scholarly journals SIZE-STRUCTURED DYNAMICS IN A JUVENILE-ADULT POPULATION WITH FIXED SEX-RATIO

2017 ◽  
Vol 7 (2) ◽  
pp. 644-658
Author(s):  
Yan Liu ◽  
Keyword(s):  
Sex Ratio ◽  
Adult Population

scholarly journals Adult sex ratios and their implications for cooperative breeding in birds

2017 ◽  
Vol 372 (1729) ◽  
pp. 20160322 ◽  
Author(s):  
Jan Komdeur ◽  
Tamás Székely ◽  
Xiaoyan Long ◽  
Sjouke A. Kingma
Keyword(s):  
Sex Ratio ◽  
Cooperative Breeding ◽  
Adult Population ◽  
Sex Ratios ◽  
Bird Species ◽  
Dispersal Distance ◽  
Sex Bias ◽  
Wide Range ◽  
Cooperatively Breeding ◽  
Using Data

Cooperative breeding is a form of breeding system where in addition to a core breeding pair, one or more usually non-breeding individuals provide offspring care. Cooperative breeding is widespread in birds, but its origin and maintenance in contemporary populations are debated. Although deviations in adult sex ratio (ASR, the proportion of males in the adult population) have been hypothesized to influence the occurrence of cooperative breeding because of the resulting surplus of one sex and limited availability of breeding partners, this hypothesis has not been tested across a wide range of taxa. By using data from 188 bird species and phylogenetically controlled analyses, we show that cooperatively breeding species have more male-biased ASRs than non-cooperative species. Importantly, ASR predicts helper sex ratio: in species with more male-biased ASR, helper sex ratio is also more male biased. We also show that offspring sex ratios do not predict ASRs, so that the skewed ASRs emerge during the period when individuals aim to obtain a breeding position or later during adulthood. In line with this result, we found that ASR (among both cooperatively and non-cooperatively breeding species) is inversely related to sex bias in dispersal distance, suggesting that the cost of dispersal is more severe for the further-dispersing sex. As females usually disperse further in birds, this explains the generally male-biased ASR, and in combination with benefits of philopatry for males, this probably explains why ASR is more biased in cooperatively breeding species. Taken together, our results suggest that a sex bias in helping in cooperatively breeding species relates to biased ASRs. We propose that this relationship is driven by sex-specific costs and benefits of dispersal and helping, as well as other demographic factors. Future phylogenetic comparative and experimental work is needed to establish how this relationship emerges. This article is part of the themed issue ‘Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies’.

Facultative sex allocation in the viviparous lizard Eulamprus tympanum, a species with temperature-dependent sex determination

2003 ◽  
Vol 51 (4) ◽  
pp. 367 ◽  
Author(s):  
Kylie A. Robert ◽  
Michael B. Thompson ◽  
Frank Seebacher
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Breeding Season ◽  
Sex Allocation ◽  
Adult Population ◽  
Selective Advantage ◽  
Adult Males ◽  
Temperature Dependent ◽  
Maternal Manipulation

Females of the Australian scincid lizard Eulamprus tympanum can manipulate the sex of their offspring in response to gender imbalances in the population using temperature-dependent sex determination. Here we show that when adult males are scarce females produced male-biased litters and when adult males were common females produced female-biased litters. The cues used by a female to assess the adult population are not known but presumably depend upon her experience throughout the breeding season. Maternal manipulation of the sex ratio of the offspring in E. tympanum illustrates a selective advantage of temperature-dependent sex determination in a viviparous species.

scholarly journals Population status and demographics of Lake Sturgeon in the Bad and White rivers, Wisconsin

2019 ◽  
Vol 10 (2) ◽  
pp. 442-457 ◽  
Author(s):  
Joshua T. Schloesser ◽  
Henry R. Quinlan
Keyword(s):  
Sex Ratio ◽  
Adult Population ◽  
Lake Superior ◽  
Return Time ◽  
Lake Sturgeon ◽  
River Population ◽  
Mature Adults ◽  
Rehabilitation Plan ◽  
Population Trajectory ◽  
Spawning Run

