Management of environmental temperature and rations for poultry production in the hot and humid tropics

This paper reviews studies that have been conducted to determine how environmental temperature affects productivity of poultry and how these effects can be alleviated so that the bird will realise its full productive capacity. It is shown that temperature primarily affects production of poultry meat and eggs through food consumption. A key factor in efficient weight gain and/or egg production of poultry is optimum nutrient intake. High environmental temperatures cause food intake to decrease and often result in inadequate nutrient intake contributing to poor performance. When nutrient intake is shifted by the influence of temperature on food intake, the adverse effect on productivity (growth or egg output) may be alleviated through improved feed formulation by adjusting the nutrient density to compensate for the altered intake of food. Improved feed management and better housing systems can partially compensate for low feed intake caused by high environmental temperatures.     

Determinants of t Flemingia congesta and t Dactyladenia barteri mulch decomposition in alley-cropping systems in the humid tropics

Effects of soil macrofauna, micro-environment and mulch quantity were investigated on an acid Ultisol in a high-rainfall area in S.E. Nigeria, using litterbags or littertubes with leaves from the trees of an alley cropping system with t Flemingia congesta or t Dactyladenia barteri as hedgerow species.There was no effect of mulch quantity on the rate of decomposition. Soil macrofauna contributed to between 30 and 40% of mulch decomposition over the period of approximately 50% of disappearance of the original material. The faunal effect became apparent after a longer incubation period (>20 weeks) with the slower decomposing t Dactyladenia than with the t Flemingia mulch (immediate effect). This is presumably related to t Dactyladenia's higher lignin content (40% compared to 22% for t Flemingia). The t Flemingia mulch decomposed faster in alley cropping with t Dactyladenia hedgerow than with t Flemingia hedgerow, irrespective of faunal access, suggesting a microclimate efffect on decomposition. There were no marked changes in chemical composition of the mulches with decomposition period, except for a rapid decrease of K content in both mulches and a rapid increase in lignin content of the t Flemingia mulch within the first 10 days of decomposition, which indicates that early decomposition affected the relatively easily degradable compounds.     

Comparative ecophysiology of CAM and C3 bromeliads. II. Field measurements of gas exchange of CAM bromeliads in the humid tropics

Abstract The results described represent the first detailed measurements of gas exchange of epiphytic plants with crassulacean acid metabolism (CAM) in the humid tropics. A portable steady-state CO₂ and H₂O porometer was used to measure net exchange rates of CO₂ and H₂O vapour (J_CO2, J_H2O), leaf temperature (T₁), air temperature (T_A), air relative humidity (RH) and photosynthetically active radiation (PAR) for bromeliads in the field during the dry season in February and March 1983 on the tropical island of Trinidad. Different lengths of tubing (up to 25 m) were used so that the gas exchange could be measured of bromeliads in situ in their epiphytic habitats. Derived parameters such as leaf-air water-vapour-concentration difference (Δ_w), water-vapour conductance of leaves (g) and internal CO₂ partial pressure (pⁱ_CO2) could be calculated. The particular problems of making such measurements in the humid tropics due to high relative humidities and high dew-point temperatures are discussed. The long and often broad, strap-like leaves of bromeliads are well suited for measurements with the steady-state porometer. It is shown that CAM activity varies along the length of individual leaves, and variability between different leaves is also demonstrated. The major phases of CAM, i.e. nocturnal stomalal opening, CO₂ uptake and dark fixation as malic acid (Phase I), daytime stomatal closure and light-dependent assimilation of CO₂ derived from decarboxylation of the malic acid (Phase III), and late-afternoon stomatal opening with direct light-dependent assimilation of atmospheric CO₂ (Phase IV) were all clearly shown by CAM bromeliads in situ. Their expression and magnitude depended on the environmental conditions. An early-morning peak of CO₂ uptake as is characteristic of Phase II of CAM was not detected during the night-day transition. A bromeliad intermediate between C₃ and CAM, Guzmania monostachia, showed substantial net CO₂ uptake in the early morning but no net uptake integrated over the whole of the night.     

