bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Competition in the Distribution of Andean Birds
Authors: Terborgh John , Weske John S.
Published: May 2006

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.
The Adaptive Significance of Variations in Life History among Local Populations of Atlantic Salmon in North America
Authors: Schaffer William M. , Elson Paul F.
Published: May 2006

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.
The Effects of Density on Resource Partitioning in Chamaesyce hirta (Euphorbiaceae)
Authors: Snell Terry W. , Burch Derek G.
Published: May 2006

The pattern of resource allocation in Chamaesyce hirta was significantly affected by both density and nutrient availability. Increased intraspecific competition and decreased nutrient levels produced decreases in the proportion of total plant energy allocated to reproductive tissues in all units tested. A 32—fold increase in density diminished reproductive effort by one—third and an 8—fold decrease in nutrient levels diminished reproductive effort by one—half. These results are in agreement with theoretical predictions that for a resource—limited population, reproductive effort should decrease with decreasing resource availability. Increased root growth seemed to be inversely related to reproductive effort.
The Role of Weather Variables and Flight Direction in Determining the Magnitude of Nocturnal Bird Migration
Authors: Able Kenneth P.
Published: May 2006

Autumn nocturnal bird migration was investigated at two stations in the southeastern United States by means of Weather Surveillance Radar (WSR—57) and visual observations. Multivariate analyses were used to examined the influence of environmental variables on the night—to—night magnitude of migration. Landbirds selectively flew with the wind, regardless of its direction or speed. As a result, they frequently migrated in seasonally inappropriate directions. The volume of migration varied by several orders of magnitude from night to night, but southward flights averaged about five times larger than those in other directions. This implies that the birds employed some selection in terms of the weather conditions under which they initiated migratory flights. Multivariate analyses showed that wind direction, 24—hr change in temperature, and an index of the synoptic weather situation accounted for 5.2% of the night—to—night varaibility in the magnitude of passerine migration. Migration volume was also related to the passage of cold fronts. Migations were heavier in northerly winds, falling temperatures, and the anticyclonic weather that usually prevails shortly after the passage of a cold front. The efficiency of downwind flight is enhanced by the facts that average winds blow roughly in the migratory directions of the birds and that the birds show behavioral selection in terms of the wind directions and synoptic weather situations in which they initiate migration. Night—to—night variations in migration density can be accounted for on the basis of interactions between the circadian nature of Zugunruhe, the energetic state of the bird, and the direct influence of weather on the initiation of migratory flights.
Resource Competition between Plankton Algae: An Experimental and Theoretical Approach
Authors: Tilman David
Published: May 2006

The results of 76 long—term competition experiments between two species of freshwater algae (Asterionella formosa and Cyclotella meneghiniana) grown along a resource gradient agree with the predictions of two different models of resource competition. Both models are based on the functional resource—utilization response of each species to limiting resources. The Monod and the Variable Internal Stores model of competition made similar predictions. Asterionella was observed to be competitively dominant when both species were phosphate limited; Cyclotella was dominant when both species were silicate limited; and both species stably coexisted when each species was growth—rate limited by a different resource. Almost 75% of the variance in the relative abundances of these two species along a natural silicate—phosphate gradient in Lake Michigan is explained by the Monod model.
Uptake, Accumulation, and Loss of Nutrients by Papyrus in Tropical Swamps
Authors: Gaudet John J.
Published: May 2006

Analysis of papyrus (Cyperus papyrus L.) indicated that N, P, and K are generally found in higher concentrations in juvenile stems while Ca, Mg, Fe, and Mn are found in higher concentrations in mature stems. Iron was found to be concentrated in the roots, while Mn was concentrated in old umbels. Silicate content increased with age. Potassium and Na were easily eluted and leached from stems, while other nutrients required more time. Over 50% of all eight elements are accumulated prior to the attainment of 50% of the biomass. The total amount of nutrients taken up and accumulated by papyrus (per m2) is higher than most other macrophytes, and this seems to be due to the high biomass of this aquatic sedge. Estimates of losses due to elution, rain, and decomposition accounted for approximately two—thirds of the total nutrient accumulated. The remainder is assumed to be deposited in the swamp as peat.
Natural Mortality of Tadpoles in a Population of Rana Aurora
Authors: Calef George Waller
Published: May 2006

