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Here, we propose a theory for the structure of communities of competing species. We include ecologically realistic assumptions, such as density dependence and stochastic fluctuations in the environment, and analyze how evolution caused by

Reproduction is a defining process of biological systems. Every generation, across all species, breeding females repopulate ecosystems with offspring. r/K selection was the first theory to classify animal species by linking the rates with which breeding females repopulated ecosystems, to the stability of ecosystems. Here, I introduce a species classification scheme that extends the reach of r-K selection and CSR selection by linking breeder investments in offspring quantity, quality, and diversity to specific natural selection pressures. The species classification scheme is predicated on the assumption that high rates of predation favor breeders that invest more in offspring quantity than quality; and that spatiotemporal scarcity favors breeders that investment more in offspring quality than quantity. I present equations that convert the species classification scheme into a maternal risk-management model. Thereafter, using the equations, I classify eighty-seven animal species into the model’s natural selection categories. Species of reptiles, fish, and marine invertebrates clustered in the predation selection category. Species of birds and mammals clustered in the scarcity selection category. Several species of apex predators clustered in the weak selection category. Several species of social insects and social mammals clustered in the convergent selection category. In summary, by acknowledging breeding females as the individuals upon which natural selection acts to repopulate ecosystems with offspring, the proposed maternal risk-management model offers a testable, theoretical framework for the field of ecology.

Adaptive topography is a central concept in evolutionary biology, describing how the mean fitness of a population changes with gene frequencies or mean phenotypes.We use expected population size as a quantity to be maximized by natural selection to show that selection on pairwise combinations of reproductive traits of collared flycatchers caused by fluctuations in population size generated an adaptive topography with distinct peaks often located at intermediate phenotypes. This occurred because r- and K-selection made phenotypes favored at small densities different from those with higher fitness at population sizes close to the carrying capacity K. Fitness decreased rapidly with a delay in the timing of egg laying, with a densitydependent effect especially occurring among early-laying females. The number of fledglings maximizing fitness was larger at small population sizes than when close to K. Finally, there was directional selection for large fledglings independent of population size. We suggest that these patterns can be explained by increased competition for some limiting resources or access to favorable nest sites at high population densities. Thus, r- and K-selection based on expected population size as an evolutionary maximization criterion may influence life-history evolution and constrain the selective responses to changes in the environment.

Selection for bacteria which are K-strategists instead of r-strategists has been shown to improve fish health and survival in aquaculture. We considered an experiment where microcosms were inoculated with natural seawater and the selection regime was switched from K-selection (by continuous feeding) to r-selection (by pulse feeding) and vice versa. We found the networks of significant co-occurrences to contain clusters of taxonomically related bacteria having positive associations. Comparing this with the time dynamics, we found that the clusters most likely were results of similar niche preferences of the involved bacteria. In particular, the distinction between r- or K-strategists was evident. Each selection regime seemed to give rise to a specific pattern, to which the community converges regardless of its prehistory. Furthermore, the results proved robust to parameter choices in the analysis, such as the filtering threshold, level of random noise, replacing absolute abundances with relative abundances, and the choice of similarity measure. Even though our data and approaches cannot directly predict ecological interactions, our approach provides insights on how the selection regime affects the composition and workings of the microbial community, providing a basis for aquaculture experiments targeted at eliminating opportunistic fish pathogens.

Among the classical models of optimization, some models maximize the ratio of returns per investment, others maximize the difference between returns and investment. However, the question under what conditions use of the ratio model is appropriate and under what conditions a difference model should be used remained unaddressed until recently. The question is important because the strategies indicated by ratio optimum can be substantially different than the ones suggested by difference optimum. We make a general case here for the set of conditions for appropriate use of ratio versus difference optimum. When the investable amount is perceived as limiting but not the investment opportunities a ratio optimum is appropriate and when the investment opportunities are perceived to be limiting but not the investable amount, difference optimum is appropriate. Taking examples of Concorde fallacy, parental investment, r and K selection, nectar production, pollinator behavior, protein synthesis and stability, viral burst size and human economic behavior we show that the ratiodifference distinction in optimization models resolves many long standing debates and conundrums in evolution, behavior and economics.

Gleaners and exploiters (opportunists) are organisms adapted to feeding in nutritionally poor and rich environments, respectively. A trade-off between these two strategies-a negative relationship between the rate at which organisms can acquire food and ingest it-is a critical assumption in many ecological models. Here, we evaluate evidence for this trade-off across a wide range of heterotrophic eukaryotes from unicellular nanoflagellates to large mammals belonging to both aquatic and terrestrial realms. Using data on the resource acquisition and ingestion rates in >500 species, we find no evidence of a trade-off across species. Instead, there is a positive relationship between maximum clearance rate and maximum ingestion rate. The positive relationship is not a result of lumping together diverse taxa; it holds within all subgroups of organisms we examined as well. Correcting for differences in body mass weakens but does not reverse the positive relationship, so this is not an artifact of size scaling either. Instead, this positive relationship represents a slow-fast gradient in the "pace of life" that overrides the expected gleaner-exploiter trade-off. Other trade-offs must therefore shape ecological processes, and investigating them may provide deeper insights into coexistence, competitive dynamics, and biodiversity patterns in nature. A plausible target for study is the well-documented trade-off between growth rate and predation avoidance, which can also drive the slow-fast gradient we observe here.

