Seasonal differences in population‐, ensemble‐ and community‐level responses of bats to landscape structure in Amazonia

The amount (composition) and spatial arrangement (configuration) of forest patches in fragmented landscapes influence the accessibility, as well as the abundance and diversity of resources available to bats. Moreover, tropical fruit and insect abundance differ seasonally in response to changes in precipitation, and many bats in the family Phyllostomidae employ seasonal reproductive strategies. Because reproductive activities involve constraints on time and energy as well as increased nutritional demands, foraging behavior and home range size may differ between wet and dry seasons. Nonetheless, seasonal variation in response to landscape structure by bats has not been examined previously. Consequently, population‐, ensemble‐ and assemblage‐level responses of phyllostomids to landscape composition and configuration were quantified separately during the wet and dry season at three circular focal scales (1, 3 and 5 km radii) for 14 sites in fragmented lowland Amazon forest. Responses to landscape characteristics were scale‐dependent, species‐specific, and seasonal. Abundances of frugivores responded to landscape composition in the dry season and to landscape configuration in the wet season. Conversely, abundances of animalivores responded to landscape configuration in the dry season and to landscape composition in the wet season. Divergent responses to landscape structure between seasons suggest that variation in resource abundance and diversity play a significant role in structuring population‐, ensemble‐ and assemblage‐level patterns. As such, considerations of the effects of dietary flexibility and reproductive constraints on foraging strategies and habitat use may be important when designing management plans that successfully promote long‐term persistence of biodiversity in fragmented landscapes.     

Season‐modulated responses of Neotropical bats to forest fragmentation

Seasonality causes fluctuations in resource availability, affecting the presence and abundance of animal species. The impacts of these oscillations on wildlife populations can be exacerbated by habitat fragmentation. We assessed differences in bat species abundance between the wet and dry season in a fragmented landscape in the Central Amazon characterized by primary forest fragments embedded in a secondary forest matrix. We also evaluated whether the relative importance of local vegetation structure versus landscape characteristics (composition and configuration) in shaping bat abundance patterns varied between seasons. Our working hypotheses were that abundance responses are species as well as season specific, and that in the wet season, local vegetation structure is a stronger determinant of bat abundance than landscape‐scale attributes. Generalized linear mixed‐effects models in combination with hierarchical partitioning revealed that relationships between species abundances and local vegetation structure and landscape characteristics were both season specific and scale dependent. Overall, landscape characteristics were more important than local vegetation characteristics, suggesting that landscape structure is likely to play an even more important role in landscapes with higher fragment‐matrix contrast. Responses varied between frugivores and animalivores. In the dry season, frugivores responded more to compositional metrics, whereas during the wet season, local and configurational metrics were more important. Animalivores showed similar patterns in both seasons, responding to the same group of metrics in both seasons. Differences in responses likely reflect seasonal differences in the phenology of flowering and fruiting between primary and secondary forests, which affected the foraging behavior and habitat use of bats. Management actions should encompass multiscale approaches to account for the idiosyncratic responses of species to seasonal variation in resource abundance and consequently to local and landscape scale attributes.     

Phosphorus cycling in rainfed lowland rice ecosystems on sandy soils

Phosphorus cycling in rainfed lowland rice ecosystems is poorly understood. Soil drying and grazing of rice straw during the long dry season, the growth of volunteer pastures during the early wet season, and intermittent loss of soil-water saturation while the rice crop is growing are important distinguishing characteristics of the rainfed lowlands in relation to P cycling. We studied P cycling in an acid sandy rainfed lowland soil that covers about 30% of the rice growing area of Cambodia. Soils with similar properties in comparable rainfed sub- ecosystems occur in Laos and northeast Thailand. We developed a general schema of P pools and fluxes in the crop and soil for rice-based cropping systems in the rainfed lowlands of Cambodia. The schema was derived from a number of field experiments carried out over five consecutive cropping seasons to quantify the residual value of P fertiliser, P mass balances, soil P fractions, the effect on subsequent rice crops of crop residues and volunteer pastures incorporated into the soils, and the dynamics of P turnover in the soil. With a single rice crop yielding 2.5–3 t ha⁻¹, application of 8–10 kg P ha⁻¹ maintained yields and a small positive P balance in the soil. However, the soil P balance was sensitive to the proportion of rice straw returned to the soil. Volunteer pastures growing during the early wet season accumulated significant amounts of P, and increased their P uptake when soils were previously fertilised with P. These pastures recycled 3–10 kg P ha⁻¹ for the succeeding rice crops. While inorganic soil P pools extractable with ion exchange resins and 0.1 M NaOH appeared to be the main source of P absorbed by rice, microbial and organically-bound P pools responded dynamically to variation in soil water regimes of the main wet, dry and early wet seasons. The schema needs to be developed further to incorporate site-specific conditions and management factors that directly or indirectly affect P cycling, especially loss of soil-water saturation during the rice cropping cycle. The paper discusses the application of results for acid sandy soils to other significant rice soils in the rainfed lowlands of southeast Asia.     

