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When analysing how individuals allocate resources, sexual display should be regarded as is any other life-history trait: patterns of allocation are expected to be individually optimised. It thus follows that the costs of sexual selection can not be studied by simply comparing unmanipulated individual effort and some measure of cost. This rather trivial consequence of life-history theory has received surprisingly little attention in studies of sexual selection despite the almostuniversal acceptance of the theory and the fact that several papers have addressed the question specifically in the context of sexual selection. We therefore again outline why sexual displays are expected to be optimised at the level of the individual and why individuals with high access to resources should generally display at higher levels than individuals short of resources. We use some recent findings fromstudies of birds and spiders particularly relevant to the above questions that illustrate these principles. The examples we present show that the cost of sexual selection could be mediated in many ways and we thus suggest that future studies should focus on such mechanisms. [ABSTRACT FROM AUTHOR]

Empirical data on many species of terrestrial orchids suggest that their between-year flowering pattern is extremely irregular and unpredictable due to costs associated with sexual reproduction and/or herbivory. In a more mathematical context, the irregular behaviour of orchids may be explained by difference equations describing deterministicgrowth of the vegetative dry weight and deterministic relationships between vegetative and reproductive dry weight. In this paper long-term data on the terrestrial orchid Epipactis albensis are used to testthis explanation of the irregular flowering patterns of orchids. [ABSTRACT FROM AUTHOR]

The effects of fishing on life history traits and life history strategies of teleost fishes are analysed by a new comparative method that splits traits into an allometric part (size effect), an autoregressive phylogenetic component, and an environmental component (fishing effect). Both intra- and inter-specific variation of age and size at maturity, fecundity, adult size and egg size are analysed by comparing 84 populations of 49 species submitted to various fishing pressures. Two axes of life history diversification are found among teleosts. One is the well-known slow-fast continuum separating short-lived and early maturing species (like Clupeiformes) from longer-lived species that mature late relative to their size and spawn larger eggs (like salmonids or Scorpaeniformes). An additional strategy involves the schedule of resource allocation to growth and reproduction. Indeterminate growth allows higher teleosts (e.g. Gadiformes) to reach a large size while maturing early and laying small eggs. Increasing fishing pressure decreases age at maturity and egg size, and increases fecundity at maturity, the slope of the fecundity-length relationship and relative size at maturity. These compensations for higher adult mortality differ among life history strategies. Indeterminate growth is associated with a greater flexibility in resource allocation to growth and reproduction that facilitates greater resilience to fishing mortality. [ABSTRACT FROM AUTHOR]

We contrasted body condition, and age-specific reproduction and mortality between a growing population of sea otters (Enhydra lutris ) at Kodiak Island and a high-density near-equilibrium population at Amchitka Island, Alaska. We obtained data from marked individuals, population surveys, and collections of beach-cast carcasses. Mass:length ratios indicated that females (but not males) captured in 1992 at Amchitka were in poorer condition than those captured at Kodiak in 1986–1987. In 1993, the condition of females at Amchitka improved in apparent response to two factors: (1) an episodic influx of Pacific smooth lumpsuckers, Aptocyclus ventricocus , from the epi-pelagic zone, which otters consumed; and (2) an increase in the otters’ benthic invertebrate prey resulting from declining otter numbers. Reproductive rates varied with age (0.37 [CI=0.21 to 0.53] births female-1 yr-1 for 2–3-yr-olds, and 0.83 [CI=0.69 to 0.90] for females ≥4 yr old), and were similar at both areas. Weaning success (pups surviving to ≥120 d), in contrast, was almost 50% lower at Amchitka than at Kodiak and for females ≥4 yr of age was 0.52 (CI=0.38 to 0.66) vs 0.94 (CI=0.75 to 0.99), respectively. Sixty-two percent of the preweaning pup losses at Amchitka occurred within a month of parturition and 79% within two months. Postweaning survival was also low at Amchitka as only 18% of instrumented pups were known to be alive one year after mother-pup separation. Adult survival rates appeared similar at Amchitka and Kodiak. Factors affecting survival early in life thus are a primary demographic mechanism of population regulation in sea otters. By maintaining uniformly high reproductive rates over time and limiting investment in any particular reproductive event, sea otters can take advantage of unpredictable environmental changes favorable to pup survival. This strategy is consistent with predictions of “bet-hedging” life history models. [ABSTRACT FROM AUTHOR]