The life history traits of blow fly Cochliomyia macellaria (Fabricius, 1775) was studied under semi-controlled laboratory conditions at 29.14°C temperature, 72.53% relative humidity, and 12-h photoperiod. The raw data were analyzed based on the age-stage, two-sex life table, considering the development rates among individuals of both sexes. Cochliomyia macellaria survival rate was 0.43 (♂) and 0.40 (♀), while life expectancy was 17.9 (♂) and 20.9 (♀) days, for adult males and females, respectively. The total fecundity was 681.15 eggs/female, with an average of 3.65 batches/female and 199 eggs/batch. The intrinsic rate of increase (r) was 0.327 days−1, the finite rate of population increase (λ) was 3.35 days−1, the mean generation time (T) was 17.15 days, and the net reproduction rate (R 0 ) was 272.46 offspring/individual. The population parameters found here corroborates that C. macellaria population act as a r selected species under laboratory conditions. Additionally, development data and accumulated degree days (ADD) for each stage of C. macellaria are provided and its implications for the forensic use are discussed.

Several universal genomic traits affect trade-offs in the capacity, cost, and efficiency of the biochemical information processing that underpins metabolism and reproduction. We analyzed the role of these traits in mediating the responses of a planktonic microbial community to nutrient enrichment in an oligotrophic, phosphorus-deficient pond in Cuatro Ciénegas, Mexico. This is one of the first whole-ecosystem experiments to involve replicated metagenomic assessment. Mean bacterial genome size, GC content, total number of tRNA genes, total number of rRNA genes, and codon usage bias in ribosomal protein sequences were all higher in the fertilized treatment, as predicted on the basis of the assumption that oligotrophy favors lower information-processing costs whereas copiotrophy favors higher processing rates. Contrasting changes in trait variances also suggested differences between traits in mediating assembly under copiotrophic versus oligotrophic conditions. Trade-offs in information-processing traits are apparently sufficiently pronounced to play a role in community assembly because the major components of metabolism—information, energy, and nutrient requirements—are fine-tuned to an organism’s growth and trophic strategy.

In a stable environment, evolution maximizes growth rates in populations that are not density regulated and the carrying capacity in the case of density regulation. In a fluctuating environment, evolution maximizes a function of growth rate, carrying capacity and environmental variance, tending to r-selection and K-selection under large and small environmental noise, respectively. Here we analyze a model in which birth and death rates depend on density through the same function but with independent strength of density dependence. As a special case, both functions may be linear, corresponding to logistic dynamics. It is shown that evolution maximizes a function of the deterministic growth rate r0 and the lifetime reproductive success (LRS) R0 , both defined at small densities, as well as the environmental variance. Under large noise this function is dominated by r0 and average lifetimes are small, whereas R0 dominates and lifetimes are larger under small noise. Thus, K-selection is closely linked to selection for large R0 so that evolution tends to maximize LRS in a stable environment. Consequently, different quantities (r0 and R0 ) tend to be maximized at low and high densities, respectively, favoring density-dependent changes in the optimal life history.

The idea that selection works in different ways during free population growth and at the equilibrium population size has been present in theoretical biology for a long time. It was first expressed as an r and K selection concept and later clarified in the debate on fitness measures in life history theory. The latest discussion related to this topic is focused on the nest site lottery mechanism and the resulting new population growth model. In this mechanistic biphasic model, the suppression of growth is induced by a shortage of free nest sites for newborns. Before it occurs, the population can grow exponentially. In this paper, the continuous version of the model and its selective properties are analysed. We show a continuous smooth transition between different fitness measures operating during the exponential growth and suppressed growth phase and at the equilibrium population size. Then, the model is extended to the case of a population of parasites, where a constant number of nest sites is replaced by the dynamics of a population of their hosts, in the role of the limiting supply. Parasite strategies are selected under exponential and suppressed growth phases of the population of hosts. Transitions between different fitness measures and conditions for extinction of hosts by parasites are analysed. An interesting result is the possibility of a continuum of fitness measures of parasites for the unsuppressed exponential growth of the host population.

