Showing papers in "The American Naturalist in 1974"
TL;DR: The relationship between the energy expended per offspring, fitness of offspring, and parental fitness is presented in a two-dimensional graphical model and the validity of the model in determining an optimal parental strategy is demonstrated analytically.
Abstract: The relationship between the energy expended per offspring, fitness of offspring, and parental fitness is presented in a two-dimensional graphical model. The validity of the model in determining an optimal parental strategy is demonstrated analytically. The model applies under various conditions of parental care and sibling care for the offspring but is most useful for species that produce numerous small offspring which are given no parental care.
2,780 citations
TL;DR: In addition, the authors found that the ubiquitous nature of these compounds would make herbivory impossible unless animals had mechanisms for degrading and excreting them, which is not the case for humans.
Abstract: Large herbivores must select food from a wide variety of plant parts, species, and strains. These differ in nutritional value (protein, carbohydrate, etc.), toughness, spinosity, etc. Even greater differences are found in types and concentrations of secondary compounds. Every plant produces its own set of secondary chemical compounds, which to a great extent are unique to it or its species. Ingestion of natural concentrations of these compounds can lead to either death or severe physiological impairment. The ubiquitous nature of these compounds would make herbivory impossible unless animals had mechanisms for degrading and excreting them. An animal displaying no obvious symptoms of poisoning is not free of the problem of ridding itself of toxic compounds; if it is eating plants, it almost certainly has this problem. Herbivores are capable of detoxifying and eliminating secondary compounds. Limitations of these mechanisms force mammalian herbivores to consume a variety of plant foods at any one time, to tr...
1,190 citations
TL;DR: The spatial component of environment, often neglected in modeling of ecological interactions, in general operates to increase species diversity due to the heterogeneity of the environment, but such heterogeneity can arise in an initially homogeneous environment due to what may be random initial events (e.g., colonization patterns).
Abstract: The spatial component of environment, often neglected in modeling of ecological interactions, in general operates to increase species diversity. This arises due to the heterogeneity of the environment, but such heterogeneity can arise in an initially homogeneous environment due to what may be random initial events (e.g., colonization patterns), effects of which are magnified by species interactions. In this way, homogeneous environments may become heterogeneous and heterogeneous environments even more so. In patchy environments, distinct patches are likely to be colonized initially by different species, and thereby a kind of founder effect results whereby individual patches evolve along different paths simply as a consequence of initial colonization patterns. Species which would be unable to invade may nevertheless survive by establishing themselves early and will moreover be found in lower densities in other areas as overflow from their "safe" areas. Spatially continuous environments may evolve toward es...
1,097 citations
TL;DR: Evidence is presented which indicates the importance of historical events in determining the structure of a variety of natural communities, and multiple stable points are an undeniable reality in space and time in these systems.
Abstract: Evidence is presented which indicates the importance of historical events in determining the structure of a variety of natural communities. In the fouling community at Beaufort, North Carolina, the order of larval recruitment determined which species monopolized the available space during initial community development. In other systems, community structure could be explained only by referring to the specific historical events which determined the presence or absence of important consumers. Since history was relevant to the observed community structure, multiple stable points are an undeniable reality in space and time in these systems.
729 citations
TL;DR: Using techniques of stochastic theory, a new aproach to predicting optimal diets is developed for a mobile predator feeding on stationary prey, predicting that an animal feeding according to the dictates of the optimal diet should show no partial preferences.
Abstract: Using techniques of stochastic theory, I develop a new aproach to predicting optimal diets. The models developed are for a mobile predator feeding on stationary prey; however, the models can easily be extended to include mobile prey. Parameters used in the models are caloric content, time to pursue and density of each prey type, and the speed of the predator. Both clumped and random prey distribution are considered. The models predict the optimal diet of a predator faced with a variety of potential prey types. The optimal diet is predicted as the set of successive prey choices which maximizes the rate of caloric intake or, alternatively, minimizes the time required to find a food ration. Also predicted are the criteria for specialization and switching from a specialist diet to a generalist diet. The criteria for specialization and for switching are independent of the density of the alternate prey type. Also, a predator feeding so as to maximize the rate of caloric intake should take a prey on every encoun...
709 citations
TL;DR: Alkaloid transport and storage are reviewed, with emphasis on problems associated with presence of toxic chemicals in living plants.
