scholarly journals Demography of the enigmatic low phase in a cyclic lemming population

2021 ◽  
Author(s):  
Dominique Fauteux ◽  
Gilles Gauthier
Keyword(s):  
Sex Ratio ◽  
Reproductive Potential ◽  
Indirect Evidence ◽  
Adult Males ◽  
Density Dependent ◽  
Live Trapping ◽  
Biased Sex Ratio ◽  
Males And Females ◽  
Cyclic Populations

Abstract Deciphering the mechanism behind the lack of growth during the prolonged low abundance phase of cyclic populations represents a major challenge due to the lack of data. However, long-term capture-mark-recapture datasets can help resolve this question through demographic analyses. We analysed the demography and movements of cyclic brown lemmings on Bylot Island, Canada, with a 16-yr (2004-2019) live-trapping program and looked for inversely density-dependent factors that could contribute to a prolonged low phase. We found that the proportion of females in the population was inversely density-dependent with a strong male-biased sex ratio at low densities but not at high densities. In contrast, survival of adult females was higher than adult males, but both had lower survival at low densities than at high ones. Distances moved by both adult males and females were density-dependent, and proportion of females in reproductive condition was weakly density-dependent. Individual body condition, measured as monthly change in body mass, was not density-dependent. Overall, the strong malebiased sex ratio at very low densities suggests a loss of reproductive potential due to the rarity of females and appears to be the most susceptible demographic factor that could contribute to the prolonged low phase in cyclic brown lemmings. What leads to this sexbias in the first place is still unclear, but indirect evidence suggests that this may be due to a higher vulnerability of nesting females to predation in winter than males.

Large-scale spatiotemporal variation in calf sex ratio in moose (Alces alces): an effect of density-dependent decrease in maternal condition?

2009 ◽  
Vol 87 (4) ◽  
pp. 346-355 ◽  
Author(s):  
K. Bjørneraas ◽  
E. J. Solberg ◽  
I. Herfindal ◽  
B.-E. Sæther
Keyword(s):  
Sex Ratio ◽  
Large Scale ◽  
Alces Alces ◽  
Recruitment Rate ◽  
Spatiotemporal Variation ◽  
Adult Males ◽  
Maternal Condition ◽  
Density Dependent ◽  
Postnatal Mortality

The harvest of Norwegian moose ( Alces alces (L., 1758)) is directed towards certain sex and age classes to maximize yield in terms of meat or number of animals. Observed side effects are declining numbers of calves per female and proportions of adult males, which may affect other demographic variables. Using long-term data, we examined whether spatiotemporal variation in the calf sex ratio was related to changes in (i) density of harvested moose, (ii) recruitment rate, and (or) (iii) the composition of the adult segment of the population. We found declining proportions of male calves in the autumn harvest over time associated with decreasing recruitment rates. Similarly, the proportion of male calves was lower when density of harvested moose was high. We suggest that the decrease in proportion of male calves was caused by increased prenatal or postnatal mortality rates of males, possibly owing to a density-dependent decline in maternal body condition. Proportion of male calves increased with the proportion of adult males in the population the previous year, indicating that low proportions of adult males may lead to lower male recruitment, particularly at high densities. Further declines in proportions of male calves recruited may be avoided by reducing the population density and changing the demographic composition of the harvest.

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.

Population parameters of ringed seals (Phoca hispida Schreber, 1775) in the Svalbard area

1987 ◽  
Vol 65 (4) ◽  
pp. 1021-1027 ◽  
Author(s):  
Christian Lydersen ◽  
Ian Gjertz
Keyword(s):  
Sex Ratio ◽  
Ringed Seal ◽  
Adult Males ◽  
Population Parameters ◽  
Phoca Hispida ◽  
Age Class ◽  
Ringed Seals ◽  
Males And Females ◽  
The Mean ◽  
Sexually Mature

