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Organisms with complex life cycles undergo ecological transitions between life stages, often resulting in stage-specific resource use. The relative contribution of each stage-specific resource to vital rates influences population dynamics and subsequently whether habitats can support viable populations. In lepidopterans, survival to reproduction requires sufficient resources for immature life stages, but the extent to which resources for adults are critical to population persistence is variable. We studied Boisduval's blue butterflies (Icaricia icarioides), in a greenhouse experiment, to quantify the effect of the adult diet, nectar, on vital rates. Butterflies fed ad libitum produced 3.4 times more eggs, on average, over their lifetime and lived 6 more days relative to those which only had access to water. We used these experimental data to parameterize a population model to test if vital rates with and without nectar result in viable population growth rates. Despite individual females laying 68 eggs without nectar, we found that Boisduval's blue butterfly populations will not persist without the improved fecundity associated with nectar resources (λ < 1). In this species, although amino acids in the adult diet contributed to various improvements in fecundity, these improvements did not translate to improvements in population growth rates. Incorporating our experimental vital rates into a population model indicates that the relative abundance and quality of nectar can alter at what threshold other resource(s) are limiting the population. [ABSTRACT FROM AUTHOR]

Predicting how organisms respond to climate change requires that we understand the temperature dependence of fitness in relevant ecological contexts (e.g., with or without predation risk). Predation risk often induces changes to life history traits that are themselves temperature dependent. We explore how perceived predation risk and temperature interact to determine fitness (indicated by the intrinsic rate of increase, r) through changes to its underlying components (net reproductive rate, generation time, and survival) in Daphnia magna. We exposed Daphnia to predation cues from dragonfly naiads early, late, or throughout their ontogeny. Predation risk increased r differentially across temperatures and depending on the timing of exposure to predation cues. The timing of predation risk likewise altered the temperature-dependent response of T and R0. Daphnia at hotter temperatures responded to predation risk by increasing r through a combination of increased R0 and decreased T that together countered an increase in mortality rate. However, only D. magna that experienced predation cues early in ontogeny showed elevated r at colder temperatures. These results highlight the fact that phenotypically plastic responses of life history traits to predation risk can be strongly temperature dependent. [ABSTRACT FROM AUTHOR]

Clinal variation in body size and related life history traits is common and has stimulated the postulation of several eco-geographical rules. Whereas some clinal patterns are clearly adaptive, the causes of others remain obscure. We investigated intra-specific body size, development time and female fecundity (egg size and number) clines across 13 European populations of the dung fly Sepsis fulgens spanning 20° latitude from southern Italy to Estonia in a genetic common garden approach. Despite very short generation times (ca. 2 weeks at 24 °C), we found a converse Bergmann cline (smaller size at higher latitudes). As development time did not change with latitude (flat cline), integral growth rate thus likely declines towards the pole. At the same time, early fecundity, but not egg size, increased with latitude. Rather than being mediated by seasonal time constraints, the body size reduction in the northernmost flies from Estonia could suggest that these are marginal, edge populations, as when omitting them the body size cline became flat as well. Most of the other sepsid species investigated to date also show flat body size clines, a pattern that strikingly differs from Drosophila. We conclude that S. fulgens life history traits appear to be shaped by similar environmental pressures and selective mechanisms across Europe, be they adaptive or not. This reiterates the suggestion that body size clines can result as a secondary consequence of selection pressures shaping an entire life history syndrome, rendering them inconsistent and unpredictable in general. [ABSTRACT FROM AUTHOR]

Successive generations of bi- and multivoltine species encounter differing biotic and abiotic environments intra-annually. The question of whether selection can independently adjust the relationship between body size and components of reproductive effort within successive generations in response to generation-specific environmental variation is applicable to a diversity of taxa. Herein, we develop a conceptual framework that illustrates increasingly independent life history adjustments between successive generations of taxa exhibiting complex life cycles. We apply this framework to the reproductive biology of the gall-forming insect, Belonocnema treatae (Hymenoptera: Cynipidae). This bivoltine species expresses cyclical parthenogenesis in which alternating sexual and asexual generations develop in different seasons and different environments. We tested the hypotheses that ecological divergence between the alternate generations is accompanied by generational differences in body size, egg size, and egg number and by changes in the relationships between body size and these components of reproductive effort. Increased potential reproductive effort of sexual generation B. treatae is attained by increased body size and egg number (with no trade-off between egg number and egg size) and by a significant increase in the slope of the relationship between body size and potential fecundity. These generation-specific relationships, interpreted in the context of the model framework, suggest that within each generation selection has independently molded the relationships relating body size to potential fecundity and potential reproductive effort in B. treatae. The conceptual framework is broadly applicable to comparisons involving the alternating generations of bi- and multivoltine species. [ABSTRACT FROM AUTHOR]

The range of a species is determined by the balance of its demographic rates across space. Population growth rates are widely hypothesized to be greatest at the geographic center of the species range, but indirect empirical support for this pattern using abundance as a proxy has been mixed, and demographic rates are rarely quantified on a large spatial scale. Therefore, the texture of how demographic rates of a species vary over its range remains an open question. We quantified seasonal fecundity of populations spanning the majority of the global range of a single species, the saltmarsh sparrow ( Ammodramus caudacutus), which demonstrates a peak of abundance at the geographic center of its range. We used a novel, population projection method to estimate seasonal fecundity inclusive of seasonal and spatial variation in life history traits that contribute to seasonal fecundity. We replicated our study over 3 years, and compared seasonal fecundity to latitude and distance among plots. We observed large-scale patterns in some life history traits that contribute to seasonal fecundity, such as an increase in clutch size with latitude. However, we observed no relationship between latitude and seasonal fecundity. Instead, fecundity varied greatly among plots separated by as little as 1 km. Our results do not support the hypothesis that demographic rates are highest at the geographic and abundance center of a species range, but rather they suggest that local drivers strongly influence saltmarsh sparrow fecundity across their global range. [ABSTRACT FROM AUTHOR]

