bluuebunny/crossref_metadata_2025 huggingface dataset:
Gull Chick Survival: The Significance of Growth Rates, Timing of Breeding and Territory Size
Authors: Hunt George L. , Hunt Molly Warner
Published: May 2006

In a 2—yr study of the survival of Glaucous—winged Gull (Larus glaucescens) chicks, pecking of trespassing chicks by neighboring adults was the major cause of chick mortality. In years of both low and high food availability chick survival was strongly correlated with growth rates. Chicks that grew slowly were more likely to be killed by neighbors than fast—growing chicks. In the year of low food availability, among slow—growing chicks, those hatched early in the season on large territories had better survival rates than chicks hatched late in the season on small territories. In the year of high food availability, timing of breeding and territory size had little bearing on chick survival. A model of chick survival in relation to timing of breeding predicts that when neighbor interference is the major cause of chick mortality, chicks hatched early in the season will have the highest probability of surviving. When predators are the major cause of chick mortality, chicks hatching in the middle of the breeding season will have highest survival. A second model relates chick survival to territory size. Chicks raised on large territories will most likely avoid neighbor interference, while predation will select for either small or large territory size, depending upon the effectiveness of group mobbing against the predator.
Dispersal of Larvae of the Tenebrionid Beetle, Zophobas Rugipes, in Relation to Weight and Crowding
Authors: Tschinkel Walter R. , van Belle Gerald
Published: May 2006

When larvae of the tenebrionid beetle, Zophobas rugipes, were allowed to disperse among 26 equivalent chambers in a circular dispersarium, distribution patterns were found to be a function of larval weight and number of larvae in the apparatus (N). Small larvae (x wt 250 mg) were significantly aggregated while larvae mature larvae ( 1000 mg) where highly overdispersed. Medium larvae were intermediate, being overdispersed when N was 26 and showing some aggregation within general overdispersion when N was 52. Larval distributions did not deviate significantly from randomness when N was 13, indicating weak interactions at low density. The increasing tendency to overdisperse with increasing larval weight correlates with the parallel increasing tendency to pupate. Since metamorphosis of Zophobas rugipes larvae is known to be inhibited by crowding, this weight—related overdispersal probably allows pupation by mature larvae by causing them to leave regions of high population density.
Coexistence, Coevolution and Convergent Evolution in Seabird Communities: A Comment
Authors: Bedard Jean
Published: May 2006

A recent article paralleling two seabird (Alcidae) communities of the North Pacific and the North Atlantic oceans in reviewed critically. The quantitative basis upon which the argument of spatial segregation is based is demonstrated to be ethereal at best. Doubts are also raised about the appropriateness of comparing a fragment of a large North Pacific community, lacking many of its important elements, with an entire North Atlantic one. The model of ecological segregation proposed for these birds in burdened with shortcomings and cannot adequately describe any significant trait of the organization of the bird communities involved.
Experimental Ecological Genetics in Plantago II. Lead Tolerance in Plantago Lanceolata and Cynodon Dactylon from a Roadside
Authors: Wu Lin , Antonovics Janis
Published: May 2006

A population of Plantago lanceolata (ribwort plantain) from a roadside was found to have higher Pb tolerance than populations away from the roadside; this reflected the sharp differences in Pb content of the soil and the plants at these sites. Tolerance tests on seedlings showed that the Pb tolerance was transmitted to seed progeny. Cynodon dactylon (Bermuda grass) showed generally a higher Pb tolerance than P. lanceolata, but there was no evidence of a greater Pb tolerance of the roadside population when compared with populations from control sites. These results suggest that the Pb level found at the roadside was sufficiently high to impose selection pressure for the evolution of tolerance in a sensitive species, but no overt effect was seen in a species with a greater inherent tolerance. This provides another example of rapid and highly localized evolutionary change in plants.
Effects of the Spawning Migration of the Alewife, Alosa Pseudoharengus, on Freshwater Ecosystems
Authors: Durbin Ann Gall , Nixon Scott W. , Oviatt Candace A.
Published: May 2006

The influx of large numbers of alewife, Alosa pseudoharengus, into relatively small freshwater systems may have a considerable impact upon pre—established food chains and nutrient cycles. We estimate the total nutrient input to Pausacaco Pond, Rhode Island, USA, from alewives amounted to 0.43 g P, 2.7 g N, and 16.8 g/Cm2 over a 2—mo period. This is largely through mortality of the spawning fish, and to a lesser extent through excretion. These inputs were much greater than the eventual nutrient loss to the system through emigration of juvenile fish. In tank experiments using pond microcosms, the initial response to the addition of the fish was a large phytoplankton bloom and an increase in litter respiration. The phytoplankton bloom was short—lived, and the most lasting effort was an increase in production and respiration in the leaf litter. This increased production in the litter community would support a long lasting supply of insect and benthic invertebrate food for young fish. The respiration rate of autumn leaves incubated in alewife streams during the migration was significantly higher than that of leaves incubated simultaneously in a stream which had no alewife run. Respiration rates of leaves incubated in the same streams before the arrival of alewives did not differ significantly. The increase in litter respiration, an indication of microbial and invertebrate activity on the leaf surface, was attributed to the additional nutrients supplied by the fish.
Prey Species Replacement along a Gradient of Nutrient Enrichment: A Graphical Approach
Authors: Armstrong Robert A.
Published: May 2006

