普氏野马雄性杀婴行为及其对野马放归的影响

2001年8月在新疆卡拉麦里有蹄类自然保护区进行普氏野马在中国的首次再引入放归实验。在放归初期,放归普氏野马的野外种群数量增长缓慢,主要原因是由于繁殖群头马的频繁更替,新出生的部分幼驹死于头马的杀婴。2003年4月至2005年11月在野外共出生13匹幼驹,新生幼驹的死亡率46%,死于头马杀婴的个体占全部新生个体的38.5%,占全体死亡个体的83.3%,雄性杀婴行为是制约放归野马种群增长的主要因素,降低繁殖群头马的更替的频率是提高新生幼驹存活率的根本所在。     

中国新疆放归普氏野马的繁殖状况

2001年8月在新疆卡拉麦里有蹄类自然保护区进行普氏野马在中国的首次再引入放归实验.2002-2006年在野外共繁殖24匹后代.平均繁殖率为38.72%,平均繁殖存活率为69.05%,繁殖季节头马的频繁更替是影响放归普氏野马繁殖率的主要因素.新生幼驹的平均死亡率为25%,其中83.3%死于头马的雄性杀婴.放归普氏野马的繁殖具有明显的季节性繁殖特征,其中有70.8%的幼驹集中在5-6月间出生,在4、5月份产驹比例分别占8.3%和37.5%.低于同期圈养18.3%和44.3%的产驹比例,6月份产驹比例占33.3%.高于同期圈养18.3%的产驹比例,结果表明:普氏野马放归后产驹高峰季节明显向后推迟,而放归后生存环境和食物资源供给方式的改变则是其繁殖季节产生推迟的主要原因.     

重引入地生境对普氏野马胃肠道寄生虫疾病感染的风险评估

野生动物重引入是保护濒危种群的重要措施之一,但重引入放归地存在的疾病风险会影响重引入物种的健康并导致重引入项目的失败。疾病风险评估是用于识别、确定风险因子优先级和设计防控策略以应对风险的重要方法。为评估普氏野马（Equus przewalskii）重引入内蒙古大青山国家级自然保护区的疾病风险,本研究在传统文献研究的基础上,结合保护区内4个村庄83份家养马科动物粪便中寄生虫卵检测结果,进行专家赋分,确定威胁因子并评级,对影响普氏野马种群健康重要因素之一的寄生虫疾病进行风险评估,并提出相应的防控建议。本研究共确定了44种胃肠道寄生虫疾病,病原体分别隶属于5纲7目8科19属;其中高风险寄生虫疾病10种,中风险13种,低风险21种。小井村、奎素村和滴水村均为低风险区域,而厂汉脑包村属于高风险区域。重引入地周围的家马（E. caballus）和家驴（E. asinus）有与放归普氏野马交叉感染寄生虫的风险,但经严格的防控措施后,可以放归普氏野马。建议保护区内村庄限定家养马科动物活动范围,定期为家畜驱虫并清理圈舍,严格实行禁牧政策,增设远离村庄的普氏野马水源地,并对放归后普氏野马种群的寄生虫疾病进行长期监测与防控,从而有效防止寄生虫疾病的发生和传播。     

荒漠草原动物的代表物种——普氏野马

普氏野马是世界性的的濒危物种。对普氏野马的形态学特征、分布、种群数量、食性、栖息地、繁殖及疾病作了简要的概述。简要介绍了普氏野马的再引入现状和现存的潜在威胁,旨在引起大众对普氏野马的关注。     

放归初期普氏野马家族群的变更及其管护意义

本研究以我国放归野化的普氏野马家族群为观测对象,在2003年1月至2006年12月系统研究了该物种家族群变更的类型及其频次。结果表明,普氏野马家族群的变更类型有5种:1)头马更替、2)群体分裂、3)群体合并、4)家族群间个体变换、5)亚成体离群。头马更替和群体分裂主要发生于6～7月份,分别占该类变更总数的50%和66%;群体合并主要发生于6月、8月,占66%;家族群间个体变换主要发生于7月、10月和11月,占89%;亚成体离群主要发生于4月和5月,占75%。普氏野马家族群变更是该物种生物学特性与放归地环境共同作用的结果。依据本研究结果,作者提出了调整放归野马群体的年龄结构,改善放归地水源空间配置,进而维护放归普氏野马家族群的稳定性的管护措施。     

