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Winemiller and Rose (1992, Can. J. Fish. Aquat. Sci. 49: 2196-2218) showed that fish life history data lie on a two-dimensional triangular surface, embedded in the three-dimensional space established by the following biological attributes: (i) age at maturity, (ii) fecundity, and (iii) juvenile survivorship (as measured by the presence/absence of parental care). The vertices of this triangular surface define three endpoint strategies (equilibrium, opportunistic, and periodic) that Winemiller and Rose viewed as boundary strategies for all fish life histories. This paper extends these ideas by showing empirically that (i) the allometric relationship linking peak ovary weight to adult body weight differs across endpoint strategies, (ii) the allometric relationship linking age at 50% maturity to adult body weight is the same across endpoint strategies with the exception of the opportunistic strategy, and (iii) the allometric relationships characteristic of Winemiller-Rose endpoint strategies, plus that of a fourth strategy (composed of the genera Salmo and Onchorynchus), combine to form constraints that bound data on reproductive effort from a sample of species that represent a broad range of fish life history strategies. We offer some hypotheses as to why such constraints might exist.

The Benthic Assemblage (B.A.) concept, developed by A.J. Boucot two decades ago principally for continental marine margins, is extended to offshore island settings. Characteristics of modern island biotas, including ecological displacement, and the effects of r and K selection, can be identified in Late Ordovician volcanic islands of central New South Wales. Two variants of B.A.1 are represented, a quiet‐water lingulide biofacies, and a rough‐water rhynchonellide biofacies. The quiet‐water Eodinobolus biofacies occupied a B.A.1–2 position, onshore of and sheltered by a Tetradium wave‐baffle (B.A.2). The offshore shelfal high diversity strophomenide biofacies is equivalent to B.A.3. Remnants of periplatformal B.A.4–5 communities are recognised in allochthonous limestone breccias which were displaced downslope into graptolitic B.A.6 sediments. Steeper offshore gradients, typical of islands, laterally compress the B.A. profiles, and also contribute to downslope slumping. Ecological displacement in island env...

The nematode Maturity Index (MI) has been proposed as a means of detecting disturbance in marine and terrestrial biotopes. However, few studies have dealt with the effect of the environment on MI. Using data taken from an extensive study of a polluted estuary, a number of variables were investigated to determine their effect on the MI. Sediment median particle diameter, nematode population density and the heavy metal elements analysed had no effect on values of the MI. However, number of species present in a sample, distance from pollution source and proportion of different nematode feeding groups, especially feeding groups 1B and 2A, had significant effects on values of the MI. The Maturity Index was found to be a robust index and in general agreement with values derived from traditional indices.

We explore the long-term developments in population biology and life history during the invasion and establishment of the fish species vendace Coregonus albula in a subarctic watercourse by comparing life-history traits and molecular genetic estimates between the source and the colonist population. The two populations exhibited highly contrasting life-history strategies. Relative to the source population, the colonist population was characterized by slower somatic growth rates, earlier sexual maturation at smaller individual size, higher mortality rates and a shorter life span. The two populations could also be significantly discriminated by the genetic markers. Limited founder effects were detected from heterozygote deficit and reduced allelic richness in the colonist population, but both populations were associated with relatively high genetic diversity. The study reveals that the invasion into a new environment induced large changes in life-history strategy, with typical r-selected traits being more prominent in the colonist than in the source population. We discuss the mechanisms that may explain the observed life-history differences between the source and the colonist population, and argue that the accelerated life history of the colonist population represents an adaptive pioneer strategy aimed at fast population increase during colonization and establishment.

1 Two closely related species of Colocasiomyia alocasiae (Okada) and C.xenalocasiae (Okada) (Diptera, Drosophilidae) breed in inflorescences of Alocasia odora C. Koch (Araceae), a hermaphroditic understorey clonal herb. 2 The two drosophilid species form a synhospitalic pair in Okinawa with alocasiae breeding in the upper half of the inflorescence and xenalocasiae breeding in the lower half. 3 C.alocasiae also has the following combination of life history traits: small body size, many eggs, and early reproductive maturity. In contrast, xenalocasiae can be described as having larger body size, fewer eggs, and delayed reproductive maturity. 4 Resource partitioning between the two species on the same host may be affected by these life history traits which are associated with their larval habitats.

