Aspects of the reproductive ecology of the Hamerkop Scopus umbretta in central Mali

In a 4-year study of Hamerkops in central Mali, territories of breeding pairs overlapped and most clutches were laid in the late rainy or early dry seasons. Clutches averaged 4–8 eggs. Different pairs laid eggs having, on average, different dimensions. Eggs laid in the late rainy and early dry seasons were larger than those laid at other times. Eggs weighed, at 27-8 g, about 6% of adult female weight. Hatching success was 79% with a fledging rate of eggs hatched of 53%. Successful nests fledged 27 young but for all completed clutches the fledging rate was 0'9. Young hatched early in the sequence had a higher survival rate than those hatched later. Mean age at fledging was 47 days. Pairs fledged between 0–5 and 0–9 young per year.     

The relationship between outbreaks, rainfall and low density populations of the African armyworm, Spodoptera exempta, in Kenya

This study has demonstrated that low numbers of African armyworms (Spodoptera exempta) (Walker) (Lepidoptera: Noctuidae) can be found throughout the year in parts of the coastal and highland regions of Kenya where there is frequent rainfall. During the study period the numbers of moths caught in pheromone traps in these regions built up during the short and long rains, and decreased dramatically during the intervening dry seasons. There was a lag of one to two months between the peaks for rainfall and moth numbers. This contrasts with the situation at sites of the seasonal outbreaks of armyworm larvae, where a sudden preceding influx of moths coincides with the rainfall. A positive correlation was found, for the long rains seasons only, between the number of armyworm outbreaks throughout the country and the peak numbers of moths in coastal and highland regions.It is suggested therefore that the peak numbers of moths trapped in the eastern highlands and coastal regions during the rainy seasons arise principally from outbreaks in the extensive seasonal grasslands. These grassland areas diminish considerably during the prolonged dry periods between the two rainy seasons, and it is only the eastern highland and coastal regions that are likely to provide suitable habitats for breeding during the dry seasons. The significance of these populations for initiating the first outbreaks of the following season is discussed.     

Population evolution of the free-living stage of goat gastrointestinal nematodes on herbage under tropical conditions in Guadeloupe (French West Indies)

In Guadeloupe (French West Indies), paddocks were contaminated with gastrointestinal helminth eggs by young goats during the rainy season and the dry season. The evolution of L3 population size on herbage was followed over a period of 56 days. The major genera were Haemonchus and Trichostrongylus. It was shown that the L3 appeared on herbage 7-14 days after the beginning of contamination (DAC), and the L3 population sizes were maximal between the 14th and the 21st DAC. The maximum duration of larval survival ranged between 49 and 56 days. There was a marked depressive effect by the dry season on eggs hatching and L3 development with some arrested egg hatching in Trichostrongylus. The climatic events and the amount of dry matter on pastures during the grazing period appeared as the main important factors which could interfere with the overall evolution of the L3 population size and there was no preferential direction of L3 migration from faeces to herbage.     

Distribution, reproduction and growth of the catfish, Chrysichthys walkeri (Gunther) in the Lekki Lagoon, Nigeria

An investigation was made on the biology of the catfish, Chrysichthys walkeri (Gunther) occurring in the Lekki Lagoon. The catfish was evenly distributed over the six sampled stations of the lagoon with the sites of the shallow water stations probably serving both as breeding and nursery grounds.
Fecundity estimates for this species ranged from 896 to 4168 eggs. The average number of eggs per female was 2084. Laboratory incubated eggs hatched after 3 days with the yolk sac being completely absorbed on the seventh day. The fry averaged 8.6 mm on their first day of life.
The catfish attained a maximum total length of 25.7 cm within a period of 2 years. There were no significant differences in the growth pattern of this species during the dry and rainy seasons.     

Differences in reproductive seasonality of the Central American cichlid Cichlasoma urophthalmus from three 'cenotes' (sinkholes)

A total of 966 cichlids, Cichlasoma urophthalmus , was sampled from three karstic water bodies ('cenotes') in the Yucatan Peninsula. Sex ratio was not different from 1. Specimens with ripe eggs were found during the dry and rainy seasons in the inland cenote and during the dry, rainy, and north winds seasons in the two wetland cenotes. With respect to relative fecundity, data show the C . urophthalmus inland population as two- to three-fold greater (53.1 ± 27.7) than the wetland populations (15.7 ± 5.1 and 18.2 ± 3.1). This is attributable to the different breeding strategies of C . urophthalmus populations inhabiting these two types of cenotes. In particular, the ichthyofauna from the two wetlands showed not only higher species richness (17 and 16 species) but also a higher number of potential predators (nine and eight species) as compared to the inland cenote (six species; two potential predators). It is hypothesized that C . urophthalmus adjusts its clutch size and extends its breeding periods as a response to riskier sites as compared to more secure ones; a higher competition for breeding sites and to increased fishing mortality.     