There are several reasons to believe that there is a predominance of suffering over wellbeing in nature. The difference grows exponentially when the suffering of invertebrates is taken into consideration. Given the relevance of the experience of pain when it comes to attributing moral considerability to an individual, the seriousness and implications of the above statements are significant due to the need to reconcile the interests of an enormous number of individuals who experience pain to some degree. Depending on the species and the ecosystem, there are variations that must be kept in mind with the aim of reducing the existing amount of suffering. Resumen Tenemos fuertes razones para creer que hay una prevalencia del sufrimiento sobre el bienestar en la naturaleza. Esta diferencia crece exponencialmente si tenemos en cuenta el sufrimiento de los invertebrados. Dada la relevancia de la experiencia del dolor para la atribución de consideración moral a un individuo, la gravedad e implicaciones de lo dicho son enormes en la medida en que tenemos que conciliar los intereses de una gran cantidad de individuos que experimentan dolor en algún grado. Dependiendo de la especie y el ecosistema, existen variaciones que tenemos que tener en cuenta en aras de reducir la cantidad de sufrimiento existente. Resum Tenim fortes raons per creure que hi ha una prevalença del patiments sobre el benestar en la naturalesa. Aquesta diferència creix exponencialment si tenim en compte el patiment dels invertebrats. Donada la rellevància de l'experiència del dolor per a l'atribució de consideració moral a un individu, la gravetat i implicacions del que s'ha dit són enormes en la mesura en què hem de conciliar els interessos d'una enorme quantitat d'individus que experimenten dolor en algun grau. Depenent de l'espècie i l'ecosistema, existeixen variacions que hem de tenir en compte per reduir la quantitat de patiment existent.

The Williams’ hypothesis is one of the most widely known ideas in life history evolution. It states that higher adult mortality should lead to faster and/or earlier senescence. Theoretically derived gradients, however, do not support this prediction. Increased awareness of this fact has caused a crisis of misinformation among theorists and empirical ecologists. We resolve this crisis by outlining key issues in the measurement of fitness, assumptions of density dependence, and their effect on extrinsic mortality. The classic gradients apply only to a narrow range of ecological contexts where density-dependence is either absent or present but with unrealistic stipulations. Re-deriving the classic gradients, using a more appropriate measure of fitness and incorporating density, shows that broad ecological contexts exist where Williams’ hypothesis is supported. Electronic supplementary material The online version of this article (10.1007/s11692-018-9458-7) contains supplementary material, which is available to authorized users.

We revisit an old theory proposed by Lynn, connecting race differences in criminality and psychopathy with r/k selection. The origin of this group-difference is attributed to cold-selection in the Pleistocene . We contend that newer models of Life History Theory provide a better rubric within which to evaluate Lynn's arguments as a) they better account for the adaptive logic of the coherence pattern among the traits characteristic of so-called ‘psychopathic personality’, b) provide a normatively free language with which group differences in behavior can be described, and c) make predictions at the level of both the individual and intra-individual (developmental) levels, which permit the role of environmental contributions to these dispositions to be better comprehended. Thus newer approaches to understanding life history are necessarily more empirically nuanced. We also consider the merits of future, more systematic studies along the lines of Lynn's contribution.

There is now considerable empirical evidence that evolutionary changes in many phenotypic characters, such as body mass, age at maturation, and timing of breeding, often occur in populations subject to intense harvesting over longer periods. Here, we analyze the evolutionary component of the selection due to nonselective harvesting, which will operate even under selective harvesting and may generate a large evolutionary response. If phenotype affects susceptibility to density dependence-for example, through resource limitation-then nonselective harvesting can induce evolutionary change through its effect on population density. We provide a model for evolution of a quantitative character in such a fluctuating density-dependent population, using the diffusion approximation to describe jointly the temporal changes in mean phenotype and log population size. We show how nonselective harvesting in particular generates r-selection governed by genetic variation in the strength of density regulation and the magnitude of population fluctuations. We show that r-selection caused by nonselective harvesting is proportional to the mean fraction of the population harvested. We then compare the short-term as well as the long-term evolutionary impact of nonselective harvesting for different harvesting strategies by using the mean harvest fraction for different strategies. This comparison is performed for three different harvesting strategies: constant, proportional, and threshold harvesting. The more ecologically sustainable strategies also produce smaller evolutionary changes.

Life history theory is an elegant instrument for describing major differences in patterns of life history traits across plant and animal taxa (Charnov, 1993; Roff, 1992, 2002; Stearns, 1992). Typical life history traits discussed in the classic evolutionary biology literature include size at birth, growth pattern, age of sexual maturation, size at maturity, age of first reproduction, number and sex ratio of offspring produced, age and size-specific reproductive investments, age and size-specific mortality schedules, and length of lifespan (see Stearns, 1992). A basic assumption of the classic optimality approach to life history theory is that, given adequate genetic variation, the evolution of species has involved natural selection of optimal combinations of these traits. However, genetic and other constraints, and trade-offs have reduced the set of possible combinations. Life history theory predicts trade-offs between energetic investment in growth, maintenance, and reproduction across species, of which a trade-off between the main constituents of reproductive investment, mating and parental effort, may be the most common (McGlothlin, Jawor, & Ketterson, 2007). It is easy to see how if organisms possess finite resources that trade-offs affecting life history traits would necessarily evolve over evolutionary time. If the “pie of finite resources” is divided up between life history traits, taking a large slice of one type of trait leaves less of the pie to be divided into other forms of investment. Among vertebrate species, for example, salmon have very different life histories than primate species. Their life history consists of relatively rapid growth, early maturation and first reproduction, small size, little parental care, and the production of a high number of offspring, followed immediately by death in semelparous species,eclipsing a postreproductive period. In contrast, the life history of human beings consists of relatively slow development, late puberty and first reproduction, iteroparity, large body size, low number of offspring, followed by high parental investment (extended to grandparental investment) and a long life span, including a female postreproductive period.

