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.     

Ungulate Reproductive Parameters Track Satellite Observations of Plant Phenology across Latitude and Climatological Regimes

The effect of climatically-driven plant phenology on mammalian reproduction is one key to predicting species-specific demographic responses to climate change. Large ungulates face their greatest energetic demands from the later stages of pregnancy through weaning, and so in seasonal environments parturition dates should match periods of high primary productivity. Interannual variation in weather influences the quality and timing of forage availability, which can influence neonatal survival. Here, we evaluated macro-scale patterns in reproductive performance of a widely distributed ungulate (mule deer, Odocoileus hemionus) across contrasting climatological regimes using satellite-derived indices of primary productivity and plant phenology over eight degrees of latitude (890 km) in the American Southwest. The dataset comprised > 180,000 animal observations taken from 54 populations over eight years (2004–2011). Regionally, both the start and peak of growing season (“Start” and “Peak”, respectively) are negatively and significantly correlated with latitude, an unusual pattern stemming from a change in the dominance of spring snowmelt in the north to the influence of the North American Monsoon in the south. Corresponding to the timing and variation in both the Start and Peak, mule deer reproduction was latest, lowest, and most variable at lower latitudes where plant phenology is timed to the onset of monsoonal moisture. Parturition dates closely tracked the growing season across space, lagging behind the Start and preceding the Peak by 27 and 23 days, respectively. Mean juvenile production increased, and variation decreased, with increasing latitude. Temporally, juvenile production was best predicted by primary productivity during summer, which encompassed late pregnancy, parturition, and early lactation. Our findings offer a parsimonious explanation of two key reproductive parameters in ungulate demography, timing of parturition and mean annual production, across latitude and changing climatological regimes. Practically, this demonstrates the potential for broad-scale modeling of couplings between climate, plant phenology, and animal populations using space-borne observations.     

The ranging behaviour of a large sexually dimorphic herbivore in response to seasonal and annual environmental variation

The allometric relationships of body size play a principle role in determining how large herbivores respond to the marked spatial and temporal heterogeneity of the savanna biome. Using location data collected over an 8‐year period from five distinct study sites, we investigated the influence of environmental variation (using phenological and rainfall data) on the ranging behaviour of the African elephant (Loxodonta africana), a species that exhibits pronounced sexual dimorphism. Both sexes expanded their annual ranges during years of high rainfall and contracted their ranges during periods of resource scarcity, concurring with the hypothesis that abiotic factors dictate the distribution of large generalist herbivores at the landscape scale. However, female elephant did not exhibit the same consistent response to rainfall at the seasonal scale. Furthermore, male elephant demonstrated a reduction in their daily displacement distances during the dry winter season, and altered their movement rates on the basis of seasonal rainfall. These results suggest that male elephant are able to consistently adapt their movement behaviour according to forage quality and abundance. Smaller‐bodied female elephant on the other hand, are unlikely to exhibit the same flexibility in their ranging behaviour because of their higher relative nutritional demands, lower tolerance to fibrous forage and the social and energetic constraints of group living with juveniles. Our study highlights the major role that body size and sociality plays in the decision making of sexually dimorphic herbivores. These differences can have important implications for effective conservation and management, particularly with regard to demographic (e.g. survival) and ecological (e.g. habitat use) factors.     

Rainfall and rats: Climatically-driven dynamics of a tropical rodent population

A five-year mark–recapture study of dusky rats (Rattus colletti) on the Adelaide River floodplain, within the Australian wet–dry tropics, revealed substantial spatial and temporal variation in demographic characteristics (abundance, condition, and rates of survival, growth, and reproduction) of the rats. Our data suggest that annual variation in the intensity and timing of monsoonal rainfall during the ‘wet-season’ is the main factor driving the demography of the rats. When total rainfall figures are modified to reflect the magnitude and duration of inundation of the floodplain each year, a link is evident between rainfall patterns and the rat population dynamics. Minor spatial variations in elevation (and hence, in the duration of inundation) across the floodplain engender large differences in rat growth rates, condition factors, survival rates, and the duration of reproductive activity each year. Because these rats have very high reproductive rates, small rain-induced differences in the duration of their reproductive season (i.e. number of litters per year) can cause massive differences in subsequent rat abundances. Hence, rat numbers can be predicted from rainfall patterns during the preceding wet-season. Similar links between rainfall, the duration of breeding, and fluctuations in abundance may typify many rodent populations in tropical and arid regions of the world.     