In this paper I develop a graphical method for visualizing and analyzing the effects of nutrient enrichment on the equilibrium characteristics of 1—predator, many—prey systems. The system considered consists of 1 nonswitching, prey—limited predator feeding on an array of prey species which complete for a single resource. The replacement of 1 prey species by another as eutrophication proceeds is an integral part of this model. The model predicts that prey species which can survive at low nutrient densities should be replaced at higher nutrient densities by species with high maximum rates of increase and by species more resistant to predation. This prediction may be reversed when the predator's population size is controlled by mechanisms which inhibit the predator's ability to respond numerically to increased prey density. Both predictions can be understood in terms of shifts in the relative importances of competition and predation as the nutrient status of a system changes. The graphical method presented should be particularly adaptable to empirical studies of species change along gradients of nutrient enrichment.
Community Structure of Neotropical Flower Visiting Bees and Wasps: Diversity and Phenology
Authors: Heithaus E. Raymond
Published: May 2006

This study examines the species richness of bees and flower visiting wasps in seasonal neotropical habitats in Costa Rica. A total of 9231 individuals were netted at flowers. These represented 192 species of bees and 138 species of wasps. Over 50% of the bee individuals were eusocial Apidae, but there were only 12% of the bee species. There was less dominance among the wasp families. Most of the species in both groups were uncommon: 50% of the bee species were represented by fewer than 8 individuals, and over 50% of the wasp species had only 1 or 2 individuals. Previous comparisons of the species richness of bees in tropical and temperature areas have been complicated by different sample sizes and a lack of distinguishing within— and between—habitat diversity components. Here, comparisons are made of within—habitat species richness for structurally similar habitats. The within—habitat species richness of bees was higher in tropical forests than in the temperate forests previously described. The tropical grassland had lower bee species richness, and it is postulated that the coevolutionary history of a habitat is an important component of bee diversity. The higher species richness of tropical forests was correlated with the abundance and diversity of animal—pollinated plants. Tropical bees were not more temporally specialized despite the longer flowering seasons, so diversity and temporal specialization were not correlated. The average flight season of tropical species was 3 times longer than that reported for bees in most temperate areas, and the turnover in species was also similar. Seasonality was correlated with the degree of species' sociality: eusocial bees were essentially aseasonal. Most seasonal bee species were encountered in the dry season. Flower visiting wasps were much more diverse in the tropical habitats than reported for temperate habitats, and they overlap with bees in resource use. Many other taxa also fed at flowers, and such diversity among competitors may be a factor in limiting bee diversity in the tropics.
Effects of Insolation on Juvenile Herring Gull Energetics and Behavior
Authors: Lustick Sheldon , Battersby Brian , Kelty Michael
Published: May 2006

The interaction of insolation, wind, and ambient temperature on the energetics and behavior of juvenile Herring Gulls was studied. At low ambient temperatures gulls can reduce their energy expenditure for thermoregulation as much as 29% by basking. Insolation at ambient temperatures above 15°C was stressful to the gulls because the thermal gradient was into the bird. The feet were found to be an important means of heat loss in birds at high and moderate ambient temperatures receiving insolation. Under natural conditions the use of the microhabitat is extremely important in minimizing the effects of radiation both during the day and at night.
The Measurement of Niche Overlap and Some Relatives
Authors: Hurlbert Stuart H.
Published: May 2006

Existing overlap indices are examined and are judged to be inadequate on the grounds (1) that they lack simple and appropriate biological interpretations, and (2) that they ignore possible variation among resource states in abundance or availability (a_i). Two indices interpretable in terms of encounters are proposed. Niche overlap (L) is measured as the degree to which frequency of interspecific encounter is higher or lower than it would be if each species utilized each resource state in proportion to its abundance (a_i). Directional overlap (Z_(xy)) is measured as the density of species Y encountered, on the average, by an individual of species X. When resource states are equal in size, L is equivalent to Lloyd's `interspecies patchiness,' and Z_(x(y)) is equivalent to his `mean crowding on species 1 by species 2.' Indices which in corporate variation in resource state abundance are also developed for mean crowding, patchiness and niche breadth.
Landscape Patterns and Forest History in the Boundary Waters Canoe Area, Minnesota: A Pollen Study From Hug Lake
Authors: Swain Albert M.
Published: May 2006

