The effect of environmental modification of predator sensory abilities remains largely unknown, despite the importance of predators to ecosystem function. I conducted a series of experiments to investigate effects of hydrodynamics on the chemosensory search behavior and foraging success of two species of marine gastropods, knobbed whelks (

This dissertation presents an evaluation of coprolite specimens from the Lower Pecos canyonlands as records of individual dietary decisions. Prior studies of coprolites from this region have greatly expanded our knowledge of Archaic subsistence patterns, but have not taken full advantage of the record of individual dietary decisions recorded in each coprolite specimen. The menu, or dietary combinations, reflected in individual coprolite specimens are assessed through the identification of several congruent botanical components derived from the same food resource, phytoliths, fiber ultimates, and epidermal sheets. The data is analyzed with hierarchical cluster analysis, an exploratory statistical technique. The resultant menus reflected in these clusters are evaluated with reference to the diet-breadth model developed for the known staple resources of the canyonlands as well as the seasonal subsistence patterns observed in the ethnohistoric record of modern-day Mexico and Texas. This same technique is also applied to the coprolite data available from previous studies in the Lower Pecos canyonlands. Overall, the combined dietary data available for the Lower Pecos canyonlands presents a similar dependence on desertic plant resources throughout the Archaic. Three main menus are apparent in the specimens. The first menu consists of prickly pear (Opuntia sp.) cladodes, or nopales, and was principally, although not exclusively, consumed in the late spring. This menu is primarily consumed when other resources were not readily available and may be considered a dependable but undesirable meal. The second menu consists of pit-baked lechuguilla (Agave lechuguilla) and sotol (Dasylirion sp.) caudices, or hearts, common throughout the cool season. This menu entails high processing costs, but would provide a reliable caloric return. The third menu exhibits a monolithic reliance on prickly pear fruits, or tunas, during the summer. The ease of harvest and consumption is reflected in the seasonal dominance of this resource, which was assuredly a highly desirable meal. The dietary patterns recorded in the coprolite specimens from the Lower Pecos canyonlands demonstrate a seasonally variable diet-breadth that incorporated low-ranked resources during times of seasonal scarcity as well as a monolithic dependence on high-ranked resources when they were available in the local landscape.

Resource variation and species interactions require organisms to respond behaviorally, physiologically, and morphologically within and among generations to compensate for spatial and temporal environmental variation. One successful evolutionary strategy to mitigate environmental variation is phenotypic plasticity: the production of alternative phenotypes in response to environmental variation. Phenotypic plasticity yields multiple characters that may enable organisms to better optimize phenotypic responses across environmental gradients. In this thesis, I trace the development of thought on phenotypic plasticity and present two empirical studies that implicate phenotypic plasticity in producing morphological variation in response to resource variation. The first empirical study addresses trophic plasticity, population divergence, and the effect of fine-scale environmental variation in western mosquitofish (Gambusia affinis). Offspring from two populations were fed either attached or unattached food items offered in three orientations: (1) water surface, (2) mid-water, (3) benthic, and (4) a daily rotation of the former three (fine-grained variation). Attached food induced wide heads, blunt snouts and rounded pectoral fins relative to morphology in the unattached treatment. Mid-water feeding induced elongated heads and deeper mid-bodies relative to benthic and surface feeding induced morphologies. The rotating treatment produced intermediate morphologies. Population divergence seemed related to both trophic and predation ecology. Ecomorphological consequences of induced morphologies and the need for inclusion of greater ecological complexity in studies of plasticity are discussed. The second study examines induced morphological plasticity and performance in red drum (Sciaenops ocellatus). I fed hatchery fish either hard or soft food for two months. Performance trials were designed to measure their ability to manipulate and consume hard food items. External morphology and the mass of pharyngeal crushing muscles were assessed for variation among treatments. A hard food diet induced deeper bodies and larger heads, more massive pharyngeal muscles, and initially more efficient consumption of hard food than fish receiving soft food. The observed morphological variation is in accordance with variation among species. Determining evolutionary mechanisms operating within red drum populations should eventually aid in developing and optimizing conservation efforts and ease the transition from hatchery facilities to estuaries.