Proximate weather patterns and spring green‐up phenology effect Eurasian beaver (Castor fiber) body mass and reproductive success: the implications of climate change and topography

Low spring temperatures have been found to benefit mobile herbivores by reducing the rate of spring‐flush, whereas high rainfall increases forage availability. Cold winters prove detrimental, by increasing herbivore thermoregulatory burdens. Here we examine the effects of temperature and rainfall variability on a temperate sedentary herbivore, the Eurasian beaver, Castor fiber, in terms of inter‐annual variation in mean body weight and per territory offspring production. Data pertain to 198 individuals, over 11 years, using capture‐mark‐recapture. We use plant growth (tree cores) and fAPAR (a satellite‐derived plant productivity index) to examine potential mechanisms through which weather conditions affect the availability and the seasonal phenology of beaver forage. Juvenile body weights were lighter after colder winters, whereas warmer spring temperatures were associated with lighter adult body weights, mediated by enhanced green‐up phenology rates. Counter‐intuitively, we observed a negative association between rainfall and body weight in juveniles and adults, and also with reproductive success. Alder, Alnus incana, (n = 68) growth rings (principal beaver food in the study area) exhibited a positive relationship with rainfall for trees growing at elevations >2 m above water level, but a negative relationship for trees growing <0.5 m. We deduce that temperature influences beavers at the landscape scale via effects on spring green‐up phenology and winter thermoregulation. Rainfall influences beavers at finer spatial scales through topographical interactions with plant growth, where trees near water level, prone to water logging, producing poorer forage in wetter years. Unlike most other herbivores, beavers are an obligate aquatic species that utilize a restricted ‘central‐place’ foraging range, limiting their ability to take advantage of better forage growth further from water during wetter years. With respect to anthropogenic climate change, interactions between weather variables, plant phenology and topography on forage growth are instructive, and consequently warrant examination when developing conservation management strategies for populations of medium to large herbivores.     

Phenology and synchrony of roe deer breeding in northern Italy

The timing and synchrony of births of roe deerCapreolus capreolus Linnaeus, 1758 population were examined for 7 consecutive years in northern Italy. From 1997 to 2003, 136 fawns, 65 females and 71 males, from 117 litters were captured. The average date of fawning (30th of May) was constant among years and between sexes. The onset of parturition was 19th of May while the total length of the parturition season was 25 days (from 19th of May to 13th of June). Births were highly synchronous, with 80% of births occurring in 17 days. Synchrony of birth did not exhibit any significant interannual or intersexual variation. The stability of the birth pattern was confirmed by the parturition date of 13 radiocollared females who all gave birth within 4 days in consecutive fawning seasons. In agreement with previous findings, our data support the hypothesis that the roe deer is constrained at both ends of the fawning season by the short time between the fawning season and rut and by the need to match optimal climate conditions and forage quality to face late gestation and lactation. All these factors result in a relatively stable and synchronous birth season.     

