Showing papers in "The American Naturalist in 1975"
TL;DR: In this article, sound propagation tests were made in forest, edge, and grassland habitats in Panama to quantify pure tone and random noise band sound transmission levels, and the sounds of birds in each habitat were analyzed to determine the emphasized frequency, frequency range, and sound type (whether pure tonelike or highly modulated).
Abstract: This study describes selection derived from habitat acoustics on the physical structure of avian sounds. Sound propagation tests were made in forest, edge, and grassland habitats in Panama to quantify pure tone and random noise band sound transmission levels. The sounds of bird species in each habitat were analyzed to determine the emphasized frequency, frequency range, and sound type (whether pure tonelike or highly modulated). Forest habitats differ from grass and edge in that a narrow range of frequencies (1,585-2,500 Hz) has lower sound attenuation than lower or higher frequencies. Attenuation increases rapidly above 2,500 Hz. Bird sounds from species occurring at the lower forest levels were found to be predominantly pure tonelike with a frequency emphasized averaging 2,200 Hz, conforming to the predictions based on sound propagation tests. The edge habitat is characterized by a wide range of frequencies having a generally similar attenuation rate. Pure tone and random noise band sounds did not diffe...
1,373 citations
TL;DR: A simple graphical model for maximization of total lifetime reproductive success is developed using the demographic parameters of current fecundity and residual reproductive value to estimate reproductive effort in single-clutched species.
Abstract: A simple graphical model for maximization of total lifetime reproductive success is developed using the demographic parameters of current fecundity and residual reproductive value. Trade-offs between present progeny and expectation of future offspring are treated in terms of costs and profits to lifetime reproductive success. Various limitations of the model and some relevant data are presented and discussed. Single-clutched species are distinguished from those that lay multiple clutches each reproductive season, because residual reproductive value in the latter group varies proportionally much more during ontogeny than in the former group. Some difficulties in measuring reproductive effort in a changing environment are pointed out.
654 citations
TL;DR: This paper inspects the role of body size in competition, using MacArthur's (1972) theoretical framework, and unifies two seemingly contradictory concepts that have become established over the past decade.
Abstract: One of the ways that animals are thought to coexist is by differences in their body sizes. Very simply, different sized animals eat different sized foods or otherwise utilize different resources, until at some point there is enough nonoverlap to allow coexistence. This paper inspects the role of body size in competition, using MacArthur's (1972) theoretical framework. As well as describing patterns of convergence and divergence, the model developed here unifies two seemingly contradictory concepts that have become established over the past decade: (1) the concept that differences in body size promote a \"niche difference\" (Hutchinson 1959; Brown and Wilson 1956; Schoener 1965, 1967, 1970, 1974a and b; Grant 1968, 1972), and (2) the concept that differences in body size set up a competitive gradient whereby the larger can exclude the smaller (Brooks and Dodson 1965; Galbraith 1967; Hall et al. 1971; but see Dodson 1974 and Zaret 1975 for alternative view).
541 citations
TL;DR: The theory thus explains how natural selection on individual parents can lead to population control through regulation of birth rates and behavioral mechanisms which seem to prevent overcrowding and starvation.
