Showing papers in "Ecology in 1975"
TL;DR: The analyses suggest that realistic classes of consumer—resource models exist which do not obey Kolmogorov's Criteria but are nevertheless globally stable, and increases in maximum feeding rate may, under certain circumstances, result in decreases in consumer population.
Abstract: A nonlinear function general enough to include the effects of feeding saturation and intraspecific consumer interference is used to represent the transfer of material or energy from one trophic level to another. The function agrees with some recent experimental data on feeding rates. A model using this feeding rate function is subjected to equilibrium and stability analyses to ascertain its mathematical implications. The anaylses lead to several observations; for example, increases in maximum feeding rate may, under certain circumstances; result in decreases in consumer population and mutal interference between consumers is a major stabilizing factor in a nonlinear system. The analyses also suggest that realistic classes of consumer—resource models exist which do not obey Kolmogorov's Criteria but are nevertheless globally stable. See full-text article at JSTOR
1,036 citations
TL;DR: In this article, an explicit means of calculating the expected number of species and the variance of (sn) in a random sample of n individuals from a collection containing N individuals and S species is presented.
Abstract: An explicit means of calculating the expected number of species [E(Sn)] and the variance of (Sn) in a random sample of n individuals from a collection containing N individuals and S species is presented. An example illustrates a new use of E(Sn): determination of the sample size required for any desired degree of accuracy in collecting species known to occur in a particular area.
890 citations
TL;DR: In old—field ecosystems in the deciduous forest, plant species diversity generally increases with succession and reaches a maximum during the forest stage when structural diversity is highest and at the time when both shade—tolerant and shade—intolerant species are present together.
Abstract: In old—field ecosystems in the deciduous forest, plant species diversity generally increases with succession and reaches a maximum during the forest stage when structural diversity is highest and at the time when both shade—tolerant and shade—intolerant species are present together. Species diversity may be exceptionally high in succesional communities when there is a high degree of vertical and horizontal heterogeneity. Diversity may be exceptionally low in old—field ecosystems when there is strong dominance by species with alleolopathic chemicals or other effective interference methods. Species distribution curves are geometric during the first few years of succession and gradually change to lognormal as more species are added to the community, the process resulting in a high degree of evenness.
553 citations
TL;DR: Nine hummingbird—pollinated species of Heliconia occur together at Finca La Selva, in the wet Caribbean lowlands of Costa Rica, and appear to be specialized for pollination by either hermits on non—hermits, largely through components of the caloric phenotype.
Abstract: Nine hummingbird—pollinated species of Heliconia occur together at Finca La Selva, in the wet Caribbean lowlands of Costa Rica. In forest habitats, Heliconia clumps (clones) are typically small; in more open areas, many clumps attain large size. This probably reflects differences in light intensity and degree of vegetative competition in these habitats. Nine species of hummingbirds regularly visit Heliconia flowers at La Selva. The four hermits are nonterritorial, traplining foragers with long, curved bills. Non—hermits frequently hold territories at Heliconia clumps, and have short, straight bills. Pollination by hermits tends to produce more cross—pollination; territorial hummingbirds increase self—pollination. Different Heliconia species appear to be specialized for pollination by either hermits on non—hermits, largely through components of the caloric phenotype: amount and timing of nectar production, rate of inflorescene and flower production, and morphological paramerters that affect the energetic efficiency of nectar—harvesting hummingbirds. Habitat may influence pollination systems through its effects on clump size and thus on the number of flowers a clump can have at any one time. Ultimately, specialization for hermits or non—hermits may depend on the degree of self—compatibility of the different Heliconia species. Hermit—pollinated Heliconia mostly show sequential and nonoverlapping flowering peaks, probably resulting from competition for pollinators and/or selection against hybridization. Two hermit—pollinated species bloom simultanesoulsy, thereby inducing the birds to utilize an other—wise little—used microhabitat. Heliconia species pollinated by non—hermits bloom in the early to middle rainy season, and are mostly separated by habitat. Isolating mechanisms among sympatric Heliconia species involve both spatial and temporal patterns of partioning available pollinators. Floral parameters include mechanical (different site of pollen deposition on the bird) and ethological (caloric and visual factors affecting flower choice) mechanisms. Selection for pollinator specificity may result in convergence of blooming peaks, provided that other isolating mechanisms are present. Human activity has broken down some habitat barriers by producing large areas of second growth.
523 citations
TL;DR: The balance between these costs and gains appears to define the conditions when territorial defense in Golden-winged Sunbirds is advantageous.