Life history theory explains how individuals decide to invest their limited resources, which involves several trade-offs. Particularly relevant to the current work, individuals can choose to invest in current or delayed reproduction (a slow life history strategy), which implicates a trade-off between the quantity and the quality of one’s offspring. Choosing to delay reproduction allows for increased self-investment, and previous research has demonstrated that traits requiring self-investment are related to higher mate value. As such, the current study hypothesizes that slow life history strategy will predict high personal mate value and high levels of partner mate-value within heterosexual partnerships. Similarly, those with a slow life history strategy should display fewer tendencies toward mate-settling. The current work employs both subjective and objective measures of mate value within mateships to investigate these hypothesized relationships. As hypothesized, significant positive relationships among life history and mate value were detected, suggesting that a slower life history strategy corresponds to high ratings of mate value for both self and partner. Also, life history strategy is a significant predictor of subjective, objective, and Mate Value Inventory ratings of partner and self. Further implications and potential future works are discussed.

Density-dependent selection occurs when the relative fitnesses of genotypes depend on population size. Under the influence of environmental stochasticity, there is also fluctuating selection, with r -selected strategies having higher fitness at low population sizes and K -selected strategies having higher fitness when competition for resources is fierce. This often results in a trade-off: being very fit at low densities precludes a strategy from being very fit at high densities. Hence, the fittest strategy will depend upon the proportion of time the population spends at high and low densities. Thus, density-dependent selection is important for phenotypic evolution in fluctuating environments.

Understanding the variation in selection pressure on key life-history traits is crucial in our rapidly changing world. Density is rarely considered as a selective agent. To study its importance, we partition phenotypic selection in fluctuating environments into components representing the population growth rate at low densities and the strength of density dependence, using a new stochastic modelling framework. We analysed the number of eggs laid per season in a small song-bird, the great tit, and found balancing selection favouring large clutch sizes at small population densities and smaller clutches in years with large populations. A significant interaction between clutch size and population size in the regression for the Malthusian fitness reveals that those females producing large clutch sizes at small population sizes also are those that show the strongest reduction in fitness when population size is increased. This provides empirical support for ongoing r - and K -selection in this population, favouring phenotypes with large growth rates r at small population sizes and phenotypes with high competitive skills when populations are close to the carrying capacity K . This selection causes long-term fluctuations around a stable mean clutch size caused by variation in population size, implying that r - and K -selection is an important mechanism influencing phenotypic evolution in fluctuating environments. This provides a general link between ecological dynamics and evolutionary processes, operating through a joint influence of density dependence and environmental stochasticity on fluctuations in population size.

This article briefly reviews and provides discussion on the evidence for, and nature of, density-dependence patterns in r and K-selected species. In this review, I discuss how life-history strategies cause different nonlinear density-dependence patterns and I provide a simple modeling recommendation to incorporate nonlinear density dependence in population growth equations. Second, I discuss the importance of incorporation of environmental stochasticity and local extinction associated with nonlinear density dependence associated with life-history patterns through a novel modeling exercise. Last, I discuss the importance of considering how life-history nonlinear density dependence could affect optimal harvest yields. Though these topics are extensive, this review should spur wildlife biologists and managers to consider more inclusive population models that incorporate life-history strategies and stochasticity in their decision-making processes. © 2012 The Wildlife Society.

1. Due to climate change, contemporary climate scenarios forecast an increase in extreme weather, which may have considerable impacts on the world's riverine ecosystems. Because the flow regime is a primary determinant of the structure and function of lotic ecosystems, changes in the weather could fundamentally alter these ecosystems through changes in hydrologic disturbance regimes. 2. In this paper, we use the abundance/biomass comparison (ABC) method, based on r/K selection theory, and event probability distribution to characterise the responses of macroinvertebrates in Taiwan mountain streams to extreme floods. 3. Severe impacts on macroinvertebrates, resulting in a large shift in community structure toward r-selected taxa, usually were observed the year after extreme floods. 4. Macroinvertebrate communities dominated by K-selected taxa had more individuals with traits conferring resistance to flooding disturbance, while those dominated byr-selected taxa had more individuals with traits conferring resilience. 5. This relationship between the changes in flow regime and the ecological response of r- and K-selected taxa may be exploited to understand the potential effects of flood extremes in the future, and to keep decision makers informed about the ecological consequences of climate-mediated changes to hydrological regimes.

Spatial patterns of entomopathogenic and other free-living nematode populations were analyzed at the landscape scale. Free-living bacterial feeder populations can be classified into trophic groups based on their functional and life history characteristics. Differences in life history traits were hypothesized to result in different spatial structures of populations. Spatial autocorrelations (Moran's I index) and exponential variogram models were calculated and estimated for each trophic group, including entomopathogenic nematodes, and comparisons were made among them. Spatial autocorrelation results showed that the spatial structure of entomopathogenic nematode populations is similar to that of relatively r-selected free-living bacterial feeders, which share several life history traits with entomopathogenic nematodes.

