Showing papers in "The American Naturalist in 1977"
TL;DR: A triangular model based upon the three strategies of evolution in plants may be reconciled with the theory of r- and K-selection, provides an insight into the processes of vegetation succession and dominance, and appears to be capable of extension to fungi and to animals.
Abstract: It is suggested that evolution in plants may be associated with the emergence of three primary strategies, each of which may be identified by reference to a number of characteristics including morphological features, resource allocation, phenology, and response to stress. The competitive strategy prevails in productive, relatively undisturbed vegetation, the stress-tolerant strategy is associated with continuously unproductive conditions, and the ruderal strategy is characteristic of severely disturbed but potentially productive habitats. A triangular model based upon the three strategies may be reconciled with the theory of r- and K-selection, provides an insight into the processes of vegetation succession and dominance, and appears to be capable of extension to fungi and to animals.
4,907Â citations
TL;DR: In the majority of natural communities succession is frequently interrupted by major disturbances, such as fires, storms, insect plagues, etc., starting the process all over again, but if not interrupted, it eventually reaches a stage in which further change is on a small scale as individuals die and are replaced.
Abstract: The sequence of species observed after a relatively large space is opened up is a consequence of the following mechanisms. "Opportunist" species with broad dispersal powers and rapid growth to maturity usually arrive first and occupy empty space. These species cannot invade and grow in the presence of adults of their own or other species. Several alternative mechanisms may then determine which species replace these early occupants. Three models of such mechanisms have been proposed. The first "facilitation" model suggests that the entry and growth of the later species is dependent upon the earlier species "preparing the ground"; only after this can later species colonize. Evidence in support of this model applies mainly to certain primary successions and in heterotrophic succession. A second "tolerance" model suggests that a predictable sequence is produced by the existence of species that have evolved different strategies for exploiting resources. Later species will be those able to tolerate lower levels...
4,068Â citations
TL;DR: It is proposed that many sounds in species' repertoires are evolved from motivation-structural rules derived from selection pressures favoring the use of communication instead of, or in conjunction with, fighting to attain resources.
Abstract: The convergent use of harsh, low-frequency sounds by hostile animals and more pure tonelike, high frequency sounds by fearful or appeasing animals is discussed in an evolutionary context. It is proposed that many sounds in species' repertoires are evolved from motivation-structural rules derived from selection pressures favoring the use of communication instead of, or in conjunction with, fighting to attain resources. The use of this concept should further the appreciation of the relationship between sound structure and function.
1,114Â citations
TL;DR: Recognition of the generalist-specialist and early-late "successional" roles of most solitary versus colonial animals leads to predictions that solitary animals should recruit more heavily and be more palatable to predators than are colonial animals.
Abstract: Most solitary and colonial animals inhabiting marine hard substrata differ fundamentally in their ability to use space. Colonial animals are superior space competitors because (1) indeterminate growth allows continuous lateral substratum occupation without requiring intervening stages of sexual reproduction and recruitment, and (2) they are less susceptible to "fouling" and overgrowth. Solitary animals survive in the seas because (1) various morphological and behavioral attributes (escape in size, aggregative behavior) protect them in spatial competition with colonial animals or because (2) predation, physical disturbance, or competition with plants prevents monopolization of substrata by colonial animals. Focus on ecological strategies circumvents arguments regarding the solitary or colonial identity of problematical groups such as sponges. The evolution of specific competition mechanisms by colonial animals has provided the basis for competitive networks which have further favored the evolution of highe...
830Â citations
TL;DR: The argument is developed that reef fishes are adapted to this unpredictable supply of space in ways which make interspecific competition for space a lottery in which no species can consistently win.