Cuticle melanism in insects is linked to a number of life history traits: a positive relationship is hypothesized between melanism, immune function, fecundity and lifespan. However, it is not clear how activation of the immune system affects trade-offs between life history traits in female mealworm beetles ( Tenebrio molitor) differing in cuticle melanization. The females with tan, brown and black cuticles examined in the present study did not differ in the intensity of encapsulation response, fecundity and longevity when their immune system was not activated. However, we found that immune activation and cuticle melanization have a significant effect on life history traits. Offspring number and lifespan decreased in females with tan and brown cuticles, while the fecundity and lifespan of black females were not affected. Importantly, we inserted the implants again and found a significant decrease in the strength of encapsulation response in females with tan and brown cuticles. In contrast, black females increased melanotic reactions against the nylon implant, suggesting immunological priming. The results show that cuticle melanization plays an important adaptive role under the risk of being infected, while the lack of these benefits before the insertion of nylon monofilaments suggests that there are costs associated with an activated immunity system. [ABSTRACT FROM AUTHOR]

In territorial species, observed density dependence is often manifest in lowered reproductive output at high population density where individuals have fewer resources or are forced to inhabit low-quality territories. The Arctic fox ( Vulpes lagopus) in Iceland is territorial throughout the year and feeds mostly on birds, since lemmings are absent from the country. Thus, the population does not exhibit short-term population cycles that are evident in most of the species' geographical range. The population has, however, gone through a major long-term fluctuation in population size. Because of the stability in hunting effort and reliable hunting records since 1958, the total number of adult foxes killed annually can be used as an index of population size ( N). An index of carrying capacity ( K) from population growth data for five separate time blocks during 1958-2007 revealed considerable variation in K and allowed a novel definition of population density in terms of K, or N/ K. Correlation analysis suggested that the reproductive rate was largely determined by the proportion of territorial foxes in the population. Variation in litter size and cub mortality was, on the other hand, related to climatic variation. Thus, Arctic foxes in Iceland engage in typical contest competition but can adapt their territory sizes in response to both temporal and spatial variation in carrying capacity, resulting in surprisingly little variation in litter size. [ABSTRACT FROM AUTHOR]

Host-parasite theory makes predictions about the influence of host abundance, competition for hosts, and parasite transmission on parasite population size, but many of these predictions are not well tested empirically. We experimentally examined these factors in ponds using two species of freshwater mussels with parasitic larvae that infect host fishes via different infection strategies. For both species, recruitment and larval survival were positively related to host abundance, but there was no apparent minimum host threshold and positive population growth occurred when an average of one fish per mussel was present. Recruitment increased rapidly with an initial increase in host abundance but appeared to approach an asymptote at moderate host abundance. Recruitment and larval survival did not differ according to whether mussel species occurred alone or in combination, providing no evidence for competition for hosts via acquired immunity. However, larval survival of the species that attracts hosts with a lure was higher than the species that infects hosts passively, but lower survival of the latter strategy was offset by higher fecundity, which resulted in comparable recruitment between the two species. The lack of evidence for competition for hosts or host saturation suggests that mussel recruitment is limited primarily by fecundity and larval transmission efficiency. Despite the lack of a minimum host abundance threshold, high variation in recruitment in all treatments suggests that population growth at low host abundance is limited by stochasticity. These results show that host-parasite interactions in natural situations may differ substantially from predictions based on models or laboratory findings. [ABSTRACT FROM AUTHOR]

Many organisms of temperate latitudes exhibit declines in reproductive success as the breeding season advances. Experiments can delay the onset of reproduction for early breeders to investigate the consequences of late nesting, but it is rarely possible to observe a distinct second round of nesting in species that normally nest only once. The colonial cliff swallow ( Petrochelidon pyrrhonota) is a migratory songbird that has a relatively short breeding season in the western Great Plains, USA, with birds rarely nesting late in the summer. Previous work suggested that ectoparasitism is a primary reason why reproductive success in this species declines over the summer. At colony sites where nests were fumigated to remove ectoparasitic swallow bugs ( Oeciacus vicarius), cliff swallows frequently undertook a distinct round of late nesting after previously fledging young that year. Mark-recapture revealed that late-nesting pairs at these colonies produced fewer offspring that survived to the next breeding season, and that survival of late-nesting adults was lower during the next year, relative to pairs nesting earlier in the season. These reproductive costs applied in the absence of ectoparasites and likely reflect other environmental costs of late nesting such as seasonal declines in food availability or a delayed start of fall migration. Despite the costs, the estimated fitness for perennial early-and-late nesters in the absence of ectoparasites was equivalent to that of birds that nested only early in the season. The collective disadvantages of late nesting likely constrain most cliff swallows to raising a single brood in the middle latitudes of North America. [ABSTRACT FROM AUTHOR]

The temporal mismatch hypothesis suggests that fitness is related to the degree of temporal synchrony between the energetic needs of the offspring and their food supply. The hypothesis has been a basis in studying the influence of climate warming on nature. This study enhances the knowledge on prevalence of temporal mismatches and their consequences in boreal populations, and questions the role of the temporal mismatch hypothesis as the principal explanation for the evolution of timing of breeding. To test this, we examined if synchrony with caterpillar prey or timing of breeding per se better explains reproductive output in North European parid populations. We compared responses of temperate-origin species, the great tit ( Parus major) and the blue tit ( Cyanistes caeruleus), and a boreal species, the willow tit ( Poecile montanus). We found that phenologies of caterpillars and great tits, but not of blue tits, have advanced during the past decades. Phenologies correlated with spring temperatures that may function as cues about the timing of the food peak for great and blue tits. The breeding of great and blue tits and their caterpillar food remained synchronous. Synchrony explained breeding success better than timing of breeding alone. However, the synchrony effect arose only in certain conditions, such as with high caterpillar abundances or high breeding densities. Breeding before good synchrony seems advantageous at high latitudes, especially in the willow tit. Thus, the temporal mismatch hypothesis appears insufficient in explaining the evolution of timing of breeding. [ABSTRACT FROM AUTHOR]

