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Summary Herbivores face various nutritional challenges in their life cycles, challenges that may become increasingly acute under ongoing environmental changes. Here, focusing on calcium, phosphorus and nitrogen, we used nutritional geometry to analyse individual-based data on foraging and extraction efficiencies, and combined these with data on reproduction and migratory behaviour to understand how a large herbivorous carnivore can complete its life cycle on a narrow and seemingly low quality bamboo diet. Behavioural results showed that pandas during the year switched between four main food categories involving the leaves and shoots of two bamboo species available. Nutritional analysis suggests that these diet shifts are related to the concentrations and balances of calcium, phosphorus and nitrogen. Notably, successive shifts in range use and food type corresponded with a transition to higher concentrations and/or a more balanced intake of these multiple key constituents. Our study suggests that pandas obligatorily synchronize their seasonal migration and reproduction with the disjunct nutritional phenologies of two bamboo species. This finding has potentially important implications for habitat conservation for this species and, more generally, draws attention to the need for understanding the nutritional basis of food selection in devising management plans for endangered species.

Summary 1In this study we address how growth rate in consumers may be regulated by nitrogen (N)- and phosphorus (P)- limitation of ribonucleic acid (RNA), using the rotifer Brachionus calyciflorus as the model organism. 2Growth rate, RNA and weight-specific concentrations of carbon (C), N and P were analyzed in B. calyciflorus fed algae with different C : N, C : P and N : P ratios. 3Growth rate correlated negatively with food C : N, but not with C : P or N : P, strongly suggesting N-limited growth. Growth rate also strongly correlated with tissue concentrations of RNA and P, in support of the growth rate hypothesis which states that specific P-content of organisms reflects their RNA-content and thus capacity for protein synthesis. 4Food C : N rather than C : P regulated the growth, RNA and P in this consumer under the food conditions applied. This suggests that availability of N can also be an important regulator of cellular acquisition of P and build-up of ribosomes in that animals released from N-limitation have an increased demand for the P-rich cellular machinery for protein synthesis. 5The data suggest a strong reciprocal regulation of consumer demands and their C : N : P stoichiometry via the intimate connections between ribosome allocation and protein synthesis and also lend support to the view that reduced protein synthesis efficiency under high growth rates may affect stoichiometry of the consumer.

Summary 1 We studied the associations among growth rate, RNA content and P content at ∼12-h intervals during the larval stage in five species of Drosophilids that specialize on host foods that differ substantially in P content. 2 Consistent with expectations based on the ‘growth rate hypothesis’ (GRH), within each species there were significant positive correlations between growth rates and RNA and P contents and in each species variation in P content was largely determined by differences in RNA content. However, there was a significant difference among species in how these three parameters were associated with each other, primarily due to differences in the intercept of the relationships rather than in their slopes. 3 Consistent with the GRH, we also observed positive associations among the average growth rates, RNA contents and P contents of the five species. Furthermore, these differences were broadly consistent with differences in the P content of their host resources: for example, Drosophila falleni, a species that specializes on P-rich mushrooms, had the highest growth rates and P and RNA contents while D. pachea and D. mettleri, species that specialize in low-P exudates from necrotic cacti and trees, had the lowest growth rates and P and RNA contents. 4 While data for additional species are needed, our findings provide further evidence consistent with the GRH and highlight a potential role of P limitation in shaping growth rate evolution in the Drosophilids.

Summary 1 Phosphorus content was measured in adult insects and arachnids from 170 species collected in the Sonoran Desert. 2 Across insect body sizes spanning four orders of magnitude, phosphorus content was inversely related to body mass. The largest species (∼1 g dry) had phosphorus contents that were only about 60% (0·62% P absolute) as high as phosphorus contents of the smallest species (∼0·0001 g dry; 0·97% P). Negative phosphorus allometry was observed within each of seven insect orders and within arachnids. 3 Phosphorus contents of insect predators and herbivores were statistically indistinguishable. 4 More recently derived orders tended to have lower phosphorus contents – with the exception of the most recently derived group (Panorpida = Diptera + Lepidoptera), which had high phosphorus contents.