Factors influencing seasonal and monthly changes in the group size of chital or axis deer in southern India

Chital or axis deer (Axis axis) form fluid groups that change in size temporally and in relation to habitat. Predictions of hypotheses relating animal density, rainfall, habitat structure, and breeding seasonality, to changes in chital group size were assessed simultaneously using multiple regression models of monthly data collected over a 2 yr period in Guindy National Park, in southern India. Over 2,700 detections of chital groups were made during four seasons in three habitats (forest, scrubland and grassland). In scrubland and grassland, chital group size was positively related to animal density, which increased with rainfall. This suggests that in these habitats, chital density increases in relation to food availability, and group sizes increase due to higher encounter rate and fusion of groups. The density of chital in forest was inversely related to rainfall, but positively to the number of fruiting tree species and availability of fallen litter, their forage in this habitat. There was little change in mean group size in the forest, although chital density more than doubled during the dry season and summer. Dispersion of food items or the closed nature of the forest may preclude formation of larger groups. At low densities, group sizes in all three habitats were similar. Group sizes increased with chital density in scrubland and grassland, but more rapidly in the latter—leading to a positive relationship between openness and mean group size at higher densities. It is not clear, however, that this relationship is solely because of the influence of habitat structure. The rutting index (monthly percentage of adult males in hard antler) was positively related to mean group size in forest and scrubland, probably reflecting the increase in group size due to solitary males joining with females during the rut. The fission-fusion system of group formation in chital is thus interactively influenced by several factors. Aspects that need further study, such as interannual variability, are highlighted.     

Primary production dynamics and climate variability: ecological consequences in semiarid Chile

Increase in rainfall variability has important consequences for organisms in arid and semiarid regions around the world. In South American and Australian deserts, the El Niño/Southern Oscillation (ENSO) phenomenon greatly influences rainfall patterns, and therefore the dynamics of plant communities. However, the field data needed to assess the effect of climate change on vegetational patterns is difficult to obtain because of the large spatial scale required for such studies. Normalized Difference Vegetation Index (NDVI) characteristics allow the use of several indexes related to vegetational structure. Due to its direct relationship with primary productivity, it is possible to obtain several measures of annual productivity. These include annual plant yield, annual maximum yield, onset of 'greening-up' and senescence phases, length of the 'green' season, vegetation peak, and therefore, the periods when more or less food is available for herbivores. After verification with ground-truth measures, we used NDVI data from two semiarid localities in north-central Chile (Fray Jorge and Aucó) to determine the relationship between rainfall patterns and vegetation cover and productivity related to El Niño phenomenon. With this information we gauge the influence of climatic processes on primary productivity in western South America, an area subject to strong climate variability. We predict significant variation in Chilean semiarid regions due to climate change, affecting mainly the extent and timing of annual growth season of vegetation, and also including a shorter and delayed greening-up season. Also, we predict that important decreases in rainfall levels will not have strong effects on primary production in these semiarid ecosystems.     

Long‐lived and heavier females give birth earlier in roe deer

In seasonal environments, parturition of most vertebrates generally occurs within a short time‐window each year. This synchrony is generally interpreted as being adaptive, as early born young survive better over the critical season than late born young. Among large herbivores, the factors involved in driving among‐ and within‐individual variation in parturition date are poorly understood. We explored this question by analyzing the relative importance of attributes linked to female quality (longevity, median adult body mass and cohort), time‐dependent attributes linked to female condition (reproductive success the previous year, relative annual body mass and offspring cohort (year)), and age in shaping observed variation in parturition date of roe deer. A measure of quality combining the effects of female longevity and median adult body mass accounted for 11% of the observed among‐individual variation in parturition date. Females of 2 yr old give birth 5 d later than older females. Our study demonstrates that high quality (heavy and long‐lived) females give birth earlier than low quality females. Temporally variable attributes linked to female condition, such as reproductive success in the previous year and relative annual body mass, had no detectable influence on parturition date. We conclude that parturition date, a crucial determinant of reproductive success, is shaped by attributes linked to female quality rather than by time‐dependent attributes linked to female condition in income breeders (individuals that rely on current resource intake rather than on accumulated body reserves to offset the increased energy requirements due to reproduction) such as roe deer.     