Abstract: Alkaloid transport and storage are reviewed, with emphasis on problems associated with presence of toxic chemicals in living plants. Many patterns in the physiology of alkaloids and other defense compounds are shaped by the twin requirements that these compounds must be inactive in the plant and yet active in the presence of herbivores. The distribution of alkaloids in the plant and changes in distribution during the plant's life are also reviewed. Within individual plants, alkaloids are generally concentrated in those parts upon which herbivore attack would have the greatest effect on the plant's fitness. The relative defense requirements of different parts, based on their contribution to fitness and their vulnerability to herbivores, shift during the plant's life. These shifts are mirrored by corresponding shifts in alkaloid concentration. Ovules, seeds, and immature fruits are often the sites of highest alkaloid concentration. Allocation of defensive chemicals between mature and immature foliage should...
704 citations
TL;DR: When the life history functions B (E) and P (E)-fecundity and postbreeding survival-are subject to environmentally induced fluctuations, one of two patterns is selected for: If the functions are concave (iteroparity in constant environments), the optimal population is monomorphic.
Abstract: When the life history functions B (E) and P (E)-fecundity and postbreeding survival-are subject to environmentally induced fluctuations, one of two patterns is selected for: If the functions are concave (iteroparity in constant environments), the optimal population is monomorphic. Variation in B (E) selects for reduced effort in all individuals; variation in P (E) for increased breeding. If functions are convex (semelparity in constant environments) and fecundity is the parameter at issue, the optimal population can be polymorphic, with only a fraction of the population reproducing annually. Increasing the severity of fluctuations reduces the optimal value of this proportion, even if the average rate of reproductive success is not changed.
651 citations
TL;DR: A property of this "optimization model" is that the contribution of a food to the diet will sometimes vary with the food's content of a particular nutrient and sometimes will not, which might explain why no consistent relations of this kind have been found experimentally.
Abstract: Ecological theory has formulated the objective of feeding strategies as to maximize the capture rate of some nutrient. But large generalist herbivores typically face a limit on how much material they can digest. Thus, their feeding strategy is best considered as aiming to achieve the best nutritional balance within a fixed total bulk of food. The problem of finding the diet which provides the best mix of nutrients can be formulated as a linear program. A property of this "optimization model" is that the contribution of a food to the diet will sometimes vary with the food's content of a particular nutrient and sometimes will not. This might explain why no consistent relations of this kind have been found experimentally. The long-delay learning mechanism is described. If this exists in large generalist herbivores, it would provide a means by which they might pursue optimization of nutrient mix in the diet. It would also account for the very large inter- and intraindividual variability in preference reported...
552 citations
TL;DR: Results can be explained by a theory of kinetics of fetal growth based on three hypotheses: the brain is the slowest-growing organ in the fetal mammal; it is also the pacemaker for growth of other tissues, which are held to its rate of growth; and brain growth proceeds at the maximum rate allowed by its intrinsic growth law.
Abstract: Duration of gestation in homothermic placental mammals has a much more precise alaxensis relation to neonatal brain size than to neonatal body size or any of three other neonatal or maternal dimensions. This was shown by a multivariate analysis of data on gestation time, neonatal and adult brain and body weight, and litter size for 91 species. These results can be explained by a theory of kinetics of fetal growth based on three hypotheses: (1) the brain is the slowest-growing organ in the fetal mammal; (2) it is also the pacemaker for growth of other tissues, which are held to its rate of growth; and (3) brain growth proceeds at the maximum rate allowed by its intrinsic growth law, so that the growth of all mammalian brains is governed in great degree by a single functional relation of attained size and time. The invariant rate constant for mammalian brain growth could be due to nutritional limitations or to the existence of an upper limit on rate of information flow during development.
429 citations
TL;DR: Unequivocal examples of dominance-mediated niche relationships are thus far confined to certain vertebrate and arthropod groups, although evidence available suggests that they are more widely spread.
Abstract: If one species is socially dominant to another, the subordinate usually narrows its niche when they occur together. When one species is dominant in some circumstances and a second in others, both narrow their niches when together. Subordinates usually have a larger fundamental niche than their dominants. The presence of dominants should result in selection for enlarged (or changed) fundamental niches by the subordinate species. Linear hierarchies of species should result in guilds whose members have different-sized fundamental and realized niches. Though large mobile species often have greater fundamental niches than small similar species, an inverse relationship between size and niche breadth usually occurs where clear dominance hierarchies exist, suggesting that social dominance has more than counteracted the effect of body size. The presence of dominants is a factor making conditions uncertain for subordinates. Limits to the niche breadth of dominants are in some cases directly set by physical factors ...
