Adult survival and recruitment and the explanation of an uneven sex ratio in a tortoise population

1990 ◽  
Vol 68 (3) ◽  
pp. 547-555 ◽  
Author(s):  
Adrian Hailey
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Adult Survival ◽  
Adult Longevity ◽  
Adult Males ◽  
Northern Greece ◽  
Female Population ◽  
Lower Survival Rate ◽  
Adult Sex Ratio ◽  
Testudo Hermanni

Survival, recruitment, and dynamics of adult Testudo hermanni at Alyki (northern Greece) were studied from 1980 to 1988. Recruitment of adult males was greater than that of females owing to their shorter time to maturity (9 vs. 11 years); recruitment of subadults (6 years old) was equal in males and females. Mean annual survival was slightly greater in males (0.914) than females (0.877), equivalent to mean adult longevity values of 11.6 and 8.1 years, respectively. Excluding tortoises that die before maturity, male and female T. hermanni are mature for about 56 and 42% of their life, respectively. Generation time was roughly twice the age at maturity, and three times the age at which secondary sexual characters develop, a pattern which may apply to other tortoises. The combination of adult survival and recruitment should lead to a stable sex ratio (males/females) of 2.1. The adult sex ratio was higher than this, but decreasing, from4.1 in 1982to3.0 in 1986, with an increase in the female population; the number of males was stable. The observed sex ratio showed a similar decline and a further fall to 2.4 in 1988. The cause of the lower survival rate of females compared with males is proposed to be damage during courtship attempts. The courtship behaviour and related anatomy of T. hermanni are compared with those of T. graeca, a species with even population sex ratios. The level of male-induced female mortality would depend on population density; the increasing number of females during the study follows the approximate halving of population density in 1980.

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.

Contribution of adult sex ratio to trauma and reproductive output in large breeding groups of rhesus macaques (Macaca mulatta)

2021 ◽  
Vol 30 (4) ◽  
pp. 479-492
Author(s):  
J Crast ◽  
MA Bloomsmith ◽  
CM Remillard ◽  
T Meeker
Keyword(s):  
Sex Ratio ◽  
Macaca Mulatta ◽  
Social Dynamics ◽  
Rhesus Macaques ◽  
Well Being ◽  
Primate Research ◽  
Adult Males ◽  
Adult Sex Ratio ◽  
Breeding Groups ◽  
Financial Burdens

Maintaining stable breeding groups of rhesus macaques (Macaca mulatta) can be challenging due to the complex social dynamics and despotic nature of the species. Trauma from aggression is a common problem in rhesus colonies and can cause social disruption, strain veterinary and animal management resources, and potentially affect reproduction. Previous research has shown that increasing the number of non-natal adult males in a breeding group can improve group stability, reduce trauma, and increase reproduction. Here, we used mixed-effects regression models to examine the effects of sex ratio and other factors on trauma and reproduction at the Yerkes National Primate Research Center using a historical dataset made up of four large rhesus groups over an eleven-year period (2003–2013). As expected, sex ratio was a significant predictor for both trauma and reproduction. However, group age since formation was a stronger predictor of trauma frequency and the amount of space available was a slightly better predictor of reproduction than sex ratio or trauma. These results indicate that improving sex ratios can be a viable management strategy to reduce trauma and improve reproduction, particularly when it is difficult to manipulate the group compositions and/or their housing situations. Reducing trauma is a primary goal for rhesus breeding colonies, as it directly impacts the monkeys' health and psychological well-being. Such improvements are necessary for the ethical treatment and care of the animals themselves, but also to reduce financial burdens and maintain a healthy colony for research purposes.

Life history and feeding biology of the predatory thrips, Aleurodothrips fasciapennis (Thysanoptera: Phlaeothripidae)

1998 ◽  
Vol 88 (3) ◽  
pp. 351-357 ◽  
Author(s):  
D.M. Watson ◽  
T.Y. Du ◽  
M. Li ◽  
J.J. Xiong ◽  
D.G. Liu ◽  
...  
Keyword(s):  
Life History ◽  
Relative Humidity ◽  
Sex Ratio ◽  
Intrinsic Rate ◽  
Natural Increase ◽  
Adult Longevity ◽  
Female Fecundity ◽  
Adult Sex Ratio ◽  
Survival And Reproduction ◽  
Low Humidity