Abstract: Natural selection favors increases in the number of offspring produced by parents. However, evolutionary trends have drastically reduced the number of newborn produced, as animals and plants have become larger and more complex. Obviously, this has been accompanied by increases in survivorship, but a more complete theory is needed to explain why such sweeping trends have occurred in some organisms but not in others. Selection for low intrinisic rates of natural increase or birth rates may involve, in part, a lower amount of energy available for reproductive activities because of the demands of increased competition or predator avoidance in some environments (Cody 1966; Gill 1974; Hairston et al. 1970; MacArthur and Wilson 1967; Pianka 1970; Ricklefs 1970). However, intrinsic rates vary to a large extent because of the way energy is apportioned among offspring, whether among few or many (Gadgil and Solbrig 1972; Lack 1948b; Menge 1974; Svhrdson 1949; Williams 1966). The proportional expenditure for total reproductive effort doubtless varies within narrower limits than do birth rates. Smith and Fretwell (1974) analytically defined the optimum compromise between producing many small and few large offspring, thus initiating a more rigorous approach to the problem of selection for clutch size. A large task before us now is to construct a predictive theory on this framework by analyzing conditions and factors which cause the optimal resource allocation per offspring, inversely related to clutch or litter size, to be high or low. I attempt here to analyze the effects of several types of intraspecific competition, nonspecific mortality, and environmental instability on the optimal reproductive effort per offspring. The idea mentioned by Miller (1969) and Gill (1974) that the evolution of low intrinsic rates of population increase is related to interference competitive behavior will be developed with more rigor. Finally, I discuss some of the existing zoological evidence for certain critical assumptions and resulting predictions and some important implications of the theory with regard to population control.
465 citations
TL;DR: The pattern of sexual transformation eventually reached in a population is predictable through the use of a simulation model developed here, which suggests that the authors should see a rather sharp break in age-specific sex ratios in protogynous or protandrous populations.
Abstract: In some cases, sequential hermaphroditism can convey a selective advantage to an individual by increasing its reproductive potential relative to nontransforming members of the population. This is because age-specific fecundity in many populations is not distributed in the same way for males and females. By functioning as that sex which has the higher fecundity in a particular age span, an individual could increase its reproductive potential relative to lifetime males or females. The magnitude of the reward that comes from such sex changes depends on both the demography of the population and its spawning habits. Protandry may be selected for in populations where female fecundity increases with age and where individuals mate at random. Factors which favor the evolution of protogyny are those which tend to depress male fecundity values at early ages, such as inexperience, territoriality, or female mate selection. Selection for protogyny can also exist when female fecundity decreases with age, although this s...
439 citations
TL;DR: It is obvious that the set of prey choices which maximizes caloric intake may or may not constitute a balanced diet for the predator, so it is important to consider the problem of diet optimization with nutrient constraints.
Abstract: There is now a considerable literature on the theory of optimal diets To my knowledge, there has been no general consideration of the problem of caloric maximization given dietary constraints as to the minimum permissible quantities of essential nutrients It is obvious that the set of prey choices which maximizes caloric intake may or may not constitute a balanced diet for the predator Thus, it is important to consider the problem of diet optimization with nutrient constraints
347 citations
TL;DR: It is advanced that a diploid species has two differing systems of genetic variability, and speciation may occur as selection operates on the perturbed genetic system to organize new coadapted closed systems which come to characterize the new species.
Abstract: A hypothesis is advanced that a diploid species has two differing systems of genetic variability. The "open" system consists of polymorphic gene loci which recombine freely without drastic effects on viability. Examples are electrophoretic, polygenic, clinal, and subspecific variability. The "closed" system consists of blocks of genes forming coadapted, internally balanced gene complexes with or without the presence of inversions as a stabilizing mechanism. Perturbation of these blocks (supergenes) by crossing over results in greatly reduced viability under normal natural selection. These blocks vary between but not within species. When natural selection is relaxed, as during a populational flush-crash-founder cycle, the coadaptive balances of the closed system may become disorganized and one or more discordant individuals may survive. Speciation may occur as selection operates on the perturbed genetic system to organize new coadapted closed systems which come to characterize the new species.
343 citations
TL;DR: An open recombination system would be of immediate and manifest value to plant species experiencing pathogen and pest pressures which are intense, systematic, and capable of redirection in the event the host alters its defensive posture.
Abstract: An open recombination system would be of immediate and manifest value to plant species experiencing pathogen and pest pressures which are intense, systematic, and capable of redirection in the event the host alters its defensive posture. These pressures are most important in climax communities, well exemplified in the tropics and on ancient islands, where open recombination prevails and is promoted. The simple genetic bases for host resistance and pathogen or pest virulence, the vulnerability of species with restricted recombinations to disease epidemics and pest outbreaks, and the ability of pathogens and pests to rapidly evolve resistance to new natural or synthetic biocides provide the empirical superstructure for postulating why the genomes of K-selected species do not congeal.
