A seasonal difference of daily energy expenditure in a free-living subterranean rodent,the silvery mole-rat (Heliophobius argenteocinereus; Bathyergidae)

In seasonal climatic regimes, animals have to deal with changing environmental conditions. It is reasonable to expect that seasonal changes are reflected in animal overall energetics. The relation between daily energy expenditure (DEE) and seasonally variable ecological determinants has been studied in many free-living small mammals; however with inconsistent results. Subterranean mammals, i.e. fossorial (burrowing) mammals which live and forage underground, live in a seasonally and diurnally thermally stable environment and represent a suitable model to test seasonality in DEE in respect to seasonal changes, particularly those in soil characteristics and access to food supply. Both factors are affected by seasonal rainfall and are supposed to fundamentally determine activity of belowground dwellers. These ecological constraints are pronounced in some tropical regions, where two distinct periods, dry and rainy seasons, regularly alternate. To explore how a tropical mammal responds to an abrupt environmental change, we determined DEE, resting metabolic rate (RMR) and sustained metabolic scope (SusMS) in a solitary subterranean rodent, the silvery mole-rat, at the end of dry season and the onset of rainy season. Whereas RMR did not differ between both periods, mole-rats had 1.4 times higher DEE and SusMS after the first heavy rains. These findings suggest that rainfall is an important environmental factor responsible for higher energy expenditure in mole-rats, probably due to increased burrowing activity. SusMS in the silvery mole-rat is comparable to values in other bathyergids and all bathyergid values rank among the lowest SusMS found in endothermic vertebrates.     

The reproductive cycle of male tomb bats, Taphozous hildegardeae (Chiroptera: Emballonuridae), in a seasonal environment of the African tropics

Two cave populations of Hildegarde's tomb bat had a reproductive cycle that corresponded closely to the rainfall-induced seasonality of coastal Kenya (4s). Males had pronounced bimodal cycles of body weight due to the deposition of fat during periods of relative food abundance in both rainy seasons, and fat depletion during competitive mating and the dry seasons, when numbers of moths were lowest. The main period of sexual regeneration coincided with the increase in body weight experienced during the 'long rains' [April-June) and led to mating. A secondary peak in the weights of male sexual glands, associated with the increase in body weight that occurred in the 'short rains' (October-December), did not result in reproduction. It is suggested that this latter period of sexual activity was related to the maintenance of year-round harems, and may represent the male response to a vestigial, bimodally polyoestrous, reproductive cycle.     

Can Saturniidae moths be bioindicators? Spatial and temporal distribution in the Brazilian savannah

Some moths species are considered good indicators of habitat quality because they are very responsive to human disturbance, vegetation type, and successional processes. However, Saturniidae moths have not yet been considered as indicators of environmental quality. Little is known on the distribution of moth species in different vegetation types and the moths’ seasonal variations in the Brazilian savannah. Therefore, this study aims to describe the spatial distribution and temporal patterns of moths belonging to the Saturniidae family in two vegetation types—Cerrado sensu stricto on rocky outcrops and semi-deciduous forest—in both the rainy and dry seasons. It addresses the influence of the climatic seasons and vegetation types on abundance, richness, and species composition to describe the temporal and spatial distribution patterns and the relationship between the ecological aspects and the life history of these moths. This study was conducted in the Cerrado phytogeographical domain, in Pireneus State Park, Goiás, Brazil. The results revealed that most Saturniidae species sampled are present during the rainy season and typically found in forest habitats. Furthermore, a clear positive connection was found between the abundance pattern and rainfall seasonality and humid habitats; this is apparently related to the physiological tolerance of these moths, due to rudimentary mouthparts during their adulthood. Thus, rainfall and a forest habitat are important to and fundamental requirements for the persistence of the Saturniidae species in the Cerrado domain. Based on the results of this study, we suggest the use of saturniid species as indicators of changes in vegetation and climatic conditions.     