Abstract: Feeding territories of Golden-winged Sunbirds contain enough energy to sup- port an individual's daily energy requirements, and the amount of nectar per flower inside a territory tends to average higher than in adjacent undefended flowers. When undefended nectar levels are low (especially below 2 /ul per flower) the costs of territorial defense can easily be offset by energy saved from shortened foraging time budgets made possible by feeding at the higher average nectar levels. At higher undefended nectar levels the costs of territorial defense should not be recoverable. The balance between these costs and gains appears to define the conditions when territorial defense in this species is advantageous.
477 citations
TL;DR: Competition for fruits was more important than competition for nectar and pollen in determining species diversity in this bat community, and a combination of the timing of plant—reproductive behavior and bat foraging characteristics promotes long—distance outcrossing and seed dispersal.
Abstract: Many tropical bats eat fruit, nectar, and pollen, and many tropical plants are pollinated or dispersed by bats. These groups make up a coevolved system that illustrates the effects plants can have on animal populations, and conversely, the effects animals can have on plant populations. This paper reports a 2—yr intensivie study of one bat—plant community in a seasonal Costa Rican forest. Seven common phyllostomatid bat species visited flowers or fruits. These were Glossophaga soricina, Phyllostomus discolor, Artibeus jamaicensis, Artibeus lituratus, Sturnira lilium, and Carollia perspecillata. The incidence of nectar ivory was high among these species, even among the species previously considered to be frugivores. Flora resources were seasonally abundant and competition for these resources appeared minimal during the period of peak abundance, but only G. ssoricina was nectarivorous during the period of low flower abundance. Fruit resources were more evenly available through the year and were more finely divided among the species of bats. There was a correlation between size of bat and the average size of fruits eaten. To the extent that competition for food has influenced the structure of this bat community, competition for fruits was more important than competition for nectar and pollen in determining species diversity. Resource distributions through space and time also infuenced bat foraging and reproductive behaviors. Small species of bats feed on resources of high abundance, whereas large species utilize resources that are patchy in time and space. The latter species probably forage in groups to maximize foraging efficiency. Reproductive behavior is seasonal and correlated with resource abundance. The flowering periods of plant species tend to be displaced, suggesting competition among plants for bat—pollinator services. A combination of the timing of plant—reproductive behavior and bat foraging characteristics promotes long—distance outcrossing and seed dispersal. These are critical factors in determining the low—density propulations characteristic of many tropical plant species.
475 citations
TL;DR: In this paper, the authors measured 15 communities along the elevation gradient from fir forest at high elevations, through pine forest, woodlands, and desert grassland, to deserts at low elevations in the Santa Catalina Mountains, Arizona, and in a Cercocarpus shrubland on limestone.
Abstract: Measurements were taken in 15 communities along the elevation gradient from fir forest at high elevations, through pine forest, woodlands, and desert grassland, to deserts at low elevations in the Santa Catalina Mountains, Arizona, and in a Cercocarpus shrubland on limestone. Eight small-tree and shrub species of woodlands and deserts were subjected to dimension analysis by the Brookhaven system. Aboveground biomass decreased along the elevation gradient from 36-79 dry kg/M2 in fir and Douglas-fir forest to 0.26-0.43 kg/M2 in the desert grassland and two desert samples. Net aboveground primary productivity similarly decreased from 1,050-1,150 g/m2 * yr in mesic high-elevation forests to 92-140 g/m2 - yr in desert grassland and deserts. Both biomass and production show a two-slope relation to elevation (and, probably, to precipitation), with a steeper decrease from the high-elevation forests to the mid-elevation woodlands, and a less steep decrease from dry woodlands through desert grassland into desert. The two groups of communities at higher vs. lower elevations also show different relations of leaf area index and chlorophyll to elevation and to productivity. The two groups may represent different adaptive patterns: surface-limiting, with low pro- ductivity in relation to precipitation but high production efficiency in relation to surface in the more arid lower elevations, vs. surface-abundant, with high productivity relative to pre- cipitation based on high community surface area, but lower production efficiency in relation to this area, in the more humid higher elevations. Vascular plant species diversity shows no simple relation to productivity, but decreases from high-elevation fir forests to the pine forests, increases from these to the open woodlands, and decreases from dry woodlands through the desert grassland and mountain slope desert to the lower bajada (creosotebush) desert.
442 citations
TL;DR: Intrinsic population growth rates calculated for eight species of prey and of their important predators showed that the prey had higher rates than their predators in two cases, in both of which the prey species are known to be self—limited.