Abstract: Data have been drawn together to demonstrate that reef fishes by and large are food and habitat generalists with a large amount of overlap in requirements among coexisting species. Suitable living space is the resource most likely to be in short supply for them, and their environment, although benign, is one in which the supply of living space is both spatially and temporally unpredictable. The argument is developed that reef fishes are adapted to this unpredictable supply of space in ways which make interspecific competition for space a lottery in which no species can consistently win. Thus, the high diversity of reef fish communities may be maintained because the unpredictable environment prevents development of an equilibrium community
662Â citations
TL;DR: The data on diversity-stability relationships in plant communities indicate that the traditional verbal model is considerably more robust in application than recent "more rigorous" mathematical models.
Abstract: In the Proceedings of the First International Congress of Ecology (1974), a strong theme was the relationship, if any, between species diversity and ecosystem stability. It is apparent from these proceedings that there is considerable variation in attitudes regarding what ecosystem properties diversity is supposed to stabilize. Some authors, for instance, argue that species diversity is supposed to stabilize species diversity and, further, that data contradict the hypothesis because greater species diversity in communities studied was accompanied by greater changes in diversity upon environmental variation (Larsen, p. 80, this and subsequent page references are to the Proceedings). Similar arguments have been developed elsewhere in the context of purported tests of the diversity-stability hypothesis (Hairston et al. 1968; Murdoch et al. 1972). Elsewhere in the proceedings, it was argued that a positive relationship between species diversity and stability would somehow conflict with our knowledge about the dynamics of individual populations. Goodman (p. 78), for instance, in rejecting the "validity" of the hypothesis, says that it contradicts evolutionary reasoning. Widely varying interpretations of the hypothesis seem remarkable given its explicit and repeated presentation (Bertalanffy 1950, 1952; MacArthur 1955; Odum and Pinkerton 1955; Bray 1958; Odum 1962, 1969; Margalef 1963, 1968; McNaughton 1968; Mellinger and McNaughton 1975). Specifically, the hypothesis is: species diversity stabilizes ecosystem functional properties. Margalef explicitly stated (p. 66), "A system, highly unstable in species composition, may be stable concerning energy flow." Purported tests based on fluctuations of individual populations within an ecosystem are irrelevant, unless it is shown that outbreaks of certain species are unaccompanied by compensating declines in other species. Similarly, retrospective tests based on data collected for other purposes should be scrutinized carefully for applicability. Initial explicit empirical tests of the diversity-stability hypothesis on planktonic (Margalef 1965) and terrestrial (MeNaughton 1968; Singh and Misra 1969) systems used indirect means of estimating stability and provided conflicting results. A more direct test (Hurd et al. 1971; Hurd and Wolf 1974; Mellinger and MeNaughton
620Â citations
TL;DR: A mechanism by which females facilitate mating with a superior genotype, as reflected by age, social rank, and sexual experience, without exerting choice is described.
Abstract: Females that mate with the most fit male available leave more viable offspring than females that mate with males of lesser fitness. We describe a mechanism by which females facilitate mating with a superior genotype, as reflected by age, social rank, and sexual experience, without exerting choice. Female elephant seals increase the probability of mating with a mature, high-ranking male by simply rejecting all copulatory attempts during early estrus. Females protest loudly when mounted; this signals all nearby males and activates the dominance hierarchy. The probability that the mounting male will be interrupted by another male is a function of the mounter's social rank. The lower his rank, the higher the probability of interruption. The result is that mature males of high social rank have more time and freedom to attempt copulation, and they succeed in doing most of the mating. The behavior of the female intensifies this monopoly by making it more difficult for young, subordinate males to copulate. A simi...
547Â citations
TL;DR: An adequate mammalian model will have to include another set of factors which oppose the evolution of polygyny by increasing the spacing or mobility of females, and explain why sexual dimorphism has evolved more frequently in large mammals than in small ones.