Pyric Herbivory and the Nexus Between Forage,Fire and Native and Introduced Large Grazing Herbivores in Australian Tropical Savannas

Earth’s tropical savannas typically support high biomass of diverse grazing herbivores that depend on a highly fluctuating resource: high-quality forage. An annual wet–dry cycle, fire and herbivory combine to influence forage quality and availability throughout the year. In the savannas of northern Australia, a depauperate suite of large native (marsupial) herbivores (wallaroos [Osphranter spp.] and the agile wallaby [Notamacropus agilis]) compete for resources with non-native large herbivores introduced in the late nineteenth century, particularly bovines (feral and managed cattle [Bos spp.] and feral water buffalo [Bubalus bubalis]) that now dominate the landscape. Anecdotal reports of recent population declines of large macropods and negative impacts of bovines highlight the need to better understand the complex relationship between forage, fire and abundance of native and introduced large herbivores. The pyric herbivory conceptual model, which posits complex feedbacks between fire and herbivory and was developed outside Australia, predicts that native and introduced large herbivores will both respond positively to post-fire forage production in Australian savannas where they co-occur. We used grazing exclosures, forage biomass and nutrient analyses and motion-sensor camera-trapping to evaluate the overall robustness of the pyric herbivory model in the Australian context, specifically whether forage quantity and quality are impacted by herbivory, season and fire activity, and which forage attributes most influence large grazing herbivore abundance. Forage quantity, as measured by live, dead and total herbaceous biomass and proportion of biomass alive, was higher inside herbivore exclosures, even at relatively low densities of herbivores. Forage quality, as measured by fibre content, was not affected by herbivory, however, crude protein content of live herbaceous biomass was greater outside herbivore exclosures. Recent fire was an important predictor of all measures of forage quantity and quality. Recent fire occurrence decreased overall quantity (biomass) but increased quality (decreased fibre content and increased crude protein content); late dry season fires resulted in forage with the highest crude protein content. The predictions of the pyric herbivory conceptual model are consistent with observations of the feeding behaviour of introduced bovines and some large macropods in northern Australian savannas, lending support to the global generality of pyric herbivory in fire-prone grassy biomes.

     

Earlier pupping in harbour seals,Phoca vitulina

The annual reproductive cycle of most seal species is characterized by a tight synchrony of births. Typically, timing of birth shows little inter-annual variation. Here, however we show that harbour seals Phoca vitulina from the Wadden Sea (southeast North Sea) have shortened their yearly cycle, moving parturition to earlier dates since the early 1970s. Between 1974 and 2009, the birth date of harbour seals shifted on average by −0.71 d yr⁻¹, three and a half weeks (25 days) earlier, in the Dutch part of the Wadden Sea. Pup counts available for other parts of the Wadden Sea were analysed, showing a similar shift. To elucidate potential mechanism(s) for this shift in pupping phenology, possible changes in population demography, changes in maternal life-history traits and variations in environmental conditions were examined. It was deduced that the most likely mechanism was a shortening of embryonic diapause. We hypothesize that this could have been facilitated by an improved forage base, e.g. increase of small fishes, attributable to overfishing of large predator fishes and size-selective fisheries.     

Controls over reproductive phenology among ungulates: allometry and tropical‐temperate contrasts

Ungulates inhabiting high latitudes schedule the timing of conceptions so that offspring are born during the most favourable nutritional conditions for reproductive success. The optimal period for births is less reliably predictable in tropical and subtropical savanna environments where plant growth is governed by rainfall, suggesting that reproductive phenology could be influenced more proximately by resources affecting the body condition of females around the time of conceptions. To assess how these controls operate, we compared the timing of births and conceptions among tropical and subtropical savanna ungulates with the patterns shown by ungulates in northern temperate or subarctic latitudes. The association between the timing of births and the onset of plant growth early in the growing season is less consistent among tropical savanna ungulates than among ungulates inhabiting northern temperate environments, and apparently subject to other influences affecting vegetation phenology. Nevertheless, birth peaks seem to coincide with the time of the year when forage quality is expected to be best for offspring survival and growth for most tropical or subtropical ungulates with gestation periods shorter than a year. When gestation time exceeds one year, proximal effects of nutritional conditions around the time of conceptions apparently become overriding and birth synchrony with early season plant growth is no longer effective. Proximate nutritional influences on conceptions may also govern the somewhat diffuse spread of births shown by ungulate populations in equatorial latitudes where photoperiod cues controlling oestrus and mating cannot be used to schedule the later timing of births.     