Paleoecological studies of the past 400 yr indicate that the mosaic of vegetation patterns in the Boundary Waters Canoe Area in northeastern Minnesota USA appears to be related to topography and presence of large lakes, and to the ways in which these features influence periodic forest fires. Pollen and charcoal analyses from a site (Hug Lake) located in primarily deciduous forest were compared to those from Lake of the Clouds which is located in a region dominated by coniferous forest. The results showed that the average interval between fires at both sites was similar (70 yr), but the absence of conifers in the area surrounding Hug Lake probably was related to the lack of effective firebreaks such as steep topography and large lakes that are essential for the survival of conifers when regional fire frequency is high. The deciduous character of the forests around Hug Lake has existed for at least 400 yr and was not the result of several large fires that occurred in the area during the 1800's.
Biomass, Production, and Changes in the Availability of Light, Water, and Nutrients During the Development of Pure Stands of the Chaparral Shrub, Ceanothus Megacarpus, After Fire
Authors: Schlesinger William H. , Gill David S.
Published: May 2006

Pure stands of the evergeen shrub, Ceanothus megacarpus, attain a mean of 4871 g/m2 in aboveground live biomass in 21 yr of growth after fire in the Santa Ynez Mountains of California. Mean net aboveground primary productivity is 850 g°m—2°y—1. In 21—yr—old stands there is also 990 g/m2 of attached dead wood as lower branches on the living shrubs and 476 g/m2 of standing dead shrubs that have died during the thinning of these stands due to intraspecific competition. During stand development, leaf—area—index increases to 1.6 m2/m2 and available light below the canopy decreases linearly with increasing leaf biomass. Foliar mineral analyses suggest no foliar deficiencies of minerals in stands up to 20 yr old. Many years are required for the development of extensive root systems which are able to decrease the water stress experienced by C. megacarpus during summer drought. Water potential measurements show that moisture is a more limited resource in young (6—yr—old) stands that in older, well—developed stands, though the latter have considerably more leaf area for transpiration. Density—dependent competition for moisture may drive the self—thinning process seen in stands of C. megacarpus during an interval from 5 to 15 yr after fire, but decreasing available light may determine steady—state levels of vertical structure and biomass in this evergreen community.
Foraging Behavior of Competing Africanized Honeybees and Stingless Bees
Authors: Roubik David W.
Published: May 2006

The colonizing success and potential influence of immigrant Africanized honeybees in the neotropics depends on their foraging style and competitive ability. Experiments were performed to compare the foraging tactics of this invading species to those of its most abundant competitors, highly social stingless bees of the genera Melipona and Trigona. In an area containing a rich assemblage of stingless bees in French Guiana, Africanized honeybees were significantly more abundant on honey—water feeders during a high "nectar flow" period than combined stingless bee and wasp species. During the last 15 min of the experiments, when bait was not replenished on feeders, Africanized honeybees abandoned the feeders but native foragers continued to arrive. None of the stingless bees, including four aggressive Trigona, displaced from the feeders the foragers of several (two to seven) colonies of Africanized honeybees. The cost of attacking Africanized honeybees at feeders apparently exceeded the benefit for large, aggressive Trigona williana and T. hyalinata branneri. These bees abandoned feeders visited by nonaggressive Africanized honeybees. Single, small Africanized honeybee colonies were displaced from feeders by aggressive foragers of T. Pallens pallens and T. h. branneri. In one instance Africanized honeybeeys shifted almost immediately to a floral resource, while abandonment of the feeders by T. williana was not followed by a shift to a natural food source. Reduction of competitive interaction with Africanized honeybees was accomplished by foragers of T. clavipes and T. p. pallens that partitioned four feeders by visiting only two, leaving the other to Africanized bees. Interspecific displacement was never absolute; a few foragers from a displaced colony always visited the feeders. Africanized honeybees and Melipona fulva foraged nonaggressively both at feeders and flowers, but Africanized bees at feeders exhibited low levels of aggression toward Melipona and polybiine wasps on one occasion. Unlike other aggressive Trigona, T. clavipes was at times unaggressive. Colonies of T. h. branneri and Africanized honeybees, the bees most successful in displacing other species from feeders, were comprised of many more workers than colonies of the other bees. The combined advantages of (1) the ability to communicate the distance and direction of a food source from the nest, (2) large forager size, and (3) large colony size provide Africanized honeybee colonies with a competitive ability superior to that of stingless bees at rich, compact resources.
Nitrogen and Phosphorus Dynamics and Budgets in Annual Grasslands
Authors: Woodmansee R. G. , Duncan D. A.
Published: May 2006

N and P dynamics were studied in a grassland ecosystem dominated by exotic annual plants in central California. Biomass and N and P concentrations were observed over a 3—yr period for the dominant grasses, forbs, and legumes and plant residues (litter). The N and P contents were determined or estimated for various components of the ecosystem (e.g., live tops, live roots, soil organic matter, dead roots, litter, microflora, soil fauna, mineral N, solution P, and labile inorganic P). We estimated that >57, 125, and 89 kg/ha of N and 13.1, 14.7, and 14.1 kg/ha of P were mineralized during the 1972—1973, 1973—1974, and 1974—1975 growing seasons, respectively. However, N uptake by plants was 119, 87, and 68 kg/ha and P uptake was 134.1, 14.5, and 10.4 kg/ha, respectively. While the data showed that P was stable, indicating its cycle was relatively closed, the data of N showed that its cycle was open, with large inputs of N from symbiotic fixation the 1st yr of the study. Large losses of N from the system were estimated.
Group Selection, Population Growth Rate, and Competitive Ability in the Flour Beetles, Tribolium Spp.
Authors: Wade Michael J.
Published: May 2006