Nutrient stocks in managed and natural humid tropical fallows

Managed fallows which recover nutrients more rapidly than natural secondary vegetation may improve the performance of shifting agriculture systems operating under inadequately long fallow cycles. Our objective was to construct nutrient balances for the soil, vegetation, and litter compartments of six planted leguminous fallows and natural secondary vegetation during 53 months. The fallows were planted on a previously cultivated Ultisol (Acrisol) in the Peruvian Amazon and included:Centrosema macrocarpum (Centrosema),Pueraria phaseoloides (Pueraria),Stylosanthes guianensis (Stylosanthes),Desmodium ovalifolium (Desmodium),Cajanus cajan (Cajanus), andInga edulis (Inga). In addition, in the natural fallow treatment secondary vegetation was allowed to establish and grow naturally. Quantities of extractable P, K, Ca, and Mg, total N, and organic C in soil to a 45 cm depth, and macrouttrients in aboveground biomass, roots, and litter were estimated at fallow planting, at 8, 17, and 29 months afterward, and at fallow clearing (53 months). Total N stocks increased by 10% in the Stylosanthes, Desmodium, Pueraria, and Inga treatments, but changed little in the Cajanus, Centrosema and natural fallows. This difference was largely due to greater net increases in both soil and vegetation compartments in the former group of treatments. In the Inga, Desmodium, and natural fallows, total stocks of P and K at 53 months were about 40% to 80% greater and 12% greater, respectively, than initial values, but Ca and Mg stocks were reduced by 25% to 40%. In the other treatments, there was generally little change in P stocks, but large (30% to 60%) reductions in K, Ca, and Mg during the course of the fallow. Although there were net decreases of stocks of P, K, Ca, and Mg in soil in all treatments during the fallow, storage of P and K in vegetation and litter in the Inga, Desmodium, and natural fallows offset losses of these nutrients from soil. These treatments also tended to accumulate more Ca and Mg in biomass and litter than the other treatments. These results suggest that leguminous fallow vegetation that accumulates large amounts of biomass may increase N, P, and K stocks, but that incomplete recuperation of Ca and Mg may limit the sustainability of short-rotation fallow-based systems on acidic, infertile soils. ei]Section editor: G R Stewart     

Intensive Farming, Agro-Diversity, and Food Security Under Conditions of Extreme Population Pressure in Western Kenya

This paper examines the impact of very high population densities and agricultural intensification on farm diversity and food security. Geertz and other researchers have suggested that intensification is likely to lead to crop specialization and a loss of diversity. Others, especially for Africa, have argued that intensification maintains or even increases agro-diversity. The case of Hamisi, in western Kenya, one of the most densely populated areas in all of rural Africa, supports the latter scenario. Farmers engage in a wide variety of sophisticated practices that maintain exceptionally high levels of agro-diversity. Their farming system includes complex patterns of intercropping, polyvariety, an emphasis on multi-purpose crops, and the close integration of crops and livestock. Despite this agro-diversity, we find that the intense population pressure in Hamisi has resulted in such small landholdings that diet quality and food security are seriously jeopardized. Despite the diversity of their farms, most families are highly dependent on market purchases and they consume very limited quantities of nutritionally dense foods, especially protein.     

Population pressure,labor availability,and agricultural disintensification: The decline of farming on Rusinga Island,Kenya

Despite a steady increase in population since the 1930s, farmers on Rusinga Island in Kenya have abandoned many traditional intensive agricultural practices, including the construction of hillside terraces. At the same time, low crop yields have led to a chronic shortage of food on the island. This paper, based on an analysis of archival materials and a detailed agronomic study of the farming system, analyzes the causes of this process of disintensification. Labor scarcity resulting from migrant wage employment and the growing importance of the fishing industry has been a major factor in the decline of agriculture on the island. The loss of soil conservation practices and serious weed infestations have contributed to the collapse of farm productivity. This study highlights the importance of understanding not only the local ecology but also the broader political and economic environment in order to explain farmers' decisions and the process of agricultural change.     

