<p> Terrestrial litterfall is a well-documented subsidy of nutrients and organic matter to adjacent aquatic ecosystems. Nitrogen-fixing plants increase nutrient dynamics via nitrogen (N) - rich litterfall in both terrestrial and aquatic ecosystems, and the effects are often more pronounced when areas lacking native N₂-fixers are invaded. This study examined differences in organic matter and nutrient inputs from the invasive, N₂-fixing tree, <i>Prosopis pallida</i>, and the native, non N₂-fixing tree, <i>Thespesia populnea</i>, to determine effects on anchialine ponds on Hawai`i Island's leeward coast. My objectives were to quantify: 1) tree basal area and density surrounding the ponds, 2) quality and quantity of <i>P. pallida</i> and <i>T. populnea</i> litter inputs, 3) inorganic N content of soil surrounding the ponds, 4) leached nutrients from <i>P. pallida</i> and <i>T. populnea</i> leaf litter. These response variables were then compared to water nutrient concentrations (i.e., phosphate, nitrate, ammonium, dissolved organic carbon (C), and total dissolved N and phosphorus (P)) in the ponds of interest. Basal area, density, litterfall mass, total N and C inputs, and leachate values were similar between pond types categorized as <i>P. pallida</i> &ndash; or <i> T. populnea</i> &ndash; dominated. Foliar N concentrations were 28 percent higher in <i>P. pallida</i> &ndash; dominated ponds compared to <i>T. populnea</i> &ndash; dominated ponds, but foliar P concentrations were three times greater in <i>T. populnea</i> ponds than <i>P. pallida</i> ponds. Total P inputs were greater beneath <i>T. populnea</i> ponds and there was a positive correlation between <i>T. populnea</i> size and abundance and pond water phosphate concentrations. These results suggest that the N if influencing water quality in Hawaiian anchialine ponds more than the invasive N₂-fixing species, although high background water nutrient levels may be inhibiting our ability to detect any significant impacts. The transfer of <i>T. populnea</i>'s P-rich litter to pond water appears to have a strong influence on ecosystem functioning.</p>

<p> While the processes that led to the formation of modern plant communities are often cryptic, biogeographic patterns of extant species can provide clues to their origin. The Midriff Islands, an archipelago in the Gulf of California at the center of the Sonoran Desert, provide an opportunity to investigate the origins of the desert. This research uses three case studies at three different time scales to better understand the factors responsible for modern biodiversity. </p><p> Chapter 1 revisits the theory of island biogeography and incorporates the long history of humans on the Midriff Islands to determine factors controlling plant species richness. Area, habitat diversity, island type, and seabird dynamics explain 98% of the variability in species richness across this archipelago. Interestingly, human presence is not predictive, suggesting an island system with ancient human interactions that functions in a pre-Anthropocene state. </p><p> Chapter 2 investigates Holocene extinctions. In 1975, bighorn sheep (<i> Ovis canadensis</i>) were introduced as a novel element to Isla Tibur&oacute;n as a conservation measure. Fossil dung found on Isla Tibur&oacute;n was 14C-dated to 1476-1632 years before present and identified as <i>Ovis canadensis </i> by morphological and ancient DNA analysis. Bighorn sheep went locally extinct on the island sometime in the last ~1500 years prior to their "unintentional rewilding." This discovery questions the definition of a non-native species and extends an ecological and conservation baseline. </p><p> Disjunct long-lived plant taxa on Isla Tibur&oacute;n suggests climate and vegetation change on the Midriff Islands in the Pleistocene. Chapter 3 is a phylogeographic study of the desert edge species <i>Canotia holacantha </i> (Celastraceae) that tests whether <i>Canotia</i> on Isla Tibur&oacute;n is a Pleistocene relict or a recent dispersal event. Results suggest long isolation and divergence of <i>Canotia</i> on Tibur&oacute;n but recent arrival in the core of its modern day distribution in Arizona. In contradiction to an expected temperate origin, <i>Canotia</i> seems to have tracked the northward shift of the desert's edge at the end of the last Ice Age from glacial refugia in Sonora or Chihuahua. </p><p> Collectively, this research helps illuminate the history of the desert and establishes baselines to support management decisions of the world's best-preserved archipelago.</p>

