Differences in transpiration rates between tropical and temperate grasses under controlled conditions

Summary Two experiments were conducted to determine the transpiration rates of tropical and temperate grasses under a range of environmental conditions. In dense populations, three temperate grasses lost considerably more water per unit leaf area than did four tropical grasses, though tropical grasses tended to produce more dry matter per unit leaf area. The efficiency of production in relation to water use was thus greater in tropical than in temperate grasses. Wheat, a temperate grass, lost water at an average rate 2.25 times that of sorghum, a tropical grass, on a unit leaf area basis when single leaves were exposed to temperatures from 17 to 32° and light intensities from 1.7 to 4.4×10⁴ ergs cm^-2 sec^-1 at 0.55 (1,100 to 2,800 ft.-c.). The measurement of transpiration and leaf temperature indicated that latent heat loss was much more important in wheat, and sensible heat loss was more important in sorghum as means of dissipating excess energy absorbed. These findings were attributed to the greater resistance to gas diffusion offered by sorghum than by wheat stomata in each environment.     

Stress responses in tropical sparrows: comparing tropical and temperate Zonotrichia

Seasonal modulation of the adrenocortical response appears to be ubiquitous in mid- to high-latitude vertebrates but has not been investigated in tropical vertebrates. Previous studies demonstrate that temperate passerines show seasonality in corticosterone secretion and corticosteroid binding globulin capacities. We examined seasonal and sex differences in the stress response in an equatorial population of Zonotrichia capensis, the only Zonotrichia that breeds in the tropics, and compared the results with those of northern Zonotrichia. Seasonal differences in tropical Zonotrichia would presumably be independent of photoperiod and thus directly related to such activities as reproduction and feather molt. In addition, we investigated the possible role of binding globulin as a sex steroid binding globulin, as suggested for temperate passerines. Similar to northern congeners, Z. capensis show seasonal modulation in total corticosterone and binding globulin capacity with higher levels during breeding than molt. However, unlike many temperate passerines, there are no sex differences in corticosterone secretion or binding globulin capacity. Furthermore, the seasonal differences in total corticosterone diminish when the free levels are calculated. The contrast between equatorial and northern congeners indicates factors such as breeding environment and life-history strategy may play important roles in shaping stress response in these species.     

Phytoplankton and its dynamics in two tropical lakes: a tropical and temperate zone comparison

Temporal patterns of phytoplankton biomass and community structure are described for two Kenyan lakes and subsequently compared with patterns reported in other tropical and temperate lakes. Lake Naivasha had a lower and more seasonally variable (10×) biomass, with a seasonal shift between diatoms and blue-greens, while the L. Oloidien biomass was less variable (3.7×) and dominated by blue-greens. Biomass and chlorophyll a were strongly correlated and in turn were coupled to the level of total phosphorus. A total of 143 and 94 taxa were described for L. Naivasha and L. Oloidien, respectively.The comparative analysis showed: a) a paucity of exclusively tropical species; b) that more than 30 percent of the species in two highly saline Kenyan lakes were also present in the two freshwater lakes; c) no evidence for a postulated decline of phytoplankton species abundance with latitude from the temperate zone to the tropics; d) that the low fraction of chrysophyte biomass in tropical lakes is a function of trophy rather than of latitude; e) that the fraction of chlorophyte biomass in tropical lakes is generally higher than in temperate lakes; f) that the proportion of nannoplankton in the two Kenyan freshwater lakes is not different from that in temperate lakes of the same trophy; g) that seasonal or annual biomass oscillations in the tropics are not systematically lower than in the temperate zone; h) evidence for large inter-year difference in the max.:min. biomass ratio in the only tropical lake (L. Naivasha) for which such data are available; i) that an average biomass ratio appears predictable for tropical lakes from the proportion of the sediment surface in contact with epilimnetic water. Overall, no evidence was found that the freshwater tropical phytoplankton composition or dynamics differ in any fundamental fashion from that observed in the temperate lakes during the summer.Contribution number 147 of the Limnology Research Centre, McGill University.     

