La chasse – comme la prédation naturelle - induit des réponses comportementales par les individus chassés qui cherchent ainsi à éviter ou à reduire le risque. Il est en particulier fréquent d'observer un changement dans leur utilisation de l'espace, mais l'articulation et les déterminants des réponses aux différentes échelles spatiales restent mal compris. De même, s'il a été suggéré que ces modifications comportementales pouvaient affecter en cascade la végétation, cela reste à tester. Pour combler ces lacunes, j'ai, (1) étudié, dans un paysage agricole du sud de la France, une population chassée de chevreuils et leur utilisation des milieux ouverts risqués et des couverts boisés, au cours de périodes de risque contrasté ; (2) testé, sur une population canadienne de cerfs à queue noire dépourvue de prédateurs et exempte de chasse, l'influence d'une chasse expérimentale sur le comportement des animaux et sur la végétation. J'ai montré que les chevreuils répondaient à une augmentation du risque à plusieurs échelles spatiales. Ils réduisaient leur utilisation des habitats risqués, et dans certains cas se rapprochaient des couverts, de jour ces deux réponses étant couplées au niveau individuel. Le gradient paysager d'ouverture du milieu contraignait cependant les niveaux de réponses observées et les stratégies individuelles. Au Canada, j'ai observé un évitement de la zone chassée par les cerfs les plus sensibles à la présence humaine, corrélé à une diminution de l'abroutissement pour deux des quatre espèces de plantes étudiées. J'ai intégré ces résultats dans une discussion sur l'utilisation de la chasse pour gérer les populations d'herbivores et leurs impacts sur la végétation. / Hunting – similarly to natural predation – induces behavioural responses of hunted individuals which aims at avoiding or reducing risk. Particularly, changes in space use are frequently observed, but the articulation and determinants of these changes at multiple spatial scales are still poorly understood. Also, although it has been suggested that these changes might cascade on the vegetation, this remains to be tested. To fill these gaps, I (1) studied a hunted roe deer population living in an agricultural landscape in southern France where roe deer can find open risky habitats and woody covers; and (2) tested black-tailed deer behavioural response to an experimental hunt in a predator- and hunting-free population in the Haïda-Gwaii archipelago (BC, Canada). I also investigated the possible cascading effects on the vegetation. I showed that roe deer responded to increased hunting pressure at multiple scales, reducing their use of the risky habitats and, in specific situations, their distance to the nearest cover. At day-time those two responses were coupled at the individual level. Generally, landscape openness constrained individual responses and strategies. In the hunting-for-fear experiment conducted on Haida Gwaii, I found that only the deer less-tolerant to human disturbance avoided the hunting area. A simultaneous reduction in browsing pressure on two out of the four plant species monitored was found however. I integrated these results in a general discussion on the possible role of hunting as a tool to manage abundant deer populations and their impacts on the vegetation.

