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139 results for “predator size”
Data from: Ecological explanations to island gigantism: dietary niche divergence, predation and size in an endemic lizard
Although rapid evolution of body size on islands has long been known, the ecological mechanisms behind this island phenomenon remain poorly understood. Diet is an important selective pressure for morphological divergence. Here we investigate if selection for novel diets has contributed to the multiple independent cases of island gigantism in the Skyros wall lizard (Podarcis gaigeae) and if diet, predation, or both factors best explain island gigantism. We combined data on body size, shape, bite force, and realized and available diets to address this. Several lines of evidence suggest that diet has contributed to the island gigantism. The larger islet lizards have relatively wider heads and higher bite performance in relation to mainland lizards than would be expected from size differences alone. The proportions of consumed and available hard prey are higher on islets than mainland localities, and lizard body size is significantly correlated with the proportion of hard prey. Furthermore, the main axis of divergence in head shape is significantly correlated with dietary divergence. Finally, a model with only diet and one including diet and predation regime explain body size divergence equally well. Our results suggest that diet is an important ecological factor behind insular body size divergence, but could be consistent with an additional role for predation.
Data from: Do intraspecific or interspecific interactions determine responses to predators feeding on a shared size-structured prey community?
1. Coexistence of predators that share the same prey is common. This is still the case in size structured predator communities where predators consume prey species of different sizes (interspecific prey responses) or consume different size classes of the same species of prey (intraspecific prey responses). 2. A mechanism has recently been proposed to explain coexistence between predators that differ in size but share the same prey species, emergent facilitation, which is dependent on strong intraspecific responses from one or more prey species. Under emergent facilitation predators can depend on each other for invasion, persistence or success in a size structured prey community. 3. Experimental evidence for intraspecific size-structured responses in prey populations remain rare and further questions remain about direct interactions between predators that could prevent or limit any positive effects between predators (e.g. intraguild predation). 4. Here we provide a community wide experiment on emergent facilitation including natural predators. We investigate both the direct interaction between two predators that differ in body size (fish vs. invertebrate predator) and the indirect interaction between them via their shared prey community (zooplankton). 5. Our evidence supports the most likely expectation of interactions between differently sized predators, that intraguild predation rates are high and interspecific interactions in the shared prey community dominate the response to predation (i.e. predator-mediated competition). The question of whether emergent facilitation occurs frequently in nature requires more empirical and theoretical attention, specifically to address the likelihood that its pre-conditions may co-occur with high rates of intraguild predation.
Data from: Body size and allometric shape variation in the molly Poecilia vivipara along a gradient of salinity and predation
Background: Phenotypic diversity among populations may result from divergent natural selection acting directly on traits or via correlated responses to changes in other traits. One of the most frequent patterns of correlated response is the proportional change in the dimensions of anatomical traits associated with changes in growth or absolute size, known as allometry. Livebearing fishes subject to predation gradients have been shown to repeatedly evolve larger caudal peduncles and smaller cranial regions under high predation regimes. Poecilia vivipara is a livebearing fish commonly found in coastal lagoons in the north of the state of Rio de Janeiro, Brazil. Similar to what is observed in other predation gradients, lagoons inhabited by P. vivipara vary in the presence of piscivorous fishes; contrary to other poeciliid systems, populations of P. vivipara vary greatly in body size, which opens the possibility of strong allometric effects on shape variation. Here we investigated body shape diversification among six populations of P. vivipara along a predation gradient and its relationship with allometric trajectories within and among populations.ResultsWe found substantial body size variation and correlated shape changes among populations. Multivariate regression analysis showed that size variation among populations accounted for 66% of shape variation in females and 38% in males, suggesting that size is the most important dimension underlying shape variation among populations of P. vivipara in this system. Changes in the relative sizes of the caudal peduncle and cranial regions were only partly in line with predictions from divergent natural selection associated with predation regime.ConclusionsOur results suggest the possibility that adaptive shape variation among populations has been partly constrained by allometry in P. vivipara. Processes governing body size changes are therefore important in the diversification of this species. We conclude that in species characterized by substantial among-population differences in body size, ignoring allometric effects when investigating divergent natural selection?s role in phenotypic diversification might not be warranted.