Marginal grassland fragments, such as road verges and field margins, may act as important supplemental habitats for grassland plants in the modern agricultural landscape. However, abundance of pollinators in such fragments has been found to decline with distance to larger natural and semi-natural habitats, and this could have corresponding effects on plant pollination. In this study, we performed a field experiment on road verges with three insect-pollinated grassland herbs to examine the relationship between distance to semi-natural grassland and plant reproductive success in two landscapes with contrasting farming intensities. In Lychnis viscaria and Lotus corniculatus, seed production tended to decrease with increasing distance to semi-natural grassland, but only in the landscape with high farming intensity. Seed production in Armeria maritima spp. maritima decreased with distance in both landscapes. Although many studies have investigated effects of natural habitat on crop pollination, little is known about the impact on pollination in native plants. The results from this study indicate that management of semi-natural grasslands improves not only biodiversity within the actual grassland but also pollination of native plants in the surrounding agricultural landscape. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms that species use to succeed in new environments is vital to predicting the extent of invasive species impacts. Food quality is potentially important because it can affect population dynamics by affecting life history traits. The New Zealand mudsnail, Potamopyrgus antipodarum, is a worldwide invader. We examined how mudsnail growth rate and fecundity responded to the C:P ratio of algal food in laboratory conditions. Mudsnails fed low-P algae (C:P 1,119) grew more slowly, matured later, produced smaller offspring, and grew to a smaller adult size than snails reared on algae with high levels of P. A relatively small increase in algal C:P (203–270) significantly increased mudsnail age at maturity. We suggest that the relatively high body P requirements of mudsnails make them susceptible to allocation trade-offs between growth and reproduction under P-limited conditions. The elemental composition of algae varies greatly in nature, and over half of the rock biofilms in streams surveyed within the introduced range of mudsnails in the Greater Yellowstone Area had C:P ratios above which could potentially pose P limitation of life history traits. High growth rate and fecundity are common traits of many species that become invasive and are also associated with high-P demands. Therefore, fast-growing consumers with high P demands, such as mudsnails, are potentially more sensitive to P limitation suggesting that limitation of growth and reproduction by food quality is an important factor in understanding the resource demands of invasive species. [ABSTRACT FROM AUTHOR]

Competition between microorganisms and arthropods has been shown to be an important ecological interaction determining animal development and spatial distribution patterns in saprophagous communities. In fruit-inhabiting Drosophila, variation in insect developmental success is not only determined by species-specific effects of various noxious filamentous fungi but, as suggested by an earlier study, also by additive genetic variation in the ability to successfully withstand the negative impact of the fungi. If this variation represents a direct adaptive response to the degree to which insect breeding substrates are infested with harmful fungi, genetic variation for successful development in the presence of fungi could be maintained by variation in infestation of resource patches with fungi. We selected for the ability to resist the negative influence of mould by maintaining replicated Drosophila melanogaster populations on substrates infested with Aspergillus nidulans. After five cycles of exposure to the fungus during the larval stage, the selected populations were compared with unselected control populations regarding adult survival and reproduction to reveal an evolved resistance against the fungal competitor. On fungus-infested larval feeding substrates, emerged adults from mould-selected populations had higher survival rates and higher early fecundity than the control populations. In the unselected populations, females had higher mortality rates than males, and a high proportion of both females and males appeared to be unable to lay eggs or fertilise eggs, respectively. When larvae developed on non-infested food we found indications of a loss of resistance to abiotic and starvation stress in the adult stage in flies from the selected populations. This suggests that there are costs associated with an increase in resistance against the microbial competitor. We discuss the underlying mechanisms that might have selected for increased resistance against harmful fungi. [ABSTRACT FROM AUTHOR]

Pond-drying is a model for understanding the causes of life history variation in metamorphic organisms. However, we know relatively little about how interactions among specific proximate cues of pond-drying affect juvenile life history, how those responses might be mitigated by diet, and the post-metamorphic consequences for adult fitness. I manipulated larval diet, water depth, and water temperature during the aquatic larval stage of a temporary pond-dwelling caddisfly, Limnephilus indivisus. I predicted that shallow depths and warm temperatures (depth × temperature) associated with pond-drying would have negative effects on larval survival, growth, development, adult size, female fecundity, and adult longevity, but that supplementation of the larval diet should mitigate the trade-off between juvenile growth and pre-reproductive mortality risk by ameliorating the negative effects of pond-drying (diet × depth, diet × temperature) on these traits. Larval survival was enhanced by diet supplementation but was not affected by depth or temperature. Larval diet and water temperatures acted independently on growth, development, and female size, and growth rates were higher when larval diets were supplemented relative to ambient diets; development times were shorter when temperatures were warmer relative to colder; adult females were larger when larvae were fed a supplemented diet but smaller when reared in warm water. Larval growth and development were not affected by depth, but female size was reduced under shallow relative to deep conditions. Female longevity and fecundity were affected by the larval diet × female size interaction. Surprisingly, this was independent of the depth × temperature interaction on female longevity and fecundity suggesting that reductions in adult fitness due to juvenile abiotic conditions can be independent of size-at-maturity. Future studies should quantify the effect of proximate cues of pond-drying on juvenile survival and life history as well as adult fitness correlates. [ABSTRACT FROM AUTHOR]

Plants with limited resources adjust partitioning among growth, survival, and reproduction. We tested the effects of water and nutrient amendments on seed production, size, and quality in Sarcobatus vermiculatus (greasewood) to assess the magnitude and importance of changes in reproductive partitioning. In addition, we assessed interactions among the environment of seed-producing plants (adult plant scale), seed size, and seedling microenvironment (seedling scale) on successful seedling establishment. Interactions of these factors determine the scale of resource heterogeneity that affects seedling establishment in deserts. Both total number of seeds produced per plant and seed quality (weight and germination) increased significantly in the enriched treatment in a 3-year field experiment. Seedling length 3 days after germination and seed N concentration, other measures of seed quality, were higher for seed from both irrigated and enriched plants than for seed from control plants. Field S. vermiculatus seed production and quality can be substantially increased with irrigation and nutrient enrichment at the adult plant scale and this allows management of seed availability for restoration. However, based on a greenhouse study, seedling environment, not the environment of the seed-producing plant or seed size, was the most important factor affecting seedling germination, survival, and growth. Thus it appears that production of more seed may be more important than improved seed quality, because higher quality seed did not compensate for a low-resource seedling environment. For both natural establishment and restoration this suggests that heterogeneity at the scale of seedling microsites, perhaps combined with fertilization of adult shrubs (or multi-plant patches), would produce the greatest benefit for establishing seedlings in the field. [ABSTRACT FROM AUTHOR]