A majority of the arid grasslands in the western U.S. have been dramatically altered by anthropogenic influences resulting in degradation and desertification. Within the arid grasslands of North America a guild of burrowing herbivorous rodents that includes kangaroo rats (Dipodomys spp.) and prairie dogs (Cynomys spp.) is often considered integral to arid grassland maintenance. As part of the larger guild of burrowing herbivorous rodents, kangaroo rats are considered to be an important keystone guild whose role as ecosystem engineers and habitat modifiers complements that of prairie dogs. Together these species organize and structure arid grassland ecosystems and the biodiversity therein, by providing a mosaic of microhabitat patches, thus increasing overall heterogeneity. In an area where black-tailed prairie dogs (C. ludovicianus) were reintroduced, I used Giving-up Density (GUD) to assess the indirect effects black-tailed prairie dogs might have on the foraging patterns of resident kangaroo rats (D. spectabilis and D. merriamii). My objective was to compare and contrast kangaroo rat foraging GUD within and along the boundary of a on a recently established black-tailed prairie dog colony with that in the surrounding unmodified native habitat. This enabled assessment of whether black-tailed prairie dogs had an influence on the perceived quality of the habitat by kangaroo rats. Kangaroo rats visited off-colony feeding trays more frequently, and collected a greater mean mass of seed per tray as well. This indicates that the kangaroo rats perceived the area off the prairie dog colony as having a lower foraging cost than on the colony or along the colony edge. I conclude that from the perspective of the seed-eating kangaroo rat, the colony is not viewed as high quality habitat. What impact the reintroduction and management of one keystone species might have on another keystone species deserves additional consideration as we attempt to restore arid grassland ecosystems.

Stereotypic behaviors in all animals are more often than not associated with poor welfare. Limited access to perform species specific behaviors is often a reason for the development of stereotypies. Elephants with their great intelligence and need of social contact, coupled with a destructive a behavior are especially difficult to house in captivity. To decrease the occurrence of stereotypic behaviors in elephants, environmental enrichment in form of food enrichment is a good option, since elephants have a great need of foraging. The aim of this study was to investigate if an extra supply of food enrichment could decrease the presence of stereotypic behaviors at night in three Asian elephants at Kolmården zoo. Already existing hay nets attached to wires in the roof were used and connected to a timer. The hay nets were lowered to vision trunk reach between 6:00 am and 6:30 am during five days and the frequencies of selected behaviors were compared with the frequencies of the same behaviors during five preceding baseline nights. The animals were filmed using mounted cameras with IR lights. There was a significant decrease of stereotypic behavior for one of the elephants, but all three showed an increase in foraging whereof the increases were significant for two of them. One of the elephants showed no stereotypic behaviors at all during the study. To keep in mind is that the elephants have different backgrounds and experiences which might have influenced the results.

R??sum?? : La reproduction entra??ne des d??penses ??nerg??tiques importantes chez les femelles mammif??res. Ces d??penses sont suppos??es diminuer l'??nergie disponible pour d'autres traits positivement corr??l??s ?? l'aptitude ph??notypique et augmenter les besoins d'alimentation. Toutefois, des diff??rences individuelles dans la capacit?? d'acquisition et d'allocation peuvent masquer l'impact n??gatif de l'effort reproducteur. La manipulation exp??rimentale de l'effort reproducteur et le contr??le statistique des effets individuels sont deux approches puissantes et compl??mentaires mises en ??uvre dans le cadre de mon ??tude afin de contr??ler pour l'h??t??rog??n??it?? individuelle. Elles ont permis de montrer clairement un co??t de la reproduction chez le kangourou gris de l'Est (Macropus giganteus). Dans un premier temps, nous avons trouv?? que le co??t de la reproduction affectait le montant d'??nergie allou?? ?? certaines fonctions somatiques (CHAPITRE I). L'effort reproducteur diminuait le gain de masse et la croissance des jambes pour des intervalles de capture sup??rieurs ?? deux ans. Chez les femelles non manipul??es, un effet n??gatif sur le gain de masse ??tait aussi observable pour un intervalle inf??rieur ?? 