<p> River-associated birds may be valuable indicators of environmental change in riverine ecosystems because they are predators of fishes and therefore often top predators in the aquatic food web. To evaluate the likely scope of one form of change - river restoration through dam removal and the expected return of abundant diadromous fish prey - we: 1) developed an appropriate river bird survey protocol; 2) documented the relative importance of sea-run fish in the diet of four river bird species, bald eagle (<i>Haliaeetus leucocephalus</i>), osprey (<i>Pandion haliaetus</i>), belted kingfisher (<i>Megaceryle alcyon</i>), and tree swallow (<i> Tachycineta bicolor</i>); 3) documented nest distribution and brood size of osprey; and 4) investigated the relationships between river bird abundance and various habitat parameters. We expect these measures will reflect changes to the river system post-dam removal as diadromous fish populations recover, proliferate, and integrate into the food web. Based on species accumulation curves and first-order Jacknifes, we concluded that biweekly or triweekly I5 minute surveys are sufficient to meet our objectives. Within the Penobscot River, stable isotope analysis of river bird diets indicated that marine nutrients are consumed by bald eagle, osprey, and belted kingfishers that reside below the lowermost dam, but not tree swallows. Despite greater connectivity for and abundance of spawning diadromous fishes (particularly river herring), in the Kennebec and Sebasticook Rivers as compare to the Penobscot River, osprey brood size was not significantly larger. We suspect other factors such as competition with bald eagles may be limiting the benefit of large river herring runs to nesting osprey. Finally, an ordination of 26 river bird species and 5 single-species (invertivore - spotted sandpiper, piscivore - osprey; piscivore - bald eagle; insectivore - tree Swallow; and omnivore - American black duck) generalized linear models, I revealed associations between estimated species abundance and water flow, water level, distance from the river mouth (river kilometer), site position in relation to a dam (e.g. above, below, or not at a dam), and adjacent land cover composition.</p>

<p> Marine resources are characteristically patchy and concealed beneath the surface of a "featureless" ocean, which makes facilitative species interactions especially advantageous to seabirds. My research addresses how behavioral mechanisms accommodate prey availability, or more specifically, how common (<i>Sterna hirundo</i>) and roseate terns (<i>S. dougallii </i>) locate and access food when it is not easily detectable. I study their foraging behavior and ecology from pre- to post-breeding, offshore in the pelagic realm (chapter 1), around the colony (chapter 2), and in nearshore waters (chapter 3). My first chapter tests the hypothesis that, as broadly-ranging seabirds, common and roseate terns forage over habitat where marine mammals and predatory fish help to find and access prey. I quantify the spatial association among foraging terns, tunas, dolphins, and their habitat, using Bayesian hierarchical models, and tests of behavioral community interactions. Facilitation explains how terns benefit from subsurface predators through local enhancement and commensal relationships: foraging tunas improve the detection and availability of prey by signaling their presence, and driving them to the surface. Chapter 2 evaluates the link between resource utilization and foraging strategy, measured by nest provisioning and patterns among foraging routes or feeding flocks. I propose that the opportunistic generalists, common terns, depend more on social cues than the specialists, roseate terns, which rely more heavily on spatial memory to find predictable prey. The results support this and suggest that increased breeding and foraging success in roseate terns relates to higher quality and abundance in their preferred prey, sandlance (<i>Ammodytes </i> spp.); in contrast, common terns seem to endure prey limitation through their use of local enhancement. In my third chapter, I hypothesize that habitat variability and prey availability predict interspecific differences in tern foraging. Behavioral tests and density-surface models, with distance sampling, show that foraging common and roseate terns respond positively to the distribution and abundance of each other and their preferred prey. Clearly, common and roseate terns use conspecifics, heterospecifics and subsurface predators to encounter prey via facilitation: such interactions create dynamic hotspots that need to be considered in an ecosystem approach to marine spatial planning.</p>