Testing the importance of nest concealment: does timing matter?

ABSTRACT.   Nest concealment by vegetation is considered an important factor affecting predation rates for many passerines and, therefore, is frequently measured in studies examining nest predation. However, the time when concealment measurements are made may affect the results of such studies, particularly in highly seasonal ecosystems where characteristics of the vegetation later in the breeding period may differ considerably from those at the time of nest-site selection. We used artificial nests baited with quail ( Coturnix sp.) eggs in a highly seasonal tropical dry forest in Jalisco, western Mexico, to test the effects of seasonal change in concealment on nest predation. We placed 40 open-cup, artificial nests in shrubs at the end of the dry season and again at the beginning of the rainy season in 2007, and monitored the fate of the nests and the degree of concealment by vegetation during both periods. Nest concealment was significantly greater during the wet season than during the dry season. The percentage of nests predated was marginally higher during the dry (100%) than the wet (72.5%) season, and daily nest survival was lower during the dry than the wet season. Our results suggest that, in highly seasonal environments such as tropical dry forests, delayed measurement of nest concealment after nest completion rather than during nesting may constitute a significant source of error.     

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.     

Restricted habitat use by an African savanna herbivore through the seasonal cycle: key resources concept expanded

Areas within regional landscapes that make a disproportionate contribution to supporting large herbivore populations have been interpreted as key resource areas, hotspots, buffers, stepping stones or serving other functional roles. We investigated the role that the restricted extent of habitat types exploited at different stages of the seasonal cycle might play in limiting the abundance of a blue wildebeest subpopulation in the Kruger National Park, South Africa. GPS collars enabled the space use patterns of the animals to be related to available habitat types, and faecal nutrient concentrations to be related to the habitats exploited at that time. Wildebeest herds occupied primarily grazing lawn grasslands associated with gabbro uplands or sodic lowlands through the wet season into the early dry season. During the late dry season, they switched to seep‐zone grasslands in mid slope regions of granitic landscapes. Use of recently burned areas enhanced forage quality at the beginning of the wet season. The seasonal habitat shifts enabled wildebeest to obtain adequate nitrogen, phosphorus and sodium throughout the year. Lawn and seep‐zone grasslands combined constituted 10% of the available area. Grazing lawns, which encompassed only ? 3% of the study area, appeared to be the primary limitation on the abundance of wildebeest. However, the greater security from predation provided by the open vegetation cover in the grazing lawns is not easily disentangled from the resource benefits that they yield. Nevertheless, findings indicate how local abundance can be restricted by the extent of portions of the landscape providing crucial benefits during particular phases of the seasonal cycle. Hence the key resources concept needs to be expanded to accommodate the functionally distinct contributions made by different habitats towards supporting local herbivore populations.     

Seasonal cues in tropical organisms. Rainfall? Not necessarily!

Summary Activity seasons of tropical organisms often start, on the average, at or about the beginning of the rainy or dry seasons. The hypothesis that the onset or cessation of the wet season provides the seasonal cues necessary of the initiation of the activity season of some tropical organisms is tested with data on Panamanian cicadas. Seasonal adult activity patterns are described for cicada species in Panama, mostly from Barro Colorado Island (BCI), some from Las Cumbres. In all species the correlation between the timing of the beginning and the end of the cicada season was low and not significant, so that the actual beginning data of a cicada season in a particular year had little or no predictive value for the end date. Seven out of eleven species on BCI started their average activity season at the average beginning of the dry season (one species) or rainy season (six species). Nevertheless, in 13 years, correlations between the start or end of the cicada seasons and that of the meteorological seasons were low and not significant. At best, the beginning and end of the rains played a minor role as seasonal cues governing cicada emergence or the termination of the cicada season. It is speculated that photoperiod might be a major seasonal cue governing emergence, through its effects on the host plants.     

