Trade-off between resource seasonality and predation risk explains reproductive chronology in impala

We investigated the variation in birth synchrony displayed by impala Aepyceros melampus populations across their distribution from southern to eastern Africa. Our analysis was based on field data from Chobe National Park in Botswana and Mala Mala Private Game Reserve in South Africa (4 and 13 years of monitoring, respectively). We compared our results with those from other studies conducted across the impala species range. Impala lambing was highly synchronized in Chobe with 90% of lambs born within 2 weeks in mid-November. Variation in rainfall in the preceding wet season explained 74% of variation in the dates of the first lamb observation in Mala Mala. In Chobe, the earliest birth peak occurred after the highest rainfall and the body condition of lambs in that cohort was also best for both males and females. No association was found between the lunar cycle and the estimated onset of the conception period, despite previous studies having found an association between the lunar cycle and the rutting behaviour in males. On a regional scale, impalas in areas with a marked dry season (several months with no rain) tend to synchronize births with the onset of the rains, when grass quality is highest. Number of months with rain explained 78% of the regional variation in birth synchrony. Neither latitude nor total rainfall contributed significantly to a stepwise multiple regression model. These data support the theory that impalas synchronize births in areas with a highly seasonal food supply, and temporally space births in less seasonal (equatorial) areas to reduce predation risks.     

Ecological cues, gestation length, and birth timing in African buffalo (Syncerus caffer)

We examined annual variation in the timing of conception andparturition in the African buffalo (Syncerus caffer) and thesynchrony of birth timing with resource cues, using 8 yearsof monthly birth, rainfall, and vegetation data, measured asNormalized Difference Vegetation Index (NDVI). Monthly birthshad the strongest significant correlations with NDVI and rainfalllevels 12 and 13 months in the past, respectively. In addition,the synchrony of current year births corresponds most stronglyto the synchrony of the previous year's NDVI distribution. Becausethe gestation period of buffalo has been estimated to be around11 months, these findings suggest that improved protein levels,occurring approximately a month after the first green flushof the wet season, are either a trigger for conception or conceptionhas evolved to be synchronous with correlated environmentalcues that ensure females enter a period of peak body conditionaround the time of conception and/or parturition. With a gestationperiod of approximately 340 days, parturition occurs to takeadvantage of the period when forage has its highest proteincontent. A comparative analysis of gestation periods withinthe subfamily Bovinae indicates that African buffalo have aprotracted gestation for their body size, which we suggest isan adaptation to their seasonal environment. We also found thatinterannual variation in the birth distribution suggests a degreeof plasticity in the date of conception, and variation in thenumber of calves born each year suggest further synchrony ata timescale longer than a single year.     

极小种群植物猪血木的种群现状及保护对策

猪血木(Euryodendron excelsum)是特产于中国的山茶科极危种, 但目前对导致猪血木种群结构改变的原因缺少相关的调查及研究, 保护策略不完善。该研究依据野外调查方法、编制标准生命表、存活曲线、致死力和寿命期望曲线, 利用德氏多度分析方法分析了广东省阳春市八甲镇极小种群野生植物猪血木种群的年龄结构和动态, 并与2007年的研究结果进行对比, 分析该种群近10年的变化情况及其原因。结果表明: (1)研究区域内野生猪血木种群的数量变化动态指数(V_pi和V′_pi)均小于0, 存活曲线趋于Deevey-III型, 种群结构属于衰退型, 幼树数量丰富, 但由于向小树发展过程受阻, 种群无法及时更新补充。(2)存活曲线、致死力和寿命期待曲线一致显示在幼树、小树2级、中龄树2级这3个阶段, 出现阻碍因素, 影响种群的自然更新。(3)三甲镇猪血木幼苗减少了39.3%, 八甲镇猪血木幼苗锐减了71.9%, 三甲镇幼苗转化率较八甲镇低了近1/2。人为干扰是导致猪血木野生种群衰退的主要驱动因素, 已实施的保护策略并不适合当前情况下的野生猪血木种群。     

Spatially mismatched trophic dynamics: cyclically outbreaking geometrids and their larval parasitoids

For trophic interactions to generate population cycles and complex spatio-temporal patterns, like travelling waves, the spatial dynamics must be matched across trophic levels. Here, we propose a spatial methodological approach for detecting such spatial match–mismatch and apply it to geometrid moths and their larval parasitoids in northern Norway, where outbreak cycles and travelling waves occur. We found clear evidence of spatial mismatch, suggesting that the spatially patterned moth cycles in this system are probably ruled by trophic interactions involving other agents than larval parasitoids.     