Made available in DSpace on 2014-12-17T14:33:11Z (GMT). No. of bitstreams: 1 AngelicaNSB_DISSERT.pdf: 1338849 bytes, checksum: e892c51257539cf2057935e233971d4c (MD5) Previous issue date: 2013-07-16 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Many prey organisms change their phenotype to reduce the predation risk. However, such changes are associated with trade-offs, and can have negative effects on prey growth or reproduction. Understand how preys assess the predation risk is essential to evaluate the adaptive value of predator-induced phenotypic and its ecological consequences. In this study, we performed a mesocosm experiment to test: i) if growth and stoichiometry of Lithobates catesbeianus tadpoles is altered in response to giant water bug presence (Belostoma spp.); ii) if these responses depend on tadpoles density in environment. Here, we show that tadpoles growth and stoichiometry are not changed by predator presence, neither in low nor in high densities. Our results suggest that tadpoles exposed to predation risk regulate their physiology to preserve the elemental stoichiometric homeostase of their body and excretion. Further, point out to need for future studies that elucidate under what conditions growth and stoichiometry are changed in response to predation risk / Muitos organismos alteram o seu fen?tipo para reduzir o risco de preda??o. No entanto, tais modifica??es est?o associadas a trade-offs, que podem ter efeitos negativos sobre o crescimento e a reprodu??o destes organismos. Compreender como as presas avaliam o risco de preda??o ? fundamental para avaliar o valor adaptativo das mudan?as fenot?picas induzidas pelo predador e suas consequ?ncias ecol?gicas. Neste estudo n?s realizamos um experimento em mesocosmo para testar: i) se o crescimento e a estequiometria dos girinos da esp?cie Lithobates catesbeianus ? alterado em resposta a presen?a de baratas d ?gua predadoras (Belostoma spp.); ii) se estas respostas dependem da densidade de girinos no ambiente. Aqui n?s mostramos que os girinos n?o t?m o seu crescimento nem a sua estequiometria afetada pela presen?a do predador, esteja os girinos em baixas ou em altas densidades. Nossos resultados indicam que os girinos expostos ao risco de preda??o regularam sua fisiologia a fim de preservar a homeostase estequiom?trica do seu corpo e excretas. Al?m disso, aponta a necessidade de experimentos que elucidem em que condi??es o crescimento e a estequiometria de girinos s?o modificados em resposta ao risco de preda??o

Predators exert strong direct and indirect effects on ecological communities by intimidating their prey. Non-consumptive effects (NCEs) of predators are important features of many ecosystems and have changed the way we understand predator-prey interactions, but are not well understood in some systems. For my dissertation research I combined a variety of approaches to examine the effect of predation risk on herbivore foraging and reproductive behaviors in a coral reef ecosystem. In the first part of my dissertation, I investigated how diet and territoriality of herbivorous fish varied across multiple reefs with different levels of predator biomass in the Florida Keys National Marine Sanctuary. I show that both predator and damselfish abundance impacted diet diversity within populations for two herbivores in different ways. Additionally, reef protection and the associated recovery of large predators appeared to shape the trade-off reef herbivores made between territory size and quality. In the second part of my dissertation, I investigated context-dependent causal linkages between predation risk, herbivore foraging behavior and resource consumption in multiple field experiments. I found that reef complexity, predator hunting mode, light availability and prey hunger influenced prey perception of threat and their willingness to feed. This research argues for more emphasis on the role of predation risk in affecting individual herbivore foraging behavior in order to understand the implications of human-mediated predator removal and recovery in coral reef ecosystems.

For over three decades, amphibian populations have been declining across the globe. Emerging infectious diseases are responsible for some of these declines. Ranaviruses have caused die-offs in wild amphibian populations on 4 continents, in 5 Canadian provinces, and in over 25 U.S. states. In order to understand host-pathogen dynamics, it is critical to establish baseline information on species susceptibility and the effects of natural stressors. The goal of my thesis research was to quantify the effects of anuran development and exposure to invertebrate predators on species-specific susceptibility to ranavirus. My experiments were designed in factorial arrangements, and consisted of exposure to ranavirus during different developmental stages or with and without predator cues in a controlled environment. I found that exposure to invertebrate predator cues did not increase susceptibility to ranavirus for 4 anuran species tested. Susceptibility differed among embryo, hatchling, larval and metamorph stages, but trends differed among species and did not follow predictions based on Xenopus laevis immune function. Low susceptibility during the embryo stage was the only consistent development result among species, perhaps owing to protective qualities of the vitelline membrane or mucoidal capsules surrounding the embryo. Across 7 anuran species tested, mean mortality rates ranged from 5 – 100%, with Lithobates sylvaticus and Scaphiopus holbrookii most susceptible. I found that infection rates and viral load were correlated with mortality rates, thus these variables are good indicators of susceptibility to ranavirus. My results indicate that ranaviruses can cause catastrophic natural mortality in some anuran species, and likely play a significant role in local population dynamics. For highly susceptible species, ranaviruses could cause local extirpations that lead to species declines. More information is needed on the role of natural (e.g., co-infection, competition) and anthropogenic stressors in driving ranavirus epizootic events. I encourage natural resource agencies to initiate ranavirus surveillance programs, especially for rare species and fragmented populations. Future studies should take an immunogenetic approach to identifying mechanisms driving susceptibility. Identifying mechanisms associated with ranavirus emergence is fundamental to developing science-based conservation strategies.