Despite the fact that density effects and individual differences in life history are considered to be important for evolution, these factors lead to several difficulties in understanding the evolution of life history, especially when population sizes reach the carrying capacity. r/K selection theory explains what types of life strategies evolve in the presence of density effects and individual differences. However, the relationship between the life schedules of individuals and population size is still unclear, even if the theory can classify life strategies appropriately. To address this issue, we propose a few equations on adaptive life strategies in r/K selection where density effects are absent or present. The equations detail not only the adaptive life history but also the population dynamics. Furthermore, the equations can incorporate temporal individual differences, which are referred to as internal stochasticity. Our framework reveals that maximizing density effects is an evolutionarily stable strategy related to the carrying capacity. A significant consequence of our analysis is that adaptive strategies in both selections maximize an identical function, providing both population growth rate and carrying capacity. We apply our method to an optimal foraging problem in a semelparous species model and demonstrate that the adaptive strategy yields a lower intrinsic growth rate as well as a lower basic reproductive number than those obtained with other strategies. This study proposes that the diversity of life strategies arises due to the effects of density and internal stochasticity.

We investigated theoretically how the sensitivity of organisms to the toxicity of chemicals varies depending on their life-history traits, which are subject to evolution. We used a resource-allocation model in which organisms allocate their resources to reproduction, maintenance of life (reduction of death), and reduction of the toxicities of chemicals. First we investigated the optimal allocation rates in the absence of chemicals. We found that when evolution occurred in low-density populations, the allocation rate for reproduction was larger than that for maintenance of life, and hence an r-strategy evolved. The r-strategists had lower sensitivity (higher resistance) against the toxicity than K-strategists, which was the optimal strategy in high-density populations. Second, we examined the optimal allocation rates in the presence of chemicals. The allocation rate for the reduction of toxicity varied depending on the shape of functions for the reduction of toxicity. When the efficiency for the reduction was low, organisms did not allocate resources to reduce toxicity, and they remained sensitive to chemicals (sensitive type). When the toxicity was efficiently reduced, the organisms allocated resources to reduce the toxicity and became insensitive to the chemicals (resistant type). When the function for the reduction had a sigmoidal shape, evolutionary bistability appeared, and the organisms eventually evolved either to allocate resources for chemical reduction or not to do so depending on the initial conditions of evolution. This result explains the large variation in the sensitivities to chemicals in organisms collected from polluted areas. We also found that the toxicity required to reduce the population growth rate by 10% (EC10) was higher for the resistant type than for the sensitive type in general; however, when the toxicity tests were conducted under a resource-poor condition, EC10 was even smaller in the resistant type than in the sensitive type (i.e., resistant organisms are more sensitive than sensitive organisms). This counterintuitive result occurred because the allocation of resources for toxicity reduction was larger than needed, and was thus an overinvestment under the resource-poor condition. Together with the results, we conclude that lacking an understanding of the evolutionary aspect may lead to insufficient risk assessment and management.

Populations of Acanthoscelides obtectus were maintained for 7 generations in either low- or high-larval densities in order to examine whether weevils life-history traits are modified in the direction predicted by r/K-selection theory. We found that r-selected population had a higher total fecundity, earlier age at first and last reproduction, and higher intrinsic rate of growth than K-selected population. Contrary to the theory, we have no evidence that preadult developmental time and adult longevity have been molded by density-dependent selection. The analysis of genetic variation of the weevils life-history traits in responses to different larval densities in both r- and K-selection populations indicates that different set of genes determining performance in two densities of analysed fecundity indices were accumulated during the course of the r- and K-selection.

The relationships between species’ functional traits and their demographic life histories are central to understanding the causes of life-history diversity. A previous study identified three independent demographic axes amongst 29 broadleaved tree species: a light-demand axis, a population turnover rate (r–K) axis, and one discriminating substrate requirements for recruitment. This study evaluates the basis of life-history variation amongst the 29 species by assessing the correlation between the three demographic axes above and 14 morphological, phenological, architectural and biomass-partitioning traits. A principal components analysis of the 14 traits revealed two main axes: (1) a ‘resource capture versus conservation’ axis separated species with large and thin leaf laminas, high leaf K, P and N concentrations, light wood and small seeds from species with opposite attributes, and (2) a ‘physiognomic’ axis separated species with compound leaves, high leaf/above-ground mass ratio, and tall first branch in saplings from species with opposite attributes. Subsequent paired correlations and a Procrustes superimposition analysis showed that species with attributes typical of high capture and low conservation of resources, small seeds and short stature had faster population turnover rates (short longevity, and high mortality and recruitment rates) than species with opposite attributes. Species with compound leaves, high leaf/above-ground mass ratio, and tall first branch as saplings (physiognomic axis) tended to be more light-demanding and to have fast diameter growth rates of stems ⩾10 cm diameter. The independence between attributes typical of resource capture or conservation and stem diameter growth rate is noteworthy; it differs from correlations often reported for saplings and could be attributed to ontogenetic changes in plant function. In addition, the clear link between attributes typical of resource capture or conservation and plant recruitment, survivorship and longevity is consistent with r–K theory and brings to light an important connection between a leading axis of plant evolutionary diversification (resource capture versus conservation) and rates of population turnover.