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.     

Histology,ultrastructure, and seasonal variations in the bulbourethral gland of the African straw-colored fruit bat Eidolon helvum

We studied the morphological characteristics and seasonal changes of the bulbourethral gland of Eidolon helvum in a typical African tropical environment. Forty-eight bulbourethral glands were examined using gross anatomical, histological, histochemical, and ultrastructural techniques during the early rainy, late rainy, and peak dry seasons. The pear-shaped bilateral bulbourethral glands were located extra-abdominally in the inguinal region. Trabeculae from the capsule divided the parenchyma into numerous lobules of tubuloalveolar glandular acini. The mucosa was covered by a simple columnar epithelium consisting up of principal secretory cells, columnar dense cells and basal cells, which were progressively pronounced during the dry season. The principal cells contained eosinophilic granules, which were PAS positive while the dense cells did not show affinity for the stains. The mean gross weights, acini diameters, and epithelial heights were greater during the rainy season than the dry season. Ultrastructural evaluation showed that the cytoplasm of the principal cells contained well-developed Golgi complexes, rough endoplasmic reticulum, mitochondria, and secretory vesicles of varying electron densities and sizes. The secretory vesicles were numerous during the early rainy season, decreased during the late rainy season and were scanty during the peak dry season. The simple columnar epithelium observed during the rainy season was replaced by an undefined stratified epithelium during the dry season, and this was associated with cellular degenerations and regenerations. In conclusion, E. helvum has a typical mammalian bulbourethral gland, with a unique cell type, the dense cell whose functions are not well-understood. The gland exhibits cyclical seasonal variation in structure and secretory activity; being active during the early rainy season (breeding season), and showing the lowest activity during the dry season (non-breeding season). Glandular epithelial cell renewal occurs during the dry season in preparation for the next breeding season.     

Characteristics of the biological cycle of Lutzomyia evandroi Costa Lima & Antunes, 1936 (Diptera: Psychodidae) under experimental conditions

Lutzomyia evandroi Costa Lima and Antunes, 1936 is found in Rio Grande do Norte, northeastern Brazil, in areas of visceral and mucocutaneous leishmaniasis and follows the same geographic distribution of L. longipalpis. The biological cycle, oviposition, morphological and behavioral characteristics of the species were studied under experimental conditions. The average number of eggs per wild caught female varied from 21 to 50 eggs along the year, with a peak occurring between January and March and another in August, with oviposition lasting for 4 to 12 days. The mean larval phase was 24 days. Ovipositing rates were influenced by rainfall and temperature indexes, with an increase of eggs per oviposition at the beginning and at the end of the rainy season, and a decrease at the peak of the rainy season.     

Seasonal changes in African ungulate groups

Size and age/sex composition were recorded for social groups of seven ungulate species over two years. Most species showed seasonal changes which were correlated with rainfall or with their breeding cycle. Group sizes tended to increase during the rainy seasons, although some species, particularly wildebeeste, also aggregated strongly on fresh burns. For all seasonally breeding species, the average male had little contact with females during the conception peak, although female herds almost invariably had about one attendant male.     

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.     

A POPULATION STUDY OF AN EQUATORIAL LAND SNAIL, LIMICOLARIA MARTENSIANA (ACHATINIDAE)

Near the equator in Uganda, the herbivorous land snail, Limicolaria martensiana , occurs in well-defined populations. These populations may be very large and the snails may in places occur at exceedingly high densities. The snails breed all the year round, but with two peaks that correspond with the two annual dry seasons. They enter dispause whenever the weather is very dry. The size of adult snails seems environmentally determined and it varies in different populations : the largest snails occur on soil rich in calcium. The shells of the snails are highly variable and polymorphic in colour and pattern. In particular, there is a streaked form that occurs in all populations, and four distinct pallid "dilute" forms. The relative frequency of the forms varies markedly in different populations. Polymorphism is greatest at high population densities and the snails are all streaked where they are rare. Polymorphism can be distinguished in Pleistocene fossil populations.     

