• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 24
  • 22
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • 3
  • 1
  • Tagged with
  • 67
  • 67
  • 67
  • 23
  • 15
  • 13
  • 12
  • 11
  • 11
  • 11
  • 10
  • 10
  • 8
  • 8
  • 8
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Parental care of peregrine falcons in interior Alaska and the effects of low-altitude jet overflights

Palmer, Angela G. 14 December 1998 (has links)
To assess the impact of low-altitude jet overflights on parental care, we examined nest attendance, time-activity budgets, and provisioning rates of 21 Peregrine Falcon (Falco peregrinus) pairs breeding along the Tanana River, Alaska in 1995 and 1996. Several intrinsic and extrinsic factors influenced attributes of nesting behavior. Female nest attendance declined substantially with progression of the nesting cycle, while male attendance patterns were consistent throughout the nesting cycle. Further, although females typically performed most of the incubating, male attendance at the nest area varied considerably among breeding pairs. Both prey item delivery rates and estimated prey mass delivery rates increased with brood size. Prey item delivery rates per nestling, however, decreased with increasing brood size; yet estimated prey mass delivery rates per nestling did not vary with brood size. Peregrine Falcons apparently maintained constant provisioning rates per nestling as brood size increased by increasing average prey size. We found evidence that nest attendance and time-activity budgets of Peregrine Falcons differed during periods of overflights compared with reference nests, but differences depended on stage of the nesting cycle and gender. Males had lower nest ledge attendance during periods when overflights occurred than males from reference nests when data from the incubation and early nestling-rearing stages of the nesting cycle were combined. Females apparently compensated for lower male ledge attendance by attending the ledge more during overflown periods compared to females from reference nests, although this trend was not significant. During late nestling-rearing, however, females perched in the nest area less during periods when overflights occurred than females from reference nests. We did not see a relationship between nest attendance and the number of overflights, the cumulative number of exposures experienced by each nesting pair, or the average sound exposure level of overflights. Nor did we find evidence that nestling provisioning rates were affected by overflights. Low altitude jet overflights did not markedly affect nest attendance, time-activity budgets, or nestling provisioning rates of breeding Peregrine Falcons. / Graduation date: 1999
22

The effects of patch size and isolation on juvenile emigration in gray-tailed voles, Microtus canicaudus

Nelson, Natasha 24 May 1996 (has links)
Graduation date: 1997
23

Over-winter demography of the gray-tailed vole (Microtus canicaudus) in fragmented and continuous habitats

Brunkal, Heidi L. 25 November 1996 (has links)
Large scale disruption of natural habitats worldwide has led to concern over the effects of habitat fragmentation on wildlife populations. Small scale experiments may be a useful tool for discovering effects of fragmentation over larger landscape scales. I sought to explore the potential for using voles as an experimental model system, at a small scale, to discover mechanisms that may affect other species at different spatial scales. I compared over-winter demography of gray-tailed voles, Microtus canicaudus, in two experimental landscapes, consisting of fragmented and continuous habitat, to assess the effects of habitat fragmentation. I chose winter as the time frame of the experiment because it poses harsh conditions for voles and because seasonal bottlenecks may affect population persistence. Population size, population growth rates, reproduction, recruitment, survival and movements, were monitored using mark-recapture methods in 8, 0.2-ha enclosures planted with alfalfa. The habitat within the enclosures was manipulated into 2 configurations of equal area, 1 large continuous patch (625 m��), and a mosaic of 25 small patches (each 25 m��), prior to the introduction of 12 pairs of animals/enclosure. I hypothesized that population size and growth rates, reproduction, recruitment, and survival would be greater for vole populations in continuous habitats than for populations in fragmented habitats. Additionally, I hypothesized that movements would be more restricted within fragmented habitat because the voles would perceive the area between habitat patches as a barrier. I did not detect significant differences between vole populations in continuous and fragmented treatments. However, populations residing in fragmented habitat showed higher variability over the study period. Populations in both treatments decreased throughout the winter period and all became extinct by the end of the study. Reproduction occurred only during the fall period, and there were no significant differences between treatments. Movements were not different between treatments, or between male and female voles, but movements did increase over time. Survival appeared to be higher for male voles in continuous habitat than in fragmented habitat, but female vole survival was similar between treatments. Survival was influenced by weather conditions, and predation. These results contrast with a previous experiment during the summer season, and indicate that seasonal bottlenecks may be important to consider when studying habitat fragmentation. Extinction of populations in both treatments demonstrates that small populations are extremely vulnerable to both environmental and demographic stochastic events. / Graduation date: 1997
24