The present study examines predictions from Rushton’s differential K theory that diverse traits covary with intelligence, reproductive strategies, speed of maturation, parental care, and longevity. The predictions are tested by inter-correlating 129 cross-national differences in IQ, birth rate, infant mortality, HIV/AIDS, and life expectancy. A K super-factor accounted for 75% of the variance. Moreover, the correlations were significantly higher with skin color, a biological variable, than they were with gross domestic product (GDP), a culturally influenced variable. The median of the 21 inter-correlations among the seven variables was 0.68.

Offspring quality and quantity are subject to a trade-off. Depending on species, ant colonies can produce either numerous winged queens that start new colonies alone (independent colony foundation [ICF]) or one propagule consisting of reproductives helped by workers (fission). Some species do both. In the Rhytidoponera impressa group, colonies with winged queens use ICF, whereas colonies with mated workers use fission. We assessed the effect of latitude and environment on colonial reproduction by collecting 79 colonies along the Australian east coast. A population dynamical model predicted that from tropical north to temperate south, seasonal fluctuations and harsher conditions should lead to a decrease in ICF success (-48%), making fission a suitable alternative. Yet, our empirical data showed that ICF persists at a higher rate than expected, presumably because it allows aerial dispersal, unlike fission. Investigation of colony demography and measurement of lean and fat weights in virgin winged queens and workers showed that, from north to south, colonies increase quality of queens relative to workers (+50%) at the cost of quantity (-86%). This modification limits the decrease in ICF success (-34%). A tremendous range of offspring phenotypes associated with quality-quantity trade-offs make ants competitive in diverse habitats.

Invasive species are often said to be r-selected. However, invaders must sometimes compete with related resident species. In this case invaders should present combinations of life-history traits that give them higher competitive ability than residents, even at the expense of lower colonization ability. We test this prediction by comparing life-history traits among four fruit fly species, one endemic and three successive invaders, in La Reunion Island. Recent invaders tend to produce fewer, but larger, juveniles, delay the onset but increase the duration of reproduction, survive longer, and senesce more slowly than earlier ones. These traits are associated with higher ranks in a competitive hierarchy established in a previous study. However, the endemic species, now nearly extinct in the island, is inferior to the other three with respect to both competition and colonization traits, violating the trade-off assumption. Our results overall suggest that the key traits for invasion in this system were those that favoured competition rather than colonization. (Resume d'auteur)

Most species with a long life span have few offspring while species with a short life span have many offspring. This evolutionary trade-off between fertility and body maintenance, based on the theory of r/K-selection, is a central theme in the theory of life history regulation. This trade-off is not only found between various species but also between individuals within one species. There is accumulating evidence for this trade-off in humans. We hypothesize that the innate immune system is a critical factor skewing an individual into the direction of either a high fertility or better maintenance strategy. As over thousands of years human survival has been highly dependent on resistance to infectious diseases, genetic adaptations resulting in inflammatory responses were favored. An inflammatory host response is critical to fight infection necessary to survive up to reproductive age. An inflammatory host response is also negatively associated with fertility and can explain for the trade-off between fertility and body maintenance. After human reproductive age, these inflammatory responses contribute also to development of chronic degenerative diseases. These will especially become apparent in affluent societies where the majority of individuals reach old age. Identifying the inflammatory host response as a critical factor both in the regulation of human life histories and in the occurrence of chronic diseases at old age implies means for intervention allowing individuals to live healthier for longer.

Yemane, D., Field, J. G., and Leslie, R. W. 2005. Exploring the effects of fishing on fish assemblages using Abundance Biomass Comparison (ABC) curves. e ICES Journal of Marine Science, 62: 374e379. The possible effect of fishing on dominance patterns in the South African south coast demersal trawl fishery is assessed using Abundance Biomass Comparison (ABC) curves for the period 1986e2003. The ABC method compares the ranked distribution of abundance among species against the similar distribution of biomass among species. The temporal pattern in the ABC curves and the W-statistic for two depth groups (!100 m and 101e200 m), and for the whole area combined, shows a gradient of change in the demersal assemblages from neutral (W R 0) towards negative (W! 0), suggesting a disturbed or stressed condition. This corresponds to the onset of longline fishing effort in 1994, still ongoing in 2003, superimposed upon declining trawl effort in the same region. The ABC method shows promise as a guide for assessing the effects of fishing on fish communities, being based on established r- and k-selection theory. More modelling and comparative work is needed to establish acceptable ranges for the W-statistic, and their application in an ecosystem approach to fisheries management.

Ecological polarities are theoretical roles of organisms, reflected in evolved behaviors and characters. Ecological polarity includes what has been called life history strategies, functional types, habitat templates, and r and K selection. Three common ecological polarities emphasize reproduction, agonistic behavior, and withstanding harsh conditions. Such organisms can be called breeders, competitors, and tolerators, respectively. Polarities of ecospace can be envisaged graphically as apices of a triangular diagram within which each species occupies a particular region. Quantitative studies of ecological polarities rely on proxy measurements of specific morphological features, such as the proportional functional area of canines (for competitors), molars (for tolerators), and incisors (for breeders) among mammals. Such proxy measures of morphospace or chemospace are traditionally judged successful by the degree to which they reveal adaptive differences between species. This approach to approximat...

