Dissertations / Theses on the topic 'Biology, Ecology|Biology, Zoology'

Seabirds are ecosystem engineers with two major impacts on island ecosystems: they bring large quantities of marine nutrients to the terrestrial environment in the form of guano, carcasses, feathers, eggs, and spilled food, and they disturb the soil surface. Burrowing seabirds can denude the soil surface of all seedlings and leaf litter, plowing them under and loosening the soil. However, seabirds are colonial, and burrows are not even spaced over the surface of an island, producing spatial variability within a single island that might reveal how seabird activities control island ecosystem function.

In this dissertation I review seabird island ecology in general, focusing on how introduced predators have reduced seabird populations, interrupting seabird activities and altering island ecology. I then describe three studies designed to quantify the effects of seabirds on soil and plant properties within individual islands and compare these patterns across islands varying in seabird density, especially where seabirds have declined because of invasive rats (Rattus spp.).

I used geostatistics to quantify the spatial variance in seabird burrows and various soil and plant properties (including soil and leaf N) within six islands of low, intermediate, and high burrow density. I found that burrow density was not a good predictor at within-island scales, and though the variance of some soil properties (pH, soil δ¹⁵N, and soil compaction) peaked on intermediate islands as expected, variables reflecting the soil N cycle (net ammonification and net nitrification potential, NH₄ ⁺ and NO₃^-) continued to increase in variability on very high-density seabird islands. Ecosystem properties clearly responded to seabirds at different spatial scales, possibly because seabirds deposit guano at different spatial scales than they dig.

Using data within three rat-invaded and three rat-free islands, I used structural equation models to examine seabird influences on N cycling. I found some mechanisms that were constant across islands, such seabird-related decreases in soil water and pH, but other mechanisms differed between invaded and uninvaded islands, suggesting that rats manifest an alternative state for island N cycles, which may or may not be reversible.

Finally, I investigated whether plants can use ammonia (NH₃ gas) volatilized from seabird islands, measuring NH₃ concentrations across 10 islands and within a single island where I also experimentally manipulated plant N demand. Both rat-invaded and rat-free islands produced meaningful concentrations of NH₃ gas, and multiple plant species including Melicytus ramiflorus and Coprosma macrocarpa used it for up to 20% and 30% (respectively) of their total leaf N. Plant N demand modified NH₃ uptake, suggesting that plants located not on seabird colonies, but downwind, may benefit the most from this gaseous N source.

I suggest that future studies attempt to estimate thresholds of burrow density at which seabird-controlled ecosystem properties can recover from rat invasion.

The main goal of this study was to determine the thermal ecology of the small tree lizard Urosaurus ornatus in a Chihuahuan Desert landscape. The study site was located at Indio Mountains Research Station (IMRS), Hudspeth County, Texas. We obtained body temperature (Tb) data on 385 lizards collected from April 2007 to June 2014 during the active period using a cloacal thermometer. Additionally, we recorded air temperature (Ta) and substrate temperature (Ts) of lizard microhabitats at the time of capture, and the operative temperature of lizard models left in the sun and shade from May to September 2014. My results showed that the mean Tb for all adult lizards was 33.6 ± 2.8°C, with a range of 24.0 to 40.2°C. This average Tb was similar but lower than those found in other populations in Southwestern United States. The results indicated that U. ornatus at IMRS displays mostly a thigmothermic behavior. Thermoregulatory behavior of these individuals showed that U. ornatus is a thermoconformer on IMRS. There was no statistical difference in mean Tb between males and females or between non-gravid females. However, there was a significant difference between lizards found in the sun and lizards found in the shade. It is expected that rising global temperatures will influence this region and therefore will have an impact on the population of U. ornatus too; possibly affecting aspects such as time for feeding, reproducing, and of course thermoregulating. Thus, it is important for us to understand the thermoregulatory needs of ectothermic organisms as they are dependent on the direct environmental temperatures for survival, especially since many recognize that rapid global warming has already been activated by human misuse of natural resources.

Amphidromous species migrate between fresh water and the sea for larval development. Many caridean shrimps, especially Macrobrachium spp., are amphidromous, and some populations are found far-upstream within continental river systems. This project tested the hypothesis that populations of Macrobrachium ohione from the Atchafalaya and Mississippi Rivers are amphidromous.

