<p> Stocking of trout into naturally fishless water bodies in the mountains of western North America has reduced populations of many native species in those systems, with benthic aquatic invertebrates being particularly impacted. Although bats are known consumers of emergent aquatic insects, almost no studies have focused on how changes to these prey populations at lakes subsequent to trout stocking could affect them. This study assessed bat activity, foraging activity, and foraging rate at nine feature-matched pairs of stocked and unstocked high elevation lakes in the central Sierra Nevada mountains in an effort to determine which provide higher quality foraging habitat for bats. Bats in the 25 kHz and 50 kHz echolocation call categories showed little to no behavioral change between lakes with trout and lakes without. In contrast, bats in the 40 kHz group had higher levels of activity at stocked lakes, which may indicate that at those lakes bats are consuming numerous small insects. If this is the case, it could represent a cost to those bats due to the lower energetic return of small prey items compared to the preferred prey species. </p>

<p> 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 (<i> Typha angustifolia</i> and <i>Phragmites australis</i>) and two native anurans (<i>Lithobates clamitans</i> and <i>Lithobates catesbeianus</i>). </p><p> 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. </p>

<p> I sampled macroinvertebrates in May, July, and October 2008 in Uvas Creek, a reservoir-regulated stream in south Santa Clara County, California, to assess what factors (including canopy closure, turbidity, and stream flow) downstream of the reservoir were related to food availability for rearing juvenile Steelhead (Oncorhynchus mykiss). I found benthic and drifting macroinvertebrate biomass was considerably greater during most months in the more open-canopied two sites in the downstream reach as compared to the densely shaded, more turbid and silty two sites in the upstream reach. Abundance of important drifting aquatic invertebrates in May (chironomids, simuliids, and baetids) was proportional to benthic abundance, but large hydropsychids were relatively scarce in the drift. Terrestrial drift abundance correlated with canopy density, but differences were small compared to the substantial increase in aquatic drift in sunnier sites. Thinning of the canopy at select locations and reduction of sediment input to Uvas Creek and its tributaries due to vineyard and other operations could increase benthic macroinvertebrate productivity in the upstream reach, which would increase food availability for rearing juvenile Steelhead.</p>

<p> Despite reductions in species diversity, few studies in wetlands investigate the relationship between biodiversity and ecosystem function (BEF). My research explores the BEF relationship in a recently restored salt marsh in Long Beach, California. I hypothesized that: (1) increasing plant diversity would result in higher primary productivity and decreased recruitment of native salt marsh plants, (2) observed variation in responses would be correlated with species-specific variation in individual demographic parameters, and (3) variation in demographic parameters and resulting ecosystem processes would be correlated with functional traits. I found that while survival over one year was correlated with elevation, overall percent cover and recruit species richness were positively affected by diversity. Performance patterns reveal variation by species in photosynthetic rate, leaf mass per area and chlorophyll a/b ratios. After one year, I found that the overall diversity patterns were driven by selection effect compared to complementarity.</p>

Nest association, a symbiotic reproductive strategy in North American minnows, has long captured the interest of scientists because of brilliant nuptial coloration of associates. Subgenus Hydrophlox of genus Notropis historically contained nine species, all of which engage in nest association with varying levels of host specificity. To understand evolutionary trends in reproductive behavior within this group, I first tested the monophyly of Hydrophlox using multiple molecular genetic markers, and analyzed representative specimens from all putative members, and multiple populations of each species. I found that Hydrophlox is composed of five nominal taxa, Notropis rubricroceus, N. chiliticus, N. lutipinnis, N. chlorocephalus, and N. chrosomus, and also contains at least two undescribed forms within N. lutipinnis and N. chlorocephalus. Although natural hybridization is not uncommon among nest associates, some of the previously undescribed diversity in Hydrophlox is threatened by hybridization between N. chiliticus and N. chlorocephalus in the Catawba River. In one population, 40% of the individuals are hybrids and introgression is common. This is a potential threat to the genetic integrity of N. chlorocephalus, a species heretofore considered robust and secure from a conservation standpoint Members of the subgenus Hydrophlox are less diverse in their host preference than previously thought. Presence of nuptial males over a nest has been viewed by many as evidence of egg deposition. I observed 29 spawning aggregations throughout the range of three nest associates, and I was able to identify eggs collected from a subset of nest sites. Spawning of N. baileyi, N. rubricroceus, and N. chlorocephalus is strongly associated with Nocomis spp. Notropis rubricroceus nuptial males aggregating over Semotilus atromaculatus nests did not successfully spawn, likely a result of highly aggressive behavior by the resident male S. atromaculatus. Additionally, I frequently observed Campostoma spp. modifying Nocomis mound nests, a behavior not previously reported, and which may have led some to conclude Campostoma were hosts of spawning aggregations. A literature review, combined with these data, suggests Hydrophlox are obligate nest associates of Nocomis species. Comparisons of monophyletic clades of nest associates, such as Hydrophlox, and clades with no or few associates are now possible. Divergence times, habitat requirements, and community structure may now be compared, and will illuminate our understanding of this fascinating reproductive behavior / acase@tulane.edu