圈养和放归成年雌性普氏野马(Equus przewalskii)夏季昼间的摄食行为

2005至2006年的6~8月间,在新疆普氏野马饲养与繁殖研究中心和卡拉麦里山有蹄类自然保护区,采用全事件取样法和目标动物取样法相结合,研究了圈养和放归成年雌性普氏野马夏季昼间的摄食行为。结果表明,两组个体在摄食行为类型上存在一定的差异,圈养个体普遍具有舔盐和食粪行为,而放归个体不存在此类行为。经独立样本t 检验,得出两组个体的摄食和站立行为的时间分配存在显著差异（P＜0.05）,而站息、卧息、运动和其它行为差异不显著（P＞0.05）,总体上,两组普氏野马的摄食行为所占时间最多。圈养个体昼间具有3个摄食高峰（8:00~10:00、13:00~15:00、19：30~20:00）,与人工投食时间相一致,而放归个体摄食高峰并不明显,仅在13:00~15:00之间出现一个明显的摄食低谷,表现出自然的摄食节律及对放归地夏季自然条件的适应。     

新疆栏养野马的繁殖状况

介绍了普氏野马在养条件下15年的繁殖和种群发展状况。至2001年底,野马在册记录达180匹,合计繁殖149匹,繁殖成活124匹,平均繁殖成活率为85％。     

圈养繁殖大熊猫生存力的影响因素分析——基于大熊猫谱系数据

提高圈养繁殖大熊猫存活率是维持圈养种群可持续发展和开展野化放归研究的基础,为了探究圈养繁殖大熊猫生存力的影响因素,基于2019年的大熊猫谱系数据,不仅统计分析了不同年代和不同龄级(月龄、年龄组)圈养繁殖大熊猫的存活率和死亡率,而且利用广义线性模型系统分析了影响圈养繁殖大熊猫存活时间的主要因素。结果表明:1960—1989年圈养繁殖大熊猫的幼仔和种群存活率分别是31.61%和68.10%,1990—2019年为78.39%和94.06%;不同年龄组圈养繁殖大熊猫的死亡率呈"凹型"曲线,即幼年和老年大熊猫死亡率较高(26.85%、26.53%),而亚成年和成年的死亡率偏低(4.56%、12.60%);不同月龄则以初生幼仔(1月龄)的死亡率最高,达22.45%,其余月龄相对较低(0～20%)。广义线性模型分析发现,个体性别、出生年代、母兽来源、母兽产仔年龄、育幼方式和胎儿数量等因素显著影响圈养繁殖大熊猫的存活、死亡和寿命长短。因此,加强大熊猫种源管理、提高人工育幼技术以及优化繁育配对等是大熊猫饲养管理的关键。     

繁衍生息之难

繁衍后代是动物的本能,也是一个物种持续的根本。放归野外的普氏野马能正常繁育后代,然而,严格的一雄多雌制度,使得家族群的内斗堪称野马版的《甄传》。头马杀婴行为和近亲繁殖现象,为野马放归后的自然繁衍带来难题。     

普氏野马重引入原生地——中国

1985年8月6日和8月22日,来自东德的5匹野马（2公3母）,和来自英国的6匹野马（2公4母）,先后运抵新疆乌鲁木齐市动物园。中国重引入普氏野马的基本思路是从国外引回种源,建立繁育种群,扩人圈养种群。     