Abstract Lake Sturgeon Acipenser fulvescens rehabilitation efforts in Lake Superior are guided by a rehabilitation plan that sets goals and criteria for a self-sustaining population, including a minimum of 1,500 mature adults, roughly equal sex ratio, and annual exploitation rates < 5%. The Bad and White rivers, Wisconsin host a genetically unique Lake Sturgeon population that is utilized by state-licensed recreational anglers and tribal subsistence fishers. Our objectives were to 1) determine if the Bad River population meets rehabilitation plan targets for a self-sustaining population, 2) assess harvest of Lake Sturgeon by recreational anglers and tribal subsistence fishers for compatibility with rehabilitation goals, 3) determine population trajectory from annual spawning runs, and 4) describe population demographics given the unique physical features of Lake Superior. We sampled Lake Sturgeon in the Bad and White rivers with gill nets over a 17-y period (2001 to 2017). The observed sex ratio in spawning runs was 2.2:1 (male : female), but calculated at 1.6:1 for the entire adult population on the basis of abundance estimates. Weight–length relationships converted to a standardized modified form factor indicated lower condition and possibly lower female fecundity compared with other large North American populations. Annual spawning run size estimates over time indicated that the population trajectory was stable to slightly increasing, and during 2016 was 739 and 241 individuals in the Bad and White rivers, respectively. Total population size (including nonspawners) exceeded 1,500 individuals, which met Lake Superior rehabilitation criteria for a self-sustaining population. Estimates of 1,426 males and 882 females were considered conservative because 472 unknown-sex fish could not be accounted for in return time and abundance models. Spawning return times were 2 or 3 y for males and 4 to 6 y for females, longer than many other populations. Exploitation by recreational anglers and tribal subsistence fishers was 1.3% or lower and met the rehabilitation plan target of < 5%, but we recommend exploitation not exceed 3.1% to maintain a self-sustaining population. These findings help gauge rehabilitation progress in Lake Superior and better describe the demographics of a remnant self-sustaining Lake Sturgeon population in Lake Superior.

scholarly journals Estimating adult sex ratios in nature

2017 ◽  
Vol 372 (1729) ◽  
pp. 20160313 ◽  
Author(s):  
Sergio Ancona ◽  
Francisco V. Dénes ◽  
Oliver Krüger ◽  
Tamás Székely ◽  
Steven R. Beissinger
Keyword(s):  
Sex Differences ◽  
Sex Ratio ◽  
Evolutionary Biology ◽  
Adult Population ◽  
Sex Ratios ◽  
Estimation Methods ◽  
Spatial And Temporal Variation ◽  
Animal Populations ◽  
Adult Sex Ratio ◽  
Males And Females

Adult sex ratio (ASR, the proportion of males in the adult population) is a central concept in population and evolutionary biology, and is also emerging as a major factor influencing mate choice, pair bonding and parental cooperation in both human and non-human societies. However, estimating ASR is fraught with difficulties stemming from the effects of spatial and temporal variation in the numbers of males and females, and detection/capture probabilities that differ between the sexes. Here, we critically evaluate methods for estimating ASR in wild animal populations, reviewing how recent statistical advances can be applied to handle some of these challenges. We review methods that directly account for detection differences between the sexes using counts of unmarked individuals (observed, trapped or killed) and counts of marked individuals using mark–recapture models. We review a third class of methods that do not directly sample the number of males and females, but instead estimate the sex ratio indirectly using relationships that emerge from demographic measures, such as survival, age structure, reproduction and assumed dynamics. We recommend that detection-based methods be used for estimating ASR in most situations, and point out that studies are needed that compare different ASR estimation methods and control for sex differences in dispersal. This article is part of the themed issue ‘Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies’.

scholarly journals Population Viability and Resource Competition on North Brother Island: Conservation Implications for Tuatara (Sphenodon Punctatus) and Duvaucel's Gecko (Hoplodactylus Duvaucelii)

2021 ◽  
Author(s):  
◽  
Joanna Wilson
Keyword(s):  
Sex Ratio ◽  
Population Size ◽  
Body Condition ◽  
Resource Competition ◽  
Adult Population ◽  
Population Viability ◽  
Adult Survival ◽  
Intraspecific Interactions ◽  
Sphenodon Punctatus