Bayesian meta-analysis of demographic parameters in three small, temperate passerines

Accurate estimates of population parameters are vital for estimating extinction risk. Such parameters, however, are typically not available for threatened populations. We used a recently developed software tool based on Markov Chain Monte Carlo methods for carrying out Bayesian inference (the BUGS package) to estimate four demographic parameters; the intrinsic growth rate, the strength of density dependence, and the demographic and environmental variance, in three species of small temperate passerines from two sets of time series data taken from a dipper and a song sparrow population, and from previously obtained frequentist estimates of the same parameters in the great tit. By simultaneously modeling variation in these demographic parameters across species and using the resulting distributions as priors in the estimation for individual species, we improve the estimates for each individual species. This framework also allows us to make probabilistic statements about plausible parameter values for small passerines temperate birds in general which is often critically needed in management of species for which little or no data are available. We also discuss how our work relates to recently developed theory on dynamic stochastic population models, and finally note some important differences between frequentist and Bayesian methods.     

Isolation and characterization of a temperate cyanophage for a tropical Anabaena strain

In this paper we describe the isolation and characterization of a temperate cyanophage N(S)1 of the genus cyanopodovirus which produces turbid plaques on the host Anabaena 77S15 isolated from tropical soil. Its properties have been compared to those of other well-characterized cyanophages. In addition, two strains of Anabaena 77S15 lysogenic for N(S)1 were isolated. N(S)1 seems to be integrated into the chromosome of the two lysogens, and a 2 kb plasmid present at a low copy number in the non-lysogenic strain is amplified significantly.     

Subcanopy gaps in temperate and tropical forests

Abstract We present a model of gaps in the vertical structure of forest vegetation. The traditional model of a forest gap assumes the existence of a ‘hole’ in the uppermost canopy layer, often extending down to near the ground. The present model extends the concept to gaps at any level, including those in lower layers below an intact canopy or subcanopy. It assumes that gaps at any level represent spaces with unused resources, especially favourable for plant growth and survival. Evidence from temperate and tropical forests indicates that gaps in the subcanopy and understorey layers below intact canopies are common, and that plants have higher growth rates in them than in non-gap sites. We also extend this model to below-ground gaps in the root zone.     

Extended parental care and delayed dispersal: northern, tropical, and southern passerines compared

Using modern comparative methods, we found that both time toindependence and time with parents were significantly longerin southern hemisphere and tropical birds than in northern hemisphereones. These differences held even after removing Australianpasserines or cooperatively breeding species, and they do notdepend on habitat, diet, or migration pattern. In southern hemisphereand tropical regions, both cooperative breeding and non-cooperativeparents continue to feed their young for a similar length oftime, but cooperative breeders allow them to stay longer intheir natal territory after they become nutritionally independent.Nevertheless, the young of non-cooperative species stay longerwith their parents than do the young of non-cooperative speciesin the temperate northern hemisphere. The fact that extendedperiods of post-fledging parental care are widespread amongpasserines provides further empirical support for the view thatlife histories of southern and tropical birds are ‘slow,’with small clutches, extended parental care, and long lifespan;parents take care of fewer young for longer. These results supportrecent theoretical models that predict that high adult survivaland low turnover of territory owners generally favor natal philopatry.We suggest that the reasons why some species (with or withoutcooperative breeding) exhibit natal philopatry and others donot lie in the balance between productivity and survival ofadults and of retained or dispersing offspring.     

Nitrogen cycling in tropical and temperate savannas

Savannas are the most common vegetation type in the tropics and subtropics, ranging in physiognomy from grasslands with scattered woody plants to woodlands with heterogeneous grass cover. Productivity and organic matter turnover in savannas are controlled by interactions between water and nutrient availability, and this basic environmental structure is modified by fire frequency and land management practices. We compared temperate and tropical savannas in order to understand the strength of nitrogen (N) limitation of productivity. American tropical and temperate savannas are N limited systems, and the N cycle differs according to the woody plant density, fire frequency, land use change, N deposition and N fixation. Grazing and conversion to pasture have been the predominant land-use changes in most savannas. In the Cerrado and the Llanos tropical savannas, intensified use of fire for pasture management is leading to decreased woody plant density. Oppositely, in the Chaco and North American temperate savannas, fire suppression and grazing are leading to increases in woody density. In addition, the higher soil P availability in the Gran Chaco and the higher N deposition in North American savannas may be contributing to increases of N cycling and net productivity rates. Some aspects of the N budget for savannas of the American continent are still unclear and require further analysis to determine rates of N fixation, and to understand how spatial and temporal soil heterogeneity control N fluxes through soil solution and into streams.     