Made available in DSpace on 2014-12-17T15:37:13Z (GMT). No. of bitstreams: 1 PedroZPMRM_DISSERT.pdf: 485516 bytes, checksum: 5e7cc13b6cdb53047d1dea3153509081 (MD5) Previous issue date: 2012-05-29 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Among placental mammals, primates are the only ones to present trichromatic color vision. However, the distribution of trichromacy among primates is not homogeneous: Old World primates shows an uniform trichromacy (with all individuals being trichromats) and New World primates exhibit a color vision polymorphism (with dichromatic males and dichromatic or trichromatic females). Visual ecology studies have investigated which selective pressures may have been responsible for the evolution of trichromacy in primates, diverging from the dichromat standard found in other mammals. Cues associated with foraging and the socio-reproductive status were analyzed, indicating a trichromatic advantage for the rapid detection of visually conspicuous objects against a green background. However, dichromats are characterized by an efficient capture of cryptic and camouflaged stimuli. These advantages regarding phenotype may be responsible for the maintenance of the visual polymorphism in New World primates and for the high incidence of color blindness in humans (standing around 8% in Caucasian men). An important factor that has not yet been experimentally taken into account is the predation risk and its effect on the evolution of trichromacy in primates. To answer this question, we prepared and edited pictures of animals with different coats: oncillas (Leopardus spp.), puma (Puma concolor) and ferret (Galictis cuja). The specimens were taxidermized and the photographs were taken in three different vegetation scenarios (dense forest, cerrado and grassland). The images of the predators were manipulated so that they fit into two categories of stimulus size (small or large). After color calibration and photo editing, these were presented to 40 humans (20 dichromats and 20 trichromats) by a computer program, which presented a set of four photos at a time (one picture containing the taxidermized animal amid the background vegetation and three depicting only the background vegetation) and recorded the response latency and success rate of the subjects. The results show a trichromatic advantage in detecting potential predators. The predator detection was influenced by the background, the predator species, the dimension of the stimulus and the observer s visual phenotype. As humans have a high rate of dyschromatopsias, when compared to wild Catarrhini or human tribal populations, it is possible that the increased rate of dichromats is a result of reduced pressure for rapid predator detection. Since our species came to live in more cohesive groups and resistant to attack by predators, with the advent of agriculture and the formation of villages, it is possible that the lower risk of predation has reduced the selection in favor of trichromats / Dentre os mam?feros placent?rios, os primatas s?o os ?nicos a apresentarem uma vis?o de cores tricromata. Contudo, a distribui??o da tricromacia dentre os primatas n?o ? homog?nea: primatas do Velho Mundo apresentam uma tricromacia uniforme (com todos os indiv?duos sendo tricromatas) e primatas do Novo Mundo apresentam um polimorfismo de vis?o de cores (com machos dicromatas e f?meas dicromatas ou tricromatas). Estudos em ecologia visual t?m investigado que press?es seletivas podem ter sido respons?veis pela evolu??o da tricromacia em primatas, divergindo do padr?o dicromata encontrado nos demais mam?feros. Pistas associadas ao forrageio e ao contexto s?cio-reprodutivo foram analisadas, indicando uma vantagem tricromata na detec??o r?pida de objetos visualmente consp?cuos no ambiente. Entretanto, dicromatas s?o caracterizados pela captura eficiente de est?mulos cr?pticos e camuflados. Estas vantagens relativas aos fen?tipos podem ser respons?veis pela manuten??o do polimorfismo visual em primatas do Novo Mundo e pelo alto ?ndice de daltonismo em humanos (situando-se em torno de 8% em homens caucasianos). Um importante fator que ainda n?o foi levado experimentalmente em conta ? o risco de preda??o e o seu efeito na evolu??o da tricromacia em primatas. Para responder esta pergunta, n?s preparamos e editamos fotografias de animais com pelagens distintas: gatos-do-mato (Leopardus spp.), puma (Puma concolor) e fur?o (Galictis cuja). Os exemplares estavam taxidermizados e as fotografias foram capturadas em tr?s diferentes cen?rios de vegeta??o (mata fechada, cerrado e campo aberto). As imagens dos predadores foram manipuladas para que eles se encaixassem em