The Survivorship, distribution, growth rates, and natural predation rates on the population of Rana aurora tadpoles in Marion Lake, British Columbia, were studied during the summers of 1969 and 1970. Natural survivorship appeared to have two phases: a rapid decline in numbers during the first 4 weeks after hatching was followed by a less rapid decline, until approximately 5% of the population remained at metamorphosis, after 11—14 weeks. The size attained by tadpoles living at any depth in the lake was strongly correlated with the accumulated degree—days since hatching (r = .93). The regression equation (degree—days vs size) obtained from the data on animals in the lake could accurately predict the growth rate of tadpoles kept in the laboratory at maximum food supply. It was concluded that animals in the lake grew at the maximum rate permitted by the temperature. Alterations of the density of tadpoles and predatory salamanders were performed in enclosures in the lake. The percentage of tadpoles surviving in the enclosures containing no salamanders was twice as high as it was in the natural population. The percentage of tadpoles surviving in the experimental enclosures was independent of density, at least up to 75 tadpoles/m2. Except at the lowest density (5/m2), no significant effects were noted at any density, on the rate of growth or time to metamorphosis. These experimental observations support the notion that food is not limiting to the tadpoles at their normal densities. Most of the mortality of tadpoles observed in the natural population was attributed to predation because: (1) Tadpoles kept in the laboratory on starvation diets survived for many weeks, even though they did not grow. (2) Tadpoles living at densities up to 100 times normal could survive and grow to metamorphosis in the absence of predators. (3) Predation rates observed in the field, and simulated on the basis of laboratory experiments, were sufficient to account for much of the mortality observed in the natural population. Laboratory studies of salamanders preying on tadpoles in multi—prey systems showed that the number of tadpoles eaten was proportional to the density of tadpoles present except at very low density, where fewer tadpoles than expected were eaten. The tadpoles also had a refuge from some predators after they had grown to a certain size. Salamanders were observed to move into areas of high tadpole density, thereby increasing locally the intensity of predation. It was concluded from the laboratory and field observations that mortality of tadpoles is density—dependent. However, the limiting factors for the Rana aurora population are unknown, since the frogs were not studied after they left the lake. The numbers of eggs laid in the 2 years of the study were very similar, but no social mechanisms for controlling the breeding population were observed.
Adaptational Biology and Energy Relationships of the Collared Peccary (Tayassu Tajacu)
Authors: Zervanos Stam M. , Hadley Neil F.
Published: May 2006

Field and laboratory investigations were conducted to determine the major seasonal adaptations exhibited by the collared peccary (Tayassu tajacu) in the desert. Emphasis was placed on the animal's thermoregulation, water relations, and energy requirements under changing environmental conditions. Body core temperatures were labile and ranged from 37.5 degrees C to approximately 40.9 degrees C during both winter and summer seasons. Skin temperatures were always above ambient and reached a high of 49.2 degrees C during summer. Heat loss across the skin of summer animals averaged 0.041 cal/cm2 min during the day and 0.038 cal/cm2 min at night. Winter animals by basking exhibited a slight heat gain during the day (0.033 cal/cm2 min) but lost heat at a rate of 0.223 cal/cm2 min at night. The pelage of the peccary had a poor insulative value; thermal conductance equaled 0.291 cal/cm2 hr degrees C. Summer animals became lighter in color over certain parts of their body and also decreased density of bristles over most of their body. Total water requirement for summer peccaries was 66.5 ml/kg day and for winter peccaries 38.6 ml/kg day. Respiratory evaporation was the major avenue of water loss and accounted for 6.1% of body wt/day for summer dehydrated pecaries. during dehydration peccaries were able to reduce evaporative water loss by as much as 68% and urinary water loss by 93%, but were unable to produce dry feces. Their maximum osmolar urine/plasm ration was 4.0. Total daily energy requirement for an 18.2 kg peccary was 794.05 Kcal/day in summer and 916.96 Kcal/day in winter. The annual energy requirement was estimated at 17,166 Kcal/kg year. On the basis of these calculations, a herd of 25 individuals occupying a home range of 388 ha at the Three—Bar wildlife Area would require approximately 20% of the annual production of prickly pear cactus (7,985.0 kg/year or 20,130.9 Kcal/ha year).
Food Size Selection Among Copepods
Authors: Wilson David Sloan
Published: May 2006

The marine copepod Acartia tonsa was fed small plastic beads (7—70 microns) in a variety of size—frequency distributions and a concentration of 3,000—4,000 beads/ml. Both selective and non—selective feeding were observed. Selective feeding was intense over a narrow size range (selected particle sizes over 20 times more abundant in the gut than in the water); the actual sizes selected depended on the size frequency distribution offered, associating always with the largest abundant particles. A hypothesis for the mechanism of food size selection is that the animals "scan" the size distribution by capturing particles larger than the previous one ingested more efficiently than those that are smaller; the copepods then "locate" an abundance peak and halt the process just to the right of it.
Biogeography of the Puerto Rican Bank: Flotsam Transport of Terrestrial Animals
Authors: Heatwole Harold , Levins Richard
Published: May 2006

Of 59 pieces of flotsam picked up at sea 0.5—16 km from its nearest probable origin, 25% contained at least one live terrestrial animal and 6% had three or more species; one green plant contained 12 species. In many cases a number of conspecific individuals occurred in the same drift item. The animals represented included 19 families of insects, as well as psuedoscorpions, snails, spiders, mites, millipedes, isopods, and worms. Some families were represented by several (up to five) species. Eight drift items recovered approximately 120 km from the nearest land lacked terrestrial animals. A piece of bamboo which washed up on the beach of Cayo Ahogado contained a dipteran and a beetle. Flotsam transport is clearly a significant biogeographic factor among the islands of the Puerto Rican Bank.
Larval Habitat Suitability and Oviposition Preference in Three Related Butterflies
Authors: Rausher Mark D.
Published: May 2006