Ecological degradation and agricultural intensification in the Andean highlands

Andean cultural ecologists have made two claims in recent years: ecological decomposition is absent due to effective indigenous management of communal resources, and agricultural intensification is inversely related to altitude. Drawing on material from the Jukumani Indians of Northern Potosi, Bolivia, these assertions are challenged. First, there is little evidence to prove or disprove ecological degradation. Second, the location of agricultural intensification, as the Jukumani data suggests, is influenced by altitude as well as by the presence of market.Fieldwork in Bolivia was carried out between January 1979 and May 1981. This essay was originally presented at a conference entitled, How Communities Resolve Common Property Problems, sponsored by the Harvard Institute for International Development and the Center for Population Studies of Harvard University in the spring semester of 1983.     

On the diversity of the Cladocera in the tropics

The mythical concept of an impoverished tropical cladoceran fauna is refuted. On a planetary scale, around half of the cladoceran species presently known occur exclusively in the tropics-subtropics, often with considerable restriction to particular geographical subzones. On a regional (political) scale, the situation is often unclear because of the continued fragmentary nature of studies, and because political units are not a good basis for biogeographical comparisons. At the finest level of resolution (lake-perlake comparisons), there appears to be an upper limit of c. 50 cladoceran species per individual lake. No significant difference between lakes in the temperate zone and in the tropics could be established here. Daphnia is largely absent from the tropics, but is replaced by more Sidids, Moinids, and Bosminids, such that the average cladoceran community in the limnetic zone of a tropical lake is not characterized by less species but rather by lower population densities. This, in turn, is considered a consequence of higher prevalent predation levels in the tropics.     

Assessment and attempt to explain the high performance of Azolla in subdesertic tropics versus humid tropics

Two similar experiments aimed at selecting performingAzolla strains at Richard Toll, Senegal (subdesertic tropics) and Los Baños, Philippines (humid tropics) show that annual mean productivity of the tested strains is higher in the first site than in the second, the best ecotypes in Senegal producing more than twice as much as in the Philippines.Attempts to explain these differences by climatic or interaction of climatic variables (in the range explored) are unsuccessful. Further analyses are thus needed to understand the reasons, climatic or other, responsible for the different behaviour ofAzolla under the two studied ecologies.     

Habitat associations and breeding success of yellowhammers on lowland farmland

1.  Yellowhammers began to decline on British lowland farmland in the late 1980s and losses are presently 10% per year. This study examined variation in the habitat selection and breeding success of yellowhammers, allowing an evaluation of whether Britain's yellowhammer decline might have been caused by recent changes in agriculture.
2.  Yellowhammer territories were associated with hedgerows, vegetated ditches and wide uncultivated grassy margins around fields. Pasture and silage leys were avoided. Nests were built among herbaceous vegetation in ditches or in the shrubby vegetation of hedgerows.
3.  Breeding started slightly earlier on organic farms than on intensively managed farms, but no measure of breeding success differed between farm types. Predation was the cause of most (64%) nest failures. A maximum of three breeding attempts (two successful) was observed per pair, with a mean clutch size of 3·3, a Mayfield nest success rate of 0·46, and 2·6 nestlings fledged per successful brood. These data, together with published estimates of adult yellowhammer survival and of post-fledging survival among other passerines, suggest that breeding productivity is too low to maintain a stable population.
4.  The removal of hedgerows or abandonment of hedge management, filling or clearing of ditches, intensification of grassland management and cropping or grazing right up to the field edge, are all likely to have adversely affected yellowhammers on lowland farmland in southern England. Policy reforms that redirect subsidy support to environmentally beneficial management of field margin habitats and retention of winter-feeding sites such as stubbles should assist in restoring populations of breeding yellowhammers on lowland farmland.
5.  Our data expand further the array of farmland bird species for which interactions between agricultural change and population change are increasingly understood.     

Population genetics in the American tropics

Summary The authors examined seasonal and plant food preferences of members of Drosophila willistoni group in three different ecosystems in Colombia. The results show that there are seasonal preferences as well as food preferences. Furthermore, there exist clear cut temporal (hours of the day) selection which would make possible the sympatric exploitation of equal ecological niches. Comparisons with melanogaster species and with obscura species group are also made.     

