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Predation Risk (predation + risk)
Kinds of Predation Risk Terms modified by Predation Risk Selected AbstractsHAUL-OUT SELECTION BY PACIFIC HARBOR SEALS (PHOCA VITULINA RICHARDII): ISOLATION AND PERCEIVED PREDATION RISKMARINE MAMMAL SCIENCE, Issue 1 2002Chad A. Nordstrom Abstract The potential for non-aquatic predators to influence habitat use by harbor seals (Phoca vitulina) in a nearshore marine environment was studied by examining haul-out site use and through an experimental approach. Distance from shore, distance to possible foraging depths, peripheral water depth, and haul-out areas were quantified for each haul-out. There was a positive relationship between the number of seals hauled out and the distance from shore for eight known haul-out sites. The hypothesis that harbor seals increasingly hauled out farther offshore to reduce predation risk was tested experimentally by measuring their response to a model of a potential terrestrial predator in comparison to a control object, and to disturbance by a human at one of the study sites. Harbor seals abandoned the haul-out in the presence of the predator model, but showed little response to the controls, suggesting they possess a threat image for terrestrial predators and avoid hauling out when it is perceived. These results support the hypothesis that harbor seals select isolated sites to reduce exposure to terrestrial carnivores. [source] Effects of Predation Risk on Vertical Habitat Use and Foraging of Pardosa milvinaETHOLOGY, Issue 12 2006Hillary C. Folz Animals face the risk of predation while engaging in regular activities, such as foraging, mate-seeking, and reproducing. In order to avoid predation, prey can modify behavior to prevent capture. Pardosa milvina may climb in response to chemotactile cues of Hogna helluo, a larger cooccurring wolf spider, to avoid predation. The purpose of this study was to test the effects of the location of predator cues on the climbing response of P. milvina and to test how this antipredator behavior affected foraging success. In experimental arenas, when cues were on the bottom of the containers, P. milvina moved upward, and when cues were on the walls, individuals moved downward. These results suggest that P. milvina respond to H. helluo cues with general avoidance and do not automatically climb in response to the cues. As H. helluo spend most of their time on the ground, P. milvina may avoid predation by spending more time climbing in areas with H. helluo cues. The presence of predator cues significantly decreased foraging by P. milvina. But within the predator cue treatments, climbing ability had no effect on foraging, possibly due to the short height of the feeding arenas. Future studies are needed to determine if climbing by P. milvina in response to cues of H. helluo has direct and indirect negative effects on herbivores in the field. [source] Development, growth, and egg production of Ageneotettix deorum (Orthoptera: Acrididae) in response to spider predation risk and elevated resource qualityECOLOGICAL ENTOMOLOGY, Issue 1 2004Bradford. Abstract., 1.,Predation risk to insects is often size- or stage-selective and usually decreases as prey grow. Any factor, such as food quality, that accelerates developmental and growth rates is likely to reduce the period over which prey are susceptible to size-dependent predation. 2.,Using field experiments, several hypotheses that assess growth, development, and egg production rates of the rangeland grasshopper Ageneotettix deorum (Scudder) were tested in response to combinations of food quality and predation risk from wolf spiders to investigate performance variation manifested through a behaviourally mediated path affecting food ingestion rates. 3.,Grasshoppers with nutritionally superior food completed development , 8,18% faster and grew 15,45% larger in the absence of spiders, in comparison with those subjected to low quality food exposed to spider predators. Growth and development did not differ for grasshoppers feeding on high quality food when predators were present in comparison with lower quality food unimpeded by predators. Responses indicated a compensatory relationship between resource quality and predation risk. 4.,Surviving grasshoppers produced fewer eggs compared with individuals not exposed to spiders. Because no differences were found in daily egg production rate regardless of predation treatment, lower egg production was attributed to delayed age of first reproduction. Results compare favourably with responses observed in natural populations. 5.,Risk of predation from spiders greatly reduced growth, development, and ultimately egg production. Increased food quality counteracts the impact of predation risk on grasshoppers through compensatory responses, suggesting that bottom-up factors mediate effects of spiders. [source] The impact of an introduced predator on a threatened galaxiid fish is reduced by the availability of complex habitatsFRESHWATER BIOLOGY, Issue 8 2007RICK D. STUART-SMITH Summary 1. The availability of complex habitats such as macrophytes may be vital in determining the outcomes of interactions between introduced predators and native prey. Introduced brown trout (Salmo trutta) have impacted numerous small native freshwater fishes in the southern hemisphere, but the potential role of complex habitats in determining the direct outcomes of brown trout , native fish interactions has not been experimentally evaluated. 2. An in-lake enclosure experiment was used to evaluate the importance of structurally complex habitats in affecting the direct impacts of brown trout on a threatened galaxiid fish. Five Galaxias auratus and a single brown trout were added to enclosures containing one of three different habitat types (artificial macrophytes, rocks and bare silt substrate). The experiment also had control enclosures without brown trout. Habitat-dependence of predation risk was assessed by analysis of G. auratus losses to predation, and stomach contents of remaining fish were analysed to determine if brown trout directly affect the feeding of G. auratus and whether this is also habitat-dependent. 3. Predation risk of G. auratus differed significantly between habitat types, with the highest mortality in enclosures with only bare silt substrate and the lowest in enclosures containing artificial macrophytes. This result highlights the importance of availability of complex habitats for trout , native fish interactions and suggests that increasing habitat degradation and loss in fresh waters may exacerbate the direct impacts of introduced predators. 