Dissertations / Theses on the topic 'Ecology|Zoology'

Habitat loss and fragmentation (hereafter fragmentation) are some of the largest conservation threats today and will increasingly put pressure on species in the future. Maintaining population connectivity helps mitigate the negative effects fragmentation has on vulnerable species, especially those of conservation concern. In this dissertation, I elucidated the movement ecology of black-capped vireos by 1) estimating and characterizing patterns of gene flow, 2) examining the relationships between land cover and connectivity, and 3) simulating how future populations respond to climatic landscape change. I additionally characterized potential biases in family-wise error rate correction across population genetic studies, a correction important for evaluating the genetic structure of a species. I genotyped 343 individuals at 12 microsatellite loci in and around Fort Hood, Texas, which houses the largest and most stable breeding population. To characterize patterns of gene flow among black-capped vireo populations, I analyzed genetic differentiation, migration rates, number of migrants and parentage. Across these independent analyses, I found evidence for asymmetrical movements from Fort Hood to the other central Texas sites consistent with source-sink dynamics and findings from demographic studies. I used gravity models to test the relationships among Euclidean distance, land cover types (water, developed, forest, scrub, open, agriculture and wetlands), brown-headed cowbird control, and genetic similarity. My findings indicate that wetlands, likely via riparian areas, may be acting as corridors among populations. Better understanding of what factors influence connectivity will be crucial for maintaining connectivity when species of conservation concern are threatened by fragmentation.

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.

Life-history research explores how environmental variation and physiological constraints shift the energy allocation decisions to competing functions of the body among individuals and populations. Variation in the energy available across the environmental landscape is of particular interest as it dictates the amount energy available for organisms to acquire and allocate to their life-history. Additionally, individuals vary in their ability to capture and assimilate energy from the environment. This dissertation seeks to understand how environmental variation in energy availability and physiological constraints of attaining this energy shape allocation decisions among individuals and populations. I examined diamond-backed watersnakes (Nerodia rhombifer) from five populations that differed in their access to energy resources of prey. I compared measures of reproduction and growth to detect the presence of differential allocation decisions. I tested whether differences in allocation among individuals and populations arose as a constraint of their ability to assimilate energy resources in the environment, or as a function of the variation in prey characteristics across the landscape. Lastly, I measured how variation in reproductive investment may limit energy acquisition among individuals.

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.

Apex predators are important indicators of ecosystem health, but little is known about the population structure of Bigg’s killer whales ( Orcinus orca; i.e. ‘transient’ ecotype) in western Alaska. Currently, all Bigg’s killer whales in western Alaska are ascribed to a single broad stock for management under the US Marine Mammal Protection Act. However, recent nuclear microsatellite and mitochondrial DNA analyses indicate that this stock is likely comprised of genetically distinct sub-populations. In accordance with what is known about killer whale vocal dialects in other locations, I sought to evaluate Bigg’s killer whale population structure by examining the spatial distribution of group-specific call types in western Alaska. Digital audio recordings were collected from 33 encounters with Bigg’s killer whales throughout the Aleutian and Pribilof Islands in the summers of 2001-2007 and 2009-2010. Recorded calls were perceptually classified into discrete types and then quantitatively described using 12 structural and time-frequency measures. Resulting call categories were objectively validated using a random forest approach. A total of 36 call types and subtypes were identified across the entire study area, and regional patterns of call type usage revealed three distinct dialects, each of which corresponding to proposed genetic delineations. I suggest that at least three acoustically and genetically distinct subpopulations are present in western Alaska, and put forth an initial catalog for this area describing the regional vocal repertoires of Bigg’s killer whale call types.

Western Screech-Owls (Megascops kennicottii) are small, nocturnal owls that occur year-round throughout most of the Trans-Pecos region in West Texas, and are associated with deciduous woodlands and riparian habitats. Roadside nocturnal callback surveys, were established along well-defined trails within the Davis Mountains Preserve, and took place from May until August for two years to ascertain the relative abundance of Western Screech-Owls within the property. Abundance indices (birds detected/visit/station) were calculated for both survey seasons. Radiotelemetry was incorporated to determine certain life-history information, while habitat was characterized from both survey and telemetry sites. Occupancy models with detection probabilities were created using Program PRESENCE based on collected presence-absence data. Based on criteria for suitable screech-owl habitat previously defined in the literature, several models were also generated within ArcGIS to compare with the field data and to help predict areas of occupancy within the property. Owl abundance averaged 1.05 owls/point in 2013 and 0.82 owls/point in 2014. Six owls were marked during the study, and 3 of 6 locations were confirmed as daytime roosting sites. Statistically, there were no significant differences between occupied survey sites and telemetry sites, with only the percentage of canopy being significantly different with a mean difference of 9.32, t₄₂ = -2.36, p = 0.023. Both owls and transmitters were discovered in dense juniper-oak mottes on north-facing slopes, indicating a preference for dense, short, closed canopy areas for roosting. Overall vegetative ground cover for the two seasons averaged 54% and 48%, respectively. It was concluded that none of the included covariates in the models influenced either occupancy or detection probabilities, though detectability demonstrated an overall trend based on time of night. GIS models did not reveal any variable that strongly influenced owl occupancy but did correspond with results from previous literature.