Comparative lime requirements of tropical and temperate legumes

Summary In a field trial using a continuous function design, calcium carbonate was applied to a nitrogen deficient Hawaiian Oxisol at rates which increased along the plant row from 0 to 22 tons/ha, producing a gradient in soil pH from 4.7 to 7.1. Inoculated legumes representing 18 species were grown.Lime response curves showed no distinct general difference between tropical and temperate legumes. Within each group, individual species varied. Responsiveness rankings of species varied depending on criterion of response.The species ranked as follows according to the amount of lime needed for 90% of the maximum attained yield: Coronilla varia (16 tons/ha) > Leucaena leucocephala (11) > Phaseolus vulgaris, Medicago sativa (9–10) > Glycine max var. Kanrich (7) > Glycine wightii var. Cooper, Lotus corniculatus (6) > Glycine wightii var. Tinaroo, Trifolium repens, Trifolium subterraneum (5) > Desmodium canum, Dolichos axillaris, Glycine max var. Kahala (4) > Arachis hypogea, Desmodium intortum, Vigna sinensis (1–2) > Stylosanthes fruticosa, Stylosanthes guyanensis (0.1).The species ranked as follows according to the magnitude of yield increase due to lime: C. varia (20-fold increase) > T. repens (9-fold) > L. leucocephala, D. axillaris, M. sativa (6-fold) > G. wightii var. Tinaroo (5-fold) > P. vulgaris (4-fold) > G. wightii var. Cooper, L. corniculatus (3-fold) > D. canum, D. intortum, T. subterraneum (2-fold) > A. hypogea, G. max, S. fruticosa, S. guyanensis, V. sinensis (30–50%).Improved calcium availability could account for plant responses to lime rates over 3 to 4 tons/ha. Only 4 tons CaCO₃ sufficed to raise soil pH to 6 and depress solution aluminum and manganese to low concentrations, but 6 tons were needed to raise soluble calcium to 1 meq/l and 20 tons to raise it to 3 meq/l.Journal series No. 1953 of the Hawaii Agricultural Experiment Station.Department of Soils and Plant Nutrition, University of California, Davis.Department of Agronomy and Soil Science, University of Hawaii, Honolulu.     

Convergence of temperate and tropical stream fish assemblages

The hypothesis of convergence takes the deterministic view that community (or assemblage) structure can be predicted from the environment, and that the environment is expected to drive evolution in a predictable direction. Here we present results of a comparative study of freshwater fish assemblages from headwater streams in four continents (Europe, North America, Africa and South America), with the general objective of testing whether these assemblages display convergent structures under comparable environmental conditions (i.e. assemblage position in the stream longitudinal continuum). We tested this hypothesis by comparing species richness and trophic guilds of those stream fish assemblages represented in available data from multiple sites on each continent. Independent of phylogenetic and historical constraints, fish assemblage richness and trophic structure in the four continents converged along the stream continua to a substantial degree. For the four continents, assemblage richness increased, the proportion of invertivorous species decreased, and the proportion of omnivorous species increased from upstream to downstream, supporting theoretical predictions of the river continuum concept. However, the herbivore/detritivore and piscivore guilds were virtually absent from our small European and North American stream sites, unlike our African and South American stream sites. This divergence can be linked to differences in energy availability between temperate and tropical systems.     