330 citations
TL;DR: One aspect of the niche width of a population refers to the variety of resources used by the entire population, which may be measured by the variance of the population's resource-utilization function.
Abstract: One aspect of the niche width of a population refers to the variety of resources used by the entire population. This aspect may be measured by the variance of the population's resource-utilization function. Two components make up a population's niche width. The within-phenotype component measures the spread of resources used by the average individual in the population. The between-phenotype component measures the variety of individual specializations in the population. The sum of these two components yields the total niche width. Calculation of these measures is illustrated with data from Anolis lizards. If the population's niche width is mostly composed of the within-phenotype component, it is virtually a monomorphic population of generalists, whereas if mostly the between-phenotype component, it is virtually a population polymorphic with pure specialists. Anolis populations tend more to be monomorphic with generalists than polymorphic with specialists. Recent ecological theory entails four predictions s...
TL;DR: The genetic basis of natural variation in Drosophila melanogaster and the effect of disruptive and stabilizing selection on the expression of a cubitus interruptus mutant in Dosophila is studied.
Abstract: Lerner, I. M. 1958. The genetic basis of selection. Wiley, New York. 273 pp. Milkman, R. 1970. The genetic basis of natural variation in Drosophila melanogaster. Advanc. Genet. 15:55-114. Roughgarden, J. 1972. Evolution of niche width. Amer. Natur. 106:683-718. Scharloo, W. 1964. The effect of disruptive and stabilizing selection on the expression of a cubitus interruptus mutant in Drosophila. Genetics 50:553-562. Scharloo, W., M. S. Hoogmoed, and A. ter Kuile. 1967. Stabilizing and disruptive selection on a mutant character in Drosophila. I. The phenotypic variance and its components. Genetics 56:709-726. Slatkin, M. 1970. Selection and polygenic characters. Proc. Nat. Acad. Sci. 66 :87-93.
TL;DR: In this paper, the authors identify causal mechanisms in the evolution of life history patterns in plants and animals, using well-studied examples from the literature, and use them to identify the necessary and sufficient environmental factors that can be used to explain the observed diversity of life histories.
Abstract: Evolutionary theory has not yet determined the necessary and sufficient environmental factors that can be used to explain the observed diversity of life history patterns in plants and animals. Although recent theoretical treatments of the evolution of life history rely heavily on the concepts of r- and K-selection, we find this framework inadequate to explain life histories of many well-known organisms. Instead, using well-studied examples from the literature, we attempt to identify causal mechanisms in the evolution of their life histories. The density of the population in relation to resources, the trophic and successional position of the population, and predictability of mortality patterns all appear to be important determinants of adaptive strategies. Therefore, consideration of many environmental dimensions seems essential to provide complete understanding of the evolution of life histories.
TL;DR: The ecological explanation of Cope's rule is suggested, which suggests that really successful K-strategists become precisely adapted to a very permanent habitat type, they become larger in size, and, because of their extreme K-type population parameters, they lose their plasticity for selection.
Abstract: Habitat is the template against which evolutionary pressures fashion the ecological strategy of a species; the instability-stability habitat spectrum gives rise to the r-K-selection continuum. Habitat stability for any animal is conveniently expressed by τ/H (τ = generation time and H = the length of time the habitat remains suitable for food harvesting). In animals whose habitats have a value of τ/H approaching unity, one generation will not affect the resources available to the next. The strategy for these habitats can allow overshooting of the equilibrium. In animals with permanent habitats (τ/H very small), overshooting, with the consequent overexploitation of resources, will be selected against. The logistic equation cannot represent a situation that involves overshooting. A more realistic approach arises from the consideration of the difference equation (2) which includes a time delay between density-dependence acting and the subsequent population change. Its three basic parameters are the equilibri...
TL;DR: Preliminary insights into the environmental parameters which influence the number of fish species occurring in lakes are obtained and four patterns of species diversity are distinguished.