Diurnal resting in brown lemurs in a dry deciduous forest, northwestern Madagascar: implications for seasonal thermoregulation

Decreased activity has been reported in both nocturnal and diurnal primates during the prolonged dry season in western Madagascar, and this has been interpreted as a reaction to the severe environment, with its food scarcity and/or thermal stress. Several day-active lemurs rest more as trees defoliate, although the reason for this is unclear. To understand the mechanism underpinning the diurnal resting of lemurs in seasonal deciduous forests, I observed common brown lemurs (Eulemur fulvus fulvus) for one year in Ankarafantsika National Park, northwestern Madagascar. In Ankarafantsika, despite high fruit availability during the dry season, brown lemurs are known to engage in diurnal resting. To examine the effects of thermal factors and defoliation on lemur inactivity, I recorded the activity of a troop at 1 min intervals, hourly ambient temperature, daily rainfall, and weather during observations (06:00-18:00). I quantified the amount of leaves biweekly for 680 trees. I tested correlations between percentages of resting time and each factor across hours during the day and across seasons. During the rainy season, resting time did not differ between sunny and cloudy days, and lemurs were active throughout the daytime. At the hourly level during the dry season, lemurs rested exclusively at midday, apparently at peak sunlight intensity rather than at peak ambient temperature. At seasonal level, percentages of total resting time from 08:00 to 16:00 were greater during dry season (81.9%) than during rainy season (62.6%), and percentages increased as ambient temperatures increased. Defoliation was related to seasonal decrease in weekly rainfall, which served as an index of water retained in the forest. Defoliation probably reflected aridification as well as the penetration of sunlight into the forest. Diurnal resting increased as both the amount of leaves and weekly rainfall decreased seasonally. These results suggest that heat stress under dry conditions may promote resting. Diurnal resting may function as behavioral thermoregulation to avoid overheating and to minimize water loss via excessive evaporative respiration.     

Rodent abundance dynamics and leptospirosis carriage in an area of hyper-endemicity in New Caledonia

Background

Widespread but particularly incident in the tropics, leptospirosis is transmitted to humans directly or indirectly by virtually any Mammal species. However, rodents are recognized as the most important reservoir. In endemic regions, seasonal outbreaks are observed during hot rainy periods. In such regions, hot spots can be evidenced, where leptospirosis is “hyper-endemic”, its incidence reaching 500 annual cases per 100,000. A better knowledge of how rodent populations and their Leptospira prevalence respond to seasonal and meteorological fluctuations might help implement relevant control measures.

Methodology/Principal Findings

In two tribes in New Caledonia with hyper-endemic leptospirosis, rodent abundance and Leptospira prevalence was studied twice a year, in hot and cool seasons for two consecutive years. Highly contrasted meteorological situations, particularly rainfall intensities, were noted between the two hot seasons studied. Our results show that during a hot and rainy period, both the rodent populations and their Leptospira carriage were higher. This pattern was more salient in commensal rodents than in the sylvatic rats.

Conclusions/Significance

The dynamics of rodents and their Leptospira carriage changed during the survey, probably under the influence of meteorology. Rodents were both more numerous and more frequently carrying (therefore disseminating) leptospires during a hot rainy period, also corresponding to a flooding period with higher risks of human exposure to waters and watered soils. The outbreaks of leptospirosis in hyper-endemic areas could arise from meteorological conditions leading to both an increased risk of exposure of humans and an increased volume of the rodent reservoir. Rodent control measures would therefore be most effective during cool and dry seasons, when rodent populations and leptospirosis incidence are low.     

The ecology of Biomphalaria sudanica in Lake Ziway, Ethiopia

A longitudinal study was made over a period of 24 months from January 2001 to December 2002 in Lake Ziway, Ethiopia, to elucidate factors influencing changes in the population density of Biomphalaria sudanica and to identify seasons of peak transmission of Schistosoma mansoni. Between January 2001 and December 2002, bimonthly visits were made to the lake to collect data on snail population density and schistosome infection in snails, vegetation and lake water level. Water samples were collected during the dry and rainy seasons and chemical analyses were made for major cations, anions, electrical conductivity, total hardness and pH using standard methods for the examination of water and wastewater. The seasonal fluctuation in the population density of B. sudanica was found to be highly associated with rainfall, water level of the lake and vegetation availability and abundance. Water chemical analysis showed that major cations and anions were all within the range reported for other African freshwaters. Both malacological and meteorological data show that snail population density in Lake Ziway peaks at the end of the long rainy season (June–August), coinciding with a seasonal transmission peak of schistosomiasis.     