Ground beetle (Coleoptera:Carabidae) communities along a successional gradient in southwestern Quebec and notes on the range expansion of introduced species

Mercado, Alida. January 2005 (has links)
Species diversity is influenced by disturbance in the environment. Ground beetles (Coleoptera: Carabidae) were used as a model taxon to study the effects of disturbance (i.e., time since disturbance) in different habitats along a successional gradient (agricultural fields, old fields, young forests and old forests). Seventy-three species (5139 individuals) were collected during both years of sampling, of which 9 species are introduced species and compose 64.8% of the total catch. In contrast to the predictions of the Intermediate Disturbance Hypothesis, diversity of ground beetles was higher in the agricultural fields and lowest in the old forests. The community composition, as seen with Nonmetric Multidimensional Scaling ordination, in the agricultural fields was the most distinct, while the difference between and among other habitats was less clear, possibly influenced by the introduced species present in the area. The introduced species collected had a significant influence in the total catch as they represented more than half of the total individuals collected and in the ground beetle community composition. The distribution of seven introduced species in Quebec was studied and compared to what was reported in 1975. Five species have a similar distribution, while the distribution range of Harpalus rufipes DeGeer has expanded south and Bembidion obtusum Audinet-Serville might have been dispersing northeast since its introduction.
25

Impacts of channelization on stream habitats and associated fish assemblages in east central Indiana

Lau, Jamie K. January 2005 (has links)
The objective of this study was to determine the relationship between fish assemblage structure and habitat in streams dominated by an agricultural landscape. Fishes from 20 natural and 20 channelized streams were sampled using electrofishing gear in East Central Indiana. Streams that had been channelized had a lower quality fish assemblage when compared to natural streams as measured by the Indiana V. Eastern Corn Belt Plain Index of Biotic Integrity (IBI). Stream habitat was evaluated using the Qualitative Habitat Evaluation Index (QHEI), which indicated that channelized streams had lower quality primarily due to a loss of heterogeneous habitat. Pearson correlation analysis relating ECB IBI and QHEI was positive and significant, and demonstrated that a reduction in riffle and pool areas associated with channelization was the most significant factor influencing the fish community. Furthermore, species lost when streams are channelized were predictable, and often represented environmentally sensitive species. The results of this study suggested that stream channel alterations have a negative and lasting influence on the fish assemblage which should be recognized prior to any stream development. / Department of Biology
26

Artificial avian nest predation in a Kansas tallgrass prairie

Goodman, James R. January 1999 (has links)
Several species of Neotropical migrant songbirds are experiencing declining population numbers. One of many proposed reasons for these declines is the dramatic loss of suitable prairie and grassland nesting habitat in the central United States. The Konza Prairie - a native tallgrass prairie preserve in central Kansas - was used to study possible edge-effect predation of artificial avian ground nests. Two Japanese quail eggs were placed in created artificial nests along transect lines from a wooded edge, a recently burned edge, and a control area. The rate of nest predation after seven days was 16.1 (±12.9%) for the control area. This was taken to represent the typical base level of artificial nest predation for the Konza Prairie. The predation rates for the wooded edge and burned edge were 21.9% (±7.4%) and 18.0% (±6.0%), respectively. These rates were not statistically different from each other or the base level rate of predation. The data suggests that no edge-effect predation occurs for artificial avian ground nests along wooded or burned edges in the Konza Prairie. Predation rates of natural bird nests may be different than these results suggest. It is recommended that future studies identify nest predators and study their foraging behavior near edge habitat. / Department of Natural Resources and Environmental Management
27

Breeding biology and habitat associations of cerulean warblers in southern Indiana

