I used enclosures with exits for emigration to test whether house mice could regulate their numbers by emigration to two levels of resources. Exits had a water obstacle likley to be crossed only by true emigrants. Enclosures had excess food and water and the number of shelters was held constant. I introduced a pair of mice into enclosures about every other night, until no more would become residents. I ran 7 trials in single enclosures and 8 in double enclosures (2 single enclosures joined with a tunnel). The number of mice that stayed within a given size enclosure was consistant, and was 2.3 times higher in double enclosures than in single enclosures. Weather, predation, starvation, and disease did not act in any trials. My data support the contention that house mice can control their population numbers through spacing and emigration.

Encroachment of woody plants has occurred in many of the world's grasslands within the past 3 centuries. Mechanisms underlying these physiognomic shifts have not been adequately described. My objectives were to elucidate the roles of interference, herbivory, acorn maturation date and timing of precipitation on emergence and survival of Emory oak (Quercus emoryi Torr.) at lower treeline; and to evaluate how different frequencies of monitoring influence the results of demographic studies with woody plants. Seedling emergence was negatively affected by delays in precipitation and decreased soil moisture content. Seedling survival was negatively affected by overstory and understory interference and vertebrate herbivory. Most seedling mortality was attributed to desiccation. Woody plants should be monitored at least monthly to evaluate emergence and survival after one year. These results indicate that abiotic constraints are the primary factors structuring southwestern oak woodlands and savannas.

I monitored and recorded human activities in bighorn sheep habitat to determine the role of human activity in the decline of an indigenous population of bighorn sheep in the Pusch Ridge Wilderness, Santa Catalina Mountains, Arizona. I recorded hiker activity, sound levels, presence of dogs, and hunting activity in off-trail areas of bighorn sheep habitat from June 1995 to June 1996. Eighteen percent of hiker-groups entering the study area hiked off-trails in bighorn sheep habitat, and 8% were accompanied by dogs. Although I observed very little hunting activity in the area, noise disturbance may be a factor in the decline of the population. The cumulative affect of these and other activities probably contributed to the decline of the herd.

I examined the efficacy of a mitigation project in Avra Valley, Arizona that was established to provide wildlife access across the barrier created by the Central Arizona Project aqueduct. I monitored movements of 17 radiocollared desert mule deer (Odocoileus hemionus crooki) to determine if deer were using the corridor for access across the aqueduct and the 26 km wide valley. I also examined deer use of vegetation associations and proximity to landscape features. Four deer crossed the canal but stayed within 500 m of the crossing site. One deer traversed the valley via the corridor. Overall, 22.4% of deer locations were in the corridor land system. Female mule deer generally used the mesquite (Prosopis velutina)-burroweed (Isocoma tenuisecta) vegetation association more than it was available and the palo verde (Cercidium spp.)-mixed cacti association less than it was available. Female deer were generally closer to the CAP, housing developments, roads, and permanent water than random points.

<p>Oak (<i>Quercus</i>) forests in the Arkansas Ozarks have been important culturally, ecologically and environmentally for centuries. Historically these forests were fire dependent and dominated by oak species. In the past century, fire suppression and land management have caused these forests to densify. As a result, oaks are increasingly less abundant following disturbance in natural hardwood stands. Many applied ecological studies have explored methods and practices to maintain oak species in newly developing stands. This study attempted to link the mechanistic physiology of oak and non-oak reproduction to the applied ecological work. Varying stand conditions were generated in an undisturbed mature hardwood forest. Photosynthesis physiology was evaluated through direct and in-direct measures for six upland hardwood species in the Springfield Plateau of the Arkansas Ozarks. Environmental conditions, including sunlight canopy penetration, were significantly different based on treatment/slope position combinations. Corresponding differences in photosynthesis, development and abundance of hardwood reproduction were also significant across treatments, topographic position, and species. In conclusion, this study demonstrates that <i>in situ</i> measurements of photosynthetic performance are a valuable tool in predicting stand performance in oaks growing in their natural environment. </p>

<p> Streams along the Copper River Delta, southcentral Alaska, exhibit contrasting thermal and hydrologic variability associated with being primarily groundwater-fed (GWF) or surface water-fed (SWF). Groundwater-fed streams are predictable both thermally and hydrologically year round, whereas SWF streams are unpredictable and exhibit more variable thermal and hydrologic regimes. These differences may strongly influence aquatic insect community structure and secondary production. Four streams, two GWF and two SWF, were sampled twice monthly from late April 2013 through August 2013 and once seasonally in fall (September) and early winter (November). Aquatic insect community structure differed markedly in both hydrologic types. Taxa richness was significantly higher in SWF (43) than in GWF (39) streams and non-metric multidimensional scaling of community structure revealed two distinct groups corresponding to the two hydrologic types. Total secondary production was higher in GWF than in SWF streams with Orthocladiinae (Diptera: Chironomidae) representing 56% of insect secondary production in GWF streams. Results from this study have strong implications for aquatic insect communities in GWF and SWF streams because of differing susceptibilities of these systems to the potential effects of climate change. Due to their thermal stability, groundwater-fed streams are less likely to be impacted by climate change, whereas SWF streams are thermally variable and more likely to be influenced. The effects of altered aquatic insect communities can cascade to higher trophic levels such as salmon and ultimately impact stream ecosystem function and the ecosystem services they provide.</p>

