The Ecological Significance of Sexual Dimorphism in Size in the Lizard Anolis conspersus.
27 Jan 1967-Science (American Association for the Advancement of Science)-Vol. 155, Iss: 3761, pp 474-477
TL;DR: Anolis conspersus selects prey from a wide range of taxa and shows no obvious intraspecific specialization not connected to differences in microhabitat and prey size.
Abstract: Adult males of Anolis conspersus capture prey of significantly larger size and occupy perches of significantly greater diameter and height than do adult females; similarly, these three dimensions of the niche are significantly larger for adult females than for juveniles. Adult males on the average eat a smaller number of prey, and the range in size of prey is larger. The relationship between the average length of the prey and that of the predator is linear when the predator size is above 36 millimeters, but becomes asymptotic when it is below that value. Subadult males as long as adult females eat significantly larger food than do the latter, but only in the larger lizards is this correlated with a relatively larger head. Anolis conspersus selects prey from a wide range of taxa and shows no obvious intraspecific specialization not connected to differences in microhabitat and prey size. The efficiency of this system for solitary species is pointed out.
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TL;DR: The atypical pattern of sexual dimorphism in Adelotus brevis seems to have resulted from sexual selection for larger body size and tusk size in males, in the context of male-male agonistic behaviour, rather than natural selection for ecological divergence between the sexes.
Abstract: At least two adaptive processes can lead to the evolution of sexual dimorphism: sexual selection (e.g. male-male combat) or natural selection (e.g. dietary divergence). We investigated the adaptive significance of a distinctive pattern of sexual dimorphism in a south-eastern Australian frog, Adelotus brevis . Male Adelotus grow larger than female conspecifics, have larger heads relative to body size, and have large paired projections (‘tusks’) in the lower jaw. All of these traits are rare among anurans. We quantified the degree of dimorphism in Adelotus , and gathered data on diets and mating systems of this species to evaluate the possible roles of sexual selection and dietary divergence in favoring the evolution of these sexually dimorphic traits. Analysis of prey items in alimentary tracts revealed significant sex differences in prey types. For example, females ate proportionally more arthropods and fewer molluscs than did males. However, this difference is likely to be a secondary consequence of habitat differences between the sexes (due in turn to their different reproductive roles) rather than a selective force for the evolution of sexual dimorphism. Calling males spend their time in moist habitats where pondsnails are abundant, whereas females are more often encountered in the drier arthropod-rich woodlands. A three-year behavioural ecology study on a field population revealed that reproductive males engage in agonistic interactions, with the sexually dimorphic tusks used to attack rivals. Larger body size contributed to male reproductive success. Small males were excluded from calling sites and, among the calling males, larger animals had higher reproductive success (numbers of matings) than did smaller individuals. Hence, the atypical pattern of sexual dimorphism in Adelotus brevis seems to have resulted from sexual selection for larger body size and tusk size in males, in the context of male-male agonistic behaviour, rather than natural selection for ecological divergence between the sexes.
65 citations
TL;DR: The seasonal food habits of Anolis limifrons, an iguanid lizard, were studied by examining the stomachs of 512 individuals collected on Barro Colorado Island, Panama Canal Zone, during three periods, finding no wet season—dry season difference in frequency of food found in the stomachS.
Abstract: The seasonal food habits of Anolis limifrons, an iguanid lizard, were studied by examining the stomachs of 512 individuals collected on Barro Colorado Island, Panama Canal Zone, during three periods. Frequency and length of prey and length of predators were determined. Frequency distributions of different size classes of potential prey were obtained from leaf litter and low vegetation samples. The lizards selected larger size classes of potential prey. All size classes of predators captured the smaller size classes of prey, but the larger prey were taken by larger predators. More female than male lizards had food in their stomachs. There was no wet season—dry season difference in frequency of food found in the stomachs.
65 citations
TL;DR: The propensity for intraguild predation is asymmetrical in favor of introduced A. sagrei in Florida and Grand Cayman, however, further study is needed to determine the importance of intrag Guild predation under field conditions.
Abstract: Since its introduction, Anolis sagrei (Sauria: Polychrotidae) has been replacing native A. carolinensis in Florida and native A. conspersus in Grand Cayman Island as the common anole of urban environments and other open habitats. To assess the likelihood that predation of juvenile native anoles by A. sagrei adults is an important interaction in this process, the propensities for intraguild predation and cannibalism were assessed for A. sagrei and A. carolinensis in Florida and for A. sagrei and A. conspersus in Grand Cayman. Predation experiments were conducted in cages, using freshly captured lizards, in which adult males of each species were presented with conspecific and heterospecific juveniles. Adult A. sagrei were (1) significantly more likely to eat juveniles than were adult A. carolinensis or A. conspersus, and (2) significantly more likely to eat heterospecific than conspecific juveniles, whereas adult A. carolinensis and A. conspersus were not. Thus, the propensity for intraguild predation is asymmetrical in favor of introduced A. sagrei in Florida and Grand Cayman. Further study is needed, however, to determine the importance of intraguild predation under field conditions.
