Abstract. Both means and year-to-year variances of climate variables such as temperature and precipitation are predicted to change. However, the potential impact of changing climatic variability on the fate of populations has been largely unexamined. We analyzed multiyear demographic data for 36 plant and animal species with a broad range of life histories and types of environment to ask how sensitive their long-term stochastic population growth rates are likely to be to changes in the means and standard deviations of vital rates (survival, reproduction, growth) in response to changing climate. We quantified responsiveness using elasticities of the long-term population growth rate predicted by stochastic projection matrix models. Short-lived species (insects and annual plants and algae) are predicted to be more strongly (and negatively) affected by increasing vital rate variability relative to longer-lived species (perennial plants, birds, ungulates). Taxonomic affiliation has little power to explain sensitivity to increasing variability once longevity has been taken into account. Our results highlight the potential vulnerability of short-lived species to an increasingly variable climate, but also suggest that problems associated with short-lived undesirable species (agricultural pests, disease vectors, invasive weedy plants) may be exacerbated in regions where climate variability decreases.

Summary 1.Resource acquisition and allocation are the physiological mechanisms integrating foraging and life-history traits. An understanding of the patterns of acquisition and allocation in different environments and organisms is critical to a predictive theory of life history. 2. Here I develop an allocation framework, which provides a template for conceptualizing the interactions among resource acquisition, allocation and life-history traits. The framework describes the process through which food is taken in by an organism at specific life stages, then allocated to growth, survival (including maintenance, defence, dispersal, etc), reproduction and further foraging. 3. I use the allocation framework to examine allocation to life-history traits in insects under both benign and stressful environments. Stressful environments result from resource scarcity or harsh environmental conditions. I consider effects of consistent stress or variable stress across time. 4. Several broad generalizations emerge from empirical studies, viewed in the allocation framework. First, resource congruence, or the requirement for specific nutrient ratios in, for example, eggs, results in different limiting nutrients for each life-history trait. Second, the timing of resource acquisition affects both allocation patterns and the identity of limiting nutrients for a given life-history trait. Third, physiological trade-offs may occur across, not just within, life stages. Fourth, apparent trade-offs may be driven by differences among traits in resource congruence constraints and deleterious effects of excess nutrients on a particular trait. Fifth, allocation response to environmental stress shows age-specific and sex-specific patterns. Sixth, physiological trade-offs are often more pronounced under environmental stress. Finally, even within insects, there is considerable variability in allocation response to environmental stress. We do not yet have sufficiently diverse and thorough case studies to understand why this is so. Studies in the wild, or relating laboratory conditions to wild environments, are also needed. 5. Senescence can also be understood in an allocation framework. The present approach provides a necessary functional basis for understanding patterns of senescence in diverse organisms and environments. 6. The allocation framework fosters a mechanistic understanding of life-history patterns, and the beginning of an understanding of the processes underlying those patterns.

The allocation of nutritional resources to reproduction in animals is a complex process of great evolutionary significance. We use compound-specific stable isotope analysis of carbon (GC͞combus-tion͞isotope ratio MS) to investigate the dietary sources of egg amino acids in a nectar-feeding hawkmoth. Previous work suggests that the nutrients used in egg manufacture fall into two classes: those that are increasingly synthesized from adult dietary sugar over a female's lifetime (renewable resources), and those that remain exclusively larval in origin (nonrenewable resources). We predict that nonessential and essential amino acids correspond to these nutrient classes and test this prediction by analyzing egg amino acids from females fed isotopically distinct diets as larvae and as adults. The results demonstrate that essential egg amino acids originate entirely from the larval diet. In contrast, nonessential egg amino acids were increasingly synthesized from adult dietary sugars, following a turnover pattern across a female's lifetime. This study demonstrates that female Lepidoptera can synthesize a large fraction of egg amino acids from nectar sugars, using endogenous sources of nitrogen. However, essential amino acids derive only from the larval diet, placing an upper limit on the use of adult dietary resources to enhance reproductive success.