AbstractDetails of the life history, the effects of relative humidity and temperature on survival and reproduction, and the predatory ability of Aleurodothrips fasciapennis Franklin were examined under laboratory conditions. Stage-specific development and adult longevity were similar between sexes, and the adult sex ratio was 1:1. Females laid 23.3 ± 18.0 eggs of which 83% hatched. The survival rate of first instars to adulthood was 82%. The intrinsic rate of natural increase (rm) was 0.04, assuming a zero or 5.4 day pre-oviposition interval. Temperature did not affect the proportion of eggs that hatched, the proportion of first instars surviving to adulthood or adult sex ratios. However, female fecundity was dependent on temperature being highest at 24 ndash 28°C. Relative humidity did not affect adult sex ratio or female fecundity but the proportion of eggs hatched and the survival of first instars to adulthood increased as relative humidity increased. Few eggs hatched when relative humidity was <65%. Larval and adult female A. fasciapennis were voracious feeders but the number of prey killed per progeny was high, suggesting A. fasciapennis was inefficient at converting prey into progeny biomass. The potential value of A. fasciapennis as a biocontrol agent of Aonidiella aurantii (Maskell) on Australian citrus is discussed in terms of its rm, prey killing power and environmental adaptability. It is concluded that population growth of A. fasciapennis should exceed that of A. aurantii under field conditions but A. fasciapennis may be of little value against A. aurantii on citrus grown under conditions of high temperature and low humidity, or when prey densities are low.

scholarly journals Population of Proboscis Monkey (Nasalis lavatus) in Manggar River, Balikpapan City, Indonesia

2021 ◽  
Vol 886 (1) ◽  
pp. 012068
Author(s):  
Ike Mediawati ◽  
Teguh Muslim ◽  
Amir Ma’ruf ◽  
Mukhlisi ◽  
Hery Seputro ◽  
...  
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Anthropogenic Activities ◽  
Proboscis Monkey ◽  
Adult Males ◽  
Conservation Area ◽  
Nasalis Larvatus ◽  
Survey Technique ◽  
Males And Females ◽  
Proboscis Monkeys

Abstract A population estimation of proboscis monkeys (Nasalis larvatus) has been conducted in Manggar River, Balikpapan. In this non-conservation area, the anthropogenic activities threaten the proboscis monkey habitat. Boat survey technique was applied along ± 17 km of the river in the morning and evening. The number of proboscis monkeys in the surveyed area was estimated to range from 57 to 69 individuals with estimated population density of 4.75 individuals/Km2. Moreover, the population of this primates was divided into 4 groups and the sex ratio between adult males and females was 1:2.33. The proboscis monkeys were distributed in the middle of the river to the upstream. The highest population was found in the upstream area with less human activities. Conservation efforts in the Manggar River need to be carried out considering the proboscis monkey habitat in the area has been fragmented and isolated. These efforts could involve local economic communities.

Effect of Irradiating Puparia of Oriental Fruit Fly (Diptera: Tephritidae) on Adult Survival and Fecundity for Sterile Insect Technique and Quarantine Purposes

2019 ◽  
Vol 112 (6) ◽  
pp. 2808-2816 ◽  
Author(s):  
Suhana Yusof ◽  
Ahmad Zainuri Mohamad Dzomir ◽  
Salmah Yaakop
Keyword(s):  
Sex Ratio ◽  
Sterile Insect Technique ◽  
Adult Emergence ◽  
Fruit Fly ◽  
Bactrocera Dorsalis ◽  
Adult Survival ◽  
Adult Longevity ◽  
Oriental Fruit Fly ◽  
New Findings ◽  
Morphological Differences

Abstract The aim of this study was to investigate the effect of gamma irradiation on survivability (adult emergence, sex ratio, adult longevity), fecundity (eggs hatchability, number of eggs produced), and morphological differences in the size of the ovary and testes of unirradiated and irradiated adults of Oriental fruit fly [Bactrocera dorsalis (Hendel)]. A dose of 100 Gy was determined as the minimum needed for inhibitory effects against B. dorsalis that would not deter adult emergence, sex ratio (male:female), and adult longevity, with 82.6 ±7.02, 1:1.09, and 107 ± 24.5, respectively. Doses from 50 to 400 Gy range did not completely prevent the adult emergence; however, the emergence decreased by increasing the radiation dose. Adult survivability significantly decreased among all the treatment groups of B. dorsalis, except for the 50 Gy and unirradiated flies. At a dose of 50 Gy, fertile females showed a significant reduction in fecundity by not producing eggs after mating with the sterile males. Meanwhile, the number of eggs laid decreased with increasing dose and no fertile egg was hatched starting at 100 Gy of irradiation. Testes and ovaries of 20-d old flies irradiated as pupae were smaller than those of control flies. In this study, 100 Gy was concluded as the minimum effective dose for the disinfestation and sterilization of B. dorsalis puparia. Results represent new findings used as a basis for sterile insect technique and quarantine programs for managing B. dorsalis, particularly in Malaysia.

scholarly journals Sex Ratio of Small Hive Beetles: The Role of Pupation and Adult Longevity