Abstract: Models of prey—predator systems incorporating the intrinsic population growth rates of each species were analyzed mathematically and were also simulated. The behavior of the two basic models led to a hypothesis: either a stable prey population possesses strong self—limitation, e.g., territoriality, or the growth rate of the prey species is less than that of its predator. Intrinsic population growth rates calculated for eight species of prey and of their important predators showed that the prey had higher rates than their predators in two cases, in both of which the prey species are known to be self—limited. The prey and predator have approximately equal rates in the snowshoe hare and lynx, known to be cyclic. Five species of ungulates, lacking intraspecific population controls, had lower growth rates than their predators. Incorporation of two habitats, one with good and a second with poor cover for the prey, changed a limit cycle to a stable focus; this fits some observations of snowshoe hares. The properties with the greatest effect on stability shown by these models are prey self—limitation and predator searching time.
372 citations
TL;DR: Salamander tissue is higher in protein content than that of birds and mammals and represents a source of high-quality energy for potential predators, and is efficient at converting ingested energy into new tissue and produce more new tissue annually than do bird populations.
Abstract: Energy flow through salamander populations in the Hubbard Brook Ecosystem is about 11,000 kcal/ha yr (=46,000 kJ/ha yr). This is approx. = 0.02% of the net primary productivity, and is approx. = 20% of the energy flow through bird and mammal populations. Salamanders are efficient (60%) at converting ingested energy into new tissue and produce more new tissue annually than do bird populations. Salamanders are insignificant agents as sinks for nutrients or as agents for nutrient cycling in the ecosystem. Sodium is the possible exception, as an amount equivalent to >8% of the Na in annual litter fall passes through salamander populations; all other nutrients (Ca, Mg, K, P, N, S, and Zn) are that of most of their invertebrate prey. There is some evidence that invertebrates rich in Ca content, such as snails and mites, are necessary components of the diet of salamanders. Salamander tissue is higher in protein content than that of birds and mammals and represents a source of high-quality energy for potential predators. Salamanders have restricted home ranges and are not significant agents in the movement of nutrients into or out of the system.
331 citations
TL;DR: Results of tests indicated that early successional annuals were significantly more palatable than early succession perennials, and no correlation was found between palatability and evolutionary association of the herbivores with the plant species.
Abstract: Theoretical considerations and evidence from the literature suggest that early successional plant species should make a lesser commitment of resources to defense against herbivores, and should then provide better food sources for generalized herbivores than later successional and climax plants. Commitment to defense by plants is estimated by determining short-term palatabilities to two slug species; one native to western Washington, Ariolimax columbianus, and one introduced from Europe, Arion ater. Results of tests with 100 plant species of three growth forms and from different seral stages indicated that early successional annuals were significantly more palatable than early successional perennials which were sig- nificantly more palatable than later successional species. No correlation was found between palatability and evolutionary association of the herbivores with the plant species.
331 citations
TL;DR: The observed patterns of variation in life history are adaptive and take the agreement between theory and nature as a validation of the hypothesis that populations will in general differ from each other in the manner of their respective optima.
Abstract: In this paper variations in life history data among local populations of Atlantic salmon have been examined. The following patterns emerge: (1) The mean age of first spawning increases with the difficulty of upstream migration as estimated by the distance the fish ascend into freshwater. Other indices of river harshness yield similar results. (2) The effect of commercial fishing has been to eliminate larger and older fish from the run. Available evidence suggests that this has selected for an early age of first return on the Miramichi River and that the frequencies of genes coding for different ages of first spawning have been altered. (3) The mean age of first spawning is positively correlated with marine growth rates after the grilse stage. Rapid growth at sea subsequent to the grilse stage is associated with delayed reproduction; slower growth with an earlier age of first breeding. This result suggests different paths of high—seas migration. (4) The variability about the mean age of first spawning first increases and then decreases as one moves north over the salmon's range from Maine to Ungava. In addition, we have observed that these results are in accord with predictions made by recent theoretical analyses of the optimal reproductive response to differing environmental conditions. We, therefore, conclude that the observed patterns of variation in life history are adaptive. We further take the agreement between theory and nature as a validation of the hypothesis that populations will in general differ from each other in the manner of their respective optima.
TL;DR: Differences between two groups of fish show that switching behavior is more efficient and should be selected for, and confirms previous generaliza- tions about switching.
