ecological factors are important in determining species diversity patterns. Additionally, different causal mechanisms are important at different spatial and temporal scales. At the regional scale, species diversity patterns can best be studied in terms of three diversity components (alpha, beta and gamma). This study used the amphibians and reptiles of Costa Rica to examine these species diversity components at the regional scale. To accomplish this, existing species lists were compiled from the literature. Additionally, three herpetofaunal surveys were conducted at under surveyed sites to fill knowledge gaps. A survey of Parque Nacional Carara, a transitional zone site on Costa Rica’s central Pacific coast, gave evidence of a rich herpetofauna, containing species from both the dry tropical forest to the north and the wet lowland forest to the south. Survey results show that Carara’s herpetofaunal assemblage is more similar to that of the wet forest than the dry forest, and suggest many species from both assemblages reach their range limit at or near the park. Surveys of four sites in the eastern Área de Conservación Guanacaste showed rich herpetofaunal diversity and validated the newly purchased Rincón Rainforest as an important conservation area. A survey of Reserva Natural Absoluta Cabo Blanco provided a preliminary list of amphibian and reptile species of the lower Nicoya Peninsula and highlighted the importance of Laguna Balsitas to the local amphibian fauna. A comparison of amphibian and reptile alpha diversity among 17 sites throughout Costa Rica showed highest alpha amphibian diversity in the lowland rainforests of the Pacific versant and highest reptile alpha diversity in lowland rainforests of the Atlantic versant. An analysis of beta diversity produced dendrograms showing sites within lowland ecoregions being most similar. A Canonical Correspondence Analysis (CCA) of environmental variables showed two climate gradients, an elevation/temperature gradient and a sun/rain gradient, to be important in determining species diversity patterns for both amphibians and reptiles in Costa Rica.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 96-118).

Environmental heterogeneity has often been suggested as a general explanation for patterns of diversity at scales ranging from individuals within populations to communities within landscapes. I evaluate this proposition using laboratory experiments with two microbial species, the unicellular chlorophyte Chlamydomonas reinhardtii and the common bacterium Pseudomonas fluorescens. These experiments contrast the fate of diversity following selection in heterogeneous and homogeneous environments. Specifically, I show that (1) an individual's breadth of adaptation evolves to match the amount of environmental variation, specialists evolving in environments that remain constant through time and generalists evolving in environments that vary through time irrespective of the scale at which environmental variation occurs relative to the lifetime of an individual; (2) the maintenance of diversity in a spatially heterogeneous environment is context-dependent, diversity being more readily maintained when environmental conditions are very different and genotypes are widely divergent; (3) selection in heterogeneous environments represents a plausible mechanism for two well-known patterns of diversity at large spatial scales, namely that between species diversity and both productivity and disturbance. This thesis thus demonstrates that environmental heterogeneity is a plausible, and perhaps very general, factor responsible for the diversity of natural communities.

This dissertation considers faunal recoveries from a selection of archaeological sites located in the Canadian Northeastern Plains that date between AD 1000 and 1600. These faunal assemblages derive from three different archaeological cultures that are thought to reflect different subsistence orientations. The analysis quantifies this variability by assessing the taxonomic abundance and intensity of bone processing evident in the recoveries. At issue is determination whether variability in the faunal assemblage reflects differences in subsistence economy deriving from the diverse origins of these societies. This requires control over other potential contributors to variability. This includes ecological comparability of the site localities, consistency of excavation, sampling and analytic methods, and similarities in site function. Particularly important is determination that the selected sites reflect comparable seasons of site occupation. This latter consideration is important since the established archaeological and ethnological literature suggests that both available resources and the economic orientation of resident populations varied significantly with season. To this end, a major research component focused on the development of more refined means of determining the season of site occupation by measuring the degree of osteological development of recovered foetal bison bones. The creation of linear regression equations based on these measurements will allow applied archaeologists to establish season of site occupation without the need for a large, difficult to obtain foetal bison comparative collection. The analysis suggests the variability in the faunal assemblages occurs independently of site cultural affiliation, and might reflect economic activities conditioned by more finely divided seasonal divisions than is apparent with the conventional four-season model deriving from agrarian European societies. Aboriginal language markers, specifically moon-names, were used to identify significant biophysical and bison reproductive events. By placing the six sites within Aboriginal concepts of seasonality, animal food subsistence choices are better understood. These results have implications for the classification scheme archaeologists have used to define subsistence strategies.