Regional environments, life-history patterns, and habitat use of spirostreptid millipedes in arid regions

Among diplopods with desert populations, only three species of Spirostreptida have been studied in an ecological context. The present review compares regional environments, life-history patterns, and uses of habitat by Orlhoporus ornatus (Girard) from southwestern North America, Archispirostreptus tumuliporus judaicus (Attems) from the eastern Mediterranean seaboard, and Harpagophora nigra (Attems) from southwestern Africa. Published and unpublished studies are used to explore evidence for convergence among these species, as opposed to traits adapting them to physical aspects of given regions or habitats. Unlike A. t. judaicus, O. ornatus and H. nigra are relatively restricted to arid habitats, although populations of all three species experience a variety of rainfall regimes and regional topographies. Where studied, O. ornatus and H. nigra hibernate during the long, often cool or cold dry season; they forage following warm-season rains. A. t. judaicus , in contrast, forages during its long, warm dry season and hibernates in the cool, wet winter. Populations from the Judaean and Negev deserts differ from those inhabiting a mesic habitat (Megiddo) closer to the coast in regard to rates of development, seasonal activity and seasonal water balance. Convergence in the form of well-developed desiccation resistance characterizes the two strictly desert species. All three species, together with other subtropical millipedes exposed to long dry seasons, are convergent with respect to patterns of diel surface activity and use of shelter. However species- and habitat-specific life-history features such as the seasonal timing of dormancy and emergence tend to mask convergence at the habitat level. Hence, the independent evolution of the three species with desert populations has resulted in life histories and habitat use that combine a moderate amount of convergence with considerable opportunistic adaptation to regional and local conditions.     

Reproductive phenology, life-forms, and habitats of the Venezuelan Central Plain

Reproductive phenology of 171 plant species belonging to 57 families of angiosperms was studied according to life-forms in four habitat types in a savanna-forest mosaic on the Venezuelan Central Plain. Flowering, unripe fruit, and mature fruit patterns were affected significantly according to life-forms and habitats respectively. Production of flowers, unripe fruits, and mature fruits showed marked seasonality for all habitats except for the forest. Flowering peaked during the rainy season, and fruiting peaked toward the end of the rainy season. The savanna and the disturbed area had similar proportions of species that flowered over the year. The percentage of species with unripe fruits produced throughout the year was more seasonal for the disturbed area than for the other habitats. Mature fruit patterns showed an increase during the late rainy season for the ecotone and savanna. A large number of herbaceous (annual and perennial) and liana species flowered during the wet season, and a smaller fraction flowered during the dry season; and trees, shrubs, and epiphytes increased flowering activity during the dry season. Unripe fruit patterns were similar to those of flowering for all life-forms, however, tree species were less seasonal. Mature fruit production by shrubs peaked in the period of maximum rainfall, while the peak for perennial herbs was in the late rainy season and the peak for annual herbs was during the transition between the rainy season and the dry season. The largest proportion of tree and liana species with ripe fruits occurred during the dry season. Differences among phenological patterns in habitats were caused mainly by life-forms and promote a wider distribution of reproductive events in habitats and overall community in the Venezuelan Central Plain.     

Further evidence for windborne movement of armyworm moths, Spodoptera exempta, in East Africa

Abstract. 1. Comparison of dominant wind directions with seasonal redistribution of Spodoptera exempta caterpillar outbreaks in East Africa provides further circumstantial evidence to support the hypothesis of downwind migration by adult moths.
2. Calculated backward and forward tracks for sixty-nine nights during the 1973–74 and 1974–75 seasons, when there were sudden increases in numbers of moths caught at six light traps, illustrate the variability of downwind movement due to the effects of temporary atmospheric disturbances.
3. Comparison of calculated tracks with known outbreaks before and after the nights of increased moth catch suggests that some outbreaks are derived from unreported sources, especially eariy in the season, and it is therefore unwise to link new outbreaks only with known earlier ones.     