This is a report of an empirical study of competition between a laboratory strain of Tribolium confusum and populations of T. castaneum selected for increased and decreased productivity by group and individual selection. A pronounced inverse relationship between productivity and competitive ability was observed: fast growing T. castaneum populations had the smallest effect on the ability of T. confusum to recruit adults and slow—growing populations had the largest effect. The average duration of fast—growing T. castaneum populations was prolonged by competition but slow—growing populations were not affected in this regard. Approximately half of the slow—growing populations were facilitated in the production of adults by the presence of a competitor. The data suggest that individual fitness, measured as relative reproductive rate, and population fitness, measured as persistence, may be in conflict. The relevance of these findings to group and individual selection in natural populations is discussed.
Enrichment of Lake Wingra, Wisconsin, by Submersed Macrophyte Decay
Authors: Carpenter Stephen R.
Published: May 2006

This study analyzes enrichment of hard—water eutrophic Lake Wingra by decomposition of submersed aquatic vegetation. A model was constructed to predict daily release of dissolved total phosphorus (DTP) and dissolved organic matter (DOM) from decaying macrophyte shoots. Inputs to the model are: daily mortality, the nitrogen and phosphorus contents of senescing tissues, and water temperature. The mechanism are modeled: leaching of phosphorus, decay of coarse particulate organic matter, and respiration of DOM. In field tests, the model predicted decay rates and the phosphorus content of decaying shoots fairly accurately. Decomposition of Myriophyllum spicatum accounts for about half of the observed flux of DTP and DOM from the littoral zone to the pelagial zone of Lake Wingra. During summer and autumn decaying macrophytes are a major source of biologically available DTP and decomposable DOM for the pelagic community of the lake. Therefore, macrophyte decay potentially stimulates pelagic production. Substantial differences in the timing of DTP and DOM release occur among comparably productive stands of different species decomposing in the same lake. Release of dissolved materials by Potamogeton pectinatus stands occurs during summer, and is nearly completed by the time release by Vallisneria americana stands begins to increase. Most of the release from V. americana stands occurs after mid—August. Release of dissolved materials by a typical stand of M. spicatum is more or less continuous during summer and autumn. When Lake Wingra was dominated by V. americana (∞1900) the rate of enrichment by macrophyte decay during summer was probably less than the present rate. During a period of domination by Potamogeton species (∞1955—1965) enrichment by macrophyte decay during summer may have exceeded the rate of internal loading that occurred after the invasion of M. spicatum.
The Adaptive Significance of Variations in Reproductive Habit in the Agavaceae II: Pollinator Foraging Behavior and Selection for Increased Reproductive Expenditure
Authors: Schaffer William M. , Schaffer M. Valentine
Published: May 2006

A coevolutionary hypothesis accounting for the evolution of Big Bang reproduction in yuccas and agaves is proposed. Particular attention is paid to the selective consequences of pollinator foraging behavior and reciprocally to the effects of plant reproductive expenditures on pollinator foraging strategies. Several lines of evidence, both observational and experimental, supporting the theory are presented. This evidence incidentally supports the notion that insect pollinators visit flowers in qualitative accord with the dictates of optimal diet theory.
Statistical Detection of Density Dependence from a Series of Sequential Censuses
Authors: Slade Norman A.
Published: May 2006

The use of simple linear regression to estimate slopes of plots of N(t + 1) against N(t) as a test of density dependence has been criticized because such date violate the assumption of negligible measurement error in the independent variable and because they represent a time series rather than independent pairs of points. Of the several alternatives which have been suggested, ordinary and standard major axes and the coefficient of first—order autoregression behave in accordance with the logic of detecting density of dependence in such plots. The power of the test of the slopes' being equal to 1 depends on the magnitude of density—dependent and independent (random) influences and on the type of error, measurement or environmental. However, slopes of major axes appear to be unbiased estimators of the true slopes, when sequential population estimates include values sufficiently displaced from equilibrium conditions. If data follow a purely autoregressive process, density dependence can be detected without such displacement.
Plant Plasticity, Phenology, and Herbivore Dispersion: Wild Parsnip and the Parsnip Webworm
Authors: Thompson John N. , Price Peter W.
Published: May 2006