Density-dependent and climatic factors affect reproduction and dynamics of wild ungulates. Parasites can also decrease reproductive success through either a direct abortive effect or a negative impact on host growth and body condition. However, few studies have investigated the effect of parasitism on fecundity of ungulates in natural conditions. We studied three bacterial infections caused by Salmonella enterica serovar Abortusovis, Chlamydophila abortus and Coxiella burnetii. These bacteria are leading causes of reproductive failure in sheep, goat and cattle, which raises the question of their influence on population dynamics of wild ungulates. A long-term study of demography and epidemiology of an alpine chamois ( Rupicapra rupicapra, L.) population (Les Bauges Reserve, France) and a generalized linear modeling approach were used to analyze the reproductive success of chamois according to population density, weather conditions and the prevalence of antibodies against the three bacteria in females. This approach enabled us to identify the confounding effect of weather and parasitism on fecundity in a natural population. After accounting for density, the prevalence of antibodies against the three bacteria explained 36% of the annual variation in reproductive success, and weather conditions explained an additional 31%. This study was, to our knowledge, the first to compare the decrease in fecundity due to bacterial infections and weather conditions in a population of wild mountain ungulates. [ABSTRACT FROM AUTHOR]

The scaling of reproductive parameters to body size is important for understanding ecological and evolutionary patterns. Here, we derived allometric relationships for the number and mass of seeds, eggs and neonates from an existing model on population production. In a separate meta-analysis, we collected 79 empirical regressions on offspring mass and number covering different taxa and various habitats. The literature review served as a validation of the model, whereas, vice versa, consistency of isolated regressions with each other and related ecological quantities was checked with the model. The total offspring mass delivered in a reproductive event scaled to adult size with slopes in the range of about 3/4 to 1. Exponents for individual seed, egg and neonate mass varied around 1/2 for most heterotherms and between 3/4 and 1 for most homeotherms. The scaling of the progeny number released in a sowing, clutch or litter was opposite to that of their size. The linear regressions fitted into a triangular envelope where maximum offspring mass is limited by the size of the adult. Minimum seed and egg size scaled with weight exponents of approximately 0 up to 1/4. These patterns can be explained by the influence of parents on the fate of their offspring, covering the continuum of r-strategists (pelagic–aquatic, arial, most invertebrates, heterotherms) and K-strategists (littoral–terrestrial, some invertebrates, homeotherms). [ABSTRACT FROM AUTHOR]

Weather variables can influence life-history traits of ungulates. In this study, we assessed the suitability of regional climate indices including the NAO and two measures of local climate—the maximal extent of ice on the Baltic Sea (MIE) and absolute values of its annual deviations from the multi-year mean (VMIE)—to examine how density-independent processes influence moose body size and fecundity. We predicted that both winter severity (large values of MIE) and variability (large values of VMIE) depress moose traits (e.g., severe winters increase energy expenditure because of large snow depth or low temperatures, while the warmer than average winters may impose greater energetic demands on thermoregulation due to wet and windy weather, or may have indirect negative effects on summer foraging conditions). We estimated direct, delayed (lag) and cumulative effects of each climate measure. Both MIE and VMIE negatively affected jawbone length, with the effect size varying between the respective climatic indices and among age classes. In contrast to results obtained using local climatic variables, the NAO index had no significant effect on jawbone length. The probability of multiple ovulation was negatively influenced by direct effects of VMIE and delayed effects of MIE and NAO. We conclude that MIE and VMIE capture different aspects of the local climate and that these indices can be used in parallel as determinants of growth and fecundity of northern ungulates in coastal regions of the Baltic Sea. [ABSTRACT FROM AUTHOR]

Life history theory often assumes a trade-off between dispersal and reproduction, and such a trade-off is commonly observed in wing-dimorphic insects. The results are less consistent for wing-monomorphic species, for which it is more difficult to assess dispersal capacity and rate. Three replicate experiments were carried out in consecutive years on the Glanville fritillary butterfly in a large outdoor population cage to study the relationship between lifetime egg production and mobility. The experimental material included females originating from newly-established and old populations, as previous studies have shown dispersal capacity to depend on population age. There was a consistent and significant interaction between mobility and population age, such that in newly-established populations mobile females had higher fecundity than less mobile females, while in old populations there was no such relationship. As selection favours individuals with the highest fecundity, selection pressure on mobility is likely to be different between the two population types, which may contribute to maintenance of variation in dispersal rate in the metapopulation as a whole. Several other female traits also affected lifetime fecundity, including lifespan, number of matings and date of eclosion, although these effects were not consistent across the years. These results highlight the importance of conducting experiments in more than one year before generalizing about patterns in life history variation. [ABSTRACT FROM AUTHOR]

