I examined the population trends of northern fur seals (Callorhinus ursinus) using an age-specific metapopulation model that allowed migration between rookeries. Mortality and birth rates were modified to simulate future population trends. I also examined the early migratory behavior and habitat associations of pups from Bering Island (BI), Russia. I instrumented 35 pups with Mk10-AL satellite tags and stomach temperature telemeters which provided diving, foraging and location data. I hypothesized that some aspects of pup behavior from the stable BI population differed from the behavior of pups from the unstable Pribilof Islands (PI). The population model revealed that emigration did not contribute significantly to the current PI population decline. However, large source populations contributed significantly to population growth in newly colonized rookeries. A stabilization of the PI population was predicted with a 10 to 20 percent reduction in both juvenile and adult female mortality rates. The diving behavior of pups showed a general progression towards longer and deeper dives as pups aged, particularly between 1600 – 0400 (local time), that was similar to PI pup behavior. However, unlike pups from the PI, I found three main diving strategies among BI pups: 1) shallow daytime divers (mean depth = 3.56 m), 2) deep daytime divers (mean depth = 6.36 m) and 3) mixed divers (mean depth = 4.81 m). The foraging behavior of pups showed that most successful ingestion events occurred between 1600 – 0400, with successful ingestion events lasting 25.36 plus/minus 27.37 min. There was no significant difference among the three strategies in the depth of successful foraging dives. I also examined the foraging search strategies in adult females and pups. Both pups and adults conducted Levy walks, although pups foraged in smaller patches (1 km scales). Using a logistic model to determine habitat associations, I found that pup locations were positively correlated with increasing chlorophyll a concentrations, distances from shore, and sea surface temperatures, and were negatively correlated with depth. There was no significant relationship between all pup locations and the regions (peripheries or centers) or types (cyclonic or anti-cyclonic) of eddies, but ingestion event locations were related to mesoscale eddy peripheries.

The concept of habitat quality is fundamental to the study of ecology, and ecologists have long recognized the importance of vegetation structure and composition in the assessment of wildlife habitat. Vegetative characteristics affect productivity in birds for a variety of reasons (e.g., predator assemblages, nesting sites, song perches, food availability). I investigated the relationship between habitat quality and prey availability and the effect these parameters have on reproductive success in golden-cheeked warblers (Dendroica chrysoparia). My objectives were to 1) determine any differences in pairing and fledging success of warbler territories within two ecosites exhibiting two distinctive tree species composition 2) explore the relationship between tree species composition, arthropod density, and foraging effort, and the effect these parameters have on reproductive success in golden-cheeked warblers and 3) investigate the connection between preferred foraging substrates and changes in arthropod abundance within golden-cheeked warbler territories throughout the breeding season. I mapped individual warbler territories and searched for fledglings, observed foraging behavior, and collected arthropods in each territory to determine productivity, foraging effort, and food availability. I conducted these methods over two seasons in juniper-oak woodlands on Fort Hood, north-central Texas within 347 territories of two vegetative types: those marked by the predominance of post oak (Quercus stellata) and those marked by the predominance of Texas oak (Quercus buckleyi). Pairing and fledging success of territories differed substantially between the two vegetative types. Movement rates differed considerably between the two vegetative types, indicating a difference in prey encounter rate. Foraging data indicated a clear switch in preferred foraging substrates from oak species early in the breeding season, to Ashe juniper (Juniperus ashei) in mid-May. Arthropod sampling revealed a correlation between preferred foraging substrates and arthropod density. Results suggested that Texas oak was an important foraging substrate for golden-cheeked warblers, and territories that lack this tree species generally did not succeed in fledging young. My study can be used to indicate areas that should be targeted for conservation by local, state, and federal government because they provide high quality habitat based on warbler productivity.