The influence of plant plasticity on the dispersion of a specialized insect herbivore was analyzed in an 8— to 9—yr oldfield. The parsnip webworm, Depressaria pastinacella (Lepidoptera: Oecophoridae), is a specialist on the flowers and developing seeds of the biennial herb Pastinaca sativa (Umbelliferae). The dispersion and abundance of larvae on isolated plants in mixed vegetation was compared with that on plants in patches in which flowing conspecific density was between 30 and 40 plants per m2. On isolated plants the number of larvae per gram umbel was 50% higher at the peak of larval abundance, the cumulative proportion of plants attacked was 80% higher, and the cumulative proportion of umbels on each plant attacked was 40% higher than on high density plants. The dispersion of larvae within the study area was governed by the plastics response of plants to increasing plant density rather than by density per se. Successful oviposition was limited to unopened umbels. Isolated plants had more unopened umbels available at any one time and maintained this availability over a longer period of time than high density plants. Most umbels harbored only 1 larva. Hence, the number of umbels and the synchrony between present of unopened umbels and moth oviposition period limited the number of early instar larvae. Within—plant dispersion of larvae was related to the patterns of umbel size and the phenological staggering of umbel appearance of each plant. Experimental introduction of larvae onto plants either synchronously or asynchronously revealed these patterns. Only large—diameter umbels supported >1 larva, and these umbels were more common on isolated plants. Staggering of the umbel production (or its simulation with asynchronous introductions) led to less aggregation of later instar larvae, because larvae arriving early preempted sections of umbel.
On Whittaker's Components of Diversity
Authors: Routledge R. D.
Published: May 2006

Suppose that the diversity of a collection of organisms is measured either by H', the Shannon—Wiener index, or by s, the species richness. For collections made from discrete habitat types, methods exist for decomposing such quantities into two components describing, respectively, the diversity within habitat types and the amount of turnover in the species composition between habitat types. The definitions of the components of H' and s are modified here to suit collections of organisms inhabiting a continuous gradient of habitat types. Since difficulties may arise in the evaluation of these components, however, an alternate set of components of s is also presented. Values of s and this latter set of components are presented for transect data obtained from salt marshes at latitudes from 44°40'N at Halifax, Nova Scotia, to 58°50'N at Churchill, Manitoba. A latitudinal diversity gradient is shown to be accompanied by a similar trend in the between—habitat component only. The lack of trend in the first component reduces the collection of possible causes of the diversity gradient.
Plant Responese to the Light Penetrating Snow
Authors: Richardson Steven G. , Salisbury Frank B.
Published: May 2006

The spectral irradiance of light penetrating 198 cm of snow was measured with a device employing a photomultiplier tube combined with each of several interference filters. In deep snow, the measured peak in transmission was near 500 nm, but in older, shallower snow the peak shifted to 550 nm. On 2 dates, measurement were made periodically under snow before and after sunrise. There was a spectral shift toward the longer wavelengths with increasing height of the sun above the horizon. Germination of Lactuca sativa cv. Grand Rapids seeds was promoted by a 3—h exposure to the light penetrating 198 cm of snow, and Brassica nigra and Brassica kaber seeds responded similarly to longer exposures under deep snow. Leaf greening, leaf unfolding, and inhibition of shoot elongation were exhibited by Camassia quamash in response to light penetrating the snow, but phototropism was not observed in an experiment designed to detect it.
The Assembly of Species Communities: Chance or Competition?
Authors: Connor Edward F. , Simberloff Daniel
Published: May 2006

We challenge Diamond's (1975) idea that island species distributions are determined predominantly by competitions canonized by his "assembly rules." We show that every assembly rule is either tautological, trivial, or a pattern expected were species distributed at random. In order to demonstrate that competition is responsible for the joint distributions of species, one would have to falsify a null hypothesis stating that the distributions are generated by the species randomly and individually colonizing an archipelago.
Analysis of Central‐Place Space‐Use Patterns: The Elastic Disc Revisited
Authors: Getty Thomas
Published: May 2006

Ideas from ecology, economics, and geography are synthesized into a central—place, space—utilization model which is analytically as well as conceptually useful. Incorporation of social and ecological factors extends common home range models, which incorporate only distance. The patch preference and competition coefficients which are "revealed" by regression on actual use—intensity patterns indicate the importance of these factors by the degree to which the perturb an appropriate distance—decay function. Proximate factors reveal themselves by deforming a Huxleyan "elastic disc." The analytical value of the model is illustrated by an example from my studies of eastern chipmunks.
Disturbance and Community Structure in a Shallow Water Sand Flat
Authors: Woodin Sarah Ann
Published: May 2006

Diopatra cuprea, an onuphid polychaete, is a large and conspicuous component of semiprotected sand flats along the east coast of North America. It builds a large tube which projects above the surface of the sediment. Infaunal abundances are greater around such tubes than elsewhere. To test the hypothesis that tubes provide a local refuge from predation, I manipulated the abundances of the conspicuous predators and sediment disruptors, Callinectes sapidus the blue crab and Limulus polyphemus the horseshoe crab. In the absence of all predators >0.625 cm, infaunal abundances no longer increased as a function of Diopatra abundance. Thus, the tube of Diopatra appears to act as a refuge from predation for infauna. Further manipulations of the predators indicated that Callinectes was far more important than Limulus. Species which were numerically dominant in the presence of predators predominated in the predator removals as well. These experiments were repeated three times over a 3—yr period (1974, 1975, 1976) and in general the results were consistent over that period. Densities of juvenile Diopatra increased dramatically inside predator exclosures. Densities of adult Diopatra did not. The abundance of this refuge—forming organism, therefore, is at least partially dependent upon the frequency with which individuals pass through the size—dependent period of susceptibility.
Removal of Wild Nutmeg (Virola Surinamensis) Crops by Birds
Authors: Howe Henry F. , Vande Kerckhove Gayle A.
Published: May 2006

