Rain,prey and predators: climatically driven shifts in frog abundance modify reproductive allometry in a tropical snake

To predict the impacts of climate change on animal populations, we need long-term data sets on the effects of annual climatic variation on the demographic traits (growth, survival, reproductive output) that determine population viability. One frequent complication is that fecundity also depends upon maternal body size, a trait that often spans a wide range within a single population. During an eight-year field study, we measured annual variation in weather conditions, frog abundance and snake reproduction on a floodplain in the Australian wet-dry tropics. Frog numbers varied considerably from year to year, and were highest in years with hotter wetter conditions during the monsoonal season (“wet season”). Mean maternal body sizes, egg sizes and post-partum maternal body conditions of frog-eating snakes (keelback, Tropidonophis mairii, Colubridae) showed no significant annual variation over this period, but mean clutch sizes were higher in years with higher prey abundance. Larger females were more sensitive to frog abundance in this respect than were smaller conspecifics, so that the rate at which fecundity increased with body size varied among years, and was highest when prey availability was greatest. Thus, the link between female body size and reproductive output varied among years, with climatic factors modifying the relative reproductive rates of larger (older) versus smaller (younger) animals within the keelback population.     

Possible causes of decreasing migratory ungulate populations in an East African savannah after restrictions in their seasonal movements

In many areas in Africa, seasonal movements of migratory ungulates are restricted and their population numbers decline, for example in the Tarangire region, Tanzania. Here, agriculture restricts migration of ungulates to their wet season ranges. We investigated whether low forage quality or supply are possible causes of population decline of wildebeest and zebra when access to these wet season ranges is restricted and migratory herds have to reside in the dry season range year-round. We simulated grazing through a clipping experiment in the dry season range during the wet season. Clipping negatively affected forage supply and had a positive effect on forage quality by increasing proportions of live and leaf biomass as well as nutrient concentrations in the leaves. However, increase in forage quality in the dry season range due to grazing was not as such that requirements of wildebeest during the wet season, when females are lactating, could be met. We conclude that low forage quality in the dry season range during the wet season could cause the decrease in migratory ungulate populations in the Tarangire region. With this study, the necessity of protecting wet season ranges from expanding human activities to safeguard migratory systems is supported.     

How season of grazing and herbivore selectivity influence monsoon tall-grass communities of northern Australia

Abstract. The hypothesis that season of defoliation and herbivore selectivity may be as important as level of use in determining plant community response to grazing was tested in a monsoon grassland in northern Australia. Plots, dominated by the tussock grasses Themeda triandra and Chrysopogon fallax, were grazed by cattle at low, medium and high rates of utilization in either the early wet, late wet or dry seasons. Effects of grazing on species composition were greatest in the early wet season when high rates of utilization significantly reduced the proportion and occurrence of Themeda and increased the proportion of forbs. Grazing in the dry season had no significant effect on composition. At medium and high levels of utilization in the early wet season, the pasture responded negatively to defoliation, only partially compensating for plant tissue lost to herbivory. The negative response to defoliation carried over to the next wet season when these same medium and high-grazing treatments produced only 80 % and 60 % growth, respectively, of that in treatments grazed at low levels of utilization or those grazed during the dry season. The frequency of Themeda was still lower, and that of annual grasses and non-leguminous forbs higher, in plots that had been grazed at a high rate of utilization for just eight weeks in the early wet season two years previously. Species richness and diversity were also significantly affected by this grazing disturbance. If species composition is to be maintained in these grasslands then stocking rates must be set at low levels to cope with the combined effect of undercompensation in response to defoliation in the wet season and strong dietary preferences for grazing sensitive species.     