duas categorias de tamanho de est?mulo (pequenos ou grandes). Ap?s a calibra??o das cores e edi??o das fotos, estas foram apresentadas a 40 humanos (20 dicromatas e 20 tricromatas) por um programa de computador, o qual apresentava um conjunto de quatro fotos por vez (uma foto contendo o animal taxidermizado em meio ? vegeta??o de fundo e outras tr?s contendo apenas a vegeta??o de fundo) e registrava a lat?ncia de resposta e a taxa de acerto dos sujeitos. Os resultados apontam uma vantagem tricromata na detec??o de potenciais predadores. A detec??o dos predadores foi influenciada pelo cen?rio de fundo, pelo tipo de predador, pela sua dimens?o e pelo fen?tipo visual do observador. Como os humanos apresentam uma elevada taxa de discromatopsias, quando comparados com popula??es selvagens de outros Catarrhini ou mesmo popula??es humanas tribais, ? poss?vel que o aumento no ?ndice de dicromatas seja resultado de uma press?o reduzida de detec??o r?pida de predadores. Uma vez que nossa esp?cie passou a viver em grupos mais coesos e resistentes aos ataques de predadores, com o advento da agropecu?ria e a forma??o de vilas, ? poss?vel que o menor risco de preda??o tenha relaxado a sele??o a favor de tricromatas

A travers l'exemple du lièvre d'Europe (Lepus europaeus), l'objectif de cette thèse est de contribuer à une meilleure compréhension des mécanismes régissant les variations d'abondance observées dans les populations animales. Dans ce cadre la dispersion est pressentie comme l'une des principales sources de variation. Après avoir rappelé les principales notions théoriques nécessaires à l'appréhension de ce travail et décrit brièvement l'intérêt du modèle d'étude, nous abordons la problématique sous deux angles différents mais néanmoins complémentaires. Le 1èr est dédié à l'identification des facteurs promouvant les départs et favorisant l'installation des dispersants. L'âge, le sexe et la densité de congénères apparaissent comme les principales variables influentes. Le 2nd angle a pour objectif d'identifier les variables pouvant moduler le succès de la dispersion. Bien qu'induisant des départs supplémentaires, la chasse apparait comme facteur déterminant dans l'échec de la dispersion en augmentant les risques de mortalité pendant le transit. Aussi, la densité dans le site de départ est proposée comme variable diminuant la qualité phénotypique des dispersants. L'ensemble de ces résultats souligne l'importance des conditions environnementales rencontrées au moment du départ, pendant le transit et à l'installation dans la réussite de la dispersion. L'action combinée de la chasse et de la densité sur la dispersion est proposée comme mécanisme probable à l'origine des fluctuations d'abondance observées sur le court terme chez le lièvre d'Europe / Through the example of the European hare (Lepus europaeus), the aim of this work is to contribute to a better understanding of the mechanisms underlying the fluctuation of abundances in animal populations. In this context, dispersal may be seen as the main source of variation. After reminding the theoretical concepts needed to understand this work and briefly describing the interest of the model, we address the topic in two different but complementary approaches. The 1st one is dedicated to the identification of the factors that promote departures and favor settlement of dispersers. Age, sex and density appear to be the main explanatory variables. The 2nd approach is designed to identify the factors that modulate the success of dispersal. Although inducing supplementary emigrants, hunting appears as an important factor decreasing the success of dispersal by increasing the mortality risk during transience. In addition, density in the original site is proposed as one potential factor decreasing the phenotypic quality of dispersers. Overall, these results emphasize the importance of the environmental conditions encountered at the time of departure, during transience and settlement in the dispersal success. The combined action of hunting and density on dispersal is proposed as one potential cause for the short term fluctuations of abundances in the European hare

