Sexual size dimorphism in relation to resource partitioning in North American dabbling ducks

1984 ◽  
Vol 62 (10) ◽  
pp. 2009-2012 ◽  
Author(s):  
Thomas D. Nudds ◽  
Richard M. Kaminski
Keyword(s):  
North American ◽  
Resource Partitioning ◽  
Sexual Size Dimorphism ◽  
Prey Size ◽  
Dabbling Ducks ◽  
Male And Female ◽  
Size Dimorphism ◽  
Bill Morphology ◽  
Size Dimension ◽  
Bill Length

Data from museum specimens were used to examine patterns of sexual size dimorphism in bill morphology in relation to resource partitioning in seven species of North American dabbling ducks (Anas sp.). All species were dimorphic with respect to bill length. Male and female bill length distributions were skewed in opposite directions in five of seven species (P < 0.01). Four of seven species were dimorphic with respect to lamellar density, but male and female distributions were skewed in opposite directions in only two species. The four dimorphic species were positioned between other species along a prey size dimension; species which were not dimorphic had only one neighbour on the prey size dimension. These results are consistent with the hypothesis that intersexual competition for food promotes niche divergence between sexes and contributes to sexual size dimorphism in ducks.

Predator–prey size relationships in North American dabbling ducks

1984 ◽  
Vol 62 (10) ◽  
pp. 2002-2008 ◽  
Author(s):  
Thomas D. Nudds ◽  
James N. Bowlby
Keyword(s):  
Prey Size ◽  
Taxonomic Composition ◽  
Size Distributions ◽  
Dabbling Ducks ◽  
Predator Prey ◽  
Caloric Density ◽  
Bill Morphology ◽  
Bill Length ◽  
Niche Dimension ◽  
Solitary Species

Diets of dabbling ducks (Anas: Anatidae) usually have been recorded only with respect to taxonomic composition and not prey size. Interspecific diet overlap thus has been termed large. However, using published taxonomic diet lists for seven species of ducks, measurements of bill morphology from museum specimens, and "handbook" data on the sizes and caloric density of invertebrates, prey size distributions were found to differ among species (P < 0.001). Also, the sizes of prey in each species' diet differed from that found in the environment. The number of lamellae per centimetre of bill negatively correlated with mean prey size (P < 0.001); body size and bill length did not. Based on the similarity of environmental and dietary prey size distributions, species were classified as specialist or generalist foragers. This classification corresponded well with one generated from analyses of foraging behaviour alone. An explanation for the diminuitive sizes of ducks on islands was advanced: if interspecific competition for food selects for niche divergence among coexisting dabbling ducks along a prey size niche dimension, then in the absence of competition from small species on islands, large solitary species have evolved to a smaller size which may be optimal for the distribution of energy among prey size classes in the environment.

scholarly journals Sex-specific microhabitat use is associated with sex-biased thermal physiology in Anolis lizards

2020 ◽  
pp. jeb.235697
Author(s):  
Michael L. Logan ◽  
Lauren K. Neel ◽  
Daniel J. Nicholson ◽  
Andrew J. Stokes ◽  
Christina L. Miller ◽  
...  
Keyword(s):  
Sexual Dimorphism ◽  
Habitat Use ◽  
Thermal Tolerance ◽  
Sexual Size Dimorphism ◽  
Microhabitat Use ◽  
Thermal Physiology ◽  
Male And Female ◽  
Size Dimorphism ◽  
Heterogeneous Habitats ◽  
Males And Females

If fitness optima for a given trait differ between males and females in a population, sexual dimorphism may evolve. Sex-biased trait variation may affect patterns of habitat use, and if the microhabitats used by each sex have dissimilar microclimates, this can drive sex-specific selection on thermal physiology. Nevertheless, tests of differences between the sexes in thermal physiology are uncommon, and studies linking these differences to microhabitat use or behavior are even rarer. We examined microhabitat use and thermal physiology in two ectothermic congeners that are ecologically similar but differ in their degree of sexual size dimorphism. Brown anoles (Anolis sagrei) exhibit male-biased sexual size dimorphism and live in thermally heterogeneous habitats, whereas slender anoles (Anolis apletophallus) are sexually monomorphic in body size and live in thermally homogeneous habitats. We hypothesized that differences in habitat use between the sexes would drive sexual divergence in thermal physiology in brown anoles, but not slender anoles, because male and female brown anoles may be exposed to divergent microclimates. We found that male and female brown anoles, but not slender anoles, used perches with different thermal characteristics and were sexually dimorphic in thermal tolerance traits. However, field-active body temperatures and behavior in a laboratory thermal arena did not differ between females and males in either species. Our results suggest that sexual dimorphism in thermal physiology can arise from phenotypic plasticity or sex-specific selection on traits that are linked to thermal tolerance, rather than from direct effects of thermal environments experienced by males and females.

