Demography of fluctuating vole populations: Phase homogeneity of demographic variables

Most research on fluctuations of arvicoline rodents has focused on changes in demographic variables across phases. Here, we examined whether demographic variables varied within a phase (trough, increase, and decline) across 30 fluctuations of Microtus ochrogaster and 14 fluctuations of Microtus pennsylvanicus over 25 years. For each species, we tested for phase homogeneity (i.e., values of demographic variables were invariant across all fluctuations within a given phase) for the following demographic variables: monthly survival (total, adult, young), proportion of reproductively active adult males and females, proportion of young, and proportion of immigrants. We found phase homogeneity for 96.7% of the 582 phase/fluctutation data sets for the seven variables, in the three phases of across all fluctuations in the three habitats for M. ochrogaster and 98.0% of 254 of those for M. pennsylvanicus in two habitats. We conclude that for each of these two species demographic variables are relatively invariant both within a phase and across fluctuations.     

Vole population dynamics: factors affecting peak densities and amplitudes of annual population fluctuations of<Emphasis Type="Italic">Microtus pennsylvanicus</Emphasis>

We studied factors affecting peak densities and amplitudes of fluctuation during 20 annual population fluctuations ofMicrotus pennsylvanicus Ord, 1815 in alfalfa and bluegrass habitats over a 25-year period. Survival was correlated with population density over the 25 years and was the most consistent variable associated with stoppage of population growth. Although not correlated with population density over the 25 years, a decline in the proportion of reproductively active adult females contributed to cessation of growth of population fluctuations that peaked in late autumn-winter, and to cessation of growth of eight of eleven population fluctuations that peaked during summer-early autumn. We conclude variation in survival to be the primary factor affecting peak densities and amplitudes of population fluctuation ofM. pennsylvanicus.     

Survival,density and population composition of bellbirds (Anthornis melanura) on the Poor Knights Islands,New Zealand

Abstract

Annual survival by age, sex and population size and structure were estimated for bellbirds (Anthornis melanura) from a banding study undertaken on 66 ha Aorangi Island, the Poor Knights Islands, during the period 1978–86. The most parsimonious model showed that survival varied little with age and between years, and survival of males was significantly greater than that of females. Recapture probabilities of males and females were similar, but did vary with age and among years. There was a greater proportion of adult males than adult females and sub‐adult males and females in the population, and among adults the male bias in the population was greater during the breeding season than at other times of the year. The high density of bellbirds on the Poor Knights and larger size of males may explain the reduced survival of females relative to that of males.     

Population regulation in the Wood Mouse Apodemus sylvaticus (L.)

Watts 1969 described the population cycle of the Wood Mouse Apodemus sylvaticus as a decline in numbers in spring, a stable period in summer and an increase phase in autumn. Aggression by adult males was considered an important aspect of population regulation limiting male survival in spring and juvenile recruitment in summer. However, recent studies of range behaviour and experimental investigations suggest that male A. sylvaticus are not relevant in population regulation and that the principal regulating factors act on female reproductive success. Female reproductive activity is determined by spatial interactions which, in turn, are determined primarily by the density of females and the proportion of female immigrants in the population. The only impact adult males may have on population size is through infanticide and competition with the females for food.     

Demography of a mediterranean microtine: the Mediterranean pine vole,Microtus duodecimcostatus

Microtus duodecimcostatus in a mediterranean vole which is not known to display spectacular increases in population numbers as in some microtine species. A population was studied in southern France with a capture-recapture method. The population included resident adults which have a high and constant survival rate (monthly estimate: 0.879), erratic adults (those caught once only), and juveniles which have a lower and constant survival rate. The adult survival rate was not sexbiased but the juvenile survival rate was higher in males (monthly estimates: 0.710 and 0.596 for males and females, respectively). Adult body weight did not vary seasonally. Residents had a higher mean body weight than erratics. Reproduction occurred all the year round. The proportion of reproductive females was higher among residents than among erratics. Population numbers varied seasonally. Our study points out thatM. duodecimcostatus is very different from microtine species which display cyclic fluctuations. Population studies on the subgenusPitymys (which containsM. duodecimcostatus and its closest related species) suggest that they are typically non-cyclic. The importance of social factors in the control of reproduction and maturation was evidenced inM. pinetorum. The role of such factors in the population regulation ofM. duodecimcostatus is discussed.     

