Movement, sex ratio, and population density in a dwarf male spider species,Misumenoides formosipes(Araneae: Thomisidae)

2015 ◽  
Vol 43 (3) ◽  
pp. 388-393 ◽  
Author(s):  
G. N. Dodson ◽  
A. G. Anderson ◽  
L. M. Stellwag
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Dwarf Male ◽  
Spider Species ◽  
Misumenoides Formosipes

scholarly journals Natural variation in social conditions affects male mate choosiness in the amphipod Gammarus roeselii

2021 ◽  
Author(s):  
Konrad Lipkowski ◽  
Sophie Steigerwald ◽  
Lisa M Schulte ◽  
Carolin Sommer-Trembo ◽  
Jonas Jourdan
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Natural Variation ◽  
Natural Populations ◽  
Social Background ◽  
Social Conditions ◽  
Background Information ◽  
Male Mating ◽  
Natural Environments ◽  
Male Mate

Abstract The extent of male mate choosiness is driven by a trade-off between various environmental factors associated with the costs of mate acquisition, quality assessment and opportunity costs. Our knowledge about natural variation in male mate choosiness across different populations of the same species, however, remains limited. In this study, we compared male mate choosiness across 10 natural populations of the freshwater amphipod Gammarus roeselii (Gervais 1835), a species with overall high male mating investments, and evaluated the relative influence of population density and sex ratio (both affecting mate availability) on male mate choosiness. We investigated amplexus establishment after separating mating pairs and presenting focal males with a novel, size-matched female from the same population. Our analysis revealed considerable effects of sex ratio and (to a lesser extent) population density on time until amplexus establishment (choosiness). Male amphipods are able to perceive variable social conditions (e.g., sex ratio) and modify their mating strategy accordingly: We found choosiness to be reduced in increasingly male-biased populations, whereas selectivity increases when sex ratio becomes female biased. With this, our study expands our limited knowledge on natural variations in male mate choosiness and illustrates the importance of sex ratio (i.e., level of competition) for male mating decisions in natural environments. Accounting for variation in sex ratios, therefore, allows envisioning a distinctive variation of choosiness in natural populations and highlights the importance of considering social background information in future behavioral studies.

Effects of phytoseiid predators on the sex ratio of the spider mite Panonychus ulmi

1991 ◽  
Vol 69 (1) ◽  
pp. 208-212 ◽  
Author(s):  
Dan L. Johnson ◽  
Heather C. Proctor
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Spider Mite ◽  
Total Population ◽  
Panonychus Ulmi ◽  
Encounter Rate ◽  
Male Mortality ◽  
Adult Sex Ratio ◽  
Biased Sex Ratio ◽  
Male Activity

The effect of predator presence on the adult sex ratio of a spider mite (Panonychus ulmi) was examined in a field experiment. Phytoseiid predators (chiefly Typhlodromus occidentalis) were removed from 32 trees harboring P. ulmi populations, and allowed to remain at natural levels on 32 other trees. Both total population density and proportion of males in the prey population were significantly higher in predator-free trees. Mechanisms that could explain the increase in the proportion of males are examined. The most probable is that greater male activity results in a higher encounter rate between predator and prey, and that subsequent higher male mortality when predators are present exaggerates the female-biased sex ratio. The theoretical effects of sex-biased predation on diplo-diploid and haplo-diploid organisms are discussed.

scholarly journals Recruitment sex ratios in gray-tailed voles (Microtus canicaudus) in response to density, sex ratio, and season

2003 ◽  
Vol 81 (8) ◽  
pp. 1306-1311 ◽  
Author(s):  
Monica L Bond ◽  
Jerry O Wolff ◽  
Sven Krackow
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Resource Competition ◽  
Sex Ratios ◽  
Female Offspring ◽  
High Population ◽  
Reproductive Value ◽  
High Population Density ◽  
Adult Sex Ratio ◽  
Sex Ratio Adjustment

We tested predictions associated with three widely used hypotheses for facultative sex-ratio adjustment of vertebrates using eight enclosed populations of gray-tailed voles, Microtus canicaudus. These were (i) the population sex ratio hypothesis, which predicts that recruitment sex ratios should oppose adult sex-ratio skews, (ii) the local resource competition hypothesis, which predicts female-biased recruitment at low adult population density and male-biased recruitment at high population density, and (iii) the first cohort advantage hypothesis, which predicts that recruitment sex ratios should be female biased in the spring and male biased in the autumn. We monitored naturally increasing population densities with approximately equal adult sex ratios through the spring and summer and manipulated adult sex ratios in the autumn and measured subsequent sex ratios of recruits. We did not observe any significant sex-ratio adjustment in response to adult sex ratio or high population density; we did detect an influence of time within the breeding season, with more female offspring observed in the spring and more male offspring observed in the autumn. Significant seasonal increases in recruitment sex ratios indicate the capacity of female gray-tailed voles to manipulate their offspring sex ratios and suggest seasonal variation in the relative reproductive value of male and female offspring to be a regular phenomenon.