3 ans. ?? l'??chelle de deux ??v??nements successifs de reproduction, le gain de masse et dans une moindre mesure la croissance des bras, mais non des jambes diminuaient avec un effort reproducteur plus important ?? la pr??c??dente reproduction. Ensuite, nous avons d??montr?? qu'il y avait un co??t de la reproduction en terme de futur succ??s reproducteur (CHAPITRE II). Les individus dont l'effort reproducteur avait ??t?? diminu?? exp??rimentalement produisaient davantage de jeunes qui survivaient au stade 'LPY', ??g??s approximativement de 7 mois, que les femelles contr??les. Ils diminuaient ??galement davantage leur taux de reproduction en allongeant l'intervalle entre les naissances, mais la survie au sevrage n'??tait pas affect??e. Le CHAPITRE III montre que les femelles adaptaient leur comportement alimentaire en fonction de leur statut reproducteur. En comparaison avec les individus manipul??s ou ayant perdu leur jeune, les femelles allaitantes augmentaient leur temps pass?? ?? s'alimenter durant la journ??e, l'intensit?? de leurs bouch??es et de leur mastication sans impliquer de compromis avec la vigilance. Nous avons aussi d??couvert que la survie au sevrage du jeune pr??c??dent menait ?? une augmentation du taux de bouch??es pour l'ann??e en cours. Les CHAPITRES I et II ont mis en ??vidence l'effet non n??gligeable des diff??rences individuelles sur la d??tection des co??ts de la reproduction. En effet, en l'absence de manipulation exp??rimentale ou de contr??le statistique, aucun compromis n'??tait d??tect?? autant en terme de croissance que de prochaine reproduction. Au contraire, des corr??lations positives entre l'effort reproducteur et les autres traits ont ??t?? trouv??es. Le CHAPITRE I sugg??rait notamment que cette variabilit?? du succ??s reproducteur ??tait li??e ?? l'h??t??rog??n??it?? individuelle dans le gain de masse maternelle qui augmentait la survie du jeune. Dans le CHAPITRE II, une corr??lation positive entre les probabilit??s d'avoir un 'LPY' lors de deux ??v??nements successifs de reproduction sugg??rait que certaines femelles ??taient capables de mener ?? bien ou non leur reproduction, mais cela ind??pendamment de l'effort reproducteur pr??c??dent. Enfin dans le dernier CHAPITRE (III), l'effet al??atoire ??tait significatif dans l'analyse de diff??rents comportements d'alimentation, ce qui pourrait ??tre li?? aux diff??rences de gain de masse des femelles pr??sent??es dans le CHAPITRE I. Certaines contraintes individuelles affectant le co??t de la reproduction ont ??t?? identifi??es. La masse et la condition corporelle augmentaient le succ??s reproducteur et diminuaient l'intervalle entre deux naissances successives (CHAPITRES I et II), mais contrairement ?? de pr??c??dentes ??tudes le comportement d'alimentation des femelles n'??tait pas affect?? par leur masse (CHAPITRE III). L'??ge des individus avait ??galement une influence. Les jeunes femelles croissaient davantage, avaient aussi une prise alimentaire plus importante et subissaient un co??t de reproduction sup??rieur. Ce dernier se traduisait par un taux d'??chec plus ??lev?? ?? la reproduction suivante si les jeunes femelles avaient eu un jeune l'ann??e pr??c??dente (CHAPITRES I, II et III). Des contraintes environnementales fortes influen??aient la reproduction des femelles. La croissance, le succ??s reproducteur, l'intervalle entre les naissances et les comportements d'alimentation variaient suivant le site et l'ann??e d'??tude. Le site du Promontory et l'ann??e 2011 apparaissaient particuli??rement limitants. En effet en 2011, le gain de masse et le succ??s reproducteur ont diminu?? et l'intervalle de naissance et la prise de nourriture pour les femelles allaitantes ont augment?? (CHAPITRE I,II et III). Nous cherchions ??galement ?? mettre au jour une allocation diff??rentielle des m??res suivant le sexe de leur jeune. Si le co??t sup??rieur d'avoir un m??le par rapport ?? une femelle ??tait ??vident quant aux taux de bouch??es (CHAPITRE III), il s'est av??r?? plus difficile ?? d??tecter sur d'autres traits. ?? Anglesea, les jeunes m??res avaient moins de probabilit?? d'avoir un jeune qui