4. Stomach contents analyses were restricted to fish in enclosures with artificial macrophytes and rocks, as most fish were consumed in enclosures with brown trout and only bare silt substrate. These analyses suggest that brown trout do not directly affect the feeding of G. auratus in complex habitats, but it is still unknown whether its feeding is reduced if complex habitats are unavailable. [source] Social biology of rodentsINTEGRATIVE ZOOLOGY (ELECTRONIC), Issue 4 2007Jerry O. WOLFF Abstract Herein, I summarize some basic components of rodent social biology. The material in this paper is summarized and condensed from a recent book "Rodent Societies: An Ecological and Evolutionary Perspective" edited by J. O. Wolff and P. W. Sherman (2007). I describe the four basic spacing patterns and illustrate how female territoriality is a function of offspring defense and male mating tactics are a function of female defensibility. The vulnerability of young to infanticide shapes female spacing and mating behavior. Food does not appear to be a defensible resource for rodents, except for those species that larder hoard nonperishable items such as seeds. Philopatry and the formation of kin groups result in genetic sub-structuring of the population, which in turn affects effective population size and genetic diversity. Dispersal is male biased and typically involves emigration from the maternal site to avoid female relatives and to seek unrelated mates. Scent marking is a major form of communication and is used in reproductive competition and to assess prospective mates, but it is also eavesdropped by predators to locate prey. Females do not appear to alter the sex ratio of litters in response to maternal condition but among arvicoline rodents daughters appear to be favored in spring and sons in autumn. Rodents are relatively monomorphic; however, females tend to be larger than males in the smallest species and smaller in the larger species. Predation risk results from an interaction among foraging time and vulnerability and in turn affects behavioral and life history characteristics. [source] Nest predators affect spatial dynamics of breeding red-backed shrikes (Lanius collurio)JOURNAL OF ANIMAL ECOLOGY, Issue 1 2004Staffan Roos Summary 1Predation may be a strong selective factor affecting individual behaviour and life histories. However, few studies have investigated whether predators affect breeding habitat selection of prey species. 2We tested whether breeding habitat selection and reproduction of a tropical migrant, the red-backed shrike (Lanius collurio L.), was related to the presence of breeding pairs of its potential nest predators, magpie (Pica pica L.), hooded crow (Corvus corone cornix L.) and jackdaw (C. monedula L.). 3Only magpie and hooded crow territories were associated with an elevated risk of predation based on an artificial nest experiment with nests mimicking red-backed shrike nests. Predation risk on real red-backed shrike nests was also higher close to nests of hooded crow and magpie than elsewhere in the landscape. 4Occupation frequency of known red-backed shrike territory sites during 3 years of study increased with increasing mean distance to the nearest magpie nest. 5Changes in spatial distribution of corvids affected the spatial distribution of red-backed shrikes. Vacant red-backed shrike territory sites were more likely to become occupied in the next year when magpie and hooded crows had moved away from the site, while occupied sites were more likely to be abandoned in the next year when at least hooded crows had moved closer. 6Our results suggest that breeding territories of nest predators may affect breeding habitat selection of prey species. Thus, a large part of an observed spatial dynamics of prey species may be caused by a corresponding spatial dynamics of predators. Because sink territories are occupied more irregularly than source territories, we suggest that the dynamics in predator sinks may be the driving force of the spatial dynamics of prey species. [source] A simulation model of foraging behaviour and the effect of predation riskJOURNAL OF ANIMAL ECOLOGY, Issue 1 2000Jane F. Ward Summary 1.,The effect of predation risk on the distribution of animals foraging in a patchy environment was explored using a simulation model based on the work of Bernstein, Kacelnik & Krebs (1988, 1991), extended to incorporate predation risk. 2.,Modelled foragers consume prey within patches, having different prey densities, at a rate that depends only on prey density and interference from other foragers in the patch. Prey density remains constant (no depletion). A forager leaves a patch if its intake rate drops below its estimate of the average intake rate available in the environment. This estimate is continually updated by taking a weighted average of current intake and the previous estimate, giving a simple learning process. Decisions on whether to leave are made at regular intervals and a forager leaving a patch may arrive at random at any other patch. 3.,Simulation results were sensitive to the computational scheme used to represent estimates of average intake rate in the environment and to the way in which foragers' decisions were distributed over time, illustrating the need for careful formulation of such models. 4.,Predation risk was modelled as a cost that reduced effective intake, and could be distributed uniformly or skewed to patches of high prey density. The effects of different levels and distributions of predation risk on distribution of foragers were examined using model parameters broadly appropriate to hedgehogs (Erinaceous europaeus L.) foraging for earthworms (Lumbricus spp.) and risking opportunistic predation by badgers (Meles meles L.). The distribution of foragers with respect to prey density took an ,ideal free' form for zero or uniform risk, and was domed when cost of predation risk was relatively high and concentrated in the richer patches, as might be the case when predators and foragers share a common food resource. [source] Reproductive Investment of a Lacertid Lizard in Fragmented HabitatCONSERVATION BIOLOGY, Issue 5 2005JOSÉ A. DÍAZ calidad de hábitat; fragmentación de bosque; Psammodromus; tamaño de puesta; tamaño de huevo Abstract:,We studied the effect of habitat fragmentation on female reproductive investment in a widespread lacertid lizard ( Psammodromus algirus) in a mixed-forest archipelago of deciduous and evergreen oak woods in northern Spain. We captured gravid females in fragments (,10 ha) and forests (, 200 ha) and brought them to the laboratory, where they laid their eggs. We incubated the eggs and released the first cohort of juveniles into the wild to monitor their survival. Females from fragments produced a smaller clutch mass and laid fewer eggs (relative to mean egg mass) than females of similar body size from forests. Lizards did not trade larger clutches for larger offspring, however, because females from fragments did not lay larger eggs (relative to their number) than females from forests. Among the first cohort of juveniles, larger egg mass and body size increased the probability of recapture the next year. Thus, fragmentation decreased the relative fecundity of lizards without increasing the quality of their offspring. Reduced energy availability, increased predation risk, and demographic stochasticity could decrease the fitness of lizards in fragmented habitats, which could contribute to the regional scarcity of this species in agricultural areas sprinkled with small patches of otherwise suitable forest. Our results