Abstract: Current models for the evolution of polygyny and sexual dimorphism are largely derived from data on passerine birds. These models are less appropriate for taxa such as mammals, in which males emphasize mating strategies, than for those such as passerines, in which males emphasize progeny rearing strategies. The Orians-Verner model is inadequate as a general explanation of the evolution of polygyny in mammals because many species do not meet one or more of its assumptions: that the need for male parental care is the main factor opposing the evolution of polygyny; that females choose to mate with particular males; and that the female raises her young on the resources contained in the territory of the male with which she mates. A two-factor model incorporating the concept of sexual bimaturism, developed by Wiley for grouse, is more appropriate for many mammals but still too simple. In mammals, large male parental investment is a good predictor of both monogamy and reduced sexual dimorphism, but small male in...
538Â citations
TL;DR: It is suggested that large animals have played a large and virtually unrecognized role in evolution of their production.
Abstract: When an animal eats "spoiled" or "rotten" food of any kind, it runs a largely unknown risk (except in the case of grains) of being injured by toxins or microbe-produced antibiotics, getting food wi...
515Â citations
491Â citations
TL;DR: A model of resource-limited population growth, competition, and predation based on what it is believed to be biologically realistic assumptions about the relationship between resources and the growth of primary consumers and about the interaction of the primary consumers with the predators that prey upon them is presented.
Abstract: We present a model of resource-limited population growth, competition, and predation based on what we believe to be biologically realistic assumptions about the relationship between resources and the growth of primary consumers and about the interaction of the primary consumers with the predators that prey upon them. Consideration is given to an equable habitat in which resources are continually supplied and wastes are continually removed. The general properties of this model are examined and two specific cases are studied in some detail: (i) one resource, one prey, and one predator, and (ii) one resource, two prey, and one predator. Particular consideration is given to the conditions which will permit the continued coexistence of the interacting populations. In conceiving this model we were guided by the specific case of bacteria and their virulent viruses. To study its validity we compare the theoretical predictions with the experimental results from continuous-culture populations of the bacterium E. co...
TL;DR: These mechanisms are enumerated and awareness of these mechanisms and their interrelationships will provide insights for those investigating the efficiency of various modes of filter feeding and the mechanisms of size-selective suspension feeding.
Abstract: We enumerate the five basic mechanisms by which any biological or manmade filter can remove particles from a fluid. These mechanisms are: (1) direct interception, (2) inertial impaction, (3) gravitational deposition, (4) motile-particle deposition, and (5) electrostatic attraction. For these mechanisms we present dimensionless indexes that indicate which measurable characteristics of the filter, the particles, and the flow affect the intensity of particle capture. By comparing the magnitudes of these indexes it is possible to determine the main mechanism a filter is using to capture particles. Awareness of these mechanisms and their interrelationships will provide insights for those investigating the efficiency of various modes of filter feeding and the mechanisms of size-selective suspension feeding.
TL;DR: The larval development of Palaeenonetes intermedius Holthius, 1949 (Decapoda, Palaemonidae) reared in the laboratory, and the type of development of prawns as a factor determining suitability for farming.