Reproduction of the Bat Glossophaga commissarisi (Phyllostomidae: Glossophaginae) in the Costa Rican Rain Forest During Frugivorous and Nectarivorous Periods1

I studied the reproduction of the 9 g nectarivorous bat Glossophaga commissarisi (Phyllostomidae: Glossophaginae) in relation to its food choice in a Costa Rican lowland rain forest over more than 2 yr. Reproduction was bimodal with birth peaks in April/May and October/November. The first birth peak coincided with a period of frugivory, whereas the second occurred during a period of almost exclusive nectarivory. All adult females recaptured in consecutive reproductive periods were reproductively active on both occasions, indicating that individual G. commissarisi females regularly reproduce twice per year at the study site. Throughout the annual cycle the mean testis length of the males correlated best with the proportion of females lactating, suggesting a post partum estrous pattern. Animals became reproductively active at about 1 yr of age. Fecal samples showed that females consumed significantly more insects than males.     

Changes in the size,composition, and reproductive condition of wild marmoset groups (Callithrix jacchus jacchus) in north east Brazil

Five groups ofCallithrix jacchus jacchus were studied in the field in north east Brazil. Group size and composition were similar to that described for other callitrichids, but changes in group membership occurred much more frequently than previously reported. There was a 50% turnover in group membership in a six month period, and adult males changed groups particularly often. Most groups contained only one reproductively active female, but there was evidence that one group contained two females that were reproductively active simultaneously. Some groups had several adult females, and the role of reproductive female switched from one individual to another with time. Individual marmosets are faced with an unusually wide range of alternative life history strategies involving different combinations of location and reproductive condition. We argue that marmoset social organization is best studied at the level of the whole population within an area, rather than at the level of the individual group.     

Social behavior and brood decline in reproductive-phase colonies ofBelonogaster petiolata (Degeer) (Hymenoptera: Vespidae)

Colonies ofBelonogaster petiolata in Gauteng (South Africa) produced reproductive offspring (gynes and males) in late January and early February of each nesting season; their appearance was associated with a decline in worker and brood numbers. Brood decline could commence in the presence of a dominant, reproductively active queen, and loss or removal of the queen was not followed directly by cessation of nest growth and brood care. An older worker usually took over the α-position in queenless colonies. Several factors appear to contribute to brood decline and, ultimately, termination of the colony cycle in this species. These include (1) cessation of the supply of solid food to colonies (and particularly their larvae) during the reproductive phase, (2) a decrease in the worker/larva ratio during the latter phase due to the progressive loss of workers, (3) increasing number of gynes and males, and (4) an adult priority over food reception from foragers.     

Global climate patterns explain range-wide synchronicity in survival of a migratory seabird

To predict the impact of climate change over the whole species distribution range, comparison of adult survival variations over large spatial scale is of primary concern for long-lived species populations that are particularly susceptible to decline if adult survival is reduced. In this study, we estimated and compared adult survival rates between 1989 and 1997 of six populations of Cory's shearwater ( Calonectris diomedea ) spread across 4600 km using capture–recapture models. We showed that mean annual adult survival rates are different among populations along a longitudinal gradient and between sexes. Variation in adult survival is synchronized among populations, with three distinct groups: (1) both females and males of Corsica, Tremiti, and Selvagem (annual survival range 0.88–0.96); (2) both females and males of Frioul and females from Crete (0.82–0.92); and (3) both females and males of Malta and males from Crete (0.74–0.88). The total variation accounted for by the common pattern of variation is on average 71%, suggesting strong environmental forcing. At least 61% of the variation in survival is explained by the Southern Oscillation Index fluctuations. We suggested that Atlantic hurricanes and storms during La Niña years may increase adult mortality for Cory's shearwater during winter months. For long-lived seabird species, variation in adult survival is buffered against environmental variability, although extreme climate conditions such as storms significantly affect adult survival. The effect of climate at large spatial scales on adult survival during the nonbreeding period may lead to synchronization of variation in adult survival over the species' range and has large effects on the meta-population trends. One can thus worry about the future of such long-lived seabirds species under the predictions of higher frequency of extreme large-scale climatic events.     

