Many species of bats primarily use echolocation, a type of active sensing wherein bats emit ultrasonic pulses and listen to echoes, for guidance and navigation. Swarms of such bats are a unique type of multi-agent systems that feature bats's echolocation and flight behaviors. In the work of this dissertation, we used bat swarming as an inspiration for multi-agent systems to study various topics which include predation success, active sensing, and collision avoidance. To investigate the predation success, we modeled a group of bats hunting a number of collectively behaving prey. The modeling results demonstrated the benefit of localized grouping of prey in avoiding predation by bats. In the topics regarding active sensing and collision avoidance, we studied individual behavior in swarms as bats could potentially benefit from information sharing while suffering from frequency jamming, i.e., bats having difficulty in distinguishing between self and peers's information. We conducted field experiments in a cave and found that individual bat increased biosonar output as swarm size increased. The experimental finding indicated that individual bat acquired more sensory information in larger swarms even though there could be frequency jamming risk. In a simulation wherein we modeled bats flying through a tunnel, we showed the increasing collision risk in larger swarms for bats either sharing information or flying independently. Thus, we hypothesized that individual bat increased pulse emissions for more sensory information for collision avoidance while possibly taking advantage of information sharing and coping with frequency jamming during swarming. / Ph. D.

All natural aquatic systems harbour a vast variety of microorganisms. In the aquatic microbial food web, the larger microorganisms (i.e. protozoa) feed on the smaller microorganisms (i.e. bacteria and phytoplankton). An increase in nutrient availability results in changes of the microbial food web structure, like altered community composition and blooms of toxic phytoplankton. In this thesis work I hypothesised that nutrient-rich aquatic environments, with strong protozoan predation, favour the occurrence of predation-resistant bacteria like F. tularensis, and that the microbial food web may provide a reservoir for the bacterium between outbreaks. By using a size-structured ecosystem food web model it was shown that the protozoan predation pressure on bacteria, defined as protozoan predation per bacterial biomass, increases with increasing nutrient availability in aquatic systems (estimated chlorophyll a 0.2 to 112 μg L-1). This dynamics was caused by increasing growth-rate of a relatively constant number of bacterial cells, maintaining the growth of an increasing number of protozoan cells. The results were supported by meta-analysis of field studies. Thus my results suggest that protozoa control the bacterial community by predation in nutrient-rich environments. In a field study in a natural productivity gradient (chlorophyll a 1.4 to 31 μg L-1) it was shown that intense selection pressure from protozoan predators, favours predation-resistant forms of bacteria. Thus, the abundance of predation-resistant bacteria increases with increasing nutrient availability in lakes. Furthermore, I could demonstrate that the bacterium Francisella tularensis, the causative agent of tularemia, was present in eutrophic aquatic systems in an emerging tularemia area. Isolated strains of the bacterium were found to be resistant to protozoan predation. In a microcosm study, using natural lake water, high nutrient availability in combination with high abundance of a small colourless flagellate predator favoured the occurrence of F. tularensis holarctica. In laboratory experiments F. tularensis strains were able to form biofilm at temperatures between 30-37°C, but not below 30°C. In conclusion, I have shown that the protozoan predation pressure on bacteria increases with increasing nutrient availability in aquatic systems. Predation-resistant forms of bacteria, such as F. tularensis are favoured in nutrient-rich environments. The complexity of the microbial food web and nutrient-richness of the water, influence the transmission of the pathogenic F. tularensis holarctica. However, over long periods of time, the bacterium survives in lake water but may lose its virulence. The temperature-regulated biofilm formation by F. tularensis may play a role in colonization of vectors or for colonization of hosts, rather than for survival in aquatic environments.