One of the central questions in evolutionary biology concerns the dynamics of adaptation and diversification. This issue can be addressed experimentally if replicate populations adapting to identical environments can be investigated in detail. We have studied 501 such replicas using digital organisms adapting to at least two fundamentally different functional niches (survival strategies) present in the same environment: one in which fast replication is the way to live, and another where exploitation of the environment's complexity leads to complex organisms with longer life spans and smaller replication rates. While these two modes of survival are closely analogous to those expected to emerge in so-called r and K selection scenarios respectively, the bifurcation of evolutionary histories according to these functional niches occurs in identical environments, under identical selective pressures. We find that the branching occurs early, and leads to drastic phenotypic differences (in fitness, sequence length, and gestation time) that are permanent and irreversible. This study confirms an earlier experimental effort using microorganisms, in that diversification can be understood at least in part in terms of bifurcations on saddle points leading to peak shifts, as in the picture drawn by Sewall Wright.

Panagrolaimus davidi is a free-living microbivore, associated with moss and algal patches in coastal regions around Ross Island, Antarctica. In laboratory experiments, temperature had a major influence on P. davidi life history parameters. The optimal temperature occurred between 25 and 30°C and the temperature at which population growth ceased was estimated at 6.8°C. Threshold temperatures for developmental processes were in the range 4.1°C (for egg incubation) to 7.6°C (for generation time). The life history strategy of P. davidi shows r-selected features and is more similar to temperate free-living nematodes than to other polar species, which show K-selected features. In the Antarctic, P. davidi is forced to remain dormant for long periods and growth occurs intermittently when conditions allow, suggesting A selection. The life history of P. davidi thus exhibits both A and r-selected features.

We investigate the notion that New Zealand's avifauna exhibits a macro‐evolutionary trend towards low reproductive rates by analysing the allometry of nesting parameters for native altricial land birds. We show that egg size, incubation periods, and nestling periods are all strongly correlated with body mass, but clutch size is not. However, egg size more accurately predicts incubation periods, and incubation periods more accurately predict nestling periods, than does body mass. Variation between and within families is explored. Neither divergence per se nor slow rates of reproduction appear related to the taxic level of endemism. “Gigantic” species breed more slowly in proportion to body mass as predicted allometrically, but as a macro‐evolutionary trend, the effect is counterpointed within New Zealand by a parallel trend towards dwarfism. We found that hollow‐ and cavity‐nesting species have longer nestling periods than open‐nesting species. Corvida passerines lay larger eggs, after controlling...

Three multivoltine species of satyrine butterflies in the genus Mycalesis (Lepidoptera: Nymphalidae) are narrowly sympatric in the wet–dry tropics of north-eastern Australia. They show a range of ecological strategies and adaptations associated with contrasting habitats and varying selective pressures. Two abiotic factors, namely favorability (the reciprocal of seasonal adversity) and predictability (broadly the reciprocal of disturbance), were examined as potential environmental selective forces in shaping their life histories. Comparison of several key life history traits of the lsquowet-season formrsquo revealed that the life histories of each species corresponded well with their habitat characteristics. M. perseus, which lives in habitats which are less favorable (i.e. adverse) and more unpredictable (i.e. temporary), shows many traits of an r-type strategy: smaller size, faster development, earlier maturation, higher fecundity, smaller egg size, and rapid population increase. By contrast, M. sirius and M. terminus, which live in more favorable and predictable (i.e. permanent) habitats, have many life history attributes and other characteristics in common which link them closer to K-type strategies. The only discrepancy is lower potential reproductive effort of M. perseus, which may be accounted for in terms of an evolutionary trade-off, such as with dispersal or dormancy. Other correlates associated with the M. perseus life history tactic include higher sex-size dimorphism, greater dispersal ability, better tolerance to adverse conditions, stronger phenotypic variation, greater degree of polyandry, and a more flexible breeding strategy. The life history patterns of these species are discussed in the context of evolutionary life history models, particularly the Southwood–Greenslade habitat templet.

Invasive species have been characterized as tolerant of environmental extremes. This hypothesis was evaluated for invasive aquatic species in North America, particularly Asian clams, Corbicula fluminea, and zebra mussels, Dreissena polymorpha. Both species have rapid growth, early maturity, short life spans, and elevated fecundity, allowing rapid population recovery after reductions by rarefractive, environmental extremes. Extensive resistance capacities offer little adaptive value to invasive, r-selected species, because population reductions occur in their unstable habitats regardless of degree of stress tolerance. Thus, both species have relatively poor physiologic resistance, depending instead on elevated growth and fecundity for rapid population recovery. In contrast, native North American bivalve species are often adapted to stable habitats where perturbation is infrequent (i.e., freshwater unionoidean bivalves). They are characterized by slow growth, extended life spans, and low effective fecundities, slowing population recoveries (K-selected), and have evolved extensive resistance adaptations to avoid extirpation during environmental extremes. Review of resistance adaptations in other North American aquatic invaders revealed poorer or equivalent physiological tolerance relative to taxonomically related native species, suggesting that extensive physiological tolerance is not required for invasive success.