<p>Detta arbete har utförts i samarbete med företaget <em>Compute</em> och fokuserar på att utveckla navigationsstöd för webbportaler med bokningssystem. Arbetet har delats upp i tre specifika mål: (1) integrera <em>Information Foraging Theory</em> (IFT) och <em>Graphical User Interface principles</em> (GUI-principer) genom att applicera dessa vid utvecklng av navigation för webbportaler med bokningssystem (2) konkretisera hur navigering kan förbättras på en webbportal med bokningssystem, utifrån ovanstående teroier och (3) arbetet skall resultera i en lista med rekommendationer som kan tillämpas vid utveckling av navigation. För att kunna  integrera IFT och GUI-principer har dessa i kombination med en teroertisk studie tillämpats vid prototyping. Prototyperna användes som verktyg för att konkretisera hur navigationen kunde förbättras på portalen. Prototyperna utvärderades och resulterade i en lista med rekommendationer. Resultaten från utvärderingen påvisade att en integrering av GUI-principer och IFT kan förbättra nvigationsförhållanden på en webbportal. Arbetes främsta bidrag är listan med rekommendationer som skall kunna tillämpas vid navigationsutveckling.</p><p> </p>

This dissertation sought to explain goal achievement at limited traffic “long tail” Web sites using Information Foraging Theory (IFT). The central thesis of IFT is that individuals are driven by a metaphorical sense of smell that guides them through patches of information in their environment. An information patch is an area of the search environment with similar information. Information scent is the driving force behind why a person makes a navigational selection amongst a group of competing options. As foragers are assumed to be rational, scent is a mechanism by which to reduce search costs by increasing the accuracy on which option leads to the information of value. IFT was originally developed to be used in a “production rule” environment, where a user would perform an action when the conditions of a rule were met. However, the use of IFT in clickstream research required conceptualizing the ideas of information scent and patches in a non-production rule environment. To meet such an end this dissertation asked three research questions regarding (1) how to learn information patches, (2) how to learn trails of scent, and finally (3) how to combine both concepts to create a Clickstream Model of Information Foraging (CMIF). The learning of patches and trails were accomplished by using contrast sets, which distinguished between individuals who achieved a goal or not. A user- and site-centric version of the CMIF, which extended and operationalized IFT, presented and evaluated hypotheses. The user-centric version had four hypotheses and examined product purchasing behavior from panel data, whereas the site-centric version had nine hypotheses and predicted contact form submission using data from a Web hosting company. In general, the results show that patches and trails exist on several Web sites, and the majority of hypotheses were supported in each version of the CMIF. This dissertation contributed to the literature by providing a theoretically-grounded model which tested and extended IFT; introducing a methodology for learning patches and trails; detailing a methodology for preprocessing clickstream data for long tail Web sites; and focusing on traditionally under-studied long tail Web sites.

Investigating alternate winter refuges for Florida manatees is increasingly important as sustained warm-water discharges from industrial and some natural sites becomes more uncertain. This study examined habitat features of possible importance to manatees by comparing a winter refuge in Charlotte Harbor, FL (the Matlacha Isles canal system) to two nearby, seemingly similar sites that are not frequented by manatees during winter. Water temperature, salinity, boat traffic, canal depth, and tidal flushing were assessed at these sites. Additionally, this study examined when and how manatees use the Matlacha Isles refuge by documenting movements, habitat use, and behaviors of manatees during the winters of 1999/2000 through 2001/2002. Water temperatures had a profound influence on manatee selection of Matlacha Isles over the two comparison canal systems. Matlacha Isles did not experience the sudden drops in water temperature following cold fronts, extreme low temperatures, or long periods of temperatures below manatees’ reported thermal tolerance of 18-20 oC that were recorded in Matlacha Pass (ambient) and the two comparison canal systems. Heat retention within Matlacha Isles may be associated with greater water depth and lower tidal flushing. Salinity and boat traffic did not seem to influence site selection by manatees. During moderately cold weather, manatees occupying Matlacha Isles forage at night in nearby Matlacha Pass and return early in the morning to Matlacha Isles, where they primarily rest all day. Neither tidal state nor boat traffic levels affected manatee travel patterns into or out of Matlacha Isles. Manatees may passively thermoregulate in the warmer waters of Matlacha Isles during the day (when they are inactive) and sustain their body temperatures at night through the heat generated during traveling to feeding sites and during ingestion (chewing) and digestion. During extreme or prolonged cold weather, Matlacha Isles provides inadequate warmth for manatees; during such times, most of them travel to a power plant on the Orange River, approximately 50 kilometers away. Findings from this study may inform resource managers as they consider attributes manatees find desirable or necessary in winter. Such information will help managers create new or enhance existing winter refuges to protect manatees.