Abstract: Barnes, H., and LI. Barnes. 1965. Egg size, nauplius size, and their variation with local, geographical, and specific factors in some common cirripedes. J. Anim. Ecol. 34: 39 1-402. Batham, E. J. 1946. Pollicipes spinosus Quoy and Gaimard. II. Embryonic and larval development. Trans. Roy. Soc. New Zeal. 75:405-418. Blake, J. A. 1969. Reproduction and larval development of Polydora from northern New England (Polychaeta: Spionidae). Ophelia 7:1-63. Costlow, J. D., Jr., and C. G. Bookhout. 1957. Larval development of Balanus eburneus in the laboratory. Biol. Bull. Marine Lab., Woods Hole 112:313-324. 1958. Larval development of Balanus amphitrite var. denticulata Broch reared in the laboratory. Biol. Bull. Marine Lab., Woods Hole 114:284-295. Dobkin, S. 1968. Abbreviated larval development in caridean shrimps and its significance in the artificial culture of the animals. FAO Fisheries Rep. 57:935-945. Gurney, R. 1942. Larvae of decapod crustacea. Ray Society, London, 306 pp. Hubschmann, J. H., and A. C. Broad. 1974. The larval development of Palaeenonetes intermedius Holthius, 1949 (Decapoda, Palaemonidae) reared in the laboratory. Crustaceans 26:89-103. Karande, H. A. 1974. Balanus variegatus Darwin: the laboratory reared larvae compared with Balanus amphitrite amphitrite Darwin (Cirripedia). Crustaceana 26:229-232. Moyse, J. 1960. Mass rearing of barnacle cyprids in the laboratory. Nature 185: 120. Nyblade, C. F. 1974. Coexistence in sympatric hermit crabs. Ph.D. thesis. University of Washington. Patel, B., and D. J. Crisp. 1960. Rates of development of the embryos of several species of barnacles. Physiol. Zool. 33:104-119. Underwood, A. J. 1974. On models for reproductive strategy in marine benthic invertebrates. Amer. Natur. 108:874-878. Vance, R. R. 1973. On reproductive strategies in marine benthic invertebrates. Amer. Natur. 107:339-352. 1974. Reply to Underwood. Amer. Natur. 108:879-880. Williamson, D. I. 1968. The type of development of prawns as a factor determining suitability for farming. FAO Fisheries Rep. 57:77-84.
TL;DR: Holling's Type II functional-response relationship is presented, and the formulations expressing the underlying organismal interactions which might generate such a relation arc generalized into the Type III response typical of predators showing learning behavior.
Abstract: Holling's Type II functional-response relationship is presented, and the formulations expressing the underlying organismal interactions which might generate such a relation arc generalized into the Type III response typical of predators showing learning behavior. An equation derived through an analogy with allosteric enzyme kinetics is given which will account for both Type II and Type III responses. The response behavior can be explained by three parameters: maximal feeding rate (F); an affinity constant (G) related to handling times, capture efficiencies, etc.; and the number of encounters (n) a predator must have with a prey item before becoming maximally efficient at utilizing the prey item as a resource. A discussion follows on the biological processes which result in shifts from Type II to Type III functional responses. Most of the learning processes involve changes in predator behavior associated with increasing encounters with prey, thus supporting parameter n as a major determinant in shifting th...
TL;DR: A method to relate foraging theory to species-packing theory is developed and it is predicted that these species occupy similar habitats and segregate on the food size axis while the third species, which is intermediate in morphology, should be excluded from these habitats and show complementarity on niche dimensions.
Abstract: A fundamental problem in ecology is to identify and relate those factors which determine the number of species that can stably coexist in an area. Interspecific competition is one such factor, and in principle it limits the similarity of competing species in relation to the abundance and diversity of critical resources. MacArthur and Levins (1967) first explored this limit with a three-species Lotka-Volterra model. The success of a species invading between two residents on a resource axis was related to the differences in mean utilization on this axis. Resource abundance was considered uniform across types, and utilization functions were assumed to be normal, differing only in position on the axis. The analysis of this problem has subsequently been extended to include factors such as environmental variability, the relative abundance of resources, the shape of the utilization curve, and predation pressure (e.g., May and MacArthur 1972; MacArthur 1972a; Roughgarden 1974b; Roughgarden and Feldman 1975). The variety of resources used by a species (i.e., niche width) is a central issue in this theory and is usually treated as a given parameter. Both the niche width and location of a species are related to functional morphology (i.e., the "tools" used in obtaining resources). In fact, one of the first observations suggesting the direction of the theory was Hutchinson's (1959) remarks on the uniformity of character displacement ratios among a wide variety of sympatric species, particularly in trophic apparatus. Morphological measurements have been widely used since as relative indices of competition or niche width (e.g., Cody 1974a; Van Valen 1965; Soule and Stewart 1970). Very seldom, however, have the differences in foraging efficiency of morphologically similar species been quantified in relation to a set of resources that change in a recognizable (hopefully orderable) manner. Careful studies in this direction would facilitate the testing and development of theory by providing a link between morphology, the efficiency of resource utilization, and the parameters of concern, usually measures of overlap in resource use. In this study I quantitatively relate the body plan in fishes to foraging efficiency on the food size dimension of the niche. Using methods derived from optimal foraging theory, cost curves are constructed on this coordinate for
TL;DR: An alternative approach, using a Prim-Kruskal network on the avoidable discordancy distances, is given together with a procedure for interpreting such networks in terms of a phylogeny that appears more natural than the dendrograms usually employed in the interpretation of singlelinkage diagrams.