In the laboratory, I tested the hypothesis that upstream populations of M. ohione have freshwater larval development. My results indicated that saline habitats are essential for M. ohione development, and larval mortality increased after 3-4 days of freshwater drifting. This provides indirect evidence that upstream populations have extended marine larval development.

Due to their limited freshwater survival, M. ohione must deliver larvae to the sea. Spatial-temporal analysis in the Atchafalaya and Mississippi Rivers reported an influx of reproductive-sized shrimps and females with near-hatching broods into coastal sites. This suggests that females are migrating downstream to hatch larvae in downstream habitats.

Stable isotope analysis indicated that the upstream juvenile migration originates from saline habitats. Video surveillance revealed that juveniles migrate throughout the night at an average speed of ∼ 0.56 km hr ^-1, and swimming speeds were related to the water velocity they swam against. From these results, I estimated that juveniles are capable of migrating to far-upstream habitats within their life span (1-2 years).

Lastly, I investigated how dams affect the juvenile migration, and tested juvenile migrant climbing abilities. This study reported greater densities of juveniles downstream of dams than upstream of dams, indicating the dams impede the juvenile migration downstream of Old River Control. Shrimp climbing studies revealed that at various inclinations and water velocities, ~ 52% of the shrimps were climbing the shrimp ramp and ~ 12% completed the climb. These results demonstrated juveniles can climb bypass structures with detectable water flows.

My findings suggest that M. ohione populations within the Mississippi River System are amphidromous, because they require marine larval development and long-distance migrations are conducted to and from the sea. This study may serve as a general model for migrations of amphidromous shrimps in comparable large rivers, and potentially contribute to freshwater shrimp conservation.

Humans introduce non-native plants to new areas at an increasing rate with the increased movement across the globe. These invasive species can become mono-cultures and extremely different from the native floral community. Amphibians, at the same time, are facing global declines with approximately one-third of all amphibians threatened or endangered. Due to the importance of amphibians as prey items for many vertebrates including small birds, mammals, and reptiles, and also predator controls over many invertebrates, including some pest species, the decline of amphibians has large implications for many environments. This study looks at a range of interactions between two invasive plants ( Typha angustifolia and Phragmites australis) and two native anurans (Lithobates clamitans and Lithobates catesbeianus).

As ecosystem engineers, plants form the basis of many communities, and sculpt the physical environment by adding complexity to the earth's surface. They also add chemical constituents either actively or passively too ward off other competitors. This change in the environment on both the chemical and physical level leads to complex possibilities for a changed plant community to impact the rest of the ecosystem, including amphibians. I focus on the physical changes by looking at behavior of amphibians in these invasive plant mono-cultures and non-invaded controls, and their appearance in invaded and non-invaded wetlands, both constructed and naturally occurring. On the chemical side of the matter, I monitor water chemistry measures in natural and constructed wetlands that are either lacking invasive plants or have a substantial presence of these plants, and correlate those measures with tadpole growth and survival.

Limited survey data and numerous anecdotal accounts indicate that the Common Nighthawk (Chordeiles minor) is experiencing population declines in Wisconsin. However, the magnitude of the decline is unclear because current avian monitoring efforts are not conducted at dusk when Common Nighthawks are most active nor do they specifically target urban areas such as cities and villages where Common Nighthawks are known to nest on flat graveled rooftops. New urban, crepuscular monitoring methods are needed in order to gain a better understanding of current Common Nighthawk demographics in Wisconsin.

The goal of this thesis was to conduct a baseline study using citizen science – based methodology to determine where Common Nighthawks persist in cities and villages in southeastern Wisconsin. The objectives of the study were to collect information on environmental factors, landscape features, and land cover types of potential importance to Common Nighthawks during the breeding season and then analyze the data collected to investigate correlations between each variable and Common Nighthawk occurrence at each survey point. The aim was to use the findings of the baseline study to inform current avian monitoring efforts such as the Wisconsin Nightjar Survey so that adjustments allowing for more effective monitoring of Common Nighthawks could be implemented in survey route placement and survey protocol.

Between June 7th and July 18th 2013, volunteers conducted 1,412 surveys at 494 points in 82 cities and villages within the Southeast Glacial Plains and Southern Lake Michigan Coastal ecological landscapes of Wisconsin. Common Nighthawks were detected in 98 surveys at 68 points in 32 cities and villages. On three different evenings at each point, volunteers conducted 10 – minute point counts in which they counted Common Nighthawks and described their behavior. During surveys, volunteers recorded the temperature ( ° F), estimated the moon phase, rated the sky condition, wind speed, noise, light pollution, and insect activity, and counted the number of potential Common Nighthawk predators (e.g. crows, gulls, raptors, and cats), and the number of Chimney Swifts. Volunteers also counted sources of artificial ambient light (e.g. street lights and stadium lights) and flat rooftops surrounding (100 meter buffer) the survey point.