We propose models for spatial binary data which incorporate covariate information, spatial interaction and spatial smoothness. We explore one of these models (Besag's autologistic model with covariates) in detail. We describe three methods for fitting the autologistic model: Besag's coding method (COD) and maximum pseudolikelihood method (MPL), and the Markov chain Monte Carlo (MCMC) method. We study the properties of the point estimates and confidence intervals obtained from the MCMC method. Some practical considerations in the use of the MCMC method, such as the choice of initial parameter values and the monitoring of convergence, are discussed. A simulation study comparing these three methods shows that the COD and MPL are very similar, but the MCMC method is superior to the others. We examine the use of MPL for preliminary model selection. In particular, we do the following: (1) We study the effectiveness of the Akaike Information Criterion (AIC) in the context of our spatial models. (2) We investigate the distribution of the reduction in deviance when adding an extra covariate. (3) We develop a test statistic to test whether a spatial interaction term is needed in our model. Finally, we apply the methodology developed in this dissertation to some data on the distribution of Florida plant species. / Source: Dissertation Abstracts International, Volume: 55-08, Section: B, page: 3398. / Major Professor: Fred W. Huffer. / Thesis (Ph.D.)--The Florida State University, 1994.

A series of experiments has demonstrated that selection of prey by predators was determined by prey accessibility rather than predator preferences. The caridean shrimp Toxeuma carolinense is one of the numerically dominant invertebrates in subtropical seagrass meadows. However, feeding analyses of dominant fishes have shown that few fish consume Tozeuma. Predator-preference experiments revealed that Tozeuma was underrepresented in the diet of Lagodon rhomboides, the dominant epibenthic predatory fish, and that large Tozeuma were preferred over small individuals. / I examined the influence of prey behavioral responses, microhabitat shifts and cryptic coloration on prey accessibility with a combination of field observations and laboratory experiments. Tozeuma's behavior and habitat choice were extremely similar in both the field and laboratory and were tightly coupled to the seagrasses Tozeuma inhabits. In the presence of predatory fishes, Tozeuma exhibited a significant increase in the proportion of time spent in certain rare behaviors and a significant decrease in certain common behaviors. Laboratory experiments revealed that Tozeuma's behavioral responses to predators resulted in a significant increase in shrimp survival and, thus, are adaptive. In addition, Tozeuma changed its microhabitat in response to predators; individuals that did not respond were often consumed. These experiments demonstrate that prey behavior and microhabitat choice reduced Tozeuma's accessibility to predatory fishes and hence, increased its survival. / Source: Dissertation Abstracts International, Volume: 44-11, Section: B, page: 3292. / Thesis (Ph.D.)--The Florida State University, 1983.

Past climate change and recent human activity have had major impacts on the distribution of habitats as well as the community and population genetic structure of the species occupying these habitats. In temperate zones, glaciation forced many taxa into southern refugia. In contrast, little is understood about the extent to which tropical taxa and habitats were affected by colder periods. In Southeast Asia, some argue that the tropical forest was replaced by savannah at the Last Glacial Maximum (LGM), whereas others suggest that the forest persisted. Studying population genetic and community structure of forest-dependent species in this region may shed light on which of these scenarios is most likely, as well as provide crucial information on the effects of recent habitat loss. To address these issues, I studied the genetic and community structure of forest-dependent insectivorous bat species in Peninsular Malaysia. Data collected at 22 sites indicated that species richness declined with latitude, consistent with post-glacial expansion of forest. To test this further, I undertook mitochondrial DNA sequencing of a widespread species, Rhinolophus affinis, and found high haplotype diversity, little phylogeographic structure and no demographic growth. These all suggest a long population history in the region with no post-LGM range expansion. Subsequent microsatellite analyses of R. affinis and the congeneric R. lepidus showed that genetic distance followed an isolation-by-distance model, and that allelic diversity was unexpectedly higher in the northern populations. Taken together, my results from the community and genetic analyses disagree with each other. These conflicts are perhaps best explained if observed clines in species richness pre-date the LGM. I conclude that there is little evidence of forest contraction in the LGM. The fact that the highest species diversity was detected in the south, which is experiencing the most forest loss due to human activity, has important conservation consequences.

acase@tulane.edu