The meadow vole, Microtus pennsylvanicus , is the most widely distributed Microtus species in North America. Across its range, it shows marked demographic differences, experiences a large range of climatic conditions, and varies considerably in body size and life-history characteristics. To study the genetic basis of the geographic variation in size and life history of this species, we subjected three populations, one from central Canada and two from eastern Canada, to quantitative genetic analysis in the lab. We studied the variance and covariance of several size and growth variables as well as age and size at maturity by means of population crosses, full-sib analysis, and parent-offspring regressions. We found that the phenotypic differences among these populations are almost entirely due to environmental effects. However, within populations, additive genetic and maternal effects explain most of the variation. We discuss possible explanations for the lack of genetic differences among the populations and speculate that a similar reaction norm is maintained in all populations through heterogeneity in the temporal or spatial environment that the populations experience. The heterogeneity may be mediated through population density fluctuations, climatic variation, or variation in site productivity. Thus, we hypothesize that M. pennsylvanicus has evolved to be the best in all possible worlds rather than in one actual world. This study highlights the crucial importance of maternal and environmental effects on the size, growth, and life history of small rodents. [ABSTRACT FROM AUTHOR]

The use of optimization models to study adaptations is discussed. The optimal value of a trait must maximize fitness, that is, lifetime reproductive success. This means that every trait under optimization must be translated into demographic parameters. Although there is no universal measure of fitness, some general rules are given about whether net reproductive rate R or intrinsic population growth rate r should be maximized in given conditions. Models maximizing R are usually simple, and they produce easy-to-interpret predictions. The scope of applicability of models assuming maximization of R broadens if we aresatisfied with post hoc explanations of natural patterns (predictions in a weak sense). Optimization models should be verified using comparative methods. With a comparative method, however, optimization models become tools for approaching general questions about selective forces and the resulting patterns, not for studying local adaptations. Hypotheses about local adaptations are always difficult to test, and optimization models seem of little help here. [ABSTRACT FROM AUTHOR]

We discuss ways in which the social environment an individual inhabits may have influenced, and continues to influence, the life history patterns it follows. We argue that the social context in which a lifehistory is expressed has the potential to influence the evolution ofthat life history in four distinct ways, and that these may not always have been fully considered in classic life history theory. First, conflicts of interest are frequent when non-clonal organisms interact, and this is particularly true for reproduction, where conflicts between the sexes and between parents and offspring have numerous potential impacts on life histories. Second, the occurrence of frequency- and density-dependent selection arising from social interactions can have important consequences for predicting the evolutionary trajectories of life histories. Third, research in sexual selection has often been free of a life-history perspective; combining the two has the potential to offer interesting insights into the process of sexual selection and the evolution of sexual ornamentation. Finally, we illustrate some of the more dramatic outcomes of these factors for life history evolution by discussing the evolution and maintenance of within population polymorphisms in life histories. An appreciation of the rolesof social interactions may provide a solution to some long-standing questions in life-history research, such as how high levels of additive genetic variance for traits closely related to fitness are maintained. [ABSTRACT FROM AUTHOR]

We discuss the mechanistic ('proximate') and selective ('ultimate') factors that cause life history trade-offs such as the trade-off between offspring quality and quantity and that between current and future reproduction. We point out that key concepts in life history theoryand evolutionary biology such as negative genetic correlations and trade-offs can be understood in terms of physiological mechanisms. More specifically, negative genetic correlations causing trade-offs between life history traits are caused by hormones and their regulatory genes that have multiple and opposing, pleiotropic effects on two or more traits. Consequently, investigations of these mechanisms is a natural complement to the classical population genetical approach. We critically dissect the argument, put forward by other workers, that experimental manipulations of organismal physiology or other phenotypic traits do not reveal genetic life history trade-offs, but only reflects phenotypic plasticity. We reject this idea and discuss the proposed alternative approach: laboratory selection experiments. We point out some problems associated with laboratory selection experiments and suggest that experimental manipulations of life history traits and secondary sexual characters in natural populations is an important and invaluable empirical method if one aims to get a better understandingof life history evolution in the wild. Finally, we discuss the proximate-ultimate dichotomy, the physiology of phylogenetic constraints, the role of physiological mechanisms in population differentiation inlife history trade-offs and the importance of phenotypic plasticity in shaping such trade-offs. We suggest that life history plasticity in many cases may stem from the same endocrine mechanisms (gonadotropin, gonadal steroids, and adrenal glucocorticoids) as those involved in life history trade-offs. In particular, attempts to dichotomize life history trade-offs and life history plasticity may be unrealistic as t [ABSTRACT FROM AUTHOR]