309 citations
TL;DR: Two measures of how stabilizing a functional response is are proposed that predation be regarded as stabilizing at a prey density of H if the predation rate is increasing then-i.e., if f(H)/H is increasing where f is the functional response.
Abstract: We propose two measures of how stabilizing a functional response is. We suggest that predation be regarded as stabilizing at a prey density of H if the predation rate is increasing then-i.e., if f(H)/H is increasing where f is the functional response. This is equivalent to asking that an increase in prey density results in an increased chance of a given prey being killed by the predator. With Hm as the maximum value of H for which this criterion holds, our measures are Hm and f(Hm). We relate this criterion and these measures to local stability and also to structural stability in a modified Lotka-Volterra model and a general multispecies model. The criteria will be used in detailed models of switching in predators (in the following paper in this issue) and of patchiness.
294 citations
TL;DR: A number of authors have related ecological conditions to group size in birds and mammals to predict not only group sizes but sex ratios, sexual dimorphism, and mate-selection systems in response to resource distributions.
Abstract: The literature concerning animal group size follows a basic dichotomy. One approach entails mathematical descriptions of numbers within groups and their rates of change (e.g., Cohen 1969, 1972; Kingman 1969). These authors developed Markov population processes where the rates of arrival, departure, and transfer of individuals among groups are linear (open systems) or quadratic (closed systems) functions of individual group sizes (Cohen 1972). Cohen has estimated that primate group size frequencies tend to follow the negative binomial or will approach a Poisson distribution, if the arrival rate is zero or independent of group size. Analyzing Struhsaker's (1965) data on the number of individuals in vervet monkey sleeping groups, Cohen (1972) found a reasonable fit to the mathematically predicted distribution. While such an approach offers interesting descriptions of group size, it considers only some possible biological phenomena regulating these groups. Crook (1970) suggested that the numbers in vervet monkey sleeping groups were related to their ecology. He interpreted the dispersal of the troop into small nocturnal groups as an antipredator defense. The vervets selected sleeping sites for proper concealment, and each site provided protection for a limited number of monkeys, thereby regulating the size of individual groups. In this view, the troop's resource-the size of concealed sites-generated Cohen's (1972) negative binomial distribution. A number of authors have related ecological conditions to group size in birds and mammals. Avian flocking behavior and flock size have been correlated with increased foraging efficiency (Cody 1971; Horn 1968), hypothesized to reduce vulnerability to predation (Hamilton 1971; Vine 1971), and related to territorial defense (Brown 1963; Schoener 1971). Jarman (1974) suggested that ecological factors regulate both the minimum and maximum group sizes for African antelopes. Crook (1972) listed the ecological determinants of primate group size as predation pressure, food abundance, the distribution of other essential resources (e.g., water holes), and the optimization of time and energy budgets in response to resource distributions. Denham (1971) proposed a similar ecological model for primate sociality to predict not only group sizes but sex ratios, sexual dimorphism, and mate-selection systems. Each work hypothesized that group sizes are a response to environmental characteristics.
256 citations
TL;DR: It is hypothesized that few intermediate species exist, because host defenses are selected so strongly that the time span over which any species shows an intermediate rejection rate is of short duration, and the number of species in transition from accepter to rejecter is always low.