Abstract: Stepwise multiple regression was used to obtain preliminary insights into the environmental parameters which influence the number of fish species occurring in lakes. Results are summarized as follows: 1. For a sample of 70 lakes and inland seas from throughout the world, surface area and latitude account for about one-third of the variability in fish species diversity. 2. For a subsample of 14 North American lakes, latitude and surface area account for about 90% of the variability in species numbers. The large effect of latitude can be explained in terms of climatic severity and isolation from sources of colonization. 3. For a subsample of 14 African lakes, surface area, depth, and conductivity were primary variables affecting species diversity. 4. For 70 lakes of the world and 14 North American lakes, the slope of the species-area curve was low (z = 0.15-0.16). Apparently this reflects the fact that, whereas a relatively large number of species are available to colonize small lakes, larger ones are impov...
TL;DR: Application of a simple model for a long-lived iteroparous organism to data for some offshore-feeding seabirds indicates that an increased reproductive effort will be selected for in these organisms only if the fractional amount by which fledging success increases is at least 19 times greater than the fractions by which parental survivorship is decreased.
Abstract: Where reproductive effort subjects the parent to a risk, the benefit of some breeding activity's contribution to present fitness must be weighed against the loss to future fitness. With risk and benefit defined in terms of life-table parameters, a simple model for a long-lived iteroparous organism permits calculation of the quantitative relation between risk and benefit necessary if an increase in reproductive effort is to be selected for. Constraints on the maximal real benefit establish a corresponding risk ceiling which represents that lowest increment to reproductive cost which can not be compensated by any realizable cost-benefit ratio. Application of this model to data for some offshore-feeding seabirds indicates that an increased reproductive effort will be selected for in these organisms only if the fractional amount by which fledging success increases is at least 19 times greater than the fractional amount by which parental survivorship is decreased. The calculated margin of possibly compensable ...
TL;DR: Observations on variability in survival and reproduction in the benthic phase over areas of increasing size would provide the strongest test of the hypothesis that spread of siblings is a function of long pelagic larval stages.
Abstract: 1. It is unlikely that individual selection simply for increasing distance between juveniles or between juveniles and parents would produce the patterns of reproduction and large-scale dispersal exhibited by many benthic invertebrates with pelagic larvae. However, these patterns are compatible with the hypothesis that pelagic larval phases of several weeks are the result of individual selection for spreading sibling larvae. 2. Selection for spread of siblings as a fixed feature of the life cycle depends on survival and reproduction in the benthic phase of life and in early and late larval stages varying independently from time to time and place to place. Data on benthic populations is apparently insufficient to determine whether or not such variation occurs. However, information on horizontal diffusion rates gained from dye diffusion experiments indicates the geographic scale of independent variation required by the hypothesis. 3. Rate of diffusion in the sea increases with time (or size of diffusing patc...
TL;DR: A geometrical model is developed, relating gape to the orientation of the superficial masseter muscle, and measurements on a variety of placental skulls demonstrated the validity of predictions derived from the model.
Abstract: The morphology of mammalian jaw systems is a product of selection for many sometimes conflicting functions, including prehension and mastication of food, agonistic behavior, respiration, and vocalization. One of the first and most challenging tasks of a functional cranial analysis is to resolve the complex resultant structure into its component parts. This paper has two purposes: first, to call attention to a hitherto rather neglected functional parameter of jaw morphology-the influence of muscle action line on gape; and second, to present a method of analyzing this influence using the "quantifunctional approach" (Gould 1970) of constructing a mathematical model to predict morphology and testing it by comparison with real animals. Masticatory muscle orientation (i.e., the direction of the action line and the positions of origin and insertion relative to the joint) is usually considered to reflect adaptation for mechanical advantage (i.e., moment arm) (e.g., Turnbull 1970, and references therein), joint protection, or special requirements for particular mandibular movements, as in rodents (Maynard Smith and Savage 1959). The effect of muscle orientation on gape is usually considered briefly and nonquantitatively or not at all. The ability of an animal to achieve wide jaw opening may, however, be an important element in its biology. We do not claim that the full range of mammalian variation can be explained by gape adaptation. As one of the numerous factors contributing to musculoskeletal morphology, the influence of gape may often be obscured by selection for other parameters. However, in certain extreme cases such as carnivores or the hippopotamus, which show particularly wide jaw opening, adaptation for gape may become a primary determinant of jaw form. The model presented below is simplistic in that it takes into account only muscle stretch and moment arm. The main advantage of modeling in biology is, however, the generation of predictions by which the model can be verified or disproved. The serviceability of the present model is indicated by the consistency of its predictions with observations on real animals. Although only one muscle, the superficial masseter, is analyzed in detail, the method is general and can be applied anywhere. Absolute proof that a given mammal is specialized for wide jaw opening would require, at the very least, analysis of all adductor muscles. As this paper deals more with methodology and broad implications, we have not performed such analysis.