show that predictable reduction of reproductive output with decreasing size of habitat patches can be added to the already known processes that cause inverse density dependence at low population numbers. Resumen:,Estudiamos el efecto de la fragmentación sobre la inversión reproductiva de hembras en una lagartija lacértida ( Psammodromus algirus) ampliamente distribuida en un archipiélago mixto de bosques deciduos y siempre verdes de roble en el norte de España. Capturamos hembras grávidas en fragmentos (, 10 ha) y en bosques (, 200 ha) y las trasladamos al laboratorio, donde pusieron sus huevos. Incubamos los huevos y liberamos a la primera cohorte de juveniles para monitorear su supervivencia. Las hembras de fragmentos produjeron una puesta de menor masa y pusieron menos huevos (en relación con la masa promedio de los huevos) que hembras con talla corporal similar provenientes de bosques. Sin embargo, las lagartijas no cambiaron puestas mayores por crías más grandes porque las hembras de fragmentos no pusieron huevos más grandes (en relación con su número) que las hembras de bosques. Entre las primeras cohortes de juveniles, la mayor masa de los huevos incrementó la probabilidad de recaptura en el siguiente año. Por lo tanto, la fragmentación redujo la fecundidad relativa de las lagartijas sin aumentar la calidad de sus crías. La disponibilidad reducida de energía, el incremento en el riesgo de depredación y la estocasticidad demográfica podrían disminuir la adaptabilidad de lagartijas en hábitats fragmentados, lo que podría contribuir a la escasez regional de esta especie en áreas agrícolas salpicadas de pequeños parches de bosque por lo demás adecuado. Nuestros resultados muestran que la reducción predecible en la reproducción al disminuir el tamaño de los parches de hábitat se puede agregar a los procesos ya conocidos que causan la inversión de la denso dependencia en tamaños poblacionales pequeños. [source] Spatio-temporal shifts in gradients of habitat quality for an opportunistic avian predatorECOGRAPHY, Issue 2 2003Fabrizio Sergio We used the conceptual framework of the theory of natural selection to study breeding habitat preferences by an opportunistic avian predator, the black kite Milvus migrans. In Europe, black kite populations are mostly found near large networks of aquatic habitats, usually considered optimal for foraging and breeding. We hypothesized that proximity to wetlands could vary among individuals and affect their fitness, and thus be subject to natural selection. We tested the hypothesis first on a population on Lake Lugano (Italian pre-Alps) which has been monitored for nine years, and then on seven other populations, each studied for four,five years, located along a continuum of habitat from large water bodies to scarce aquatic habitat of any kind. In the Lake Lugano population, black kite abundance was negatively related to distance to the lake in all the nine years of study, consistent with long-term natural selection. There was evidence of ongoing directional selection on strategic nest location in three of the years, and evidence of stabilizing selection in two years. In eight of the nine years the trend was for a linear increase in fitness with increasing proximity to the lake. At the population level, results were consistent with adaptive habitat choice in relation to the previous year's spatial variation in fitness: higher associations between fitness and distance to the lake (i.e. higher selection gradients) resulted in higher density variations in the following year, in turn related to the availability of fish, the main local prey. The progressive decline of inland pairs and increase in the density of lakeshore pairs caused a directional long-term trend of declining mean distance to the lake. Breeding near aquatic habitats was associated with higher foraging success, and higher frequency and biomass of prey deliveries to offspring. There was weak evidence of selection in other populations. The inland-wetland gradient of habitat quality may have been affected by predation risk, as estimated by density of a major predator of adults and nestlings, the eagle owl Bubo bubo. Behavioral decisions at the level of the individual probably translated into population effects on density and distribution at various spatial scales. Populations in optimal habitats showed higher density and produced six times as many young per unit space as those in sub-optimal habitats. [source] Behavioural activity levels and expression of stress proteins under predation risk in two damselfly speciesECOLOGICAL ENTOMOLOGY, Issue 3 2009STEFANIE SLOS Abstract 1.,It has become apparent that predators may strongly decrease prey fitness without direct contact with the prey, as they induce the development of defence systems that limit the availability of energy for growth and reproduction. Recent studies suggest that stress proteins may help prey organisms deal with this stress. The pattern is not general, however, and little is known about species differences in physiological traits in coping with predator stress, and covariation of physiological with other antipredator traits. 2.,To explore these issues, we quantified levels of constitutive and fish-induced stress proteins (Hsp60 and Hsp70) and anti-predator behaviours in larvae of two damselfly species that differ in lifestyle. Both stress proteins were fixed at higher levels in Erythromma najas, which has a slow lifestyle, than in Lestes sponsa, which has a fast lifestyle. Similarly, anti-predator behaviours were fixed at safer levels in E. najas than in L. sponsa. 3.,These results suggest that stress proteins may be part of anti-predator syndromes of damselfly larvae, and there may be trait co-specialisation between stress proteins and behavioural anti-predator traits. Studies formally testing these hypotheses in more species may prove rewarding in advancing our understanding of the functional integration of physiological anti-predator traits in relation to the prey's lifestyle. [source] Development, growth, and egg production of Ageneotettix deorum (Orthoptera: Acrididae) in response to spider predation risk and elevated resource qualityECOLOGICAL ENTOMOLOGY, Issue 1 2004Bradford. Abstract., 1.,Predation risk to insects is often size- or stage-selective and usually decreases as prey grow. Any factor, such as food quality, that accelerates developmental and growth rates is likely to reduce the period over which prey are susceptible to size-dependent predation. 2.,Using field experiments, several hypotheses that assess growth, development, and egg production rates of the rangeland grasshopper Ageneotettix deorum (Scudder) were tested in response to combinations of food quality and predation risk from wolf spiders to investigate performance variation manifested through a behaviourally mediated path affecting food ingestion rates. 