Control of invasive American bullfrog Lithobates catesbeianus in small shallow water bodies

Setting up cost-efficient control programs for alien invasive species requires the development of adequate removal methods in combination with insights in population size and dynamics. American bullfrog Lithobates catesbeianus is an alien invasive species, which is suspected to cause substantial ecological damage around the globe. However, control of bullfrog populations is difficult, as no conclusive management measures have yet been determined. We investigated how double fyke nets could contribute to bullfrog management by assessing the tadpole population size in 10 permanent small shallow water bodies. Two population size estimate methods were applied, being the catch–depletion and mark–recapture method. Catchability of bullfrog tadpoles proved to be very consistent over ponds and methods, with one catch per unit of effort (one double fyke net for 24 h) retaining on average 6 % of the tadpole population. Population density varied considerably among ponds, ranging from 950 to 120,804 larger tadpole individuals/ha. Using these insights in developing a cost-efficient eradication program for the species, we projected the number of catch efforts needed to reduce tadpole numbers to a threshold that more than likely affects final bullfrog population size. Predictions indicated that for the specified thresholds the use of eight double fyke nets at a time is most cost-efficient in high abundance populations, while using five double fyke nets seems most suitable in low abundance populations. What the exact threshold number of remaining tadpole individuals should be is uncertain, but forecasts demonstrate that only half of the budget would be needed when aiming at a drop to fewer than 100 remaining tadpoles than when a decrease to fewer than 10 remaining tadpoles is pursued. Given the fairly limited cost of bullfrog management with double fyke nets, however, it may be worthwhile to fully reduce the tadpole population.     

Sexual dimorphism and intraspecific aggression,and their relationship to sex ratios in Caprella gorgonia Laubitz & Lewbel (Crustacea: Amphipoda: Caprellidae)

The amphipod Caprella gorgonia Laubitz & Lewbel is an obligate commensal on gorgonian octocorals. Its primary host is Lophogorgia chilensis (Verrill), found below 20 m.C. gorgonia breeds throughout the year, with wide fluctuations in abundance. Mating and oviposition follow molting. Sex reversal does not occur; two distinct sexes are present from the first instar after emergence from the brood pouch.Young males and females grow at approximately the same rate, but males are larger by a relatively constant increment. Males continue to grow at their original rate to a maximum size (about twice that of females). The growth rate of females is not limited by the onset of reproduction and brooding, but rather by an approach to maximum size when the rate is greatly reduced. Fecundity of females is not affected by size.The population sex ratio is about 1:3 (males:females), and about 1:4 among adults. The secondary sex ratio is 1:1. The post-emergence sex ratio bias is a result of heavier mortality among males. Sex ratios drop from 50% at emergence to 25% as females approach maximum size, then rise to 100% in larger size classes.Differential predation on males did not appear to be a source of any sex ratio bias. Adult males possess a “poison spine”, a puncturing weapon on the large second gnathopod, which functions in mating-related intraspecific combat with other males. Intraspecific male aggression during mating is a major cause of sex ratio bias. In the laboratory, increased density in breeding groups may affect mortality due to male aggression. In nature, adult sex ratios are negatively correlated with population density. The reproductive capacity of the population is not limited by a shortage of adult males, despite the low adult sex ratio.     

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.     

Females as intraguild predators of males in cross-pairing experiments with phytoseiid mites

Studies on intraguild interactions between phytoseiid species have shown that intraguild predation occurs and is most commonly manifested as adult females of one species feeding on juveniles of another. Whether such intraguild interactions can also occur between adult females of one species and adult males of another, is not known. Herein, we report on intraguild interactions between adults of the two sexes in cross-pairing experiments involving three related phytoseiid species (Neoseiulus paspalivorus, N. baraki and N. neobaraki) that are potential candidates for controlling the coconut mite Aceria guerreronis, a serious pest of coconut palms in tropical countries. For comparative reasons, the experiments were repeated with larvae instead of males, and with only males or only females of two different species together. In the presence of an ample supply of prey, females of N. neobaraki never fed on individuals of their own species, yet appeared to be very aggressive against males, as well as larvae of the other two phytoseiid species. They also fed on females of N. paspalivorus, but rarely on females of N. baraki. Males of N. neobaraki did not suffer mortality when together with females of either of the two other phytoseiid species. Males of N. baraki did not suffer predation from females of N. paspalivorus, but males of N. paspalivorus suffered some mortality (15 %) from N. baraki females. Larvae of each of the three species were vulnerable to intraguild predation by heterospecific adult females, except for N. neobaraki larvae when together with N. baraki females. The absence or presence of intraguild predation is largely explained by the size ratios of the individuals that were put together: large individuals feed on smaller ones, but never the reverse. For each sex, size declines in the following order: N. neobaraki > N. baraki > N. paspalivorus. Moreover, for each species, females are larger than males and males are larger than larvae. Strikingly, however, females did not kill males and larvae of their own species. We propose that niche competition between related phytoseiid species is not only determined by intraguild predation on heterospecific larvae, but also by imposing great mortality on males from the intraguild prey because phytoseiid females being pseudo-arrhenotokous require insemination to produce offspring of both sexes.     