Adjustment of fecundity and sex ratio in response to social environments in a haplodiploid mite

2022 ◽  
Author(s):  
Nuwan Weerawansha ◽  
Qiao Wang ◽  
Xiong Zhao He
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Population Size ◽  
Local Population ◽  
Female Offspring ◽  
Social Environments ◽  
Positive Interaction ◽  
Offspring Sex Ratio ◽  
Offspring Sex ◽  
Large Populations

Animals can adjust reproductive strategies in favour of corporation or competition in response to local population size and density, the two key factors of social environments. However, previous studies usually focus on either population size or density but ignore their interactions. Using a haplodiploid spider mite, Tetranychus ludeni Zacher, we carried out a factorial experiment in the laboratory to examine how ovipositing females adjust their fecundity and offspring sex ratio during their early reproductive life under various population size and density. We reveal that females laid significantly more eggs with increasing population size and significantly fewer eggs with increasing population density. This suggests that large populations favour cooperation between individuals and dense populations increase competition. We demonstrate a significant negative interaction of population size and density that resulted in significantly fewer eggs laid in the large and dense populations. Furthermore, we show that females significantly skewed the offspring sex ratio towards female-biased in small populations to reduce the local mate competition among their sons. However, population density incurred no significant impact on offspring sex ratio, while the significant positive interaction of population size and density significantly increased the proportion of female offspring in the large and dense populations, which will minimise food or space competition as females usually disperse after mating at crowded conditions. These results also suggest that population density affecting sex allocation in T. ludeni is intercorrelated with population size. This study provides evidence that animals can manipulate their reproductive output and adjust offspring sex ratio in response to various social environments, and the interactions of different socio-environmental factors may play significant roles.

scholarly journals Age- and sex-specific response to population density and sex ratio

2010 ◽  
Vol 21 (2) ◽  
pp. 356-364 ◽  
Author(s):  
A.N. Dreiss ◽  
J. Cote ◽  
M. Richard ◽  
P. Federici ◽  
J. Clobert
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Specific Response ◽  
Age And Sex

POPULATION DENSITY AND SEX RATIO DYNAMICS OF OVERWINTERING MAIZE WEEVILS (COLEOPTERA: CURCULIONIDAE) INFESTING FIELD CORN

1986 ◽  
Vol 21 (4) ◽  
pp. 368-375 ◽  
Author(s):  
D. E. Dix ◽  
J. N. All
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Cold Tolerance ◽  
Sitophilus Zeamais ◽  
Winter Mortality ◽  
Weather Extremes ◽  
Maize Weevil ◽  
Monthly Basis ◽  
Field Corn ◽  
Cold Hardy

Natural infestations of the maize weevil, Sitophilus zeamais (Motschulsky) were monitored in selected corn fields located in each of five major climatic or edaphic environments of Georgia. The population density and sex ratio of each population was recorded on a monthly basis during the fall and winters of 1982–83–84. Females suffered higher winter mortality than males, resulting in increasingly male-skewed sex ratios (from 0.8/1.0 to 1.6/1.0) as winter progressed. The degree of male-skewedness was positively correlated with the amount of subzero weather experienced by each population. Surviving weevil populations decreased in size as winter progressed, with the greatest reductions at the higher latitudes. No weevils survived through spring north of 33° 57′N where winter weather extremes of −15°C occurred. No true diapausing stage was found; however, cold tolerance tests indicated that winter-collected weevils were significantly more cold hardy than laboratory-reared weevils.

Notes on the biology of Lacerta andreanszkyi (Reptilia: Lacertidae)

1987 ◽  
Vol 8 (3) ◽  
pp. 231-236 ◽  
Author(s):  
Stephen D. Busack
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Feeding Ecology ◽  
Thermal Environment ◽  
Limited Data ◽  
High Atlas ◽  
Atlas Mountains ◽  
High Atlas Mountains ◽  
Elusive Species

AbstractReported only from three general areas at elevations between 2500-3700 m within the High Atlas Mountains of Marrakech Prefecture, Morocco, Lacerta andreanszkyi appears little studied (Saint Girons, 1953; Pasteur and Bons, 1960; Bons, 1967; Klemmer, 1969). Since Werner's (1929) description of this apparently restricted apecies, nothing has been published regarding its biology. The following limited data concerning population density, biomass, sex ratio, feeding ecology, reproduction, frequency of injury, and thermal environment and response of this elusive species are presented below to partially fill this void.

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