Some aspects of the breeding biology of the equatorial land snail Limicolaria martensiana (Achatinidae: Pulmonata)

A study of the breeding season of the polymorphic equatorial land snail Limicolaria martensiana Smith (Achatinidae: Pulmonata) lasting six years and six months in populations in the Kampala District (lat. 0 20') and the Equator line shows that the snail breeds continuously throughout the year but has bimodal peaks in its breeding which occurs during the dry seasons, while during the rainy seasons breeding is low. It is the decrease in the amount of rainfall which induces peak breeding and as a result there is an inverse relationship between the amount of rainfall and the breeding intensity. The evolution of ovoviviparity with the ability to retain eggs and/or young in utero during aestivation is the phenomenon that enables L. martensiana to have peak breeding during the dry seasons. Moisture which enables young to feed and thus grow is an ultimate factor in determining breeding in L. martensiana . The gestation period is 10 to 14 days during the rainy seasons but the snail retains its eggs and/or young in utero during the dry seasons and only deposits them when rain returns. The eggs take 18.6±5.43 days ( N= 130) to hatch after they are laid. Hatching in utero and outside occurs by the young eating the egg shells. Oogenesis in the snails occurs at all times. L. martensiana stores viable allosperms which it can use for further reproduction.     

Thelazia rhodesii (Desmarest, 1828) in cattle of Central Province, Zambia

Sanga cattle from Central Zambia were examined during the dry and the rainy seasons for the presence of the adult stage of eyeworm Thelazia rhodesii. Prevalences were recorded according to age/sex groups. The occurrence of ocular diseases was also noted. Differences between the total prevalences of infection with the parasite in the dry and rainy seasons were observed: respectively 3.1% and 26.6% of all cattle examined (p less than 0.001), which numbered 223 head in the dry season and 248 in the rainy season. In both seasons, adult males showed the highest prevalence and calves the lowest. In the dry season the parasite was found in two of the 23 males (8.7%) but in none of the 24 calves. During the rains, eight of the 22 adult males (36.4%), and two of 53 calves (3.8%) were parasitized (p less than 0.001). A comparison of the prevalences in the latter season between a group of cows sprayed weekly with a synthetic pyrethroid and an untreated group showed no significant difference between the two groups (p greater than 0.1). No correlation was found between T. rhodesii infection and the occurrence of eye lesions (p greater than 0.1). It is concluded that in traditionally managed Zambian cattle the infection is seasonal, is more frequent in adult male animals and is not associated with eye infections (i.e., pink-eye).     

Seasonality,diaspore traits and the structure of plant-frugivore networks in Neotropical savanna forest

Complex frugivory networks are common in heterogeneous environments, but how the structure of those networks varies due to seasonality and other environmental factors remains unclear. For example, seasonal variation in rainfall can influence fruit production and diaspore characteristics, which could alter the quantity and quality of resources available to different animals in the network and, hence, network structure. We investigated how a frugivory network varied seasonally in Brazilian savanna (Cerrado), where there are well-defined dry and wet seasons and fructification mainly during the rainy season for most tree species. We recorded fruit consumption by animals during the dry and wet seasons in two different gallery forests and used these data to test the hypotheses that connectance, links per species and nestedness would be higher in the dry season than rainy season due to low available food in the former that would be consumed by various species of frugivores. Concomitantly, we also measured seed width and lipid content from diaspores of the fruiting trees to determine if these characteristics influenced interaction properties between fruiting trees and frugivores. Among the measured network parameters, connectance, links per species and specialization varied between seasons in one site but not in the other, indicating that seasonal variation in networks is not necessarily consistent over time or space. The number of tree species with small diaspores with high lipid content differed between seasons, and those characteristics were key factors increasing the interaction parameter of fruiting trees. We suggest that network stability between seasons may be related to local frugivore diversity, resource availability, and fruit quality.     