Climatic seasonality, resource bottlenecks, and abundance of rainforest birds: implications for global climate change

We demonstrate that within-year climatic variability, particularly rainfall seasonality, is the most significant variable explaining spatial patterns of bird abundance in Australian tropical rainforest. The likely mechanism causing this pattern is a resource bottleneck (insects, nectar, and fruit) during the dry season that limits the population size of many species. The patterns support both the diversity–climatic–stability hypothesis and the species–energy hypothesis but clearly show that seasonality in energy availability may be a more significant factor than annual totals or means. An index of dry season severity is proposed that quantifies the combined effect of the degree of dryness and the duration of the dry season. We suggest that the predicted increases in seasonality due to global climate change could produce significant declines in bird abundance, further exacerbating the impacts of decreased range size, increased fragmentation, and decreased population size likely to occur as a result of increasing temperature. We suggest that increasing climatic seasonality due to global climate change has the potential to have significant negative impacts on tropical biodiversity.     

Climate‐driven fluctuations in surface‐water availability and the buffering role of artificial pumping in an African savanna: Potential implication for herbivore dynamics

Abstract In arid and semiarid environments surface‐water strongly constrains the distribution and abundance of large herbivores during the dry season. Surprisingly, we know very little about its variability in natural ecosystems. Here we used long‐term data on the dry‐season occurrence of water at individual waterholes to model the surface‐water availability across Hwange National Park, Zimbabwe, under contrasted climatic and management scenarios. Without artificial pumping only 19.6% of the park occurred within 5 km of water under average climatic conditions. However surface‐water availability was strongly influenced by annual rainfall, and over 20 years the variability of the surface area of the park occurring within 5 km of water was slightly larger than the variability of rainfall. This contrasts with the usual buffered response of vegetation production to rainfall fluctuations, and suggests that the variability in dry‐season foraging range determined by surface‐water availability could be the main mechanism regulating the population dynamics of large herbivores in this environment. Artificial pumping increased surface‐water availability and reduced its variability over time. Because changes in surface‐water availability could cause the greatest changes in forage availability for large herbivores, we urge ecologists to investigate and report on the variability of surface‐water in natural ecosystems, particularly where rapid climate changes are expected.     

Influence of seasonal variation to the population growth and ecophysiology of Typha domingensis (Typhaceae)

Journal of Plant Research - Precipitation is an important climatic element that defines the hydrological regime, and its seasonal variation produces annual dry and wet periods in some areas. This...     

Elephant spatial use in wet and dry savannas of southern Africa

The influence of elephants on woody vegetation cover varies from place to place. In part this may be due to the way elephants utilize space across landscapes and within their home ranges in response to the availability and distribution of food. We used location data from 18 cows at six study sites across an east to west rainfall gradient in southern Africa to test whether wet- and dry-season home-range sizes, evenness of space use within seasonal home ranges and range overlap between seasons and between years, differed between wet and dry savannas. We then tested whether the quantity, distribution and seasonal stability in vegetation productivity, a coarse measure of food for elephants, explained differences. Elephants in wet savannas had smaller wet- and dry-season home ranges and also returned to a higher proportion of previously visited grid cells between seasons and between years than elephants living in dry savannas. Wet-season home-range sizes were explained by seasonal vegetation productivity while dry-season home-range sizes were explained by heterogeneity in the distribution of vegetation productivity. The influence of the latter on dry-season home ranges differed among structural vegetation classes. Range overlap between seasons and between years was related to inter-seasonal and inter-annual stability in vegetation productivity, respectively. Evenness of elephant spatial use within home ranges did not differ between savanna types, but it was explained by seasonal vegetation productivity and heterogeneity in the distribution of vegetation productivity during the wet season. Differences in elephant spatial use patterns between wet and dry savannas according to vegetation structure and season may need to be included in the development of site-specific objectives and management approaches for African elephants.     

The role of wetlands in wildlife migration in the Tarangire ecosystem,Tanzania

Twenty-two years of rainfall data from six sites, 5 years of animal migration data and 2 years of water quality at 13 sites were explored to quantify the role of water in the Tarangire ecosystem. Inter-annual fluctuations in rainfall were large and not predictable solely from the Southern Oscillation Index. Seasonal fluctuations of rainfall were pronounced, with marked wet and dry seasons. In the dry season, the only drinking water available for wildlife was the Tarangire River and a number of small, scattered wetland-fringed water holes. Their salinity was often high (>8 ppt) and was higher in dry years than in wet years, as well as at the start of the wet season. Water quantity and quality may control the annual migration of wildebeest, zebra, elephants and buffaloes. These animals aggregate in the dry season in areas with the least salty water. The timing of seasonal variations in rainfall is largely predictable and controls annual migration. All wildebeest and most zebras migrated out of Tarangire National Park and into the wider Tarangire ecosystem at the start of the wet season, and they returned into the park in the dry season. Some elephants and buffaloes also migrated in out of the park and a larger resident population remained, whose size may vary inter-annually depending on surface water quantity and quality. The extent of the migration zone may also vary inter-annually.This revised version wa published online in March 2005 with corrections to the issue cover date.     