Abstract: Guppies (Poecilia ieticulatus) were given two prey: Drosoplhila (on the water surface) and tubificid worms (on the aquarium bottom). The densities of the two prey were varied gradually over 12 days, from 4:1 to 1:4, and we measured the predators' diets, time of each meal, and time spent at the top, middle, and bottom of the aquarium. The guppies switched, attacking disproportionately whichever of the two prey was more abundant. Switching resulted when the fish increased the fraction of time spent at the surface as the fraction of Drosoplhila available increased. They did this in response to changing reward rates. Switching caused density-dependent mortality. Differences between two groups of fish show that switching behavior is more efficient and should be selected for. The result confirms previous generaliza- tions about switching.
TL;DR: Compared the distributions of bird species common to two Andean localities, it now appears that competition, both direct and diffuse, accounts for something more than two—thirds of the distributional limits of Andean birds whose ranges end somewhere between the lowland plain and tree line.
Abstract: The object of our study was to compare the distributions of bird species common to two Andean localities in order to improve our understanding of the factors involved as primary causes in imposing distributional limits. A previous paper (Terborgh 1971) had evaluated the importance of three mechanisms in the avifauna of a control locality: (1) factors that vary continuously and in parallel with the elevational gradient, (2) competitive exclusion, and (3) ecotones. As was discussed in that paper, the method, when applied to a single transect, leads to a systematic underestimation of the incidence of competition—mediated limits and to an overestimation of ecotone effects. By studying appropriately selected test localities, we could overcome many of these deficiencies and obtain results that are several steps closer to expressing reality. The control locality, the Cordillera Vilcabamba, is a sector of the Cordillera Oriental, or eastern chain of the main body of the Peruvian Andes. It carries what may be regarded as a complete avifauna, as the transect sliced through a continuous belt of forested terrain which, at any elevation, is exposed to invasion by appropriately adapted species from above and below as well as laterally. It differs in this respect from the test locality (Cerros del Sira), which is an isolated massif that rises out of the Amazonian plain some 100 km east of the main Andes. Because of this isolation, the upper portions of the Sira are exposed to invasion principally from below. An estimated 80%—82% of the species that would have occupied the summit zone of the Sira, had it been a portion of the main body of the Andes, were missing. Such a species deficit provides an ideal test of the efficacy of competition in limiting distributions, because it invites whatever species are available as colonists (in this case, those lower on the mountain) to invade until the community is effectively filled. Of the species that had the opportunity to expand their elevational ranges in the absence of high—elevation congeners that apparently excluded them on the control transect, a minimum of 71% did so, confirming the original assignments of these as competition—limited species in the control locality. In addition, a majority (58%) of the species that had no high—elevation congener on the control transect (assigned to the gradient mechanism), and that had the opportunity to expand into the species—deficit zone of the Sira, were found to do so. This reveals that diffuse competition (as distinguished from the directly observable exclusion of congeners) was really the primary limiting mechanism for most of the species that had been assigned to the gradient mechanism in the control study. Instead of accounting for approximately a third of all distributional limits, as was concluded in the earlier report, it now appears that competition, both direct and diffuse, accounts for something more than two—thirds of the distributional limits of Andean birds whose ranges end somewhere between the lowland plain and tree line.
TL;DR: It is found that fish predation on a population of Bosmina longiros- tris is feeding according to visibility selection and that body-size selection is of negligible importance under these circumstances.
Abstract: We examine the effects of fish predation on a population of Bosmina longiros- tris (0. F. Muller), a small, limnetic cladoceran, in Gatun Lake, Panama. We test the relative importance of two different modes of predator selection: body-size selection, in which fish choose the largest of otherwise identically appearing individuals, and visibility selection, in which fish choose individuals having the greatest amount of body pigmentation. In B. longiros- tris, this pigmentation is most heavily concentrated in the large, black, compound eye of these otherwise transparent animals. We find that these predators are feeding according to visibility selection and that body-size selection is of negligible importance under these circumstances. We then discuss the general applicability of these findings, and the evolutionary consequences for prey populations under this type of selective pressure.
TL;DR: Computer studies by Gardner and Ashby (1970) show that large randomly connected systems have a decreasing probability of being stable as the number of connections increases, but if the food web is characterized by low assimilation efficiencies, a bias toward strong self-regulation of higher trophic level species, or a biases toward donor dependence the probability of stability can increase with increasing connectance.