Data from: Size, sex, and individual-level behavior drive intra-population variation in cross-ecosystem foraging of a top-predator
1. Large-bodied, top-predators are often highly mobile, with the potential to provide important linkages between spatially distinct food webs. What biological factors contribute to variation in cross-ecosystem movements, however, have rarely been examined. 2. Here, we investigated how ontogeny (body size), sex, and individual-level behavior impacts intra-population variation in cross-ecosystem foraging (i.e., between freshwater and marine systems), by the top-predator Alligator mississippiensis. 3. Field surveys revealed A. mississippiensis uses marine ecosystems regularly and are abundant in estuarine tidal creeks (from 0.3–6.3 individuals/km of creek, n = 45 surveys). Alligator mississippiensis captured in marine/estuarine habitats were significantly larger than individuals captured in freshwater and intermediate habitats. 4. Stomach content analysis showed that small juveniles consumed marine/estuarine prey less frequently (6.7% of individuals) than did large juveniles (57.8%), sub-adult (73%), and adult (78%) size classes. Isotopic mixing model analysis (SIAR) also suggests substantial variation in use of marine/estuarine prey resources with differences among and within size classes between sexes and individuals (range of median estimates for marine/estuarine diet contribution = 0.05–0.76). 5. These results demonstrate the importance of intra-population characteristics (body size, sex, and individual specialization) as key determinants of the strength of predator-driven ecosystem connectivity resulting from cross-ecosystem foraging behaviors. Understanding the factors which contribute to variation in cross-ecosystem foraging behaviors will improve our predictive understanding of the effects of top-predators on community structure and ecosystem function.
Data from: Brood size matching: a novel perspective on predator dilution
A primary benefit of grouping is diluting the individual risk of attack by predators. However, the fact that groups are formed not always by solitary adults but also by subgroups (e.g., families) has been overlooked. The subgroup-specific benefit of predator dilution depends on its relative contribution to total group size. Therefore, the willingness of a subgroup to merge with others should increase the less it contributes to total group size, but the conflicting preferences of partners may result in the preferential merger of similar-sized subgroups. Here, we evaluate how the proportional contribution of subgroups to diluting risk affects group formation. We generate predictions using a bidding game over parental care and test them using data on common eiders (Somateria mollissima), in which females with variable-sized broods may form brood-rearing coalitions. The predictions (1) that size-matched subgroups should have a higher propensity to merge, (2) that predation should increase group formation propensity, and (3) that increased bargaining power, as proxied by female body condition, should increase the time needed to establish partnerships were all supported. Partners do negotiate over their relative contributions to predator dilution, accepting or rejecting partnerships on the basis of this criterion. Our results show that consideration of the size of subgroups before merger is critical in understanding the process of group formation under the threat of predation.
Data from: Predation risk affects growth and reproduction of an invasive snail and its lethal effect depends on prey size
The behavior of invasive species under predation risk has been studied extensively, but their growth and reproductive responses have rarely been investigated. We conducted experiments with juveniles and adults of the invasive freshwater snail Pomacea canaliculata, and we observed changes in growth and reproduction in response to predation risk from a caged predator (Trachemys scripta elegans). P. canaliculata produced eggs earlier in the presence of predators and injured conspecifics compared with the control group (no risk), although the total number of egg masses laid by per female was exceeded by that of the controls after 15 days. Egg hatching success noticeably decreased under predation risk, and the incubation period was significantly prolonged; however, the oviposition height of the snails was not affected. A lethal effect of predation risk was detected in juvenile snails but not in adults. The growth of juvenile P. canaliculata was inhibited under predation risk, probably due to a reduction in food intake. Adult females exhibited a greater reduction in growth under predation risk than males, which likely resulted in part from the high reproductive investment of females in egg laying. These results indicate that P. canaliculata snails under predation risk face a trade-off between predator avoidance and growth and reproduction, where the lethal effect of predation risk is linked to the size of the prey.