Insects ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 133 ◽  
Author(s):  
Anna Papach ◽  
Jérémy Gonthier ◽  
Geoffrey R. Williams ◽  
Peter Neumann
Keyword(s):  
Sex Ratio ◽  
Field Studies ◽  
Differential Mortality ◽  
Adult Longevity ◽  
Published Data ◽  
Larval Feeding ◽  
Intraspecific Interactions ◽  
Adult Sex Ratio ◽  
Biased Sex Ratio ◽  
Small Hive Beetles

The sex ratio of sexually reproducing animal species tends to be 1:1, which is known as Fisher’s principle. However, differential mortality and intraspecific competition during pupation can result in a biased adult sex ratio in insects. The female-biased sex ratio of small hive beetles (SHBs) is known from both laboratory and field studies, but the underlying reasons are not well understood. Here, we used laboratory mass and individual pupation to test if differential mortality between sexes and/or intraspecific interactions can explain this sex ratio. The data show a significant female-biased adult sex ratio in both mass and individual rearing, even when assuming that all dead individuals were males. Our results therefore suggest that neither differential mortality during pupation nor intraspecific interactions are likely to explain the female-biased sex ratio of freshly emerged adult SHBs. We regard it as more likely that either competition during the larval feeding stage or genetic mechanisms are involved. In addition, we compared our data with previously published data on the sex ratio of both freshly emerged and field-collected SHBs to investigate possible gender differences in adult longevity. The data show a significantly greater female bias in the sex ratio upon emergence, compared to field-collected SHBs, suggesting that adult females have a shorter longevity.

Sex ratio variation in gastrointestinal nematodes of Svalbard reindeer; density dependence and implications for estimates of species composition

Parasitology ◽  
2004 ◽  
Vol 130 (1) ◽  
pp. 99-107 ◽  
Author(s):  
A. STIEN ◽  
M. DALLIMER ◽  
R. J. IRVINE ◽  
O. HALVORSEN ◽  
R. LANGVATN ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Species Composition ◽  
Density Dependence ◽  
Sex Ratios ◽  
Gastrointestinal Nematodes ◽  
Late Winter ◽  
Adult Males ◽  
Svalbard Reindeer ◽  
Ratio Variation ◽  
Adult Sex Ratio

Estimates of the intensity and abundance of species provide essential data for ecological, evolutionary and epidemiological studies of gastrointestinal nematode communities. These estimates are typically derived from the species composition of adult males when only males have readily scorable species-specific morphological traits. Such estimation assumes that all species in the community have the same adult sex ratio. We evaluated this assumption for the trichostrongyle nematodes Ostertagia gruehneri and Marshallagia marshalli in infracommunities in Svalbard reindeer by identifying to species adult females using a polymerase chain reaction assay. The proportion of males was found to be slightly higher in O. gruehneri than in M. marshalli. Evidence for seasonal variation and density dependence in the adult sex ratio was only found for O. gruehneri. Possible demographic mechanisms for such sex ratio variation are discussed, and stochastic models that generate density-dependent sex ratios proposed. Sex ratio variation caused substantial bias in some male-based estimates of intensity of infection, while substantial and consistent bias in estimates of abundances was only evident in late winter samples. Our results suggest that estimating sex ratios can be particularly important in individual host level studies of nematode species of low abundance.

scholarly journals Sex ratio of breeding Common toads (Bufo bufo) – influence of survival and skipped breeding

2010 ◽  
Vol 31 (4) ◽  
pp. 509-524 ◽  
Author(s):  
Thomas Madsen ◽  
Jon Loman
Keyword(s):  
Sex Ratio ◽  
Deterministic Model ◽  
Breeding Site ◽  
Breeding Population ◽  
Bufo Bufo ◽  
Adult Males ◽  
Breeding Sites ◽  
Lower Survival Rate ◽  
Biased Sex Ratio ◽  
Males And Females

AbstractAnuran sex ratio at breeding sites is typically male biased. Such sex ratios may be due to poor female survival, to females not breeding as frequently as males and/or to males becoming sexually mature earlier than females. In the present study, the first two factors are analyzed in a common toad (Bufo bufo) population in southern Sweden. Toads were captured, marked and recaptured at the breeding site during 5 years. Within season capture patterns were analyzed using the Jolly-Seber model and among-year captures using the Closed robust design model. Population estimates of males and females yielded an among year variation in breeding population sex ratio, ranging from 16% to 34% females. On average, 41% (proportion adult alive but not breeding) of the females skipped breeding seasons, whereas the corresponding estimate for males was less than 5%. Yearly survival averaged 42% for adult female and 63% for adult male toads. First year adult males and females had a lower survival rate than older toads. Our results demonstrate that both a female biased mortality rate and a higher proportion of skipped breeding in females contribute to the observed male biased sex ratio. However, a deterministic model suggests other factors may also be involved to obtain this degree of male biased sex ratio, the most likely being that females mature at a later age than male toads.

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