The land cover surrounding each survey point (500 meter buffer) was analyzed from the National Land Cover Database (NLCD) 2011 using Geographic Information Systems (GIS). The number and total area of flat graveled rooftops surrounding each point (500 meter buffer) were estimated from aerial photos taken in 2011 using GIS. Results from statistical analysis of land cover classes suggests that in cities and villages, Common Nighthawks are more likely to be found in areas with higher percentages of impervious or built-up land cover. Agricultural land cover was the only land cover class that demonstrated a statistically significant negative correlation with Common Nighthawk presence. Strong, statistically significant positive correlations were found between Common Nighthawk presence and both the number of flat graveled rooftops and the total area of flat graveled rooftops.

Mann -Whitney U analysis of environmental variables recorded by volunteers suggests a statistically significant negative correlation between Common Nighthawk presence and percent moon illumination. A statistically significant positive correlation was also found between Chimney Swift (Chaetura pelagica) , counts and Common Nighthawk presence. A statistically significant positive correlation was also found between Common Nighthawk presence and the two landscape features measured by volunteers (100 meter buffer) – the number of flat rooftops, and the number of sources of artificial ambient light.

Like many imperiled fishes, the endangered Pahrump Poolfish ( Empetrichthys latos latos) is managed in ex situ refuges. I investigated life history characteristics of females from two such populations at Lake Harriet and Shoshone Stock Pond. Lake Harriet is a relatively large lake with low fish densities located at relatively low elevation and low latitude, while Shoshone Stock is a small pond with high fish densities at a higher elevation and latitude. Females from the Lake Harriet population were larger, and had greater fat content, reproductive allocation, and ‘clutch’ size than females from the Shoshone Pond population. This divergence, which occurred in three decades, may result in a phenotypic mismatch if the fish are used as a source for restocking their native habitat or stocking new refuges.

Poolfish conservation may require establishing new populations; however, many sites are inhabited by non-native fish and/or other protected fish species. Thus, managers may wish to consider establishing multi-species refuges that may even already include undesirable species. I established experimental communities that included allopatric and sympatric communities of Poolfish, Amargosa Pupfish (Cyprinodon nevadensis), and invasive Western Mosquitofish (Gambusia affinis). Pupfish persisted in sympatry with both poolfish and mosquitofish, but had higher juvenile production when maintained in allopatry. By contrast, poolfish juvenile production was high in allopatry, but virtually absent in the presence of other species.

To evaluate the generality of these findings, I established experimental allopatric and sympatric communities of poolfish or pupfish with mosquitofish from two populations that differed in body size: Garrett mosquitofish were approximately twice the mass of Wabuska mosquitofish. Poolfish juveniles had high survival in allopatry, but produced virtually no juveniles when sympatric with either of the two mosquitofish populations. Pupfish juvenile survival was higher in allopatry than sympatric with Garrett mosquitofish, which in turn was higher than sympatric with Wabuska mosquitofish. These results were consistent with the earlier experiment suggesting that poolfish were functionally extirpated but pupfish maintained substantial production in the presence of mosquitofish. These findings suggest that poolfish should be maintained in single species refuges, but that multi-species refuges may protect imperiled pupfish species.

The white shrimp Litopenaeus setiferus is harvested throughout its range in the western Atlantic Ocean and is particularly important in supporting a commercial fishery in the northern Gulf of Mexico (nGoM) concentrated in Texas and Louisiana. Mortality rates of young (juvenile) white shrimp in estuarine nursery areas may have a large effect on the adult population. Understanding the temporal and spatial variation in mortality rates and other population parameters (i.e., density, growth rate, and secondary production) is important for the management of white shrimp in determining how estuaries function as nursery areas and can also be useful in identifying coastal habitats that best support white shrimp populations. My objective was to examine and describe the population dynamics, with a focus on mortality, of juvenile white shrimp populations in Sabine Lake, an estuary of the nGoM. I estimated density, growth, mortality, and secondary production in three areas along the estuarine salinity gradient. Most of these metrics were generally higher in areas of high salinity and total secondary production was relatively high in all three areas. Approximately half of the potential fish predators collected in my study area had preyed upon juvenile penaeid shrimps based on an examination of fish gut contents. Given their abundance within estuaries of the nGoM, these fish predators may have a large impact on populations of juvenile white shrimp. Mortality rates of juvenile white shrimp estimated with mark-recapture and length-frequency data were relatively similar to each other and within the range of the few values previously reported. Two commonly used age-based mortality estimators originally developed for fishes provided reasonably unbiased mortality rates for juvenile penaeid shrimps, although both estimators provided relatively high biased estimates at the lowest mortality rates considered.