A simple agar plating method for the description of microbial communities is described. This method is based on the quantification of the numbers of bacterial colonies in 6-7 age-based classes as they appear on agar media over a period of 6-10 days. The method can be used to quantify microbial communities in different habitats (roots and soil) and can be related to the ecophysiology of the microbial communities present. Significant differences in distribution patterns were found in time and depth on the roots. In general, as roots matured, the microbial communities changed from one dominated by r-strategists to one that was more distributed towards K-strategists. The soil had the greatest percentage of organisms that could be characterized as K-strategists. The method was also used to compare microbial communities on wheat roots and in soil in both the field and in microcosms in the glasshouse. In general, the method enabled differentiation between r- and K-strategists in environmental samples, something that could not be done using an ecophysiological index (a modification of the Shannon diversity index) or total bacterial numbers alone.

Miller's (1993, Personality and Individual Differences, 15, 665–675) theory of the origin of “the African Personality” is not new. The focus on testosterone as a mediator of male-male agonistic interaction and strong sexuality has been a component of the r-K analysis of human race differences from the outset. Several aspects of Miller's paper are discussed.

Rushton has shown that Negroids exhibit many characteristics that biologists argue result from r selection. However, the area of their origin, the African Savanna, while a highly variable environment, would not select for r characteristics. Savanna humans have not adopted the dispersal and colonization strategy to which r characteristics are suited. While r characteristics may be selected for when adult mortality is highly variable, biologists argue that where juvenile mortality is variable, K characteristics are selected for. Human variable birth rates are mathematically similar to variable juvenile birth rates. Food shortage caused by African drought induce competition, just as food shortages caused by high population. Both should select for K characteristics, which by definition contribute to success at competition. Occasional long term droughts are likely to select for long lives, late menopause, high paternal investment, high anxiety, and intelligence. These appear to be the opposite to Rushton's r characteristics, and opposite to the traits he attributes to Negroids.

The Gipsies, a particular ethnic and social group living mostly in the Eastern European countries, have been studied in terms of r - and K -selection. Considering the variables of fertility, birth spacing, mortality, age distribution, and physical parameters, they proved to be more r -selected than the Hungarians. The main factors bringing about these differences on the scale of r - and K -strategy come from both genetic and cultural biases. Resource unpredictability and social uncertainty, important components of the Gipsies' way of life, contribute to their higher fertility and mortality. Other characteristics, such as a female surplus in the birth sex ratio and the good survival capacity of the "premature" Gipsy infants, seem to show genetic influences as "racial" traits. Finally, a particular family arrangement characteristic of Gipsies, the father-absent household, is likely to have influence on their early sexual activity, even promiscuity, and unstable pair bonds. These analyses, that should be completed with further detailed investigations of social factors, may contribute to the understanding and improvement of the Gipsies' living conditions, after their ignorance in the Communist regime.

We examined associations between timber harvesting (clear-cutting and associated activities) and structure of assemblages of stream fishes across 89 localities in the Little River drainage, Oklahoma. Timber-harvesting activities were quantified as the percentage of the watershed (upstream from each locality) covered by clear-cuts in each of eight different age-classes. We found significant associations with one or more age-classes of clear-cut for three indices of species diversity, 14 of 29 common fish species, and three of five multivariate axes (principal components) of covariation among species abundances. Further analyses indicated a nonrandom association between life history strategy (r- or K-selection) and whether the abundance of individual species was related positively or negatively to clear-cuts of different ages. The results suggest that r-selected species (small, short-lived) may respond quickly to clear-cutting perturbations whereas K-selected species (large, long-lived) exhibit a d...

Age, growth and mortality of red bandfish, Cepola macrophrhalma (L.), from the western Aegean Sea were studied using the otoliths from 1113 fish and the length and weight of 3351 fish. Two regions were established (north and south of the Euripos Strait). The red bandfish grows allometrically (slope of length-weight regressions ≤2) and relatively rapidly until age 4 or 5 years. It is proposed that this rapid linear growth represents an adaptation which evolved to reduce the vulnerability of red bandfish to whole-fish swallowers. Back-calculated lengths-at-age showed significant differences between regions and between sexes. Males were larger than females after age 2 years. Maximum age of northern fish was also higher than southern fish (8 and 5 years respectively). Southern fish grow at a faster rate (K=0.379) but to a significantly smaller size (Lx=424.8mm t.l., Wx=25.1 g) than northern fish (K=0.214, Lx=676.1 mm t.l., Wx=90.9 g). Mortality rates (total and natural instantaneous mortalities) of southern fish were also higher than northern fish. We suggest that these variations represent responses to the different conditions of temperature and food availability prevailing in the two regions.

A theory of social stratification is proposed that was derived from combining two conceptual continuums, both referring to phenomena that appear to be genetically influenced: pro/antisociality and r/K selection. Pro/antisociality refers to behavioral tendencies epitomized at one end by altruism, and, at the other end, by victimizing behavior (particular violent offenses). r/K selection refers to a variety of physiological and behavioral traits, epitomized at the r-end by organisms that reproduce in large numbers, while committing minimal time and energy to the nurturing of each offspring, and at the K-end by organisms that reproduce in small numbers, but make maximum commitments to nurturing each offspring. The theory postulates that the space created by the right-angle intersection of these two variables gives rise to human social stratification. Variations in educational achievement, earnings, and occupational prestige within the theoretical space created by these two variables in industrial societies are hypothesized and discussed.