Abstract: Computer studies by Gardner and Ashby (1970) show that large randomly connected systems have a decreasing probability of being stable as the number of connections increases. These conclusions are not appropriate to some plausible food web models. If the food web is characterized by low assimilation efficiencies, a bias toward strong self-regulation of higher trophic level species, or a bias toward donor dependence, the probability of stability can increase with increasing connectance.
TL;DR: Analyses of the movements and web-site characteristics of the desert spider Agelenopsis aperta (Gertsch) demonstrate that web locations offering the following habitat features are actively selected: shrubs, depressions, litter, and flowering herbs.
Abstract: Analyses of the movements and web-site characteristics of the desert spider Agelenopsis aperta (Gertsch) demonstrate that web locations offering the following habitat features are actively selected: shrubs, depressions, litter, and flowering herbs. A model of the effects of the thermal environment and prey avalability on the reproductive success of spiders occupying various web-site types is developed. The estimated productivity for an excel- lent web site (grassland depression with attractants) is 13X that determined for a poor site (lava surface). Model results suggest that more energy is to be obtained from selection of a favorable thermal environment (eight-fold difference) than from a site offering greater num- bers of prey (two-fold difference). The presence of flowers at web sites increases the prob- ability of receiving an occasional high prey density, whereas litter and habitat features pro- viding shade (shrubs and depressions) allow increased spider activity through limitation of body temperature.
TL;DR: The special adaptation of P. pugio to the low-oxygen environment of the decomposer system appeared to limit predation and competition, allowing the shrimp to develop large populations necessary to carry out its role effectively.
Abstract: The grass shrimp, Palaemonetes pugio, is a dominant species uniquely adapted to a highly stressed tidal marsh embayment. Monthly sampling of length and dry weight revealed that its life cycle was a single year, with spawning in May, June, and July and most rapid growth in late summer and fall. Mark and recapture estimates conducted quarterly and quadrat net estimates calculated monthly indicated that shrimp were present throughout the year and that densities peaked in the fall (over 1.2 million in 0.01 km2 in October). Pro- duction of biomass (growth) equaled loss to predation (including decomposition) over the annual cycle, averaging 0.2 kcal m-2 day-'. Respiration averaged 1.1 kcal m-2 day-'. Average daily production per square meter of "total consumables" (fecal pellets = 0.8 kcal, dissolved organic matter (DOM) - 0.7 kcal, biomass = 0.2 kcal) was 60% of total ingestion (2.9 kcal); production of feces and DOM thus outweighed biomass production 15:2. Microcosm studies and observations by scanning electron microscope revealed that shrimp macerated detritus into a heterogeneous assortment of uneaten particles by plucking away the cellular matrix from surfaces of large detrital fragments. This action provided cavities that became heavily invaded by pennate diatoms, and particles that became suspended in the water column and populated by bacteria. Nutrient analyses indicated the shrimp excreted large quantities of ammonia and phosphate which together with DOM release was presumably responsible for heavy growth of microflora and increased protein fraction in both feces and large and small uneaten detrital fragments. Palaemonetes pugio, while supporting its own trophic requirements, accelerated breakdown of detritus, preventing blockages or accumulations that might have occurred from pulses of emergent grass and macroalgal detritus in the embayment. This repackaging into feces, hetero- geneous fragments, DOM, and shrimp biomass made detrital energy available at a variety of trophic levels, smoothing out organic pulses over time and space, and raising the efficiency of transfer to the food web. The special adaptation of P. pugio to the low-oxygen environment of the decomposer system appeared to limit predation and competition, allowing the shrimp to develop large populations necessary to carry out its role effectively.
TL;DR: It is hypothesized that increased suibstratum complexity leads to greater species richness based on several lines of evidence: different species showed different substratum preferences, colonization of mixed stubstrata generally resulted in greater mean species richness than did colonization of a single substratum type, and both species diversity and substratum complexity were greatest at the within-microhabitat level.