Mass transfer during lactation of an ice-breeding pinniped, the grey seal (Halichoerus grypus), in Nova Scotia, Canada

The land planarian Microplana termitophaga is one of three invertebrate predators feeding at the open chimneys of the mound of the termite Odontotermes transvaalensis in Harare. This paper records over 4000 field observations of the mound and reports on the planarians over three rainy seasons from 1990 to 1993. Microplana termitophaga is crepuscular with a large early morning and a smaller evening activity peak. Rainfall appears to be of over-riding importance; activity is confined to the rainy season, occurring once the cumulative rainfall reaches 150-250 mm and being suspended during longish dry spells. Activity is also favoured by ambient relative humidity above 70%, light intensity below 50,000 lux (but not total darkness) and ambient temperature between 13 and 23C. Planarians on sun-exposed, but not on shaded, mounds disappeared after a drought. Dispersal occurs during prolonged wet weather.
Microplana termitophaga occurs with two predatory spider species and a commensal phorid fly and they all utilize the same termites. These four species exhibit temporal separation, probably related to their specific micro-climatic needs.     

典型岩溶洼地土壤水分的空间分布及影响因素

在桂西北典型岩溶洼地的旱季和雨季,用地统计学结合GIS方法研究了洼地表层(0—16cm)土壤水分的空间分布特征及其影响因素。结果表明:土壤含水量受前期降雨量的影响,且旱季土壤水分对降雨量的反应较雨季敏感。土壤水分均呈中等变异且变异系数随着平均含水量的增加而减少。土壤水分的半方差参数显示土壤水分空间变异及其主导因素随旱、雨季而不同。此外,不同取样区域及取样时段内土壤含水量高低差别明显,分布格局及空间变异程度各异,这主要与当地环境和人为因素的综合影响有关。旱、雨季土壤水分均与前期降雨导致的土壤平均含水量变化呈相反趋势,且不同土地利用方式下的土壤含水量不同。土壤含水量还与土壤有机碳含量呈显著正相关,此外,地势及裸岩率也是造成洼地土壤水分变异及其分布差异的重要因素。下一步应根据旱季和雨季土壤水分分布及影响因素的差异,在岩溶洼地采取有针对性地土壤水资源利用及其水分管理策略。     

Evaluation of the efficacy of Trichogramma evanescens Westwood (Hym., Trichogrammatidae) inundative releases for the control of Maruca vitrata F. (Lep., Pyralidae)

Abstract: The bean podborer, Maruca vitrata (F.), is a serious pest on leguminous crops in the tropics. There are several natural enemies of M. vitrata present in the Philippines, but none of them suppress pest populations naturally below an economic threshold. The egg parasite Trichogramma evanescens Westwood is commercially available for augmentative biological control and a known parasite of podborer eggs. The objective of the present study was to evaluate the efficacy of inundative releases of the egg parasite T. evanescens for controlling M. vitrata in the Philippines. In 1999 and 2000, controlled releases of T. evanescens were made in fields of yardlong bean, Vigna unguiculata, during the dry and rainy seasons in Central Luzon, Philippines. Adult populations of M. vitrata were monitored using light traps. Population density of M. vitrata was found to be positively correlated with rainfall and was subsequently higher during the rainy season, relative to that in the dry season. In quality control experiments, emergence of locally available T. evanescens was found to be highly variable between years, 72% in 1999 and 58% in 2000. The percentage of female parasites was 54% in both years. Survival of T. evanescens in the laboratory after 7 days was found to be only 29 and 21% in 1999 and 2000, respectively. Four parasite releases (each 150 000 wasps per hectare) spaced 7 days apart during the reproductive stage of V. unguiculata were made in three 5 × 5 m plots. Host finding efficacy was identified by exposing M. vitrata eggs laid on cowpea leaves in rearing chambers for 24 h in the fields. Percentage parasitism was higher during the dry season, relative to that in the rainy seasons. In release plots, parasitism increased by 53% during dry and by 43% during rainy season compared with control plots. Despite significant reductions in larval numbers during the dry season, no difference in percentages of pods damaged was found. In the rainy season, the number of larvae per plant and the percentage of pods damaged by M. vitrata larvae were not reduced by T. evanescens releases. The experimental results are critically discussed as a possible part of an integrated pest management system.     