Effects of seed size and emergence time on tree seedling establishment: importance of developmental constraints

Arafura filesnakes (Acrochordus arafurae) are large (up to 2.5 m, 5 kg) aquatic nonvenomous snakes that feed entirely on fishes. A 10-year field study in the Australian wet-dry tropics revealed strong correlations between rainfall patterns, fish abundance, and snake population dynamics. All of these characteristics showed considerable annual variation. High rainfall late in the wet season (February–March) caused prolonged inundation of the floodplain. Following such years, dry-season sampling revealed that fishes were abundant, filesnakes were in good body condition, and a high proportion of adult female filesnakes were reproductive. Annual variation in recruitment to the population (as judged by the relative abundance of yearling snakes) was also correlated with fish abundance and thus, with rainfall patterns in the late-wet season. Our results fit well with those from other studies on a diverse array of aquatic and terrestrial species within the wet-dry tropics. Annual variation in rainfall patterns, via its effects on prey abundance, may drive the population dynamics of many tropical predators. Received: 28 June 1999 / Accepted: 29 February 2000     

埃塞俄比亚Senkele Swayne保护区斯韦恩麋羚的种群现状与结构

于2005年10月至2006年4月调查了埃塞俄比亚森可勒斯韦恩麋羚保护区旱季和湿季斯韦恩麋羚(Alcelaphus buselaphus swaynei)的种群现状与结构.根据植被类型、道路和沟谷,将研究区划分为5个区域,并且调查了保护区外的一块休耕农地.利用全部计数法计数了每个区域内的斯韦恩麋羚,在28 km2的区域内共统计到283只(湿季)和351只(旱季)麋羚,湿季和旱季的麋羚数量变化显著,其季节间差异是由旱季的出生高峰造成的.斯韦恩麋羚种群中雌性个体占42.7%、雄性占36.0%、幼羚占21.3%.某些区域的麋羚数量要高于其它区域,且无论湿季或旱季斯韦恩麋羚多集中在狼尾草高草地中.斯韦恩麋羚的种群结构随季节而变化,其大集群经常出现在湿季而旱季集群较小.斯韦恩麋羚的种群动态因保护程度的不同在不同时期呈不规则性变化     

Linking Vital Rates of Landbirds on a Tropical Island to Rainfall and Vegetation Greenness

Remote tropical oceanic islands are of high conservation priority, and they are exemplified by range-restricted species with small global populations. Spatial and temporal patterns in rainfall and plant productivity may be important in driving dynamics of these species. Yet, little is known about environmental influences on population dynamics for most islands and species. Here we leveraged avian capture-recapture, rainfall, and remote-sensed habitat data (enhanced vegetation index [EVI]) to assess relationships between rainfall, vegetation greenness, and demographic rates (productivity, adult apparent survival) of three native bird species on Saipan, Northern Mariana Islands: rufous fantail (Rhipidura rufifrons), bridled white-eye (Zosterops conspicillatus), and golden white-eye (Cleptornis marchei). Rainfall was positively related to vegetation greenness at all but the highest rainfall levels. Temporal variation in greenness affected the productivity of each bird species in unique ways. Predicted productivity of rufous fantail was highest when dry and wet season greenness values were high relative to site-specific 5-year seasonal mean values (i.e., relative greenness); while the white-eye species had highest predicted productivity when relative greenness contrasted between wet and dry seasons. Survival of rufous fantail and bridled white eye was positively related to relative dry-season greenness and negatively related to relative wet-season greenness. Bridled white-eye survival also showed evidence of a positive response to overall greenness. Our results highlight the potentially important role of rainfall regimes in affecting population dynamics of species on oceanic tropical islands. Understanding linkages between rainfall, vegetation, and animal population dynamics will be critical for developing effective conservation strategies in this and other regions where the seasonal timing, extent, and variability of rainfall is expected to change in the coming decades.     