<p> Abstract As invasive predators spread across landscapes, their sudden presence may have significant effects on the behavior patterns of their new found prey. Here, I examined how predator-naive foxes responded to colonization by non-native golden eagles on Santa Cruz Island, California. First, using radio-telemetry, I investigated the effects of this diurnal, aerial predator on fox activity patterns. In 1992, just prior to the arrival of golden eagles, foxes showed substantial diurnal activity, but diurnal activity was 37.0% lower in 2003-7, after golden eagle colonization; concurrently, overall activity declined and nocturnal activity increased. Moreover, on nearby Santa Catalina Island, where golden eagles were absent but where the fox population recently crashed due to a disease epidemic, remaining foxes were significantly more diurnally active than were those on Santa Cruz Island. The weight of evidence suggested that the change in activity pattern was a response to predation, not to low population density, and that this was probably a heritable, rather than a learned, behavioral trait. Second, I used radio-telemetry, camera traps, sightings to investigate spatial patterns and habitat use in the wake of eagle colonization. When comparing pre- and post-colonization conditions, foxes demonstrated an inverse home range-density relationship, as fox core areas and home ranges expanded significantly in the low-density conditions following eagle colonization. I found that diurnal ranges were 11% smaller than nocturnal home ranges in post-colonization conditions, perhaps reflecting restricted diurnal movement as a form of predator avoidance of the diurnally hunting eagles. In terms of habitat preference, foxes preferred shrubland &ndash; a habitat which provides cover from aerial predators &ndash; over other habitat types. This suggested a way in which foxes may have mitigated golden eagle predation risk. Finally, I examined changes in fox diet before and after colonization using scat analysis. Because this invasion reduced the endemic fox population by 95% in a decade, these dietary changes could have been be attributed to behavioral change (e.g., reduced diurnal activity and movement), demographic change (e.g., reduced intra-specific density), and/or community level change (e.g., increased intra-specific competition with island spotted skunks), all of which were shifts associated with eagle predation. Concurrently, there were marked changes in the island's vegetation community, with the removal of introduced grazers and the subsequent increase in recruitment of shrubland. I hypothesized that these effects would cause fox diets to differ from historic diets, as indicated by scat analysis. I also evaluated seasonal differences and dietary breadth in the post-eagle colonization period. Although I did not observe an overall large scale modification of fox dietary patterns, statistically significant dietary changes were observed before and after eagle colonization. Results suggested that all four factors may have had an effect on fox diet, although evidence suggested that grazer removal may have had a more pronounced effect. Seasonal patterns and dietary breadth reflected the seasonal availability of fruiting shrubs in the dry season, and an emphasis on other food items, primarily mice and insects, in the wet season, as expected. While this fox population has subsequently rebounded successfully, understanding how animals respond to the sudden arrival of an invasive predator is crucial to improving approaches to conserving endangered species in the future.</p>

<p> Noise associated with human activity is widespread and expanding rapidly in terrestrial environments, but there is still much to learn about its effects on animals. To determine the effect of introduced noise on lek attendance and strutting behavior, I played back recorded continuous and intermittent anthropogenic sounds associated with natural gas drilling and roads at leks of Greater Sage-Grouse (<i>Centrocercus urophasianus</i>). For 3 breeding seasons, I monitored sage-grouse abundance at leks with and without noise. Peak male attendance (i.e., abundance) at leks experimentally treated with noise from natural gas drilling and roads decreased 29% and 73% respectively relative to paired controls. Decreases in abundance at leks treated with noise occurred in the first year of the study and were sustained throughout the experiment. There was limited evidence for an effect of noise playback on peak female attendance during the experiment or on male attendance the year after the experiment ended. These results suggest that sage-grouse avoid leks with anthropogenic noise and that intermittent noise has a greater effect on attendance than continuous noise. To quantify the potential for noise from natural gas infrastructure to mask sage-grouse vocalizations over both long and short distances, I analyzed both the individual notes of mating vocalizations produced by male sage-grouse and recordings of such noise. Noise produced by natural gas infrastructure is predicted to mask sage-grouse vocalizations substantially, reducing the active space of detection and discrimination of all vocalization components, particularly impacting notes that are low frequency and low amplitude. Such masking could increase the difficulty of mate assessment for lekking sage-grouse. Significant impacts to sage-grouse populations have been measured at noise levels that predict little to no masking. I investigated whether male sage-grouse adjust the repetition and timing of their strut displays in response to playback of noise associated with natural gas development. I compared the signaling behavior of male sage-grouse on leks with long-term drilling and road noise playback to that of males on similar leks with no noise playback. Males exposed to long-term drilling noise playback strutted at higher rates and in longer bouts than males on control leks, while males on road noise leks strutted at lower rates and in shorter bouts than males on control leks; these differences were only observed during close courtship, when strut rate is most important in influencing female mate choice. I did a short-term playback of intermittent traffic noise and compared the strut timing of individuals during noisy and quiet periods. Males performed fewer struts overall during noisy periods, but male strutting behavior was related to female proximity. Males that were not closely approached by females strutted less during noisy periods than quiet periods and males that engaged in close courtship with females strutted at similar rates during noisy and quiet periods, even when females were far away. Introduced noise associated with natural gas development causes large declines in sage-grouse lek attendance and is likely to cause substantial masking of sage-grouse vocalizations. However, masking is not likely to be the only mechanism of noise impact on this species. Sage-grouse may at least partially reduce masking impacts through behavioral plasticity, adjusting the timing of their signals in a manner that may reduce the impacts of masking on communication.</p>

<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> 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>

<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>