Abstract: Experiments investigating host defenses against the brood parasitism of the brown-headed cowbird revealed that, within most species, nearly all individuals either accept or reject cowbird eggs. Therefore, species are easily designated as "accepters" or "rejecters". The results of these experiments differ somewhat from data on natural cowbird parasitism, where some species seem to be variable in their response. However, much of what appears in natural cowbird parasitism to be variable expressions of host defenses are probably not responses specific to cowbird parasitism but are manifestations of standard avian behavior patterns. I hypothesize that few intermediate species exist, because host defenses are selected so strongly that the time span over which any species shows an intermediate rejection rate is of short duration. Hence, the number of species in transition from accepter to rejecter is always low. Most accepters did show low rates (less than 20%) of apparent rejection to experimental cowbird paras...
TL;DR: A model for the functional response of a predator feeding on two species of prey is considered, assuming that the predator searches randomly, at constant speed, for randomly distributed prey, but that whether it attacks a contacted prey will depend on the species of the prey, the species that was eaten last, and the time since the last meal.
Abstract: We consider a model for the functional response of a predator feeding on two species of prey. We assume that the predator searches randomly, at constant speed, for randomly distributed prey, but th...
TL;DR: Hard and soft selection are compared in a population subdivided into random mating subpopulations and the possibility for protected polymorphism is greater with soft than with hard selection.
Abstract: Hard and soft selection are compared in a population subdivided into random mating subpopulations. The possibility for protected polymorphism is greater with soft than with hard selection. Protected polymorphism is more readily achieved with increasing isolation, an effect that is more pronounced with hard selection. The results are discussed in relation to selection components.
TL;DR: Power-law equations of the type y = mxb (allometric equations) were used to compare a parameter y, such as brain weight, to another parameter x, often body weight, in individuals representing species of different size within a phyletic group and produced consistent empirical descriptions of the effects of growth and body size differences in adults.
Abstract: Since Cope (1885) argued that a persistent theme in evolution is a tendency for body size to increase during phylogeny, comparative zoologists have looked for regular rules which would characterize the change in animal form with body size. Beginning with DuBois (1898, quoted in Stahl and Gummerson 1967), power-law equations of the type y = mxb (allometric equations) were used to compare a parameter y, such as brain weight, to another parameter x, often body weight, in individuals representing species of different size within a phyletic group. The method produced consistent empirical descriptions of the effects of growth and body size differences in adults. Brody (1945, pp. 615-617) made extensive use of the method in his Bioenergetics and Growth. Davis (1962) reported on organ weight relationships in cats, and Stahl (1965) and Stahl and Gummerson (1967) presented data on organ weights and somatic measurements in primates. Stahl (1963) also reviewed the literature on biological similarity. Writers seeking the meaning of allometric rules have mainly followed Huxley's (1932) interpretation for "relative growth": a particular variable y (e.g., brain weight, or perhaps metabolic rate) and another variable x (e.g., body weight) are like two sets of capital that grow in the bank at different rates of interest. These rates of interest are a given fixed multiple of each other, so that (dy/ydt) = b(dx/xdt). Although this interpretation has been repeated by many authors, its usefulness seems scant, because it does not illuminate the question why some anatomical or physiological parameters would grow at different rates of interest than others. Allometry literally means "by a different measure," as opposed to isometry, "by the same measure" (Gould 1966). In the case of isometry, an organism or piece of machinery is scaled up in such a way as to maintain geometric similarity, so that all the dimensions of the small object are multiplied by the same factor in designing the larger one. It is frequently impossible to design a large machine to work the same way a small model works while maintaining perfect isometry between the two. A large pendulum clock, for example, will not keep time synchronously with a perfect model of itself made to a smaller scale, because the period of the pendulum depends on the square root of its length. Only if one makes changes in the gearing can the hands of the small clock keep time with those of the large.
TL;DR: The main aim of this paper is to present an orderly framework within which to assemble such data, and to unify a large number of numerical simulations of such situations, some of which have been done for a stepped environmental gradient and others for a continuous selection gradient.
Abstract: Suppose we have a cline in gene frequency which results from spatially varying selection forces (which tend to establish the cline) opposed by gene flow (which tends to blur the cline). The charact...
TL;DR: It is concluded that certain insects cross hard-surface roads by the shortest possible route in a tropistic response to the symmetry of radiant energy coming from up and down the road.