The reproductive success of predators depends on abiotic environmental conditions, food abundance and population density, and food abundance, density and their interactions may respond to changes in climatic conditions. Timing of reproduction by five of the eight numerically most common prey of the sparrowhawk Accipiter nisus advanced significantly since 1971, during a period of temperature increase. There was no evidence that mean laying date or any other reproductive parameter of sparrowhawks changed consistently during the study period 1977–1997. Laying date advanced and percentage of unsuccessful female sparrowhawks decreased with beech mast in the current year, an index of food abundance for avian prey. Mean laying date of sparrowhawks was advanced in warmer springs, and although mean clutch size was not larger in warm than in cold springs, mean brood size of successful pairs and breeding success increased in such springs, showing that sparrowhawks enjoyed a fitness gain when reproducing early. The timing of sparrowhawk reproduction with respect to the peak in abundance of fledgling prey increased, from a good match between mean timing of fledging by prey and maximum demand for food by the predator in 1977, to reproduction occurring later than the peak in fledging prey availability in 1997. The size of the breeding population of sparrowhawks was not predicted by mean spring temperature, the size of the breeding population the previous year or beech mast crop. The size of the post-breeding population was predicted by size of the breeding and post-breeding population the previous year and by the proportion of unsuccessful females the current year. These findings imply that sparrowhawks did not respond to change in climate, although climate changed the timing of reproduction by the main prey species. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Pregnancy is associated with reduced locomotor performance in many types of animals, but we do not know to what degree this correlation is caused by simple physical burdening, versus physiological changes associated with pregnancy, or to confounding variables (such as season or female body size) that simultaneously influence both reproductive investment and locomotor speeds. To identify causal effects of burden on locomotion, we need to experimentally manipulate the size of the load being carried. Injection of sterile fluid into the peritoneal cavities of 84 garden skinks (Lampropholis guichenoti) showed that speeds decreased with increasing burdens. Lizards with a burden equivalent to 25% of their body mass ran about 15% slower, mirroring the situation seen in gravid lizards of this population. Thus, simple physical burdening appears to be the primary causal component of the locomotor cost of reproduction within these animals. A lizard's sex, body size and shape had little effect on its running ability either before or after treatment, but faster lizards showed a greater performance decrement after burdening than did their slower conspecifics. [ABSTRACT FROM AUTHOR]

Senescence is a general decline of physiological state that accompanies advancing age. It affects nearly all organisms, but patterns of senescence vary markedly, even among closely related taxa. Understanding the evolution of this diversity requires information about environmental effects on the expression of variation among taxa. I examined genetically-based variation of senescence within and between two species complexes of Daphnia in four environments. The environments were defined by large differences in food and temperature, two factors known to influence senescence. The species studied were chosen to represent sister species that likely experience divergent (D. pulex and D. pulicaria) or similar (D. mendotate and D. dentifera) selection pressures on senescence. Overall, D. pulex expressed the greatest demographic senescence, D. mendotae and D. dentifera were intermediate, and D. pulicaria expressed the least. In environments representative of typical natural conditions, D. pulex had greater senescence than D. pulicaria, regardless of how late-life performance was assessed. This shows that genetic-environment interactions do not confound the interpretation of senescence differences between these species as the result of selective differences between their habitats. Comparison of D. mendotae and D. dentifera primarily revealed similar life histories, although differences in reproductive declines occurred in some environments. The joint observation of similar mortality patterns but dissimilar fecundity declines suggests that the trade-off between survival and reproduction changes with age. This calls into question the utility of only studying mortality for understanding evolutionary change of senescence in nature. [ABSTRACT FROM AUTHOR]

The mast depression hypothesis has been put forward to explain the 9- to 10-year population cycle of the autumnal moth (Epirrita autumnata; Lepidoptera: Geometridae) in northern Fennoscandia. We analysed long-term data from Finnish Lapland in order to evaluate the critical assumption of the mast depression hypothesis: that better individual performance of herbivores, followed by high annual growth rate of populations, occurs in the year following mast seeding of the host, the mountain birch (Betula pubescens ssp. czerepanovii). Since mast seeding has been suggested to occur at the expense of chemical defence against herbivores, we bioassayed the quality of birch leaves from the same trees by means of yearly growth trials with autumnal moth larvae. We also measured the size of wild adults as a determinant of potential fecundity of the species in different years. The relative growth rate of larvae was poorer in post-mast years compared to other years, rather than better as assumed by the hypothesis. Conversely, a slight indication of the increase in potential fecundity was observed due to the somewhat larger adult size in post-mast years. Population growth rate estimates, however, showed that the increase in fecundity would have to be much higher to facilitate population increase towards a cyclic peak with outbreak density. Accordingly, our two data sets do not support the assumption of a higher annual growth rate in autumnal moth populations subsequent to mast seeding of the host, thereby contradicting the predictions of the mast depression hypothesis. Temperatures, when indexed by the North Atlantic Oscillation and accumulated thermal sums, were observed to correlate with the abundance or rate of population change of the autumnal moth. The factors underlying the regular population cycles of the autumnal moth, however, remain unidentified. Overall, we suggest that the causal agents in cyclic insect population dynamics should be clarified by field experimentation, since trophic interactions are complex and are further modified by abiotic factors such as climate. [ABSTRACT FROM AUTHOR]

Strong correlation between female body size and potential fecundity is often observed in insects. Directional selection favouring increased body sizes is thus predicted in the absence of opposing selection pressure. The evolutionary forces capable of counterbalancing such a 'fecundity advantage' are poorly documented. This study focuses on revealing the costs of large body size in the wingless females of Orgyia antiqua and O. leucostigma, two related species of lymantriid moths. Extreme behavioural simplicity of these animals allows systematic assessment of various fitness components in conditions that are close to natural. A linear relationship between pupal weight and potential fecundity was observed. This association was found to be independent of particular rearing conditions. There was no evidence that the relationship between fecundity and body mass becomes asymptotic when body sizes increases. No component of fitness showed a negative phenotypic correlation with body size; some displayed a weakly positive one. In particular, pupal mortality, adult longevity, mating and oviposition success, as well as egg hatching rate and egg size, were established as independent of body size in a series of field and laboratory experiments. There was a very high overall efficiency of converting resources accumulated during the larval stage to egg masses. With no costs of large adult size, selective forces balancing the fecundity advantage should operate in the course of immature development. The strong dependence of realized fecundity on body size is considered characteristic of the capital breeding strategy. [ABSTRACT FROM AUTHOR]