Figure 3 in Prey-predator interactions and body size relationships between annual cicadas and spiders in Japan
Figure 3. Comparison of prey–predator size ratio among predator spider species. Data indicate at least three observations per prey–predator interaction (see Materials and methods). Different prey species are indicated by different colours on plots. Dashed line indicated the prey–predator body size ratio of 1.0. Data set = subset that excluded rare prey-predator interactions (n <3).
Figure 2 in Prey-predator interactions and body size relationships between annual cicadas and spiders in Japan
Figure 2. Number of incidents of prey–predator interactions between spiders and annual cicadas. Data set = total data.
Figure 1 in Prey-predator interactions and body size relationships between annual cicadas and spiders in Japan
Figure 1. Cases of the predation of annual cicadas by orb-web spiders (Araneidae). a) Female Araneus ventricosus feeding on Hyalessa maculaticollis; b) Female Argiope bruenichii feeding on Graptopsaltria nigrofuscata; c) Female Trichonephila clavata feeding on Tanna japonensis.
Data from: Seed masting causes fluctuations in optimum litter size and lag load in a seed predator
The episodic production of large seed crops by some perennial plants (masting) is known to increase seed escape by alternately starving and swamping seed predators. These pulses of resources might also act as an agent of selection on the life histories of seed predators, which could indirectly enhance seed escape by inducing an evolutionary load on seed predator populations. We measured natural selection on litter size of female North American red squirrels (Tamiasciurus hudsonicus) across 28 years and five white spruce (Picea glauca) masting events. Observed litter sizes were similar to optimum litter sizes during non-mast years but were well below optimum litter sizes during mast years. Mast events, therefore, caused selection for larger litters (' = 0.25) and a lag load (L = 0.25) on red squirrels during mast years. Reduced juvenile recruitment associated with this lag load increased the number of spruce cones escaping squirrel predation. Although, offspring and parents often experienced opposite environments with respect to the mast, we found no effect of environmental mismatches across generations on either offspring survival or population growth. Instead, squirrels plastically increased litter sizes in anticipation of mast events, which partially, although not completely, reduced the lag load resulting from this change in food availability. These results, therefore, suggest that in addition to ecological and behavioural effects on seed predators, mast seed production can further enhance seed escape by inducing maladaptation in seed predators through fluctuations in optimal trait values.
Distribution. Now restricted to the Channel Country of SW Queensland and the Lake Eyre Basin in NE South Australia. Descriptive notes. Head-body 95-120 mm, tail 105-160 mm, ear 23-29 mm, hindfoot 32-37 mm; weight 30-50 g. The Fawn Hopping Mouse has body form typical of hopping mice, with very long hindfeet, long tail with distal brush of longer hairs, very long ears, and large protruberant eyes. Dorsal fur is of variable color, from pale pinkish fawn to gray; ventral fur white. Unlike most other hopping mice, it has no throat pouch, but males have a glandular area of naked skin on the chest. Habitat. Occurs in low shrublands and tussock grasslands on stony ("gibber") plains and claypans. Shows marked habitat segregation from the Dusky Hopping Mouse (N. fuscus), which is closely associated with sandy substrates. Food and Feeding. The Fawn Hopping Mouse is mostly granivorous, but also eats other plant material (stems, leaves) and occasionally invertebrates. It uses succulent, salt-adapted plants around edges of claypans as a source of water. Breeding. Reproduction is probably largely opportunistic and aseasonal, with high reproductive output from near-continuous breeding after periods of high rainfall; reported littersize is 1-5, most commonly three; gestation period 38-43 days for nonlactating females. Females may mature later than other hopping mice, with reproductive maturity reached at about six months. Activity patterns. Terrestrial and nocturnal. Fawn Hopping Mice shelter during day in burrow systems that are typically simpler and shallower than those of other hopping mice. Movements, Home range and Social organization. Fawn Hopping Mice generally live singly or in small groups; typically uncommon within range, but population density may increase by an order of magnitude following periods of high rainfall. Status and Conservation. Classified as Near Threatened on The IUCN Red List. The Fawn Hopping Mouse has shown marked decline in range (estimated at greater than 50%), and presumably population size, since European settlement of Australia. This is mostlikely due to predation by the introduced house cat and Red Fox (Vulpes vulpes), and to habitat degradation associated with pastoralism. Bibliography. Brazenor (1934), Burbidge et al. (2008), Finlayson (1939), Gould (1853), Jackson & Groves (2015), Murray et al. (1999), Ogilby (1892), Thomas (1921h), Van Dyck & Strahan (2008), Waite (1898), Watts & Aslin (1981), Woinarski et al. (2014), Wood Jones (1925). in Muridae