We observed birds and mammals visiting individual plants in a Panamanian population of the rainforest tree Virola surinamensis (Wild Nutmeg) to determine (1) relative importance of different dispersal agents, and (2) the relationships between crop size, crop quality, and seed removal. Arils of this tree are exceptionally nutritious (63% fat, 9% nonstructural carbohydrate, 3% protein), but draw remarkably few species of fruit—eating animals. Six birds take 77% of the seeds handled by animals. One toucan (Ramphastos°swainsonii) accounts for 35% of the seeds handled; other birds (Penelope purpurascens, Trogon massena, Baryphthengus martii, Pteroglossus torquatus, Ramphastos sulfuratus) play lesser roles. The smallest visitor, a cotinga (Tityra semifasciata) eats arils but does not disperse seeds. One monkey (Ateles geoffroyi) removes 3% of the seeds handled by frugivores, but smells and rejects or otherwise wastes 9%. Such a small assemblage is anomalous in a forest with at least 78 species of fruit—eating animals; other trees with arillate seeds of similar size draw as many as 23 frugivores. We hypothesize that the size of the assemblage is limited by seed size, small crop size, and perhaps by defensive compounds in the arils. Despite the small assemblage, an average of 62% (range: 13—91%) of the fruits available to animals are taken. Fruits are so nutritious that trees with both small and large crops are depleted; no variance in the percentage of seeds removed can be attributed to crop size. Fruits of different individual trees do vary in size; 59% of the variation in the percentage of seeds taken can be attributed to mean seed size. Fruit—eating animals preferentially deplete trees with small seeds, and coincidentally favor trees with high aril—to—seed ratios. No significant portion of the variance in dispersal success can be explained by aril mass alone. We hypothesize that consistent differences in seed size could result in dramatic differences in dispersal, and hence reproduction, over the lifetime of individual trees. On the other hand, selection may alternatively favor small seed size and high dispersability in years when frugivores are abundant, and large seed size and enhanced seedling vigor in the parental stand when fruit—eating birds are scarce. Small—seeded plants are likely to colonize new sites; large—seeded individuals are likely to produce offspring that fare well in competition with other seedlings near parent trees.
Relationships between Temperate Forest Bird Communities and Vegetation Structure
Authors: James Frances C. , Wamer Noel O.
Published: May 2006

General patterns of density, species richness, and relative abundance of breeding birds are examined in a wide variety of North American forests. Taking data from censuses published in American Birds, we use rarefaction to ordinate the species richness of communities in terms of samples of equal numbers of individuals. By this criterion young forests in secondary succession and mature deciduous forests can be equally rich in bird species; coniferous forests and dense successional stands having only one or two species of trees have the fewest species of birds. For our data set the density of birds is higher in mature deciduous forests than in successional stands. The species/area relationship (s/a) is a function of both this species/individuals relationship (s/n) and the individuals/area relationship (n/a). According to the Jonckheere—Terpstra statistic there is a statistically significant pattern to the order in which bird communities fall with regard to s/n and n/a. To see these relationships in terms of the structure of the vegetation, we present the positions of 56 stands in a graphic space determined by principal components. Tree species richness and canopy cover dominate the first axis, and variation in canopy height the second. Tree density has a somewhat independent pattern of variation and is expressed by the third axis. In the bivariate space of principal components one and three, a SYMAP contour diagram of the number of bird species expected in 10 ha (s/a) shows maximal values in mature deciduous forests, but not in those that have the highest trees species richness, canopy height, or tree density. The number of individual birds/10 ha (n/a) shows a similar pattern except that maximal density occurs at maximal values of tree species richness and canopy height. By this criterion both bird species richness and density are minimal in coniferous forests characterized by high tree density, low canopy, and few species of trees. These patterns are not discernible by the classic bird species diversity/foliage height diversity method proposed by Mac Arthur and Mac Arthur in 1961. They are masked by correlation coefficients, partly because the coefficients are insensitive to nonlinear relationships. We recommend rarefaction, principal components analysis, and contour diagrams to display relationships among communities.
Energetics of Reproduction in Large‐Littered Cotton Rats (Sigmodon Hispidus)
Authors: Mattingly D. Kevin , McClure Polley A.
Published: May 2006