Summary 1. Temperature strongly affects virtually all biological rate processes, including many central to organismal fitness such as growth rate. A second factor related to growth rate is organismal chemical composition, especially C : N : P stoichiometry. This association arises because high rates of growth require disproportionate investment in N- and P-rich biosynthetic cellular structures. Here the extent to which these factors interact is examined ‐ does acclimation temperature systematically affect organismal chemical composition? 2. A literature survey indicates that cold-acclimated poikilotherms contain on average 30‐50% more nitrogen [N], phosphorus [P], protein and RNA than warm-exposed conspecifics. The primary exception was bacteria, which showed increases in RNA content but no change in protein content at cold temperatures. 3. Two processes ‐ changes in nutrient content (or concentration) and in organism size ‐ contribute to the overall result. Although qualitatively distinct, both kinds of change lead to increased total catalytic capacity in cold-exposed organisms. 4. Temperature-driven shifts in nutrient content of organisms are likely to resonate in diverse ecological patterns and processes, including latitudinal and altitudinal patterns of nutrient content, foraging decisions by organisms living in strong temperature gradients, and patterns of biodiversity.

Summary 1. We examined the relative importance of resource composition (carbon : phosphorus molar ratios which varied between 9 and 933) and growth rate (0·5‐1·5 h - 1 ) to biomass carbon : nitrogen : phosphorus stoichiometry and nucleic acid content in Escherichia coli grown in chemostats, and in other heterotrophic prokaryotes using published literature. 2. Escherichia coli RNA content and the contribution of RNA-P to total cellular P increased with increasing growth rate at all supply C : P ratios. Growth rate had a much stronger effect on biomass C : P than did supply C : P, and increased RNA content resulted in low biomass C : P and N : P ratios. 3. However, we observed only twofold variations in biomass C : P and N : P ratios in the experiments, despite a difference of two orders of magnitude in C : P and N : P supply. The response of biomass C : P and N : P ratios to alteration of the supply C : P and N : P ratios revealed that E. coli was strongly homeostatic in its elemental composition. 4. This result, and a literature survey, suggest that each heterotrophic bacterial strain regulates its elemental composition homeostatically within a relatively narrow range of characteristic biomass C : P and N : P ratios. 5. Thus shifts in the dominance of different bacterial strains in the environment are probably responsible for the large variation in bacterial biomass C : P, as has been suggested for crustacean zooplankton. These findings indicate that bacteria are more like animals than plants in terms of biomass C : P and N : P homeostasis.

1. Nitrogen (N) and phosphorus (P) availabilities are important ecological determinants of resource use in nature. Despite the wide range of hosts used by species of the genus Drosophila, elemental composition of natural resources of these flies has never been investigated. 2. Total body N and P contents were determined in seven species of wild-caught Drosophila, their natural hosts, and artificial diets routinely used to rear these flies in the laboratory. The flies tested included D. hydei, D. arizonae, D. simulans and D. pseudoobscura collected from rotting fruit (melons), and the cactophilic D. nigrospiracula, D. mojavensis and D. pachea collected from their specific host plants, Saguaro, Organpipe and Senita cactus, respectively. 3. Natural hosts varied in elemental composition, with fruit showing higher N (2·8–4·3% dry mass) and P (0·50–0·67%) levels compared with cacti (0·5–1·6% N; 0·01–0·29% P). No consistent differences in N and P levels were found between healthy and necrotic cactus tissue. 4. Total body N and P also varied among Drosophila species. This variation mirrored the levels of N and P found in the respective hosts and laboratory diets. N:P ratios were consistently lower in female flies compared with conspecific males suggesting phosphorus demands during oogenesis are high. 5. Potential mechanisms by which Drosophila deal with N or P limitation in nature are discussed.