3.,Grasshoppers with nutritionally superior food completed development , 8,18% faster and grew 15,45% larger in the absence of spiders, in comparison with those subjected to low quality food exposed to spider predators. Growth and development did not differ for grasshoppers feeding on high quality food when predators were present in comparison with lower quality food unimpeded by predators. Responses indicated a compensatory relationship between resource quality and predation risk. 4.,Surviving grasshoppers produced fewer eggs compared with individuals not exposed to spiders. Because no differences were found in daily egg production rate regardless of predation treatment, lower egg production was attributed to delayed age of first reproduction. Results compare favourably with responses observed in natural populations. 5.,Risk of predation from spiders greatly reduced growth, development, and ultimately egg production. Increased food quality counteracts the impact of predation risk on grasshoppers through compensatory responses, suggesting that bottom-up factors mediate effects of spiders. [source] Mass regulation in response to predation risk can indicate population declinesECOLOGY LETTERS, Issue 10 2007Ross MacLeod Abstract In theory, survival rates and consequent population status might be predictable from instantaneous behavioural measures of how animals prioritize foraging vs. avoiding predation. We show, for the 30 most common small bird species ringed in the UK, that one quarter respond to higher predation risk as if it is mass-dependent and lose mass. Half respond to predation risk as if it only interrupts their foraging and gain mass thus avoiding consequent increased starvation risk from reduced foraging time. These mass responses to higher predation risk are correlated with population and conservation status both within and between species (and independently of foraging habitat, foraging guild, sociality index and size) over the last 30 years in Britain, with mass loss being associated with declining populations and mass gain with increasing populations. If individuals show an interrupted foraging response to higher predation risk, they are likely to be experiencing a high quality foraging environment that should lead to higher survival. Whereas individuals that show a mass-dependent foraging response are likely to be in lower quality foraging environments, leading to relatively lower survival. [source] Top predator control of plant biodiversity and productivity in an old-field ecosystemECOLOGY LETTERS, Issue 2 2003Oswald J. Schmitz Abstract Predators can have strong indirect effects on plants by altering the way herbivores impact plants. Yet, many current evaluations of plant species diversity and ecosystem function ignore the effects of predators and focus directly on the plant trophic level. This report presents results of a 3-year field experiment in a temperate old-field ecosystem that excluded either predators, or predators and herbivores and evaluated the consequence of those manipulations on plant species diversity (richness and evenness) and plant productivity. Sustained predator and predator and herbivore exclusion resulted in lower plant species evenness and higher plant biomass production than control field plots representing the intact natural ecosystem. Predators had this diversity-enhancing effect on plants by causing herbivores to suppress the abundance of a competitively dominant plant species that offered herbivores a refuge from predation risk. [source] Trading off the ability to exploit rich versus poor food qualityECOLOGY LETTERS, Issue 5 2002Alan J. Tessier Abstract Lakes differ in the quality of food for planktonic grazers, but whether grazers adapt to this resource heterogeneity is poorly studied. We test for evidence of specialization to resource environment within a guild of suspension feeding daphniids inhabiting lakes that differ in food web structure. Using bioassays, we demonstrate that food quality for grazers increases from deep to shallow to temporary lakes, which also represents a gradient of increasing predation risk. We compare growth rates and reproductive performance of daphniid taxa specific to each of the three lake types and find they differ greatly in minimum resource requirements, and in sensitivity to the resource gradient. These differences express a trade-off in ability to exploit rich vs. poor resources. Taxa from deep lakes, poor in resources, have low minimal needs, but they do relatively poorly in rich resource environments. We conclude that grazer distribution is consistent with an adaptive match of exploitation ability to resource environments. [source] Does morphological variation between young-of-the-year perch from two Swedish lakes depend on genetic differences?ECOLOGY OF FRESHWATER FISH, Issue 2 2010M. Heynen Heynen M, Hellström G, Magnhagen C, Borcherding J. Does morphological variation between young-of-the-year perch from two Swedish lakes depend on genetic differences? Ecology of Freshwater Fish 2010: 19: 163,169. © 2009 John Wiley & Sons A/S Abstract,,, Different local environmental conditions have often been found to generate phenotypic diversity. In the present study we examined morphological differences between young-of-the-year perch from two lake populations with differences in size-specific predation risk. A common garden setup was used to examine the genetic and environmental components of the morphological variation. We found differences in head and jaw length and slight differences in body depth between the wild young-of-the-year perch from Lake Ängersjön and Lake Fisksjön. The differences found between the wild fish from the two lakes were not maintained under common garden rearing. The observed morphological divergence between the wild young-of-the-year perch from Lake Ängersjön and Lake Fisksjön seems to stem mainly from a plastic response to different environmental conditions in the two lakes. It is clear that the morphological traits are not influenced by direct reaction to the size-specific risk of cannibalism, but probably stem from a combination of different environment characteristics, including resource and habitat use, and the density of other piscivores, such as pike. [source] Food abundance affects both morphology and behaviour of juvenile perchECOLOGY OF FRESHWATER FISH, Issue 2 2008J. Borcherding Abstract,,, Behaviour and morphology were both shown to differ between 1+ perch from two lakes that in earlier studies showed differences in size-specific predation risk. As the level of nourishment is known to affect behaviour and morphology, we fed perch of the two lakes in tanks for 40 days with two food levels, to study whether observed differences remain stable with changes in food availability. The perch fed in excess grew significantly, while the perch at the low food conditions lost weight, clearly indicating undernourishment. In aquarium experiments, the starved perch from both lakes were much bolder in the trade-off between foraging and predator avoidance than their well-fed conspecifics. In addition, the shape of perch differed significantly between feeding treatments. At low food levels perch got a more slender body, while at high food levels they developed a deeper body and a relatively smaller head. Independent of feeding level, the comparison