Neglected tropical diseases and mental health: a perspective on comorbidity

Mental health conditions will be the largest contributor to the global health burden by 2030. Our review suggests that neglected tropical diseases (NTDs) predispose individuals to poor mental health. Factors predisposing to poor mental health include stigma and discrimination, exclusion from participating fully in society, reduced access to health and social services, lack of educational opportunities, exclusion from income-generation and employment opportunities, and restrictions in exercising civil and political rights. These characteristics are all features of NTDs, but the mental health of these sufferers has been ignored. This review raises an issue of concern and highlights the opportunities for research by psychiatrists and psychologists on NTDs.     

Biotechnology and the improvement of silage (tropical and temperate) rumen digestion: a mini-review

Summary As with forage diets in general, ensiled tropical residue feeds and temperate grass and legume herbage tend to have lower fibre digestibility, ruminal biomass production and feed bypass, resulting in limited protein nutrition and intake in the animal. Various modified (recombinant and mutated) microbial inculants might be used mainly to: (1) boost lactic acid production in temperate silage to stabilize against further clostridial protein breakdown during the ensiling process and effect silage fibre (lignin, cellulose, and hemicellulose) digestion to increase digestibility and (2) increase microbial digestion of fibre along with boosting microbial protein synthesis to increase microbial biomass production in the rumen.     

Biogeography of sponge chemical ecology: comparisons of tropical and temperate defenses

Examples from both marine and terrestrial systems have supported the hypothesis that predation is higher in tropical than in temperate habitats and that, as a consequence, tropical species have evolved more effective defenses to deter predators. Although this hypothesis was first proposed for marine sponges over 25 years ago, our study provides the first experimental test of latitudinal differences in the effectiveness of sponge chemical defenses. We collected 20 common sponge species belonging to 14 genera from tropical Guam and temperate Northeast Spanish coasts (Indo-Pacific and Mediterranean biogeographic areas) and conducted field-based feeding experiments with large and small fish predators in both geographic areas. We use the term global deterrence to describe the deterrent activity of a sponge extract against all of the predators used in our experiments and to test the hypothesis that sponges from Guam are chemically better defended than their Mediterranean counterparts. Sympatric and allopatric deterrence refer to the average deterrent activity of a sponge against sympatric or allopatric predators. All of the sponges investigated in this study showed deterrent properties against some predators. However, 35% of the sponge species were deterrent in at least one but not in all the experiments, supporting the idea that predators can respond to chemical defenses in a species-specific manner. Tropical and temperate sponges have comparable global, sympatric, and allopatric deterrence, suggesting not only that chemical defenses from tropical and temperate sponges are equally strong but also that they are equally effective against sympatric and allopatric predators. Rather than supporting geographic trends in the production of chemical defenses, our data suggest a recurrent selection for chemical defenses in sponges as a general life-history strategy.     

Life history strategies of cladocerans: comparisons of tropical and temperate taxa

We review recent works on different life history variables of cladoceran taxa in tropical and temperate freshwater bodies, comparing the strategies that cladocerans have evolved to adapt to contrasting environmental conditions in the two geographical regions. These life-history parameters relate to age and size at maturity, survival, fecundity, life-expectancy at birth, lifespan, gross, and net reproductive rates, generation time, the rate of population increase, peak population density and day of peak abundance. We also discuss the role of photoperiod and temperature on some of these life history parameters. We found a general paucity of experimental work and field data in tropics on cladocerans. There is very limited information on the few Daphnia species found in the tropics. The misconception of low species diversity of cladocerans in the tropics arose due to several reasons including lack of extensive and intensive field collections. Higher water temperatures apparently promote permanent infestation of tropical waters with toxic cyanobacteria, which reduce the zooplankton diversity. In addition to higher temperatures in the tropics, the year-round high predation pressure of planktivorous fish probably causes the tropical species, particularly in pelagic habitats, to reach maturity earlier (< 3 days) than in temperate regions. Species of Daphnia in temperate regions are particularly adapted to living at food concentrations that are much lower and seasonably more variable than those for tropical genera such as Diaphanosoma. This is further corroborated by the more than an order of magnitude higher threshold food concentration (TFC) for tropical Cladocera than for their temperate counterparts. Fecundity patterns differ between tropical and temperate cladoceran taxa: cultured under optimal temperature regimes, tropical taxa have fewer eggs than temperate species of a comparable body size. Predation pressure may act differently depending on the size of the cladoceran neonates and thus on their population size structure. Global warming and climate changes seem to affect the behaviour (migration), distribution, and abundance of cladocerans. Apparently, in direct response to these changes, the possibility of encountering the tropical cladocerans in the northern, temperate hemisphere (bioinvasions) is on the rise.     

