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Journal ArticleDOI

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
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Journal ArticleDOI
TL;DR: Sexual dimorphism in adults resulted from both a higher growth rate and prolonged growth period in males and was greatest in mass, followed by foreleg guard hair length, head width, body length, and head length.
Abstract: Sexual dimorphism in body mass, body length, head width, head length, and foreleg guard hair length of polar bears (Ursus maritimus) was examined from live-captured polar bears in Svalbard, Norway. Limited evidence of sexual dimorphism was apparent in cubs shortly after den emergence but was marked after the 1st year of life. Sexual dimorphism in adults resulted from both a higher growth rate and prolonged growth period in males. In mature animals, sexual dimorphism was greatest in mass, followed by foreleg guard hair length, head width, body length, and head length. Foreleg guard hair length was age related and hypothesized to be a form of ornamentation. Geographic variation in sexual dimorphism was evident for mass and body length for seven different populations but there was no evidence of a hyperallometric relationship in sexual dimorphism.

75 citations

01 Jan 2016
TL;DR: An analysis of 30 food webs suggests that a niche space of dimension 1 suffices, with unexpectedly high frequency and perhaps always, to describe the trophic niche overlaps implied by real food webs in single habitats.
Abstract: If the trophic niche of a kind of organism is a connected region in niche space, then it is possible for trophic niche overlaps to be described in a one-dimensional niche space if and only if the trophic niche overlap graph is an interval graph. An analysis of 30 food webs, using the combinatorial theory of interval graphs, suggests that a niche space of dimension 1 suffices, with unexpectedly high frequency and perhaps always, to describe the trophic niche overlaps implied by real food webs in single habitats. Consequently, real food webs fall in a small subset of the set of mathematically possible food webs. That real food webs are compatible with one-dimensional trophic niche spaces, more often than can be explained by chance alone, has not been noticed previously.

75 citations

Journal ArticleDOI
01 Jul 1996-Ecology
TL;DR: This work examined the proximate causes of SSD in a population of a South American iguanian lizard, Microlophus occipitalis, finding that adult males tended to live longer than females, which affected adult age and size distributions.
Abstract: Among iguanian lizards, males are often larger than females. As a result, much attention has been directed toward understanding the evolution of sexual size dimorphism (SSD) in this group. SSD can result from a number of developmental, physiological, and demographic processes, which may cause sex differences in growth trajectories, timing of maturity, and adult age distributions. Knowledge of these proximate mechanisms can improve our understanding of the evolution of SSD. Only recently, however, have efforts been directed toward understanding proximate mechanisms. I examined the proximate causes of SSD in a population of a South American iguanian lizard, Microlophus occipitalis. The majority of the SSD in this population resulted from continued postmaturity growth in males and reduced postmaturity growth in females. Additionally, adult males tended to live longer than females, which affected adult age and size distributions. The proportion of young individuals in samples had strong effects on temporal fluctuations in SSD in the population. I discuss the importance of studying proximate mechanisms for evolutionary analyses of SSD in organisms that continue to grow after reaching maturity.

74 citations

Journal ArticleDOI
01 Dec 1994-Ecology
TL;DR: The asymmetry between sexes in the morphology of reproductively more successful individuals points to a potential for a resource—based evolutionary origin of sexual dimorphism in jojoba, arising from different morphological optima for each sex.
Abstract: The reproductive success of an individual plant is in part a function of its capacity to assimilate resources, and this in turn is partially a result of plant morphology. Simmondsia chinensis, jojoba, a dioecious desert shrub, is dimorphic in secondary sexual characters in some desert populations, where females on average have larger leaves and more open canopies than males. The function of this sexual dimorphism was examined by investigating the importance of shoot morphology to reproductive components of plant fitness. The reproductive behavior of individuals tended to be associated with different morphological attributes for both males and females. Males with more “male—type” morphology tended to have more inflorescences and a greater likelihood of flowering than did males structured more like females, though they also had smaller inflorescences. Females with more “female—type” construction produced more flower buds in one of the study years and also produced heavier seeds than females with more male—like structure. Females from four different morphological classes allocated 1.5–4.5 times as much to reproduction as did males, but showed wide variability in whether or not they set fruit. Therefore females either had a much higher or a much smaller reproductive allocation than most males. Fruit set in the population studied is not limited by pollen availability, but is presumably constrained by abiotic resource availability. The asymmetry between sexes in the morphology of reproductively more successful individuals points to a potential for a resource—based evolutionary origin of sexual dimorphism in jojoba, arising from different morphological optima for each sex.

74 citations

Journal ArticleDOI
TL;DR: Species accumulation curves showed that dietary richness and composition were similar between size‐dimorphic sexes; however, female lizards had greater per‐sample dietary richness than males, and overall diet composition was significantly different across seasons, and the authors found more pronounced interindividual variation in December than in May.
Abstract: Understanding community assembly and population dynamics frequently requires detailed knowledge of food web structure. For many consumers, obtaining precise information about diet composition has traditionally required sacrificing animals or other highly invasive procedures, generating tension between maintaining intact study populations and knowing what they eat. We developed 16S mitochondrial DNA sequencing methods to identify arthropods in the diets of generalist vertebrate predators without requiring a blocking primer. We demonstrate the utility of these methods for a common Caribbean lizard that has been intensively studied in the context of small island food webs: Anolis sagrei (a semi-arboreal ‘trunk-ground’ anole ecomorph). Novel PCR primers were identified in silico and tested in vitro. Illumina sequencing successfully characterized the arthropod component of 168 faecal DNA samples collected during three field trips spanning 12 months, revealing 217 molecular operational taxonomic units (mOTUs) from at least nine arthropod orders (including Araneae, Blattodea, Coleoptera, Hemiptera, Hymenoptera, Isoptera, Lepidoptera and Orthoptera). Three mOTUs (one beetle, one cockroach and one ant) were particularly frequent, occurring in ≥50% of samples, but the majority of mOTUs were infrequent (180, or 83%, occurred in ≤5% of samples). Species accumulation curves showed that dietary richness and composition were similar between sizedimorphic sexes; however, female lizards had greater per-sample dietary richness than males. Overall diet composition (but not richness) was significantly different across seasons, and we found more pronounced interindividual variation in December than in May. These methods will be generally useful in characterizing the diets of diverse insectivorous vertebrates.

74 citations


Cites background from "The Ecological Significance of Sexu..."

  • ...Previous studies have found evidence for intersexual niche partitioning in some cases (e.g. Anolis conspersus: Schoener 1967) and not in others (e.g. Carlia skinks: Manicom et al. 2014) based on prey size alone....

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  • ...For example, precise diet profiles for sympatric male and female lizards would aid in evaluating the hypothesis that sexual size dimorphism evolved in part to minimize intraspecific resource overlap (Schoener 1967; Shine 1989; Manicom et al. 2014)....

    [...]

  • ...Most of what is known about lizard diets has been learned by sacrificing and dissecting animals (Wolcott 1923; Schoener 1967, 1968; Andrews 1979; Spiller & Schoener 1990; Huang et al. 2008), which is problematic in the context of longitudinal field studies....

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References
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Journal ArticleDOI

292 citations

Journal ArticleDOI
01 Oct 1964-Ecology
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

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)....

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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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