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.

Seabird populations are declining worldwide. Two major causes of decline are non-native predators and seabird (indirect or direct) overexploitation; these have been suspected but not assessed in the Caribbean region, including in the southern Grenadine islands. Using cameras, questionnaire surveys, and nest monitoring, I explored the potential of invasive predator presence and seabird harvest in affecting nesting productivity of five species in five uninhabited islands during 2014–2017. Overall, nesting productivity increased (n = 567 nests) despite the confirmed presence of non-native rats. However, my survey of Grenada residents (n = 32 responses) and physical evidence found on the islands (e.g., gun shells) suggest that seabird harvest still occur and may be responsible for previous declines. Additionally, most contributors to harvest did not seem aware of any seabird-protective laws. Therefore, I recommend establishing a community-based monitoring program that educates and empowers residents to prevent seabird harvest and continue nest monitoring.

Coyote distribution and habitat use, diet and foraging behavior, and space use patterns were investigated in the greater Detroit area of southeastern Michigan. We found evidence of coyotes on 24 of 30 (80%) suburban and 7 of 11 (64%) urban plots. Overall fifty-eight percent of coyote evidence was found within edge habitats, with den sites and tracks the only types of evidence found strictly in interior habitats. Land cover around evidence points included more wooded land cover than expected in suburban areas, suggesting the importance of tree cover for coyote occupancy, and more open space and wooded land cover than expected in urban areas, highlighting their avoidance of heavily populated areas. Coyote diet was assessed through identification of remains of food items recovered in coyote scat. White-tailed deer, eastern cottontail rabbit, and small rodents were the most consumed prey in both urban and suburban areas. Coyote consumption of white-tailed deer biomass was 7.2% greater than expected in suburban areas and 10.0% less than expected in urban areas and the difference was significant (P < 0.004). More white-tailed deer, raccoon, and woodchuck biomass was consumed compared to other studies, likely due to high use of road-kill. In suburban areas, coyote selection for road-killed white-tailed deer was positive regardless of white-tailed deer or rabbit abundance. Coyotes in urban areas used a foraging strategy that incorporated both prey selection and switching, with no strong discernable pattern. Radio-telemetry technology was used to gather relocations of coyotes for analysis of home range and cores areas frequented by coyotes. Smaller home ranges were made up of greater proportions of urban land than natural land cover, although there was variation. Core areas were dominated by relatively large patches of natural land cover and had greater connectivity compared to home range areas. Radio-telemetry data suggested that coyotes were selective in their use of space, avoiding urban land in favor of natural land cover.

Recreational activities have been shown repeatedly to have negative effects on wildlife. Appropriate management to minimize the effects of such activities, especially to species of conservation concern, is therefore a goal of utmost importance. This study characterized the visual ecology and anti-predator behaviors of the California Towhee, Melazone crissalis, in the context of parameterizing models for estimating the size and shape of wildlife buffer areas. Contrary to expectation, explicitly incorporating species-specific data on the towhee's visual system and individual-level data on physiological condition and life history traits did not significantly alter estimated buffer area requirements relative to models based solely on behavior. Similarly, towhees exhibited no differences in average alert or flight initiation distances with respect to direct versus tangential approaches. In contrast, data collected across a variety of habitat types in the field suggest that minimum approaching distances for the birds were highly dependent upon local vegetation parameters that included percent cover, density, and height. In general, more vegetative cover was associated with smaller alert and flight initiation distances. Together, these results suggest that a simple management solution (e.g., calculating buffer areas based on mean alert distance alone) may be adequate for this species, but that local habitat conditions will need to be taken into consideration for optimal management solutions.

This thesis qualifies functional and ecological aspects of mucus trails deposited by Elimia potosiensis collected from the Meramec River. Freshwater snails are most often recognized for their significant role in river and stream ecosystem function as primary consumers and prey items. However, their form of locomotion is the most energetically expensive found in the animal kingdom. Found in large numbers and densities, E. potosiensis is capable of coating large swaths of substratum with carbohydrate- and protein-rich mucus. This has the potential to affect ecosystem function at the most basal trophic level both energetically, by contributing nutrients and energy to the surrounding water body, and functionally, as a sticky substance to which microheterotrophs become adhered.

In marine studies, researchers have found that bacteria can readily degrade gastropod mucus and that it can act as the basis for biofilm formation. There have also been studies that show unique employment of energy saving strategies by snails that use their trails to capture food items and to reduce production needs by following trails laid by conspecifics. Very little research has been conducted on freshwater gastropods. This study is the first to focus solely on the ecological and functional aspects of freshwater snail mucus.

For this study, collections of E. potosiensis were made from a single site along the Meramec River to qualify the effect deposited mucus has on the adherence of microalgae and its potential for formation of biofilms. Overall, mucus-coated surfaces significantly more particles in flow than non-coated surfaces. The water velocity at which a trail is laid was not found to have an affect on the thickness, adhesive ability or persistence of a trail. However, the water velocity in which a trail is incubated in stream does have effect on the adherence rate of a trail. In this study, it was found that this was most likely due to the fact that trails in high water velocity come into contact with more particles during a given period of time due, in part, to its higher carrying capacity.

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.