TL;DR: Because of differences in geographic distribution, species able to live as shallow as 1 meter should be less likely to speciate or go extinct than species restricted to deeper waters, and low-diversity species associations should also be evolutionarily more stable than high-Diversity (>1 meter) associations.
Abstract: Infaunal bivalves able to live in depths of 1 meter or less have significantly wider geographic distributions than infaunal bivalves restricted to deeper waters (not including deep-sea species). Shallower species tolerate a wider range of environmental conditions and probably have longer-lived larvae than species limited to depths greater than 1 meter. As a result of differences in geographic distribution, species able to live as shallow as 1 meter should be less likely to speciate or go extinct than species restricted to deeper waters. Low-diversity species associations (⩽ 1 meter) should therefore also be evolutionarily more stable than high-diversity (>1 meter) associations. These predictions are supported by evidence from the fossil record.
TL;DR: The competition coefficient follows from MacArthur's (1968) consumer-resource system when the ratio of the carrying capacity to intrinsic rate of increase is constant for all resources.
Abstract: When relative frequencies of resource kinds in the diet are known, the competition coefficient giving the effect of competitor j on i may be computed as \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage{wasysym} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document}$$\alpha_{ij}=\left(\frac{T_{j}}{T_{i}}\right)\left[\frac{{\sum\limits_{k=1}^{m}}(d_{ik}/f_{k})\:(d_{jk}/f_{k})\:b_{ik}}{\sum\limits_{k=1}^{m}(d_{ik}/f_{k})^{2}\:b_{ik}}\right],$$\end{document} where Tj/Ti= the ratio of the number of items consumed by an individual of competitor j to that consumed by an individual of competitor i, measured over an interval of time that includes all regular fluctuations in consumption for both species; dik = the frequency of resource k in the diet of competitor i (and similarly for djk); fk = the standing frequency of resource k in the environment; bik = the net calories gained by an individual of competitor i from an item of resource k, or more approximately the calories contained in an item of resource k, or still more approximately the weight or volume of an item of resource k; and the summations are taken over all resources eaten by at least one of the competing species The coefficient follows from MacArthur's (1968) consumer-resource system when the ratio of the carrying capacity to intrinsic rate of increase is constant for all resources When relative frequencies of time spent foraging in habitat kinds are known, the competition coefficient may be computed as \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage{wasysym} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document}$$\alpha_{ij}=\left(\frac{T_{j}}{T_{i}}\right)^{\prime} \frac{\sum\limits^{m}_{k=1}p_{ik}p_{jk}b_{ik}}{\sum\limits^{m}_{k=1}p_{ik}{}^2b_{ik}}$$\end{document} where (Tj/Ti)' = the ratio of the total time spent searching for food by an individual of competitor j in all habitats to that spent by an individual of competitor i; bik = as above, except resource k is the average food item in habitat k; and summations are taken as before This coefficient, with the same resource restrictions and assuming equal consumption rates per unit search time for the competitor species, follows also from MacArthur's system It equals the Levins-MacArthur α (eq [3]) when it is assumed or known that (Tj/Ti)' = 1 and the b 's are equal
TL;DR: A long-term approach to optimal foraging strategy in response to a regularly varying environment is presented, with parameters and assumptions chosen to match qualitatively the food availability and time-energy demands of actual animals.
Abstract: A long-term approach to optimal foraging strategy in response to a regularly varying environment is presented. A dynamically optimal animal uses this regularity to produce the best strategy vis-a-vis a single long-range objective. (No long-range planning ability need be postulated, however. There need only be selection for behaving via environmental cues as if planning occurred.) This dynamic optimization approach is applied to a model of the African weaver bird Quelea quelea (documented by Ward 1965a, 1965b, 1971). This model includes the effect upon the animal's condition of past and present behavior and variations (with time) in environmental and foraging characteristics, but contains a number of simplifications: (1) considering food availability only in terms of calories, ignoring other differences between foods; (2) ignoring the distinction between components (e.g., skeleton, fat) of body weight; (3) assuming that Quelea's sole control over its food energy input is its daily feeding time, which impli...