Distribution. Now restricted to the Channel Country of SW Queensland and the Lake Eyre Basin in NE South Australia. Descriptive notes. Head-body 95-120 mm, tail 105-160 mm, ear 23-29 mm, hindfoot 32-37 mm; weight 30-50 g. The Fawn Hopping Mouse has body form typical of hopping mice, with very long hindfeet, long tail with distal brush of longer hairs, very long ears, and large protruberant eyes. Dorsal fur is of variable color, from pale pinkish fawn to gray; ventral fur white. Unlike most other hopping mice, it has no throat pouch, but males have a glandular area of naked skin on the chest. Habitat. Occurs in low shrublands and tussock grasslands on stony ("gibber") plains and claypans. Shows marked habitat segregation from the Dusky Hopping Mouse (N. fuscus), which is closely associated with sandy substrates. Food and Feeding. The Fawn Hopping Mouse is mostly granivorous, but also eats other plant material (stems, leaves) and occasionally invertebrates. It uses succulent, salt-adapted plants around edges of claypans as a source of water. Breeding. Reproduction is probably largely opportunistic and aseasonal, with high reproductive output from near-continuous breeding after periods of high rainfall; reported littersize is 1-5, most commonly three; gestation period 38-43 days for nonlactating females. Females may mature later than other hopping mice, with reproductive maturity reached at about six months. Activity patterns. Terrestrial and nocturnal. Fawn Hopping Mice shelter during day in burrow systems that are typically simpler and shallower than those of other hopping mice. Movements, Home range and Social organization. Fawn Hopping Mice generally live singly or in small groups; typically uncommon within range, but population density may increase by an order of magnitude following periods of high rainfall. Status and Conservation. Classified as Near Threatened on The IUCN Red List. The Fawn Hopping Mouse has shown marked decline in range (estimated at greater than 50%), and presumably population size, since European settlement of Australia. This is mostlikely due to predation by the introduced house cat and Red Fox (Vulpes vulpes), and to habitat degradation associated with pastoralism. Bibliography. Brazenor (1934), Burbidge et al. (2008), Finlayson (1939), Gould (1853), Jackson & Groves (2015), Murray et al. (1999), Ogilby (1892), Thomas (1921h), Van Dyck & Strahan (2008), Waite (1898), Watts & Aslin (1981), Woinarski et al. (2014), Wood Jones (1925).
Data from: Size‐dependent stress response in juvenile Arctic charr (Salvelinus alpinus) under prolonged predator conditioning
Predator conditioning can be used to improve post-release antipredator recognition of hatchery-reared salmonids. However, possible negative stress-related effects of prolonged predator conditioning on juvenile fish physiology are poorly understood. We studied the effects of prolonged (91 days) predator odour exposure on whole-body cortisol level and spleen size in six full-sib families of juvenile hatchery-bred Arctic charr (Salvelinus alpinus). Chemical cues from water containing charr-fed pikeperch (Sander lucioperca) were used as the predator exposure stimuli, and lakewater was used as a chemical control. Our study revealed that juvenile body cortisol levels post-predator conditioning were affected by treatment, fish size and their interaction. Importantly, among the smaller (i.e. slowest growing) charr, the predator-exposed fish had higher cortisol levels than control fish, while the opposite pattern was true for the larger fish. These results suggest that chemical cues from charr-fed predators induce a prolonged stress response in juvenile charr. As prolonged predation exposure seems to elevate stress levels in a size-dependent manner, the larger, faster growing fish could possibly have intrinsically lower stress responses to predation threats than smaller, slower growing fish. Possible coupling between stress sensitivity and growth requires further attention due to the likely implications for the management of unintended domestication among captive-reared salmonids.