Influence of female-biased sexual size dimorphism on dominance of female Townsend’s chipmunks

2006 ◽  
Vol 84 (12) ◽  
pp. 1859-1863 ◽  
Author(s):  
A.J. Edelman ◽  
J.L. Koprowski
Keyword(s):  
Body Size ◽  
Reproductive Success ◽  
North American ◽  
Sexual Size Dimorphism ◽  
Large Female ◽  
Small Female ◽  
Access To Resources ◽  
Size Dimorphism

Female-biased sexual size dimorphism (SSD), a condition common in North American chipmunks, occurs when females are larger than males in a species. We examined the influence of body size on dominance of captive female Townsend’s chipmunks ( Tamias townsendii Bachman, 1839), a species that exhibits female-biased SSD, in all-female and mixed-sex dyadic encounters. In all-female dyads, large female chipmunks were more frequently dominant over small female opponents. In mixed-sex dyads, large females were always dominant over small males. Female-biased SSD in Townsend’s chipmunks appears to indirectly allow large females to more frequently dominate small female and male conspecifics. Greater dominance could increase reproductive success of large female chipmunks by increasing access to resources.

Environmental factors affecting sexual size dimorphism in the hermit crab Pagurus middendorffii

1999 ◽  
Vol 79 (5) ◽  
pp. 953-954 ◽  
Author(s):  
Satoshi Wada
Keyword(s):  
Environmental Factors ◽  
Interspecific Competition ◽  
Hermit Crab ◽  
Sexual Size Dimorphism ◽  
Sympatric Species ◽  
Shell Size ◽  
Male And Female ◽  
Factors Affecting ◽  
Size Dimorphism ◽  
Population Comparisons

The effects of shell resource and interspecific competition on sexual size dimorphism of the hermit crab, Pagurus middendorffii (Decapoda: Paguridae), were examined from population comparisons. Degree of size dimorphism and mean shell size occupied by male and female P. middendorffii differed among adjacent sites, and there was a significant correlation between them. Although most large P. middendorffii occupied large Chlorostoma lischkei shells in both shell-limited and shell-unlimited populations, P. lanuginosus, a sympatric species, occupied large C. lischkei shells more frequently than P. middendorffii did in a shell-limited population. Environmental factors, shell availability and interspecific competition for shells, might play important roles in determining the degree of sexual size dimorphism of P. middendorffii.

Development time of male and female rotifers with sexual size dimorphism

Hydrobiologia ◽  
2015 ◽  
Vol 767 (1) ◽  
pp. 27-35 ◽  
Author(s):  
Xu-Wang Yin ◽  
Bing-Bing Tan ◽  
Yan-Chun Zhou ◽  
Xiao-Chun Li ◽  
Wei Liu
Keyword(s):  
Development Time ◽  
Sexual Size Dimorphism ◽  
Male And Female ◽  
Size Dimorphism

Sex biases in parasitism of neotropical bats by bat flies (Diptera: Streblidae)

2008 ◽  
Vol 24 (4) ◽  
pp. 387-396 ◽  
Author(s):  
Bruce D. Patterson ◽  
Carl W. Dick ◽  
Katharina Dittmar
Keyword(s):  
Sex Differences ◽  
Sexual Size Dimorphism ◽  
Species Level ◽  
Male And Female ◽  
Size Dimorphism ◽  
Bat Flies ◽  
Neotropical Bats ◽  
Males And Females ◽  
Heavy Loads ◽  
Sex Biases

AbstractWe describe levels of parasitism of ectoparasitic bat flies (Hippoboscoidea: Streblidae) on male and female bats from an extensive Neotropical survey. The collection resulted from coordinated vertebrate-parasite surveys undertaken by the Smithsonian Venezuelan Project (SVP) from 1965–1968, which sexed 24 978 bats of 130 species. Streblid parasites were recovered from 6935 individuals of 87 bat species, but only 47 species were captured frequently enough (≥ 20 infested individuals) to permit reliable estimates of streblid parasitism on males and females. Well-sampled species included 39 phyllostomids, four mormoopids, two noctilionids, one natalid and one molossid. Prevalence of streblid parasitism (proportion of individuals infested) of male and female bats was generally not significantly different, and averaged 0.34 across infested species. In species-level analyses assessed against captures, significant sex differences in infestation levels were noted in six species; all had mean prevalence below 0.5 and females were parasitized disproportionately in each. Sex differences in total numbers of flies were noted in 21 species, and in 16 of these, females carried disproportionately heavy loads. Sex differences were also found for eight species of bat in the number of fly species infesting an individual; seven of eight showed heavier female parasitism. In analyses weighted by infestation levels, sex differences in total number of flies were found in only 12 species, with seven showing excessive parasitism of females, and no species showed sex differences in the number of fly species infesting them. These significant biases were not associated with sexual size dimorphism among the bat species. Generally higher levels of parasitism among female bats accords with theory, given their generally higher survivorship and enhanced probabilities of lateral and vertical transmission of host-specific parasites, but contrasts with patterns shown by many other parasitic arthropods. Future analyses should target social groupings of bats, not passively sampled foragers, to better address the mechanisms responsible for this pattern.

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