Carol L. Boggs

Climate change hastens population extinctions

Climate change is expected to alter the distribution and abundance of many species. Predictions of climate-induced population extinctions are supported by geographic range shifts that correspond to climatic warming, but few extinctions have been linked mechanistically to climate change. Here we show that extinctions of two populations of a checkerspot butterfly were hastened by increasing variability in precipitation, a phenomenon predicted by global climate models. We model checkerspot populations to show that changes in precipitation amplified population fluctuations, leading to rapid extinctions. As populations of checkerspots and other species become further isolated by habitat loss, climate change is likely to cause more extinctions, threatening both species diversity and critical ecosystem services.

LONGEVITY CAN BUFFER PLANT AND ANIMAL POPULATIONS AGAINST CHANGING CLIMATIC VARIABILITY

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.

A general model of the role of male-donated nutrients in female insects' reproduction.

Male insects of many species donate nutrients to their females at mating, and the females can use these nutrients for egg production and somatic maintenance. These male-derived nutrients represent male investment in reproduction. The relative investment by each sex in reproduction has been postulated to be a determinant of the mating system and possible operation of sexual selection. However, the effect of male nutrient donations on female fitness is not well understood. I examine the effect on female fitness of male nutrients donated at mating in terms of the role of male nutrients in the females nutrient budget for egg production. Nonnutritional constraints on total egg mass, the timing of egg production, the quality and quantity of adult female feeding, and alternative functions of male nutrient donations are incorporated into a model describing the role of male-derived nutrients. The model predicts the conditions under which changes in the availability of male-derived nutrients to individual females will be accompanied by changes in female fecundity, in adult female feeding, and/or in the allocation of the total nutrient pool to egg production. The model also can be used to predict the relative importance of male nutrient donations to female reproduction and hence the likelihood of sexual selection mediated by nutrient donations. Furthermore, the model can be used to predict associations of reproductive and foraging traits within a species or population. Data from the literature corroborate the assumption that male-derived nutrients may differ in composition from nutrients available to the female from adult feeding. Literature data also support the predictions that changes in male nutrient donation result in changes in female fecundity only when adult female feeding is restricted and that, given the opportunity, females on restricted adult diets ingest more nutrients from males. Data are not currently available to test other predictions of the model adequately. Finally, new data for two species of Lepidoptera with rich adult diets are presented that support the models prediction that adult female feeding and the acquisition of male nutrients via mating should be inversely correlated when fecundity is constrained by nonnutritional factors. Thus, male-derived nutrients may affect female fitness through effects on foraging as well as on fecundity.

Renewable and nonrenewable resources: Amino acid turnover and allocation to reproduction in Lepidoptera

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 (GC/combustion/isotope 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 females 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 females 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.

The Effect of Adult Food Limitation on Life History Traits in Speyeria Mormonia (Lepidoptera: Nymphalidae)

Variation in food availability is likely to occur in the wild, and may affect resource allocation to various life history traits. Quantitative adult diet restriction had no effect on life-span or mean individual egg mass, but reduced fecundity in the butterfly Speyeria mormonia. The sum of fecundity plus unlaid oocytes remaining in the ovaries at death declined in direct proportion to the reduction in the adult diet. This indicates that oocytes were resorbed and resources re-allocated away from reproduction under resource stress, since the sum of laid and unlaid eggs for butterflies fed ad libitum did not differ from the number of oocytes present in the ovaries at eclosion. In this nectivorous species, then, life-span is conserved at the expense of reproduction under adult resource stress. Further, for butterflies fed ad libitum, the volume of honey-water imbibed declined with age for both sexes. Daily volume imbibed by females fed ad libitum was directly correlated with daily egg production and life-span, suggesting that factors as yet unexplored may be affecting both resource intake and life history traits when resources are available ad libitum.

Ovarian Dynamics in Heliconiine Butterflies: Programmed Senescence versus Eternal Youth.

New oocytes are generated throughout long lives in butterflies of the genus Heliconius, which as adults feed on amino acids from pollen. In Dryas julia, a related heliconiine that feeds only on nectar and is relatively short-lived, the original oocyte supply is eventually depleted. Such divergent ovarian dynamics in closely related organisms are significant in terms of both their evolutionary basis and their physiological controls.

Nutritional and Life-History Determinants of Resource Allocation in Holometabolous Insects

In organisms with complex life cycles, potential reproductive effort at adult emergence may be defined as the sum of the proportion of the body nutrient content devoted to reserves earmarked for reproduction and the proportion of expected adult nutrient intake to be devoted to reproduction, and is proportional to expenditure in reproduction. For organisms with similar larval nutrition and survivorship, the ratio of reproductive reserves to soma at adult eclosion is predicted to vary inversely with expected adult nutrient intake and directly with expected reproductive output of nutrients. These predictions are supported by data from heliconiine butterflies. That is, variation in the ratio of reproductive reserves to soma at adult eclosion among heliconiine species and sexes having relatively equivalent larval survivorship and availability of nutrients correlates with patterns of expected intake of nutrients and output of nutrients in the act of reproduction. In general, changes in the ratio over adult life are then determined by actual nutrient intakes and reproductive outputs.