Brain size affects responsiveness in mating behavior to variation in predation pressure and sex-ratio
<p>Despite ongoing advances in sexual selection theory, the evolution of mating decisions remains enigmatic. Cognitive processes often require simultaneous processing of multiple sources of information from environmental and social cues. However, little experimental data exist on how cognitive ability affects such fitness-associated aspects of behavior. Using advanced tracking techniques, we studied mating behaviors of guppies artificially selected for divergence in relative brain size, with known differences in cognitive ability, when predation threat and sex-ratio was varied. In females, we found a general increase in copulation behavior in when the sex-ratio was female biased, but only large-brained females responded with greater willingness to copulate under a low predation threat. In males, we found that small-brained individuals courted more intensively and displayed more aggressive behaviors than large-brained individuals. However, there were no differences in female response to males with different brain size. These results provide further evidence of a role for female brain size in optimal decision-making in a mating context. In addition, our results indicate that brain size may affect mating display skill in male guppies. We suggest that it is important to consider the association between brain size, cognitive ability and sexual behavior when studying how morphological and behavioral traits evolve in wild populations.</p>
Figure 3 in Size, spines and crochets: defences of luna moth caterpillars against predation by brown anoles
Figure 3. Close-ups of luna moth caterpillars sporting scoli equipped with spines that are effective as defence against anoles. Scoli may deliver an aposematic signal as they can vary in colour from green (freshly molted fourth instar, top left) and black (late fourth instar, bottom left) to blue (freshly molted fifth instar, top right) and red (late fifth instar, bottom right).
Figure 2 in Size, spines and crochets: defences of luna moth caterpillars against predation by brown anoles
Figure 2. Top and middle: caterpillars of the luna moth, Actias luna; bottom: caterpillar of the io moth, Automeris io (Saturniidae).
Figure 1 in Size, spines and crochets: defences of luna moth caterpillars against predation by brown anoles
Figure 1. Left: the brown anole (Anolis sagrei); right: the green anole (Anolis carolinensis). Both species are common in Florida and exhibit excellent climbing abilities, which allow them to hunt for caterpillars on plants.
Figure 1 in Predatory habits of the grasshopper-hunting wasp Stizus continuus (Hymenoptera: Crabronidae): diet preference, predator-prey size relationships and foraging capacity
Figure 1. Relationship between the maximum theoretically possible load and the prey weight in 2008. Note: The thin line refers to the actual data, while the bold line is the theoretical data when prey weight = maximum load.
Habitat traits and predation interact to drive abundance and body size patterns in macroalgae associated fauna
<p>Habitat-forming organisms provide three-dimensional structure that supports abundant and diverse communities. Variation in the morphological traits of habitat-formers will therefore likely influence how they facilitate associated communities, either via food and habitat provisioning, or by altering predator-prey interactions. These mechanisms, however, are typically studied in isolation and thus we know little of how they interact to affect associated communities. In response to this, we used naturally occurring morphological variability in the alga <em>Sargassum</em> <em>vestitum</em> to create habitat units of distinct morphotypes to test whether variation in the morphological traits (frond size and thallus size) of <em>S. vestitum</em>, or the interaction between these traits, affect their value as habitat for associated communities in the presence and absence of predation. We found morphological traits did not interact, instead having independent effects on epifauna that were negligible in the absence of predation. However, when predators were present, habitat units with large fronds were found to host significantly lower epifaunal abundances than other morphotypes, suggesting large frond alga provided low-value refuge from predators. The presence of predators also influenced the size structure of epifaunal communities from habitat units of differing frond size suggesting the refuge value of <em>S. vestitum </em>was also related to epifauna body size. This suggests that habitat-formers may chiefly structure associated communities by mediating size-selective predation, and not through habitat-provisioning. Furthermore, these results also highlight that habitat traits cannot be considered in isolation, for their interaction with biotic processes can have significant implications for associated communities.</p>
Data from: Personality, predation, and group size: Unravelling behavioural drivers of lionfish (<em>Pterois volitans</em>) invasion success
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Data from: Protection of large predators in a marine reserve alters size-dependent prey mortality
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