Amphibian decline is a major concern worldwide, and a lack of basic ecological and life history information for many species significantly limits our ability to evaluate the degree and possible causes of such declines, and to develop effective conservation strategies for threatened and endangered species. Not only is there a shortage of adequate long-term datasets necessary for robust analyses of population variability, but the elusive nature and obscure microhabitats of many species make it difficult to collect even the most basic natural history data. In a series of observational and experimental studies, I employed both traditional and novel ecological methodologies to examine environmental correlates of temporal population variability, foraging ecology and anti-predator behavior in endangered Barton Springs Salamander (Eurycea sosorum) from Austin (Travis County), Texas. Though headwater springs are typically thought of as habitats with relatively stable environmental conditions, I discovered that E. sosorum population abundance was strongly influenced by periodic extremes of rainfall that affect cycles in spring flow rates, water temperature, and other physico-chemical variables. I also found that population dynamics in E. sosorum are highly consistent with those expected for organisms with a storage effect life-history strategy, in which a few long-lived females capable of high fecundity and prolonged survival in subterranean habitat during adverse environmental conditions may be sufficient for population persistence. In addition, juveniles may use subterranean habitat as a thermal refuge. Using stable isotope analyses and macroinvertebrate prey censuses, I determined that at the population level, adult E. sosorum exhibits high electivity for planarian flatworms (Dugesia sp.). This would not have been detectable using traditional methods of dietary analysis such as stomach or fecal content analysis because Dugesia are soft-bodied animals. Additionally, stable isotope analyses revealed that adult E. sosorum exhibits inter-individual diet variation and is capable of diet switching. Finally, I discovered that anti-predator behavior in E. sosorum is influenced more strongly by visual and bioelectric cues from potential predators, but not olfactory cues. This is the first known demonstration of anti-predatory response mediated only by bioelectric stimuli in an amphibian, and one of very few to observe this phenomenon among aquatic vertebrates. / text

Natural enemies are ubiquitous in nature. In many communities, natural enemies have a major effect on the diversity of their prey. Their effects are very diverse: they can promote or undermine the ability of their prey to coexist through a variety of mechanisms. As such, an important step in understanding how diversity is maintained will be to understand how different forms of predator behavior affect prey coexistence. In this dissertation, I study how two major types of predators affect plant coexistence in two different communities. First, I study natural enemies in tropical forests, using both theory and empirical work. In tropical forests, most natural enemies are thought have a narrow host range, and be distance-responsive (i.e., mainly harm seeds and seedlings that are near adults of their main host). Previous theoretical work has shown that specialized natural enemies can maintain diversity of their prey, whether or not they are distance-responsive. However, it is unknown whether specialist natural enemies are more or less able to promote prey coexistence if they are distance-responsive. Using theoretical models, I show that distance-responsive predators are less able to maintain diversity. Additionally, I show that habitat partitioning does not interfere with the ability of distance-responsive predators to maintain diversity, even if it causes seedling survival to be highest near conspecific adults. From an empirical aspect, I studied the host range of seed-associated fungi. Soilborne microbes, such as fungi, are thought to play an important role in maintaining diversity in tropical forests. However, the microbial community itself is often treated as a black box, and little is known about which microbes are causing major effects, or how 8 specialized seed-microbe associations are. Here I use experimental inoculations to examine the host range and effect of a guild of seed-associated fungi that are thought to be mainly pathogens. I show that fungal species are differentially able to colonize different seed species, and have species-specific effects on seed germination. I show that in many cases, plant phylogeny, and to a lesser extent fungus phylogeny, are good predictors of colonization. Finally, I study how an optimally foraging granivore can promote (or undermine) coexistence amongst annual plants, using theory. Optimal foraging theory is one of the major theories for how predators behave; despite this, little is known about whether an optimally foraging predator could promote coexistence amongst a diverse community of prey. Previous models have shown than two species can coexist due to optimal foraging, but did not test whether multiple prey can coexist, nor if the effect is altered by environmental variation. Here, I show that if the predators specialize on different prey at different times, the predators can allow multiple prey species to coexist. In this case, environmental variation has little effect on the ability of predators to maintain diversity. If the predators are generalists, they cannot maintain diversity. Additionally, I show that generalist predators will create a negative storage effect, undermining coexistence.