THE ANNUAL CYCLE IN A TROPICAL WET FOREST HUMMINGBIRD COMMUNITY

In the Caribbean lowlands of Costa Rica, rainfall is moderately seasonal, although even in the driest month over 100 mm of rain usually fall. Flowering of hummingbird food plants shows a peak in the dry season (February-April) and another in the early wet season (July-September), with a severe flower shortage at the end of the rains (November-December). The dry season peak involves largely canopy epiphytes, the wet season peak large herbs of light gaps and edges and forest understory plants. This study examines the responses of the associated community of 22 species of hummingbirds (of which 13 breed, and 12 are common for at least parts of most years) to these spatial and temporal patterns of resource availability. Nearly all common breeding species show a peak of reproductive activity in the dry season, coinciding with the first flowering peak, followed by a discrete moulting season that coincides with the wet season peak of flowering. Of the three species with extended breeding seasons, the two species of hermit, Phaethornis, show moult-breeding overlap to varying degrees on an individual basis. In a number of species moult and breeding appear antagonistic. The annual peak of body weight and fat deposits in all species occur during the second flowering peak, approximately corresponding to the moult. The annual minima of body weight and fat occur in the lean season and the breeding season respectively. The lack of concordance of these two possibly reflects the use of muscle protein as a nutrient source during the lean season. Several species show pronounced habitat shifts through the year, with the sexes sometimes occupying different microhabitats, especially during the dry season. At least five species show pronounced seasonal migrations, largely or entirely leaving La Selva for part of the year. Overall hummingbird numbers are greatest early in the rainy season, lowest in the lean season, with the non-hermits (Trochilinae) showing a more pronounced annual cycle of numbers than the hermits (Phaethorninae). Comparisons with other tropical lowland hummingbird-flower communities are made with respect to the roles of flowers as proximate and ultimate factors regulating the annual cycles and affecting the population biology of the birds.     

FACTORS AFFECTING THE FOOD SUPPLY AND BREEDING SEASON OF RESIDENT BIRDS AND MOVEMENTS OF PALAEARCTIC MIGRANTS IN A TROPICAL AFRICAN SAVANNAH

The fact that Palaearctic migrants arrive in the northern tropical savannah of Africa during the dry season suggests potential competition for food with African species. Moreover, in the southern tropical savannah African species breed during the rainy seasons, when Palaearctic migrants are present. In the equatorial area of Serengeti, East Africa, an index of the food supply for insectivorous birds was obtained from 3 years of light-trap measurements and sweep net samples. Adults of Lepidoptera, Coleoptera, Orthoptera and Isoptera are sparse in the dry season but become locally abundant after the first rainstorms that mark its close. They are apparently blown by converging winds ahead of the inter-tropical front and settle to lay eggs where rain has fallen. These early storms therefore produce localized superabundances of food. In the ensuing rainy seasons insect abundance remains high. African insectivorous birds breed during the wet period, reaching a peak two months after the insect increase. It is suggested that this lag is due to the need to recover body condition, build up reserves for eggs, develop gonads and wait for vegetation and insect larvae to develop. In the samples available, breeding records of above-ground nesters peaked in the first rains, while ground-nesters peaked in the second (main) rains. Predators bred towards the end of the rains, when there is an abundance of fledglings and small mammals. Thus the food supply could act as the ultimate factor determining the timing of the breeding season in this area. Palaearctic migrants arrive in the Serengeti 4–10 weeks ahead of the main rain front. However, most species are only found where rain has fallen recently. When conditions dry up they move on to other wet areas. Thus they overlap with African species only where there is a superabundance of insects. When the rains become widespread Palaearctic migrants disperse into their usual habitats, and therefore appear not to compete for available resources with closely related species of African birds. The situation in West Africa, where residents and migrants overlap throughout the dry season, cannot be explained in the same terms.     