An appreciation of the role of mutualism is essential when studying ecology and evolution in most ecosystems. Information covering aspects of mutualistic interactions can serve as a complement to the somewhat one-sided perspective from the 1950’s and 60’s that is used when teaching biology. In this thesis I applied an in-depth approach in which variation in the interspecific interaction between Aphis fabae aphids and Lasius niger ants was studied both in the field and in the laboratory. An emphasis was put on studies spanning several consecutive aphid generations. This approach revealed important differences between ant tended aphids and those without ants. In the lab, I found an initial decrease in aphid adult size and reproductive investment in the first generations after the start of ant tending, which was followed by a recovery to the pre-tending situation after about four generations. Another laboratory experiment showed an increase in alate (winged aphid) production from exposure to aphid alarm pheromones, and an even stronger decrease in alate production from ant attendance, suggesting that ants have gained the upper hand in an evolutionary conflict over aphid dispersal. Results from a field experiment further emphasized the possibility of negative effects of ants on aphids, showing that ant-tended aphid colonies experienced a higher rate of parasitoid attacks, produced fewer alates and embryos in adult aphids. The thesis highlights the scope for variation in the net effect of the interaction for aphids, and argues that, depending on the environmental circumstances, the interaction may sometimes and perhaps even often not really be a case of mutualism. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

White-tailed deer (Odocoileus virginianus) are a highly charismatic game species with considerable ecological and economic impacts across most of their range. In the Central Appalachian Mountains, deer are a keystone species in forested ecosystems. Regionally, populations vary in herd growth or decline. These fluctuations are important in that they often drive many aspects of population management and regulation, which are dependent on herd demographics. Some key population vital rates allowing better understanding of these changes in white-tailed deer herds are survival, cause-specific mortality, home-range variation, both broad and fine-scale resource selection, and ultimately population growth trends in response to changes in both population vital rates and hunter harvest regulations. In this study, I address each of these concepts within a deer population in Bath County, Virginia, that has presumably been in overall decline since the early 1990's. From June-September, 2019-2020, I monitored survival and cause specific mortality of 57 neonate white-tailed deer until 12 weeks of age. Fawn and adult female survival was 0.310 (95% CI = 0.210-0.475) and 0.871 (95%CI=0.790-0.961) respectively. During the study, I observed a total of 37 fawn mortalities and identified the cause of death using field evidence and through analyzing genetics from residual predator salvia recovered on deer carcasses. Mortalities included 28 predation events and 9 deaths from other causes (e.g., abandonment, malnutrition, or disease). Black bears accounted for 48.6% of all mortality and 64.2% of known predations within our study. My top model identified elevation as a significant predictor of fawn survival, with mortality risk increasing 20% for every 100m increase in elevation. My model using observed vital rates predicted an increasing population of λ = 1.10 (interquartile range, IQR 1.06-1.14). The population was predicted to increase by 2% with a 10% increase in doe harvest (λ = 1.02, IQR = 0.97-1.06) but declined by 7% at 20% harvest (λ = 0.93, IQR = 0.89-0.96). I found that fawning home ranges of females that successfully reared fawns to the end of the season had significantly larger home ranges than those that were unsuccessful at higher elevations. Fawning home ranges for females with fawns increased approximately 71ha in size for every 100m increase in mean home range elevation, whereas seasonal home ranges of females without fawns decreased approximately 1.5 ha for every 100m increase in mean home range elevation. Deer selected fawn-rearing areas nearer to forested edges, open habitats, and at higher elevations, while they avoided areas near disturbed and mature forests. Within the fawn rearing area, females selected locations closer to disturbed forest, open habitats, and forested edge, while avoiding mature forest habitats, and higher elevations. Females selected birth sites with higher levels of visual obstruction. Using a step-selection method for real-time resource selection across biological seasons, we found that female deer selected for open areas during the fawning, breeding, early gestational, and late gestational seasons. During the fall breeding season, females avoided forested edge, but selected for areas at higher elevations. During early gestational seasons females selected disturbed habitats and areas at higher elevations while again avoiding forested edge. Overall, my work highlights variations in population dynamics