TL;DR: The conclusions are sufficiently general to imply that vertical migration in thermally stratified waters confers a demographic advantage to individuals of this copepod and other zooplankters in which size and fecundity are negative functions of temperature.
Abstract: Recent explanations of the adaptive values of vertical migration by zoo-plankton are difficult to express in terms of individual fitnesses. An earlier explanation of the demographic consequences of vertical migration incorporated an unnecessary and probably erroneous metabolic model. From empirical data on the effects of temperature on fecundity and development rates of the copepod Pseudocalanus minutus, the demographic effects of vertical migration in thermally stratified waters are worked out. In seasonal or otherwise interrupted life cycles, increased fecundity from part-time residence in colder waters is advantageous in near-equilibrium populations, but this is not always true where life cycles are continuous and adequate food is present. However, residence in colder waters during later developmental stages is shown to be advantageous for near-equilibrium populations if mortality rate is sufficiently higher in earlier stages. The conclusions are sufficiently general to imply that vertical migration in...
TL;DR: It is argued that nonlinear (higher-order) interactions between species are probably very important in many competitive relationships and subsequent calculations based on an α matrix to predict the number of species expected in the community are inappropriate to the assumptions of the model.
Abstract: In response to recent elaborations of the community matrix concept, I argue that nonlinear (higher-order) interactions between species are probably very important in many competitive relationships. Several competition coefficients calculated from populations of microcrustaceans in equilibrium microcosm communities change significantly with changes induced in the species composition of the remainder of the community. Because of interdependence among first-order competition coefficients, interpretation of community perturbation experiments becomes exceptionally difficult and subsequent calculations based on an α matrix to predict the number of species expected in the community are inappropriate to the assumptions of the model.
TL;DR: It is concluded that species dominance in competition can not in principle be predicted from knowledge of r or K alone.
Abstract: The concepts of natural selection and competition are distinguished, and the competition coefficients are rigorously defined; r-selection is not relevant to competition, but K-selection is a consequence of exploitative competition wherein consumers and resources are directly interconvertible. When only a single resource limits a population, competition coefficients are proportional to the ratio of saturation densities and are reciprocal. When several limiting resources exist, competition coefficients must be ≤1 and competitive exclusion will not occur. Under exploitative competition K and competitive ability are inversely related. Alpha-selection is defined as the evolutionary process by which competitive ability increases and refers to the acquisition of interference phenomena whereby individuals impair the reproductive rate dN/Ndt of competitors. Possession of interference mechanisms may require adjustments of energy budgets, so that α-selection is a mechanism of evolutionary reduction of r and K. Inter...
TL;DR: Data on the mortality and survivorship of several species of birds are analyzed and alternative models of age-dependent mortality are discussed.
Abstract: Birds have been assumed to have a constant adult mortality rate in which a constant fraction of a cohort dies in each age interval. Average annual mortality rates reported for many species would result in exceedingly long potential life spans, and it seems more reasonable to assume that avian mortality is age dependent. Data on the mortality and survivorship of several species of birds are analyzed and alternative models of age-dependent mortality are discussed.
TL;DR: Prudent predation evolves as a consequence of several well-supported biological observations and theoretical assertions, namely: a) Mortality sources tend to become synchronous in life history by natural selection and tend to concentrate on ages with low reproductive value and b) By a predator acting as a strong age-selective mortality source it selects for shifts in the life history distribution which lowers the reproductive value of its preferred prey.
Abstract: 1. Contrary to the assertion by Maynard-Smith and Slatkin (1978), the concept of prudent predation does not involve group selection. 2. While an "evolutionary race" may exist between predators and prey, there is reason to believe the prey mm keep ahead in that race. 8. Prudent predation evolves as a consequence of several well-supported biological observations and theoretical assertions, namely: a) Mortality sources tend to become synchronous in life history by natural selection and tend to concentrate on ages with low reproductive value. b) By a predator acting as a strong age-selective mortality source it selects for shifts in the life history distribution which lowers the reproductive value of its preferred prey. c) Consuming animals of low reproductive value is optimally prudent predatory behavior.
TL;DR: Play appears to constitute behavioral experimentation and may contribute behavioral variation to evolution in higher vertebrates and with model systems support these hypotheses.