Abstract: The problem of discovering the most parsimonious tree is defined in terms of a set of linearly arrayed sequences. Simplifications are introduced to reduce the total amount of work including the elimination of uninformative positions and the recognition of equivalent positions. The procedure can be applied to any array of sequences, including amino acid. It is shown, however, that failure to convert such sequences, through the genetic code, into nucleotide sequences is very wasteful of pertinent information. Parsimony is shown as a procedure that minimizes discordancies (parallel and]or back substitutions). A procedure (a discordancy diagram) is given that enables one to recognize when two characters (nucleotide positions) will necessitate the acceptance of such discordancies and how many, at least, will be unavoidable. Subtraction of these unavoidable discordancies from a matrix of potential discordancies leads to a matrix of avoidable discordancies that generally give at least two pairs of taxa that are ...
TL;DR: Two models are developed which predict life-history adaptations resulting from intraspecific competition for avian dispersers and one suggests stabilizing selection for a rate of fruit production necessary to maintain a limited and specialized guild of dispersers.
Abstract: Two models are developed which predict life-history adaptations resulting from intraspecific competition for avian dispersers. One suggests stabilizing selection for a rate of fruit production necessary to maintain a limited and specialized guild of dispersers. The other suggests directional selection for high fecundity which is mediated by intraspecific competition for a variety of opportunistic birds drawn from alternative sources of plant or animal food. Operational procedures are suggested which would test for the applicability of either model. Relevant literature is discussed.
TL;DR: Models are presented for warning cries and other donor-recipient relations, resource notification, the evolution of prudence in exploitation and interference competition, and the effect of differential trait-group extinction.
Abstract: 1. Most organisms interact with a set of neighbors smaller than the deme (its trait group). Demes therefore are not only a population of individuals but also a population of groups (structured demes). 2. Trait groups vary in their composition. The minimum variance to be expected is that arising from a binomial distribution. Most populations have a higher variance than this due to (a) differential interactions with the environment and (b) the effects of reproduction inside the trait groups. 3. As a consequence of this variation, an individual on the average experiences its own "type" in a greater frequency than actually exists in the deme. Its behaviors are therefore directed differentially toward fellow types, and this is the fundamental requirement for the evolution of altruism. 4. Models are presented for warning cries and other donor-recipient relations, resource notification, the evolution of prudence in exploitation and interference competition, and the effect of differential trait-group extinction. ...
TL;DR: The model provides a reasonable explanation for the large numbers of desert plants with deciduous, mesophytic leaves and for the great variations reported in R/S ratios in desert plants.