Abstract: So we may conclude that certain insects cross hard-surface roads by the shortest possible route in a tropistic response to the symmetry of radiant energy coming from up and down the road. The response is made by both flying and crawling insects, but it is not made by all flying insects (e.g., dragonflies). Such behavior has survival value for crawling insects, for it causes them to spend the least possible time on hot and heavily traveled highways. Similarly, this response leads insects to cross bare spots of the earth in the shortest possible time.
TL;DR: A linear model for population dynamics in stochastic environments is introduced by linearizing the logistic equation in discrete time for small stochastically variations around a large average carrying capacity and population extinction due to a fluctuating K is shown to be related to two issues.
Abstract: 1. A linear model for population dynamics in stochastic environments is introduced by linearizing the logistic equation in discrete time for small stochastic variations around a large average carrying capacity. The analysis of this model involves the relatively simple mathematics of time-series analysis and is not restricted to white noise (i.e., totally unpredictable) environments. 2. In this linear model the population size at any time is a reflection of many historical effects. The intrinsic rate of increase, r, is a measure of the responsiveness of the population to changes in k. A responsive population (r ≈ 1) does not retain historical effects for long, whereas a sluggish population (r ≈ 0) does. 3. The variance of the population size through time always increases with r. But the presence of much predictability in the environment, as measured by the serial correlation between consecutive values of K, reduces the influence of r. High serial correlation allows time for even a sluggish population to ac...
TL;DR: A cautionary moral is given: simple competition systems that appear to be unstable and random may be stable and deterministic.
Abstract: A three-species Lotka-Volterra competition community may exhibit population oscillations of a neutral or undamped nature. Nontransitive interference competition, in which 1 can exclude 2, 2 can exclude 3, but 3 can exclude 1, is the underlying mechanism. If immigration, incomplete spatial overlap, or any other mechanism prevents extinction, then such a three-species system must go into true limit cycles. For higher-dimension systems, limit cycles are more likely in communities with an odd number of species. Such limit cycles are most likely to be found in the tropics. A cautionary moral is given: simple competition systems that appear to be unstable and random may be stable and deterministic.
TL;DR: The genetic substructuring of the L. cylindracea population is attributed to restricted gene flow, and the role of pollinator behavior and seed dispersal in population substructureuring is discussed.
Abstract: An analysis of genetic population structure and local differentiation was conducted in the obligatory outbreeding prairie herb Liatris cylindracea. A single population located along an environmental gradient on a hillside in Zion, Lake County, Illinois, was divided into 60 3-m2 quadrats, the quadrat size approximating the neighborhood size of Liatris. Gene frequencies of 15 polymorphic and 12 monomorphic allozyme loci were determined on a per quadrat basis. The population exhibited marked local genetic differentiation; gene frequencies sometimes varied as much as 20% between adjacent quadrats. Correlation of gene frequency with edaphic factors at the site proved non-significant at 13 loci and negatively correlated at two loci, Est3 and Per-. Population structure was analyzed by both χ2 and F statistics. Both FIS, the within-subdivision deviation from Hardy-Weinberg equilibrium frequencies, and FST, the degree of population substructuring, are significant, with FIS values ranging from 0.1 to 0.506 and FST ...
TL;DR: It is shown that a haploid model embodying the latter two assumptions violates the first, forming larger and larger clumps of individuals separated by greater and greater distances, so the model is biologically irrelevant, even though it is possible to use it to calculate probabilities of genetic identity at different distances.