Alternative male reproductive tactics in a natural population of prairie voles <Emphasis Type="Italic">Microtus ochrogaster</Emphasis>

Alternative reproductive tactics have been described in male mammals, but little information exists regarding fitness benefits and whether males change tactics. Adult male prairie voles Microtus ochrogaster (Wagner, 1842) display alternative tactics described as resident and wanderer. Enclosure studies provide conflicting data concerning the relative success of each tactic and whether males display one tactic throughout adulthood. To characterize further residents and wanderers in this species, we examined data collected during 5 years of monitoring a natural population in Illinois, USA. We found that during the breeding period, wandering males survived longer, moved longer distances, and were more likely than residents to have scrotal testes. During the nonbreeding period, wandering and resident males differed only in whether or not they established residency. Data on sources and fates of resident and wandering males revealed that a substantial proportion of males switched tactics. Our estimate of the reproductive contribution of wandering males to the population, which is based on the premise that wandering males typically mate with single females, suggests that wanderers contribute 34–38% of young recruited during March through October and 4–12% in November, when single females are less common. Parentage studies in natural populations are necessary to test our estimates.     

Alternative male mating tactics of the endemic Red Sea parrotfish Scarus ferrugineus

The present study shows that small non‐territorial terminal‐phase males of the rusty parrotfish Scarus ferrugineus are reproductively active and are comparable with initial‐phase males in behaviour, rates of participation during group‐spawning and success in streaking into pair spawning. Large territorial terminal‐phase males defend contiguous territories for several hours during the morning where they pair spawn with initial‐phase females.     

Population demography of frillneck lizards (Chlamydosaurus kingii,Gray 1825) in the wet‐dry tropics of Australia

We explore the effects of biotic and abiotic factors on the population demography of frillneck lizards (Chlamydosaurus kingii) in the Australian wet‐dry tropics. Annual growth rates of males were significantly higher across all body sizes compared to females, resulting in a significant larger maximum body size in males. Both male and female lizards were highly philopatric and 81% of the among‐year recapture distances were less than 200 m. Juvenile and adult frillnecks were subjected to low but highly variable annual survival rates. Both proportion of juveniles and relative proportion of reproductive females showed extensive among‐year variations. No relationship was, however, observed between proportion of gravid females and that of juveniles captured during the subsequent year. High rainfall in January was negatively correlated with recruitment most likely caused by increased egg/embryo mortality due to flooding of nest sites. We therefore suggest that the lack of association between female reproduction and juvenile recruitment was due to the effects of stochastic variation in January rainfall. Lizard numbers increased during the first five years of the study followed by a decline during the subsequent four years. Our analyses show that annual variation in survival constituted the main determinant in driving the annual change in frillneck numbers. Surprisingly, no relationship was observed between fillneck population dynamics and annual variation in juvenile recruitment. We suggest that the 7‐years over which these analyses were conducted were insufficient to detect any significant effects of recruitment on lizard numbers, demonstrating the need for long‐term studies to accurately document vertebrate population demographic processes in areas experiencing stochastic variations rainfall such as the Australian wet‐dry tropics.     

Population parameters and reproductive biology of the Iberian hareLepus granatensis in southern Iberia

To analyse the population structure and reproductive biology of the Iberian hareLepus granatensis Rosenhauer, 1856, 498 hares (264 males and 234 females) were collected in monthly samples from October 1998 to September 1999. Females reached larger sizes than males, with approximately 400 g difference in body mass on reaching sexual maturity. The total sex ratio was 1∶1, with a bias in favour of males in winter. Sexually active males and females appeared in every month but August, when no sexually active female was found. Births occurred in every month and were more frequent between March and July. Seasonal variation in kidney fat index (KFI) followed a similar pattern in males and females, with an increase in mid-autumn and a decline at the end of winter. Reproductive activity appeared in every month, with a maximum from February to June. Reproductively hyperactive females (simultaneously pregnant and nursing) appeared in every month except in January, with a first peak in March and a second lower peak in May–June. Litter size fluctuated between 1 and 7 leverets. The most frequent gestations involved 1 or 2 foetuses. The mean annual litter size was 2.08 and the average number of litters per productive female per year was estimated to be 3.48. The maximum productivity was recorded between March and May. The total annual production of young per adult female was estimated to be 7.21. The minimum annual survival rate of young was 27.91%. On the basis of these results we propose to maintain the limit of the hunting period between October and December. We discuss the relationship between the low young/adult ratio obtained and the hunting method used.     