Pedigree and herd characterization of a donkey breed vulnerable to extinction

Most donkey and local horse breeds are vulnerable to extinction as mechanization of agriculture progress throughout the world. The present study analyzed the pedigree and herd records of the donkey Asinina de Miranda breed (RAM), identifying genealogical and human factors that may affect the breed genetic diversity in the future and suggesting suitable strategies to breed preservation, early on the conservation program. The breeding rate was very low, with a ratio of foaling/live animals of 0.23 (178/760). The estimated number of founders and ancestors contributing to the reference population was 128 and 121. The number of founder herds in the reference population was 64, with an effective number of founder herds for the reference population of 7.6. The mean age of herd owners was 65.50±0.884 years, with a negative association among the herd size and owner’s age (P<0.001). In contrast, the size of the herd and the ownership of a male were both positively associated (P<0.001) with the herd number of in-born foals. Both the owners’ age and the herd location (RAM home region v. dispersal region) were negatively associated with the foaling number (P<0.001). The main identified risk factors were: low breeding rates; low number of males and their unequal contribution to the genetic pool; unequal contribution of the herds to genetic pool; and advanced age of herd owners.     

Timing of reproduction in a Darwin''s finch: temporal opportunism under spatial constraints

We investigated whether predation by the minor grison ( Galictis cuja , a small mustelid) played a key role in limiting a wild cavy population ( Cavia magna ), ultimately leading to its local extinction. Radio-telemetry and capture-mark-recapture techniques were used to estimate grison predation rates (kill rates), time-specific probabilities of apparent mortality (population loss rate), overall mortality and grison predation for the cavy population. Additionally, we present data on alternative prey species, grison diet and reproduction to show potential proximate mechanisms of grison predation on wild cavies. The predictions specified were mostly confirmed: (1) grison predation was responsible for almost 80% of the cavies killed by known predators; (2) grison predation probabilities paralleled those of overall mortality of cavies over time; and (3) also those of the apparent mortality of the population. Thus, the population dynamics and the local extinction of the cavy population were not due to emigration processes. (4) Grison predation rates were not density-dependent, but showed pronounced peaks during the austral summer. The grison mainly preyed on small mammals: two water-rat species and the wild cavies. When the availability of alternative prey decreased in summer, the grison appeared to specialise on cavies. The onset of grison reproduction was somewhat delayed in relation to the onset of cavy reproduction. The lack of alternative prey coincided with high grison food demands due to reproduction, leading to a very high predation pressure ultimately resulting in the local extinction of the cavy population. We conclude that grison predation was indeed the main factor driving changes of the cavy population studied and speculate why caviomorph rodents might be especially susceptible to local extinction processes.     

Out of the frying pan: Reintroduction of toad‐smart northern quolls to southern Kakadu National Park

Invasive species are a leading cause of native biodiversity loss. In Australia, the toxic, invasive cane toad Rhinella marina has caused massive and widespread declines of northern quolls Dasyurus hallucatus. Quolls are fatally poisoned if they mistakenly prey on adult toads. To prevent the extinction of this native dasyurid from the Top End, an insurance population was set up in 2003 on two toad‐free islands in Arnhem Land. In 2015, quolls were collected from one of these islands (Astell) for reintroduction. We used conditioned taste aversion to render 22 of these toad‐naïve quolls toad averse. Seven quolls received no taste aversion training. The source island was also predator‐free, so all quolls received very basic predator‐aversion training. In an attempt to re‐establish the mainland population, we reintroduced these 29 northern quolls into Kakadu National Park in northern Australia where cane toads have been established for 13 years. The difference in survival between toad‐averse and toad‐naive quolls was immediately apparent. Toad‐naive quolls were almost all killed by toads within 3 days. Toad‐averse quolls, on the other hand, not only survived longer but also were recorded mating. Our predator training, however, was far less effective. Dingo predation accounted for a significant proportion of toad‐smart quoll mortality. In Kakadu, dingoes have been responsible for high levels of quoll predation in the past and reintroduced animals are often vulnerable to predation‐mediated population extinction. Dingoes may also be more effective predators in fire degraded landscapes. Together, these factors could explain the extreme predation mortality that we witnessed. In addition, predator aversion may have been lost from the predator‐free island populations. These possibilities are not mutually exclusive but need to be investigated because they have clear bearing on the long‐term recovery of the endangered northern quoll.     