Natal dispersal in relation to population density and sex ratio in the field vole,Microtus agrestis

Summary In a sample of 240 juvenile field voles 8% of the males and 22% of the females reached sexual maturity within their natal home range. Among individuals retrapped as adults, 58% of males and 23% of females had dispersed, i.e. had moved more than one home range diameter. The mean distance moved for males (58.5 m) exceeded that for females (28.6 m). Male movement distances were negatively associated with total density, and with density of adult females, but not with male density. Female movements were not related to population density. There were no relation between sex ratio and distance moved. The distribution of distances moved for both males and females fit a geometrical distribution, suggesting the importance of competitive processes.     

Summer mortality in the hazel dormouse (Muscardinus avellanarius) and its effect on population dynamics

In the period 2000–2012, 38.3 % of 950 marked overwintered hazel dormice (Muscardinus avellanarius) were not recaptured at a study site in Lithuania in autumn. As adult dormice are sedentary, it is presumed that those dormice not recaptured died between late April and August. The highest total number of dormice captured for the last time was recorded in May and the lowest in August. The total summer mortality was significantly higher in females (42.5 %) than in males (34.6 %), but it did not depend on dormouse age or body weight. Tawny owl (Strix aluco) is the main known dormouse predator in Lithuania, and likely, it has the highest impact on summer mortality of M. avellanarius. Over the years, the total summer mortality of adult dormice ranged from 27 % to 52 %. The increased summer mortality resulted in decreased total dormouse population density and particularly decreased density of adult females in summer. Decreased densities led to more intensive breeding in the dormouse population, specifically breeding by young-of-the-year females, a pattern that is not common for this species. The number of breeding cases by young-of-the-year females was inversely related to the density of adult overwintered females in summer and to the number of breeding cases of these females. Breeding by young-of-the-year females was the main factor in the restoration of decreased population density in summer. Lithuanian populations of M. avellanarius are unique in their high proportion of breeding cases by young-of-the-year females amongst all populations investigated in the entire species distributional range.     

Site fidelity of Svalbard polar bears revealed by mark-recapture positions

Quantifying the degree of site fidelity in polar bears’ (Ursus maritimus) use of denning and mating areas in spring is of considerable interest for both basic and applied purposes. We analyzed 276 spring-to-spring movements (displacements) of 178 polar bears obtained from mark-recapture in the period 1987–2010 in Svalbard, Norway. Male and female subadults and adults showed site fidelity (only subadult females non-significantly) when their movements were compared to a scenario of random movements between all capture locations. The median observed displacement was 47.6 km (bootstrapped 95 % CI: 38.6–57.8 km), significantly smaller than the median potential displacement for random movements of 206.3 km (bootstrapped 95 % CI: 187.3–219.6 km). Subadult females tended to have the longest displacements, followed by adult males and adult females. However, large individual variation both in displacement distances and recapture frequency tended to blur age and sex differences. Analysis restricted to one movement for each bear showed that the difference between adult males and adult females was small and non-significant. This indicates that findings based on telemetry, which is almost always restricted to females, may be relatively representative of the whole adult Barents Sea population in the spring season.     