of white-tailed deer in areas of the Central Appalachian Mountains that are primarily characterized by poor habitat quality and provides novel insights into fine-scale spatial ecology of female deer across biological seasons within the region. Ultimately, while the deer population in our study was not predicted to be in decline, this work supports predation risk as being a significant factor associated with habitat quality. / Doctor of Philosophy / White-tailed deer (Odocoileus virginianus) are a game species with extensive ecological and economic impacts across most of their range. In the central Appalachian Mountains, many populations across the region vary in terms of herd size growth, stability, or decline. These fluctuations are important in that they often drive many aspects of population management and regulation, which are dependent on the status of herd demographics. Some key population vital rates that aid us in better understanding these changes in white-tailed deer herds are survival and cause-specific mortality, home-range variation in association with habitat quality and the ability to successfully reproduce, population trends under hypothetical management scenarios, and resource selection of various habitats that are available across the landscape. In this study, I address each of these concepts within a deer population in Bath County, Virginia, which has presumably been in decline since the early 1990's. As expected, fawn survival was lower than previously reported from other study areas of the Central Appalachians Mountains. Predation was the leading cause of fawn mortality, with black bears being responsible for most predation events. Fawn mortality risk was significantly associated with elevation - where fawns at higher elevations were those at greater risk. Surprisingly, the deer population in Bath County was projected to be increasing under current conditions and was also projected to be stable-to-increasing even under some hypothetical scenarios which would negatively impact population growth (i.e., 10% increase in female harvest or 17% reduction in fawn survival). Fawning home ranges of collared females which successfully reared known fawns to the end of the biological season were significantly influenced by elevation; such that females with fawns had home ranges that increased in size with increasing elevation, whereas females without fawns had home ranges which decreased slightly in size with increasing elevation. At birth sites, females selected locations characterized by higher levels of visual obstruction compared to randomly sampled areas. Of the habitat types analyzed, both selection or avoidance of specific habitats varied across both biological season and spatial scale. Ultimately, while I found that some deer populations associated with poor quality habitats in the Central Appalachians may not be in decline, deer were likely influenced greatly by habitat quality – especially pertaining to predation risk – throughout Bath County.

Umweltveränderungen kommen natürlicherweise vor und viele Spezies waren im Laufe ihrer Evolutionsgeschichte davon betroffen. Durch die Aktivitäten des Menschen jedoch finden diese in höherer Geschwindigkeit und größerem Umfang statt und stellen so für viele Spezies eine neue Herausforderung dar. Einen großen Einfluss auf die Umwelt nimmt der Mensch durch Verschmutzung, welche zu Veränderungen der Physiologie der Organismen und deren Verhalten führen und damit Einfluss auf die Populationsdynamik und letztendlich auf die Biodiversität haben kann. In meiner Dissertation untersuchte ich den Einfluss durch Bergbau ausgelöster Trübung auf das Verhalten und die soziale Struktur des Guppys. Er nutzt soziale Interaktionen für eine höhere Effizienz bei der Nahrungssuche und Räubervermeidung. Die Nutzung sei-nes dafür eingesetzten Sehsinns ist bei Trübung stark eingeschränkt. Ich untersuchte die Reaktion Trübung unerfahrener Fische aus Labor und Feld auf Trübung. Es zeigte sich, dass beide ihre sozialen Interaktionen in trübem Wasser verringerten. Eine zusätzliche Markow-Ketten-Analyse ergab aber auch, dass Laborfische Kontakte zu bestimmten In-dividuen der Gruppe verstärkten und Feldfische ihre initiierten Kontakte behielten. An-schließend studierte ich den Unterschied der sozialen Struktur Trübung erfahrener und - unerfahrener Fische. Trübung erfahrene Fische erhöhten die Gesamtzahl der Interaktio-nen, reduzierten jedoch die Anzahl der initiierten Kontakte im Gegensatz zu unerfahre-nen Fischen. Diese Strukturänderung, vermute ich, erhöht den Zusammenhalt und damit den In-formationsfluss im Schwarm. Die Ergebnisse von Folgeversuchen, nämlich der Erhalt der