Reproductive strategies of males and females usually differ and, as a consequence, may impose asymmetric costs of reproduction on the twosexes and result in conflict between the sexes. In spiders, males donot provide parental care and females can store sufficient sperm forseveral clutches. These characteristics define the stage for a conflict between males and females that occurs mainly over the frequency of mating. Factors such as sexual size dimorphism, operational sex ratio, mating system and life-history strategies are likely to influencethe degree of conflict and its outcome for different species. Male spiders may suffer large costs of mating due to mate search, assessment of female condition, courtship and cannibalistic tendencies of their mates. Courtship may reduce cannibalism, although in some cases, males benefit from being cannibalised by having an increased fertilisation rate or greater offspring fitness. In some species, limited mating capacities will increase the value of the current mating relative to future reproduction. Apart from a possible benefit of genetic variability within a clutch, females may not benefit from multiple mating and multiple mating may even be costly. Exceptions occur if additional resources are provided by males or when offspring fitness increaseswith additional mating. Forced copulation, prey theft, loss of the web and reduction of foraging time can all result in reduced reproductive success for females. We discuss the interacting influences of life-history traits (especially patterns of growth and maturation and sexual size dimorphism) and the reproductive strategies of males and females, using a semelparous spider, Stegodyphus lineatus (Eresidae), as an example of a species in which males and females can have strongly conflicting interests. [ABSTRACT FROM AUTHOR]

Recent advances in understanding mammalian reproductive patterns mirror general developments in phylogenetic, physiological, and ecological research. We provide an overview of the diverse approaches used instudying mammalian litter size and discuss recent advances in evolutionary ecological theory and experimental data concerning reproductive patterns. Extensively documented natural history studies and breeding data from work in applied zoology and animal husbandry constitute a rich source of information for comparative studies. Such studies have helped identify fundamental differences in reproductive 'strategies' depending on whether taxa produce altricial or precocial young andwhether a given reproductive effort results in a single offspring ora litter. On the other hand, research on ecological and physiological correlates of litter size is providing new insights about reproductive energetics, the relationship between resource availability and litter size, and optimality in varying environments in general. Continuing experimental approaches are broadening our understanding of the mechanistic bases of patterns of mammalian litter size, but such studies, especially those involving manipulation of litter size, must carefully consider the potential biases introduced by experimentally induced non-congruence between pre- and postnatal litter sizes. For example, without accounting for the effects of placental hormones on mammogenesis and lactation, postnatal manipulations of litter size might be based on faulty assumptions implicit in such manipulations. To conclude, despite substantial advances in these diverse approaches, our degree of understanding of optimal litter size in mammals remains unclear because of inconsistencies in data often used in comparative studies and because of physiological and ecological constraints on littersize adjustments that hinder or bias experimental approaches. These areas should be addressed in future studies. [ABSTRACT FROM AUTHOR]

We studied effects of the non-lethal presence of a predator on behaviour and larval life history of two species of anuran tadpoles, common frog, Rana temporaria, and common toad, Bufo bufo. We manipulated predator diet to study whether differences in chemically perceived predation risk affect the tadpoles. Tadpoles of both species were raisedat two food levels either in the absence of the predator or in the presence of an insect-, frog- or toad-fed larval dragonfly Aeshna juncea. R. temporaria tadpoles lowered their activity in the presence of a predator and also avoided the predator spatially. Furthermore, theyshowed the strongest response to tadpole-fed predators. The number of days elapsed since the last provisioning of food affected the behaviour of both species. In R. temporaria, differences in activity levelbetween predator treatments vanished as the food resources were depleted. In B. bufo, activity was lower in the presence of a toad-fed predator shortly after food had been added to the containers. Spatial avoidance of predators by B. bufo was stronger in the presence of a toad-fed predator than when an insect- or frog-fed predator was present. In both tadpole species growth rate was higher at the high food level but remained unaffected by the predator treatments. In both species individuals at higher food level metamorphosed earlier and at larger size. The metamorphic responses to predator treatments differed between the species. R. temporaria metamorphosed later and at larger size in the presence of tadpole-fed predators than in the control treatment or in the presence of an insect-fed predator. B. bufo metamorphosed earlier in the presence of a toad-fed predator, but this was only slightly correlated to metamorphic size. Manipulations of predator diet affected tadpole life history in both species. However, predator effects on larval life history were not mediated by tadpole behaviour in either species. [ABSTRACT FROM AUTHOR]