Abstract: The richness of plant-life forms, ranging from unicellular algae to large trees, from trailing herbs to large climbing vines, and from ephemerals to long-lived perennials, suggests that a variety of environmental factors exert important influences on plant shapes (Terborgh 1973). In this paper we describe a model in which the inevitable association between water loss and entrance of carbon dioxide through stomates, together with cell-morphological and physiological traits that affect these exchanges, prevent any one plant-life form from being the best adapted to more than a fraction of the earth's complex patterns of temperature and moisture availability. These relationships may also explain apparently stable mixtures of plants with different life forms in a single environment. The tight linking of water loss and carbon uptake affects all aspects of the total photosynthetic and materials uptake system of vascular plants, because reducing water loss lowers rates of carbon uptake and hence lowers rates of net photosynthesis per unit area of photosynthesizing surface. The combination of characters that yields maximum net photosynthesis per unit time under moist conditions reduces the maximum rate under drier conditions, and vice versa. There are, of course, mechanisms, such as C4 photosynthesis and opening stomata only when atmospheric humidity is high, which reduce water loss per molecule of carbon fixed, but these mechanisms are of limited effectiveness and have associated costs. Any model of natural selection assumes both some "goal" that is being optimized (or maximized) and the constraints within which the organisms operate. A reasonable short-range goal for plants might be the maximization of photosynthetic rate; a plant capable of increasing photosynthesis within the constraints of its available resources and the physical environment should gain advantages in competition with other plants, defenses against herbivores, and should have more energy to devote to reproduction. We assume in our model that total fitness is strongly correlated with net gain in calories and that it is reasonable to treat allocations of resources to leaves, stems, and roots in terms of calories. Thus, we ignore other potentially significant factors, e.g., nonuniform mortality risks due to herbivory or pathogens, which should influence the
TL;DR: It is suggested that individuals who have the most difficulty interacting with littermates will not develop strong social ties with their siblings and will be the most likely individuals to disperse of their own accord.
Abstract: Explanations of dispersal mechanisms in mammals that have stressed the importance of aggression by dominant (?) individuals as the immediate cause of the dispersal of less aggressive (more subordinate?) individuals are insufficient for explaining recent data collected on a variety of mammals. In fact, avoidance of social interaction at the time of dispersal is more characteristic of some species in which individuals emigrate. Studies that have investigated genetic correlates of dispersal in rodent populations that undergo regular cycles are few and have not provided any "causative" explanations. In various canids and rodents, behavioral interactions at the time of dispersal do not appear to provide the necessary stimuli for dispersal. These observations suggest that knowledge of the behavioral interactions that occur before dispersal may provide a key to understanding both interspecific and intraspecific differences in social organization and dispersal patterns. It is suggested that individuals who have t...
TL;DR: Simple and sufficient conditions for generalized Lotka-Volterra models to be globally stable in the positive orthant are described, which imply that if each species in a complex ecosystem sustains density-dependent mortalities due to intraspecific interactions and the interspecific interactions are not too strong then the ecosystem is globally stable.
Abstract: Simple and sufficient conditions for generalized Lotka-Volterra models to be globally stable in the positive orthant are described. Similar conditions for global stability in general nonlinear population models are also given. These conditions imply that if each species in a complex ecosystem sustains density-dependent mortalities due to intraspecific interactions and the interspecific interactions are not too strong then the ecosystem is globally stable.
TL;DR: Frequency of female digamy in a natural population of the olive fruit fly Dacus oleae as found by using enzyme polymorphism and Concurrent multiple paternity in natural and laboratory populations of Drosophila melanoqaster.
Abstract: Anderson, W. W. 1974. Frequent multiple insemination in a natural population of Drosophila pseudoobscura. Amer. Natur. 108: 709-711. Birdsall, D. A., and D. Nash. 1973. Occurrence of successful multiple insemination of females in natural populations of deer mice (Peromyscus rnoaniculatus). Evolution 27: 106-110. Dobzhansky, T. H., and 0. Pavlovsky. 1967. Repeated mating and sperm mixing in Drosophila pseudoobscura. Amer. Natur. 101: 527-533. Hedgecock, D., K. Nelson, R. A. Shelser, and M. L. Tracey. 1975. Biochemical genetics of lobsters (Homarus). II. Inheritance of allozymes in H. americanus. J. Hered. 66: 114-118. Herrick, F. H. 1911. Natural history of the American lobster. Bull. U.S. Bureau Fisheries 24:153-408. Milkman, R., and R. R. Zeitler. 1974. Concurrent multiple paternity in natural and laboratory populations of Drosophila melanoqaster. Genetics 78: 1191-1193. Murray, J. 1964. Multiple mating and effective population size in Cepaea nemoralis. Evolution 18:283-291. Richmond, R. C., and L. Ehrman. 1974. The incidence of repeated mating in the superspecies Drosophila paulistorumr. Experientia 30:489-490. Sandler, L., and E. Novitski. 1957. Meiotic drive as an evolutionary force. Amer. Natur. 91: 105-110. Strickberger, M. WV. 1968. Genetics. Macmillan, New York. 868 pp. Tracey, M. L., K. Nelson, D. Hedgecock, R. A. Shleser, and M. L. Pressick. 1975. Biochemical genetics of lobsters (Homarus): genetic variation and the structure of American lobster populations. J. Fisheries Res. Board Can. 32:2091-2101. Zouros, E., and C. B. Krimbas. 1970. Frequency of female digamy in a natural population of the olive fruit fly Dacus oleae as found by using enzyme polymorphism. Entomol. Exp. et Appl. 13:1-9.