Paarungsanzahl und die effektivere Vermeidung einer Räuberattrappe bei Trübung er-fahrenen Fischen, unterstützen diese Vermutung. Die Arbeit zeigt, dass Guppys in der Lage sind, sich durch Änderung Ihrer sozialen Struktur an trübe Verhältnisse anzupas-sen. Dies könnte auch Einfluss auf ihre Populationsstruktur haben. / Most species have been subjected to environmental changes during their evolutionary history. However, due to human activity, environmental changes are currently occurring at higher speeds and on a greater scale, presenting new challenges for many species. Pollution, as a major type of human-induced environmental change, may not only affect physiology but also behaviour, thereby affecting population dynamics and consequently biodiversity. The topic of my dissertation is the effect of turbidity from quarrying on the behaviour and social association pattern of the guppy (Poecilia reticulata). Turbidity impairs the fish’s ability to use visual cues during social interactions, which in turn helps increases efficiency of foraging and avoiding predators. I investigated the initial re-sponse of guppies to turbidity and subsequently tested whether turbidity-experienced vs turbidity-inexperienced populations differ in their social association patterns and how they cope with ecological challenges. Both lab-reared and wild-caught guppies that were inexperienced with turbidity reduced social associations in turbid water in con-trast to turbidity-experienced fish. A Markov chain analysis revealed that lab-reared guppies increased associations with particular neighbours. Similarly, wild-caught gup-pies maintained the number of initiated associations under turbid conditions. The in-crease in non-initiated associations suggests a stronger connectivity within the shoal, leading to higher information transmission in a poor visual environment. Additional results showed that this altered social structure enabled turbidity-experienced fish to maintain the frequency of mating attempts in turbidity and to avoid predation risk. This suggests that guppies have the ability to adjust to turbidity, but with major changes in their social structure, which might have an impact on population dynamics.

A socioecologia investiga o efeito de fatores ecológicos sobre padrões de sistema social. Para muitos animais, o risco de predação tem sido apontado como a principal força seletiva favorecendo a sociabilidade. Entretanto, como determinante na variação dos sistemas sociais de primatas, esse fator tem sido considerado menos importante do que a competição por alimento. Os objetivos deste estudo foram (1) investigar a influência da disponibilidade de alimento e do risco de predação no uso do habitat pelo grupo estudado, para avaliarmos se o risco de predação é um fator relevante para essa população, (2) caracterizar o sistema social e (3) investigar se o risco de predação e/ou a oferta de alimento afetam o sistema social de Sapajus xanthosternos, espécie Criticamente ameaçada devido à caça e destruição do seu habitat, o que a torna relevante para o teste de hipóteses. Esta pesquisa foi realizada na Reserva Biológica de Una, cuja vegetação é classificada como floresta de tabuleiro e, na qual a população estudada ainda sofre pressão de caça. Um grupo foi acompanhado por 16 meses, num total de 2126 horas. O risco de predação foi avaliado em função do comportamento de vigilância, vocalizações de alarme, encontros com predadores e indícios de caça. Por meio do método focal árvore alimentação avaliamos o tamanho e qualidade das fontes agregadas. As interações agonísticas e afiliativas foram registradas pelo método de todas as ocorrências. A área de vida e os percursos diários foram calculados para avaliarmos a competição indireta intra e entre grupos. Os resultados foram comparados com os obtidos para uma população de S. nigritus e uma de S. libidinosus. O uso do habitat pelo grupo foi influenciado tanto pela distribuição e disponibilidade de recursos alimentares quanto pelo risco de predação. Os macacos-prego na Rebio Una formam grupos grandes e coesos, com filopatria de fêmeas e, a população é caracterizada por fissão de grupos grandes. O grande tamanho dos grupos favorece a hipótese de que o tamanho mínimo de grupo é determinado pelo risco de predação. O grupo apresentou um elevado número de machos (esperado devido ao número de fêmeas), o que também é considerado por alguns estudos como evidência de alto risco de predação. A estratégia reprodutiva das fêmeas foi relacionada à organização social e, consequentemente, ao risco de predação. S. xanthosternos consome tanto recursos agregados quanto dispersos e despendeu uma alta proporção de tempo