The ultimate causes of bird migration are largely unknown despite more than a century of research. By studying partially migratory short-distance tropical migrants and by employing comparative methods, some difficulties in testing hypotheses for evolution of migration can be overcome. Using comparative methods I tested the evolutionary precursor hypothesis, a major hypothesis for why migration evolved in some lineages and not in others. The results of this study conflicted with many assumptions and predictions of the evolutionary precursor hypothesis. Most importantly, migratory behavior was not related to diet and habitat in simple ways. The interaction between diet and habitat, as well as consistent associations between flocking behavior and migration suggested that food variability is poorly captured by the surrogates embodied in the evolutionary precursor hypothesis. I then employed comparative methods to studying tropical altitudinal migration. Comparisons of diets and fruit preferences between species pairs showed that migrants are more frugivorous, eat a broader diversity of fruits, and have diets that more strongly resemble their preferences than do residents. Although providing evidence that food limitation plays a role in altitudinal migration, these results do not support the hypothesis that interspecific competition explains variation in migratory behavior. Next, I provided the first test of a predation-based hypothesis to explain altitudinal migration. Migrants breed at higher elevations than where they spend their non-breeding season. Thus, birds may migrate uphill to escape high nest predation risk at lower elevations. Results from this experimental study are largely consistent with this hypothesis, but anomalies between predicted and observed patterns suggest that either migration of lowland birds occurs in response to other factors, or that anthropogenic change has altered the tradeoffs involved in migratory decisions. Finally, I focus on a single migrant species and evaluate (a) two food-based hypotheses to explain the destination of migration movements, and (b) mechanisms underlying intra-specific differences in migratory strategy. Food can explain why Corapipo altera migrate uphill, but not why they migrate downhill. My data on sex bias and body condition leads to a new hypothesis explaining the complete annual cycle of this tropical migrant bird.