Estimating preharvest density,adult sex ratio,and fecundity of white‐tailed deer using noninvasive sampling techniques

Adult sex ratio and fecundity (juveniles per female) are key population parameters in sustainable wildlife management, but inferring these requires abundance estimates of at least three age/sex classes of the population (male and female adults and juveniles). Prior to harvest, we used an array of 36 wildlife camera traps during 2 and 3 weeks in the early autumn of 2016 and 2017, respectively. We recorded white‐tailed deer adult males, adult females, and fawns from the pictures. Simultaneously, we collected fecal DNA (fDNA) from 92 20 m × 20 m plots placed in 23 clusters of four plots between the camera traps. We identified individuals from fDNA samples with microsatellite markers and estimated the total sex ratio and population density using spatial capture–recapture (SCR). The fDNA‐SCR analysis concluded equal sex ratio in the first year and female bias in the second year, and no difference in space use between sexes (fawns and adults combined). Camera information was analyzed in a spatial capture (SC) framework assuming an informative prior for animals’ space use, either (a) as estimated by fDNA‐SCR (same for all age/sex classes), (b) as assumed from the literature (space use of adult males larger than adult females and fawns), or (c) by inferring adult male space use from individually identified males from the camera pictures. These various SC approaches produced plausible inferences on fecundity, but also inferred total density to be lower than the estimate provided by fDNA‐SCR in one of the study years. SC approaches where adult male and female were allowed to differ in their space use suggested the population had a female‐biased adult sex ratio. In conclusion, SC approaches allowed estimating the preharvest population parameters of interest and provided conservative density estimates.     

Extinction risk of <Emphasis Type="Italic">Zamia inermis</Emphasis>: a demographic study in its single natural population

Demographic studies of endemic and threatened plant species are essential for establishing effective conservation strategies. This paper aims to determine the structure and dynamics of the only natural population reported for Zamia inermis. All individuals were mapped to determine the spatial structure and patterns of association between categories and sexes. Matrix analysis were conducted to determine the population dynamics based on three on-site visits. The population is distributed randomly, although seedlings were found to be aggregated at all scales, juveniles are aggregated in smaller radii up to 4.5 m and males at radii above 3.5 m. Seedlings and juveniles are associated with males over greater radii of 3 m, the dependence of adults from earlier categories and females is less than 1.5 m. The population growth rate confirms that the population is in decline (λ = 0.963 ± 0.011). Although few juveniles were identified and no seedling survival was observed in the field, also the amount of viable seeds per female cone is low. However, inhabitants of the region are cultivating the species by germinating seeds in backyard nurseries with 92 of 954 seeds reaching the juvenile category to date. It is clear that the population has lost its regenerative potential and is simply holding on to persistence of adults, this implies a great risk to the species. Ex situ propagation is encouraged.     

Density and population structure of the jaguar (<Emphasis Type="Italic">Panthera onca</Emphasis>) in a protected area of Los Llanos,Venezuela, from 1 year of camera trap monitoring

Density is crucial for understanding large carnivore ecology and conservation, but estimating it has proven methodologically difficult. We conducted 1 year of camera trapping to estimate jaguar (Panthera onca) density and population structure in the Los Llanos region of Venezuela on the Hato Piñero ranch, where hunting is prohibited and livestock are excluded from half of ranch lands. We identified 42 different jaguars and determined their sex, age class, and reproductive status. We estimated adult jaguar densities with spatial capture-recapture models, using sex/reproductive state and session as covariates. Models without temporal variation received more support than models that allowed variation between sessions. Males, reproductive females, and nonreproductive females differed in their density, baseline detectability, and movement. The best estimate of total adult jaguar population density was 4.44 individuals/100 km². Based on reproductive female density and mean number of offspring per female, we estimated cub density at 3.23 individuals/100 km² and an overall density of 7.67 jaguars/100 km². Estimated jaguar population structure was 21% males, 11% nonreproductive females, 26% reproductive females, and 42% cubs. We conclude that extending the sampling period to 1 year increases the detectability of females and cubs and makes density estimates more robust as compared to the more common short studies. Our results demonstrate that the Venezuelan Llanos represent important jaguar habitat, and further, they emphasize the importance of protected areas and hunting restrictions for carnivore conservation.     