Rushton and Bogaert's (1987, 1988) differential K selection interpretation of racial differences in sexual development, morphology, behavior, and fertility was contrasted with an ecological interpretation. The reliability of racial differences on some variables was questioned in light of methodological limitations in the original research, and cross-cultural evidence for intraracial variability in development and performance. Cross-species comparisons suggested problems with the r K selection construct, and indicated that sexuality was not inversely related to intelligence. Analyses of 1960–1985 U.S. fertility data revealed that differences in black versus white birth rates were strongly associated with differences in infant mortality rates. As black infant mortality rates declined, black birth rates also declined at rates parallel to that of whites. Such findings suggest that the sexual behavior of blacks and whites may be equally responsive to their ecologies, rather than a function of genetic differences in K-selection reproductive strategies.

Summary Arvicanthis (Rodentia, Muridae) is widespread in tropical Africa, and its ecology has been studied in both East and West Africa under various climatic regimes. In order to take an overall look at the reproductive ecology of Arvicanthis in Africa, data were extracted from the literature on the climate and reproductive ecology and weight of Arvicanthis at eight localities. Relationships between aspects of reproductive ecology and climate were explored statistically. The length of the breeding season of Arvicanthis shows a strong, non-linear relationship with the number of ‘humid’ months in a year (as determined from a standard climograrn), but weight of adult males and females, number of implanted embryos and proportion of reproductively active females do not appear to be correlated with climate. The available evidence does not support the hypothesis that populations of Arvicanthis in hotter-drier environments are more r-selected, and that populations in cooler-wetter localities are more K-selected. The necessity for consistent interpretations of r-K theory and standardization of measures of ‘stress’ and ‘predictability’ is discussed. Resume Arvicanthis (Rodentes, Muridae) est repandu en Afrique tropicale et on a etudie son ecologie en Afrique de 1'Est et de 1'Ouest sous differents regimes climatiques. Pour obtenir une vue generale de l'ecologie de la reproduction d'Avicanthis, en Afrique, nous avons repris des donnees dans la litterature sur le climat, la reproduction et le poids, en huit endroits. On a etudie les relations statistiques entre la reproduction et le climat. La duree de la saison de reproduction d'Arvicanthis montre une relation etroite non lineaire avec le nombre des mois humides par an, (On l'a determine avec un clirnogramme standard), rnais le poids des adultes mâles et femelles, le nombre d'embryons implantes et la proportion de femelles qui participent a la reproduction ne semblent pas lies au climat. Les chiffres ne confirment pas l'hypothese colon laquelle les populations d'Arvicanthis sont plus r-selectionnees, ni que les populations d'emplacements plus froids et plus humides sont plus K-selectionnees. On discute la necessite d'interpretations fiables de la theorie r-K et de la standardisation de mesures de ‘stress’ et de ‘probabilite’.

An optimization technique named r/KPSO (particle swarm optimization with r- and K-selection) was developed in this paper. In Ecology, two evolutionary ldquostrategiesrdquo are termed, r-selection for those species that breed many ldquocheaprdquo offspring and live in unstable environments and K-selection for those species that produce few ldquoexpensiverdquo offspring and live in stable environments. r-selection can be characterized as: quantitative, little parent care, large growth rate and rapid development and K-selection as: qualitative, much parent care, small growth rate and slow development. r/KPSO selects r- and K-selection to produce the progenies in the iterative procedure according to the concerned particlepsilas fitness value. K-selection is performed for those particles (K-subswarm called in this paper) in high fitness, and K-subswarm only can produce few progenies but the progenies are nurtured delicately with much parent care. On the other hand, r-selection is performed for those particles (r-subswarm called) in relatively low fitness. And with little parent care, r-subswarm can produce a large number of progenies, the progenies have to compete with the r-subswarm for survival according to fitness and only the best ones can survive. In r/KPSO, the particles performed r-selection mainly explore the search space as possible as they can to find more potential solutions in large speed, and those particles performed K-selection keep the current optimum solutions and exploit the space as they can to find more ideal solutions. Combined the advantages of r-selection and K-selection, r/KPSO can converge in higher speed and higher precision.