Abstract: A bstract. Distributional patterns and species diversity of benthic insects in an alpine stream in Gunnison County, Colorado, USA were investigated on several levels of spatial scale, from faunal replacement over 1,000 vertical m to microdistribuLtion within the stony substratum. Ecotones including zonation in terrestrial vegetation and in trout distribution did not appear to affect faunal replacement. Competition among congeners accounted for 7-30% of the cases, while in the majority of species, faunal replacement appeared to be associated with gradual changes in the physical gradient. Trout zonation may affect total numbers of insects, however, as the trotut-free headwaters had two to six times higher insect densities. Microdistribution was investigated by measures of species and substratunm patterning in a series of microhabitats (0.093 mi) at a series of sites (separated by 75-150 vertical m), and by field colonization experiments with various substratum choices. I hypothesize that increased suibstratum complexity leads to greater species richness based on several lines of evidence: (I ) different species showed different substratum preferences, (2) colonization of mixed stubstrata generally resulted in greater mean species richness than did colonization of a single substr-atum type, and (3 ) both species diversity and substratum complexity were greatest at the within-microhabitat level. However, substratum composition showed little variation along the elevational gradient and did not appear to be a cause of faunal replacement. The several scales of investigation were complementary, as congeners exhibiting sharp mutuLal exclusion in vertical distribution had similar microhabitat preferences, while othercongeners showed less exclusion and differed in microhabitat preferences. Most of species diversity as measured by H' was found within habitats rather than between habitats while species richness depended equally upon within-habitat variation (owing to rare species) and between-habitat variation (owing to faunal replacement).
TL;DR: Summer movements of the fish Fundulus heteroclitus in a fluctuating tidal creek in Delaware were determined; most individuals maintained spatial position in an environment with no distinct break such as the riffle—pool structure of freshwater streams.
Abstract: Summer movements of the fish Fundulus heteroclitus in a fluctuating tidal creek in Delaware were determined. The majority of individuals in the population exhibited a home range of 36 m near a bank. Individuals transferred directly across the stream returned to the bank where originally captured. The home range persisted from July through September. Individuals were absent from the lower part of the creek from November through March, but were present in the headwater areas. There was a continuum of individuals along each bank; most individuals maintained spatial position in an environment with no distinct break such as the riffle—pool structure of freshwater streams. See full-text article at JSTOR
TL;DR: The potential general importance of age- and/or size-specific competition in reducing the efficiency of resource utilization in communities of organisms other than terrestrial homeotherms is suggested and contrasted to the current community models of competition.
Abstract: Studies of perturbed laboratory microcosm communities composed of algae and competing herbivorous microcrustaceans were conducted to assess the role(s) of various species compositions and patterns of resource consumption on the efficiency of resource utilization. Equilibrium microcosm communities, consisting of four competing species, three cladocerans, and an amphipod, were perturbed by different intensities of highly size-specific fish predation that resulted in altered species compositions (two or three additional species) and new equi- librium densities. Analyses of food particle consumption patterns, spatial distributions, and life history characteristics under the different predation intensities indicated the importance of microhabitat and food specializations in permitting coexistence of some species but exclusion of others. Age- and size-specific competition for limiting small (3-6 ,um) particles was especially important among young animals at low predation levels, whereas under high pre- dation, competition for larger particles among adults was more important. Analyses of particle uptake efficiencies in the different communities revealed very uneven use of available resources when the presence of efficient competitors for some foods produced developmental bottlenecks among the young of competing species. Resource utilization efficiencies were much less vari- able at equilibrium when predation reduced competition on the young. The potential general importance of age- and/or size-specific competition in reducing the efficiency of resource utilization in communities of organisms other than terrestrial homeotherms is suggested and contrasted to the current community models of competition.
TL;DR: The oviposition of the beetle fits a computer simulation that makes decisions after com- paring the weight and egg load of the present bean with the last bean encountered and shows that the beetle gains about 70% of the fitness that it could evolve.
Abstract: A sizeable fraction (7%-17%) of the mung beans that are the preferred food of Callosobruchus maculatus are not large enough to support two larvae. Whenever two or more eggs are on a bean, development takes 40 days rather than 33 days, and only 8% of the second eggs develop even in beans with resources enough for two larvae. This larval competition confers an advantage on females that disperse eggs uniformly. Females tend to avoid adding second eggs as long as there are unused beans. Survivorship of single eggs on beans increases with weight (1l = .005 mg + .368) and females oviposit on the largest of the unused beans first. Survivorship of the second egg (12 = .31), due principally to mortality of the first egg, is about half that of the first egg; a second or third egg is added after nearly all the beans carry one or two eggs respectively. With these constraints the beetle may maximize fitness if it knows the weights and egg loads of all available beans. The actual performance falls short of achieving maximum fitness and the oviposition of the beetle fits a computer simulation that makes decisions after com- paring the weight and egg load of the present bean with the last bean encountered. The per- formance of the beetle can be appropriately evaluated against models for unspecialized beetles that oviposit randomly and for beetles with maximum fitness. This shows that the beetle gains about 70% of the fitness that it could evolve.