Habitat preferences,seasonal abundance and diets of rodents in Alage,Southern Ethiopia

To understand habitat preferences, seasonal abundance and diets of rodents in wet and dry season surveys were conducted in Alage, Southern Ethiopia. Sherman and snap traps were used to capture rodents from the four habitats: bushland, Acacia woodland, maize and wheat farmlands. A total of 3312 trap nights, from the four trapping habitats, yielded 776 individuals that represented 11 species of rodents. The distribution of rodents varied between habitats and seasons. Wet season rodent abundance was 52.3% while in the dry season it was 47.7%. Seasonal differences in species abundance were insignificant. Bushland habitat had high wet and dry season abundances with 137 and 211 individuals, respectively. Abundance was low in maize farm (57 individuals) in the wet season and wheat farm (10 individuals) in the dry season. Stomach content composition analysis of snap‐trapped rodents from different habitats showed differences between species and across seasons. Six rodent species were recorded as pests on the farmlands in this study area. In conclusion, variation in habitat preferences and diet of rodents in different habitats and across seasons might be due to the role of ground cover and food sources.     

Current population estimate and distribution of the African buffalo in Chebera Churchura National Park,Ethiopia

An investigation into the population status and distribution of the African buffalo (Syncerus caffer Sparrman, 1779) in Chebera Churchura National Park, Ethiopia, was carried out during the wet and dry seasons of 2012–2015. This study tested the hypothesis that buffalo would demonstrate seasonal habitat preferences and changes in population density. Sample counts were carried out in an area of 1215 km². The estimated buffalo population was 5193 individuals, with the population density of 4.3/km². The population showed an increase from 2617 to 5194 individuals during 2006–2015. Males comprised 42.6%, while females 46.7% of the population. Age structure was dominated by adults, which constituted 52.5% of the total population. Subadults comprised 24.3% and young 12.4% of the population. Larger herds of up to 30 individuals were observed during the wet season, and smaller herds of a minimum of four individuals were seen during the dry season. The mean herd sizes during the wet and dry seasons were 29.59 and 16.95, respectively. They were observed more in the riverine vegetation types during the dry season. Of the total, 57.6% utilized riverine habitat during the dry season, whereas 39.8% used this habitat during the wet season. Relative abundance of food sources, green vegetation cover and availability of water were the major factors governing their distribution in the present study area.     

A preliminary investigation of temporal patterns in semiarid ant communities: Variation with habitat type

Abstract This study reports on preliminary findings of habitat‐contingent temporal variability in ant assemblages in Purnululu National Park in northern Australia's semiarid tropics, by sampling at the end of the dry season (October 2004) and the end of the wet season (April 2005). Six grids of 15 pitfall traps were established in each of the spinifex, sandplain and gorge habitats. Community composition was dominated by behaviourally dominant ants (Iridomyrmex spp.) and climate specialists (Melophorus and Meranoplus spp.). Ant activity was higher in the wet season sampling period, with greater species richness and abundance. Interestingly, temporal variation in ant assemblage richness, abundance and composition varied markedly with habitat type. While there were large differences between sampling periods for the spinifex and sandplain habitat, this was not the case in the gorges. These temporal changes in ant assemblages are postulated to be linked with major environmental differences between the two sampling periods, driven by seasonal climatic conditions. It is likely that these changes influenced the ant assemblages through species differences in physiological tolerance levels, ecological requirements and competitive ability. This study demonstrates the need, in highly seasonal environments, to consider the temporal context of studies in relation to habitat type, particularly when undertaking biodiversity surveys and monitoring.     

Abundance and Leaf Damage Caused by Gall‐Inducing Insects in a Mexican Tropical Dry Forest1