Theory posits that reproduction carries a cost in terms either of future fecundity, growth or survival. Different life history strategies may evolve in response to different external sources of mortality. In ectothermic organisms, such as insects and reptiles, reproductive characteristics may also vary due to effects of differences in body temperature on activity and physiological performance. In this study, female pygmy grasshoppers [Tetrix subulata (L.) Orthoptera: Tetrigidae] belonging to four different colour morphs were maintained under two different temperatures, and data on reproductive life history traits were used to test for costs of reproduction, plasticity of reproductive characteristics in response to temperature and variation among colour morphs in reproductive strategies. The results revealed that average clutch size decreased progressively from the first to third clutch, and that females producing relatively large clutches displayed a greater reduction (in both absolute and relative terms) in the number of eggs to the following clutch, as expected from the hypothesis that present reproduction negatively affects future fecundity. Great expenditure on present reproduction also negatively influenced the time to next clutch:the decrease in mean clutch size with clutch number was associated with a reduction in inter-clutch interval, and clutch interval increased with clutch size across individuals within colour morphs. Females maintained in a warm environment were more likely to oviposit, laid their first clutch earlier, produced more clutches and had shorter intervals between sequential clutchesthan females in a cold environment, suggesting that differences in body temperature may contribute to variation in reproductive performance within and among natural populations. A comparison among colour morphs maintained under identical conditions suggested that females belonging to certain morphs produce relatively large clutches at the expense of fewer clutches per unit time. However, experimental data revealed no difference in relative fat content between dark and pale individuals maintained either in sun-exposed outdoor enclosures (where they were unable to increase their body temperature by basking) or in shaded enclosures. This suggest that the divergence in life history strategies among colour morphs may reflect a response to morph-specific differences in adult survival imposed by visually searching predators, rather than being due to the effects of differences in body temperature. [ABSTRACT FROM AUTHOR]

Snail hosts of different ages constitute different resource environments for larval trematodes because each individual has a particular energy budget and energy allocation pattern at the time of infection. Effects of monomiracidial trematode infections on shell growth, body dry weight and reproductive effort of the snail host were compared between controls and infected juvenile and adult snails during the prepatent and patent periods. The results demonstrate phenotypic plasticity in the host response. There is an age/size-specific effect characterized by limitation of growth rate when snails are infected as juveniles and reduction of reproductive effort when snails are infected as adults, and a time-specific effect with early enhancement of growth rate and reproductive effort for infected juvenile and adult snails respectively during prepatency, before reduction and cessation during patency. The parasite is considered as a generalist in its energy exploitation strategy of the snail host, but taking into account the differential host responses observed relative to the host age, the possibility of a host preference for juvenile or adult snails is discussed. [ABSTRACT FROM AUTHOR]

The cycad Cycas armstrongii is endemic to the north-western corner of the Northern Territory in Australia. Here we provide data on its life history and population structure from four populations across its range. Few plants reproduced before they were 1 m in height. There was considerable variation in the proportion of reproductive plants between sites and years, but the sex ratio in all populations was close to 1:1. The growth rate of plants was approximately 4.5 cm year−1 which indicates that most plants are less than 100 years old and that the tallest individuals are likely to be little older than this. The annual fecundity of female plants ranged from 12 to 80 seeds; there was no evidence that fecundity varied with plant height. Dispersal was restricted generally to less than 1 m and the distribution of dispersal distances was fitted well by a gamma distribution. Recruitment occurred through both seedlings and vegetative sprouts and the proportion of juveniles (plants without trunks) in the populations varied between one-quarter and two-thirds. The data indicate that recruitment is episodic, but occurs more frequently under the current fire regime than amongst the canopy trees. It is shown that there is considerable variation in the dynamics of populations between sites and that the long term dynamics of a population cannot readily be inferred from an examination of the size structure at a single point in time. [ABSTRACT FROM AUTHOR]

The general female bias in body size of animals is usually attributed to fecundity selection. While many studies have demonstrated a positive relationship between body size and fecundity, the most common interpretation of fecundity selection is that larger females have larger abdomens and can hold more eggs, yet the relationship between abdomen size and fecundity has rarely been examined. For the waterstrider, Aquarius remigis, we find a significant relationship between body size and fecundity and demonstrate that the target of fecundity selection is abdomen size. Thus, larger females have higher fecundities because they have larger abdomens and not because of their total size per se. The rate at which fecundity increases with increasing abdomen size exceeds that which would be expected due to a simple volume constraint and suggests that other factors, such as increased ability to obtain resources, may contribute to the increase in fecundity with body size. Selection intensities estimated from our data indicate that fecundity selection could be a significant selective force on both total and abdomen lengths. Previous studies have found that abdomen size increased faster than body size and thus, larger females had relatively larger abdomens. The relationship of abdomen length and thorax length in A. remigis is hypoallometric and indicates that larger females have relatively smaller abdomens. We hypothesize that this may reflect conservation of abdomen size in females developing under poor conditions. Finally, while egg size is not directly related to body size, we find a trade-off between egg size and number when female abdomen length is held constant, suggesting that selection on egg size may influence abdomen length only indirectly through its effects on fecundity. [ABSTRACT FROM AUTHOR]

I examined the relationship between age, body size and fecundity in 833 female moose ( Alces alces) from 14 populations in Sweden sampled during 1989-1992. Data on population density, food availability and climatic conditions were also collected for each population. Age and body mass were both significantly positively related to fecundity, measured as ovulation rate, among female moose. The relationship between the probability of ovulation and body mass was dependent on age with (1) a higher body mass needed in younger females for attaining a given fecundity, and (2) body mass having a stronger effect on fecundity in yearling (1.5 year) than in older (≥2.5 year) females. Thus, a 40 kg increase in yearling body mass resulted in a 42% increase in the probability of ovulation as compared to a 6% increase in older females. The lower reproductive effort per unit body mass, and the relatively stronger association between fecundity and body mass in young female moose compared to older ones, is likely to primarily represent a mechanism that trades off early maturation against further growth, indicating a higher cost of reproduction in young animals. In addition to age and body mass, population identity explained a significant amount of the individual variation in fecundity, showing that the relationship between body mass and fecundity was variable among populations. This variation was in turn related to the environment, in terms of climatic conditions forcing female moose living in relatively harsh/more seasonal climatic conditions to attain a 22% higher body mass to achive the same probability of multiple ovulation (twinning) as females living in climatically milder/less seasonal environments. The results suggests that the lower fecundity per unit body mass in female moose living in climatically harsh/more seasonal environments may be an adaptive response to lower rates of juvenile survival, compared to females experiencing relatively milder/less seasonal climatic conditions. [ABSTRACT FROM AUTHOR]