TL;DR: There is some evidence for the hypothesis that ease of food obtainment may be an important factor in determining summer territorial size and location for the insectivorous lizard Sceloporus jarrovi.
Abstract: This study was designed to determine how food abundance affects territory size for the insectivorous lizard Sceloporus jarrovi Observations and experiments were per- formed in the field in southeastern Arizona during 1971 and 1972 summers Territories were defined as defended areas, and the convex polygon method was used to determine territorial boundaries Preliminary studies showed that all adult and most juvenile lizards defended territories against lizards of the same species, size, and sex Sex and body size influenced territory size Within size classes, territories of 8 8 averaged more than twice territory size of Y Y Lizards in the larger size class had territories more than twice those of smaller animals Natural food abundance, determined with adhesive-coated Masonite? boards, was inversely correlated with territory size Summer territories compressed significantly when food was added even though natural food supplies seemed adequate Territories returned to initial sizes with the removal of additional food Experiments involving the locations of concentrated food sources within the territory pro- vided some evidence for the hypothesis that ease of food obtainment may be an important factor in determining summer territorial size and location
TL;DR: All such indices, including equitability as measured by Pielou's J and J', Lloyd and Ghelardi's ratios, redun- dancy, and the scaled diversity formulations of Fager, are inappropriate for most ecological applications.
Abstract: Diversity indices are frequently applied in the form of ratios of absolute diver- sity to the maximum diversity possible. Regardless of whether the maximum diversity is de- fined to be limited by the number of species or by the number of individuals present, the re- sultant indices can be shown to possess mathematically undesirable qualities. All such indices, including equitability as measured by Pielou's J and J', Lloyd and Ghelardi's ratios, redun- dancy, and the scaled diversity formulations of Fager, are inappropriate for most ecological applications.
TL;DR: Some little-known properties of these forms for estimating competition matrix elements, aij, from utilization coefficients pia (which measure the relative utilization of the ath resource category by the ith species) are discussed.
Abstract: Recent theoretical and field work on communities of interacting species has employed various forms for estimating the competition matrix elements, aij, from utilization coefficients pia (which measure the relative utilization of the ath resource category by the ith species). Some little-known properties of these forms are discussed. When more than one resource dimension is involved, there is in general no substitute for measuring the species' full multidimensional utilization functions; a critical discussion is given of the estimation of such multidimensional competition coefficients aij by products or sums of one-dimensional coefficients.
TL;DR: The hypothesis that predation pressure permits increased niche overlap among prey species is sustained by analysis of a model in which a predator population has been added to the three species "limiting similarity" model of MacArthur and Levins (1967).
Abstract: The hypothesis that predation pressure permits increased niche overlap among prey species is sustained by analysis of a model in which a predator population has been added to the three species "limiting similarity" model of MacArthur and Levins (1967). Also, it is predicted that there is a relation between the niche separation distances among prey and properties of the predators, and that if predation pressure is strong enough there is no limiting similarity among prey; i.e., complete niche overlap should be possible.
TL;DR: The adult body size within species is inversely correlated with the length of the feeding season and directly correlated with prey availability during that period, as differences in diversity of prey and/or their year-round availability become less marked between hemispheres.
Abstract: Standard metabolism is estimated for the fin whale, Ba/aenloptera physalus, from the energy yield of lipid stores consumed while in regions of limited prey availability. The metabolic rate appears better described by a surface rather than a volumetric rule. The larger body size of some Antarctic Balaenoptera compared with those of the Northern Hemi- sphere is attributed to selection for body proportions that reduce the specific metabolic rate and establish an optimal surface area for deposition of a lipid cache. Such proportions allow short-term forays into areas where prey is extremely dense but of restricted seasonal avail- ability, and permit extended use of lipid stores during exclusion to warmer but less productive waters. Thus, adult body size within species is inversely correlated with the length of the feeding season and directly correlated with prey availability during that period. As differences in diversity of prey and/or their year-round availability become less marked between hemispheres, so do the body-size differences of the lesser rorquals. This is also applied to odontocetes. Thermal homeostasis is considered to be equally dependent upon morphology and behavior. Minimal densities of prey necessary for the maintenance of rorquals could be estimated from certain known parameters.
TL;DR: Polynomial and Gaussian regressions of cover against indirect ordination axes indicate that hog rooting within Gray Beech Forest is most intense in the mesic portion of the moisture gradient and decreases both on xeric, south—facing slopes and on more mesic, north-facing slopes.