atteigne le stade 'LPY' apr??s avoir eu un fils qu'une fille (CHAPITRE II). Toutefois, des r??sultats contraires ?? nos attentes ont ??t?? trouv??s, du moins au premier abord, sur la croissance et le succ??s reproducteur subs??quent. Ainsi, les femelles qui avaient eu une fille perdaient davantage de masse (CHAPITRE I) et avaient g??n??ralement une probabilit?? moindre de produire un jeune qui atteigne le stade 'LPY' ou qui soit sevr?? par la suite (CHAPITRE II). En revanche, l'intervalle de naissance n'??tait pas diff??rent suivant le sexe du jeune alors qu'il ??tait fortement affect?? par le co??t de la reproduction d??montr?? gr??ce ?? la manipulation, invoquant une autre explication qu'un co??t sup??rieur des filles par rapport aux fils. En effet, les femelles qui ??taient en mauvaise condition corporelle gagnaient de la masse quand elles produisaient une fille, mais pas un fils (CHAPITRE I). De surcro??t, les jeunes m??res avaient moins de chances de sevrer un jeune ?? l'??v??nement de reproduction suivant si elles avaient eu un fils plut??t qu'une fille, et le succ??s reproducteur des m??res des fils n'??tait plus diff??rent de celui des m??res des filles dans les ann??es plus difficiles (CHAPITRE II). Enfin, les m??res des fils augmentaient la quantit?? de nourriture ing??r??e si elles avaient sevr?? un jeune l'ann??e pr??c??dente, mais les m??res des filles la diminuaient. Ces diff??rents r??sultats sugg??raient fortement qu'un ajustement du sexe-ratio ??tait utilis?? quand les ressources individuelles ou environnementales contraignaient davantage la reproduction. En conclusion, pour limiter le d??calage entre les besoins ??nerg??tiques et la disponibilit?? en nourriture, les femelles chez le kangourou gris de l'Est pourraient modifier l'allocation de leurs ressources ?? la reproduction en reportant la prochaine mise bas et en produisant un jeune du sexe le moins co??teux en accord avec les contraintes individuelles et environnementales. Ces r??sultats soulignent l'importance d'??tudes avec un suivi individuel sur plusieurs ann??es afin de pouvoir comprendre la variabilit?? des strat??gies de reproduction et leurs cons??quences sur la dynamique des populations. // Abstract : Reproduction in living beings, particularly in female mammals that produce milk, is costly, potentially involving trade-offs with life-history traits if resources are limited and an increase in foraging effort. Individual differences may, however, hide the negative effects of this cost on life-history traits. I used two powerful and complementary approaches, to deal with individual heterogeneity: experimental manipulation of reproductive effort and statistical control of individual effect. Using both approaches, I investigated the effect of presence, size and sex of young on growth, subsequent reproduction and individual foraging behaviours of females. I used data of tagged free-ranging eastern grey kangaroos (Macropus giganteus) collected over six years at five study sites in Victoria, Australia. There was a clear cost of reproduction. Reproductive effort decreased mass gain and limb growth for inter-capture intervals greater than two years. Over two successive reproductive events, mass gain and arm growth were reduced but leg growth was independent of reproductive effort (CHAPTER II).In addition, survival to Large Pouch Young ('LPY') stage, about 7 months of age, was higher and birth rate lower in manipulated compared to control females but survival to weaning was not affected (CHAPTER III). CHAPTER IV shows that lactating females cope with current reproductive costs by increasing ivtime spent foraging as well as bite and chewing rates without decreasing vigilance comparedto non lactating ones. Bite rate was also greater for females that weaned a young at the previous reproductive event. My study supports reproductive cost hypothesis while showing substantial individual differences. To limit mismatch between energetic needs and resource availability, females of eastern grey kangaroo could modify resource allocation to reproduction by delaying birth date of subsequent young and producing the less costly sex according to individual and environmental constrains. My thesis shows the importance of experimental approach and individual monitoring over multiple years to understand the diversity of reproductive strategies and their consequences in evolutionary ecology and population dynamic.