Temporal population genetic structure of eastern mosquitofish in a dynamic aquatic landscape

We analyzed the effect of periodic drying in the Florida Everglades on spatiotemporal population genetic structure of eastern mosquitofish (Gambusia holbrooki). Severe periodic drying events force individuals from disparate sources to mix in dry season relatively deep-water refuges. In 1996 (a wet year) and 1999 (a dry year), we sampled mosquitofish at 20 dry-season refuges distributed in 3 water management regions and characterized genetic variation for 10 allozyme and 3 microsatellite loci. In 1996, most of the ecosystem did not dry, whereas in 1999, many of our sampling locations were isolated by expanses of dried marsh surface. In 1996, most spatial genetic variation was attributed to heterogeneity within regions. In 1999, spatial genetic variation within regions was not significant. In both years, a small but significant amount of variation (less than 1% of the total variation) was partitioned among regions. Variance was consistently greater than zero among long-hydroperiod sites within a region, but not among short-hydroperiod sites within a region, where hydroperiod was measured as time since last marsh surface dry-down forcing fishes into local refuges. In 1996, all sites were in Hardy-Weinberg equilibrium. In 1999, we observed fewer heterozygotes than expected for most loci and sites suggesting a Wahlund effect arising from fish leaving areas that dried and mixing in deep-water refuges.     

Natural history of small mammals of subtropical montane areas in central Taiwan

Based on samples collected in 1989–90, I report on several aspects of the natural history of species of small mammals from seasonal montane areas in subtropical central Taiwan, including their reproduction, demography, sex ratio and body size. The climatic seasonality in the areas is striking. The wet season lasts from May through September and the dry season from October through April. The phenology of plant life is related to this seasonality: vegetative growth occurs primarily in the wet season, but fruit and seed production is concentrated in the dry season. Variation in the reproduction and demography are analysed between the wet and the dry season for six species, Apodemus semotus, Niviventer culturatus. Eothenomys melanogaster, Microtus Kikuchii, Anourosorex syuamipes and Soriculus fumidus . Two murid rodents. A semotus and N. culturatus. are capable of breeding year-round, whereas the microtine rodents, E. melanogaster and M. Kikuchii , have discrete breeding seasons. The shrews, A. squamipes and S. fumidus are both seasonal breeders. but they differ in the timing of their breeding cycles. While S. fumidus breeds primarily in the late dry season, A. syuamipes reproduces in the wet season. Finally, seasonal variation in reproduction is discussed in relation to phylogenetic and physio-ecological characteristics of these six species.     

Factors affecting seasonal habitat use,and predicted range of two tropical deer in Indonesian rainforest

There is an urgent recognized need for conservation of tropical forest deer. In order to identify some environmental factors affecting conservation, we analyzed the seasonal habitat use of two Indonesian deer species, Axis kuhlii in Bawean Island and Muntiacus muntjak in south-western Java Island, in response to several physical, climatic, biological, and anthropogenic variables. Camera trapping was performed in different habitat types during both wet and dry season to record these elusive species. The highest number of photographs was recorded in secondary forest and during the dry season for both Bawean deer and red muntjac. In models, anthropogenic and climatic variables were the main predictors of habitat use. Distances to cultivated area and to settlement were the most important for A. kuhlii in the dry season. Distances to cultivated area and annual rainfall were significant for M. muntjak in both seasons. Then we modelled their predictive range using Maximum entropy modelling (Maxent). We concluded that forest landscape is the fundamental scale for deer management, and that secondary forests are potentially important landscape elements for deer conservation. Important areas for conservation were identified accounting of habitat transformation in both study areas.     