Energy costs of reproduction were measured in the laboratory for individual large—littered (° = 7.0) cotton rats, Sigmodon hispidus, from Kansas, and less extensively for individual small—littered (° = 4.7) cotton rats from Texas. These estimates were compared with previously studied small—littered (° — 5.0) S. hispidus from Tennessee. Reproductive Kansas S. hispidus (KSh) increased ingestion above nonreproductive rates by 19% during pregnancy and 111% during lactation. This represents extra ingestion of 766 kJ during 26 d of pregnancy and 2111 kJ during 12 d of lactation. Extra ingestion throughout reproduction was dependent on litter size. Total extra ingestion cost per 12—d—old KSh offspring was 415 kJ, a constant unaffected by litter size. Digetive efficiency of KSh rats fed a commercial standard lab chow was 85% and did not changes as a result of pregnancy and lactation. Metabolic rate of reproductive KSh rats was not significantly different from that of nonreproductive rats. The average body mass of KSh females on the day of conception was 175 g, vs. 169 g at the end of 12 d of lactation, a loss of 6 g. This loss of body mass during reproduction increased with increasing litter size: KSh females giving birth to litters of eight to ten young lost an average of 19 g below conception mass, while females giving birth to five to seven young gained an average of 1 g. KSh young averaged 6.8 g at birth and 21.7 g at 12 d of age. Reproductive Texas S. hispidus (HSh) increased ingestion over nonreproductive rates by 22% during pregnancy and 70% during lactation. This represents extra ingestion of 854 kJ during pregnancy and 1161 kJ during lactation. Total extra ingestion cost per 12—d—old offspring was 434 kJ for HSh litters. The average body mass of females on the day of conception was 134 g and, at the end of 12 d of lactation, averaged 138 g. HSh young averaged 6.7 g at birth and 1802 g at 12 d of age. Kansas cotton rats produced relatively large litters and large individual young primarily by markedly increasing ingestion and drawing upon maternal storage during lactation. Both of these responses were probably facilitated by the KSh female's large body size. These results and comparisons among similarly studied species suggest the importance of the common constraits and correlated responses associated with changes in body size and litter size when considering energy utilization during reproduction.
Environmental Control of Food Web Structure
Authors: Briand Frédéric
Published: May 2006

The structure of 40 real food webs, representing aquatic and terrestrial communities from all latitudes, is found to be markedly affected by the degree of variability of the physical environment. In particular, food webs in fluctuating ecosystems are characterized by a significantly lower connectance than webs representative of more constant systems. This is interpreted within the context of stability theory as a means to optimize feeding in the face of increasing disturbance. It is shown further than the nature of the habitat itself imposes additional constraints on food web structure in intertidal, pelagic, estuarine, and forest ecosystems.
Seasonal Changes in Nitrogen and Phosphorus Fractions and Autumn Retranslocation in Evergreen and Deciduous Taiga Trees
Authors: Chapin F. Stuart , Kedrowski Richard A.
Published: May 2006

The concentrations and pool sizes of nitrogen— and phosphorus—containing chemical fractions were followed seasonally in leaves and young stems of four Alaskan tree species: larch (Larix laricina), black spruce (Picea mariana), birch (Betula papyrifera), and alder (Alnus crispa). We found no major differences in patterns of N and P distributions among major chemical fractions in nutritionally distinct deciduous trees. In the three diciduous species, all N and P fractions were highest in young leaves and declined in concentration through the season, first as concentration was diluted by increasing leaf biomass and later as organic N and P fractions were hydrolyzed and inorganic P and amino acid N were translocated out of leaves. The quantities of nucleic acids and phospholipids hydrolyzed in autumn were equivalent to 40—47% and 26—38%, respectively, of the total P retranslocated from leaves of deciduous species prior to abscission. Protein hydrolyzed and subsequently retranslocated as amino acids was equivalent to 82—91% of the N removed from senescing leaves. Leaching was much less important than retranslocation in removing nutrients from senescing leaves. In buds and stems, P was stored during winter primarily as phospholipid, nonhydrolyzable ester P, and nucleic acid P and was converted to inorganic P in spring. All species stored N primarily as protein and to lesser extent as nucleic acids; larch also stored some N in amino acids. In the evergreen spruce, N and P were stored in the same types of compounds as in deciduous species, but this nutrient storage occurred in leaves and involved no winter translocation to stems. Based on this study and a survey of the literature, we suggest that trees with low N and P status retranslocate a similar or smaller proportion of leaf N and P prior to leaf abscission than do trees with more favorable nutrients status. We conclude that tree have not adapted to nutrient stress through major changes in biochemical use of N and P. However, during the growing season there are important changes in allocation of N and P to different chemical fractions, associated with changing plant requirements.
The Comparison of Usage and Availability Measurements for Evaluating Resource Preference
Authors: Johnson Douglas H.
Published: May 2006

Modern ecological research often involves the comparison of the usage of habitat types or food items to the availability of those resources to the animal. Widely used methods of determining preference from measurements of usage and availability depend critically on the array of components that the researcher, often with a degree of arbitrariness, deems available to the animal. This paper proposes a new method, based on ranks of components by usage and by availability. A virtue of the rank procedure is that it provides comparable results whether a questionable component is included or excluded from consideration. Statistical tests of significance are given for the method. The paper also offers a hierarchical ordering of selection processes. This hierarchy resolves certain inconsistencies among studies of selection and is compatible with the analytic technique offered in this paper.
Comparative Census Procedures Using Single Mark‐Recapture Methods
Authors: Skalski John R. , Robson Douglas S. , Simmons Mary Ann
Published: May 2006