In order to meet their energy budget animals must often increase their risk of predation, either through their choice of foraging location or by decreasing anti-predation behaviours, which are incompatible with foraging. I investigated the starvation-predation risk trade-off in redshanks overwintering in the area of the Firth of Forth in Scotland over different spatial scales. On a small spatial scale, where redshanks foraged in an area where risk of attack was high I investigated the role of competition for food and decreased individual vigilance within groups and how this related to predation risk, additionally I looked at the relative roles of individual variation in time spent exposed to risk and variation in anti-predation behaviours on individual survival time. On larger spatial scales of 100s of meters and over several kilometres, I considered how choice of overwintering site was affected by predation risk, profitability and population density. Time available to feed increased with increased group size, allowing redshanks to compensate for increased competition and allowing large groups to form, thus decreasing individual predation risk. Individuals that spent less time exposed to attacking predators survived for longer, however individuals constrained by cold weather to spend long periods exposed to risk could increase their survival through increased intake rates and vigilance. On an intermediate spatial scale redshanks selected overwintering sites based on profitability rather than risk, and only used less profitable site when population density was high. On a large spatial scale redshanks increased their use of less profitable sites in warmer weather, but did this without increasing their risk of predation. Overall this suggests that across most spatial scales redshanks can minimise their predation risk by their choice of foraging location, but when forced by weather conditions or competition to be exposed to attack, capture reducing behaviours also reduce predation risk.

Animal community structures, life histories and individual foraging behaviour are all an outcome of a trade-off between competition for resources (and thus the risk of starvation) and survival (and thus the risk of predation). The relative importance of these factors however, differs between ecosystems, and especially when comparing temperate to tropical ones, we usually find marked differences. The seasonality of tropical ecosystems is much reduced compared to temperate ones, and weather conditions are less extreme. Accordingly tropical systems are characterised by higher species diversity, and different life history traits have been found between temperate and tropical birds. However, how the different environmental factors interact, and how predation and starvation risk vary to cause these differences still remains largely unknown. We studied the feeding behaviour of several granivorous Estrildid finches in scrub savannah habitat in central Nigeria to test how they respond to varying degrees of starvation and predation risk. During field observations and aviary experiments we investigated whether there is seasonal variation in the birds’ foraging behaviour correlating with the abundance of grass seeds and tested how they respond to different group sizes and differing distances from cover (representing a difference in predation risk). Further we also carried out field observation on the natural feeding behaviour of several closely related sympartic Estrildid finches to investigate inter-specific and seasonal differences in competition and microhabitat choice to see if this could explain their coexistence. Finally we studied habitat choice, movement behaviour and breeding biology of the potentially threatened endemic Rock Firefinch (Lagonosticta sanguinodorsalis) between the wet and the dry season via radio-tracking to establish its habitat requirements and gain the first information in its life history traits and population trends. We found little seasonal variation in the species’ foraging behaviour, and parameters that varied did not do so in a consistent manner. Thus, we found little evidence for a seasonal change in the risk of starvation. However, the abundance of several bird species varied widely between seasons and species leaving during periods of food shortage might have released competition for remaining resources. Birds did not show a strong response in their feeding behaviour with respect to cover in either intake rate or timing of feeding. However, intake rate increased with group size, which we believe to be due to scramble competition rather than risk dilution. We therefore conclude that predation did not shape the foraging behaviour of tropical granivorous passerines as markedly as that of temperate ones. Rock Firefinches were found to breed between the late rainy and the early dry season. They selected inselberg habitat, where most nests were found between rocky boulders. During the dry season, when water sources in inselberg habitat had dried out, they had to fly distances of up to 700 m to the gallery forest to get water and this led to the inclusion of more scrub savannah and gallery forest within their home ranges. Daily egg survival was 0.89 ± 0.03 calculated after the Mayfield analysis and most failing nests were depredated probably mainly by lizards. We suggest that in addition to nest predation, water availability might limit breeding time and thus reproductive output of Rock Firefinches. Predation risk did not seem to be of high importance in shaping the birds’ feeding behaviour because there was no seasonal variation in the risk of starvation. We found some suggestive evidence that competition might be important and it is likely that bird populations constantly stay close to carrying capacity. In contrast to temperate regions the need to conserve water might be of higher importance in shaping the birds’ feeding behaviour. High adult survival rates might be due to reduced seasonality in the risk of starvation thereby leading to reduced predation risk on adult birds. High nest predation might also be of higher importance in shaping the life history traits of tropical passerines, but at present this suggestion remains speculative. The results fit into the general framework that there is a trade-off between starvation and predation risk, and in the absence of starvation risk for some species in tropical areas, predation risk is also relatively unimportant.