Mountain ecosystems are considered highly sensitive to the impacts of climate change, and are experiencing a magnitude of change that far exceeds global averages, particularly with respect to increases in average temperature and precipitation. As such, scientists are predicting a rapid habitat reduction or even the loss of the coolest climatic alpine zones, thus threatening the continued survival of high elevation specialists. However, many of these ‘doomsday’ predictions are based primarily on models with coarse-resolution changes to atmospheric climate parameters, and do not take into account the potential buffering effects of other environmental gradients known to structure alpine plant communities, related to topography and soils. To assess the accuracy of predictions regarding the state of vulnerability of alpine plant communities to climate change, this thesis examined the relative importance of climate, topography and soils as determinants of regional alpine plant diversity for all species, as well as for forbs, graminoids and woody species separately, in alpine meadows of southwestern British Columbia. Through redundancy analyses and variation partitioning, results show that topography and soils are more important than climate as determinants of regional alpine plant diversity. Within these groups, elevation, slope, soil moisture and mean summer temperature were most significant. Interestingly, precipitation played only a small role, even though the study area spanned a precipitation gradient of over 1200 mm/year. The stronger influence of temperature, especially for woody species beta diversity, supports findings of shrub expansion in arctic-alpine systems. The lower importance of climate as a determinant of regional alpine plant diversity, especially for forbs, the dominant life form in alpine meadow ecosystems, suggests that these productive environments may be more resilient to on-going changes in atmospheric climate conditions than previously believed. / Graduate

Thesis (Ph. D.)--University of Hawaii at Manoa, 1994. / Includes bibliographical references (leaves 166-191). / Microfiche. / xiii, 191 leaves, bound ill. 29 cm

The secondary productivity of communities is inherently influenced by the availability and quality of food resources. Movement of organic matter (OM) across landscapes can connect adjacent systems by providing subsidies of carbon and nutrients, implying that alterations of environments from their natural state may affect the productivity of neighboring food webs. The intact terrestrial and marine environments of Fiordland provide a setting to study linkages between the land and the sea. The first general objective of this study was to determine if large but nutritionally poor (nitrogen-poor, carbon-rich) inputs of forest litter support marine secondary production, and to identify pathways for incorporation of this material into upper trophic levels. Pools of marine and terrestrial OM had distinct values of [delta]�⁵N, [delta]��C and [delta]�⁴S, providing high power to estimate the relative use of these sources by the food webs of the fjord-head deltas. Deposit feeding invertebrates (e.g. Echinocardium cordatum, Pectinaria australis) directly assimilated plant detritus. Heterotrophic bacteria on the surface of the sediment assimilated forest litter and provided a potential food source for invertebrates. Chemoautotrophic bacteria fix CO₂ that originates from decomposing forest litter, thus providing an indirect pathway for incorporation of forest litter into the food webs. In the deep basins the strength of the flux of uptake by chemoautotrophic bacteria through the benthic food web into the upper trophic levels was demonstrated by hagfish (Eptatretus cirrhatus) obtaining 38-51% of their nutrition from these bacteria. The ability of a community to utilize discrete sources of OM relies on the presence of specific functional feeding guilds. Marine algae provide a highly nutritive (nitrogen-rich) food source for the fjord communities and fluxes of algae into food webs are facilitated by grazing invertebrates and filter feeders. The second general objective of this study was to determine how the effective loss of filter feeders from inner Doubtful Sound would alter the flux of marine-derived OM to the food webs of the delta communities. The low salinity environment imposed by the hydroelectric power station in Doubtful Sound caused a large reduction in the abundance of the infaunal bivalves Austrovenus stutchburyi and Paphies australis from delta habitats. Clams could tolerate periods of freshwater exposure of [less than or equal to]20 days duration, but the constant freshwater conditions in Doubtful Sound decreased survivorship. In 2004/05 the biomass of these species in inner Doubtful Sound (7.28 tonnes) was 29 times smaller than in Bradshaw Sound (214.12 tonnes). The associated loss of biodeposits (~91 tonnes(DW) yr⁻� in Bradshaw Sound vs. 1 tonne(DW) yr⁻� in inner Doubtful Sound) may have also altered the flux of nutritive OM to the infaunal community. The river delta communities in inner Doubtful Sound appear to have a higher reliance on forest litter than those in Bradshaw Sound, which is apparent as low values of [delta]�⁵N and [delta]��C for estuarine fish (Notolabrus celidotus, Hemerocoetes monopterygius), which act as integrators of the benthic community. This study demonstrates important linkages between terrestrial and coastal marine ecosystems and highlights the role of functional diversity in facilitating fluxes of organic material through food webs.

Thesis (Ph.D.)--Victoria University of Wellington, 2008. / Includes bibliographical references.

Thesis (M.A.)--Humboldt State University, 2009. / Includes bibliographical references (leaves 58-61). Also available via Humboldt Digital Scholar.

Thesis (M.Sc.), Memorial University of Newfoundland, 1999. / Bibliography: p. 208-219.