between the two lakes revealed a clearly deeper body and a larger head area for one population, a shape difference that remained stable after the feeding period. The results give evidence that the level of nourishment is an important factor that quickly alters risk-taking behaviour. In body morphology, however, more stable shape characteristics must be distinguished from more flexible ones. Consequently, the level of nourishment is a potential factor that may quickly hide other proximate cues and must be considered attentively in studies, in which shape changes and behaviour are related to environmental factors like diet, predation pressure or habitat diversity. [source] Effects of predator-induced visual and olfactory cues on 0+ perch (Perca fluviatilis L.) foraging behaviourECOLOGY OF FRESHWATER FISH, Issue 2 2006V. N. Mikheev Abstract,,, Foraging juvenile fish with relatively high food demands are usually vulnerable to various aquatic and avian predators. To compromise between foraging and antipredator activity, they need exact and reliable information about current predation risk. Among direct predator-induced cues, visual and olfactory signals are considered to be most important. Food intake rates and prey-size selectivity of laboratory-reared, naive young-of-the-year (YOY) perch, Perca fluviatilis, were studied in experiments with Daphnia magna of two size classes: 2.8 and 1.3 mm as prey and northern pike, Esox lucius, as predator. Neither total intake rate nor prey-size selectivity was modified by predator kairomones alone (water from an aquarium with a pike was pumped into the test aquaria) under daylight conditions. Visual presentation of pike reduced total food intake by perch. This effect was significantly more pronounced (synergistic) when visual and olfactory cues were presented simultaneously to foraging perch. Moreover, the combination of cues caused a significant shift in prey-size selection, expressed as a reduced proportion of large prey in the diet. Our observations demonstrate that predator-induced olfactory cues alone are less important modifiers of the feeding behaviour of naive YOY perch than visual cues under daylight conditions. However, pike odour acts as a modulatory stimulus enhancing the effects of visual cues, which trigger an innate response in perch. [source] A comparison of habitat use and habitat-specific feeding efficiency by Eurasian ruffe (Gymnocephalus cernuus) and yellow perch (Perca flavescens)ECOLOGY OF FRESHWATER FISH, Issue 1 2006A. H. Fullerton Abstract ,, Eurasian ruffe are invading habitats in the North American Great Lakes watershed occupied by commercially important native yellow perch. We conducted laboratory experiments to evaluate potential overlap in habitat (macrophytes, mud, cobble) and food (benthic invertebrates) use. Ruffe and yellow perch both preferred macrophytes > cobble > mud in the light, but only ruffe increased their use of mud in the dark. Neither fish density nor food availability affected habitat preferences, and competition for habitat was not evident. For both species, feeding rates were marginally lower in macrophytes but did not differ between species. Our experiments suggest that if ruffe and yellow perch share a habitat (e.g., during invasion or because of predation risk), competition for space will be weak or absent. However, within a shared habitat, competition for food may occur when food is limiting because neither species has a clear advantage in its ability to consume invertebrates in any habitat. Resumen 1La especie exótica Gymnocephalus cernuus está invadiendo áreas de los Grandes Lagos de USA, ocupadas por la especie nativa Perca flavescens de manera que podrían competir por recursos de hábitat y alimenticios. La probabilidad de competición por alimento depende, en parte, de si estos peces se sobrelapan espacial y temporalmente y también de su habilidad para consumir tipos de alimento asociados a hábitats dados. Desarrollamos dos grupos de experimentos de laboratorio para cuantificar niveles de similitud en el uso de hábitat (barro, cubierta, macrófitas) y de alimento (invertebrados bénticos). El primer conjunto de experimentos examinó las preferencias de hábitat en ambas especies, la influencia de la densidad de individuos y de la presencia de alimento sobre esas preferencias y si los peces competían por el espacio del hábitat. En el segundo conjunto de experimentos cuantificamos la habilidad relativa de cada especie para consumir invertebrados bénticos (quironómidos, oligoquetos y anfípodos) en tres hábitats distintos. 2Tanto G. cernuus and P. flavescens prefirieron de macrófitas a piedras y de piedras a barro en períodos de luz. Solamente G. curnuus aumentó el uso de barro en la oscuridad. Ni la densidad de individuos ni la presencia de alimento afectó la selección de hábitat y no obtuvimos evidencia de competición por el hábitat. Para ambas especies las tasas alimenticias fueron marginalmente menores en macrófitas que en piedras o en barro y no difirieron significativamente entre especies. 3Aunque G. cernuus y P. flavescens pueden ocupar diferentes hábitats en la naturaleza, nuestros experimentos sugieren que si se vieran forzadas a ocupar el mismo hábitat (i.e., durante un proceso de invasión o debido a riesgo de predación), la competición por el espacio seria pequeña o nula. Sin embargo, en un hábitat compartido, la competición por el alimento podría ocurrir cuando el alimento esté limitado porque ninguna de las dos especies tiene una ventaja clara en su habilidad para consumir invertebrados en cualquier que sea el hábitat. [source] Predation risk allocation or direct vigilance response in the predator interaction between perch (Perca fluviatilis L.) and pike (Esox lucius L.)?ECOLOGY OF FRESHWATER FISH, Issue 3 2005A. Vainikka Abstract , Predation risk allocation hypothesis predicts that a prey's response to predator depends on prey's previous experience on predator. Here we tested whether the group of three perch respond differentially to pike, predator of perch, depending on the timing of high constant (HC) and high unpredictable (HU) risk periods within low constant risk periods in short-term (10 h) experiments, and whether the response is stronger during a HU risk period than during a HC risk period. Perch clearly erected the dorsal fin in response to predation risk treatments (pike odour only, odour and visible pike). Decrease in activity and increase in shoaling behaviour were observed mainly during high risk periods. However, the perch's responses to pike did not differ statistically between periods of various levels of predation risk or depending on the timing of high risk situations within constant low risk periods, and thus, suggesting that perch respond mainly to changes in the current predation risk. Resumen 1. La hipótesis de la asignación de riesgo a la predación predice que la respuesta a un predador depende de la experiencia previa de la presa al predador. En este trabajo analizamos si un grupo de tres individuos de Perca fluviatilis respondían de forma distinta a la presencia de Esox lucius, (un predador común de esta especie) y si éstas dependían del momento en el que se producen periodos de alto riesgo constante y de alto riesgo impredecible, en experimentos de corto plazo (10 horas) de riesgo bajo y constante y si la respuesta era mayor durante perí odos de riesgo impredecible y alto que durante períodos de riesgo constante alto. 2. Claramente P. fluviatilis respondió levantando la aleta dorsal en respuesta a los tratamientos de riesgo a la predación (solamente olor y olor + visibilidad de E. lucius). Una menor actividad y una mayor tendencia a la formación de bancos fueron observados durante períodos de alto riesgo. Sin embargo, las respuesta de P. fluviatilis a E. lucius no difirieron estadísticamente entre períodos de varios niveles de riesgo a la predación o entre aquellos que dependieron del momento en el que se produjeron situaciones de alto riesgo dentro de períodos de bajo riesgo constante. 