Abstract: The European wild boar Sus scrofa L., an exotic species, entered the Great Smoky Mountains National Park during the 1940s. Because of their high reproductive potential and their adverse impact on the native flora and fauna, the wild hogs have become a major management problem within the park. During the summer of 1973, quadrat sampling of the canopy and understory of Gray Beech Forest was conducted in both the hog—free and hog—occupied sectors of the park. Removal of the herbaceous understory and other types of hog rooting damage showed no direct relationship to the importance of any individual canopy species, including beech Fagus grandifolia. Cover reduction was related, however, to the importance of mesic herbs in a plot. Polynomial and Gaussian regressions of cover against indirect ordination axes indicate that hog rooting within Gray Beech Forest is most intense in the mesic portion of the moisture gradient and decreases both on xeric, south—facing slopes and on more mesic, north—facing slopes. Understory cover in the most severely damaged plots was between 2% and 15%, while understory cover in hog—free plots in the same position on the moisture gradient was usually between 80% and 110%. Hog rooting significantly reduced the number of species in the most disturbed plots but had no effect on the H' values of the largest plot sizes sampled. High H' values for the damaged plots are related to the lack of succession after disturbance of the understory without removal of the canopy.
TL;DR: A possibility for Daphnia resting egg dispersal by fish-eating birds and mammals feeding on planktivores that prey selectively on ephippial Daphnian populations is suggested.
Abstract: In the spring and autumn, Daphnia populations may produce resting eggs con- tained in pigmented envelopes called ephippia. Pumpkinseed sunfish and yellow perch preyed selectively on ephippial over similarly sized, nonephippial Daphnia galeata mendotae Birge in Fuller Pond, Connecticut. The D. galeata mendotae with darker ephippia were consumed at a greater frequency than those with less pigmented ephippia. In the laboratory pumpkinseeds and red-spotted newts preyed selectively on ephippial over nonephippial Daphnia pulex Leydig under natural light intensities. Ephippium tanning and hardening probably evolved and persisted because of the increased protection given to the resting eggs after natural release of the ephippia from the maternal Daphnia. Darker ephippia retained their normal complement of two resting eggs twice as well as less pigmented ephippia did during passage through newt and perch digestive tracts. D. galeata mendotae and D. pulex ephippial eggs hatched after passage through pumpkinseed and yellowbelly sunfish, golden shiners, and newts. Seventy percent of the 27 planktivorous fish collected from Fuller Pond in October and November contained ephippia. Large numbers of ephippia were found within the digestive tracts of some of these perch and sunfish. Daphnia pulex and D. galeata mendotae ephippial eggs hatched after passage through a Black-Crowned Night Heron and laboratory rats. This suggests a possibility for Daphnia resting egg dispersal by fish-eating birds and mammals feeding on planktivores that prey selectively on ephippial Daphnia.
TL;DR: The wet tundra near Barrow, Alaska, is dominated by three species of graminoids: Dupontia fischeri, Carex aquatilis, and Eriophorum angustifolium, each species having a distinctive pattern and phenology.
Abstract: The wet tundra near Barrow, Alaska, is dominated by three species of graminoids: Dupontia fischeri, Carex aquatilis, and Eriophorum angustifolium. Root production, root turnover, and root distribution patterns of these three species were studied by direct observations of growing roots and by analysis of whole, interconnected tiller systems dug from the soil. Root weight per unit length and density of individual tillers were also measured in the field. Production of new roots was found to be strongly correlated with age of individual tillers, each species having a distinctive pattern and phenology. Root turnover rates also varied considerably; the range is from an annual turnover in E. angustifolium to 6—8(10) yr in C. aquatis. An estimated of root turnover on an ecosystem basis is about 100 g ° m—2 ° yr—2, or 25% of the live root biomass. Species with the shallowest and longest lived roots have the greatest weight per unit length of root, and vice versa. Each species has a characteristic root distribution pattern with depth and in relation to the progress of soil thaw.
TL;DR: It is concluded that many invertebrates and larval vertebrates eat prey as they are encountered while adult vertebrates feed as energy maximizers.
Abstract: Two models to predict the food of predators are proposed. They assume that prey size and prey abundance are the only availability factors of importance to predators. One model assumes that the predator consumes prey as they are encountered, and the other that predators feed to maximize their energy intake. Previous work, principally from aquatic situations, is examined to test the models. It is concluded that many invertebrates and larval vertebrates eat prey as they are encountered while adult vertebrates feed as energy maximizers. The limitations of the models are discussed and their relation to models of optimal diet examined.