Life history trade-offs are often hierarchical with decisions at one level affecting lower level trade-offs. We investigated trade-off structure in female side-blotched lizards (Uta stansburiana), which exhibit two evolved strategies: yellow-throated females are K-strategists and orange-throated are r-strategists. Corticosterone treatment was predicted to differentially organize these females’ reproductive decisions. Corticosterone-treated yellow females suppressed reproduction but survived well, and augmented egg mass without decreasing clutch size. Conversely, corticosterone enhanced mortality and reproductive rates in orange females, and increased egg mass only after lengthy exposure. Corticosterone did not affect post-laying condition, suggesting that corticosterone increased egg mass through enhanced energy acquisition (income breeding). Corticosterone enhanced survival of lightweight females, but decreased survival of heavy females, introducing a foraging vs. predation trade-off. We conclude that rather than being a direct, functional relationship, observed trade-offs between offspring size and number represent evolved differences in hierarchical organization of multidimensional trade-offs, particularly in response to stress.

Density-independent and density-dependent factors and events differ fundamentally in their effects on natural selection and on populations. Populations that experience crowded conditions at high population densities and keen competition have been called ‘equilibrium populations’. In contrast, competition is lax in populations that exist at low densities, which are known as ‘opportunistic populations’. Natural selection favors different adaptations under such varying conditions. For example, r-strategists exhibit early reproduction, small body size, high fecundity, and poor competitive ability, whereas K-strategists show delayed reproduction, larger body size, reduced fecundity, and higher competitive abilities. A continuum exists from density-dependent to density-independent selection. Any statement about the position of a particular species along this r–K-selection continuum is invariably comparative. Compared to a microbe, a mouse would be considered to be a K-strategist, but when compared to a larger longer-lived mammal, the same mouse would be labeled an r-strategist.

The earthworm Octodrilus complanatus (Duges, 1828) is a large-sized species often found in grasslands and pastures, with a wide distribution area in Europe and North Africa. In order to determine the characteristics of its life cycle, earthworms of this species were cultured from hatching until they reached maturity. Development rates, cocoon production, and incubation period were recorded under controlled conditions. On average, individuals of O. complanatus reared in isolation from hatching reached maturity at day 150 and body weight at maturity ranged between 6 and 8 g. The cocoon incubation period was 66 days, and only one individual hatched from each cocoon, with a mean hatchability of 55%. Reproductive rate showed by O. complanatus after mating was of 52 cocoons per earthworm per year. The results showed that the life cycle of O. complanatus was characterized by both low growth rates and low fecundity. Specific features in life history traits of O. complanatus were compared with those of species of the genus Octodrilus and other related earthworms.

If different phenotypes have different age-specific birth and death rates, their growth rates, and hence their fitness (see Chapter 10) will vary. Thus, natural selection shapes both the survivorship ( l x ) and fecundity ( m x ) curves, and we will look at this particular aspect of evolution in this chapter. However, the life-history characteristics of organisms also include such traits as body size, size of the offspring at birth, the degree of parental care provided to the young, and so on, and consequently our review will also consider some of these life-history traits. A simplistic view of natural selection would suggest that all organisms should adopt an ideal life history in which they live as long as possible, start to reproduce at an early age, reproduce frequently, and produce a vast number of offspring which have a high rate of survival. However, even a cursory look at the life-history traits of different organisms shows that this is not the case in nature. Consider the following three examples of large, long-lived organisms. Adult blue whales ( Balaenoptera musculus ) are about 27 metres long, weigh about 150 tonnes, and may live for about 80 years. After a gestation period of about one year, females normally produce a single, well-developed offspring that weighs as much as an adult elephant. The young calves suckle for about a year, and are provided with considerable parental care and protection during their early life. Their survival is quite high.

Here we explore the adaptation of vesicular stomatitis RNA virus to different population densities and the existence of a trade-off between r- and K-selection. Increasing population density represents a challenging special situation for viruses, since different selective pressures arise depending upon the number of available host cells per virus. Adaptation to low density represents a prototypical case of r-selection, where the optimal evolutionary solution should be a high replication rate. Adaptation to high density represents a case of K-selection. In this case, genotypes optimally exploiting the resources, instead of faster replicating ones, should be selected. Five independent populations were maintained in two environments, called r and K, for 100 generations. In the r environment, effective population size was small. In contrast, the effective population size in the K environment was large. Our results support the existence of the expected trade-offs between these two types of selections. Viral populations evolved at low density performed worse as population density increased. Similarly, viral populations evolved at high density showed reduced fitness at low density. Finally, we compare our results with those obtained for other RNA viruses.

