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1. Nutrients are a critical resource for plant growth, but the elements limiting growth in tropical forests have rarely been determined. 2. We investigated the influence of nitrogen (N), phosphorus (P), potassium (K) and micronutrients on seedling biomass and nutrient allocation in a factorial nutrient fertilization experiment in lowland tropical forest at the Barro Colorado Nature Monument, Panama. We also measured 8 years of herbivory and growth for 1800 seedlings. We sought to determine the identity of limiting elements and possible nutrient interactions. 3. The five study species were Alseis blackiana, Desmopsis panamensis, Heisteria concinna, Sorocea affinis and Tetragastris panamensis. Plants grew in deeply shaded understorey with a mean canopy openness of 4.9% (±0.7%; 1 SE). 4. Tissue N concentration increased by 11% with N addition. Tissue P concentration increased by 16% with P addition. Tissue K increased by 4% with K addition. K addition reduced root‐to‐shoot biomass ratio. There was no significant effect of fertilization on specific leaf area or leaf area ratio. 5. The proportion of leaves damaged and the mean level of damage by herbivory increased with P and K addition and showed a significant P × K interaction. 6.7ensp;Across all species and years, relative growth rate of height increased with K addition and with N and P in combination. Relative growth rate of leaf count trended 8.5% higher with K addition (P = 0.076). 7. We also added micronutrients in a parallel experiment. There was no effect of micronutrient addition on any seedling parameter. 8. Synthesis. K addition affected seedlings by enhancing tissue nutrient concentration, increasing herbivory, reducing root‐to‐shoot biomass ratio and increasing height growth. Additional effects of N or P on tissue chemistry, herbivory and growth offer support for the multiple limiting resources hypothesis. Our results suggest that seedling growth is limited by nutrients, especially K, even under highly shaded conditions in this lowland tropical forest.

We used nitrogen isotope analysis from pectoral muscle of the Egyptian fruit bat Rousettus aegyptiacus (Chiroptera: Pteropodidae) to determine intrapopulation variation in sources of dietary protein throughout the year in northern Israel. In Mediterranean climates, winter and summer are stable seasons, whereas spring and fall are transitional seasons. Number of species of fruit-bearing plants is higher during the transitional periods, and we therefore predicted that intrapopulation variation would be higher during spring than in winter and summer; we made no prediction for fall because sample size was small. We also reconstructed sources of dietary protein for each individual using nitrogen isotope ratios ([[delta].sup.15]N) to determine whether individuals foraged on the same sources of food within each season. Intrapopulation variation in [[delta].sup.15]N was significantly higher in spring ([[delta].sup.15]N range: 9.7-17.5%o) compared to winter (8.8-11.1%o) and summer (9.5-11.2%o), suggesting that individuals during this period varied more in their use of protein sources. Dietary reconstruction revealed intrapopulation partitioning among the bats in the use of plant food items, and interspecific partitioning among plants in their dependence on dispersal by bats. Key words: dietary mixing models, dietary protein, intrapopulation variation, pteropodid bats, Rousenus aegyptiacus, stable-isotope analysis

The controlled adjustment of body temperature ( Tb) by animals in relation to ambient temperature ( Ta), or heterothermy, is a phenomenon that has a clear adaptive value. Heterothermy results in a substantial reduction in energy expenditure and water loss, but it also incurs costs, such as the energy cost required for rewarming, energy cost of excretion of metabolic wastes, delayed development of offspring and fitness costs of increased vulnerability to predators. A general index quantifying heterothermy would be useful, since heterothermy is often correlated with important physiological variables that determine fitness., We used metabolic rate ( MR), Tb and Ta to develop a thermoregulatory index ( TRi), a continuous variable that describes the thermoregulatory effort of animals. TRi is expressed by an equation with two terms: the deviation of actual heat gain/dissipation to heat gain/dissipation predicted by first principles and the temperature dependence of metabolic reactions., TRi can be interpreted as a measure of the amount of time an animal needs to generate an amount of heat, estimated from physical principles, to reach a certain Tb along a temperature gradient., TRi eliminates the need to define a threshold for Tb and can be used to compare positions of animals along a thermoregulatory continuum within and among species of diverse taxonomic affiliation. In addition, TRi unveils the relationship between the energy expended for thermoregulation and important physiological variables that determine survival and reproduction. TRi requires knowledge of MR, which may be a disadvantage since information on MR for free-living animals may be difficult to obtain. However, with the advent of methods to measure field metabolism, this impediment may be surmountable in many species. [ABSTRACT FROM AUTHOR]

Anthropogenic habitat modification often has a profound negative impact on the flora and fauna of an ecosystem. In parts of the Middle East, ephemeral rivers (wadis) are characterised by stands of acacia trees. Green, flourishing assemblages of these trees are in decline in several countries, most likely due to human-induced water stress and habitat changes. We examined the importance of healthy acacia stands for bats and their arthropod prey in comparison to other natural and artificial habitats available in the Arava desert of Israel. We assessed bat activity and species richness through acoustic monitoring for entire nights and concurrently collected arthropods using light and pit traps. Dense green stands of acacia trees were the most important natural desert habitat for insectivorous bats. Irrigated gardens and parks in villages and fields of date palms had high arthropod levels but only village sites rivalled acacia trees in bat activity level. We confirmed up to 13 bat species around a single patch of acacia trees; one of the richest sites in any natural desert habitat in Israel. Some bat species utilised artificial sites; others were found almost exclusively in natural habitats. Two rare species (Barbastella leucomelas and Nycteris thebaica) were identified solely around acacia trees. We provide strong evidence that acacia trees are of unique importance to the community of insectivorous desert-dwelling bats, and that the health of the trees is crucial to their value as a foraging resource. Consequently, conservation efforts for acacia habitats, and in particular for the green more densely packed stands of trees, need to increase to protect this vital habitat for an entire community of protected bats. [ABSTRACT FROM AUTHOR]