Correlated patterns of variation in phenology and seed production in populations of two annual grasses along an aridity gradient

I applied a comparative approach to reveal correlated patterns of variation in phenology and seed production in four populations of two annual grasses Hordeum spontaneum and Avena sterilis, sampled in the same environments distributed along an aridity gradient in Israel. The steep aridity gradient in Israel represents two parallel clines of environmental productivity (annual rainfall) and predictability (variation in amount and timing of annual rainfall) that is likely to induce similar responses in natural plant populations distributed along the gradient, if (1) selection is strong, (2) species share the same ecological niche, and (3) there is genetic variation for ecologically important traits. I found in plants of both species (1) ultimate advance in onset of flowering, and (2) more but smaller seeds, with increasing aridity. The broad sense heritabilities of onset of flowering, seed size and seed yield in both species were very high, moderate and low, respectively. It appears that the observed adaptive complex of traits have evolved in both species in response to this specific array of environments.     

Seasonal and annual variability in the quality of important forage plants on Banks Island,Canadian High Arctic

Abstract. In vitro acid‐pepsin digestibility (IVDMD), crude protein (CP), fibre, lignin, and energy content were measured for a variety of forage plants collected annually from Banks Island over five summers and three winters from 1993–1998. Summer samples were collected during mid‐June (start of growing season), mid‐July (peak of growing season), and mid‐late August (senescence). Winter samples were collected in early (November), mid‐ (February), and late‐ (April/May) winter. Samples, collected in areas of both high and low muskox density, included Carex aquatilis, unidentified Carex, Salixarctica, Dryasintegrifolia, Cassiope tetragona, Saxifraga spp., Astragalus spp., Oxytropis spp., lichen, and grass. Seasonal dynamics in forage quality during the growing season were similar to those reported elsewhere in the arctic and high arctic and were consistent across years. However, there were significant year effects in lignin, fibre, and energy content of forages and the crude protein (CP) content of C. aquatilis in winter, indicating annual differences in the quality of forage available to herbivores. The quality of forages on Banks Island was similar between areas subjected to different densities of muskox (ca. 1.6–1.9 versus 0.3 ‐ 0.4/km²) implying that quality was not affected by these grazing intensities. The Banks Island high arctic ecosystem supports an abundance of herbivores. It has been hypothesized that this is because forage quality and/or quantity are superior on Banks Island than elsewhere in the high arctic. Our results regarding forage quality are equivocal. Although the maximum CP content of forages from Banks Island was generally higher than reported elsewhere in the arctic and high arctic, CP content reported elsewhere fell within the interannual range reported from Banks Island. Fibre and energy content of forages from Banks Island were similar to slightly lower than elsewhere in the arctic and high arctic. Such comparisons must be considered in light of the interannual variability in quality we report.     

Spatial variability in the nutrient composition of Populus tremuloides: clone-to-clone differences and implications for cervids

Summary Populus tremuloides, a clonal angiosperm, is a major food item for many temperate-region herbivores. Clonal variation in chemical composition has potentially important implications for vertebrate herbivores because a single clone may be areally large and hence, may comprise a large part of available forage. The objectives of this study were: (1) to examine spatial variability in nutrient concentrations and quality within and among 24 clones of trembling aspen, and (2) to evaluate these differences with respect to cervid nutritional requirements; notably Cervus elaphus and Odocoileus hemionus. Between-clone concentrations of all chemical components were significantly different. In terms of cervid nutrition, most clones provided adequate concentrations of Ca, Mg, Mn, and Zn. Crude protein was limiting in some clones and P in most. Additionally, P metabolism may be impaired by the high Ca:P ratios typical of some clones. Of the structural constituents, neutral detergent fiber showed the greatest intraclonal variability. Dry-matter digestibility varied sufficiently to conjecture that cervid energy balances may be affected. Overall, although clone-to-clone differences were not so substantial to conclude that selective browsing would be nutritionally cost-effective, it is proposed that cervids stand to benefit by fortuitously browsing on nutritionally superior clones owing to the multiplier effect.     