A recent study of seasonal influences on energetics in the southern flying squirrel, Glaucomys volans (Stapp, 1992, Journal of Mammalogy, 73:914–920), compares metabolic and life-history variables in gliding and nongliding arboreal sciurids and interprets them largely in the context of thermoregulatory constraints. We consider an alternative explanation for the “ K -selected” traits of flying squirrels from evolutionary senescence theory and the comparative life-history literature. Comparative analyses reveal convincing evidence for the impact of mortality patterns on life histories of mammals and for gliding and flying as adaptations promoting the evolution of longevity.

Episodic switching between Tropodiaptomus spectabilis and Metadiaptomus meridianus in L. Midmar (29°30′S, 30° 12′ E), and transitory seasonal alternation of these taxa in L. Albert Falls (29° 26′ S, 30°26′ E), recorded in comparative studies of these inter-leading reservoirs between 1989 and 1999, along with historical records for Midmar extending back to 1978, are updated and re-evaluated in light of subsequent and additional findings. In the longer term, an ‘exclusive’ occupancy by one or another species has been maintained in these and other inter-leading impoundments on the quasi-subtropical Mgeni River. Sympatry was invariably transitional. It lasted several months in the upper Midmar system, and where protracted over several years as in the downstream Albert Falls system, was effectively negated by seasonal separation of the taxa. Possible influences of parasitism, changes in water turbidity or pH, dependent or independent of inter-basin water transfers, and such water transfers themselves, are explored and rejected as proximate causes of species replacement. Because evidence for the existence of resting eggs was contradictory (respectively present and absent in preserved and live samples), emergence from diapause is considered an unlikely source of re-colonisation. The guild complement of invertebrate planktivores is comparable in both lakes, seemingly removing predation as a determinant factor. The comparability of food thresholds for various measures of demographic performance suggests remarkable similarity in the competitive potential of these species, which additionally show considerable niche overlap in terms of adult diet, and comparable vulnerability to ellobiopsid parasitism. Ecological separation is thus limited to differentiation of thermal optima, functional feeding biology of juvenile stages - especially nauplii, and sediment tolerance. Evidence now available supports previous arguments that species separations remain attributable largely to marginal species differences in thermal optima, mirrored in the pattern of seasonal separation during an episode of sympatry (1990 to early 1994) in the downstream Albert Falls system. While no causal explanation can be substantiated from evidence gleaned during this decade of study, the species replacements observed in Midmar appear to reflect alternative stable states, induced by presently unknown factor(s), plausibly temperature, or improbably, human translocation. By contrast, alternative stable states are not manifest in Albert Falls, wherein the longer term, T. spectabilis seemingly represents the only stable state, a feature apparently shared by other warmer reservoirs down the Mgeni cascade. The unpredictability of chaotic dynamics precludes its analysis in this situation, while conversely, the system provides a unique model for meta-population analysis, related to uni-directionality of natural dispersal. However, the cost-effectiveness of continued monitoring for unforeseeable events poses a serious practical dilemma.

R and K selection strategies are about tradeoffs between between quantity of offspring (productivity = numbers of offspring) and quality of offspring (efficiency = a few very fit offspring) (Pianka 1970). R strategists produce as many offspring as possible with low investment in each offspring. K strategists invest considerable resources in a few, very fit offspring (Pianka 1970). Scientific papers can be seen as the offspring of scientists. Scientists with an r selected publication strategy publish lots of papers, with relatively little investment in each, whereas scientists following a K selected publication strategy publish fewer papers with more investment in each paper. The number of scientific papers being published is increasing, per scientist and overall, due to pressure on scientists to publish and the proliferation of journals from commercial publishing houses (Wagner 2011, Fischer et al. 2012). Publishing scientific papers is now big business for publishers (Beverungen et al. 2012, Recher 2013, Van Noorden 2013). The number of scientists has increased over time, along with the greater number of papers published per scientist, but the latter is greater (Wagner 2011). This editorial focuses on impacts of the increasing pressure to publish lots of papers on the publication strategies of individual scientists.

The intrinsic rate of natural increase (r m) is calculated for 72 primate species, using Cole's (1954) equation. The value of r m relative to body mass is then calculated by use of allometric analysis. Both r mand relative r m are used to test the prediction that animals in unpredictable and/or harsh habitats will have a higher r mthan will those in more predictable and/or less harsh habitats. No significant link between habitat type and r mis found. However, correlations between ecology and relative r msuggest that relative r mis high in primate species living in more open habitats and low in species found in primary rainforest. Although there are few correlations between relative r m and climate parameters, those that are found suggest that variable climates, dry climates and hot climates will select for a high relative r m.

Six populations of Drosophila melanogaster have been kept at extreme population densities, three high and three low, for 175 generations. Larvae from the high density populations pupate 50%-100% higher than larvae from the low density populations. At high larval test densities there is both a directional and a stabilizing component to selection, with viabilities ranging from 0.14 to 0.992, depending on the choice of pupation site. The directional component is stronger on the populations which have evolved at low densities, while the stabilizing component is stronger on the populations which have evolved at high densities. There is no indication that the evolution of this trait, in response to density, has altered its phenotypic plasticity.

