Browsing by Subject "population dynamics"
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Item Behavioral ecology and conservation of large mammals: historical distribution, reintroduction and the effects of fragmented habitat(2009-05-15) Gilad, OranitConservation biologists have used reintroduction as a method to reestablish extirpated species in their native habitat. Three important aspects of a successful reintroduction effort include: (1) a habitat suitability study of the reintroduction area, including effects of migration corridors; (2) identification of possible predators of the reintroduced species; and (3) a post-reintroduction assessment including an evaluation of the species' population dynamics. In this study I examine the suitability of Guadalupe Mountains National Park (GUMO) as a reintroduction area for desert bighorn sheep. The study used landscape metrics to compare GUMO to a nearby mountain range that is currently supporting an estimated population of 400 bighorn sheep. This study identified migration corridors for bighorns throughout the region and evaluated mountain lion (a potential predator of bighorn sheep) numbers either residing in or passing through the park between the years 1997 to 2004. Results on the studies in GUMO revealed 15,884 ha of suitable habitat for bighorn sheep and provided evidence of migration routes between GUMO and neighboring mountain ranges. In terms of potential predators, a minimum of 32 resident and/or transient mountain lions occurred in GUMO over a seven year period, and a minimum of 15 cats used the park in 2002. Based on estimates of individual home range of males and females, GUMO should be able to support four to five individuals. The genetic data indicates a high number of transients or perhaps an unstable population of mountain lions that may be the result of intense hunting pressure of cats in Texas. Finally, my study simulates parameters of the population dynamics of a different species, the Arabian oryx that was reintroduced as three separate populations to the Israeli Negev between 1998 and 2005. I simulated population growth and the effect of migration corridors on species persistence. Results suggest that migration corridors are essential for a self-sustaining viable metapopulation under current natality rates. In the event that natality rates increase (as was evident in a reintroduced population of Arabian oryx in Oman), metapopulation can reach viable size with only two of the release sites (open, flat terrain) connected by migration corridors.Item Modeling aspects of the ecological and evolutionary dynamics of the endangered Houston toad(2009-05-15) Swannack, Todd MichaelThe goal of my dissertation was to describe the dynamics of a group of Houston toads located at the Griffith League Ranch (GLR), Bastrop County, Texas. My research included using statistical modeling to predict activity and abundance, mark-recapture techniques to estimate survivorship, and simulation modeling to explore the impacts of the difference in age at first reproduction and to project the future dynamics of the population at the GLR. From 2001 ? 2005, 225 individual Houston toads (199 M : 26 F) were captured using two methods: breeding pond surveys and drift fences. Houston toads were neither caught equally among capture methods, nor across years. Toad activity was mostly confined within their breeding season, and activity was not continuous. A logistic regression indicated activity depended on time of year, mean precipitation, mean minimum daily temperature, and mean percent lunation as well as two-way interactions with moon-phase and other variables. Abundance depended on time of year, current precipitation, minimum temperature, and two-way interactions between time of year and the other two variables. Twenty-one of the 199 males (10.5%) and no females were recaptured among years. The probability of male survival was estimated using program MARK. Eight of 16 candidate models were supported and all but one contained precipitation as a covariate, indicating precipitation is important for Houston toad survival. Survivorship estimates varied from 0.1 to 0.41. The sex ratio was significantly male-biased. The odds of catching females in traps were 3.5 greater than capturing females in a pond, while the odds of capturing males in a trap were 0.28 compared to ponds. Results from a simulation model indicated the sex ratio is biased because of the difference in maturation times between males and females, coupled with high juvenile mortality. Results from an individual-based, spatially-explicit, stochastic simulation model, indicated a relatively low probability (~ 0.013) of B. houstonensis going extinct at the GLR within the next 10 years. Emergent properties of the model were similar to results observed in the field or reported in the literature. The model also identified that dispersal of Houston toads should be a future research priority.Item Regional Climate Effect on Population Abundance of Major Duck Species in Interior Plains of Canada(2013-05-06) Sun, MengmengPopulation dynamics of ducks is a complex process influenced by both biotic and abiotic factors, and good understanding about the mechanisms behind this process is needed not only for the management of duck harvest but also for the conservation of wetland, which is under threat in the face of land change and climate warming. Basic time series analysis techniques, such as correlogram, partial correlogram and periodogram, cluster analysis and partial least squares regression (PLSR) are applied to the long-term breeding population data gathered by Waterfowl Breeding Population and Habitat Survey and monthly weather data from Environment Canada in order to explore the pattern in the duck abundance data and the effect of local weather on population dynamics of ducks. Results of above analysis show that the duck abundance of previous years has short but strong correlation with the duck abundance of following years suggesting a large part of variability in duck abundance is explained by the abundance of previous years, especially that of last year. There is also clear periodic pattern in the duck abundance data, but the length of the cycle varies both for duck species and ecozones suggesting separating duck species and ecozones for analysis is necessary. The effects of weather on duck populations appear weak or absent in most PLSR models; this is consistent with previous studies. More detailed information, such as age structure of the duck populations and interspecific interactions, will be needed for future modeling. Among the small number of PLSR models exhibiting the weather effect, results suggest potential mechanisms, such as the impact of weather on recharge and discharge of wetland basins and nest failure caused by flooding.Item The Texas Quail Index: Evaluating Predictors of Quail Abundance Using Citizen Science(2009-05-15) Reyna, Kelly ShaneAnnual abundance of northern bobwhite (Colinus virginianus) and scaled quail (Callipepla squamata) fluctuates drastically in Texas, which complicates a quail manager?s ability to forecast quail abundance for the ensuing hunting season. The Texas Quail Index (TQI) was a 5-year citizen-science project that evaluated several indices of quail abundance and habitat parameters as predictors of quail abundance during the ensuing fall. I found that spring cock-call counts explained 41% of the variation in fall covey-call counts for all study sites in year 1?4, and 89% of the variation in year 5. Further investigation revealed that year 5 was a drought year and had a significantly lower percentage of juveniles in the hunter?s bag. These results suggest that during drought years, fall quail abundance is more predictable than during non-drought years and that low breeding success may be the reason. If these data are correct, quail managers should have a better ability to predict the declines of their fall quail abundance in the dry years. The TQI relied on citizen scientists (cooperators) to collect data. Since most (66.1%) cooperators dropped out of the program, and <8% of all data sets were complete, I surveyed the cooperators by mail to determine the rate and cause of cooperator decline and to identify characteristics of a reliable cooperator (i.e., one that did not drop out of the study). I found that cooperator participation declined earlier each year for year 1?4, and that year 5 demonstrated a steady trend with the least amount of cooperators. Most respondents who dropped out (61.5%) reported their motive for leaving was that it was too time consuming. I found no difference in mean cooperator demographics, satisfaction, or landownership goals between those respondents who dropped out and those that did not. However, 38% of those who dropped out were not completely satisfied with communication from TQI coordinators compared to only 15% of those who did not drop out, indicating that communication, or perhaps overall volunteer management, might have been improved. Future studies should maintain better communication with participants, require less time, and provide an incentive for retention.