3. Concluimos que P. fluviatilis puede utilizar señales olfatorias como determinantes de respuestas al riesgo a la predación y responder a aumentos de riesgo, sin excluir la posibilidad de que amenazas repetidas decrezcan la intensidad de la respuesta. Nuestros resultados, obtenidos en experimentos realizados a pequeña escala temporal, no niegan la posibilidad de la P. fluviatilis y otras especies puedan balancear la alimentación con actividades anti-predación, de acuerdo a cambios en el riesgo de predación a lo largo de escalas temporales de varios días. [source] Plesiomorphic Escape Decisions in Cryptic Horned Lizards (Phrynosoma) Having Highly Derived Antipredatory DefensesETHOLOGY, Issue 10 2010William E. Cooper Jr Escape theory predicts that the probability of fleeing and flight initiation distance (predator,prey distance when escape begins) increase as predation risk increases and decrease as escape cost increases. These factors may apply even to highly cryptic species that sometimes must flee. Horned lizards (Phrynosoma) rely on crypsis because of coloration, flattened body form, and lateral fringe scales that reduce detectability. At close range they sometimes squirt blood-containing noxious substances and defend themselves with cranial spines. These antipredatory traits are highly derived, but little is known about the escape behavior of horned lizards. Of particular interest is whether their escape decisions bear the same relationships to predation risk and opportunity costs of escaping as in typical prey lacking such derived defenses. We investigated the effects of repeated attack and direction of predator turning on P. cornutum and of opportunity cost of fleeing during a social encounter in P. modestum. Flight initiation distance was greater for the second of two successive approaches and probability of fleeing decreased as distance between the turning predator and prey increased, but was greater when the predator turned toward than away from a lizard. Flight initiation distance was shorter during social encounters than when lizards were solitary. For all variables studied, risk assessment by horned lizards conforms to the predictions of escape theory and is similar to that in other prey despite their specialized defenses. Our findings show that these specialized, derived defenses coexist with a taxonomically widespread, plesiomorphic method of making escape decisions. They suggest that escape theory based on costs and benefits, as intended, applies very generally, even to highly cryptic prey that have specialized defense mechanisms. [source] Effects of Predation Threat on the Structure and Benefits from Vacancy Chains in the Hermit Crab Pagurus bernhardusETHOLOGY, Issue 11 2009Mark Briffa Vacancy chains occur when individuals occupy discrete re-useable resource units, which once abandoned by the current owner can then be occupied by a new owner. In order to enter the newly vacated resource the new owner must first vacate its current resource unit, such that a vacancy chain consists of a series of linked moves between resource units of different value, equivalent to different ,strata' in the chain. Vacancy chains may represent an important route by which resources are distributed through populations. Indeed, the arrival of a new resource has the potential to initiate a series of moves propagating beyond the individual that encounters the new resource unit. Thus, the chain participants as a whole may experience ,aggregate benefits' from the arrival of the new resource unit. The extent of these benefits, however, may not necessarily be evenly distributed between all chain participants; some individuals could receive greater than average benefits by moving through more than one stratum (,skipping') and some individuals could experience a reduction in resource value by moving to a resource unit of lower quality than that occupied initially (a ,backward move'). Such moves represent deviations from the ,ideal' vacancy chains assumed by theory. Here we analyse the aggregate benefits and benefits to individuals participating in vacancy chains of empty gastropod shells in the hermit crab Pagurus bernhardus. We also investigate the effect of predation risk on these two levels of benefits and on chain structure. Adding a new shell at the top of the chain causes an overall increase in shell quality after 24 h but the distribution of benefits between strata in the chain varies with the presence and absence of the predator cue. Although there was significant concordance between chain structure in the presence and absence of the predator cue, the structure was significantly different from an ideal vacancy chain in the absence but not the presence of the predator cue. [source] Interspecific Differences in Responses to Predation Risk May Confer Competitive Advantages to Invasive Freshwater Turtle SpeciesETHOLOGY, Issue 2 2008Nuria Polo-Cavia The nature of competitive interactions between native and introduced invasive species is unclear. In the Iberian Peninsula, the introduced red-eared slider (Trachemys scripta elegans) is an invasive species that is competing and displacing the endangered native Spanish terrapin (Mauremys leprosa). We hypothesized that interspecific differences in antipredatory behavior might confer competitive advantages to introduced T. scripta. We examined whether interspecific differences in responses to predation risk affect the time that turtles remained hidden in the shell before using an active escape to water. Both turtle species adjusted hiding times by balancing predation threat, microhabitat conditions and the costs of remaining hidden. However, introduced T. scripta showed longer hiding times before escaping than native M. Leprosa, which, in contrast, switched from waiting hidden in the shell to escape to deep water as soon as possible. These interspecific differences might result from the risk of facing different types of predators in different microhabitats (land vs. water) in their original habitats. However, in anthropogenically altered habitats where predators have been greatly reduced, T. scripta may avoid potential costs of unnecessary repeated escape responses to water (e.g. interruption of