SOME ASPECTS OF THE BEHAVIOUR OF THE WATTLED PLOVER AFRIBYX SENEGALLUS (LINNAEUS)

The question of how aridity might influence avian clutch size, through the influences of rainfall seasonality and environmental stochasticity (unpredictability), has received little attention. A marked east-west gradient in aridity across South Africa provides a unique opportunity to test for such influences. Using an extensive collection of nest records for 106 terrestrial bird species from the South African Nest Record Card Scheme, we tested three predictions related to rainfall seasonality and stochasticity. Analyses were conducted at two levels, the first examining each species independently, and the second grouping species into five dietary guilds. The first prediction, that clutch size should generally increase with higher rainfall seasonality (i.e. higher seasonal fluctuation of food availability), was supported, particularly in the most arid environments where food abundance is more closely linked to rainfall. Controlling for rainfall seasonality, the second prediction, that clutch size should generally decrease as a bet-hedging strategy in arid, stochastic environments, was also supported. Although the timing of the rainy season differs among regions in South Africa (winter, early summer, later summer, year-round), birds primarily nest during spring. The relative timing of rainfall and breeding is expected to have different consequences for seasonal variation in clutch size among rainfall regions. The third prediction, of different patterns of seasonal variation in clutch size between rainfall regions, was also supported. In the winter and early-summer rainfall regions, early-nesting birds (breeding with or soon after the rains) generally had a larger clutch size than late-nesting birds. In the late-summer rainfall region, early-nesting birds (breeding well before the rains) had a smaller clutch size than late-nesting birds.     

Seasonal Patterns of Flowering and Fruiting in a Dry Tropical Forest in Jamaica1

Tropical dry forests occupy more area and are more endangered than rainforests, yet their regeneration ecology has received less study and is consequently poorly understood. We recorded the flowering and fruiting phenology of a tropical dry forest in Jamaica over a period of 26 mo within ten 15 × 15‐m plots. Community‐wide recruitment reached a maximum in the wet season, whereas no recruitment occurred during the dry season. We observed a unimodal peak in rainfall and fruit production, and the periodicity and intensity of seed production were significantly correlated with rainfall seasonality (the optimal time for germination). Flowering at the community and system levels lagged behind a significant increase and subsequent decrease in rainfall by 7 and 3 mo, respectively, indicating that the dominant factor controlling flowering periodicity is the passage of the major (4‐mo long) rainy season and changes in soil moisture conditions. Fruiting lagged behind flowering by 2 mo and a significant increase in fruiting occurred 2 mo prior to a significant increase in rainfall. At the population level, a correspondence analysis identified a major dichotomy in the patterns of flowering and fruiting between species and indicated two broad species groups based on their time of peak fruiting and the number of times they were in fruit. These were either individuals which were usually in peak fruit 1–2 mo prior to the start of the major rainy season or those that were in fruit more or less continuously throughout the year with no peak fruiting time. This study supports the view that seasonal variation in rainfall and hence soil water availability constitutes both the proximate and the ultimate cause of flowering periodicity in tropical dry forests.     

Female stress and birth seasonality in Tanzania

Delivery records from hospitals in Ikwiriri and Ifakara show that the number of births increases throughout the dry season (June-October) and declines throughout the rainy season (November), reaching a peak just before the rains and the lowest level at the end of the rainy season. This pattern does not correspond with the usual explanations of birth seasonality. Conceptions are most frequent at the period of highest temperature, which is contrary to the theory that predicts them to be more frequent during the dry season. The drop of the conception rate during the wet agricultural season suggests that stress on women may be the main cause of birth seasonality in Tanzania. Due to wet conditions and frequent staying on in the rice fields, exposure to malaria increases during the rainy season's latter part. The negative association of the number of births with rainfall in the months preceding conception indicates that almost half of the variation in the number of births may be due to the effects of malaria and physical exhaustion on fecundity. The remainder may be attributable to seasonal variations in pregnancy loss and sexual behavior. The absence of strong birth seasonality in nonholoendemic areas of Tanzania and the low birth rate in holoendemic areas provide further support for a critical role for malaria infection. The fact that the magnitude of seasonal variation in births increases with high parity and has decreased over the past decade results from recent changes in Tanzania's rural economy. Young people in Tanzania are progressively withdrawing from agriculture, especially when they have no children yet.     