While variability in recruitment of young reef fish is now recognised, the question remains how the variation in recruitment will contribute to determining assemblage structure. This has been the basis for an active debate about whether patterns in abundance are determined by the supply of planktonic larvae or whether it results from competition (for space, food, etc.) between potential recruits leading to density-dependent recruitment. We tested population regulation of newly recruited juveniles of Sparidae in the north-western Mediterranean Sea. Recruitment of three species of Sparidae was followed over a three-month period in each of two years to estimate the peak density of new recruits settling from the ocean, the rate of mortality occurring during the first three months after settlement, and the final density after three months. Sites and species were carefully chosen in order to avoid migration during the survey. Initial density of recruited larvae of Diplodus spp. varied among species and sites from 0.045 to 3.8 individuals per metre of coastline. Mortality estimates also variedenormously. Between 24.3% and 99.4% of the initial population disappeared within three months. Our survey demonstrated that both post-settlement mortality (r = 0.847; p < 0.0001; n = 18) and final density (r = 0.818; p < 0.0001; n = 18) were correlated with density of recruitment and consequently that both pre-recruitment (larval phase) and post-recruitment processes regulated sparid populations of the Mediterranean Sea. [ABSTRACT FROM AUTHOR]

Life-history traits and secondary sexual characters often demonstrate condition-dependence, and reproductive success thus ultimately appears to be determined by condition. Here we test the hypothesis that anti-parasite defense is condition-dependent and thus ultimately limits fitness. Animal hosts defend themselves against parasites by an efficient immune system that changes its activity level depending on level of infection. Since immune function is costly, as demonstrated by several field studies, we predicted that large immune defence organs should be maintained when the costs of an elevated immune response were reduced, or when the benefits were increased. Hence, the size of immune defence organs was predicted to increase in response to diseasedue to increased benefits of investment in immune function, and the size was predicted to increase in response to high body condition because of reduced costs of investment in immune function. A comparativestudy of birds demonstrated that the size of the spleen was significantly increased among individuals suffering from parasitic infectionsand signs of disease as compared to healthy individuals. Furthermore, we found evidence for a positive association between spleen size and body condition. These findings are consistent with the hypothesisedcost of immune function and hence a cost of anti-parasite defence. [ABSTRACT FROM AUTHOR]

Energy storage is an important component of life-history variation. Some organisms ('income breeders') fuel reproductive expenditure by simultaneous feeding, whereas others ('capital breeders') fuel reproduction from energy gained earlier, and stored prior to use. Most published discussions of this topic have focused primarily on endothermic animals (birds and mammals), and have interpreted the costs and benefits of these alternative breeding tactics in the context of endothermy. The far more diverse array of ectothermic animals has received less attention in this respect. Many features associated with ectothermypreadapt organisms to store energy for long periods prior to use (i.e. to rely on 'capital' rather than 'income'). For example, birds andmammals experience high costs (in terms of mobility and thermoregulatory efficiency) if they store large body reserves. By contrast, the energetic and demographic costs associated with storage, maintenance,and utilisation of body reserves are low in many ectotherms. Thus, capital breeding (which may also be more efficient energetically in many situations) is extremely common in these low energy systems. Ectotherms comprise the most extreme examples of capital breeders, with a strong tendency towards semelparity where the capital of reserves is massively invested into a single reproductive event. Overall, theoretical and empirical studies of the evolution of capital versus income breeding as alternative strategies of resource use should take account of the important role played by alternative thermoregulatory and metabolic systems. The acquisition of endothermy in avian and mammalianlineages has involved a massive shift towards reliance on 'income breeding', and the full spectrum of life-history variation in this respect cannot be appreciated without detailed examination of ectothermicorganisms. [ABSTRACT FROM AUTHOR]

Procellariiform seabirds such as Manx Shearwaters, Puffinus puffinus, accumulate large quantities of lipid during the nestling period, the purpose of which remains unclear. This paper examines temporal and age-specific variation in the pattern of food delivery to nestling Manx Shearwaters, to determine whether food delivery was likely to be determined primarily by the availability of food to adults at sea or by a chick's short-term nutritional requirements. The variability in daily food delivery to chicks in the context of nestling obesity is then discussed. 2. For all but the youngest and oldest age classes, individual meals delivered by adults averaged 49 g, which was 12% of mean adult mass over the same period. More than 80% of chicks were led each night and the maximum interval between feeding events for any chick was four nights. Feeding conditions did exert some influence over the ability of adults to feed their offspring, but deviations from expected values for both feeding frequency and meal size were restricted to a small number of nights, included values both higher and lower than expected and did not persist for more than one night in succession. These results were not compatible with the notion that large lipid reserves accumulated by chicks during their development provide insurance against prolonged interruptions to feeding. 3. Although adultsdid not appear to modulate food delivery over the nestling period, there was some evidence of short- term adjustment of feeding frequency(but not meal size) according to a chick's immediate nutritional requirements. This suggests that variation in the provisioning rates of chicks did not result solely from stochastic variation in parental foraging success. However, the effect was slight and despite such minoradjustments, the coefficient of variation in daily provisioning ratewas not substantially lower than in other species where the chick has no influence on parental food delivery. This suggests that even among t [ABSTRACT FROM AUTHOR]