<p>Population viability for small, isolated populations is determined by many factors, particularly demographic stochasticity. Coexistence of communities is promoted through resource partitioning, particularly if species share similar niche requirements. Demographic characteristics, long-term trends and patterns of partitioning were investigated for two reptile species: tuatara (Sphenodon punctatus) and Duvaucel's gecko (Hoplodactylus duvaucelii), using mark recapture techniques on North Brother Island, New Zealand. Capture time and location were recorded as well as snout-vent length, mass and sex of individuals. Adult population size, sex ratio, survival and recapture probability for both species were estimated. Intervention will be needed to prevent population collapse for tuatara, as the population is male-biased (3.24 males: 1 female), with sub-adults exhibiting a stronger bias (4.1 males: 1 female). The total population size is estimated at 390-437 adults, with high adult survival (95%). The Duvaucel's gecko population is stable enough to be harvested for translocation, as the population was estimated at 583-677 adults, with an even sex ratio. Adult survival was high (92%) and longevity is at least 43-50 years. Patterns in partitioning suggest tuatara are excluding Duvaucel's gecko as tuatara occupy vegetated areas and few animals were caught at the same time in the same place as a member of the other species (~10%). Long-term site fidelity appears to occur in both species as the majority of animals were captured previously within 10m (tuatara) or 15m (Duvaucel's gecko) of their 2008 location, and travelled less than 2m per year on average. Tuatara show an overall decline in body condition since 1957, which is more rapid in females, and may be related to intraspecific interactions and density-dependent effects. Gecko body condition is not declining, suggesting no negative effects at the population level are occurring as a result of competitive exclusion. This study indicates that characteristics that have implications for population viability have the capacity to differ, even for species with similar niche requirements occupying the same habitat, and supports the considerable value of long-term monitoring.</p>

Aspects of the Demography of the Western Grey-Kangaroo, Macropus-Fuliginosus-Melanops, in Semiarid Northwest Victoria

1988 ◽  
Vol 15 (3) ◽  
pp. 257 ◽  
Author(s):  
GL Norbury ◽  
GM Coulson ◽  
BL Walters
Keyword(s):  
Sex Ratio ◽  
National Park ◽  
Adult Population ◽  
Severe Drought ◽  
Energy Costs ◽  
Age Classes ◽  
North West ◽  
Adult Age ◽  
Grey Kangaroo ◽  
Western Grey Kangaroo

The study was carried out at Hattah-Kulkyne National Park in semiarid north-west Victoria, during 3 years immediately following a severe drought. A sample of animals which died as a result of the drought (n= 196) and a shot sample (n=546) were examined to determine patterns of breeding, mortality and age structure. Births were concentrated in spring and summer, with a peak in November. Only 46% of mature females bred during the drought, whereas 100% bred two seasons later. The sex ratio of pouch young was not significantly different from parity, but showed a slight male-bias, however, the sex ratio of the adult population was markedly female-biased (1:3). Projected population growth was not realised in the years following the drought because of high mortality. There was evidence of male-biased mortality which was apparently accentuated during the drought. This biased mortality appeared similar in all adult age classes, and may have been a consequence of the disparate energy costs imposed by sex differences in body size and in mobility.

scholarly journals Effective population size/adult population size ratios in wildlife: a review

1995 ◽  
Vol 66 (2) ◽  
pp. 95-107 ◽  
Author(s):  
Richard Frankham
Keyword(s):  
Sex Ratio ◽  
Population Size ◽  
Effective Population Size ◽  
Family Size ◽  
Adult Population ◽  
Effective Population ◽  
Total Size ◽  
Relevant Variables ◽  
Population Sizes ◽  
Census Population Size

SummaryThe effective population size is required to predict the rate of inbreeding and loss of genetic variation in wildlife. Since only census population size is normally available, it is critical to know the ratio of effective to actual population size (Ne/N). Published estimates ofNe/N(192 from 102 species) were analysed to identify major variables affecting the ratio, and to obtain a comprehensive estimate of the ratio with all relevant variables included. The five most important variables explaining variation among estimates, in order of importance, were fluctuation in population size, variance in family size, form ofNused (adults υ. breeders υ. total size), taxonomic group and unequal sex-ratio. There were no significant effects on the ratio of high υ. low fecundity, demographic υ. genetic methods of estimation, or of overlapping υ. non-overlapping generations when the same variables were included in estimates. Comprehensive estimates ofNe/N(that included the effects of fluctuation in population size, variance in family size and unequal sex-ratio) averaged only 0·10–0·11. Wildlife populations have much smaller effective population sizes than previously recognized.