The Optimal Foraging Theory, rooted in the processual archaeology, uses a measuring methodology where the foraging strategy that gives the highest payoff measured as the highest ratio of energy gain per time unit is analysed (Mac Arthur & Pianca 1966, Emlen 1966). The theory is a branch of evolutionary ecology why much attention is paid to the interdependence of humans and preys and environmental conditions caused by climatologically and geographical changes or by overexploitation or other changes caused by humans. The analysis of Early Mesolithic pioneers onGotland, who settle in a transforming landscape, leaves indications of a Maglemose culture origin, probably from flooded original settlements in the south/southwest Baltic basin. The pioneers have to adapt to a seal-hunting economy dominated by grey seal which give the best cost-benefit outcome as big terrestrial mammals are missing and only mountain hare is available. The diet is narrow and there is a great risk for deficiency diseases as well as for acquiring hypervitaminosis and osteoporosis caused by excess of seal food. There is a hiatus c. 5000-4500 BC in the archaeological records on Gotland and the south-western Baltic region, and the master thesis hypothesises that Littorina Transgression I with a severe cold dip called the “8.2 ka BP cold event” has a delayed, but such a severe impact also on fauna and flora on Gotland, that the ecological system is destroyed. The possibility for humans to survive in a sustainable society is questionable. The extremely cold winters during this c. 400 years cold event, with glaciers moving southwards, delayed the blooming season, diminished the harvest and changed both flora and fauna. When the ecological niche for the grey seal is destroyed with flooded beaches close to the pioneers, human overexploitation is reinforced. With a diminishing population of mountain hare, which eventually gets extinct at the end of the Mesolithic, there are no alternatives but some birds and fish, hard to catch. Probably the pioneers abandon Gotland or move to a higher level on Gotland but no records are yet found why the period is called a hiatus. Extinction is the worst scenario or survival in such a small number that a sustainable society is lost. If so, new population groups repopulatedGotlandafter the Littorina transgressions. The origin is still unknown of the Pitted-ware and Funnelbeaker cultures that are populating Gotland after the transgressions. This master thesis can not confirm an affluent life style but rather a suffering starving society flooded by Littorina transgressions and struggling with the severe cold, caused by the “8.2 ka cold event” that makes the environmental conditions even worse. The subsistence economy is successively destroyed which probably causes the hiatus in archaeological records. The Littorina Transgression I with the “8.2 cold event” and the lack of terrestrial big animals are bottle necks. / Optimal Foraging Theory, med sina rötter i den processuella arkeologin, använder en metodik utgående från mätningar där insamlingsstrategin som ger den högsta avkastningen per tidsenhet analyseras (Mac Arthur & Pianca 1966, Emlen 1966). Teorin är en undergrupp inom den evolutionära ekologin och därför ägnas stor tid åt att uppmärksamma det ömsesidiga beroendet och påverkan som sker i miljön p.g.a. klimatologiska och geologiska orsaker men också p.g.a. mänsklig påverkan som exempelvis överförbrukning.  Analysen av tidigmesolitiska pionjärbosättare på Gotland, som möter ett landskap i förvandling, lämnar spår efter sig som tyder på ett ursprung i Maglemosekulturen i södra/sydvästra Östersjöregionen. De tvingas bli adapterade till en säljägarekonomi dominerad av gråsäl som ger det bästa energiutbytet, eftersom stora landdäggdjur saknas och endast bergshare finns tillgänglig. Dietvalet är smalt och det föreligger stor risk för både bristsjukdomar och A-vitaminförgiftning och osteoporos p.g.a. överkonsumtion av sälprodukter. Det finns ett uppehåll i de arkeologiska fynden c. 5000-4500 BC på Gotland liksom i södra Östersjöområdet. Magisteruppsatsens hypotes är att den kalla perioden med temperatursänkning som kallas ”8.2 ka BP cold event” under Littorinatransgression I har en fördröjd men så kraftigt övergripande effekt, på både djur- och växtliv på Gotland, att den förstör det ekologiska systemet och därmed möjligheten för människor att överleva i ett hållbart samhälle. De mycket hårda vintrarna under de c. 400 årens ”cold event” medför att glaciärerna dras sig söderut, blomningssäsongen fördröjs, skörden minskar och både fauna och flora förändras. När den ekologiska nischen för gråsälen förstörs av översvämmade stränder nära bosättarna förstärks överexploateringen, och då det inte finns någon alternativ föda utom en minskande harstam, svårfångade fåglar och fiskar, blir situationen fatal för de tidigmesolitiska bosättarna. Troligtvis flyttar de till andra platser inom Östersjönätverket eller till en högre nivå på Gotland, men fynd saknas hittills varför detta tomrum benämns ”hiatus”. Det värsta scenariot är att bosättarna dör ut eller överlever i ett så litet antal att det hållbara samhället går under.Om så är fallet återbefokas Gotland av gropkeramisk kultur och trattbägarkultur i anslutning till Littorinatrasgressionernas slut. Denna magisteruppsats kan inte konfirmera en livsstil i överflöd, utan snarare ett lidande svältande samhälle som översvämmas av Littorinatransgressioner med miljömässiga förhållanden som förvärras av den allvarliga kylan orsakad av ”8.2 ka cold event”.  Försörjningsmöjligheterna förstörs succesivt och befolkningen försvinner vilket troligen orsakar ett hiatus i de arkeologiska fynden. Littorina Transgression I med ”8.2 ka cold event” och bristen på stora landdjur är stora flaskhalsar.