Nitrification and mineralization potentials in a limed Ultisol in the humid tropics

Summary We studied the effect of liming on the rates of mineralization and nitrification in a coarse-textured kaolinitic Ultisol. Soil samples were taken from field plots which received lime rates from 0 to 4mt/ha three years prior to the study. The pH of the soil samples varied from 4.2 to 6.1. Ammonification of soil organic N and added urea source proceeded readily and was not affected by lime rate. Nitrification occurred in both limed and unlimed soils but the rate of nitrification depended upon the rate of lime application. Soil pH, exchangeable Ca and exchangeable A1 were significantly correlated with the amount of NO₃-N accumulated at the end of the 65 days incubation period. Nitrification of NH₄-N from ammonium sulfate was absent in soils receiving lower rates of lime which gave pH values ranging from 4.2 to 4.8. Added ammonium source was nitrified readily after a 3-week delay period in the soil (pH 6.1) which received a higher rate of lime (4 mt/ha).     

Nitrogen use efficiency of monoculture and hedgerow intercropping in the humid tropics

The design of productive and efficient intercropping systems depends on achieving complementarity between component species resource capture niches. Spatiotemporal patterns of capture and use of pruning and urea nitrogen (N) by trees and intercrops were elucidated by isotopic tracing, and consequences for nitrogen use efficiency were examined. During the first cropping season after applying urea–¹⁵N, maize accounted for most of the plant ¹⁵N recovery in Peltophorum dasyrrachis (33.5%) and Gliricidia sepium (22.3%) hedgerow intercropping systems. Maize yield was greatest in monoculture, and maize in monoculture also recovered a greater proportion of urea ¹⁵N (42%) than intercropped maize. Nitrogen recovery during active crop growth will not be increased by hedgerow intercropping if hedgerows adversely affect crop growth through competition for other resources. However, hedgerows recovered substantial amounts of ¹⁵N during both cropping cycles (e.g. a total of 13–22%), showing evidence of spatio-temporal complementarity with crops in the spatial distribution of roots and the temporal distribution of Nuptake. The degree of complementarity was species-specific, showing the importance of selecting appropriate trees for simultaneous agroforestry. After the first cropping season 17–34% of ¹⁵N applied was unaccounted for in the plant-soil system. Urea and prunings N were recovered by hedgerows in similar amounts. By the end of the second (groundnut) cropping cycle, total plant ¹⁵N recovery was similar in all cropping systems. Less N was taken up by the maize crop from applications of labelled prunings (5–7%) than from labelled urea (22–34%), but the second crop recovered similar amounts from these two sources, implying that prunings N is more persistent than urea N. More ¹⁵N was recovered by the downslope hedgerow than the upslope hedgerow, demonstrating the interception of laterally flowing N by hedgerows.     

Generalised regressions provide good estimates of insect and spider biomass in the monsoonal tropics of Australia

Abstract  The estimation of arthropod biomass is often important in studies of terrestrial ecosystem structure and function, including analyses of the relative importance of different arthropod taxa in the diet of insectivorous animals. In order to estimate arthropod biomass in eucalypt woodlands and rehabilitated mine-land in the monsoonal tropics of northern Australia, insect morpho-species ( n  = 693) and spider morpho-species ( n  = 100) were collected, sorted, then weighed and measured. Body length–weight regressions were determined for spiders, nine insect orders and all insects combined. There was a significant relationship between body length and weight for all taxonomic groups, with the power model being a better predictor than linear or exponential models for all groups except Diptera (which was best predicted by the linear model). Whilst Schoener (1980) found that the length–weight regression slopes of neotropical insects (all orders combined, as well as several individual orders) differed from those of their temperate North American counterparts, our comparisons between monsoon-tropical and temperate Australian arthropods suggested differences among Dipterans and spiders only. We conclude that generalised regressions provide adequate estimates of arthropod biomass across Australia, providing that the body proportions of the dominant taxa do not vary substantively.     