Can a spider web be too sticky? Tensile mechanics constrains the evolution of capture spiral stickiness in orb-weaving spiders

Owing to habitat loss and fragmentation, large mammal populations all over the world are becoming increasingly small and isolated. It is therefore a conservation priority to understand mechanisms influencing the demography of such populations, which can easily be driven to extinction. The Przewalski's horse Equus ferus przewalskii remains one of the world's most endangered species and reintroduced animals are still vulnerable. Over 9 years, we analysed factors affecting mortality and female fecundity at the individual level in a predator-free, closed population of Przewalski's horses, which grew from 11 to 55 individuals. Similar to other wild equids, the annual growth rate of the population was r =0.169. Typically, adult mortality was much lower than juvenile mortality, the latter being correlated with neither inbreeding coefficient of foals nor population density. We found no link between female fecundity and operational sex ratio of the herd, or inbreeding coefficient, lactation status and body condition of the mares. Although food therefore seemed not to be limiting in this population, density (number of horses ha⁻¹) clearly reduced fecundity, especially in subadult mares. Thus, our results show that space can slow the growth rate of a population before resources become limited, a potential source of concern for increasingly shrinking habitats of endangered large mammals. Possible mechanisms causing this may be found in incest avoidance or other social parameters. Finally, in large herbivores, population density is said to exert influence in a sequential order: juvenile survival first, followed by fecundity of young females, then adult females, and adult survival last. Although we observed no link between density and juvenile survival in the studied population, our results otherwise support this hypothesis.     

Ancestral ecological regime shapes reaction to food limitation in the Least Killifish,Heterandria formosa

Populations with different densities often show genetically based differences in life histories. The divergent life histories could be driven by several agents of selection, one of which is variation in per‐capita food levels. Its relationship with population density is complex, as it depends on overall food availability, individual metabolic demand, and food‐independent factors potentially affecting density, such as predation intensity. Here, we present a case study of two populations of a small live‐bearing freshwater fish, one characterized by high density, low predation risk, low overall food availability, and presumably low per‐capita food levels, and the other by low density, high predation risk, high overall food availability, and presumably high per‐capita food levels. Using a laboratory experiment, we examined whether fish from these populations respond differently to food limitation, and whether size at birth, a key trait with respect to density variation in this species, is associated with any such differential responses. While at the lower food level growth was slower, body size smaller, maturation delayed, and survival reduced in both populations, these fitness costs were smaller in fish from the high‐density population. At low food, only 15% of high‐density fish died, compared to 75% of low‐density fish. This difference was much smaller at high food (0% vs. 15% mortality). The increased survival of high‐density fish may, at least partly, be due to their larger size at birth. Moreover, being larger at birth enabled fish to mature relatively early even at the lower food level. We demonstrate that sensitivities to food limitation differ between study populations, consistent with selection for a greater ability to tolerate low per‐capita food availability in the high‐density population. While we cannot preclude other agents of selection from operating in these populations simultaneously, our results suggest that variation in per‐capita food levels is one of those agents.     

Predation, group size and mortality in a cooperative mongoose, Suricata suricatta

1. In social mammals where group members cooperate to detect predators and raise young, members of small groups commonly show higher mortality or lower breeding success than members of large ones. It is generally assumed that this is because large group size allows individuals to detect or repel predators more effectively but other benefits of group size may also be involved, including reduced costs of raising young and more effective competition for resources with neighbouring groups.
2. To investigate the extent to which predation rate affects survival, we compared mortality rates in two populations of suricates ( Suricata suricatta ), one living in an area of high predator density (Kalahari Gemsbok Park) and one living in an area of relatively low predator density (neighbouring ranchland). Most aspects of feeding ecology and growth (including time spent feeding, daily weight gain, growth, adult body weight, breeding frequency and neonatal mortality) were similar in the two populations. In contrast, mortality of animals over 3 months old was 1·7 times higher in the Park than on ranchland.
3. Mortality of juveniles between emergence from the natal burrow and 6 months of age was higher in small groups than large ones in the Park but significantly lower in small groups than large ones on ranchland. Adult mortality declined in larger groups in both areas.
4. The tendency for survival to be low in small groups had far-reaching consequences for the risk of group extinction. During a year of low rainfall in the Park, all groups of less than nine animals became extinct and population density declined to around a third of its initial level. We argue that high group extinction rates are to be expected in species where survival declines in small groups and mortality rates are high.     