Extreme precipitation variability,forage quality and large herbivore diet selection in arid environments

Nutritional ecology forms the interface between environmental variability and large herbivore behaviour, life history characteristics, and population dynamics. Forage conditions in arid and semi‐arid regions are driven by unpredictable spatial and temporal patterns in rainfall. Diet selection by herbivores should be directed towards overcoming the most pressing nutritional limitation (i.e. energy, protein [nitrogen, N], moisture) within the constraints imposed by temporal and spatial variability in forage conditions. We investigated the influence of precipitation‐induced shifts in forage nutritional quality and subsequent large herbivore responses across widely varying precipitation conditions in an arid environment. Specifically, we assessed seasonal changes in diet breadth and forage selection of adult female desert bighorn sheep Ovis canadensis mexicana in relation to potential nutritional limitations in forage N, moisture and energy content (as proxied by dry matter digestibility, DMD). Succulents were consistently high in moisture but low in N and grasses were low in N and moisture until the wet period. Nitrogen and moisture content of shrubs and forbs varied among seasons and climatic periods, whereas trees had consistently high N and moderate moisture levels. Shrubs, trees and succulents composed most of the seasonal sheep diets but had little variation in DMD. Across all seasons during drought and during summer with average precipitation, forages selected by sheep were higher in N and moisture than that of available forage. Differences in DMD between sheep diets and available forage were minor. Diet breadth was lowest during drought and increased with precipitation, reflecting a reliance on few key forage species during drought. Overall, forage selection was more strongly associated with N and moisture content than energy content. Our study demonstrates that unlike north‐temperate ungulates which are generally reported to be energy‐limited, N and moisture may be more nutritionally limiting for desert ungulates than digestible energy.     

Environmentally cued parturition in a desert rattlesnake,Crotalus atrox

Embryonic development in animals is dynamically regulated by physiological, behavioural, and environmental factors (temperature, precipitation, humidity), which in turn influence the timing of birth or hatching. In the present study, we provide evidence that parturition in a large‐bodied North American pitviper, the western diamond‐backed rattlesnake (Crotalus atrox), is environmentally cued. Specifically, we tested the hypothesis of births coinciding with rainfall events during the second‐half of the monsoon season (late July to mid September) using randomization modelling. Twenty‐one adult females surgically implanted with radio‐transmitters were tracked for extended periods from 2001–2010. From 2003 to 2007, the 21 females gave birth to 38 litters, generating sufficient data to test our hypothesis. In all years, births were restricted to a 4‐week period from 5 August to 7 September, which spanned between 6 and 19 days (mean ± SD, 15 ± 5.2 days). Most births (92.1%) occurred in August. Births were significantly associated with rainfall events in 2007, although births in 2003 and 2005 occurred closer to rain events than randomly generated births for respective years. However, when birth events across all 5 years were pooled, the model indicated a significance difference in mean rain‐days versus random rain‐days. Hence, births occurred more closely to rain events than random days. Other variables associated with monsoon events (increases in cloud cover and humidity; changes in barometric pressure) were not measured but constitute potential cues. The present research is the first long‐term, individual‐based radio‐telemetric study of a snake species to investigate environmental cues related to parturition using procedures of randomization modelling. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 866–877.     