forrageando por invertebrados. A hierarquia de dominância entre fêmeas foi parcial e as fêmeas de alto posto alimentaram-se conjuntamente com as fêmeas de baixo posto em fontes agregadas, enfatizando que fêmeas apresentaram relações tolerantes. A maioria das fontes agregadas utilizadas foi de tamanho intermediário em relação ao tamanho do grupo e produtiva e a competição direta por alimento envolvendo fêmeas intra-grupo não foi baixa. A competição indireta intra-grupo foi elevada, o que se constata pelas altas taxas de deslocamento e pelas grandes distâncias diárias percorridas. A competição direta entre grupos foi baixa e o risco de predação percebido foi alto em comparação com outros estudos. O padrão de sistema social, com grupo grande, elevado número de machos, e fêmeas com alto grau de afiliação e tolerância não está de acordo com o esperado por modelos que só consideram o efeito da competição por alimento, e sugere que o risco de predação afeta os componentes que caracterizam o sistema social deste grupo. Em conclusão, o sistema social de S. xanthosternos nesta população é uma resposta à pressão de predação e à oferta de alimento / Socioecology studies the effect ecological factors have on social system patterns. The predation risk has been said as the main selective force to favoring the sociability in many animals. However, as a determinant in variation of primates social systems, this fact has been considered less important than competition for food. The objectives of this study were (1) investigating how much the availability of food and the predation risk affect the habitat use by the group followed, in order to evaluate if the predation risk is a relevant issue in this population, (2) characterizing the social system and (3) investigating if the predation risk and/or availability of food affect the social system of Sapajus xanthosternos, a critically endangered species, owing to its hunting and habitat destruction, such fact makes it relevant for the hypothesis test. This study was made at the Una Biological Reserve, where the vegetation is classified as tabuleiro forest. The population in focus suffers from hunting stress. A group was followed during 16 months, a total of 2126 hours. The predation risk was evaluated concerning their vigilance behaviour, alarm vocalization, encounters with predators and hunting indication. We evaluated the size and the quality of the clumped food sources through the focal tree food method. Agonistic and affiliative interactions were recorded through all occurrences method. Home range and the daily traveling distances were calculated to evaluate if females experienced scramble competition within and between groups. The results were compared to the ones that had been obtained from a previous study with the population of the species S. nigritus and S. libidinosus. The use of habitat by the group was not only influenced by the distribution and availability food resources but also by the predation risk. The capuchin monkeys in Rebio Una live in large and cohesive groups, show female philopatry, and fission of very large groups. The large size of the groups favours the hypothesis that the minimum size of a group is determined by the predation risk. The group has shown a high number of males (expected due to the high number of females), a fact that is also considered by some studies as evidence of high predation risk. Female reproductive strategies were related to social organization and, therefore, to predation risk. S. xanthosternos consumes clumped and dispersed resources and spent more time foraging for invertebrates. There was a partial dominance hierarchy among females and the high-ranking females ate with the low-ranking females in clumped food sources. Such fact emphasizes that females hold tolerant relations. The majority of used clumped food sources had an intermediate size, concerning the size of the group, and was productive. The contest competition within group for food involving females was not low. Scramble competition within group was high, as shown by the high moving rates and the long daily travel distance. Contest competition between groups was low and the perceived predation risk was high in comparison to other studies. The social system pattern - large group size, high sex ratio, and females that show a high level of affiliation and tolerance - is not in accordance with the expected by models that only consider the result of competition for food. It suggests that the risk of predation affects the elements of social system in this group. As a conclusion, the social system of S. xanthosternos is affected by the risk of predation and food availability