basking). These behavioral asymmetries could contribute to the greater competitive ability of introduced T. scripta within anthropogenically disturbed environments. [source] The Bold and the Variable: Fish with High Heterozygosity Act Recklessly in the Vicinity of PredatorsETHOLOGY, Issue 1 2008Sampsa Vilhunen Variation in the innate behavioral response to predation threat is often assumed to reflect genetic differences among the prey individuals. To date, no published results, however, exist that would offer explanation for the origin of this behavioral variation within populations. Using microsatellites as markers, we estimated the genetic variability of juvenile brown trout (Salmo trutta) individuals whose behavior had been individually recorded in a trade-off situation where both predator chemical cues and food were present. Mean overall heterozygosity and the internal relatedness of fish associated significantly with their activity and foraging, so that the genetically more variable individuals showed more risk-prone behavior under predation risk. No association between genetic variability and behavior was found in trials where predator odors were not present. These results were consistent over the three study populations of brown trout with different backgrounds, suggesting that the phenomenon is of general nature in this species. Of the possible mechanisms suggested to enable the existence of the positive association between neutral microsatellite variation and fitness-related trait, the local effect hypothesis gained more support from our data than the general effect hypothesis. [source] Nest Crypsis, Reproductive Value of a Clutch and Escape Decisions in Incubating Female Mallards Anas platyrhynchosETHOLOGY, Issue 8 2004Albrecht In cryptically coloured birds, remaining on the nest despite predator approach (risk-taking) may decrease the likelihood that the nest will be detected and current reproductive attempt lost. By contrast, flushing may immediately reveal the nest location to the predator. Escape decisions of incubating parents should therefore be optimized based on the risk-to-parent/cost of escape equilibrium. Animal prey may assess predation risk depending on a variety of cues, including the camouflage that vegetation provides against the predator. We examined interactive effects of nest crypsis and the current reproductive value of a clutch on flushing distances in incubating mallards (Anas platyrhynchos) approached by a human. Our results were consistent with predictions of parental investment theory: flushing distances were inversely correlated with measures of the reproductive value of the current clutch, namely with clutch size, stage of incubation and mean egg volume. Independently of a reproductive value of a clutch, nest concealment explained a significant portion of the variation in flushing distance among females; individual females tended to increase/decrease flushing distances according to change in nest cover. The results further suggest that vegetation concealment greatly influenced the risk of nest detection by local predators, suggesting that vegetation may act as a protective cover for incubating female. A female's ability to delay flushes according to the actual vegetation cover might thus be viewed as an antipredator strategy that reduces premature nest advertising to visually oriented predators. We argue, however, that shorter flying distances from densely covered sites might be maladaptive in areas where a predator's ability to detect incubating female does not rely on visual cues of nests. [source] Predator Inspection Behaviour in a Characin Fish: an Interaction between Chemical and Visual Information?ETHOLOGY, Issue 9 2003Grant E. Brown Recent evidence suggests that predator inspection behaviour by Ostariophysan prey fishes is regulated by both the chemical and visual cues of potential predators. In laboratory trials, we assessed the relative importance of chemical and visual information during inspection visits by varying both ambient light (visual cues) and predator odour (chemical cues) in a 2 × 2 experimental design. Shoals of glowlight tetras (Hemigrammus erythrozonus) were exposed to a live convict cichlid (Archocentrus nigrofasciatus) predator under low (3 lux) or high (50 lux) light levels and in the presence of the odour of a cichild fed tetras (with an alarm cue) or swordtails (Xiphophorus helleri, with an alarm cue not recognized by tetras). Tetras exhibited threat-sensitive inspection behaviour (increased latency to inspect, reduced frequency of inspection, smaller inspecting group sizes and increased minimum approach distance) towards a predator paired with a tetra-fed diet cue, regardless of light levels. Similar threat-sensitive inspection patterns were observed towards cichlids paired with a swordtail-fed diet cue only under high light conditions. Our data suggest that chemical cues in the form of prey alarm cues in the diet of the predator, are the primary source of information regarding local predation risk during inspection behaviour, and that visual cues are used when chemical information is unavailable or ambiguous. [source] Sex-Specific Aggression and Antipredator Behaviour in Young Brown TroutETHOLOGY, Issue 7 2001Jörgen I. Johnsson Sex differences in adult behaviour are often interpreted as consequences of sexual selection and/or different reproductive roles in males and females. Sex-specific juvenile behaviour, however, has received less attention. Adult brown trout males are more aggressive than females during spawning and juvenile aggression may be genetically correlated with adult aggression in fish. We therefore tested the prediction that immature brown trout males are more aggressive and bolder than immature females. Because previous work has suggested that precocious maturation increases dominance in salmonids, we included precocious males in the study to test the prediction that early sexual maturation increase male aggression and boldness. Aggression and dominance relations were estimated in dyadic contests, whereas boldness was measured as a response to simulated predation risk using a model heron. Independent of maturity state, males initiated more than twice as many agonistic interactions as females in intersexual contests. However, males were not significantly more likely to win these contests than females. The response to a first predator attack did not differ between sex categories, but males reacted less to a second predator attack than females. Sexual maturity did not affect the antipredator response in males. Since there is no evidence from field studies that stream-living immature male and female salmonids differ in growth rate, it appears unlikely that the sex differences demonstrated are behavioural consequences of sex-specific investment in growth. It seems more likely that sex-specific behaviour arises as a correlated response to sexually selected gene actions promoting differential behaviour in adult males and females during reproduction. Alternatively, sex differences may develop gradually during juvenile life, because a gradual