Das Ziel der vorliegenden Arbeit war es, die Eignung von vierzehn Pflanzenarten des Wirtschaftsgrünlands für die Etablierung von Grasnarben für die Hühnerfreilandhaltung zu untersuchen. Neun Gräser und fünf Kräuter, deren hohe Leistungsfähigkeit aus intensiv bewirtschafteten Systemen, und deren gute Schnitt-, Weide- und Trittverträglichkeit bekannt sind, wurden vergleichend bewertet. In einem Feldexperiment wurde die Verträglichkeit der Pflanzen gegenüber Beweidung mit Hühnern untersucht. Die Hypothese lautete, dass sich die Leistungsfähigkeit der Arten deutlich unterscheiden würde, da die Störung, die durch Beweidung mit Hühnern erzeugt wird, stärker und von anderer Natur ist als in anderen Bewirtschaftungssystemen. Monokulturen und eine Mischsaat der vierzehn Arten wurden einer Umtriebsbeweidung mit Legehennen in drei Stufen der Weidedauer unterzogen. Die Wirkung der Faktoren Pflanzenart, Weidedauer und Umtrieb auf Bodendeckung, Dichte der Triebe und Vegetationspunkte, und Wachstum der oberirdischen Biomasse wurde analysiert. Aus ersteren Zielgrößen wurde die Resistenz der Grasnarbe gegenüber der Beweidung abgeleitet, aus der dritten ihre Resilienz. Die Hypothese, dass sich die untersuchten Arten stark im Hinblick auf ihre Resistenz und Resilienz gegenüber Beweidung mit Hühnern unterscheiden würden, wurde bestätigt. Unsere Ergebnisse deuteten darauf hin, dass Gräser prinzipiell besser für die Bepflanzung von Auslaufflächen geeignet sind als Kräuter. Die Arten Festuca arundinacea und Poa supina zeigten mit einer Bodendeckung von über 80 %, einer konstanten Triebdichte und einer gleich bleibenden, vergleichsweise hohen Wachstumsrate von mehr als 4,8 g Trockenmasse m-2 d-1 die beste Leistungsfähigkeit bei wiederholter Beweidung und langer Weidedauer. In einem ergänzenden Gefäßversuch im Gewächshaus wurde untersucht, welche mit der Wuchsform in Zusammenhang stehenden Eigenschaften die Toleranz der Pflanzen gegenüber Beweidung mit Hühnern erklären. Die Hypothese bestand darin, dass die Biomasseallokation vor der Störung und die Lage von Speicherorganen und Knospen für klonales Wachstum die Schädigungstoleranz bestimmen würden; sie würde bei Arten hoch sein, bei denen diese Organe konzentriert an der Sprossbasis und unterhalb von oder nahe der Erdoberfläche liegen. Eine Auswahl der im Freilandversuch verwendeten Pflanzenarten, die drei Wuchsformen repräsentierte (Arten ohne Ausläufer; Arten mit Stolonen; Arten mit Rhizomen) wurde einer standardisierten mechanischen Schädigung in drei Intensitäten ausgesetzt, welche zugleich auf Spross und Wurzel wirkte. Die Ergebnisse dieses Versuchs zeigten, dass die Pflanzenart, nicht aber die Wuchsform die Toleranz gegenüber Schädigung bestimmten. Die höchste Toleranz wurde bei F. arundinacea und Poa pratensis festgestellt. Der Wiederaufwuchs oberirdischer Biomasse war über alle Arten und Intensitäten der Behandlung hinweg stark mit der relativen Wurzelbiomasse (der Wurzelbiomasse der behandelten Pflanze im Verhältnis zu der der Kontrollpflanze) korreliert, allerdings nicht mit der Wurzelbiomasse vor der Behandlung. Die Resistenz der Wurzel gegenüber mechanischer Schädigung ist daher offenbar eine wesentliche Determinante der Toleranz gegenüber der untersuchten Störung. Schließlich wurde der Einfluss von botanischer Zusammensetzung und Degradierung der Grasnarbe auf das Nahrungssuchverhalten der Hühner untersucht. In dem oben erläuterten Feldexperiment war die Häufigkeit der Verhaltensweisen Picken an Pflanzen, Picken am Boden und Scharren aufgezeichnet worden. Aus den Daten ging hervor, dass Pflanzenart und Degradierung der Grasnarbe das Nahrungssuchverhalten der Hühner signifikant beeinflussten. Eine steigende Weidedauer reduzierte die Bodendeckung grüner Vegetation signifikant; allerdings unterschieden sich die untersuchten Pflanzenarten deutlich im Hinblick auf das Ausmaß der Degradierung, die durch standardisierte Beweidungsdauer erzeugt wurde. Bei steigender Weidedauer und sinkender Bodendeckung grüner Vegetation war bei den meisten Pflanzenarten