Impacts of savanna trees on forage quality for a large African herbivore

Recently, cover of large trees in African savannas has rapidly declined due to elephant pressure, frequent fires and charcoal production. The reduction in large trees could have consequences for large herbivores through a change in forage quality. In Tarangire National Park, in Northern Tanzania, we studied the impact of large savanna trees on forage quality for wildebeest by collecting samples of dominant grass species in open grassland and under and around large Acacia tortilis trees. Grasses growing under trees had a much higher forage quality than grasses from the open field indicated by a more favourable leaf/stem ratio and higher protein and lower fibre concentrations. Analysing the grass leaf data with a linear programming model indicated that large savanna trees could be essential for the survival of wildebeest, the dominant herbivore in Tarangire. Due to the high fibre content and low nutrient and protein concentrations of grasses from the open field, maximum fibre intake is reached before nutrient requirements are satisfied. All requirements can only be satisfied by combining forage from open grassland with either forage from under or around tree canopies. Forage quality was also higher around dead trees than in the open field. So forage quality does not reduce immediately after trees die which explains why negative effects of reduced tree numbers probably go initially unnoticed. In conclusion our results suggest that continued destruction of large trees could affect future numbers of large herbivores in African savannas and better protection of large trees is probably necessary to sustain high animal densities in these ecosystems.     

驯养林麝(Moschus berezovskii)的繁殖节律:分娩定时及同步化

于2013年3—10月在四川马尔康麝场开展,记录了178例驯养林麝(Moschus berezovskii)的分娩,分析了其分娩定时、同步化及关键影响因素。结果表明,马尔康麝场的驯养林麝分娩发生于5—7月间,分娩期长达66d,平均分娩时间为5月25日(17.60±0.98,n=178),分娩季节(75%的分娩完成时间)长22d(即5月7日至5月28日间)。马尔康林麝分娩的强季节性是对当地季节性水热条件和食物资源的适应。驯养林麝的分娩时间与其年龄的相关不显著(r=-0.121,P=0.1060.05),虽亚成体雌麝(2—3岁)的分娩时间(5月26日,18.81±1.47,n=75)有迟于成体麝((4—9岁)(5月24日,16.97±1.41,n=95)和老龄雌麝(≥10岁)(5月21日,13.63±2.24,n=8)的趋势,但差异未达显著水平(P0.05)。此外,麝场各饲养区内的雌麝分娩时间格局无显著差异(P0.05),泥地基底的改装圈舍内的雌麝分娩(5月22日,15.31±1.48,n=62)略早于砖地基底的原装圈舍雌麝分娩(5月26日,18.82±1.27,n=116),差异未达显著水平(P0.05)。     

Succession and herbivory in monsoonal wetlands

This paper considers the applicability of the Gleasonian succession model to monsoonal wetlands, particularly those in Australia and India. The similarities in climate and taxa shared among these wetlands produce a setting in which successional cycles may be replicated. The Gleasonian succession model was first designed to describe cyclic changes in prairie pothole wetlands in response to water flux and herbivore activity over 5–25 year intervals. However, monsoonal wetlands change over an annual cycle. The Gleasonian succession may therefore be faster in these wetlands than in temperate ones. Herbivores create openings in flooded vegetation during the wet season in India by killing emergent species. During the dry season, Paspalum distichum revegetates these openings via the sprouting of vegetative fragments (VS-I; establishment by vegetative means in drawndown conditions). In Australia, in those monsoonal wetlands dominated by the annual Oryza meridionalis (AS-II; establishment by seed germination in flooded conditions), revegetation is from the seed bank during the wet season. The Gleasonian succession model can help to explain the invasion of exotics in monsoonal wetlands; in Australia, sites dominated by Oryza meridionalis (wet season annual) can be invaded during the dry season by Mimosa pigra (PS-I; perennial, establishment by seed germination in drawndown conditions). Thus the role of herbivores in succession is more complicated than current predictive models of vegetation change encompass. Herbivores select specific habitats over plant species, and also can form symbiotic relationships with plants as seed dispersers. Nonetheless, if appropriately modified with respect to the life history requirements of these plant species, the Gleasonian succession model is useful in describing annual and long-term changes in the vegetation of monsoonal wetlands.