The aim with this review was to investigate whether a reconnection of an oxbow lake can contribute to higher biodiversity. However, oxbow lakes can be divided in three categories: Lentic- (connected with both ends to the river bed), semi-lentic- (connected with one end) and lotic oxbow lakes (Isolated from the riverbed). Aquatic organisms such as fish, aquatic invertebrates, amphibians and macrophytes has been studied. The result showed that hydrological connectivity determines both biodiversity and water quality in oxbow lakes. Lotic oxbow lakes consisted low biodiversity and it’s dominated by amphibians. Semi-lentic oxbow lakes contributes with highest biodiversity of macrophytes, fish and aquatic invertebrates. Lentic oxbow lakes consisted less biodiversity and was dominated by fish. In conclusion, reconnection of an oxbow lake can be used as a restoration project to improve biodiversity.

L'augmentation de populations de cerfs pose d'importants problèmes écologiques et socio-économiques à l'échelle locale et mondiale. Des signes de densité-dépendance sont souvent observés, mais les cerfs restent abondants malgré l'importante dégradation du milieu qu'ils provoquent. Ceci soulève la question de l'ajustement des cerfs aux changements de milieu qu'ils créent ? Nous avons abordé cette question en recherchant comment les cerfs gèrent leur ressource alimentaire en fonction du risque de prédation. La prédation, en plus de son effet consommateur (élimination de proie), peut moduler le comportement et la physiologie des proies (effet non consommateur) qui doivent balancer le fait de se nourrir et le risque de prédation. Cette étude contribue à mieux comprendre comment les cerfs maintiennent d'abondantes populations dans des milieux qu'ils ont eux-mêmes appauvris.Notre projet s'est intéressé au cerf-à-queue-noire Sitka (Odocoileus hemionus sitkensis) sur trois îles de l'archipel d'Haïda Gwaii (B.C., Canada). Ces îles sont dépourvues des principaux prédateurs naturels du cerf (loup et puma) et ont été colonisées par les cerfs il y a plus de 60 ans. Lors de notre étude, ces îles présentaient des niveaux contrastés de nourriture et de risque de prédation : sur deux îles, les cerfs vivaient sans prédateur mais avaient fortement appauvri leur milieu (îles sans risque/pauvre). Sur la troisième île, les cerfs étaient chassés et bénéficiaient d'un sous-bois forestier partiellement restauré comme nourriture (île risquée/riche).Dans ce cadre, nous avons étudié : 1) sur quelles ressources les cerfs pouvaient maintenir de denses populations dans des milieux très abroutis ?; 2) comment le stress alimentaire ou le risque de prédation influençaient la réponse physiologique au stress des cerfs?; 3) les cerfs naïfs à la prédation ont-ils maintenu des niveaux de vigilance dans des milieux très abroutis et comment répondaient-ils à des stimuli olfactifs de prédateurs ?; et 4) comment, dans des milieux très abroutis, les cerfs naïfs à la prédation répondaient-ils à une chasse expérimentale pour faire peur et comment cela affectait la végétation ?Notre étude a montré que : 1) les chutes de feuilles de la canopée et la pousse annuelle de plantes rhizomateuses offraient une grande quantité d'énergie pour les cerfs et contribuaient au maintien de denses populations de cerfs dans des milieux appauvris ; 2) La présence de stress alimentaire ou de risque de prédation n'affectaient pas la réponse physiologique au stress des cerfs, suggérant l'existence d' ajustements comportementaux et/ou physiologiques permettant de réduire l'exposition des cerfs à ces deux stresseurs ; 3) sur les îles sans risque/pauvre, les cerfs ont maintenu la vigilance malgré 60 ans d'isolation à la prédation. En outre, les cerfs naïfs à la prédation évitaient de manger en présence d'urine de loup (dangereux) mais pas en présence d'urine d'ours (moins dangereux), suggérant que les cerfs présentaient une stratégie innée de nourrissage sensible au risque. Les cerfs restaient aussi moins longtemps aux stations d'appâtage en présence d'urine de loup mais n'augmentaient pas leur niveau de vigilance, suggérant qu'ils géraient le risque spatialement plutôt que par la vigilance ; 4) En réponse à une chasse expérimentale pour faire peur réalisée sur une des îles sans risque/pauvre, seuls les cerfs les moins tolérant à la perturbation humaines évitaient la zone chassée. Ceci souligna l'importance de la sélection des traits comportementaux induis par l'homme dans la gestion de la faune et de la flore. Nous avons aussi suivi la croissance de quatre espèces de plantes côtières à croissance rapide et avons montré que notre chasse expérimentale favorisait la croissance de la moitié d'entre elles, soulignant l'interaction complexe entre le comportement de nourrissage et les caractéristiques des plantes, ainsi que l'importance des objectifs dans le choix des outils de gestion. / In many temperate environments deer populations