Canopy-related adult density and sex-related flight activity of Monochamus alternatus (Coleoptera: Cerambycidae) in pine stands

Monochamus alternatus Hope is an important vector of the pinewood nematode Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle, which causes pine wilt disease. To determine canopy-related differences in the activity density of M. alternatus adults in pine stands, sticky screen traps with no lure were suspended under and in the canopy at 3.8 and 10 m above the ground of a Pinus densiflora Siebold et Zuccarini stand during a flight season. The five upper and five lower traps caught 338 and 54 adults, respectively, during a flight season from 9 June to 12 October 2011, indicating that activity density was six times as high in the canopy as under it. Male-biased sex ratio was observed for trap catches during a season: The sex ratio was male-biased in the early half of the flight season and 1:1 in the late half. There was no difference in sex ratio between the inside and outside of the canopy. To determine the sex-related difference in flight activity, the adults were captured by two different measures in two other mixed stands of P. densiflora and P. thunbergii Parlatore. Kicking tree trunks to cause beetles to drop revealed a 1:1 sex ratio of catches, whereas sticky screen traps tended to show a male-biased sex ratio in a 4-year study, suggesting that males were more active fliers than females.     

Life cycle of Ornithodoros rostratus (Acari: Argasidae) under experimental conditions and comments on the host-parasite relationship in the Pantanal wetland region, Brazil

The genus Ornithodoros is represented by 15 species in Brazil, on which no detailed life cycle studies have been published, except for O. talaje and O. mimon. The aim of the present study was to evaluate life cycle parameters of O. rostratus based on ticks collected in the Pantanal wetland region of the state of Mato Grosso do Sul, Brazil, using domestic rabbits as experimental hosts. The periods of pre-attachment and feeding of the larvae lasted an average of 39 min (range 15–76 min). Five or six nymphal instars were found. The emergence of adults started with N3 in the following sequence: N3—two males; N4—13 males; N5—three males and 16 females; and N6—two females. Mean weight of N4 that molted to males was 31.7 ± 13.6 mg, whereas mean weight of N5 that molted to females was 100.1 ± 36.2 mg. The overall sex ratio was 1:1. Oviposition lasted 14 days, with a sharp decline beginning with the 7th day. The overall duration of the life cycle of O. rostratus ranged from approximately 66 to 136 days. Comments on the tick-host relationship in the Pantanal region are offered.     

Mating system and sex allocation in the gregarious parasitoid Cotesia glomerata

The gregarious parasitoid Cotesia glomerata (L.) is often presumed to possess the characteristic attributes of a species that manifests local mate competition (LMC), as it commonly produces female-biased broods. However, our field surveys of sex ratio and laboratory observations of adult behaviour showed that this species is subject to partial local mate competition caused by natal dispersal. On average, 30% of males left their natal patch before mating, with the proportion of dispersing males increasing with an increase in the patch's sex ratio (i.e. proportion of males). Over 50% of females left their natal patch before mating, and only 27.5% of females mated with males emerging from the same natal patch. Although females showed no preference between males that were and were not their siblings, broods from females that mated with siblings had a significantly higher mean brood sex ratio (0.56) than broods from females that mated with nonsiblings (0.39). Furthermore, brood sex ratios increased as inbreeding was intensified over four generations. A field population of this wasp had a mean brood sex ratio of 0.35 over 3 years, which conformed well to the evolutionarily stable strategy sex ratio (r=0.34) predicted by Taylor's partial sibmating model for haplodiploid species. These results suggest that the sex allocation strategy of C. glomerata is based on both partial local mate competition in males and inbreeding avoidance in females. In turn, this mating system plays a role in the evolution of natal dispersal behaviour in this species.Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

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.     

Effects of temperature and rainfall variation on population structure and sexual dimorphism across the geographical range of a dioecious species

The effects of climate (precipitation and temperature) on sexual dimorphism and population structure were analysed along a broad-scale environmental gradient covering the distributional range of the endemic dioecious species Corema album, along the west coast of the Iberian Peninsula. We aimed to assess distribution constraints and sex-related differences in demography and size associated with higher reproductive investment in females. Nine populations were chosen from across the geographic range of C. album and ten 10 × 10 m plots were established (10 m apart) along a 200-m transect. All male, female and non-reproductive shrubs were quantified within each plot and plant size, photosynthetic layer, height, sex ratio, population density and structure, and spatial segregation of sexes, under environmental conditions ranging from temperate to Mediterranean climate, were recorded and analysed. Increased aridity was related to lower population density and less structured populations, indicating an effect of higher temperature and lower precipitation on regeneration. Sexual dimorphism was influenced by climate, with size differences between sexes varying with aridity. However, demographic differences between sexes reflected in sex ratio deviations or the occurrence of spatial segregation were unrelated to any climatic variable, suggesting the existence of compensatory mechanisms that may counterbalance the higher reproductive effort of female plants. The results show the vulnerability of this endemic species to the increase in aridity expected in the southernmost limit of the biogeographical area due to global climate change, and demonstrate the importance of broad scale studies in the assessment of sexual dimorphism.     