Samples were taken from 284 ringed seals (Phoca hispida) in the Svalbard area during April–July 1981 and March–April 1982. The age of 283 seals was determined by reading annuli in the cementum of the canine teeth. The mean age of the males was 11.3 years, and of the females, 14.9 years. Females were found to be significantly older than males. The mean length of sexually mature ringed seals was 128.9 cm for both sexes. The mean weight of adult males and females was 53.5 and 61.4 kg, respectively. Females were found to be significantly heavier than males. The sex ratio was 47.8% males and 52.2% females. Studies of microscopic sections of testis and epididymis from ringed seal males showed that 63, 75, and 80% of 5-, 6-, and 7-year-old animals, respectively, were sexually mature. The weights of testis and epididymis, diameters of tubuli, and the size of testis all showed a marked increase in the 5-year age-class. Macroscopic sections of ovaries from ringed seal females showed that 20, 60, and 80% of 3-, 4-, and 5-year-old animals, respectively, were sexually mature. The size of the ovaries showed a marked increase in the 5-year age-class. The ovulation rate of ringed seals from Svalbard was calculated to be 0.91.

scholarly journals Offspring and adult chemosensory recognition by an amphisbaenian reptile may allow maintaining familiar links in the fossorial environment

PeerJ ◽  
2021 ◽  
Vol 9 ◽  
pp. e10780
Author(s):  
José Martín ◽  
Ernesto Raya-García ◽  
Jesús Ortega ◽  
Pilar López
Keyword(s):  
Parental Care ◽  
Chemical Cues ◽  
Kin Recognition ◽  
Social Groups ◽  
Tongue Flick ◽  
Adult Males ◽  
Stable Family ◽  
Males And Females ◽  
Family Groups

Kin recognition is a phenomenon with an important function in maintaining cohesive social groups in animals. Several studies have examined parent–offspring recognition in species with direct parental care. Few studies have, however, explored parent–offspring recognition in animals that, at best, only show apparent indirect parental care, such as some reptiles. In this study, we investigated reciprocal parent–offspring recognition in the fossorial amphisbaenian Trogonophis wiegmanni, a viviparous species that shows potential stable ‘family groups’ in the form of parent-offspring long-term associations. We examined whether adult males and females could discriminate via chemical cues between familiar juveniles which associate with them within their family groups, and are potentially their offspring, to that of unfamiliar juveniles, and whether juveniles could discriminate between familiar adult males and females of their family group (probably their parents) and unfamiliar unrelated adults. We measured tongue flick behavior to study chemosensory responses to the scent of conspecifics. We found that adult female amphisbaenians, but not males, could discriminate between scents of familiar and unfamiliar juveniles. Juvenile amphisbaenians did not discriminate between familiar and unfamiliar adult females, but recognize familiar from unfamiliar males. We discuss our results of parent–offspring recognition according to its potential social function in an ecological fossorial context where visibility is limited and chemosensory kin recognition may contribute to the establishment of stable family groups.

The spatial pattern of a Juniperus communis var. depressa population on a continental dune in subarctic Québec, Canada

1999 ◽  
Vol 29 (4) ◽  
pp. 446-450 ◽  
Author(s):  
Gilles Houle ◽  
Mario Duchesne
Keyword(s):  
Sex Ratio ◽  
Nearest Neighbor ◽  
Dispersion Pattern ◽  
Neighbor Distance ◽  
Juniperus Communis ◽  
Biased Sex Ratio ◽  
Males And Females ◽  
Nearest Neighbor Distance ◽  
Population Dispersion ◽  
Crown Size

We performed a nearest-neighbor analysis to determine the population dispersion pattern and the association between males and females in a Juniperus communis L. var. depressa Pursh population occupying a continental dune in subarctic Quebec, Canada. The overall dispersion pattern was contagious, and males (or females) were proportionately as likely to have a male as they were to have a female nearest neighbor. Crown size was positively related to nearest-neighbor distance for the male-male comparison only, suggesting a somewhat stronger intrasex competition between males. Nearest-neighbor distance increased with crown size (significantly related to age) suggesting a change in the intensity of aggregation with age possibly related to self-thinning. Higher mortality as a result of stronger male-male competition could explain the female-biased sex ratio and the absence of spatial segregation between sexes. The overall contagious dispersion pattern in the population may be related to the fact that most seed cones fall directly underneath the mother plant. Birds can eat the cones of J. communis and thus disperse seeds. However, these seeds are deposited in clumps, a process that may also explain contagion within the population.