When multiple predators foraging together have different individual consumption rates than predators foraging in isolation, they exhibit non-independent multiple predator effects on prey. I examined multiple predator effects in a system consisting of invasive green crabs (Carcinus maenas L.), native rock crabs (Cancer irroratus Say) and benthic macrofauna prey. First, I examined multiple predator effects when green crabs and rock crabs forage on soft-shell clams (Mya arenaria L.) in different habitat types (sand, sand with artificial seagrass) and assessed the behavioural mechanisms responsible for the observed predation effects. Independent multiple predator effects on prey were detected for most conspecific and heterospecific pairs in both habitat types. In general, crab foraging behaviours were not affected by the presence of another predator. Interactions between predators did not influence foraging behaviours because encounters were infrequent, short in duration and predominantly non-aggressive. A non-independent multiple predator effect on prey (marginally significant) was observed when green crabs foraged with rock crabs in artificial seagrass. This effect, however, could not be explained by the observed crab behaviours. Second, I investigated multiple predator effects when green crabs and rock crabs forage on a soft-sediment macrofauna community. Because crabs did not have significant predation effects on the community throughout the experiment, I did not evaluate multiple predator effects on prey. It is possible that crab predation was not important in regulating the macrofauna community, in which case multiple predator effects were non-existent. Predation may have been suppressed due to a combination of factors, including interactions between predators, harsh environmental conditions or a sub-optimal prey field. Alternatively, my ability to detect significant predation effects may have been hindered because of prey movement in and out of cages or low statistical power. Overall, results from this thesis demonstrate that multiple predator effects on prey may differ with habitat and highlights the importance of conducting behavioural observations to better understand interactions between predators and the resulting consequences for prey. Multiple predator effects on a soft-sediment community should be re-evaluated to assess the importance of these crab species in regulating benthic macrofauna under natural conditions.

No description available.

Changes in the marine ecosystem can affect the distribution, survival, and reproductive success of seabirds. Therefore, a better understanding of factors influencing the marine distribution and abundance of seabirds can provide insight into ecological hypotheses and have important conservation implications. Yet at-sea habitat selection by seabirds has received far less attention than have investigations of their breeding biology. I studied the patterns and processes of marine habitat selection by seabirds in nearshore waters of Pacific Rim National Park Reserve, Vancouver Island, British Columbia. The study focused on comparative analyses among five sympatric species: marbled murrelet (Brachyramphus marmoratus), common murre (Uria aalge), rhinoceros auklet (Cerorhinca monocerata), pigeon guillemot (Cepphus columba) and pelagic cormorant (Phalacrocorax pelagicus). I used a multi-scaled and multi-disciplined approach combining shore-based telescope observations, vessel-based surveys, and developed new techniques for mapping nearshore seabird distributions. Patterns of habitat selection were examined through vessel-based surveys and species-habitat modeling. Vessel-based transects are fundamental to studies of seabird ecology, yet standardized protocols often fail to account for detectability biases. Distance-sampling methods were used to quantify seabird detectability along transects and showed extensive variability (20-80% of birds detected) depending on species, year, and observer. Corrected estimates of bird densities were used in habitat selection modeling, which demonstrated inter-specific and inter-annual differences in species-habitat associations. Most species showed distinct partitioning in habitats, particularly with respect to substrate and along gradients of depth and sea-surface temperature/salinity. Thus, environmental variability is a key factor structuring habitat use and coexistence in this community of piscivorous seabirds. Processes of habitat selection were studied through observations of foraging behaviour, estimates of prey availability, and spatial-statistical analysis of seabird distributions. Marbled murrelets increased foraging effort in years and seasons with scarce prey and poor oceanographic conditions and decreased foraging effort at sites with high prey availability. Despite their flexible activity budgets, increased foraging effort was inadequate to buffer reproductive success in a poor prey year, suggesting that prey availability is a limiting factor in habitat use and population growth for murrelets. Theodolite-based mapping studies examined the fine-scale distribution patterns of murrelets and murres. Nearest neighbour spatial statistics tested for competition over foraging space and showed avoidance of murres by murrelets. The results of these studies have implications for the management and conservation of the imperiled marbled murrelet in British Columbia and elsewhere in their range. I demonstrate a clear link between prey availability and consequences for reproductive success. Habitat selection models provide a step towards identifying critical marine habitats which must be protected under the Species at Risk Act. Murrelets show high forage site fidelity and associations with spatially fixed habitat components (beaches), suggesting that marine protected areas may have an important role to play in the conservation, management and recovery of murrelet populations.