65 citations
TL;DR: Females were found to grow faster, and to reach a larger size than males, and female fecundity was found to increase with size.
Abstract: Growth rate and age at sexual maturation in male and female grass snakes are examined. Females were found to grow faster, and to reach a larger size than males. Female fecundity was found to increase with size. Large size permits females to exploit both larger and also different prey species than males. Males reached maturity during their third year; females during their fourth or fifth year. The ecological significance of sexual size dimorphism and age at maturation are discussed.
64 citations
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...This is consistent with Schoener's (1969) model which assumes that larger...
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TL;DR: It is hypothesized that the body size of a bumblebee will be that size which maximizes its average net rate of energy intake while collecting nectar, and there should be a positive correlation between the size of the bumblebees and the average amount of nectar obtained per flower.
Abstract: It is hypothesized that the body size of a bumblebee will be that size which maximizes its average net rate of energy intake while collecting nectar. A mathematical model is developed with the result that the net rate of energy intake of a nectar-collecting bumblebee is expressed as a function of the body size of the bumblebee. From this model the body size which maximizes the net rate of energy intake (i.e., optimal body size) is found (as the solution of an implicit equation). In this situation the advantage of large size is that larger bumblebees fly faster and hence take less flight time than smaller bumblebees. The disadvantage of larger size is greater energetic costs. The parameters of the model are estimated using data obtained from the foraging behavior of bumblebees on monkshood (Aconitum columbianum). The optimal body size is then calculated for workers of Bombus appositus which obtained almost all their nectar from monkshood. The observed and expected (i.e., optimal) body size are found to be close and not significantly different. The model also predicts that, from the bumblebee's point of view, there should be a positive correlation between the size of the bumblebee and the average amount of nectar obtained per flower. Evidence of this correlation is presented and the possible significance of the correlation from the plant's point of view is discussed. A possible extension of the model to general relationships between predator body size, prey size and prey density is discussed.
64 citations
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TL;DR: The eight species of the genus Anolis in Puerto Rico can be divided into four morphological similarities as discussed by the authors : perch height, perch diameter, high-shade preference and low-shading preference.
Abstract: The eight species of lizards of the genus Anolis in Puerto Rico can be divided into four morphological similarities. One, Anolis curvieri, is very different from the rest and has not been discussed here. The other seven species fall into three groups. Each of these groups occupies a different structural habitat which can be defined in terms of perch height and perch diameter. Within each of these three groups the species have very similar but not indential structural habitats but differ very widely in climatic habitat defined in terms of shade. Shade preferences seem to result from the temperature preferences of the species involved. In each group there is one species with high shade preference which is essentially restricted to the mountains. Each group also has a species with a lower shade preference which occurs in the lowlands and extends up into the mountains in exposed or sunny situations. One of the three groups has an additional species which is restricted to the hot and southwest corner of Puerto Rico. When one compares the temperature preferences or eccritic temperatures of the various species, one finds in each group that the highland species has a lower eccritic temperature than does the lowland species. There is little temperature difference between the lowland species and arid southwest species in the group where this additional third species is present. The species within each structural habitat show many morphological similarities which may be the result of their being closely related or may be the result of adaptation to similar environments. The differences in microhabitat between the Puerto Rican anoles separate them spatially though not completely. In species occupying different structural habitats in the same area the overlap may involve part of the home range of most of the individuals in the area. In species occupying the same structural but different climatic habitats the overlap may involve all of the home range of some individuals but of only a small fraction of the individuals in the total population. The spatial separation among Puerto Rican Anolis can be suggested to be of ecological significance because it reduces interspecific competition and because it allows the various species to adapt more precisely to different parts of the available habitat. Thus members of a genus may exploit the habitat more efficiently.
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01 Jan 1964
TL;DR: The life of the rainbow lizard , The life of a rainbow lizard, مرکز فناوری اطلاعات £1,000,000 ($2,000; £1,500,000)
Abstract: The life of the rainbow lizard , The life of the rainbow lizard , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی
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"The Ecological Significance of Sexu..." refers background in this paper
...On the basis of essentially the same pattern of staining, other investigators have reached the same conclusion (3, 4), or have attributed staining additionally or alternatively to the processes of the bipolar cells (5, 6), the ganglion cells (4, 5), or centrifugal fibers from the optic nerve (7)....
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...A greater proportion of large insects were found in larger adult males than in adult females of Anolis lineatopus and Agama agama (4, 5); similarly, juveniles take smaller food than adults (5-7)....
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