Larval food limitation in butterflies: effects on adult resource allocation and fitness

Allocation of larval food resources affects adult morphology and fitness in holometabolous insects. Here we explore the effects on adult morphology and female fitness of larval semi-starvation in the butterfly Speyeria mormonia. Using a split-brood design, food intake was reduced by approximately half during the last half of the last larval instar. Body mass and forewing length of resulting adults were smaller than those of control animals. Feeding treatment significantly altered the allometric relationship between mass and wing length for females but not males, such that body mass increased more steeply with wing length in stressed insects as compared to control insects. This may result in changes in female flight performance and cost. With regard to adult life history traits, male feeding treatment or mating number had no effect on female fecundity or survival, in agreement with expectations for this species. Potential fecundity decreased with decreasing body mass and relative fat content, but there was no independent effect of larval feeding treatment. Realized fecundity decreased with decreasing adult survival, and was not affected by body mass or larval feeding treatment. Adult survival was lower in insects subjected to larval semi-starvation, with no effect of body mass. In contrast, previous laboratory studies on adult nectar restriction showed that adult survival was not affected by such stress, whereas fecundity was reduced in direct 11 proportion to the reduction of adult food. We thus see a direct impact of larval dietary restriction on survival, whereas fecundity is affected by adult dietary restriction, a pattern reminiscent of a survival/reproduction trade-off, but across a developmental boundary. The data, in combination with previous work, thus provide a picture of the intra-specific response of a suite of traits to ecological stress.

Reproductive strategies of female butterflies: variation in and constraints on fecundity

ABSTRACT. 1 This study first examines the reproductive strategy of female Speyeria mormonia Edwards (Lepidoptera: Nymphalidae): 2 Egg weight and number laid per day decrease with age. 3 Survival and daily egg number may be affected by temperature; mean daily egg weight is not affected by temperature. 4 Daily egg number is not correlated with body size. In the central range of body size, egg weight is also not correlated with body size. However, exceptionally large or small females lay respectively heavier or lighter eggs than average. 5 A simple trade‐off between offspring size and number does not occur within females on a daily basis, or among females averaged over their lifespans. 6 Fat body resources are depleted at a rate independent of body size. 7 Females are essentially monogamous. 8 Age‐specific fecundity data reported here for S.mormonia are next compared with data for other Lepidoptera with different adult feeding habits and egg maturation patterns, and hence different possibilities for adult feeding to play a role in egg production. Based on these comparisons, I propose that the shape of the age‐specific fecundity curve for each species under optimal conditions is constrained by the potential importance of adult nutrients in egg production.

Resource allocation : exploring connections between foraging and life history

Foraging determines an organisms intake of resources (water, nutrients or energy), while life-history patterns (survival, reproduction, growth) result from resource expenditure on fitness-related activities. Allocation of a limited resource pool among competing life-history traits links foraging and lifehistory strategies (Fig. 1). Although foraging, allocation and life history can be studied independently, they must be integrated in order to understand an organisms ecology and population dynamics in contrasting or variable environments (Pianka 1976; Boggs 1981; Mooney & Chiariello 1984; Gatto, Matessi & Slobodkin 1989). In particular, integration allows us to study ecological dynamics via the effects of input and output variation on the whole system through time. Allocation is arguably both the most important and least understood element in the chain from foraging to life-history strategy. The physiological processes and the life-history effects of allocation have been studied extensively, but they have generally been examined separately. For example, life-history studies have examined correlations between offspring size and number, or among reproduction, storage, maintenance and growth, but have assumed a given resource intake and utilization efficiency (e.g. Cohen 1971; Smith & Fretwell 1974; Snell & King 1977; Reznick 1985; Parker & Begon 1986; Lloyd 1987; Reekie & Bazzaz 1987a-c). Physiological studies have focused on efficiencies of resource utilization, and resultant rates of growth or reproduction, but usually do not relate the results to integrated life-history strategies (e.g. Lei & Armitage 1980; Milne 1987; Briegel 1990; Glazier 1990). Foraging studies have considered patterns of resource intake in variable environments, but generally do not address resource use, even on further foraging effort (e.g. Chapin 1980; Real & Caraco 1986; Hutchings 1988; Tuttle, Wulfson & Caraco 1990). Here I argue that these three sorts of studies must be blended and expanded if we are to understand life-history strategies in variable resource environments. Much life-history and resource allocation work has recently focused on the evolution of specific strategies, for which an understanding of the underlying