We evaluated the temporal and spatial patterns of abundance and the amount of damage caused by gall‐inducing insects (GII) in deciduous and riparian habitats in a seasonal tropical dry forest in Mexico. Plants occurring in these habitats differ in their phenology and moisture availability. Deciduous habitats are seasonal and xeric, while riparian habitats are aseasonal and mesic. We found 37 GII species and each one was associated with a specific plant species. In total, 19 species (51.3%) were present in deciduous habitats, 13 species (35.2%) in riparian habitats, and only 5 species (13.5%) occurred in both. Abundance and leaf damage by GII were greater in deciduous than in riparian habitats during the wet season. For each GII species that occurred in both habitats, host plant species supported greater abundance and leaf damage by GII in deciduous habitats during the wet season. These results indicate a greater association of GII species with host plants in deciduous than in riparian habitats during the wet season. In riparian habitats, 11 plant species (61.1%) had greater density of GII in the dry than in the wet season. Similarly, leaf damage by GII was significantly greater in the dry than in the wet season in riparian habitats for 12 plant species (66.7%). Dry forest plants of riparian habitats presented two peaks of leaf‐flushing: GII colonized leaves produced in the first peak at the beginning of the wet season, and accumulated or recolonized leaves in the second peak at the beginning of the dry season. The levels of leaf damage by GII detected in this study in the rainy season were considerably higher than those obtained for folivorous insects in other neotropical forests, suggesting that this GII guild might have an important impact on their host plant species in this tropical community.     

Dry season habitat use by critically endangered white-shouldered ibis in northern Cambodia

We present the first scientific study of white-shouldered ibis Pseudibis davisoni habitat preferences in dry dipterocarp forest. Foraging sites included seasonal pools, forest understorey grasslands and fallow rice fields, with terrestrial sites used more following rainfall. Habitat and anthropogenic effects in logistic models of foraging site selection were examined by multimodel inference and model averaging. White-shouldered ibis preferred pools with greater cover of short vegetation (<25 cm) and less of the boundary enclosed, and forest sites with greater cover of bare substrate and lower people encounter rate. At forest sites, livestock density was positively related to bare substrate extent and thus may improve suitability for foraging ibis. At pools, livestock removed tall vegetation between the early and late dry season indicating their importance in opening up foraging habitats after wet season growth. However, by the late dry season, pools with greater livestock density had less short vegetation, the habitat favoured by ibis. Conservation strategies for white-shouldered ibis must consider a range of habitats, not just seasonal wetlands, and should incorporate extensive grazing and associated burning practises of local communities. Further understanding of the effects of these practices on vegetation, prey abundance and prey availability are therefore needed for effective conservation of this species. This will also develop our understanding of potentially beneficial anthropogenic influences in tropical environments.     

Impacts of climate change on rice production in Africa and causes of simulated yield changes

This study is the first of its kind to quantify possible effects of climate change on rice production in Africa. We simulated impacts on rice in irrigated systems (dry season and wet season) and rainfed systems (upland and lowland). We simulated the use of rice varieties with a higher temperature sum as adaptation option. We simulated rice yields for 4 RCP climate change scenarios and identified causes of yield declines. Without adaptation, shortening of the growing period due to higher temperatures had a negative impact on yields (?24% in RCP 8.5 in 2070 compared with the baseline year 2000). With varieties that have a high temperature sum, the length of the growing period would remain the same as under the baseline conditions. With this adaptation option rainfed rice yields would increase slightly (+8%) but they remain subject to water availability constraints. Irrigated rice yields in East Africa would increase (+25%) due to more favourable temperatures and due to CO2 fertilization. Wet season irrigated rice yields in West Africa were projected to change by ?21% or +7% (without/with adaptation). Without adaptation irrigated rice yields in West Africa in the dry season would decrease by ?45% with adaptation they would decrease significantly less (?15%). The main cause of this decline was reduced photosynthesis at extremely high temperatures. Simulated heat sterility hardly increased and was not found a major cause for yield decline. The implications for these findings are as follows. For East Africa to benefit from climate change, improved water and nutrient management will be needed to benefit fully from the more favourable temperatures and increased CO2 concentrations. For West Africa, more research is needed on photosynthesis processes at extreme temperatures and on adaptation options such as shifting sowing dates.     

First observation on mating and reproductive seasonality in maned sloths <Emphasis Type="Italic">Bradypus torquatus</Emphasis> (Pilosa: Bradypodidae)

Information on mating season is of paramount importance for our understanding of reproductive behavior, yet little is currently known about the breeding season of Xenarhtra as a whole and sloths in particular. A pair of maned sloths was observed copulating in September 2005 in the Atlantic Forest region of south-eastern Brazil. Our studies on mating of the manned sloth as well of other hitherto unpublished records of newborn sloths seen in the wild, together with a review of previous information, indicate that B. torquatus is a seasonal breeder. Infants are born predominantly at the end of the wet season and beginning of the dry season (February–April), and copulation concentrates in the late dry and early wet seasons (August–October). This strategy allows for the energy-demanding gestation and lactation to take place during the less stressful period of the year.     