Over the fluctuation in population density of tent caterpillars, Malacosoma californicum pluviale and M. disstria, fecundity changes from being high at peak density to low for several years during the decline. During the increase phase, fecundity rapidly returns to moderately high levels with a further increase occurring to-ward the end of the increase phase. Two hypotheses which might explain these shifts are that (1) mortality from viral disease which is common during population declines selects for resistant individuals with low fecundity as an associated characteristic, and (2) sublethal viral disease reduces fecundity of moths during population decline. In this study we observed rapid shifts in the frequencies of large and small egg masses and in the mean fecundity between different phases of the population fluctuation. Viral disease was more common in caterpillars from small egg masses of the forest tent caterpillar. These observations are consistent with the hypothesis that sublethal effects of virus reduce the fecundity of moths during the population decline, but high fecundity is quickly restored when disease is rare during the population increase. [ABSTRACT FROM AUTHOR]

The body length and body weight of all adult common toads ( Bufo bufo) breeding at a pond in south Dorset were measured between 1983 and 1993. Each toad was placed into one of four categories depending on its sex and whether it was either a first time breeder or an animal that had previously bred. The body condition of each male and female toad for each year was compared with the average body condition of all the male and female toads captured over the 11 years of the study so that between-year differences in condition could be detected. Changes in body condition were compared with changes in body condition were compared with changes in toad density, rainfall and climatic temperature during the previous summer (March-September), during hibernation (October-February) and during the month preceding the start of spawning. During the study there was a decline in the body condition of all toad categories and these changes were significantly correlated with changes in toad density and climatic temperature. Toads were also more likely to enter hibernation in poor condition following a hot dry summer than after either cool wet or hot wet summers. Body condition explained 41% of the size-specific variation in fecundity. [ABSTRACT FROM AUTHOR]

Life-history theory predicts that the allocation of energy to current reproduction is associated with a decrement in future fecundity, future survival, or both. I treated this notion as the 'cost hypothesis', and tested the assumption that current reproduction exacts a 'cost' in future survival and fecundity. Surgical manipulations of egg production were applied to natural populations of the tree lizard, Urosaurus ornatus, in south western New Mexico by yolkectomy surgery in two different years. I reduced the number of eggs produced in the first clutch during vitellogenesis by approximately 50% in yolkectomized females relative to controls. Subsequent survival, fecundity, and growth of females were followed for two or three years, depending on the cohort. Treated females in both cohorts showed significantly higher growth and survivorship throughout the experiment than in controls. After 2 years, yolkectomized females had grown an additional 2 mm (snout-vent length) compared to controls, enough for them to add on average an additional egg to their next clutch. This demonstrated a cost in terms of future fecundity through a reduction in growth and an increase in mortality in these lizards. [ABSTRACT FROM AUTHOR]

Using field and laboratory observations and experiments over 3 years, I investigated whether reproductive trade-offs shape individual life histories in two natural populations of the water strider, Aquarius remigis, in which univoltine and bivoltine life cycles coexist. Both later eclosion dates and food shortages, even after adult eclosion, induced diapause in females, thus deferring reproduction to the following spring. Adult body size was positively affected by food availability during juvenile development. Higher food levels also increased the reproductive output of females, but not their longevity or oviposition period. When compared to spring breeders (univoltine life cycle), direct (summer) breeders (bivoltine life cycle) experienced reduced lifetime egg numbers and longevity, as well as reduced survivorship of their second-summer-generation offspring; these reproductive costs offset, at least in part, the advantage in non-decreasing populations of having two generations per year. Fecundity was correlated with body size, and among summer-generation females direct breeders were larger than non-breeders. The time remaining before the onset of winter and/or the time since adult eclosion augmented cumulative energy uptake, and consequently the lipid reserves and winter survival probability of non-breeding (diapausing) summer adults approaching hibernation. Overwintered spring reproductives died at faster rates than non-reproductive summer individuals despite greater food availability in spring, indicating a mortality cost of reproduction. Body length correlated with absolute and not with proportional lipid content but showed no consistent relationship with survivorship in the field. These results are in agreement with current theory on the evolution of insect voltinism patterns, and further indicate high degrees of life history flexibility (phenotypic plasticity) in the study populations in response to variable environmental factors (notably photoperiod and food availability). This may be related to their location in a geographic transition zone from uni- to bivoltine life cycles. [ABSTRACT FROM AUTHOR]

Females of Zeiraphera canadensis Mut. & Free., the spruce bud moth, were reared in the laboratory at constant and alternating temperatures, and in an outdoor insectary, to (1) determine the effects of temperature, age and size on several reproductive parameters and, (2) to test the hypothesis that body size-temperature interactions influence longevity and realized fecundity. Egg maturation was linearly related to age and large moths developed eggs at a higher rate than small ones. Mcan lifetime oviposition rate reached a maximum and remained stable at temperatures ≥20° C while the mean lifetime rate of egg maturation increased linearly with temperature, indicating that higher temperatures adversely affect oviposition. The production of nonviable eggs increased with age but also with temperature, suggesting high temperature (≥25° C) reduces egg quality and/or hinders fertilization. The realized fecundity and longevity of females reared under an alternating temperature regime (mean 20° C) was significantly less than that of females reared at constant 20° C. Similar realized fecundity, longevity and mean lifetime oviposition rates for females reared at temperatures alternating between 10 and 25° C (mean 20° C) and those at constant 25° C reflected the inability of females to recover from elevated diurnal temperatures. Longevity was positively related to female body size at constant 15 and 20° C but the relationships were negative for moths exposed to diurnal temperatures equal to or exceeding 25° C. Due to the reduced longevity of large moths at high temperatures, linear regressions between size and realized fecundity were only significant at constant temperatures ≤20° C. At higher temperatures, the size-fecundity relationship became curvilinear as a result of the diminished reproductive output of large individuals. Reduced fecundity and longevity of large females at high temperatures may have been due to elevated internal temperatures of large-bodied moths. Large females in a controlled-environment chamber maintained at 25° C developed an internal temperature excess (i.e. temperature above ambient) of nearly 2° C while small-bodied females exceeded ambient by only 0.3° C. However, when held at 20° C, the temperature excess of large-bodied moths was much less than 1° C and small-bodied females did not differ from ambient. Such interactions between temperature and body size suggest that there should be stabilizing selection toward moderate-sized individuals and may explain the absence of size-related effects on fecundity and longevity previously reported for several other lepidopterans. [ABSTRACT FROM AUTHOR]