Differences in leaf phenology between juvenile and adult individuals of two tree species in a seasonally dry tropical woodland

In temperate forests, juvenile trees anticipate leaf phenology compared to adults, thus avoiding shading and herbivory. This is also expected to occur in seasonal tropical forests due to intense herbivory and shading during the rainy season; however, the anticipation of leaf phenology by juveniles in seasonal tropical forests has yet to be demonstrated. Stem‐succulent species are expected to be prone to juvenile phenological anticipation because these species are able to use water stored in their stems for leaf flushing in the dry season. We investigated this hypothesis by comparing leaf phenology (bud break, leaf expansion) of juveniles and adults of two species with contrasting wood densities in the transition between dry and rainy seasons in a tropical dry woodland. We also investigated the level of light limitation that juveniles experience in the rainy season. Both species exhibited bud break during the dry season, but only expanded their leaves with the occurrence of the first rains. In general, the stem‐succulent species had a more precocious bud break; however, anticipation by juveniles occurred only in the species with more dense wood. Canopy openness was lower than in temperate deciduous forests, but the fact that the full expansion of leaves occurred only with rainfall indicates that bud break in anticipation of canopy closure contributes only to keeping leaf photosynthetic balance from going negative, and not to higher carbon gain. The importance of anticipated budding for escaping herbivory remains an alternative explanation in need of investigation.     

Day-journey length and daily diet of solitary male gorillas in lowland and highland habitats

We compared day-journey length and daily diets of solitary male gorillas in lowland versus highland habitats. Solitary males in tropical forests of Zaire tend to travel longer distances, to visit more types of vegetation, and to consume more kinds of food than a solitary male mountain gorilla in the Virunga Volcanoes did. The number of feeding sites per day is larger and the mean distance between feeding sites is far longer for the former than the latter. These observations may reflect differences in food breadth and availability between highland and lowland habitats. The herbaceous plants that are eaten by mountain gorillas are densely and evenly distributed in the higher montane forest of the Virungas, where gorillas need not cover long distances to search for food. In contrast, herbaceous plants are scarce in primary and ancient secondary forests of lowland habitats, where gorillas travel long distances and eat various fruits and insects. The patchy and unpredictable distribution of foods may extend the distances over which gorillas search for food in the lowland habitat. However, solitary males showed a prominent reduction in day-journey length and changed their choices of food during the nonfruiting season (the long rainy and dry seasons) in the lowland habitats. This strategy may have developed during the Pleistocene and may have enabled them to enlarge their ranges to the higher montane forests, where fruits are sparse throughout the year.     

The influence of rainfall on diet and reproduction in four African rodent species

Arvicanthis nitoticus was found, during two seasons of the study, to begin breeding some two to three months after the start of the rains; at this time weed seeds first appeared in the stomach contents. Breeding continued during the rains and into the early part of the dry season while weed seeds and cereals formed the major part of the diet. Breeding declined during the early part of the dry season, and fat was laid down while weed seeds and cereals were still present but less abundant in the diet. Later in the dry season, breeding ceased and the diet was switched dramatically, first to the leaves and stems of dicotyledonous plants then almost exclusively to grass, and fat deposits were rapidly utilized. Arvicanthis living in an area where cereals were artifically supplied bred almost continuously. Mastomys natalensis also bred when seeds and cereals were most plentiful, but, by ranging widely over open ground, often managed to continue to find these foods, and insects, during the dry season. Supplied cereals failed to produce a reproductive response in Mastomys –instead, unprecedented fat deposits developed. Unseasonal reproduction in this species was, however, observed in an unseasonal wheat crop. Rhabdomys pumilio bred when cereals were plentiful but was also found breeding when its diet was mainly clover–a crop that is noted for its high crude protein content. The herbivorous Otomys angoniensis bred throughout the year and was unaffected by supplied cereals. It seems clear that the food supply of grani-vorous species is dependent on rainfall, and that prolongation of the normal rainy season may generate excess food and cover, resulting in and extended breeding season and unusually large numbers of these rodents.