Abstract: Malecot's models of isolation by distance seem to assume random distribution in space, Poisson distribution of offspring number, and independent migration of individuals. These assumptions are inconsistent. By calculating the probability of joint occupancy of two locations at a distance x, it is shown that a haploid model embodying the latter two assumptions violates the first, forming larger and larger clumps of individuals separated by greater and greater distances. Thus the model is biologically irrelevant, even though it is possible to use it to calculate probabilities of genetic identity at different distances. The formation of these clumps is verified by computer simulation. The same phenomenon occurs in two- and three-dimensional models. In models of finite regions (a circle or a torus), the formation of clumps takes the form of the certainty of ultimate local extinction of the organism in each region. This does not occur if we hold the number of individuals on the circle or torus constant, but con...
TL;DR: The studies described here were undertaken to evaluate possible correlations among altitude, latitude, and vegetation with some properties of the song of the rufous-collared sparrow,* Zonotrichia cacpensis.
Abstract: The studies described here were undertaken to evaluate possible correlations among altitude, latitude, and vegetation with some properties of the song of the rufous-collared sparrow,* Zonotrichia cacpensis. Zonotrichia capensis occurs from the state of Chiapas, in southern Mexico, to Cape Horn, in southernmost Patagonia, a transequatorial distance of 6,400 kin. Zonotrichia casensis can be found from sea level to 4,700 in in the Bolivian high Andes (Chapman 1940). It is a bird typical of open spaces; in forested areas it is found in clearings and along streams and roads. Song in the rufous-collared sparrow is a typically male behavior (Miller and Miller 1968; King 1972; Nottebohm and Nottebohm 1975). Though usually delivered in a territorial context, it can also be heard from birds in migratory flocks. Over most of its range the song of the rufous-collared sparrow is composed of one to five usually dissimilar introductory whistles, followed by a series of identical repetitions of another, usually briefer, note. The introductory whistles often vary considerably between individuals singing at the same locality, and determine the \"theme\" sung by each bird. The terminal trill can remain relatively homogeneous over vast areas, and its characteristics tend to be shared by all birds at one locality, thus determining the \"dialect\" sung by a bird. Whereas a majority of rufous-collared sparrows sing just one song type, a small percentage of individuals have song repertoires of two or three different songs (Nottebohm 1969; King 1972). Some individuals singing at or near dialect interphases have two themes, each ending with a different trill which matches one of the two dialect variants coming into contact. A pilot experiment (Egli 1971) suggests that Z. capensis learns its song by imitating other conspecifics and that choice of model occurs during the first 40 days after hatching,
TL;DR: It appears from manipulation of the parameters of the theoretical model that in general mid-latitude streams contain more regionally controlled rheophile species and that those species have the effect of being able to rapidly exploit the resources to the temporary exclusion of some locally controlled species.
Abstract: A quantitative comparison based on statistically smooth species-sample curves between tropical and mid-latitude species richness for rheophile insects from seven mid-latitude and nine tropical stream samples is presented. Actual data in the form of accumulated numbers of species compared with numbers of rocks taken from riffle sites are applied to a mathematical model in order to estimate numbers of species that should be present in a given area. Species-sample curves show that species richness of rheophile insects is significantly higher at a theoretical sample size of 100 rocks for tropical streams than it is for mid-latitude streams. This trend is not obvious until 20 or 25 rocks have been sampled. The results suggest to us that earlier studies indicating no differences in species richness between the two latitudinal regimes were based on inadequate sampling. Altitudinal trends exist between lowland and mid-elevation tropical sites. Seasonal differences were also observed for a tropical stream sampled ...
TL;DR: Properties of population samples of three species of Typha conformed to the theory that r-selected genotypes have a greater developmental speed and higher fecundity and there is a selective trade-off between mechanisms contributing to colonization potential and those contributing to competitive potential.
Abstract: A comparison of environmental and population parameters between sites differing in length of frost-free period indicated that populations from short growing season locations should be more subject to r-selection, while populations from locations with a long growing season should be more subject to K-selection. Properties of population samples of three species of Typha conformed to the theory. Specifically, the following hypotheses were confirmed: (i) r-selected genotypes have a greater developmental speed; (ii) r-selected genotypes have higher fecundity; (iii) r-selected genotypes produce more offspring, but invest less energy in each offspring; (iv) r-selected genotypes show less evidence of selection for traits increasing competitive ability in high density situations; (v) there is a selective trade-off between mechanisms contributing to colonization potential and those contributing to competitive potential. Superimposed on the selection pattern along the climatic gradient was an r-K dichotomy between t...