Ahnfeltia durvillaei and Gymnogongrus furcellatus, two intertidal red algae from central Chile, often grow sympatrically and their gametophytic phases are dominant in the field, but recruitment is low. A shortterm comparative analysis of the reproductive behavior of their gametophytes was carried out to determine quantitative levels of reproduction and their degree of functional similarity. Size, rather than age, was evaluated as predictor of fecundity. Both species showed the same qualitative patterns, although maintaining quantitative differences. Reproductive plants were recorded throughout the size range, and fecundity increased continuously and directly with size. A size-independent threshold in reproductive effort was found for each species, and the variance of effort values decreased inversely with size. Vertical, size-specific life tables revealed low dependence of survivorship with size, and reproductive values exhibited a maximum at the same size class for both species. This last pattern, and a negative relationship found between fecundity and survivorship, suggest the existence of costs or trade-offs operating at the phenotypic level, but they would not be supported in a selective context. [ABSTRACT FROM AUTHOR]

To examine the importance of covariance between stages in traits related to foraging, we quantified the relationships between reproductive success and sizerelated variability in weight gain in juvenile and adult instars of the crab spider Misumenoides formosipes (Araneae: Thomisidae). Prereproductive weight and fecundity are both highly correlated with carapace width, a linear measure of size which does not change within an instar. In field populations, adult females with larger carapaces gain more weight and are more likely to reproduce than females with smaller carapaces. The growth rate of spiders fed ad libitum in the laboratory is unrelated to size, suggesting that size-related differences in the field are due to variation in prey-capture success. Adult females with a carapace width less than 3.4 mm comprised 22% of the population, but were never found to reproduce. Of the individuals that did reproduce, a 17% increase in carapace width resulted in a 100% increase in fecundity. Juvenile stages must be examined to understand adult foraging and reproductive success, because the net weight gained by juvenile instars determines adult size. The final weight gained by spiders in the antepenultimate and penultimate instars explained nearly all the variation in carapace width in the penultimate and adult instars, respectively. We found that constraints on foraging in late juvenile stages are different from the adult stage. Penultimate foraging behavior differs from that of adults, because of constraints on foraging in the period preceding ecdysis. Additionally, in both late juvenile instars, carapace width had little or no effect on the final weight gained within the instar suggesting that factors that affect foraging are different between the juvenile and adult stages. These analyses stress the fact that to fully understand the effects of foraging on reproductive success, we must examine stage-specific constraints throughout an organism's life history. [ABSTRACT FROM AUTHOR]

Female lifetime reproductive success in a small population of individually-marked adders in southern Sweden was studied over a period of seven years. Reproductive characteristics varied little from year to year and were consistent through time in individual females. Most females mature at four years of age and reproduce every two years. The total number of offspring produced by a female depends on her adult body size (and thus, litter size) and longevity (and thus, number of litters per lifetime). Adult body size in females is influenced mainly by subadult growth rates. Offspring size depends on maternal body size and a tradeoff between offspring size and offspring number. Maternal age does not affect litter sizes and offspring sizes except through ontogenetic changes in maternal body size. Survival of females after parturition is low because of the high energy costs of reproduction, compounded by low feeding rates of gravid females because of their sedentary behaviour at this time. About one-half of females produce only a single litter during their lifetimes, although some females live to produce four or five litters. On a proximate basis, rates of energy accumulation for growth (in subadults) and reproduction (in adults) may be the most important determinants of fitness in female adders. [ABSTRACT FROM AUTHOR]

Female Canada thistle seed flies ( Orellia ruficauda) preferentially oviposit into seed heads which are a single day from opening. When flies are forced to oviposit into flower heads at other stages of development, offspring typically do slightly poorer: they attain a mature mass of about 15% less than do larvae derived from preferred hosts. Larval mass correlates strongly with reproductive success: heavy larvae develop into adults that produce eggs at a faster rate than do those developing from small larvae. After laying a clutch of eggs, flies circumscribe the rim of the flowerhead with their extended ovipositor and deposit a clear fluid. Flies reject previously-attacked hosts, bearing this apparent marking pheromone, significantly more often than they reject unattacked hosts. Costs of superparasitism in this system are relatively small, inasmuch as there is only a weak relationship between clutch size and larval success at the densities measured in this study. We speculate that flies are highly selective, when the apparent costs of making a mistake are rather low, because the information provided by phenological cues and by the putative marking pheromone is highly reliable, and low fecundity and time costs allow sufficient time to express a high level of discrimination. [ABSTRACT FROM AUTHOR]

The epidemiology of rust caused by the fungus Melampsora lini and the effects of infection by this pathogen on its host, the herbaceous perennial Linum marginale, were determined in the field and in garden experiments. There was considerable natural variability in disease levels over the four years (1986-1989) of the study. In two years (1986, 1989) major rust epidemics occurred. In the field, the main effect of disease was to reduce survivorship during the winter following infection. Plants which were heavily infected during the 1986 or 1989 growing seasons had reduced survivorship relative to more lightly infected plants. Melampsora lini infections did not appear to affect survivorship in either 1987 or 1988. Flowering was correlated with environmental factors and the number of stems a plant possessed. A severe drought in 1987 completely inhibited flowering. In the other three years the number of flowers produced by a plant was strongly positively correlated with the number of stems it possessed. Disease levels had no consistent effect on flowering. Controlled garden experiments were also used to examine the response of seedlings and adult plants to infection. These showed that both the timing and severity of disease appears to determine the effect of M. lini infections on L. marginale. Early, severe infection reduced growing season and overwintering survivorship as well as capsule production. However, plants in the field were most often infected only after flowering had begun, and the predominant effect of infection was a reduction in overwintering survivorship. The high variability in disease levels from year to year and the deferred nature of the effect of the rust on its host have significant implications for the design of experiments aimed at assessing the role of diseases in plant communities. [ABSTRACT FROM AUTHOR]