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.
Citations
More filters
TL;DR: The hypothesis that sexual dimorphism in size is correlated with the intensity of intrasexual competition for mates is supported, but the hypothesis that species with single-male breeding systems have relatively smaller testes than species with mating systems characterized by a high potential for sperm competition was supported only for polygynous species.
Abstract: Sexual body-length dimorphism and relative size of testes were compared among 16 species (25 subspecies) of North American Microtus and Clethrionomys by use of data collected from museum specimens. Species with polygynous mating systems and territorial males had the greatest degree of sexual size dimorphism with males larger than females, and relatively small testes. Promiscuous species tended to show little or no sexual size dimorphism and relatively large testes. Species considered monogamous had no size dimorphism, and also had large testes. These data support the hypothesis that sexual dimorphism in size is correlated with the intensity of intrasexual competition for mates. However, the hypothesis that species with single-male breeding systems (single-male polygyny and monogamy) have relatively smaller testes than species with mating systems characterized by a high potential for sperm competition (promiscuity) was supported only for polygynous species.
158 citations
TL;DR: It is concluded that many of the characteristics that distinguish mammals from reptiles, including endothermy, viviparity, and even lactation, may be related to the marked decrease in body size that occurred in the evolution of mammals from advanced therapsids.
Abstract: The evolution of the endothermy of mammals can be traced to the ectothermy of early reptiles It is suggested that small endotherms cannot be directly derived from small ectotherms because of the requirement for the simultaneous change in thermal conductance and the rate of metabolism Instead, small ectotherms probably gave rise to large ectotherms (thereby increasing thermal inertia), a fur coat may have been added to increase thermal stability, and a decrease in size with only a modest decrease in the total rate of metabolism converted "inertial" homoiothermy to endothermy Measurements of skull size in cynodont therapsids conform to this suggestion A secondary palate is formed in cynodonts during the decrease in body size and is interpreted as a correlate of increased ventilation rates produced by a decrease in size and a conversion of ectothermy to endothermy A decrease in size and the formation of a secondary palate also occurred in bauriamorphs, which suggests that they too independently evolved
152 citations
TL;DR: It is demonstrated that population responses to density changes may represent the sum of many unique individual foraging responses and would be obscured by pooled sampling programs.
Abstract: Individual foraging specializations are an important source of intraspecific variability in feeding strategies, but little is known about what ecological factors affect their intensity or development. We evaluated stomach contents in marked individual largemouth bass (Micropterus salmoides) and tested the hypothesis that diet specialization is most pronounced during periods with high conspecific densities. We collected diet data over 10 years from an unexploited population of largemouth bass that displayed a greater than threefold variation in density. Although diet composition of the aggregate bass population did not change during the study, bass body condition was inversely correlated with population size. Individual marked bass exhibited high diet consistency (diet overlap between successive captures) during years with high population densities. Diet overlap between randomly assigned pairs of bass was not correlated with population size. We did not detect the expected positive relationship between diet breadth and population size. Our analyses demonstrate that population responses to density changes may represent the sum of many unique individual foraging responses and would be obscured by pooled sampling programs. Behavioral flexibility of individuals may contribute to the ability of largemouth bass to function as a keystone predator in many aquatic communities.
149 citations
TL;DR: I observed major differences between male and female A. arafurae in prey types, prey sizes and habitat utilization (shallow versus deep water), and it is more parsimonious to interpret these differences as independent adaptations of each sex to increase foraging success, given pre-existing sexually-selected differences in size, habitat or behavior.
Abstract: Filesnakes (Acrochordus arafurae) are large (to 2 m), heavy-bodied snakes of tropical Australia. Sexual dimorphism is evident in adult body sizes, weight/length ratios, and body proportions (relative head and tail lengths). Dimorphism is present even in neonates. Two hypotheses for the evolution of such dimorphism are (1) sexual selection or (2) adaptation of the sexes to different ecological niches. The hypothesis of sexual selection is consistent with general trends of sexually dimorphic body sizes in snakes, and accurately predicts, for A. arafurae, that the larger sex (female) is the one in which reproductive success increases most strongly with increasing body size. However, the sexual dimorphism in relative head sizes is not explicable by sexual selection.The hypothesis of adaptation to sex-specific niches predicts differences in habitats and/or prey. I observed major differences between male and female A. arafurae in prey types, prey sizes and habitat utilization (shallow versus deep water). Hence, the sexual dimorphism in relative head sizes is attributed to ecological causes rather than sexual selection. Nonetheless, competition between the sexes need not be invoked as the selective advantage of this character divergence. It is more parsimonious to interpret these differences as independent adaptations of each sex to increase foraging success, given pre-existing sexually-selected differences in size, habitat or behavior. Data for three other aquatic snake species, from phylogenetically distant taxa, suggest that sexual dimorphism in food habits, foraging sites and feeding morphology, is widespread in snakes.
147 citations
TL;DR: Overall structural habitat data show a greater difference between the sexes than actually exists in their feeding locations, and overall structural habitats show that intraspecific classes use perches of significantly different heights and diameters.
Abstract: Structural habitat data generally support the interpretation that competition for food results in habitat partitioning. In this investigation, the importance of ethological factors in determining the structural habitat of Anolis lizards is demonstrated by examining the structural habitat of Anolis polylepis during foraging and social interaction, its two major activities. Overall structural habitats show that intraspecific classes use perches of significantly different heights and diameters. Perch heights of adult males and females are also shown to be related to the type of activity in which they are engaged. Overall structural habitat data show a greater difference between the sexes than actually exists in their feeding locations. Ecological differences between insular and continental Anolis potentially affecting the structural habitat are also discussed. See full-text article at JSTOR
141 citations
References
More filters
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.
218 citations
129 citations
Book•
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
119 citations
"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)....
[...]
...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)....
[...]