TL;DR: Analysis of the size, abundance, and motility of insectivores, including insectivorous insects, should predict the relative abundance in particular habitats of species of the various guilds of web and nonweb spider modes, as well as the species, degree of specialization for prey size or for habitat.
Abstract: Several classifications of foraging manner are related along two axes: the time (from within feeding bouts to among generations) during which locomotion occurs, and the actual level of locomotion. Habitat specialization as "searchers" seems to occur in large species of araneid (orb-web) spider and in small species of salticid (jumping) spider, while small araneid and large salticid species seem to show more specialization for size of prey as "pursuers." The use of larger prey by web than by nonweb spiders is related to the peaked lognormal curve of abundance of insects. Specialization for prey size as a pursuer, then, seems more common in spiders using prey of intermediate sizes, which are most abundant. Specialists for habitat are more usual at the two tails of the insect (prey) abundance curve. The use of nets and poison apparently increases the size of prey used, relative to the predator's size, since web spiders take larger prey than nonweb spiders and the latter take larger prey than chewing insectiv...
TL;DR: Data are consistent with the thesis that congeneric and conspecific populations in different habitats have partially independent evolutionary pathways and that where populations have been displaced from a less to a more uniform environment, characters which are no longer maintained by selection pressure are lost.
Abstract: Past studies of ecogeographic character variations have failed to provide a quantitative relationship between the character being measured and the environmental parameter which impinges upon that character. We offer an example in amphibians directly relating a character variation, the range of temperature tolerance, and the critical environmental parameter for that character, the environmental temperature variation. In this example, the range of temperature tolerance is closely related to the environmental temperature variations. Where the environmental temperature variation increases so does the range of temperature tolerance. In addition, where environmental temperatures decrease, the capacity to tolerate such temperatures is lost. These data are consistent with the thesis that congeneric and conspecific populations in different habitats have partially independent evolutionary pathways and that where populations have been displaced from a less to a more uniform environment, characters which are no longe...
TL;DR: It is predicted that the territorial species or sexes of hummingbirds within any given community will be found to have higher wing disc loading than the nonterritorial birds.
Abstract: Nectivorous hummingbirds have two distinct foraging strategies. Territorial individuals exploit and defend high densities of flowers; nonterritorial ("traplining") individuals visit but do not defend dispersed flowers. Wing disc loading (ratio of body weight to area swept out by wings) and the cost of hovering flight were estimated for species in both groups. Trapliners have longer wings relative to body size, lower wing disc loading, and apparently lower energy requirements for hovering flight than territorial birds. This relationship of wing disc loading to foraging strategy also occurs within species that exhibit sexual dimorphism in foraging behavior. Therefore, we predict that the territorial species or sexes of hummingbirds within any given community will be found to have higher wing disc loading than the nonterritorial birds.
TL;DR: A theory of habitat selection is developed which is intended to apply with some realism to the settlement behavior of planktonic larvae of marine organisms and the relative attractiveness of species of fucoid algae as substrates for Spirorbis larvae is shown to differ between populations of SpirorbIS.
Abstract: A theory of habitat selection is developed which, although fairly general in form, is intended to apply with some realism to the settlement behavior of planktonic larvae of marine organisms. It is assumed that different substrates represent different habitats and that the environment can be heterogenous on two scales of distance: (1) a "fine grained" heterogeneity in which larvae are exposed to a homogeneous mixture of substrate types during the settlement period, and (2) a "course grained" heterogeneity in which the composition of the mixture varies from place to place. The objective is to predict whether settlement will occur on both substrates in the fine grained mixtures or only on one--in other words, whether larvae will exhibit habitat preference. Settlement behavior is treated as an absorbing Markov chain in which the transition probabilities are the probability on encountering a substrate, the probability of metamorphosing on it, the probability of adult survival and the probability of death in th...