Abstract: Young of many species of mammals and birds "play" That is, they exhibit active, oriented behavior whose structure is highly variable, which apparently lacks immediate purpose, and which is often accompanied by specific signal patterns It has often been suggested that play may serve to practice, rehearse, and perfect adaptive responses; play may also provide raw material for social and behavioral evolution by generating increased behavioral variability, including novel or innovative acts that may be propagated to other individuals via observational learning These plausible suggestions have been difficult to verify experimentally, possibly because they fail to specify particular psychological and evolutionary mechanisms that could result in adaptive behavior having "playful" characteristics "Practice" hypotheses presuppose special learning processes of adaptive value to the organism, which function only in play, while "innovation" hypotheses require selection for playful behavior in a population of animals capable of observational learning In surveying the literature on play, I identify two very different historical approaches to the topic This review also focuses on two mechanisms, one psychological and one evolutionary, which may provide some justification for the continued use of the term "play" by behavioral biologists
TL;DR: The prevalence of intense predation on eggs suggests that predators are important selective agents for egg characteristics.
Abstract: Recent decades of fieldwork have thoroughly established that the eggs of most animals are subject to intense predation. For example, temperate-zone open-nesting bird species lose about 35% of their eggs to predators (Lack 1954, 1968); among tropical species, the figure is as high as 50% (Ricklefs 1969). Indirect evidence from egg care and from life history characteristics of reptiles and amphibians (Tinkle et al. 1970) suggests high egg loss to predators. The same may be said for fish, and those with pelagic and demersal eggs have particularly high egg mortality from predation (Barnaby 1944; Foerster and Ricker 1941; Sette 1943). Losses of eggs of insects to predators and parasites are often high (e.g., Clausen 1940; Clark et al. 1967). While some animals appear to be specialists at eating eggs (e.g., Emydocephalus sea snakes [Voris 1966]; myrid bugs [Lord 1971]; mites [Lindquist 1969]; Dasypeltis terrestrial snakes [Ditmars 1910]; Trichogramma parasitic Hymenoptera [Clausen 1940]), almost all carnivores and many omivores regularly include many kinds of eggs in their diets. Humans not only consume large numbers of many species of vertebrate eggs, but \"at Lake Texcoco [Mexico] the natives collect the eggs of several species of corixid [bugs] by submerging a sheath of straw on stems of hay into the water where corixids are abundant. The egg-laden stems are later exposed to the sun, dried, and prepared as an edible delicacy\" (Peters and Ulbrich 1973). A single species of egg parasite, Trichogramnma minutum, has been reared from 162 species of insect eggs (Thompson 1958), which strongly suggests that insect eggs are generally palatable. The prevalence of intense predation on eggs suggests that predators are important selective agents for egg characteristics. Cryptic coloration of eggs of open-nesting birds is well documented (Cott 1952, 1953, 1954; Lack 1968). Egg protection by nesting on sea cliffs, islands, trees, or even near colonies of ants and wasps (Janzen 1969a; Meyers 1929, 1935; Moreau 1936, 1942) is commonplace. Frogs may lay their eggs on inaccessible foliage high over water (e.g., Pyburn and Glidewell 1971), and insects and fish display a wide variety of behaviors that render eggs inaccessible to predators.
TL;DR: The concordant variation in oil content and seed weight from one habit to another and the discordant pattern of variation from one latitudinal zone to another are considered both in terms of its cause and as both parameters relate to r- and K-selection.
Abstract: The oil content of seeds (on a percentage dry weight basis) and seed weight are independent variables which reflect the energy capital of the seed. Here, these parameters are related to plant habit and latitudinal zone for over 300 species of the Leguminosae and over 1,000 species of flowering plants as a whole. The species in each case are representatives of a world-wide flora. In legumes, oil content and seed weight increase with plant woodiness and shade tolerance, the mean oil content of herbs is 5.6% as compared with 7.8% in shrubs, 10.6% in shrubby trees, and 11.4% in trees. Mean seed weight is 0.012 g in herbs, 0.047 g in shrubs, 0.087 g in shrubby trees, and 0.186 g in trees. Plants from temperate, subtropical, and tropical areas did not display conspicuous differences in either seed parameter. In angiosperms, temperate herbs have oilier but not heavier seeds as the illumination of habitat declined. Mean oil content for herbs is 17.9% in contrast to 20.8% in vines, 23.5% in shrubs, 22.3% in shrubb...