Theories of density-dependent natural selection predict that evolution should favor those genotypes with the highest per capita rates of population growth under the current density conditions. These theories are silent about the mechanisms that may give rise to these increases in density-dependent growth rates. We have observed the evolution of six populations of Drosophila melanogaster recently placed in crowded environments after nearly 200 generations at low-population density in the laboratory. After 25 generations in these crowded cultures all six populations showed the predicted increase in population growth rates at high-population density with the concomitant decrease in their growth rates at low densities. These changes in rates of population growth are accompanied by changes in the feeding and pupation behavior of the larvae: those populations that have evolved at high-population densities have higher feeding rates and are less likely to pupate on or near the food surface than populations maintained at low densities. These changes in behavior serve to increase the competitive ability of larvae for limited food and reduce mortality under crowded conditions during the pupal stage of development. A detailed understanding of the mechanisms by which populations evolve under density-dependent natural selection will provide a framework for understanding the nature of trade-offs in life history evolution.

The history of diverse mammal taxa is characterized by evolutionary increase in size and by relatively higher rates of extinction among species of larger size (Cope's rules). I suggest that sexual selection accounts for both observations because: (1) the degree of sexual dimorphism, indicative of strong sexual selection, is greater in larger species, and (2) elaboration of male secondary sexual traits coincided with advances in size. I hypothesize that sexual selection on males to control access to females favors larger size and other characters involved in male-male combat, especially as harem size increases. The greater the intensity of sexual selection, which is proportional to harem size, the greater the forfeiture of adaptedness to prevailing ecological conditions and consequently the greater the vulnerability to extinction

Density-dependent natural selection and age-specific natural selection are important determinants of life-history evolution. A variety of laboratory populations of Drosophila melanogaster have been created to study the effects of these selection mechanisms. Two types of populations have been selected for reproduction early (B) and late (O) in life. These have exhibited changes in life span and resistance to stresses, such as desiccation, starvation, ethanol vapours and flying to exhaustion. Similarly, two types of populations have been selected at high adult and larval densities (K) and low adult and larval densities (r)

Genetic variability in the relationship between plant size and fecundity (fecundity allocation) was investigated in 10 inbred lines (genotypes) of Arabidopsis thaliana. For each genotype, a range of plant sizes was established by planting seeds at various densities. Plant size (above-ground biomass exclusing seeds), fecundity (number of seeds produced), and percentage germination of seeds were recorded for 20 individuals representative of the range of plant sizes displayed for each genotype as a result of the density treatments. There was a significant (P

Growth rates and ages at maturity of five syntopic species of scincid lizards of the genus Ctenotus were studied in spinifex grasslands near Alice Springs in central Australia. Most species repro- duced only once during the 3-year study (in the second year). There was a diversity of growth rates and ages at maturity in these lizards. The von Bertalanffy growth model described growth of Ctenotus better than did logistic-by-length or logistic-by-mass models; however, the von Bertalanffy model underestimated the growth rates of hatchling Ctenotus. Female Ctenotus grew slower than male Ctenotus but reached larger asymptotic body sizes in most species. Most juvenile C. pantherinus and C. piankai continued to grow during winter and reached sexual maturity by 10 to 11 months of age, but there were year-to-year differences in growth rates of female C. pantherinus. Some juvenile C. cf. helenae and C quattuordecim- lineatus reached the minimum size at maturity by 11 months and could have reproduced in the summer of their first year, but most would not have reproduced until their second spring (22 months). Ctenotus leonhardii was the slowest-growing species and did not reach maturity until at least 18 months of age. Growth rate and age at maturity did not correlate with the absolute body size of the species: the fastest growing species were the largest and smallest species, respectively. The results do not support the pre- dictions of the r-K selection model for species living in variable environments. Predictions of the de- mographic life-history models are more consistent with these results.