Beberapa Aspek Reproduksi Siput Lambis lambis di Pesisir Perairan Yenusi, Biak

2016 ◽  
Vol 1 (3) ◽  
pp. 1
Author(s):  
Andriani Widyastuti ◽  
Ludi Parwadani Aji
Keyword(s):  
Sex Ratio ◽  
Management Strategies ◽  
Gonadal Development ◽  
Shell Size ◽  
Gonad Maturity ◽  
Males And Females ◽  
Over Exploitation ◽  
Number Of Males ◽  
Time Of Harvest

<strong>Some Aspects of Reproduction in Conch Lambis lambis of Yenusi Coastal Waters, Biak.</strong> Lambis lambis is a very popular conch species that has been harvested in all sizes encountered. This condition is very alarming because in the long term, its existence in nature will be reduced because there is no chance to reproduce naturally. This study aims to determine the sex ratio and gonad maturity levels of L. lambis in Yenusi waters, so the appropriate time of harvest can be arranged. Samples were collected every month from January to December 2013. Testing and histological analysis were performed in the laboratory. Samples collected were 99 individus with the number of males 45 individus and females 54 individus. The sex ratio of males and females was 1.0:1.2. Gonad maturity level found included all four stages of gonadal development, from TKG I to TKG IV. Gonadal development showed the process of formation and maturation, and the spawning occured throughout the year, with peak spawning in January until March 2013. The size of the shell length obtained ranged from 4.55 to 13.72 cm indicating over-exploitation. Due to the custom local where residents harvested the conches in all sizes found, sustainable management strategies are urgently needed, including moratorium period  when L. lambis is at the peak of spawning, and harvest should only be performed on adult individuals with a minimum shell size of 7 cm, while observing the thickness of the shell and marginal digitations have been formed. <br /><br />

Demography of Eurotestudo hermanni in a mesic area of Central Italy

2007 ◽  
Vol 28 (1) ◽  
pp. 87-95 ◽  
Author(s):  
Valeria Ramacciato ◽  
Massimo Capula ◽  
Anna Loy ◽  
Federica Gentilotti
Keyword(s):  
Sex Ratio ◽  
Central Italy ◽  
Average Density ◽  
High Density ◽  
Environmental Constraints ◽  
Adult Males ◽  
Males And Females ◽  
European Populations

AbstractHermann's tortoise (Eurotestudo hermanni) from a mesic area of Central Italy (Isernia, Molise) was investigated during a two-year period (2003-2004). The population is characterized by a fairly high density when compared to other Italian and European populations, with density ranging from 16.16 individuals/ha in 2003 to 25.08 individuals/ha in 2004 (average density 20.84/ha). The sex ratio was 1:1 both in 2003 and 2004. Females were captured in higher percentages from May to July in both years, while males were most abundant from August to October. These differences can be related to the different needs and behaviour of males and females in the two periods, and to the environmental constraints of the study area. All the marked tortoises were found aged between 10 and 21 years. Adult males and females from the study area were small-sized when compared to those from other Italian and European populations.

Long-term survival, length of breeding season, and operational sex ratio in a boreal population of common frogs, Rana temporaria L.

1990 ◽  
Vol 68 (1) ◽  
pp. 121-127 ◽  
Author(s):  
Johan Elmberg
Keyword(s):  
Sex Ratio ◽  
Breeding Season ◽  
Rana Temporaria ◽  
Return Rate ◽  
Operational Sex Ratio ◽  
Adult Males ◽  
Term Survival ◽  
Size Dependent ◽  
Survival Selection

A population of individually marked adult Rana temporaria was studied during the breeding season in 1979–1988 in east-central Sweden. Annual return rate averaged 31% (range 16–51%) in males and 16% (range 5–33%) in females. Return rate was not size dependent but increased with every successful previous hibernation, indicating an increased survival rate with age. Return rate was not correlated with winter harshness. Once adult, males had on average 1.5 (maximum 6) seasons with the possibility of reproducing. Corresponding values for females were 1.4 and 4. Mean length of the breeding season was 20 (SD = 2) days. Calling generally started at water temperatures below 3 °C. The lowest spawning temperature was 1 °C. Average temperatures at spawning onset and peak spawning were 5 and 6 °C, respectively. Large males tended to arrive earlier at the pond than small males. Males arrived earlier and stayed longer than did females. The overall population sex ratio was close to unity. The operational sex ratio (OSR) varied during the breeding season, averaging 0.54 (one female to two males). No male was observed to mate more than once per season. I argue that survival selection is more important to male lifetime mating success than is competition in the breeding pond (sexual selection as affected by OSR and length of the breeding season).

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