have been increasing, raising serious ecological and socio-economic concerns both locally and globally. Signs of density dependence are often observed in such populations, but deer abundance often remains high with regard to the dramatic degradation of the environment they have induced. This raises the question: How do deer do to adjust to the environmental changes they created? The present study addressed aspects of this question focusing on how deer manage their food resource in relation to predation risk. In addition to its consumptive effect (prey removal), predation is increasingly recognized for its non-consumptive effect on prey behavior and physiology, the importance of which is linked to the strength of the trade-off between foraging and predation risk. A better understanding on how deer manage food resource and predation risk in heavily browsed environment may thus help to better understand how deer maintain abundant populations in self-induced depleted environment.We tackled this question by studying Sitka black tailed deer (Odocoileus hemionus sitkensis) on three islands of the Haida Gwaii archipelago (B.C., Canada). These islands are devoid of the main natural predators of deer (wolves and cougars) and were colonized by deer over 60 years ago. At the time of the study, these islands presented contrasted levels of food and predation risk: on two islands, deer were predator-free but had strongly depleted their environment (safe/poor islands). On the third island, deer were culled by means of regular hunts and had access to a partially recovered forest understory in terms of food supply (risky/rich island).We considered four questions: 1) on what resources do abundant deer populations rely in heavily browsed environment?; 2) how do deer physiological stress response vary with either food stress or predation risk?; 3) do predator-naïve deer maintain anti-predator behaviors, like vigilance, in heavily browsed environments and how do they respond to predator olfactory cues?; and 4) how do predator-naïve deer respond to an experimental hunting for fear in a heavily browsed environment and how does it affect the vegetation? We showed that: 1) the subsidies from canopy litterfall and the annual growth from rhizomatous plants offered a large energy supply for deer and contributed to maintain abundant deer population in forests with depleted understory; 2) deer did not mount a physiological stress response in presence of either starvation or predation risks, and we suggested that behavioral and/or physiological adjustments allowed deer to mitigate their exposure to either stressor; 3) on safe/poor islands, deer maintained vigilance despite 60 years of isolation from predation. Predator-naïve deer avoided eating bait in presence of urine of wolf (dangerous) but not of bear (less dangerous). This suggested an innate threat-sensitive foraging strategy in deer. Deer also remained less time at the bait stations in presence of wolf urine but did not increase their vigilance levels. This suggested that deer were likely to manage risk more by space use than by vigilance; 4) In response to an experimental hunting for fear conducted on one of the safe/poor island, we showed that the deer less-tolerant to humans avoided the hunting area; The deer more-tolerant to human disturbance did not. This stressed the importance to consider the human-induced selection of behavioral traits during wildlife management. We also monitored the growth of four fast-growing coastal plant species and showed that the hunting for fear promoted the growth of half of them. This highlighted the intricate interaction among deer foraging behavior and plant characteristics and emphasized the importance of management targets in the choice of management tools. We discussed the long-terms effect of hunting as management tool for deer.

<p>Detta är ett naturvetenskapligt arbete som omfattas både av en kvantitativ och en kvalitativ undersökning. Syftet med arbetet är att undersöka mellanskarvens födoval i sjön Sommen, samt att närmare studera huruvida det unika beståndet av röding och öring ingår i mellanskarvens födoval. Sommens Fiskevårdsområde har fått tillstånd till skyddsjakt på mellanskarv av Länsstyrelsen och det främsta skälet skulle vara att fågeln prederar röding och öring. Genom att analysera mellanskarvens spyboll och jämföra innehållet med referensfiskar fångade från samma sjö ska vi se om beslutet från Länsstyrelsen är befogat. Insamling av spybollar och referensfiskar utfördes i fält medan analys av spybollar utfördes på laboratorium. I resultatet av undersökningen konstaterades att mellanskarven i Sommen nästan uteslutande äter abborre. I de analyserade spybollarna som omfattas av denna undersökning återfanns inte röding och öring. Detta skulle innebära att Länsstyrelsens beslut om skyddsjakt på mellanskarv i Sommen p.g.a. predation av röding och öring inte är befogad.</p>

