Morphology and muscle stress of chelae of temperate and tropical stone crabs Menippe mercenaria

Chela morphology and muscle stress were compared between temperate and tropical populations of stone crabs Menippe mercenuriu (Say) to test whether environmental differences might result in greater crushing strength in the tropics. Such differences include increased crab diversity in the tropics (which might lead to greater fighting among congeners), increased prey exoskeleton calcification in the tropics, and year round chela use in the tropics as opposed to seasonal chela use in the temperate population.
No latitudinal differences were found in any aspect of chela morphology, including relative chela size, mechanical advantage, apodeme surface area, and angle of muscle fibre pinnation. Summer measurements of crusher chela muscle stress were also similar between the two populations.
The maximum muscle stress determined for M. mercenariu was 220 N ∼r n -∼, much higher than stress levels previously reported for crustaceans. Other researchers have typically measured forces either from autotomized chelae or by measuring forces required to open a closed chelae. I have determined muscle stress using a force transducer that measures active gripping strength in live crabs.     

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.     

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.     

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.     

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.     

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.     

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.     

Screening for dioxin-degrading basidiomycetes from temperate and tropical forests

A total of 500 strains of basidiomycetes isolated from temperate forests in Japan and 379 strains from tropical forests in Indonesia were subjected to a laboratory screening for dioxin-degrading ability. At first, about 200 fungal strains were selected by their ability to decolorize Remazol Brilliant Blue R dye as an indicator of ligninolytic activities. Next, for excluding the factor of dioxin sorption by mycelia, we prepared two series of living cultures exposed either long-term or short-term to 2,7-dichlorodibenzo-p-dioxin (2,7-DCDD), and compared the decreases in the remaining amounts of this model compound. We chose Bjerkandera adusta strain VH57 as a promising new candidate for dioxin degradation, because it gave 40% difference in 2,7-DCDD levels between the two treatments after 30 days of exposure.     

Land crabs as key drivers in tropical coastal forest recruitment

Plant populations are regulated by a diverse assortment of abiotic and biotic factors that influence seed dispersal and viability, and seedling establishment and growth at the microsite. Rarely does one animal guild exert as significant an influence on different plant assemblages as land crabs. We review three tropical coastal ecosystems–mangroves, island maritime forests, and mainland coastal terrestrial forests–where land crabs directly influence forest composition by limiting tree establishment and recruitment. Land crabs differentially prey on seeds, propagules and seedlings along nutrient, chemical and physical environmental gradients. In all of these ecosystems, but especially mangroves, abiotic gradients are well studied, strong and influence plant species distributions. However, we suggest that crab predation has primacy over many of these environmental factors by acting as the first limiting factor of tropical tree recruitment to drive the potential structural and compositional organisation of coastal forests. We show that the influence of crabs varies relative to tidal gradient, shoreline distance, canopy position, time, season, tree species and fruiting periodicity. Crabs also facilitate forest growth and development through such activities as excavation of burrows, creation of soil mounds, aeration of soils, removal of leaf litter into burrows and creation of carbon-rich soil microhabitats. For all three systems, land crabs influence the distribution, density and size-class structure of tree populations. Indeed, crabs are among the major drivers of tree recruitment in tropical coastal forest ecosystems, and their conservation should be included in management plans of these forests.     

Energy limitation of hummingbird populations in tropical and temperate communities

Summary Regular censuses were conducted at both a temperate alpine and a tropical lowland site to determine seasonal changes in the composition of hummingbird communities and the availability of their food. From these data we calculated the total daily energy demand by the hummingbirds (Daily Energy Expenditure; DEE) and the daily energy supply available from floral nectar (Daily Energy Production; DEP) for each community census. Despite differences in habitat type and hummingbird community structure between these two sites, the hummingbird populations were often at or near carrying capacity. On average, all of the daily nectar production was cropped by the birds. We suggest that the supply/demand economics of coevolved mutualisms favour the evolution of complete resource use.     

The carbon balance of tropical, temperate and boreal forests

Forest biomes are major reserves for terrestrial carbon, and major components of global primary productivity. The carbon balance of forests is determined by a number of component processes of carbon acquisition and carbon loss, and a small shift in the magnitude of these processes would have a large impact on the global carbon cycle. In this paper, we discuss the climatic influences on the carbon dynamics of boreal, temperate and tropical forests by presenting a new synthesis of micrometeorological, ecophysiological and forestry data, concentrating on three case-study sites. Historical changes in the carbon balance of each biome are also reviewed, and the evidence for a carbon sink in each forest biome and its likely behaviour under future global change are discussed. We conclude that there have been significant advances in determining the carbon balance of forests, but there are still critical uncertainties remaining, particularly in the behaviour of soil carbon stocks.     