developmental program should be less costly than a sudden behavioural change at the onset of sexual maturity. [source] Age-Related Microhabitat Segregation in Willow Tit Parus montanus Winter FlocksETHOLOGY, Issue 11 2000Lluís Brotons It is expected that through flexibility in behaviour, flock living birds respond to the asymmetries in resource access derived from dominance relationships. We analysed the microhabitat use of willow tits in winter flocks and assessed possible factors which shape habitat segregation between adults and juveniles in different temperature regimes. When foraging in mild conditions (ambient temperature >,0°C), flocks split up into subgroups with adults foraging in inner parts of trees more often than juveniles. However, no differences were recorded in the vertical position occupied in trees. In harsh conditions (< , 4°C), flocks re-united and juveniles further moved to outer parts of trees, increasing horizontal segregation between age classes. In mild conditions, vigilance behaviour was not related to the position of birds in trees, but in harsh conditions, scanning frequency was higher in outer parts of trees only for adults. In mild weather, juvenile position in trees was associated with body size and mass. The foraging microhabitat segregation detected in harsh conditions fits the age-related hoarding distribution previously described in the same population. This supports the hypothesis that hoarded food is important in determining future foraging habitat use. Adult preference and intraspecific competition for safer or richer inner parts of trees as foraging sites during harsh conditions seems to determine the habitat segregation between adults and juveniles. Furthermore, we suggest that in mild weather, when foraging in the absence of adults, juveniles balance the costs of using a potentially dangerous microhabitat with the benefits of building energetically cheap and large food reserves through hoarding. The expected patterns of microhabitat segregation may differ in parids, depending on whether predation risk or other factors such as food availability are the main factors controlling habitat quality. [source] DOES VARIATION IN SELECTION IMPOSED BY BEARS DRIVE DIVERGENCE AMONG POPULATIONS IN THE SIZE AND SHAPE OF SOCKEYE SALMON?EVOLUTION, Issue 5 2009Stephanie M. Carlson Few studies have determined whether formal estimates of selection explain patterns of trait divergence among populations, yet this is one approach for evaluating whether the populations are in equilibria. If adaptive divergence is complete, directional selection should be absent and stabilizing selection should prevail. We estimated natural selection, due to bear predation, acting on the body size and shape of male salmon in three breeding populations that experience differing predation regimes. Our approach was to (1) estimate selection acting within each population on each trait based on an empirical estimate of reproductive activity, (2) test for trait divergence among populations, and (3) test whether selection coefficients were correlated with trait divergence among populations. Stabilizing selection was never significant, indicating that these populations have yet to attain equilibria. Directional selection varied among populations in a manner consistent with trait divergence, indicating ongoing population differentiation. Specifically, the rank order of the creeks in terms of patterns of selection paralleled the rank order in terms of size and shape. The shortest and least deep-bodied males had the highest reproductive activity in the creek with the most intense predation and longer and deeper-bodied males were favored in the creeks with lower predation risk. [source] RAPID GROWTH RESULTS IN INCREASED SUSCEPTIBILITY TO PREDATION IN MENIDIA MENIDIAEVOLUTION, Issue 9 2003Stephan B. Munch Abstract Several recent studies have demonstrated that rapid growth early in life leads to decreased physiological performance. Nearly all involved experiments over short time periods (<1 day) to control for potentially confounding effects of size. This approach, however, neglects the benefits an individual accrues by growing. The net effect of growth can only be evaluated over a longer interval in which rapidly growing individuals are allowed the time required to attain the expected benefits of large size. We used two populations of Menidia menidia with disparate intrinsic growth rates to address this issue. We compared growth and survivorship among populations subject to predation in mesocosms under ambient light and temperature conditions for a period of up to 30 days to address two questions: Do the growth rates of fish in these populations respond differently to the presence of predators? Is the previously demonstrated survival cost of growth counterbalanced by the benefits of increased size? We found that growth was insensitive to predation risk: neither population appeared to modify growth rates in response to predation levels. Moreover, the fast-growing population suffered significantly higher mortality throughout the trials despite being 40% larger than the slow-growing population at the experiment's end. These results confirm that the costs of rapid growth extend over prolonged intervals and are not ameliorated merely by the attainment of large size. [source] EVOLUTION OF PREY BEHAVIOR IN RESPONSE TO CHANGES IN PREDATION REGIME: DAMSELFLIES IN FISH AND DRAGONFLY LAKESEVOLUTION, Issue 3 2003R. Stoks Abstract In a large behavioral experiment we reconstructed the evolution of behavioral responses to predators to explore how interactions with predators have shaped the evolution of their prey,behavior. All Enallagma damselfly species reduced both movement and feeding in the presence of coexisting predators. Some Enallagma species inhabit water bodies with both fish and dragonflies, and these species responded to the presence of both predators, whereas other Enallagma species inhabit water bodies that have only large dragonflies as predators, and these species only responded to the presence of dragonflies. Lineages that shifted to live with large dragonflies showed no evolution in behaviors expressed in the presence of dragonflies, but they evolved greater movement in the absence of predators and greater movement and feeding in the presence of fish. These results suggest that Enallagma species have evolutionarily lost the ability to recognize fish as a predator. Because species coexisting with only dragonfly predators have also evolved the ability to escape attacking dragonfly predators by swimming, the decreased predation risk associated with foraging appears to have shifted the balance of the foraging/predation risk trade-off to allow increased activity in the absence of mortality threats to evolve in these lineages. Our results suggest that evolution in response to changes in predation regime may have greater consequences for characters expressed in the absence of mortality threats because of how the balance between the conflicting demands of growth and predation risk are altered. [source] | ||||||||||||||||||||||||||||||||||