The theory of r- and K-selection was one of the first predictive models for life-history evolution. It helped to galvanize the empirical field of comparative life-history and dominated thinking on the subject from the late 1960s through the 1970s. Large quan- tities of field data were collected that claimed to test predictions of the theory. By the early 1980s, sentiment about the theory had changed so completely that a proposal to test it or the use of it to interpret empirical results would likely be viewed as archaic and naive. The theory was displaced by demographic models that concentrated on mortality patterns as the cause of life-history evolution. Although demographic models are known for their density-independent approach and focus on extrinsic mortality, these models can incorporate many ecological features captured by r- and K-selection, such as density-dependent pop- ulation regulation, resource availability, and environmental fluctuations. We highlight the incorporation of these factors in recent theory, then show how they are manifest in our research on life-history evolution in Trinidadian guppies (Poecilia reticulata). Explanations of the repeatable suites of life-history differences across populations of guppies originate from demographic models of predator-driven age-specific mortality. Recently, careful ex- amination of guppy demography and habitat has revealed that density-dependent regulation and resource availability may have influenced the evolution of guppy life histories. In the field, these factors covary with predation risk; however, they can be uncoupled experi- mentally, providing insight into how they may have synergistically driven guppy life-history evolution. Although life-history theory has shifted away from a focus on r- and K-selection, the themes of density-dependent regulation, resource availability, and environmental fluc- tuations are integral to current demographic theory and are potentially important in any natural system.

It is often hypothesized that bacteria that are superior competitors when resources are abundant must be inferior competitors when resources are scarce, and vice versa. Most previous studies that sought to test this trade-off hypothesis compared kinetic parameters of extant strains of bacteria, with mixed results. We employed an experimental approach in which bacterial populations were propagated for many generations under two distinct regimes and their evolutionary responses were monitored. Thirty-six populations of bacteria were allowed to adapt evolutionarily to either abundant (batch culture) or scarce (chemostat culture) resource regimes. The competitive fitness of each derived line, relative to its ancestor, was then measured under both regimes. The trade-off hypothesis predicts that adaptation to either selective regime causes a concomitant loss of fitness under the alternative regime. Overall, our findings failed to support this hypothesis, and several cases contradict it. Only two derived lines showed clear trade-offs, having significantly adapted to the selective regime while becoming significantly less fit in the alternative regime. By contrast, five derived lines significantly improved in the alternative regime even as they adapted to their selective regime. Summing over all 36 derived lines (including those for which the observed fitness changes were nonsignificant under one or both regimes), 15 cases support the trade-off hypothesis, whereas 21 indicate the opposite result. These data therefore refute the necessity, or even general tendency, for evolutionary trade-offs in performance under conditions of resource abundance vs. scarcity. Instead, these data suggest that bacteria are able to adapt to a particular level of resource via multiple evolutionary pathways, which may produce either gains or losses in fitness at some different level of resource.

Using mathematical models, we investigated how infection and sporulation characteristics of competing plant pathogens determine the density and frequency dependence of relative fitness. Two models, one for the infection stage and one for the sporulation stage of a pathogen's life cycle, describe reproductive output of pathogen strains in mixture as a function of the strains' population densities. Model parameters include infection and sporulation efficiencies, carrying capacities on leaves for sporulating lesions and spore production, and coefficients of interstrain competitive effects in both life cycle stages. Although the models were originally developed for rust fungi, they are generally applicable to any organism with distinct colonization (e.g., infection) and propagative (e.g., sporulation) life cycle stages. In this work, paired hypothetical strains were assigned equal baseline parameter values. Parameters were then altered one at a time for one or both strains, and relative fitness was calculated over a range of densities and strain frequencies. Except for infection efficiency, the fitness benefit conferred by an advantage in a single parameter was always density dependent. Relative fitness was frequency dependent whenever inter- and intrastrain competitive effects were not equal. These results suggest that the fitness of pathogens in nature is rarely fixed, but, rather, may typically be highly dependent on the densities and frequencies of all coexisting strains in a habitat.

The development of theory on density-dependent natural selection has seen a transition from very general, logistic growth-based models to theories that incorporate details of specific life histories. This transition has been justified by the need to make predictions that can then be tested experimentally with specific model systems like bacteria or Drosophila. The most general models predict that natural selection should increase density-dependent rates of population growth. When trade-offs exist, those genotypes favored in low-density environments will show reduced per capita growth rates under crowded conditions and vice versa for evolution in crowded environments. This central prediction has been verified twice in carefully controlled experiments with Drosophila. Empirical research in this field has also witnessed a major transition from field-based observations and conjecture to carefully controlled laboratory selection experiments. This change in approach has permitted crucial tests of theories of density-dependent natural selection and a deeper understanding of the mechanisms of adaptation to different levels of population crowding. Experimental research with Drosophila has identified several phenotypes important to adaptation, especially at high larval densities. This same research revealed that an important trade-off occurs between competitive ability and energetic efficiency.