TL;DR: In the literature, the concept of stability is often implicit and vague as discussed by the authors, which may reflect an analytic approach developed in one area because it was useful and then transferred to another where it may not be.
Abstract: Recently, many articles and books, both popular and scientific, have discussed perturbations and other disturbances of natural ecosystems. Many of these discussions are predicated on concepts of stability. However, explicit analyses of stability generally occur in contexts of specific mathematical models, and the specificity of these models may obscure the ecological significance of the definition of stability employed. As Holling (1974) has said: \"Our traditions of analysis in theoretical and empirical ecology have been largely inherited from developments in classical physics and its applied variants. . . . It is similarly important, if a quantity fluctuates, to know its amplitude and period of fluctuation. But this orientation may simply reflect an analytic approach developed in one area because it was useful and then transferred to another where it may not be.\" In the anecdotal literature, the concept of stability is often implicit and vague. Where defined explicitly, the concept is borrowed from, or equivalent to, the classical mechanics definition of a system that will tend to return to its equilibrium state, at rest, after being perturbed; we label this property static stability.' For example, the International Biological Program Grassland Biome \"Glossary of Systems Ecology Terms\" (Woodmansee 1974) defines a stable system as \". . . one that tends to return to initial conditions after being disturbed. It may overshoot and oscillate (like a simple pendulum that is set in motion), but the disturbances decline and die out.\" Equivalent definitions of stability occur in modern ecology texts such as Krebs (1972), Odum (1971), McNaughton and Wolf (1973), and Smith (1974). May (1973) presents an extensive account of the elegant mathematical analysis of ecosystem static stability. Static stability underlies the definitions of stability found in standard treatises on systems theory, e.g., Freeman (1964), Lee and Marcus (1967), Schwartz and Friedlanld (1965), and Zadeh and Desoer (1963).
TL;DR: A model of nutrient-limited phytoplankton growth, based on Michaelis-Menten uptake kinetics, is offered as an explanation of the so-called paradox of the plankton.
Abstract: A model of nutrient-limited phytoplankton growth, based on Michaelis-Menten uptake kinetics, is offered as an explanation of the so-called paradox of the plankton. The model suggests that an assemblage of coexisting phytoplankton may be limited by several nutrients, each species principally limited by the availability of a different nutrient. The principal requirement of the model is that each species be less effective at obtaining at low concentration the nutrient of which it requires larger amounts for continued growth. The model offers an explanation for the continued coexistence of associated phytoplankters in a stable equilibrium. It also offers a possible explanation for the decreased diversity commonly observed in eutrophic lakes and is consistent with observations that a larger number of different nutrients are in short supply in oligotrophic waters.
TL;DR: The sunbird foraging behavior is consistent with predictions based on maximizing foraging efficiencies as a function of relative energy value of the two flower types, and those species which should derive greater energy benefits by taking higher proportions of closed flowers tend to do so.
Abstract: Sunbirds (Nectariniidae) feeding on nectar of the mistletoe, Phragmanthera dshallensis, in central Kenya encounter two types of flowers. Closed flowers, which have not been visited previously and must be opened by the feeding bird, contain more nectar and require more feeding time than open flowers. Open flowers result from the visitation and explosive opening of closed flowers. Closed flowers are rarer overall than open flowers, although occasionally a local area may have a majority of closed flowers. The different-sized sunbird species tend to take different proportions of open and closed flowers; generally there is a positive relation between bird size and percentage of closed flowers taken. We examined benefits and costs for each bird species feeding in local patches of mistletoe. The benefits were the same for each species. The time costs varied inversely with bird size. These differences were reduced by the lower energetic costs of the smaller species. For all species the caloric benefit to cost rat...