Demographic responses of eastern bluebirds to climatic variability in northeastern Arkansas

As climate change continues to alter temperature and precipitation patterns, numerous species have declined. However, populations of some species that show responses to climate change, such as eastern bluebirds (Sialia sialis), have increased or remained stable nationwide. To understand how species are adapting to climate change, we estimated demographic parameters and their responses to climatic variability, using nesting and banding-recapture data between 2003 and 2018 in a northeastern Arkansas eastern bluebird population. Increasing variability in precipitation in the nonbreeding season negatively affected hatchability. Hatching success was negatively affected by increasing variability in maximum temperatures and the number of hot days during the breeding season, but positively affected by increasing winter snow depth. Adult survival was positively affected by increasing snow depth and variability in the number of hot days during the breeding season, but negatively affected by increasing variability in nonbreeding season temperatures. Our results demonstrate that for this study population, annual breeding parameters, though canalized against interannual environmental variation, were affected by seasonal climatic variability. Although climate change may benefit bluebird survival due to increasing variability in winter temperatures and the number of hot days, climatic variability negatively affected breeding parameters and is expected to increase. Because breeding parameters are typically the drivers of population growth rate in short-lived species, these results raise concern for the future of this population of eastern bluebirds.     

Climate variability and change over southern Africa: impacts and challenges

In this paper, the influence of climate variability and change on the environment was studied over southern Africa using ground-based and remotely sensed data. A time series analysis of rainfall and temperature anomalies indicated that there was a high rainfall and temperature variability in the region. The influence of global teleconnections on rainfall patterns over southern Africa showed that in some areas there was a spatial variation in their strength, increasing from west to east. Maps of NDVI, from 1982 to 2004, showed that changes in vegetation cover were more apparent during the dry season than during the wet season. The study also revealed that climate variability and change are linked to decreasing rainfall and hence, decreasing regional water resources and biodiversity and increasing environmental degradation. With the regional population expected increase, this depletion of resources poses the greatest regional environmental challenge to humankind.     

Scales of spatiotemporal variability in macroinvertebrate abundance and diversity in monsoonal streams: detecting environmental change

1. We quantified spatial and temporal variability in benthic macroinvertebrate species richness, diversity and abundance in six unpolluted streams in monsoonal Hong Kong at different scales using a nested sampling design. The spatial scales were regions, stream sites and stream sections within sites; temporal scales were years (1997–99), seasons (dry versus wet seasons) and days within seasons. 2. Spatiotemporal variability in total abundance and species richness was greater during the wet season, especially at small scales, and tended to obscure site‐ and region‐scale differences, which were more conspicuous during the dry season. Total abundance and richness were greater in the dry season, reflecting the effects of spate‐induced disturbance during the wet season. Species diversity showed little variation at the seasonal scale, but variability at the site scale was apparent during both seasons. 3. Despite marked variations in monsoonal rainfall, inter‐year differences in macroinvertebrate richness and abundance at the site scale during the wet season were minor. Inter‐year differences were only evident during the dry season when streams were at base flow and biotic interactions may structure assemblages. 4. Small‐scale patchiness within riffles was the dominant spatial scale of variation in macroinvertebrate richness, total abundance and densities of common species, although site or region was important for some species. The proportion of total variance contributed by small‐scale spatial variability increased during the dry season, whereas temporal variability associated with days was greater during the wet season. 5. The observed patterns of spatiotemporal variation have implications for detection of environmental change or biomonitoring using macroinvertebrate indicators in streams in monsoonal regions. Sampling should be confined to the dry season or, in cases where more resources are available, make use of data from both dry and wet seasons. Sampling in more than one dry season is required to avoid the potentially confounding effects of inter‐year variation, although variability at that scale was relatively small.     

