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 results from A. sagrei are consistent with the hypothesis that intraspecific competition is more important than predation in shaping the selective landscape for traits central to the adaptive radiation of Anolis ecomorphs.
Abstract: Field experiments that measure natural selection in response to manipulations of the selective regime are extremely rare, even in systems where the ecological basis of adaptation has been studied extensively. The adaptive radiation of Caribbean Anolis lizards has been studied for decades, leading to precise predictions about the influence of alternative agents of selection in the wild. Here we present experimental evidence for the relative importance of two putative agents of selection in shaping the adaptive landscape for a classic island radiation. We manipulated whole-island populations of the brown anole lizard, Anolis sagrei, to measure the relative importance of predation versus competition as agents of natural selection. We excluded or included bird and snake predators across six islands that ranged from low to high population densities of lizards, then measured subsequent differences in behaviour and natural selection in each population. Predators altered the lizards' perching behaviour and increased mortality, but predation treatments did not alter selection on phenotypic traits. By contrast, experimentally increasing population density dramatically increased the strength of viability selection favouring large body size, long relative limb length and high running stamina. Our results from A. sagrei are consistent with the hypothesis that intraspecific competition is more important than predation in shaping the selective landscape for traits central to the adaptive radiation of Anolis ecomorphs.
122 citations
TL;DR: Investigation of the limiting effects of food and water on juvenile growth rates in the lizard Anolis aeneus suggests that limited water availability reduces growth rates for most of the dry season, whereas food levels are sufficiently low to limit growth during the weeks of thedry season when rainfall is sufficient for growth.
Abstract: The limiting effects of food and water on juvenile growth rates in the lizard Anolis aeneus were investigated in the field (Grenada, West Indies) and laboratory Growth rates of lizards in the field were unrelated to their snout-vent lengths, but both prey biomass and rainfall had signif- icant effects on juvenile growth rates Laboratory experiments indicated that water had a primary limiting effect on growth; even when food supplies were superabundant, growth rates were low when drinking water was curtailed Laboratory and field experiments suggest that limited water availability reduces growth rates for most (67%) of the dry season, whereas food levels are sufficiently low to limit growth during the weeks of the dry season when rainfall is sufficient for growth During the wet season there is no evidence of water scarcity, food levels are high and average growth rates are 85% of the maximal rates observed under optimal conditions in the laboratory
122 citations
TL;DR: It is hypothesized that early season nests should produce male-biased sex ratios, and that this provides an adaptive explanation for temperature-dependent sex determination in A. muricatus.
Abstract: The jacky dragon, Amphibolurus muricatus (White, ex Shaw 1790) is a medium sized agamid lizard from the southeast of Australia. Laboratory incubation trials show that this species possesses temperature-dependent sex determination. Both high and low incubation temperatures produced all female offspring, while varying proportions of males hatched at intermediate temperatures. Females may lay several clutches containing from three to nine eggs during the spring and summer. We report the first field nest temperature recordings for a squamate reptile with temperature-dependent sex determination. Hatchling sex is determined by nest temperatures that are due to the combination of daily and seasonal weather conditions, together with maternal nest site selection. Over the prolonged egg-laying season, mean nest temperatures steadily increase. This suggests that hatchling sex is best predicted by the date of egg laying, and that sex ratios from field nests will vary over the course of the breeding season. Lizards hatching from eggs laid in the spring (October) experience a longer growing season and should reach a larger body size by the beginning of their first reproductive season, compared to lizards from eggs laid in late summer (February). Adult male A. muricatus attain a greater maximum body size and have relatively larger heads than females, possibly as a consequence of sexual selection due to male-male competition for territories and mates. If reproductive success in males increases with larger body size, then early hatching males may obtain a greater fitness benefit as adults, compared to males that hatch in late summer. We hypothesize that early season nests should produce male-biased sex ratios, and that this provides an adaptive explanation for temperature-dependent sex determination in A. muricatus.
120 citations
TL;DR: This paper considers the possible effects of three major environmental factors-number of sympatric congeners, latitude, and island size-and several minor ones on the absolute and relative body sizes of males and females and proposes a set of patterns describing size differences that should extend or delimit the domain of tendencies noted for birds.
Abstract: Schoener, Thomas W. (Biological Laboratories, Harvard Univ., Cambridge, Mass. 02138) 1969. Size pattern in West Indian Anolis lizards: I. Size and species diversity. Syst. Zool., 18:386-401.-Anolis lizard species have solitary populations on certain West Indian islands. These populations have a narrow range in mean body size, very different for the two sexes, though they inhabit islands varying greatly in area and environmental diversity. Smallsized exceptions to this uniformity are northerly. Sizes of males for solitary forms are collectively significantly larger than sizes of males on the richest islands. With increasing species diversity from island to island, species size distributions for males irregularly decrease in median but increase in range and skewness. On the three richest islands, smaller species are significantly more often restricted in geographic range. From simple assumptions about competition for resources, a relation is derived which holds that snout-vent length or some power thereof for a given species is equal to some multiple of the reciprocal of the number of closely related species on its island plus some constant. This relation is shown to better describe data than two alternatives. The ratio of the length of the principal trophic structure (the head) to the entire body length of a given species is sometimes but not always predictable from the number of congeneric species on its island. [Anolis; West Indies; size; diversity; convergence; evolution]. Among terrestrial vertebrates, West Indian lizards of the genus Anolis are notable in numerical abundance, species diversity, and observability. These features have stimulated abundant research on the ecology and evolution of this genus, mostly yet unpublished (see Williams, in press, for a review). Recently, E. E. Williams and I were struck by the opportunity which Anolis offered for making the sort of inductive generalizations about interspecific size differences in trophic structures and total bulk that have been made for birds (Lack, 1947; Hutchinson, 1959; Klopfer and MacArthur, 1961; Schoener, 1965; Grant, 1968 and included references). Our aims were twopronged. First, the resulting set of patterns describing size differences should extend or delimit the domain of tendencies noted for birds. But more importantly, the extensive lode of habitat and distributional information for this more narrowly defined group should permit a more exact statement of t-he relation of spatial overlap to size differences. This paper considers the possible effects of three major environmental factors-number of sympatric congeners, latitude, and island size-and several minor ones on the absolute and relative body sizes of males and females. Other results are presented elsewhere (Schoener,
120 citations
Additional excerpts
...foods wherever studied (Rand, 1967a; Schoener, 1967; Schoener and Gorman, 1968; Schoener, 1968)....
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TL;DR: This dichotomy in growth rate and age at sexual maturity supports the hypothesis that island anoles may be generally food limited and mainland anoles not so limited and suggests other differences in life history characteristics for these two groups of anoles.
Abstract: Growth data for Anolis lizards were fitted to the logistic growth equation and the calculated rate constant was used for interpopulation comparisons of growth rates. The major result was that most of the relatively small-sized anoles studied belong to one of two exclusive groups: Insular species with low growth rates and mainland species with high growth rates. As a result of their lower growth rates, the age at sexual maturity is greater for island (5-9 months) than for mainland species (2-4 months). This dichotomy in growth rate and age at sexual maturity supports the hypothesis that island anoles may be generally food limited and mainland anoles not so limited and suggests other differences in life history characteristics for these two groups of anoles.
119 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.
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
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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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