Animals that live in groups face a dual challenge of effectively exploiting their environment while at the same time maintaining cohesion with other group members. Maintaining cohesion requires group members to come to consensus about when and where to move, despite the fact that they may not always agree. In this thesis, I investigate how individuals in groups make movement decisions, and how these individual decisions scale up to group-level properties. Using a laboratory experiment with golden shiners (Notemigonus crysoleucas ), I first investigate the interaction network over which information spreads, finding that decisions are better predicted by whom individuals can see rather than whom they are close to, with potential consequences for the global spread of information (Chapter 2). I then investigate collective movement behavior in the wild using high-resolution GPS data from members of a troop of olive baboons (Papio anubis). I first show that baboons are consistent in the spatial positions they occupy within the group, and that the observed patterns may be understood based on a very simple mechanism by which individuals maintain cohesion with different numbers of their neighbors (Chapter 3). By quantifying how group members move relative to one another, I then show that baboon movement decisions are consistent with a shared decision-making process, rather than despotic leadership by dominant individuals, and that the patterns of decision-making are consistent with simple models of collective motion (Chapter 4). Finally, by incorporating a fine-scale, three-dimensional reconstruction of the habitat through which the baboons move, I show that habitat structure, in addition to social factors, also exerts an important influence on individual movement decisions, resulting in changes in the emergent structure and movement of the group (Chapter 5). Taken together, these results highlight that by combining high-resolution animal tracking, remote sensing, and analytical methods, we can begin to extend our understanding of collective animal movement from laboratory studies to complex animal societies living in the wild.

Community ecology investigates questions related to the density, growth/decline and movements of species over time in given geographical regions. This study investigated similar questions regarding communities of endemic bat species in Connecticut. White-nose syndrome (WNS) has recently killed millions of bats in New England, yet few large-scale conservation efforts have occurred in Connecticut and few data have been published on the status of Connecticut bats post-WNS. This study aimed to: 1) survey bats persisting in WNS regions to document whether changes have occurred in species biodiversity, richness, distribution and habitat use; and 2) measure seasonality effects from summer through pre-hibernal months. Bat presence and activity were recorded using bat detectors set in grassland and forested habitats, near bodies of water and near anthropormorphic and geologic structures across Connecticut. Bioacoustics data have been analyzed by using Sonobat^© software. Combined, these data show that bat activity varies significantly across habitat type (p = 0.02) and over seasons (p = 0.05). Additionally, these data provide insight regarding relationships between individual species, and clumped species groups, with habitat types and across seasons. Ultimately, these data show how bat communities have changed over time in a post-WNS environment. Combined, these data can help drive future wildlife conservation, outreach, education and management practices.

Prey species defend themselves behaviorally and morphologically, and often utilize varied antipredator strategies against dissimilar predator types (i.e. terrestrial vs. aerial). Striped skunks (Mephitis mephitis) spray noxious secretions at predators and advertise this danger with deterrent behaviors and black-and-white aposematic coloration. Evidence suggests skunks are effective at deterring terrestrial mammalian predators but are vulnerable to aerial predators; how skunks assess the risk posed by different predator types, however, has not been examined empirically. I recorded the behavioral responses of skunks to audio playbacks of coyotes and great horned owls (the primary terrestrial and aerial predators of skunks, respectively), and peregrine falcons and white noise as controls, as well as to a visual remote controlled model. Skunks engaged in vigilance and running away more often in response to owl vocalizations, suggesting skunks perceive owls as more threatening relative to coyotes. Skunks were more likely to foot stomp and run away in response to the remote controlled model compared with coyote vocalizations, implying visual cues were perceived as more risky than audio cues. This study elucidates how a well-defended mammal can determine which perceived threat is most risky and alter its behavior when its main defense strategy is not successful against all predator types.