Climatic variation and the distribution of an amphibian polyploid complex

The establishment of polyploid populations involves the persistence and growth of the polyploid in the presence of the progenitor species. Although there have been a number of animal polyploid species documented, relatively few inquiries have been made into the large-scale mechanisms of polyploid establishment in animal groups. Herein we investigate the influence of regional climatic conditions on the distributional patterns of a diploid-tetraploid species pair of gray treefrogs, Hyla chrysoscelis and H. versicolor (Anura: Hylidae) in the mid-Atlantic region of eastern North America. Calling surveys at breeding sites were used to document the distribution of each species. Twelve climatic models and one elevation model were generated to predict climatic and elevation values for gray treefrog breeding sites. A canonical analysis of discriminants was used to describe relationships between climatic variables, elevation and the distribution of H. chrysoscelis and H. versicolor. There was a strong correlation between several climatic variables, elevation and the distribution of the gray treefrog complex. Specifically, the tetraploid species almost exclusively occupied areas of higher elevation, where climatic conditions were relatively severe (colder, drier, greater annual variation). In contrast, the diploid species was restricted to lower elevations, where climatic conditions were warmer, wetter and exhibited less annual variation. Clusters of syntopic sites were associated with areas of high variation in annual temperature and precipitation during the breeding season. Our data suggest that large-scale climatic conditions have played a role in the establishment of the polyploid H. versicolor in at least some portions of its range. The occurrence of the polyploid and absence of the progenitor in colder, drier and more varied environments suggests the polyploid may possess a tolerance of severe environmental conditions that is not possessed by the diploid progenitor. Our findings support the hypothesis that increased tolerance to severe environmental conditions is a plausible mechanism of polyploid establishment.     

Dry season watering alters the significance of climate factors influencing phenology and growth of saplings of savanna woody species in central Zambia,southern Africa

Although tree growth in southern African savannas is correlated with rainfall in the wet season, some studies have shown that tree growth is controlled more by rainfall in the dry season. If more rainfall occurred in the dry season in future climates, it would affect the growth of savanna trees, especially saplings that have shallower roots which limit access to subsoil water during the dry season when leaf flush and shoot extension occur. Recent paleobotanical evidence has revealed that there was relatively more precipitation in the dry season in eastern Africa in the Eocene than under the current climate. Saplings therefore can be expected to respond more to water addition during the dry season than mature trees that have more stored water and deeper roots that access subsoil water. Accordingly, I hypothesized that irrigation in the dry season should (i) advance the onset of the growing season, (ii) increase growth rates and (iii) alter the growth responses of saplings to climate factors. To test these hypotheses saplings of five savanna woody species were irrigated during the hot‐dry season at a site in central Zambia and their monthly and annual growth rates compared to those of conspecifics growing under control conditions. Although the responses among the species were variable, all irrigated saplings had significantly higher monthly and annual growth rates than control plants. In addition, dry season watering significantly altered the climatic determinants of sapling growth by either strengthening the role of the same climatic factors that were important under control conditions or displacing them altogether. In conclusion, more precipitation during the hot‐dry season is likely to have significant positive effects on sapling growth and consequently reduce the sapling‐tree transition periods and promote future tree population recruitment in some southern African savanna tree species.     

Drought acclimation among tropical forest shrubs (Psychotria,Rubiaceae)

Summary Mechanisms of dry-season drought resistance were evaluated for five evergreen shrubs (Psychotria, Rubiaceae) which occur syntopically in tropical moist forest in central Panama. Rooting depths, leaf conductance, tissue osmotic potentials and elasticity, and the timing of leaf production were evaluated. From wet to dry season, tissue osmotic potentials declined and moduli of elasticity increased in four and five species, respectively. Irrigation only affected osmotic adjustment by P. furcata. The other seasonal changes in leaf tissue properties represented ontogenetic change. Nevertheless, they made an important contribution to dry-season turgor maintenance. Small between-year differences in dry season rainfall had large effects on plant water status. In 1986, 51 mm of rain fell between 1 January and 31 March, and pre-dawn turgor potentials averaged <0.1 MPa for all five Psychotria species in March (Wright 1991). In 1989, 111 mm of rain fell in the same period, pre-dawn turgor potentials averaged from 0.75 to 1.0 MPa for three of the species in April, and only P. chagrensis lost turgor. The relation between leaf production and drought differed among species. P. limonensis was buffered against drought by the lowest dry-season conductances and the deepest roots (averaging 244% deeper than its congeners) and was the only species to produce large numbers of leaves in the dry season. P. chagrensis was most susceptible to drought, and leaf production ceased as turgor loss developed. For the other species, water stress during severe dry seasons may select against dry-season leaf production.