Proportional abundance is defined as the ratio of the animal abundance of one population (N2) to that of another (N1), say K = N2/N'1. Confidence interval estimators of K for paired populations are presented using single mark—recapture studies. Two alternative estimators of K based on assumptions about catchability are constructed, and power curves developed using computer simulations. Tests of homogeneity are presented which test the assumption of equal catchability among animals of the two populations. When the homogeneity assumption is valid, the proportional abundance estimator based on two indices of relative abundance is from 2 to 20 times more efficient than the comparable estimator based on absolute abundance. Analytic approximations for power calculations and sampling precision are presented which may be used in the design of comparative census studies.
Episodic Flowering and Sexual Dimorphism in Guarea Rhopalocarpa in a Costa Rican Rain Forest
Authors: Bullock Stephen H. , Beach James H. , Bawa Kamaljit S.
Published: May 2006

Two years of intensive phenological observations of Guarea rhopalocarpa showed that a population of this dioecious species flowered and fruited several times per year, in discrete episodes at irregular intervals. The percentage of participating trees differed between episodes by a factor of 3, but the total numbers of male and female inflorescences and fruit differed more among episodes (38x, 11x, and 77x, respectively). The patterns of relative fecundity among episodes were different between sexes. Nearly all males flowered at least twice per year, while nearly all females flowered at least once; the tendencies to additional flowerings were similar. Males flowered more abundantly than females and often showed oscillations in fecundity between episodes. In females, fruiting in one episode clearly diminished the probability of fruiting in the next. Fruit—sex was not linearly related to flowering effort. Fecundity in both sexes was poorly explained by trunk size. The sex ratio among adults was not significantly different from unity, and the sexes were similar in trunk size distribution and growth rates. The phenological patterns, fecundity, and dimorphism are considered in relation to pollination, energetics, and sexual selection.
Ecological Correlates of a Neotropical Mutualism: Ant Assemblages at Costus extrafloral Nectaries
Authors: Schemske Douglas W.
Published: May 2006

The species richness and composition of ant assemblages at the extrafloral nectaries of four Costus spp. (Zingiberaceae) in Panama were quantified to determine (1) the relative specificity of these ant—plant mutualisms, and (2) the ecological factors that influence ant assemblages. Although inflorescences of Costus spp. commonly produce extrafloral nectar for several months (species means 1—2 mo, range to 4 mo), there was little turnover in ant—species composition on individual inflorescences. A total of 34 ant species in five subfamilies were observed, but plant species varied significantly in ant species richness. The number of ant species expected from equal sampling (40 inflorescences per Costus sp.) was 9 for C. pulverulentus, 13 for C. scaber, 15 for C. allenii, and 20 for C. laevis. Among—species differences in ant species richness were not a function of plant distribution, the volume or composition of extrafloral nectar, or the duration of nectar flow. The number of ant species was positively correlated with inflorescence height, which varied from 0.6 to 2.0 m. The differences in ant species richness with inflorescence height were due primarily to the addition of arboreal ants, which increased from 3 species representing 3% of all ant species observations on the shortest plant, C. pulverulentus, to 12 species representing 62% of all ant observations on the tallest plant, C. laevis. The number of terrestrial ant species varied only from six to eight. Cumulative ant—species curves as a function of number of inflorescences sampled (N = 41—80) did not plateau for any Costus sp., indicating that a large number of ant species can utilize extrafloral nectar in this system. The high ant species richness and the similarity in nectar characteristics among Costus spp. suggest these are relatively generalized mutualisms with limited coevolution between the plants and their attendant ants. The brief period of extrafloral nectar production (° = 36—55 d), coupled with spatial variation in ant species distributions, probably limit the degree of specialization among mutualists. This is in contrast to more specialized ant—plant mutualisms where plants are relatively predictable sources of food and/or nest sites for ants.
Pressurized Ventilation in the Yellow Waterlily
Authors: Dacey John W. H.
Published: May 2006

Current models of gas transport in aquatic plants hold that gases diffuse in an essentially static gas phase within the lacunae according to gradients in their individual partial pressures. This study introduces a new model of gases gas transport wherein the gases move through waterlilies in a mass flow. The internal gas spaces in Nuphar constitute a pressurized flow—through system, with ambient air entering the youngest emergent leaves against a small gradient in total gas pressure. This pressurization phenomenon is the result of purely physical processes driven by the gradients in temperature (thermal transpiration) and water vapor (hygrometric pressure) between the atmosphere and the lacunae of the youngest emergent leaves. The lacunae are continuous throughout the entire plant, and the older leaves vent the elevated pressure generated by the younger leaves. This arrangement gives rise to a flow—through pattern, accelerating both the rate of O2 supply from the atmosphere to the roots, and the rate of CO2 and CH4 transport from the roots towards the atmosphere. This ventilation system represents an important adaptation by the waterlily to life in anaerobic sediments.