鼠类种群动态:食物资源影响力的实验评估

本研究在美国伊利诺斯州中东部测定了中等食物质量(莓系属的牧草)和低食物质量(高杆草牧场)栖息地内橙腹田鼠(Microtusochrogaster)和草原田鼠(M.pennsylvanicus)种群对附加食物的响应。在中等食物质量栖息地内投放附加食物,橙腹田鼠种群的波动幅度高于对照样地,但同类型食物质量栖息地内,种群平均密度和波动模式无显著的差异。仅在低等食物质量的高杆草栖息地内,投放附加食物可导致草原田鼠的种群密度高于对照样地。附加食物不直接影响两种栖息地内橙腹田鼠的成活率或成熟率,在中等食物质量栖息地中投放附加食物,繁殖活跃的成熟雌性个体比例及雄性成体的体重高于对照。附加食物不影响莓系属牧草内草原田鼠,也不能影响该动物在高杆草环境中的存活率。然而,投放附加食物,可缩短低等食物质量栖息地内草原田鼠的成熟期,提高繁殖活跃雌性的比例和迁入个体比例,增加并引起雄性个体体重增加。据此,本研究证明食物资源在橙腹田鼠和草原田鼠种群动态中只起极小的作用。     

Aggressive behavior of adult meadow voles (Microtus pennsylvanicus) towards young

Summary Field evidence indicates that adult microtines, especially females, may be a major cause of poor juvenile survival and this may be instrumental in their population regulation. This suggests that males and females behave differently towards young animals. To examine how adult males, nonlactating females, and lactating females behave towards strange young, I introduced young animals into the home cage of the adults. Lactating females were most aggressive towards young; most males investigated them; most nonlactating females ignored them. However, discriminant function analysis indicated a great deal of overlap in the behavior of the classes. None of the classes behaved differently towards young of either sex. Females did not vary their behavior during lactation. Behavior varied among lactating females, with 55% showing little aggression and 20% showing a great deal. Most lactating females showed similar behavior in each of their bouts: docile females remained docile, aggressive females remained aggressive. I conclude that lactating females are most aggressive towards strange young. These results are consistent with the field evidence, which suggests that adult females depress juvenile survival and recruitment and that the main culprits are breeding females.     

Survival and population persistence in the critically endangered Tuamotu kingfisher

A wide range of threats affect populations of Pacific island birds and conservationists have been challenged to identify factors upon which to focus management. The Tuamotu kingfisher (Todiramphus gambieri) is one of the most endangered vertebrate species in the world, yet little has been published about basic biology or causes of the population decline. We used 4 years of mark-resight and territory resource information to model survival in juvenile and adult Tuamotu kingfishers. Annual survival of adult males (ϕ = 0.77) was similar to congeneric species, whereas survival of adult females (ϕ = 0.40) and juveniles (ϕ = 0.12) was much lower. The best-supported survival model indicated adult female survival was positively related to territory size, whereas adult male survival was negatively related to atoll forest within territories. We used parameter estimates from survival models in a life-stage simulation analysis to evaluate the relative influence of vital rates and territory habitats on population processes. Results indicated that adult female and juvenile survival had the greatest impact on Tuamotu kingfisher populations, accounting for 58% and 32% of variation in the finite rate of population increase, respectively. Nocturnal predation by rats (Rattus spp.) on incubating kingfishers may explain the lower survival of females than males, whereas juvenile birds may be especially vulnerable to predation by cats (Felis catus). Thus, conservation management for Tuamotu kingfishers should include use of metal guards on cavity trees to protect nests and incubating females, and control predator access during fledging periods. © 2012 The Wildlife Society.     

Density-related changes in sexual selection in red deer.