<p> Within Mediterranean ecosystems, conservation and restoration action is becoming increasingly necessary to preserve biological diversity within these working landscapes. Many of these systems have been managed to increase forage production through the removal of canopy trees and shrubs, resulting in understories dominated by herbaceous species. In California, woody plant regeneration can be constrained by exotic annual grasses, particularly in the presence of grazing. <i>Quercus douglasii</i> and other oak species are known to indirectly facilitate and provide spatial refuges to native plants through competitive suppression of herbaceous productivity. Mature trees can also compete with understory recruits and shrub species, limiting their occurrences to interstitial canopy gaps and resulting in reduced competition for resources. This study surveyed the overstory composition of 34 study plots at the Sierra Foothill Research and Extension Center to determine the effects of tree canopies on the occurrence and distribution of native woody species in the undergrowth. Because other studies have shown safesites, which include rock outcroppings, woodpiles, and nurse plants to facilitate woody plant establishment in this system, the microsites containing individual plants were recorded to determine the distribution of different woody species. Multivariate regressions showed that understory plant richness and abundance increased with higher levels of canopy cover, suggesting that mature trees play a role in maintaining understory diversity. The majority of stems were found growing directly underneath the canopy, with only one species established primarily in interstitial areas. Restoration strategies can utilize the natural distributions of woody species in the understory in order to increase the survival of plantings while continuing to manage these systems for multiple ecosystem services.</p>

<p> My research was focused on greater sage-grouse (<i> Centrocercus urophasianus</i>; hereafter "sage-grouse") nest-site selection, nest success, and hen survival in relation to avian predators. The trade-off between using habitat and avoiding predators is a common decision for prey species including sage-grouse. In Chapter 2, I compared avian predator densities at sage-grouse nest and brood locations to random locations. Sage-grouse were located where densities of small, medium, and large avian predators were 65-68% less than random locations. </p><p> The effects of anthropogenic and landscape features on habitat use of sage-grouse hens have not been evaluated relative to avian predator densities. In Chapter 3, I compared anthropogenic and landscape features and avian predator densities among sage-grouse locations (nest, early-brood, late-brood) and random locations. I found sage-grouse hens chose locations with lower avian predator densities compared to random locations, and selected locations farther away from anthropogenic and landscape features. </p><p> Depredation of sage-grouse nests can be an influential factor limiting their productivity. Predator removal has been simultaneously proposed and criticized as a potential mitigation measure for low reproductive rates of sage-grouse. In Chapter 4, I hypothesized that sage-grouse nest success would be greater in areas where Wildlife Services lowered common raven (<i> Corvus corax</i>: hereafter "raven") density. I found that Wildlife Services decreased raven density by 61% during 2008&ndash;2011 but I did not detect a direct improvement to sage-grouse nest success. However, sage-grouse nest success was 22% when ravens were detected within 550 m of a sage-grouse nest and 41% when no raven was detected within 550 m. In Chapter 5, I assessed interactive effects of corvid densities relative to anthropogenic and landscape features on sage-grouse nest success. I found that sage-grouse nest success was positively correlated with rugged habitat. </p><p> Survival of breeding-age birds is the most important demographic parameter driving sage-grouse abundance. In Chapter 6, I evaluated the effect of raptor densities, proximity to anthropogenic and landscape features, and hen behavior on survival of sage-grouse hens. I found that sage-grouse hen survival was negatively correlated with golden eagle (<i>Aquila chrysaeto</i>s) density, proximity to anthropogenic and landscape features, and hen parental investment (nesting and brood-rearing).</p>