scholarly journals Population Viability and Resource Competition on North Brother Island: Conservation Implications for Tuatara (Sphenodon Punctatus) and Duvaucel's Gecko (Hoplodactylus Duvaucelii)

2021 ◽  
Author(s):  
◽  
Joanna Wilson
Keyword(s):  
Sex Ratio ◽  
Population Size ◽  
Body Condition ◽  
Resource Competition ◽  
Adult Population ◽  
Population Viability ◽  
Adult Survival ◽  
Intraspecific Interactions ◽  
Sphenodon Punctatus

<p>Population viability for small, isolated populations is determined by many factors, particularly demographic stochasticity. Coexistence of communities is promoted through resource partitioning, particularly if species share similar niche requirements. Demographic characteristics, long-term trends and patterns of partitioning were investigated for two reptile species: tuatara (Sphenodon punctatus) and Duvaucel's gecko (Hoplodactylus duvaucelii), using mark recapture techniques on North Brother Island, New Zealand. Capture time and location were recorded as well as snout-vent length, mass and sex of individuals. Adult population size, sex ratio, survival and recapture probability for both species were estimated. Intervention will be needed to prevent population collapse for tuatara, as the population is male-biased (3.24 males: 1 female), with sub-adults exhibiting a stronger bias (4.1 males: 1 female). The total population size is estimated at 390-437 adults, with high adult survival (95%). The Duvaucel's gecko population is stable enough to be harvested for translocation, as the population was estimated at 583-677 adults, with an even sex ratio. Adult survival was high (92%) and longevity is at least 43-50 years. Patterns in partitioning suggest tuatara are excluding Duvaucel's gecko as tuatara occupy vegetated areas and few animals were caught at the same time in the same place as a member of the other species (~10%). Long-term site fidelity appears to occur in both species as the majority of animals were captured previously within 10m (tuatara) or 15m (Duvaucel's gecko) of their 2008 location, and travelled less than 2m per year on average. Tuatara show an overall decline in body condition since 1957, which is more rapid in females, and may be related to intraspecific interactions and density-dependent effects. Gecko body condition is not declining, suggesting no negative effects at the population level are occurring as a result of competitive exclusion. This study indicates that characteristics that have implications for population viability have the capacity to differ, even for species with similar niche requirements occupying the same habitat, and supports the considerable value of long-term monitoring.</p>

EFFECT OF COLOR ON STICKY-TRAP CATCHES OF PHOLETESOR ORNIGIS (HYMENOPTERA: BRACONIDAE), A PARASITE OF THE SPOTTED TENTIFORM LEAFMINER PHYLLONORYCTER BLANCARDELLA (LEPIDOPTERA: GRACILLARIIDAE)

1985 ◽  
Vol 117 (12) ◽  
pp. 1559-1564 ◽  
Author(s):  
R.M. Trimble ◽  
E.J. Brach
Keyword(s):  
Sex Ratio ◽  
Adult Population ◽  
Sticky Trap ◽  
Apple Orchards ◽  
Trap Color ◽  
Relative Attractiveness ◽  
Males And Females ◽  
Phyllonorycter Blancardella ◽  
Trap Catches ◽  
Pholetesor Ornigis

AbstractThe effect of trap color on sticky-trap catches of Pholetesor ornigis Weed was studied in experimental and commercial apple orchards during each of the parasite's 3 yearly activity periods during 1982–1984. Seven enamel and 5 fluorescent paints were compared in 8 trials. There was considerable between-trial variation in the percentage of the total number of P. ornigis caught on a trap of one color. Trap color had a significant effect on the total number of parasites caught. There were no consistent differences in the relative attractiveness of the different colors to males and females. During 1984, males comprised more than 75% of all parasites trapped during each of the 3 activity periods. The sex ratio of the adult population emerging in study orchards during 2 of these activity periods was approximately 1:1.

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