Seasonal patterns of egg parasitism and natural biological control of rice brown planthopper in Indonesia

1 Egg mortality is known to be an important factor in brown planthopper (BPH) (Nilaparvata lugens) population dynamics in tropical Asia, but few quantitative data are available on the role of egg parasitoids. 2 Field studies are reported at two sites in Java, Indonesia, over a period of 4 years in both wet and dry seasons, where no chemical pesticides were used. Rice plants previously infested in the laboratory with BPH eggs were exposed to natural parasitism and predation in experimental fields for periods of 5 days. 3 Egg batches were dissected from both experimental and control plants after field exposure at seven fortnightly intervals through the rice growing season and BPH nymphs and adult parasitoids were allowed to emerge. 4 Parasitism by species of Oligosita (Hymenopera, Trichogrammatidae) and Anagrus (Hym., Mymaridae) varied between 18% and 61% in dry, and from 1% to 65% in wet, seasons. There was generally a trend from low to higher rates through wet seasons, contrasting with more uniform higher levels through dry seasons. 5 Reduction in BPH survival as a result of egg parasitism varied between 29% and 91%. Generally parasitism was density independent. 6 It is suggested that lower initial levels of parasitism in dry seasons may be due to the longer fallow period between dry and wet, than between wet and dry, resulting in lower local populations of appropriate natural enemies. 7 Unlike previous studies in Asia, little evidence was found for egg predation as an important mortality factor. 8 The conservation of egg parasitoids should form part of any rice pest management programmes in tropical Asia.     

Predicting seasonal habitat suitability for the critically endangered African wild ass in the Danakil,Ethiopia

The African wild ass (Equus africanus) is the most endangered wild equid in the world and is listed as a Critically Endangered (CR) on the IUCN Red list. Today, only relict populations remain in Ethiopia and Eritrea. The current Ethiopian population persists in the Danakil Desert at a very low density. Wildlife managers need to identify the extent of the remaining suitable habitat and understand human–wildlife interactions for appropriate conservation strategies. This study employed the maximum entropy model (Maxent) to determine suitable habitat and seasonal distribution of African wild ass in the Danakil Desert of Ethiopia. Field surveys were conducted four times annually, twice during the wet season and twice during the dry season, for 2 years. Field data and predictor variables were separated into the dry and wet seasons, and models were generated for each season independently. Distance from water, distance from settlements, herbaceous cover and slope were the best predictors of suitable habitat for both dry and wet seasons. Evaluations of model performances were high with area under the curve (AUC) values of 0.94 and 0.95 for the dry and wet seasons, respectively. Our results will be critical for identifying the available suitable habitat that should be conserved to safeguard this species from extinction.     

Seasonal influence on reproduction in chimpanzees of gombe national park

Although wild chimpanzees are not seasonal breeders, there are seasonal effects on several aspects of chimpanzee reproduction. I examined the seasonal incidence of anogenital swelling in cyclic, pregnant, and acyclic female chimpanzees in Gombe National Park, May 1975–April 1992, and surveyed important reproductive events to determine whether there is a seasonal effect. I analyzed data by season (wet vs. dry) and seasonal quarter;early dry season = May–July;late dry = August–October;early wet = November–January;late wet = February–April. When data for the 17 years are combined, the percentage of females in each reproductive state remains consistent throughout the year. In a given month, 30–35% of subjects were in the cyclic category, 11–15% were pregnant, and 54–61% were acyclic. Cyclic females showed full swelling more often during the late dry season. Pregnant females exhibited anogenital swelling more often during the late dry and early wet seasons. Acyclic females also exhibited a seasonal effect with more anogenital swelling during the late dry season. There is no seasonal difference in frequency of live births (dry, 20;wet, 23). However, the timing of conception showed a seasonal effect (dry, 32;wet, 16). Consistent with earlier reports, the onset of postpartum cycles is highly seasonal;30 occurred during dry season, 9 during wet season. The occurrence of first full swellings for young females is also concentrated in the late dry season. It appears that the dry season is a time of great change for Gombe chimpanzee reproductive physiology. Previous studies indicated that seasonal changes in food availability play a role in increasing group size during the dry season and social contact between females can enhance cyclicity. Accordingly, I suggest that seasonal changes in diet may play a role, either directly (food content) or indirectly (social contact), to alter reproductive physiology.     