<p> What drives invasive species success? My research consists of four studies aiming to answer this question for <i>Ligustrum sinense</i>. The four projects are: (1) Synthesis of invasion literature within passenger-driver-backseat driver frameworks; (2) hydrochory investigation of water as a dispersal mechanism for invasion; (3) ecohydrology investigation of inundation effects on seed viability of <i>L. sinense</i>; (4) dendrochronology study of the effects of stream channelization and <i>L. sinense</i> invasion on bottomland oak tree growth. Results suggest that <i>L. sinense</i> initially invaded habitats that were hydrologically altered, resulting in drier conditions and a "novel niche." Dispersal <i>via</i> hydrochory allowed <i>L. sinense</i> to quickly colonize the novel niches. Once established, <i>L. sinense</i> competed with native oak species contributing to reduced growth rates, an "invasion meltdown." Control strategies should aim to remove <i>L. sinense</i> and return natural hydrologic regimes, or should consist of human-assisted re-establishment of native species that can thrive in altered conditions.</p>

<p>I investigated percent coverage, plant height, species richness, and woody stem density in plant communities in ten study plots during spring and fall (2010&ndash;2012) within 3 different treatments (continual mowings, one fall mowing, and one fall mowing with native wildflower seeds) on Highway 25 right-of-way in Oktibbeha and Winston counties, Mississippi. I recorded 277 plant species including native and non-native forbs, legumes, grasses, rushes/sedges, and woody plants. Non-native agronomic grasses exhibited greatest coverage greater than 90 percent occurring in all treatments. Percent coverage of plants less than 0.46m height category exceeded 100 while, greater than 0.46m plant height categories averaged 55 percent. Woody stem density ranged from 7,772 year 1 to 10,025 stems/hectare year 2. I detected no significant differences in plant height or woody stems among treatments. One mowing per year retained agronomic plant cover for erosion control and annual cost savings up to 75 percent for roadside maintenance. </p>

<p> Pristine landscapes are decreasing throughout the world, and many of Earth's species can no longer survive exclusively in the remaining small and isolated reserves. At the same time, urban landscapes are increasing, and can serve as potential habitat for many wildlife species. Amphibians are facing striking global declines and are particularly impacted by urban development as they often reside in areas attractive for human settlements such as flat, productive lowland areas with abundant fresh water. My dissertation aims to increase understanding of amphibian use of these landscapes and how management and planning can adapt to benefit their persistence. I conducted observational studies of amphibians and associated habitat features in two very difference landscapes and constructed experimental ponds to examine relationships between a native frog, a common pollutant, and common urban wetland plants. One observational study was in Portland, Oregon where formerly abundant wetlands have been destroyed and altered while many have also been restored or created. The other was throughout the relatively understudied urban and agricultural centers of Vietnam where biodiversity and human population growth are high. In both Portland and Vietnam I found that most regionally occurring native amphibians were breeding within city landscapes and in human-constructed water bodies. A common pollutant, nitrate, was strongly negatively associated with amphibians in Portland. In a mesocosm experiment I found that correlated contaminants are likely driving the pattern. In both Portland and Vietnam, presence of aquatic vegetation and amount of surrounding upland habitat were highly influential for native amphibians. Aquatic vegetation can take many forms, and in urban areas is often dominated by introduced species. I conducted experimental ponds studies to examine the relationship between a native frog and common native and introduced aquatic plant species. I found that the frog preferred and performed better in introduced reed canary grass than any other plants offered. This demonstrates that introduced plants are not universally detrimental to native wildlife species, and that management of these plants should consider the potential negative effects of control actions, especially in urban areas where restoration to a former pristine state is unlikely. Urban areas do not have to be devoid of diverse native amphibian communities, and instead should be viewed as potential habitat for conservation and environmental education. Amphibian use of human-constructed ponds, potted ornamental plants, and introduced reed canary grass demonstrates the adaptability of many species and the need for an integrated view of conservation that includes non-pristine areas. Using the information from this dissertation, city planners and managers can maintain and improve human-dominated landscapes to benefit native amphibians and promote their continued coexistence with humans in these areas.</p>