It is well established that genetic correlations between multiplicative fitness components determine the response to countervailing selection pressures such that for many traits a balance is struck between the opposing forces of natural and sexual selection. The proportion of variance in lifetime reproductive success contributed by variation in sexually selected traits is inversely proportional to the rate of juvenile mortality. Thus, extreme expression of sexually selected traits, is more likely in K-tan in r-selected species. Sexual dimorphism in size is consistent with this prediction; males are larger in K-selected species, representing response to sexual selection, while females are larger in r-selected species, representing response to natural selection for fecundity enhancement

We propose a revision of the habitat templet approach for modelling the relationship between r/K selection and selection related to the level of resource impoverishment within vegetation. The latter is represented as a continuum on one axis of the templet by the mean annual environmental carrying capacity of the habitat. This is perpendicular to the second axis representing the traditional r/K selection continuum and defined by the mean annual distance below environmental carrying capacity that the vegetation is maintained at, usually as a consequence of different levels of disturbance (...)

r- and K-theory can be used to compare the life strategies of plant pathogens, at least during the parasitic phase. While, as a group, plant pathogens tend to be r-selected, individual species display certain tactics that may best be described by either r- or K-descriptors. Characteristics such as the ability to survive prolonged periods and the flexibility to time activities are more closely associated with "bet-hedging" than r- or K-selection. A conceptual model is proposed to show how pathogens can be positioned along an r-K continuum based on their relative allocation of resources to maintenance, growth, and reproduction. Superimposed on resource allocation is the nature of the parasite-host relationship, determined in part by whether the interaction is obligatory or facultative, whether nutrient is derived from living or dead cells of the host, and the extent of destruction of the host habitat. In general, obligately biotrophic parasites which exhibit narrow host ranges, specialization as biotypes or...

An r-selected approach to reproduction emphasizes producing large numbers of offspring with minimal care given to each offspring by its parents. At the other end of the continuum, K-selection is an approach in which few offspring are produced, but maximal care is taken to insure reproductive viability of each offspring. This article argues that several heretofore seemingly unrelated factors which have been found associated with serious victimful criminal behavior (i.e. serious violent and property offenses) in numerous countries are predictable by hypothesizing that criminal behavior is part of an r-selected approach to reproduction.

Dawkins (36, p. 293) observes that "ecologists enjoy a curious love/hate relationship with the r/K concept, often pretending to disapprove of it while finding it indispensable." Others have suggested that the model of rand K-selection is inadequate and outmoded and does not further our understanding of life history phenomena (105, 120, 123). These views unfortunately result from frequent misuse and overgeneralization of the model. I contend that rand K-selection may have important ramifications for our understanding of life history evolution, but for the model to be useful, it must be interpreted strictly as it was originally formulated: as a model of density-dependent natural selection. To minimize confusion, I begin this review with an outline of rand K-selection explicitly as a model of density-dependent natural selection. I then attempt to place this model within a historical context with other life history theory. As with recent criticisms of competition theory (109), I find that rand K-selection suffers from a lack of true tests of its hypotheses. Although it may play a significant role in the evolution of life histories, there are few empirical studies that can identify density dependence that is independent of other potential selective forces.

A continuous, analytical model of the selection of size-number compromises is presented and applied to the selection of the amount of parental investment in each offspring until its independence. At the evolutionarily stable strategy, the proportional gain in the success of an offspring from an increment in the investment in the offspring equals the proportional loss in offspring numbers. A parallel marginal-value theorem applies to discontinuous variation in the amount of care. When selection acts directly on offspring size rather than on number, the evolutionarily stable level of care depends only on the fitness curve relating the fitness of single offspring to the amount of resources received. General conditions for brood reduction are described. A more-specific rapid-gain version of the continuous model suggests that the amount of parental care is influenced primarily by the level of care at which offspring success increases rapidly. The model can explain various observed differences in amounts of par...

Theory on r-K selection is used as a basis for examining correlations between instantaneous rate of natural mortality (M), gonad-body weight index, age at maturity, longevity, and Bertalanffy growth parameters (k, L∞) for 10 species of marine fish. All correlations were consistent with r-K selection theory. The gonad-body weight index was found to be more highly correlated with M than any of the other life history parameters examined (r2 = 0.62), and stepwise multiple regression showed that additional variables added little to the predictive ability of the model. The gonad-body weight index appears to be quite useful in predicting M, and development of an analogous index on an energetics basis might enhance its utility in this regard.Key words: natural mortality, r-K selection, life history parameters

Over its range, the pitcher-plant mosquito, Wyeomyia smithii, experiences a gradient in density-dependent development. In each of 12 populations from six geographical regions over a range of 19⚬ latitude and 900 m in altitude, we determined capacity for increase and its components at four densities. We reared experimental populations in intact pitcher plants receiving near-natural conditions of light, temperature, and feeding. Capacity for increase and its components, replacement rate and mean generation time, exhibited significant variation among densities and among localities within regions but not among regions. There was no trade-off among populations in capacity for increase at high and low densities. Consequently, variation in these fitness traits did not reflect major differences in climate or degree of densitydependent selection prevailing at the locality of origin. Hybrids between populations exhibited heterosis in capacity for increase and in both of its components. These results indicate that l...