Wildlife–water quality interactions in the Serengeti National Park, Tanzania

Surveys of water quality in the surface waters in the Serengeti National Park were undertaken in both the wet and dry seasons of 1996. Most rivers were ponded, with ponds having a flushing time of 1 month in the wet season and zero flushing in the dry season. pH values varied spatially from extremely alkaline conditions (pH>10) in the southern plains to acidic conditions in the northern region (pH=5·9). In the southern plains at the end of the dry season the salinity of surface waters was high (5–17‰) while there was abundant surface water and the zebras and wildebeest had started to migrate away, a finding suggesting excessive salinity may be the trigger initiating the annual migration. Most surface waters were heavily eutrophicated as a result of animal dung. As a result, the dissolved oxygen concentration near the surface fluctuated widely between 1 and 200% of saturation, smaller values occurring deeper in the water column. Stirring and mechanical aeration by hippos, crocodiles and mammals crossing the rivers prevented the formation of anoxic conditions. The oxygen stress was measurably lessened in wetland‐fringed water bodies as a result of filtering. Light penetration was high (≥10 cm) in saline waters as a result of flocculation enhanced by bacteria and vegetation detritus, elsewhere the euphotic zone was less than 1 cm thick and the waters generally inhospitable to aquatic life. The discontinuity between wooded savanna and grassland coincides with the occurrence of alkaline, high salinity waters in the dry season.     

African Vultures Don’t Follow Migratory Herds: Scavenger Habitat Use Is Not Mediated by Prey Abundance

The ongoing global decline in vulture populations raises major conservation concerns, but little is known about the factors that mediate scavenger habitat use, in particular the importance of abundance of live prey versus prey mortality. We test this using data from the Serengeti-Mara ecosystem in East Africa. The two hypotheses that prey abundance or prey mortality are the main drivers of vulture habitat use provide alternative predictions. If vultures select areas based only on prey abundance, we expect tracked vultures to remain close to herds of migratory wildebeest regardless of season. However, if vultures select areas where mortality rates are greatest then we expect vultures to select the driest regions, where animals are more likely to die of starvation, and to be attracted to migratory wildebeest only during the dry season when wildebeest mortality is greatest. We used data from GSM-GPS transmitters to assess the relationship between three vulture species and migratory wildebeest in the Mara-Serengeti ecosystem. Results indicate that vultures preferentially cluster around migratory herds only during the dry season, when herds experience their highest mortality. Additionally during the wet season, Ruppell’s and Lappet-faced vultures select relatively dry areas, based on Normalized Difference Vegetation Index, whereas White-backed vultures preferred wetter areas during the wet season. Differences in habitat use among species may mediate coexistence in this scavenger guild. In general, our results suggest that prey abundance is not the primary driver of avian scavenger habitat use. The apparent reliance of vultures on non-migratory ungulates during the wet season has important conservation implications for vultures in light of on-going declines in non-migratory ungulate species and use of poisons in unprotected areas.     

Comparative analysis of population characteristics of the brown planthopper,Nilaparvata lugens stål,between wet and dry rice cropping seasons in West Java,Indonesia

Population dynamics of the brown planthopper (BPH),Nilaparvata lugens Stål, were investigated in paddy fields in the coastal lowland of West Java, Indonesia, where rice is cultivated twice a year, in the wet and dry cropping seasons. Distinct differences in the basic features of population dynamics were detected between the two rice cropping seasons: (1) In the wet season, BPH populations multiplied rapidly in the period from initial to peak generation, reaching quite often the destructive level despite the low density of initial immigrants. However, in the dry season, the population growth rate and the peak population density were much lower than those in the wet season. The abundance of natural enemies such as arthropod predators played a major role in determining such a difference in seasonal population development. (2) The density at the peak generation or the occurrence of outbreaks in each field was predictable in the wet season with fairly high accuracy on the basis of the density at the initial or previous seasonal generations. In the dry season, however, the rate of population growth and the peak population density widely varied among the fields depending on the water status in each field. (3) Density-dependent processes to regulate the population density were detected in both cropping seasons. In the wet season, the regulatory processes were only detected in such high densities as cause the considerable deterioration of host plants, which suggested that the processes were largely attributable to intra-specific competition. In the dry season, however, the regulatory processes operated at a much lower density in the earlier stages of the crops. The results of an analysis of adult longevity or residence period suggested that the density-dependent dispersal of macropterous adults played an important role in stabilizing the population fluctuation among the fields in the early dry season.