TL;DR: The effects of changes in the distribution of the resource over space upon the relative colonization rates of species must be known to predict accurately the impact of competition upon resource partitioning and organization of fugitive plant populations into a guild.
Abstract: Badger disturbances on tall-grass prairies constitute a limiting resource for a guild of fugitive plants. These plants partition the resource along several dimensions. Divergent centers of resource utilization result from different suites of adaptive life-history characteristics important during colonization. While overlap of utilization functions is considerable along single dimensions of the resource, complementary adaptations of species result in reduced overlap along a complex gradient integrating the separate dimensions. We predict that the number, packing, and organization of species into a guild will change as the nature of the limiting resource changes. Specifically, changes in the abundance of the resource alter the heterogeneity of the resource over space, and as a result relationships among the adaptive centers of resource utilization for species also change. Predictions of changes in resource partitioning and guild organization, based upon assumptions concerning competition among species popul...
TL;DR: The empirical study of life history patterns has revealed a complex of interrelated adaptations that cannot easily be explained by reference to the models of demographers, and some fundamental differences between angiosperms and vertebrates are demonstrated.
Abstract: The empirical study of life history patterns has revealed a complex of interrelated adaptations that cannot easily be explained by reference to the models of demographers. Parental investment can be expended in many ways by manipulating propagule size, propagule number, and the pattern of propagule dispersal in time and space. Each aspect of reproduction entails a balance between the benefits and cost of current reproduction versus future reproduction. Natural selection results in the pattern of reproduction that maximizes the lifetime contribution of an individual to future generations. The compromise between propagule size and propagule number is modeled by the effects of competitive challenges during the early juvenile period, dispersal mechanisms, and mechanisms of predator defense. The position of the balance is modeled by the interaction of the level of investment per clutch and the functional dependence of early juvenile survival on propagule size. The spatial pattern of egg deposition is modeled b...
TL;DR: Optimization of reproductive risk with respect to adult mortality exerts a minor influence on fecundity and explains little of the variation of reproductive rates among species of birds.
Abstract: A model is developed for the optimization of fecundity (B) with respect to adult mortality (M) in populations of birds. Special assumptions of the model include constant age-specific survival and fecundity and adult risk due to reproduction (m) related to fecundity by the expression m = (B/f)Z. The term f is interpreted as the level of resources available to reproduction. For large values of Z, optimized fecundity is insensitive to variation in M, although risk is always a constant proportion of (1/Z) of M. Values of Z estimated for natural populations as the ratio of M to m were found to vary between four and 10 with an average of about six. The direct relationship between fecundity and adult mortality observed in natural populations is interpreted as reflecting primarily the density-dependent feedback of adult survival on resources for reproduction (f). Optimization of reproductive risk with respect to adult mortality exerts a minor influence on fecundity and explains little of the variation of reproduc...
TL;DR: The possibility that females which provision a number of small cells (thus producing several small males) may be as fit as or fitter than females that divide their investment into relatively few packets and produce a few large males is examined.