Single‐parentage assignments reveal negative‐assortative mating in an endangered salmonid

Understanding reproductive patterns in endangered species is critical for supporting their recovery efforts. In this study we use a combination of paired‐parent and single‐parent assignments to examine the reproductive patterns in an endangered population of sockeye salmon (Oncorhynchus nerka) that uses Redfish Lake in central Idaho as a spawning and nursery lake. Recovery efforts include the release of maturing adults into the lake for volitional spawning. The lake is also inhabited by a population of resident O. nerka that is genetically indistinguishable, but phenotypically smaller, to the maturing adults released into the lake. The resident population is difficult to sample and the reproductive patterns between the two groups are unknown. We used results of paired‐ and single‐parentage assignments to specifically examine the reproductive patterns of male fish released into the lake under an equal sex ratio and a male‐biased sex ratio. Assignment results of offspring leaving the lake indicated a reproductive shift by males under the two scenarios. Males displayed an assortative mating pattern under an equal sex ratio and spawned almost exclusively with the released females. Under a male‐biased sex ratio most males shifted to a negative‐assortative mating pattern and spawned with smaller females from the resident population. These males were younger and smaller than males that spawned with released females suggesting they were unable to compete with larger males for spawning opportunities with the larger, released females. The results provided insights into the reproductive behavior of this endangered population and has implications for recovery efforts.     

Summer heterothermy in Rafinesque’s big-eared bats (Corynorhinus rafinesquii) roosting in tree cavities in bottomland hardwood forests

Many small mammals are heterothermic endotherms capable of maintaining an elevated core body temperature or reducing their thermoregulatory set point to enter a state of torpor. Torpor can confer substantial energy savings, but also incurs ecological costs, such as hindering allocation of energy towards reproduction. We placed temperature-sensitive radio transmitters on 44 adult Rafinesque’s big-eared bats (Corynorhinus rafinesquii) and deployed microclimate dataloggers inside 34 day roosts to compare the use of torpor by different sex and reproductive classes of bats during the summer. We collected 324 bat-days of skin-temperature data from 36 females and 4 males. Reproductive females employed fewer torpor bouts per day than non-reproductive females and males (P < 0.0001), and pregnant and lactating females had higher average (P < 0.0001) and minimum (P < 0.0001) skin temperatures than non-reproductive females. Pregnant females spent less time torpid (P < 0.0001) than non-reproductive females, but lactating females used relatively deep, long torpor bouts. Microclimates varied inside tree species with different configurations of entrances to the roost cavity (P < 0.0001). Bats spent more time torpid when roosting in water tupelo (Nyssa aquatica) trees possessing only a basal entrance to the cavity (P = 0.001). Of the tree species used as roosts, water tupelo cavities exhibited the least variable daytime and nighttime temperatures. These data demonstrate that use of summer torpor is not uniform among sex and reproductive classes in Rafinesque’s big-eared bat, and variation in microclimate among tree roosts due to species and structural characteristics facilitates the use of different thermoregulatory strategies in these bats.     

Distribution and habitats of <Emphasis Type="Italic">Phengaris</Emphasis> (<Emphasis Type="Italic">Maculinea</Emphasis>) butterflies and population ecology of <Emphasis Type="Italic">Phengaris</Emphasis><Emphasis Type="Italic">teleius</Emphasis> in China

Many species of the butterfly genus Phengaris are regarded as endangered in many parts of their distribution. Several species are also widely distributed across northern China. Due to land use change and overgrazing, their habitats are declining and many patches have been lost. This paper investigates the distribution and habitats of the Chinese Phengaris species (of the subgenus Maculinea). Shrub-grassland near forests seem the most frequent habitat for Phengaris, while flat open grasslands are mostly over-grazed and thus survival for Phengaris butterflies there seems difficult. Throughout Europe, P. teleius is an endangered species, while there is still no information on its status in China. To improve the knowledge on the population ecology of P. teleius, its population structure, adult behaviour and movement were studied through mark–release–recapture methods in the Qinling Mountains of Taibai County. Eight grassland patches which were potentially suitable were found in the area in 2013. In total, 480 individuals (274 females) were marked, resulting in an overall recapture rate of 16 %. The average daily population size was 44 butterflies (±23 SD) during the adult flight period. Sixty-seven percent of the females and 38 % of the males moved less than 50 m, and 17 % of recaptured females and 38 % of males moved more than 200 m. The mean movement distance was 107 ± 177 m for males and 182 ± 122 m for females. The majority of the recaptures (86 %) were made within the patches, only a few individuals (14 %) moved between patches. Due to human disturbance and destruction, all of the eight potentially suitable patches are becoming smaller and increasingly isolated, thus these populations of P. teleius may face an increasing risk of extinction, which may well be a tip of the iceberg of habitat loss and fragmentation of P. teleius in Taibai County and possibly beyond. Hence we hope our initial study of P. teleius could have positive impacts on the conservation of Phengaris butterflies in China.     