The present study is based on a 14-yr time series of light trap dataof moths (Lepidoptera) species in an undisturbed alder swamp forest in Central Europe. Vegetation change was followed on five permanent plots. The biomass of all plant species in the portion of the forest surrounding the light trap was determined. As the feeding specificity of all the moth species was known, we were not only able to categorize moth species according to their potential feeding specificity, but were also able to estimate total food supply and its diversity in thestudied ecosystem. In monophagous species, moth population size. characterized by mean annual catch, was positively correlated with food supply, whereas in oligo- and polyphagous species the correlation wasclose to zero. Although the ability of plant species to support a monophagous moth is positively dependent on its biomass, there are somerelatively rare plant species supporting monophagous moths. and somecommon species not supporting monophagous moths. Directional changeswere found both in plant and moth species; directional changes in moth species are more pronounced than changes in plant cover. There is no evidence suggesting that directional changes in moth population sizes are caused by the changes in food supply. Pronounced directional changes were found mainly in species not confined to the closed alderforest and are related to changes in wider areas, in some cases withknown changes in species distribution. Non-directional year-to-year variability, described by Lloyd's index, is best explained by the potential population growth rate of a moth species estimated on the basis of species fecundity. Correlation of Lloyd's index with number of food plant species is significantly positive, but low (r = 0.25); no significant differences were found between categories of feeding specificity. This shows that the dependence of population variability on species feeding specificity, both potential and expressed as number offood pla [ABSTRACT FROM AUTHOR]

Results of current computer simulations suggest that a pathogen-mediated version of Hamilton's spite hypothesis may play an unexpected role in the evolution of host-parasite interactions. Theory predicts that hosts’ ability to influence parasite transmission to conspecifics is a neutral character provided that transmission routes are random. There are two possible deviations from this. Firstly, vertical transmission is biased in favour of kin, and this selects hosts to decrease pathogen transfer. Secondly, horizontal transmission is biased against kin and this selects hosts to increase pathogen transfer to conspecifics. Unfortunately, we typically do not know transmission statistics in relation to genetic kinship within a host population, thus cannot easily predict whether there is a selective pressure upon hosts either to transmit pathogens or not to transmit. Here I aim to show that even simple descriptive information on host and parasite life-histories may be used to make rough estimations about transmission routes and selection pressures. Interspecific predictions suggest that pelagic hosts, passively aerial hosts, and the intermediate hosts of pathogens transmitted along the predator-prey transmission routes are not selected to influence pathogen transmission. Intraspecific predictions suggest that parasitism and disease should facilitate emigration, and immigrants surrounded by non-related conspecifics should adaptively enhance pathogen transmission to conspecifics. This behaviour may select social animals, like humans, for an adaptive xenophobia in the context of an intraspecific arms race. [ABSTRACT FROM AUTHOR]

We developed a description of a central New England deciduous hardwood forest based on the distribution within the community of morphological and life history traits (N = 34) and environmental factors. Classification by TWINSPAN of 186 species based on morphological and lifehistory traits identified six major functional groups of species largely corresponding to growth form. A data matrix of plots x traits was ordinated using PCA. Each of the resulting four PCA axes was associated with a major environmental gradient: drainage, site exposure, disturbance due to past land use and degree of disturbance in the 1938 New England Hurricane (24.9, 19.8, 11.7 and 8.4% of the variation respectively). Two patterns suggested that a suite of potentially functional traits, rather than a few key characters (e.g. vital attributes), govern the distribution of species in this community: (1) each of the four axes was largely associated with a different group of traits and (2) each axis was associated with several traits that appeared tosort independently (i.e. not to co-occur within species). Evaluatingone often-examined trait, there was no evidence that dispersal ability limited the colonization of species into secondary woodlands. We also found that landscape-scale abundance was associated with a small number of traits. Production of fleshy fruits and few diaspores per plant were positively associated with landscape-level abundance. Our results suggest that attempts to understand the overall structure and function of this plant community based on a few key characters, such as dispersal ability, will meet with limited success. However, when focusing on one aspect of the community, such as frequency across the landscape, relatively few characters may be important. [ABSTRACT FROM AUTHOR]