Species richness and niche space for temperate and tropical folivores

We measured structural and chemical traits of the leaves of native, broad-leaved trees in two temperate localities [southern Ontario, Canada (34 species), and Missouri (36 species)] and one tropical locality [central Panama (samples of 21 and 23 species)] to test the hypothesis that the greater diversity of tree species and herbivore species in the tropics is associated with greater resource niche space for herbivores. Variables were leaf toughness, water content, dry mass per unit area, several structural and nutritional carbohydrates, common mineral elements, including nitrogen and phosphorus, and several defensive compounds, including tannins and alkaloids. The four samples were almost fully separable by discriminant analysis on the basis of these leaf traits. Variance in log-transformed trait values among species was lowest in the most northern sample, but did not differ significantly between Missouri and Panama. Niche space, estimated as the square root of the total variance in the log-transformed variables within each locality, varied approximately as Panama = 1, Missouri = 0.8, Ontario = 0.5. Although niche space decreases towards higher latitudes, the change does not match the ca. sixfold decrease in tree species richness or the ca. fourfold decrease in Lepidopteran species richness over the latitude range of our samples. Accordingly, tropical folivore diversity is associated with greater resource niche overlap, greater niche specialization, and/or more completely filled niches, or with variation in niche dimensions not measured in this study.     

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.     

Sperm competition in tropical versus temperate zone birds

Sperm competition represents an important component of post-copulatory sexual selection. It has been argued that the level of sperm competition declines in birds towards the equator. However, to date, sperm competition estimates have been available mainly for avian species inhabiting the northern temperate zone. Here we apply a novel approach, using the coefficient of between-male variation (CV_bm) in sperm size as an index for sperm competition risk, in a comparative analysis of 31 Afrotropical and 99 northern temperate zone passerine species. We found no difference in sperm competition risk between the two groups, nor any relationship with migration distance. However, a multivariate model indicated that sperm competition risk was highest in species with a combination of low body mass and few eggs per clutch. The effect of clutch size was most pronounced in tropical species, which indicates that sperm competition risk in tropical and temperate species is differently associated with particular life-history traits. Although tropical species had lower sperm competition risk than temperate zone species for overlapping clutch sizes, the idea of a generally reduced risk of sperm competition in tropical birds was not supported by our analysis.     

Traits and ecological strategies of Australian tropical and temperate climbing plants

Aim Understanding large scale patterns in trait variation in climbing plants (lianas, vines, scramblers, twiners) is important for the development of a stronger theoretical understanding of climbing plant ecology and for more applied issues such as prediction of community assembly under changing climatic conditions. We compared values of five key functional traits for 388 species of climbing plant from tropical and temperate regions of Australia to quantify variation between these two biogeographic regions. Location Australia. Methods Data on dispersal mode, growth habit, leaf form, leaf size and seed mass were compiled from field measurements and published sources. Comparative analyses were performed in three ways: (1) across species where each species was treated as an independent data point, (2) using evolutionary divergence analyses for each trait, and (3) in multidimensional space using a matrix of similarities between species. Results Tropical climbing plants had 22‐fold greater seed mass and four times greater leaf size than did temperate species. Tropical climbers were more likely to be woody (63%) than were temperate species (40%). Surprisingly we found a similar proportion of animal‐dispersed seeds in the two regions, although we expected animal‐dispersed seeds to be more prevalent in the tropics. We also found similar proportions of simple‐ and compound‐leaved species between the two regions. All of our findings were consistent between cross‐species and phylogenetic analyses indicating that patterns in present‐day species are reflected in the evolutionary history of Australian climbers. Multivariate analyses suggested that there is a spectrum of variation among climbing plants, with tropical species having greater seed mass, leaf size and woody growth compared with temperate climbing plant species. Main conclusions Tropical and temperate climbers of Australia exhibit a mixture of similar and contrasting traits and ecological strategies. Understanding strategy variation along latitudinal gradients will be particularly informative for predicting ecosystem and community structure with climate change.     

Nitrogen and phosphorus content of some temperate and tropical freshwater fishes

The nitrogen and phosphorus content of two temperate fishes, Rutilus rutilus and Perca fluviatilis , and six tropical fishes, Oreochromis niloticus , Cichla monoculus , Serrassalmus rhombeus , Plagioscion squamosissimus , Prochilodus brevis and Hoplias malabaricus , were investigated to test the hypothesis that variation in body P content and N:P ratio is related to body size. Regressions of %P and N:P ratios against fish size (length and mass) confirmed the hypothesis for P. fluviatilis and P. squamosissimus , suggesting that body size is an important factor driving body P content and N:P ratios in some fishes. Moreover, significant increases in %N and N:P ratio with body size was found for H. malabaricus , a common piscivorous fish of the Neotropics. Interspecific variation in %P and N:P ranged two-fold and significant differences ( P < 0·05) were found among the tested species. The mean ± s . d . elemental content across all fishes ( n = 170) was 10·35 ± 1·29% for N and 3·05 ± 0·82% for P, while the N:P ratio was 8·00 ± 2·14. Data on fish body nutrient content and ratio will improve parameterization of bioenergetics and mass balance models and help clarify the role of fishes in nutrient cycles in both temperate and tropical freshwaters.