Population dynamics of animals in unpredictably-changing tropical environments

We studied population dynamics of a solitary phytophagous beetle,Epilachna viqintioctopunctata and a social stingless bee,Trigona minangkabau, in Sumatra, Indonesia for 5 years from 1981. Population increase ofEpilachna vigintioctopunctata was suppressed in months of normal rainfall (≥300mm) but was released in the 1982–1983 El Nino-Southern. Oscillation when rainfall dropped to 50% of the long-term average. Mechanisms might be direct; rainfall lowered egg hatchability and the time of adult’s residence on host plants. When dry weather continued for more than three generations, theEpilachna vigintioctopunctata population reached a density at which food shortage due to defoliation occurred. Although parasitism of immature stages was high, it was not a population-regulating factor. Thus, there were two types of ecological crunch: competition for food resources at the end of favourable dry periods and high mortality during heavy rainfall periods that usually followed El Nino-Southern Oscillation dry conditions. By an experimental addition of artificial nest sites, colony density ofTrigona minangkabau increased 2.5 times the original density of natural colonies. One-half of artificial nest sites were occupied by arboreal ants and thus competition for nest sites with ants suppressed further increase ofTrigona minangkabau. Intermediate rainfall was favourable forTrigona minangkabau because the rate of colony foundation decreased both during dry El Niño-Southern Oscillation months and months with heavy rain. Colony death was independent from rainfall. Many colonies that survived for 6 months persisted for >2 years and colony density was quite stable.Trigona minangkabau colonies could survive even under unfavourable periods, by hoarding resources in the nest. There was no significant ecological crunch during the study period and colony density almost always tracked the carrying capacity of the habitat, which was basically determined by nest-site abundance. Climatic conditions, especially rainfall, changed with various periodicities, 4–5 years for El Nino-Southern Oscillation, and 2 years for the monsoon and other shorter periods. The contribution of periodicities of 1 and 0.5 years, that were linked to movement of the sun, were weak, indicating that animals could not use seasonal changes of environments,e.g. daylength, to predict environmental changes. We discuss traits adaptive to such unpredictably-changing tropical environments. Separation of predictability of temporal environmental change and synchronous changes among patches improves our understanding. Low oviposition rate and resulting prolonged life-span ofEpilachna vigintioctopunctata, usually associated withK-selected traits of life history, seem to be adaptations for unpredictable environmental changes.     

Reproductive response in supplemented heifers in the humid tropics of Costa Rica

To evaluate the effect of two supplementary diets to determine the consequence on productive and reproductive performance in heifers (Bos indicus x Bos taurus) averaging between 24 and 36 months of age and grazing tropical pastures, two trials were conducted. Thirty animals (initial BW 325.1+/-33.6 kg) were divided in two groups in the initial study: supplemented (SG) and control (CG); SG received a concentrate (5.5% CP and 2.85 Mcal/kg of DE dry matter basis) at 1% of body weight (BW). In the second study, 45 heifers (initial BW 332.6+/-29.3 kg) were assigned in two treatments, with the same amount of supplement (1% BW) but with a greater nutrient content (13% CP and 3.15 Mcal/kg of DE). The proportion of animals with a corpus luteum at the end of each study was greater in the supplemented groups (P<0.05). Ovarian follicular dynamics was similar between groups in the first study, but in the second study there were more heifers in the SG group with follicles larger than 9 mm in diameter (P<0.05). Pregnancy rate was similar for SG and CG (P>0.05). The response to a regimen of estrous synchronization in both trials was numerically superior in the SG group. No differences were observed in the length of estrus. Daily gain and body condition score were similar for supplemented and control groups (0.27 compared with -0.06 in the first study and 0.90 kg compared with 0.60 in the second study, respectively). Dietary supplementation improved the number of animals initiating estrous cycles and the expression of estrus when compared with unsupplemented control heifers. The dietary regimens imposed in these studies appear to be an adequate for the management of growing heifers destined to a reproductive program.     

海南睑虎种群密度调查研究

关于睑虎属Goniurosaurus物种的研究主要集中在新种描述和系统进化等方面,对种群密度量化的研究较少。为研究海南吊罗山国家级自然保护区海南睑虎Goniurosaurus hainanensis种群的资源现状,2019年7—9月,在保护区内选取2个不同海拔梯度的样区(A样区551～688 m和B样区289～448 m),采用标记重捕法对该物种的种群密度进行了调查,并分别采用Schnabel法和Lincoln指数法进行种群密度估算。结果显示:采用Schnabel法估算的种群密度A样区为501只/hm²,B样区为1 999只/hm²;采用Lincoln指数法估算的种群密度A样区为583只/hm²,B样区为1 403只/hm²。结果表明:该物种的种群密度随海拔升高呈下降趋势。