It is shown using several models that r and K selection may result from random environmental variation. Probabilities of extinction are derived for both colonizing and well-established species using stochastic models similar to the logistic model, and it is shown that the probability of extinction of a population can be reduced by increasing the birth rate or the carrying capacity or by decreasing the death rate or the effects of the environmental variation on population growth. It is probable that random environmental variation mainly facilitates r selection.

In 1976, I reviewed (84) two models which give alternative explanations for the adaptation of life history traits to stable and fluctuating environments. Deterministic models (rand Kselection) predict that organisms exposed to high levels of densityindependent mortality, wide fluctuations in population density, or repeated episodes of colonization will evolve towards a combination of earlier maturity, larger broods, higher reproductive effort, and shorter lifespans than will organisms exposed to density-dependent mortality or constant population density (48, 65). Stochastic models (58, 77) predict the evolution of the same combinations of life history traits, but for different reasons: when fluctuations in the environment result in highly variable juvenile mortality, then a syndrome of delayed maturity, smaller reproductive effort, and greater longevity should evolve. Several years ago I set out to test these predictions by measuring the reproductive traits of two species of small fish that had been introduced to Hawaiian reservoirs in 1907 and 1922. Ambiguities appeared in the interpretation of the results, some of them inherent in the theory, others in the observations. I could not decide which of several possible causal systems had produced the pattern I observed. To determine what my results meant, I first tried to understand what life history data could mean in general, given the present state of our knowledge. In brief, the theory is not yet refined enough to be tested by crucial experiments that can pinpoint flaws. Under these circumstances, observation and experiment cannot falsify predictions definitively, but they can profitably arbitrate among the various simplifying assumptions that theorists may want to try out in their pursuit of unambiguous predictions that cleanly touch reality.

Of the ecological forces which shape evolution of life histories, competition seems especially important. When competition is absent, those genotypes which reproduce more rapidly and prolifically are favored; when resources are limiting, the advantage goes instead to those best able to compete. MacArthur and Wilson (1967) termed the extreme cases rand K-selection, respectively, after terms in the widely-used logistic equation of population growth. They understood that environments imposing pure ror K-selection were only ideals, ends of a continuum, and that most actual situations would be somewhere intermediate. A characteristic set of traits is thought to result from selection for one extreme or the other: among other things, r-selected populations should develop more rapidly, have a higher intrinsic rate of increase (r), reproduce earlier, develop to a smaller size, invest less in each offspring, and tend toward semelparity (i.e., to reproduce only one time); K-selected species should have a higher carrying capacity (K), invest more energy into each offspring, develop more slowly but eventually attain a larger size, and tend toward neoteny and iteroparity (i.e., to reproduce more than once). Comprehensive discussions of the rationale and history of these expectations may be found in the reviews by Pianka (1970), Stearns (1976), and Gould (1977). In spite of this assumed correspondence between ecological circumstances and type of life history, we know of no demonstration that r-selection results in one life history, while K-selection results in

Previously published field studies have suggested that the concept of r/K selection may be applied to terrestrial ciliates. A census was taken of the dominant groups, the Colpodea and Polyhymenophora, to determine species composition and absolute abundances in climatically unpredictable alpine and predictable lowland sites. In addition, two typical representatives of each of the two taxa (Colpoda aspera and Grossglockneria acuta, and Blepharisma undulans and Gonostomum affine, respectively) were selected for examination under laboratory conditions. Variables investigated were: the C/P index (ratio of Colpodea to Polyhymenophora), fertility, tolerance of altered environmental conditions, incidence in predictable or unpredictable biotopes, opportunism, competitive ability, and body size. Our own observations were supplemented by reference to the literature. The field census produced a higher C/P index in the unpredictable sites than in the predictable ones. The experiments show that C. aspera and G. acuta are less sensitive to changes in temperature and exhibit a more rapid rise in individual density as well as a higher number of individuals than do B. undulans and G. affine, although the former species have longer generation times at low temperatures. The explosive increase in number of individuals can be ascribed to the special reproductive strategy of the Colpodea (quadripartition in cysts). These results imply that the Colpodea are more r-selected as compared with the Polyhymenophora. That might be an explanation for their wide distribution and high density in unfavourable terrestrial habitats.

The reproductive effort of 49 Angiosperms from the herb layers of Oak-Hornbeam forest, Black Pine forest, rock steppe andBromus erectus meadow was determined on a dry weight basis. The average reproductive effort of these communities appears to depend on habitat factors and competition (e.g. water, temperature and light) and not on the position within the successional position. The general validity of the r- and K-selection concept therefore is questioned.

(1988). Seasonal phytoplankton r- and K-selection in oligotrophy Lake Tahoe. SIL Proceedings, 1922-2010: Vol. 23, No. 2, pp. 672-676.