Strategic emphases for tropical diseases research: a TDR perspective

Setting priorities for health research is a difficult task, especially for the neglected diseases of the poor. A new approach to priority setting for tropical diseases research has been adopted by the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (known as the TDR). Priorities are defined on the basis of a comprehensive analysis of research needs and research opportunities for each of the ten major tropical diseases in the TDR portfolio. The resulting strategic emphases matrix reflects the priorities for tropical diseases research from the perspective of the TDR. Its purpose is not to impose global research priorities, but we believe the results could be useful to other organizations.     

Strategic emphases for tropical diseases research: a TDR perspective

Setting priorities for health research is a difficult task, especially for the neglected diseases of the poor. A new approach to priority setting for tropical diseases research has been adopted by the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (known as the TDR). Priorities are defined on the basis of a comprehensive analysis of research needs and research opportunities for each of the ten major tropical diseases in the TDR portfolio. The resulting strategic emphases matrix reflects the priorities for tropical diseases research from the perspective of the TDR. Its purpose is not to impose global research priorities, but we believe the results could be useful to other organizations.     

Phenology of temperate trees in tropical climates

Several North American broad-leaved tree species range from the northern United States at 47°N to moist tropical montane forests in Mexico and Central America at 15–20°N. Along this gradient the average minimum temperatures of the coldest month (T_Jan), which characterize annual variation in temperature, increase from –10 to 12°C and tree phenology changes from deciduous to leaf-exchanging or evergreen in the southern range with a year-long growing season. Between 30 and 45°N, the time of bud break is highly correlated with T_Jan and bud break can be reliably predicted for the week in which mean minimum temperature rises to 7°C. Temperature-dependent deciduous phenology—and hence the validity of temperature-driven phenology models—terminates in southern North America near 30°N, where T_Jan>7°C enables growth of tropical trees and cultivation of frost-sensitive citrus fruits. In tropical climates most temperate broad-leaved species exchange old for new leaves within a few weeks in January-February, i.e., their phenology becomes similar to that of tropical leaf-exchanging species. Leaf buds of the southern ecotypes of these temperate species are therefore not winter-dormant and have no chilling requirement. As in many tropical trees, bud break of Celtis, Quercus and Fagus growing in warm climates is induced in early spring by increasing daylength. In tropical climates vegetative phenology is determined mainly by leaf longevity, seasonal variation in water stress and day length. As water stress during the dry season varies widely with soil water storage, climate-driven models cannot predict tree phenology in the tropics and tropical tree phenology does not constitute a useful indicator of global warming.     

Self-similar land cover heterogeneity of temperate and tropical landscapes

Landscapes are complex objects often showing self-similar properties. For example, some power law exponents and fractal dimensions have been extensively used as global metrics for describing spatial arrangements of landscape land covers. This paper presents some newly found invariance properties for rural landscapes, with the hope to prepare further theory capable to link these properties mechanistically with generating processes. For this purpose, I propose a new surface-pattern analysis computing heterogeneity metrics into moving windows in a specific way. This generic method provides Multiscale Heterogeneity Maps (MHMs) and Heterogeneity Profiles (HPs) of almost any kind of landscape. Six landscapes, covering a wide range of observed mosaics have been analyzed by this way: four of them exhibit strong self-similar evenness (diversity) heterogeneity over two orders of magnitude with an apparent universality of the power law exponents (γ = ?0.19 ± 0.02). Such landscape self-organization is interpreted in terms of spatial arrangements of numerous land covers and fine scale patchy mosaics. This study suggests that most of terrestrial landscapes could exhibit power law behaviors in terms of evenness heterogeneity and could be the result of a hidden optimization of ecological and/or socio-economic processes.