Seasonal mortality factors of the coffee leafminer, Leucoptera coffeella

Seasonal population fluctuation of the coffee leafminer, Leucoptera coffeella (Guérin-Méneville & Perrottet) (Lepidoptera: Lyonetiidae), led to an investigation of its natural mortality factors during the rainy season when the population level is low and during the dry season when population peaks occur. Life-table data were collected from insecticide-free plots within a 3 ha coffee plantation on the upper, medium and lower canopy. Leafminer mortality was similar among the canopy parts but varied in the two seasons studied. During the rainy season, the generational mortality averaged 94.3%, with 50.2, 33.7 and 10.4% occurring during egg, larval and pupal stages, respectively. During the dry season, total mortality was 89%, with 13.2, 61.0 and 14.8% occurring during egg, larval and pupal stages, respectively. Marginal mortality rates during the rainy season were highest for physiological disturbances, rainfall and egg inviability; but, in the dry season, they were highest for predaceous wasps, physiological disturbances and parasitoids. Egg and larval stages accounted for most of the mortality variation in the rainy season, while the combination of larval and pupal mortality better described the generational mortality in the dry season. Variation in mortality during the rainy season was primarily associated with egg inviability, rainfall and parasitoids. In contrast, predatory wasps and physiological disturbances were the main factors associated with mortality variation during the dry season. These results suggest that weather conditions, natural enemies and plant quality attributes are the main determinants of the population dynamics of L. coffeella.     

Effects of dietary calcium on growth and oviposition of the African land snail Limicolaria flammea (Pulmonata: Achatinidae)

In an attempt to elucidate the role of calcium in the life of the edible Achatinid snail, Limicolaria flammea (Miller) I investigated short and long term effects of calcium added to the food. The short term experiments lasted for 18, 30 and 32 weeks respectively, while the long term experiment to determine life time utilization of calcium carbonate lasted for 15 months. In the short term experiments, hatchlings were divided into densities of one, ten and 50 snails. In the 10 snail group, there was a positive correlation between calcium provision, body weight (t test, p < 0.01; r = 0.96, p < 0.0001) and shell length (t test, p < 0.01; r = 0.96, p < 0.00001). There was also a positive correlation between increase in shell length and availability of calcium in the 1 snail group (t test, p< 0.01; r = 0.99, p < 0.00001). In the 50-snail group, the correlation was positive for shell length of the snails (t test, p < 0.05; r = 0.99, p < 0.0001) and body weight (t-test, p < 0.05; r = 99, p < 0.00001). Mortality was very high in the snails deprived of calcium and they did not produce eggs. In the long term experiment, there were three feeding peaks in L. flammea. In the first feeding peak, amount of food and calcium ingested by the snails increased in the first three months of life. The second feeding peak occurred at six months of age, while the last occurred at 10 months of age. The amount of calcium ingested during the second peak decreased gradually in the 4th and 5th month. The amount of calcium ingested was lowest during the 3rd feeding peak. The period of highest weight gained by the snails was between the 1st and 6th month and then dropped at between six and 12 months of age which corresponds to the period of egg production. There were also three peaks of egg production; the first was between six and eight months (535 eggs), the second at between 10 and 11 months (350 eggs) and the third at 13 to 14 months (310 eggs) respectively.     

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.     

Field observations on the population dynamics of Bulinus globosus, the intermediate host of Schistosoma haematobium in the Ifakara area, Tanzania

The population dynamics of Bulinus globosus were studied in a stream and an adjacent pool near Ifakara, Tanzania. Experiments with caged snails were used to determine fecundity, hatching rates, growth and mortality. Growth and mortality rates were also estimated for the natural population from successive size frequency distributions. Oviposition began in snails as small as 6.6 mm and there was a positive correlation between the size of the snails at oviposition and the number of embryos per egg mass. Fecundity was season-dependent. In the pool, snail growth was constant throughout the year, while in the stream, growth was markedly reduced during the rainy season. Mortality rates correlated with fluctuations in snail population density and were highest during the rainy season and among young snails. The high intrinsic rate of natural increase observed for B. globosus enables it to exist in habitats which alternate frequently between favorable and adverse conditions.     

Impact of a Rhabditid Nematode on Survival and Fecundity of Cernuella virgata (Mollusca: Helicidae)

Pairs and single adults of the terrestrial snail Cernuella virgata were exposed to various densities of the rhabditid isolate R954 during breeding experiments in the laboratory. Fecundity and viability of C. virgata breeding in nematode-free and in nematode-infested soil was compared. Exposure to R954 significantly reduced the number of eggs produced by C. virgata and the survival of adult snails. Differences in nematode densities (50, 100 and 150 nematodes cm -2 ) had no effect on egg production or snail survival. Snail eggs laid during the breeding experiments were fertile and young hatched after 2-3 weeks. R954 was not able to penetrate eggs of C. virgata but nematodes were observed inside the hatchlings and caused high mortality.     

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.