Abstract: This paper documents the existence of a striking example of dimorphism in the male mating behavior of a large anthophorid bee, Centris pallida, abundant in deserts of the southwestern United States. Bees of this genus have been relatively little studied, although Dodson (1962), Dodson and Frymire (1961), Frankie and Baker (1974), and Raw (1975) have found that males of various species establish territories primarily by orchids or around flowering trees in tropical Central and South America and in Jamaica. Elsewhere we describe how males of C. pallida dig up buried females and males, mnating with the former (Alcock et al. 1976). The focus of this report will be on the alternative mating strategies employed by males of this species. We shall show that mate-location techniques, size variation, and the fitness of males as well as the parental investments of their mothers are intimately related to one another. Other known cases of intraspecific dimorphism in male mating behavior are limited in number and restricted primarily (but not exclusively) to vertebrates (e.g., Morris 1952; van den Assem 1967; Barlow 1967; Keenleyside 1972; Gadgil 1972; Constantz 1975; Brown 1975; Wells, in press). These studies have shown that selection for competitive ability in males may result in extremely high investments in adaptations that promote success in male-male conflicts. In this situation, some males may enjoy reproductive success by "dropping out" of the competition and by exploiting an alternative pathway to females or their gametes. Work with C. pallida provides additional support for this generalization while at the same time demonstrating how important parental investment may be in some species in determining the mating strategy of male offspring.
TL;DR: For example, this article found that the house, winter, Bewick's, Carolina, cactus, and canyon wrens repeat a song type several times before changing to another, that is, AAA... BBB.
Abstract: Of the nine North American wrens, the house, winter, Bewick's, Carolina, cactus, and canyon wrens repeat a song type several times before changing to another, that is, AAA... BBB..... The rock, long-billed marsh, and the short-billed marsh wrens use frequently or exclusively song organizations involving more immediate variety, for example, ABCABC... MNOMNO.... These latter three wrens have larger song repertoires and occur in high densities in communities of low avifaunal diversity, where intraspecific interactions are likely to be more frequent and intense. Rates of presentation of new song types to conspecifics are highest in the long-billed marsh wren, a very polygynous species; and, of the six AAA... BBB... songsters, the winter wren is the most polygynous (according to European studies); has by far the longest and most complex songs; and, during a song bout, spends the highest percentage of time actually singing. Such correlations suggest that (1) strong sexual selection in polygynous mating systems ...
TL;DR: It is concluded that biochemical restructuring for activity at high tissue temperatures has evolved, in part, because it has extended the ability to be maximally active beyond the short time otherwise required to "overheat."
Abstract: The evolution of thermoregulation in endothermic animals is analyzed by asking two different but related questions: Why have animals evolved to regulate stable body temperatures, and why are the evolved temperature set points generally much higher than ambient temperature? The answer to the first question is probably related to enzyme specialization for the maintenance of high activity rates. By specializing to operate at specific temperatures (either high or low) enzymes improve their potential to promote high rates of substrate turnover while still remaining subject to necessary mechanisms of metabolic control. On the other hand, temperature-independent activity rates in ectotherms have been shown to be associated with comparatively low rates of aerobic metabolism, resulting probably from inefficiency that is a "cost" of biochemical temperature modulations. High temperature set points may have evolved from inability to rapidly dissipate all of the heat produced as a by-product of high activity rates. La...
TL;DR: The causes of alternation, some probably related to density regulation and some not, can all operate at the size scale of single large trees, excepting, of course, dispersal.
Abstract: In virgin forests, individual trees tend to be succeeded in time by those of another species. The phenomenon was recognized by a French forester and named "alternation of species" as early as 1905 (Schaeffer and Moreau 1958). The process is frequency dependent, not only setting the ratio of two species but driving the community toward equilibrium. The causes of alternation, some probably related to density regulation and some not, can all operate at the size scale of single large trees, excepting, of course, dispersal. Trees themselves serve as microhabitats for seedlings and saplings, and that is sufficient for mediating tree coexistence.