In sexually dimorphic mammals, high population density is commonly associated with increased mortality of males relative to females and with female-biased adult sex ratios. This paper investigates the consequences of these changes on the distribution of male breeding success, the intensity of competition for females and the opportunity for sexual selection. After the red deer (Cervus elaphus L.) population of the North Block of Rum (Inner Hebrides) was released from culling, female numbers rose and male numbers declined, leading to an adult sex ratio of around one male to two females. This change was the result of increased mortality of males relative to females during the first two years of life; of increased emigration rates by young males; and of reduced immigration by males from outside the study area. The increasing bias in the adult sex ratio affected the timing of breeding as well as the distribution of mating success in males. As the adult sex ratio became increasingly biased towards females, the degree of skew in mating success (calculated across all harem-holders) increased, but mature males defended harems for shorter periods and a higher proportion of males held harems. In addition, a higher proportion of calves were fathered by immigrant males and the proportion fathered by males born in the study area declined. These results support the contention that, where high population density is associated with a female-biased adult sex ratio, competition for mates is likely to decline.     

Reproductive biology of bisexual and all-female populations of chaetodontid fishes from the southern Great Barrier Reef

Synopsis The reproductive biology of three species of chaetodonts from One Tree Reef (southern GBR) is described by analysis of gonads and population structure. Reproductive biology is related to age by a capture-markrecapture study of growth. For Chaetodon rainfordi there was a significant habitat effect. On the reef slope, females outnumbered males by 5.6: 1 and both sexes became reproductively active by the age of 2 years. In the lagoon, no males were found and females were reproductively inactive. For C. plebius, males were essentially missing from all samples and no reproductively active females were found. For Chelmon rostratus (1 :1 sex ratio) some males had mature testes but there was no evidence of female reproductive activity. This species is likely to be gonochoristic, but the reproductive mode of the other two species remains ambiguous.     

The influence of immigration on demography of sympatric voles

We studied the influence of immigration on the dynamics ofMicrotus ochrogaster Wagner, 1842 andM. pennsylvanicus Ord, 1815 populations in alfalfa, bluegrass, and tallgrass prairie in east-central Illinois for 25 years. The numbers of immigrants in a site were positively correlated with overall population densities of the species in the vicinity of the study sites and within the study site. Population density of the other species was not correlated with immigration of either species. Immigrants did not differ significantly from residents with respect to sex-ratio and reproductive condition. Persistence of immigrantM. pennsylvanicus was lower than that of resident adults in all three habitats, while that of immigrantM. ochrogaster was lower than that of resident adults in alfalfa, where the species was most abundant. Neither the absolute number of immigrants nor the proportion of the population composed of immigrants indicated an effect of immigrants on among- and within-habitat differences in demography and population fluctuations of either species. Immigrants may have been an important factor in maintenance ofM. pennsylvanicus in alfalfa, a low-quality habitat, but the influence of immigration on the dynamics of populations inhabiting other habitats was insubstantial.     

Effects of population structure and density on calf sex ratio in red deer (<Emphasis Type="Italic">Cervus elaphus</Emphasis>)—implications for management

There is ongoing interest to assess what factors affect offspring sex ratio, especially in ungulates. Wildlife managers might be interested in influencing this sex ratio for two reasons: either in order to limit population growth more effectively by reducing the proportion of females born or to increase revenues by a higher proportion of trophy bearing males in the population. While previous studies mostly focused on how maternal traits affect offspring sex ratio, we included here also male traits in our analysis. We achieved this by investigating data from 30 areas covering entire Lower Austria, collected over the past 12 years from both hunted red deer and those killed in road accidents. We focused our analyses on parameters that can be easily assessed by managers on the population and individual level, i.e. the numbers of animals culled in different age/sex classes and their body mass. We found that the proportion of females among calves increased with population density. Furthermore, we found that calf sex ratio (i.e. the proportion males among calves aged between 2 and 7 months) increased with increasing proportions of adult females and males older than 10 years, independent of the density effect. We conclude that wildlife managers interested in the effective reduction of red deer abundance and/or increasing the proportion of males among offspring should select a culling regime leading to a low population density dominated by adult, prime-aged females and males. This can be achieved by over-proportional removal of young females and warranting that a high number of strong males reach an age of at least 10 years.