eine Abnahme der Häufigkeit des auf die Grasnarbe gerichteten Pickverhaltens (Picken an Boden und Pflanzenteilen summiert) nachweisbar. Dieses Ergebnis wird als bedeutsam für das Tierwohl erachtet, da in Umwelten, die wenig Anreiz zu Picken an Objekten bieten, die Gefahr besteht, dass die Tiere vermehrt Federpicken zeigen. Wir leiten aus diesen Ergebnissen ab, dass die Wahl von Pflanzenarten wie P. supina, die sowohl eine hohe Resistenz gegenüber der durch Beweidung verursachten Störung aufweisen, als auch einen starken Anreiz zu Nahrungssuchverhalten, und insbesondere zu Picken liefern, als Begrünung den Beitrag der Auslauffläche zu Tierwohl und –gesundheit fördern können. Zusammenfassend haben unsere Experimente gezeigt, dass die Wahl der Pflanzenart zur Auslaufbegrünung ein wichtiger Faktor zur Gewährleistung der Multifunktionalität der Grasnarbe ist. Pflanzen, die bei langer Beweidung eine stabile Bodendeckung und starkes Wachstum aufweisen, können einen höheren Anteil der im Auslauf anfallenden Nährstoffmengen binden und tragen somit zum Schutz von Boden und Wasser bei. Eine Grasnarbe, die zusätzlich das Nahrungssuchverhalten anregt, begünstigt Tierwohl und -gesundheit. Von den untersuchten Arten zeigte P. supina insgesamt das beste Ergebnis in Bezug auf diese Kriterien; F. arundinacea zeichnete sich zwar durch eine hohe Resistenz gegenüber der Störung durch die Beweidung aus, allerdings schien diese Art weniger stark bepickt zu werden. Wir schließen daraus, dass die Wahl der Pflanzenart für die Auslaufbegrünung als eine wichtige Methode des Auslaufmanagements betrachtet werden kann, die etablierte Methoden der Auslaufpflege, wie Umtriebsbeweidung mit ausreichenden Beweidungspausen und eine Gestaltung des Auslaufs, welche die Tiere zur Nutzung der gesamten Fläche animiert, ergänzen sollte.

The sexes have different life histories that can influence their parental care strategies. I studied northern flicker, Colaptes auratus, parents and simultaneously radio-tracked mates during the nestling and post-fledging periods. I tested hypotheses about sex differences in parental care strategies by examining foraging patterns, provisioning effort and habitat use. Males and females used the same microhabitats, but avoided overlap of their foraging areas on the home range consistent with the hypothesis that mates separate the home range to reduce competition. During temporary (i.e., 24 hr) brood size manipulations, both parents decreased provisioning to reduced broods, but did not increase provisioning to enlarged broods or alter their foraging pattern on the landscape. I suggest flickers were energy limited and were incapable or unwilling to respond to increased brood demands. During the post-fledging period, males spent more time near their fledglings, and cared for their fledglings longer than females (16 days versus 12 days, respectively). Approximately 36% of females abandoned their brood in the post-fledging period and females with high levels of feather corticosterone were more likely to abandon. Older males and those with high provisioning rates in the nestling period fed their fledglings longer. Nearly 45% of fledglings died within the first week after leaving the nest, but survival was higher for fledglings with intermediate body mass and those that occupied areas of dense cover. Families moved a greater distance from the nest during the first 4 days post-fledging when there was less tree cover within 250 m of the nest site. Parents brought fledglings to areas with dense vegetation within the first week post-fledging, but subsequently shifted to open grassland habitats. My results show that parents invest in their offspring indirectly by taking them to habitats that increase survival. This research stresses the importance of studying parental care during the post-fledging period to gain a more complete understanding of the total parental investment of males versus females and how each sex may react differently to trade-offs between investing in the current brood versus self-maintenance.