Register, Sarah M. January 2007 (has links)
The Cerulean Warbler (Dendroica cerulea), a once common summer inhabitant and breeder in southern Indiana, has declined at both local and continental population levels. Effects of specific silvicultural practices on the distribution and abundance of the Cerulean Warbler is unknown. During the summers of 2005 & 2006, Cerulean Warblers were surveyed within the Morgan-Monroe and Yellowwood state forests, as well as the Hoosier National Forest in southern Indiana. Three forest types were surveyed; unharvested reference sites were compared with single tree selection treatments and treatments where a combination of group and single tree selection was used. Mean bird abundance was estimated from bird surveys to determine if a correlation exists between silvicultural regimes and Cerulean Warbler abundance. Cerulean Warblers were located in all treatment types, with no significant differences in abundance between or among treatment types examined. These results suggest that uneven-age management practices, such as single tree and group selection harvesting, provide suitable breeding habitat for Cerulean Warblers.Knowledge of Cerulean Warbler (Dendroica cerulea) male pairing status based on song rates and frequencies, as well as familiarity with non-song vocalizations could be an effective management tool when studying this species. Cerulean Warblers were recorded throughout the breeding season, and 18 song variables were measured and compared between paired and unpaired males using Logistic Regression. Unpaired males had higher song rates and higher minimum frequencies than paired male counterparts. Female and fledgling call notes were also recorded and quantitatively analyzed. These analyses offer further understanding of intraspecific call functions of this species. / Department of Biology
28

Ecology and management of overabundant koala (Phascolarctos cinereus) populations

McLean, Natasha January 2003 (has links) (PDF)
Overabundant species may have considerable impacts on their habitat, other species and their own populations, thereby threatening biodiversity. Koalas (Phascolarctoscinereus) are overabundant at a number of locations in southeastern Australia due to low mortality and the inability of individuals to emigrate. This has led to the over-browsing of their food resources. Active management is required in order to prevent habitat degradation and the starvation of koalas particularly in populations without Chlamydia-infection, a disease that can cause infertility in females. Predictive population modelling is required if we are to understand the dynamics of the overabundant populations and investigate the consequences and effectiveness of different management strategies. Accurate data for the parameters that contribute to population growth, such as age structure, sex ratio, and age-specific schedules of mortality and fecundity, are therefore needed. In this study, the values of these parameters were determined for overabundant koala populations at Snake Island, Framlingham, Mt Eccles and French Island (Victoria). Data from additional populations were used to ascertain some parameters. These data were used to build stage-structured models to predict population growth of one Chlamydia-free and one Chlamydia-infected koala population.
29

Response of ant communities to vegetation clearing and habitat fragmentation in Central Queensland

Schneider, Kathryn Erica January 2004 (has links)
Habitat fragmentation involves the break-up of continuous native vegetation into remnant patches that are set in a matrix of altered habitat. The consequences of habitat fragmentation include the loss of original habitat which is followed by reductions in remnant size that increase edge effects and reduce habitat quality, and also increase the isolation of remnants from one another. Habitat fragmentation is an international environmental concern that also effects Australia. Over the last ten years Queensland has been responsible for some ninety percent of the clearing occurring in Australia, and as a result recorded some of the highest vegetation clearing rates in the world. / thesis (PhDEnvironmentalManagement)--University of South Australia, 2004.
30

Comparative phylogeography of five swallowtail butterfly species (Lepidoptera: Papilionidae) in South Africa : ecological and taxonomic implications.

Neef, Götz-Georg January 2014 (has links)
With current biota under constant threat of extinction, it is important to ascertain where and how biological diversity is generated and partitioned. Phylogeographic studies can assist in the identification of places and processes that indicate the origin and maintenance of biodiversity. Forest fragmentation has a big effect on local extinction and loss of genetic diversity of forest-restricted taxa, along with divergence and speciation of forest biota. This study aims to understand the effects of these processes on a number of forest-dwelling butterflies using a comparative phylogeographic approach. Mitochondrial DNA of five different Papilio species with different degrees of forest specificity was analysed using phylogenetic methods. In addition, the subspecific taxonomy of P. ophidicephalus was investigated using morphometrics of discal spots on the wings and nuclear DNA analysis along with mitochondrial DNA analysis. The results show that the forest-restricted species (P. ophidicephalus and P. echerioides) have more genetic structure and less genetic diversity than the more generalist species (P. dardanus, P. demodocus and P. nireus). This could be due to inbreeding depression and bottlenecks caused by forest fragmentation. As forest patches become smaller, the population size is affected and that causes a loss in genetic diversity, and increasing habitat fragmentation disrupts gene flow. The intraspecific taxonomy of P. ophidicephalus is far from revealed. However, this study shows there is evidence for the different subspecies when comparing morphological results and genetic results. From the evidence provided here it is suggested that P. ophidicephalus should be divided into two separate species rather than five subspecies.

Page generated in 0.1183 seconds