Detta är ett naturvetenskapligt arbete som omfattas både av en kvantitativ och en kvalitativ undersökning. Syftet med arbetet är att undersöka mellanskarvens födoval i sjön Sommen, samt att närmare studera huruvida det unika beståndet av röding och öring ingår i mellanskarvens födoval. Sommens Fiskevårdsområde har fått tillstånd till skyddsjakt på mellanskarv av Länsstyrelsen och det främsta skälet skulle vara att fågeln prederar röding och öring. Genom att analysera mellanskarvens spyboll och jämföra innehållet med referensfiskar fångade från samma sjö ska vi se om beslutet från Länsstyrelsen är befogat. Insamling av spybollar och referensfiskar utfördes i fält medan analys av spybollar utfördes på laboratorium. I resultatet av undersökningen konstaterades att mellanskarven i Sommen nästan uteslutande äter abborre. I de analyserade spybollarna som omfattas av denna undersökning återfanns inte röding och öring. Detta skulle innebära att Länsstyrelsens beslut om skyddsjakt på mellanskarv i Sommen p.g.a. predation av röding och öring inte är befogad.

La variabilitat de la depredació de llavors en l'espai i temps poden oferir oportunitats a les males herbes per escapar dels depredadors. Els nivells de depredació en cereals de secà van ser dels més alts mai registrats cultius extensius (46-100%). El moment de producció de les llavors de males herbes es superposava amb el període de major demanda. La distribució espacial dels nius era no aleatòria. Els nius grans estaven més regularment distribuïts, els nius petits més agrupats. Les formigues van respondre amb taxes de depredació extremadament elevades (99-100%) a totes les densitats de llavors aplicades L. (1000-20.000 llavors m-2), amb una resposta denso-independent. La mida de rodal va influir en les taxes de depredació per formigues. Va ser major en els rodals més grans (99-100%) i menor en els més petits (78-94%). Aquesta investigació va quantificar la variabilitat espaciotemporal en la depredació de llavors de cereals de secà i l'eficàcia.Summary / La variabilidad de la depredación de semillas en el tiempo y espacio ofrecen oportunidades a las malas hierbas para escapar de los depredadores. Los niveles de depredación en cereales de secano fueron entre los más altos registrados jamás en cultivos extensivos (46-100%). El momento de producción de semillas de las malas hierbas se superponía con el período de mayor demanda. La distribución espacial de los nidos era no aleatoria. Los nidos grandes estaban más regularmente distribuidos, los nidos pequeños más agrupados. Las hormigas respondieron con tasas de depredación extremadamente elevadas (99-100%) a todas las densidades de semillas aplicadas (1.000 a 20.000 semillas m-2), con respuesta denso-independiente. El tamaño de parche influyó en las tasas de depredación por hormigas. Fue mayor en los parches más grandes (99-100%) y menor en los más pequeños (78-94%). Esta investigación cuantificó la variabilidad espacio-temporal de la depredación de semillas en cereales de secano y la eficacia. / The variability of seed predation in time and space may provide opportunities to weeds to escape predation. Seed predation rates by harvester ants in dryland cereals were among the highest ever recorded on arable fields (46-100%). The timing of weed seed shed overlapped with the period of highest demand. The spatial nest arrangement appeared to be non-random. The large nests were more or less regularly distributed, small nests tended to be more clumped. Harvester ants responded with extremely high predation rates (99-100 %) to all densities of Lolium multiflorum L. seeds applied (1000-20000 seeds m-2), and the response was density independent. Patch size influenced predation rates by harvester ants. Estimated seed predation rate was highest in the largest patches (99-100%), and lowest in the smallest patches (78-94 %). The current research quantified temporal and spatial variability in seed predation in dryland cereals and the influence to the efficacy of granivory.

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 119-131). Also available on the World Wide Web.