新疆濒危野生樱桃李的种群结构与动态

为了解野生樱桃李种群结构和种群生态现状,采用“空间序列代替时间变化”的方法,对新疆天然分布区内的野生樱桃李不同种群的径级结构、冠幅结构及株高结构进行了分析,运用静态生命表描述了野生樱桃李种群年龄结构的动态变化规律.结果表明,樱桃李天然种群的株高和冠幅结构呈现为一定的衰退趋势,冠幅在总体呈现为近乎对数型的衰减趋势;种群的径级结构趋于稳定型,但种群结构表现出较强的波动性,种群衰退风险较高;同时,不同样地种群因所处微环境等的差异,在径级、株高和冠幅结构上表现出一定差异.野生樱桃李种群的存活曲线接近于B1型(台阶型),说明幼龄的死亡率较高,且不同生活史时期的死亡率差异较大.新疆的野生樱桃李天然种群表现出一定的不稳定性,亟待补充低龄级的个体,并减少对成年树的砍伐破坏,从而为种群的保育和恢复提供保障.     

Northern Atlantic Oscillation effects on the temporal and spatial dynamics of green spruce aphid populations in the UK

1. The role of climate variability in determining the spatial and temporal patterns of numerical fluctuations is a central problem in ecology. The influence of the North Atlantic Oscillation (NAO) index on the population dynamics and spatial synchrony of the green spruce aphid Elatobium abietinum across the UK was shown. 2. Fifteen overlapping time series within the UK were analysed; we used nonparametric models for determining the feedback nonlinear structure and the climatic effects. The spatial synchrony of these populations and the relationship between synchrony and NAO was estimated. 3. From the 15 time series across the UK, 11 showed positive and significant NAO effects. In most of the cases the NAO effects were nonlinear showing strong negative effects of low values. The NAO variation improve the explained variance of the first-order feedback models in 14.5%; ranging from 0% to 48%. All data showed strong-nonlinear (concave) feedback structure. In most of the localities the explained variance by the first-order feedback was about 50-60%. 4. The spatial synchrony of the per capita growth rates and residuals is high across long distances for those populations affected by NAO. The correlation function predicts a spatial scale of synchrony of about 350-400 km for NAO influenced populations. 5. We think that simple population theoretical models describing the link between NAO fluctuations and green spruce aphid dynamics may be fundamental for predicting and simulating the consequences of different climatic scenarios of the future.     

Age-specific birth rate and lifetime reproductive success of chimpanzees at Bossou,Guinea

Preliminary calculations of the age-specific birth rate for wild female chimpanzees were based on demographic records from a long-term study at Bossou, Republic of Guinea. Primiparous age was 12-14 years. Birth rate for a female reached a peak of 0.333 a year at 20-23 years, and then decreased until menopause at more than 40 years of age. Mean birth rate for a female of more than 12 years was 0.197 a year. Mean interbirth interval was 4.6 years overall, but 5.1 years, if all cases in which the previous infant had died within its first three years were excluded. Infant survival rate for the first four years was 0.727 and that of juveniles (four to seven years) was 0.714; however, that of adolescents (eight to 11 years) was only 0.222. Some adolescents who disappeared from Bossou are thought to have migrated to adjacent habitats. From age-specific birth rate and survival rate, the lifetime reproductive success was calculated as only 0.74 offspring per female. This rose to 2.39 when adolescent survival rate was assumed to be the same as that of juveniles. This must be less than the minimum reproductive success required for continued survival of the population. The recent and continuing degradation of the environment will lead to the extermination of this species from the area in the near future. © 1994 Wiley-Liss, Inc.