Can reintroductions to degraded habitat succeed? A test using the common brushtail possum

Habitat degradation contributes to species decline, and habitat quality is an important factor influencing reintroduction success globally. Habitat quality can include a range of physical resources such as nest sites and food resources but also anything that can restrict the use of these resources such as predation risk or competition. In arid Australia, introduced predators are thought to be the primary cause of mammal extinction and reintroduction failure although habitat clearance and alteration are also major causes of population decline. Common brushtail possums are one arid Australian marsupial close to regional extinction. To understand whether habitat quality was limiting their recovery, we reintroduced 148 possums into an area where introduced red foxes were controlled but historic overgrazing had degraded the habitat. We measured both direct (hollow availability, midstorey cover and high‐quality plant foods) and indirect (survival, condition, reproduction, movement) measures of habitat quality. Sixty‐seven released possums and 26 post‐release recruits were radiocollared for up to 2 years after release. Post‐release survival of radiocollared possums was high after 12 months (0.70), and there were no deaths from starvation. Predation by feral cats was the most common cause of mortality, and the open, degraded habitat may have exacerbated predation risk. Continuous breeding, good body condition and comparative home ranges with other sites suggested that food resources were not limiting. Possums used natural tree hollows in Eucalyptus spp. with no use of artificial nest boxes. Results suggest that historically degraded habitat was not a barrier to short‐term reintroduction success when foxes were controlled and natural tree hollows were plentiful. However, demographic data on hollow‐bearing tree species suggest a possible future decline in availability of hollows. These factors, combined with the unknown effects of drought, and synergistic effects of predation and poor quality habitat, suggest long‐term reintroduction success may require improved habitat and cat control.     

Metapopulation extinction risk: Dispersal’s duplicity

Metapopulation extinction risk is the probability that all local populations are simultaneously extinct during a fixed time frame. Dispersal may reduce a metapopulation’s extinction risk by raising its average per-capita growth rate. By contrast, dispersal may raise a metapopulation’s extinction risk by reducing its average population density. Which effect prevails is controlled by habitat fragmentation. Dispersal in mildly fragmented habitat reduces a metapopulation’s extinction risk by raising its average per-capita growth rate without causing any appreciable drop in its average population density. By contrast, dispersal in severely fragmented habitat raises a metapopulation’s extinction risk because the rise in its average per-capita growth rate is more than offset by the decline in its average population density. The metapopulation model used here shows several other interesting phenomena. Dispersal in sufficiently fragmented habitat reduces a metapopulation’s extinction risk to that of a constant environment. Dispersal between habitat fragments reduces a metapopulation’s extinction risk insofar as local environments are asynchronous. Grouped dispersal raises the effective habitat fragmentation level. Dispersal search barriers raise metapopulation extinction risk. Nonuniform dispersal may reduce the effective fraction of suitable habitat fragments below the extinction threshold. Nonuniform dispersal may make demographic stochasticity a more potent metapopulation extinction force than environmental stochasticity.     

To breed, or not to breed? Predation risk induces breeding suppression in common voles

Breeding suppression hypothesis (BSH) predicts that, in several vole species, females will suppress breeding in response to high risk of mustelid predation; compared to breeding females, suppressing females would gain higher chances of survival. Seminal evidence for BSH was obtained in the laboratory, but attempts to replicate breeding suppression under field conditions were less conclusive. We tested whether breeding suppression occurs in common voles (Microtus arvalis), and how population density and predation risk combined affect voles’ reproductive activity. We found that, in contrast to males, female common voles suppress reproductive activity when faced with high predation risk. Population size was not reduced despite breeding suppression. A model of the interaction between predation risk and population density revealed that predator-induced breeding suppression depends on the density of conspecifics. We concluded that breeding suppression is a viable adaptation only at low vole densities, when per capita predation risk is high. Finally, we identified the key issues of experimental design required for the consistency of future studies on breeding suppression.     

The role of age of first breeding in modeling raptor reintroductions

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