Managing hunted populations through sex-specific season lengths: a case of the Common Eider in the Baltic-Wadden Sea flyway population

Management of harvested wildlife populations aims to protect species from overexploitation and ultimately extinction, by regulating exploitation towards achievable sustainable levels. However, assessments of impact and sustainability of implemented management actions on a population level are scarce. This study assesses effects of changes in hunting season length imposed on the Baltic-Wadden Sea Common Eider Somateria mollissima population, including differential restriction on hunting of the sexes. The potential impact of these changes on the population was assessed by simple demographic matrix projections. Since the early 1990s, this population has declined at ca. 6.3 % per annum, and the male/female ratio among shot birds has fallen from 3:2 to about 3:1. Concerns in Denmark regarding the conservation status and sustainability of contemporary levels of exploitation resulted in shortening the open season by 44 and 46 days for females and 13 and 15 days for males from the hunting seasons 2004/2005 and 2011/2012 onwards, respectively. These reduced the kill of adult females by 82 %, adult males by 31 %, juvenile females by 58 % and juvenile males by 55 %. The observed reduction in the kill of adult females following both changes in 2004/2005 and 2011/2012 matched the expected changes based on the seasonal distribution of sexes in the bag prior to the change. Post 2004/2005 hunters killed more adult males, but shot markedly fewer juvenile birds than expected. Demographic modelling of the female population showed that the effects of the reduced hunting would correspond to an increase in the annual population growth rate from the previous ?6.3 to ?3.6 % (post 2004) and ?1.6 % (post 2011). The model also predicted that a full ban on hunting female eiders (adults and juveniles) would lead to a positive population growth rate of 0.7 %. Taking into account the conservative model estimates and natural variations in annual breeding success, the implemented changes in sex-specific regulation of hunting may potentially be an effective management tool to halt the decline of the Baltic-Wadden Sea eider population, potentially rendering such levels of hunting sustainable under prevailing conditions.     

Spatial patterns and density dependence in the dynamics of a roe deer (<Emphasis Type="Italic">Capreolus capreolus</Emphasis>) population in central Italy

The demography of roe deer living in a mountain area of central Italy was studied from 1995 to 1999 with 104 radio-tagged animals, including fawns and adults of both sexes. From spring surveys we estimated population density by mark-resighting (average: 53.8dž.8 individuals km^-2) and found an average fawn/doe ratio of 0.75ǂ.4. The fawn/doe ratio was negatively correlated to density suggesting density-dependent regulation in this population. Using culled and net-trapped individuals we evaluated the dressed body weights of adult males (23.1ǃ.0 kg) and females (22.0ǃ.0 kg), which indicated a low level of sexual dimorphism. The potential litter size (1.44ǂ.1 embryos) depended on female body weight and a threshold of 20.9ǃ.4 kg separated adult females carrying one or two embryos. Both fawn (0.38ǂ.07) and adult survival (0.90ǂ.07) were evaluated from radiotagged individuals and no gender effect was observed in either age class. During the study period we recorded a population decline in one part of the study area and an increasing fawn mortality, which was attributed to the spreading of an enteropathogenic desease. The study revealed an unexpected spatial structure in population dynamics at a scale of few square kilometres. In the two studied subareas, which are very close and ecologically similar, we documented significant differences in several demographic parameters: females in the subarea with the highest deer density produced smaller litters and allocated their reproductive effort preferentially to males, which is consistent with the hypothesis that local resource competition determines sex allocation in roe deer. The importance of spatial variability with respect to roe deer demography was overlooked in previous studies and our results raise new interesting research questions relative to the study of population equilibria which are also relevant for the management of this important game species.