A simple hypothesis about habitat choice by ovipositing butterflies is that females prefer to lay their eggs on plants in habitats where juvenile growth and survival are best. This hypothesis was evaluated by studying 3 Aristolochia—feeding swallowtail butterflies (Papilionidae: Troidini). Results show that the eggs and larvae of all 3 butterfly species survive significantly better in shady habitats than in sunny habitats. Pupal survival is similar in the 2 habitats for at least 1 species. Larval growth rates were similar in the 2 habitats for all 3 species. Thus, for all 3 species shady habitats appear to be more suitable for juvenile development and survival than sunny habitats. Only Parides montezuma lays most of its eggs in shady habitats, however; Battus philenor and B. polydamus females lay most of their eggs in sunny habitats. The original hypothesis is therefore not upheld by this study. Three alternative explanations for the discrepancy between the relative suitability of habitats for the juvenile stages and habitat choice by ovipositing females are suggested.
Fungi and Bacteria Associated with Leaves During Processing in a Woodland Stream
Authors: Suberkropp K. , Klug M. J.
Published: May 2006

Autumn—shed leaves of white oak (Quercus alba) and pignut hickory (Carya glabra) were fastened together and incubated in a third order hardwater stream in south—western Michigan. At biweekly intervals, leaves were removed and the microbial populations assessed. Direct counts of bacteria increased logarithmically with time, but viable counts were generally lower. Flexibacter, Achromobacter, Flavobacteria, Pseudomonas, and Cytophaga were isolated from leaves. No apparent bacterial succession was detected. The mycoflora was assessed in five ways, including direct examination and incubations ranging from environment simulating to particle platings on nutrient medium. Although this last technique suggested that common soil and litter fungi dominated, direct examination and environment—simulating incubations showed that aquatic hyphomycetes, particularly Alatospora acuminata, Flagellospora curvula, and Tetracladium marchalianum were the dominant members of the mycoflora. The successional pattern of these fungi on both leaf species is discussed. It is concluded that the aquatic hyphomycetes are actively growing and completing their life cycle in this environment and that the terrestrial fungi are normally present mainly in a dormant state, growing and sporulating only in greatly enriched conditions. The highest ATP levels observed corresponded to the periods of highest fungal frequencies .
Thermoregulation and Reproductive Activity in Tropical Dragonflies of the Genus Micrathyria
Authors: May Michael L.
Published: May 2006

Observations of behavior, including time budgets, and measurements of body temperature are reported for four species of Micrathyria in the Panama Canal Zone. Larger species maintained an elevated body temperature by flying continuously at low ambient temperatures. All species probably thermoregulated behaviorally at high temperature. From data on body temperature during continuous fight and on heat exchange rates it is possible to estimate the energetic requirements for thermoregulation. In the smaller species, endothermy is prohibitively expensive. Temporal patterns of activity at breeding sites differed among species. The species that thermoregulated well extended their activity periods early and late in the day while the smaller, poorly thermoregulating species were restricted to midday activity. The extended activity periods of the large species apparently allowed them to reduce competition for perches and interference with mating and oviposition by other dragonflies.
The Adaptive Significance of Interspecific Territoriality in the Reef Fish Eupomacentrus Leucostictus
Authors: Ebersole John Paul
Published: May 2006

Observations were made on the fishes trespassing in 50 territories of the reef pomacentrid Eupomacentrus leucostictus, and on the responses of the territory—holders to the trespassers. The extent to which each of the tresspasser species elicited agonistic responses from territorial E. leucostictus individuals was quantified: number agonistic acts/total trespass time. Using data on feeding habits, the diet overlap of each trespassing species on E. leucostictus was computed according to the formula &alpha = ϵpihPjh/ϵPih2. Following a log—log transformation to correct for heteroscedasticity, a Pearson product—moment correlation between number gonistic acts/total trespass time revealed a significant positive correlation between these 2 variables. An expression for Potential Competitive Impact that combines trespasser size with diet overlap, α(VB)75, showed a highly significant correlation with number agonistic acts/total trespass time (again using a log—log transformation) and a higher correlation coefficient (r =.613, P<.01). When this correlation was recalculated with the exclusion of the 9 trespassing species known to eat eggs, the correlation coefficient improved to r =.744, P <.01. These 9 egg—eating species have a significantly greater tendency to elicit agonism beyond that expected on the basis of their Potential Competitive Impact than do the other tresspassing species. (t =2.940, P <.02). This pattern of agonism indicates that interspecific territoriality is an adaptive behaviorthat reduces the loss of food in the territory to competitors and protects the nest from egg predators.
Toxic Terpenes from Artemisia Californica
Authors: Halligan J. Pat
Published: May 2006

The essential oil from Artemisia californica yeilds five terpenoids in major amounts: 1,8—cineole, artemisia ketone, α—thujone, isothujone, and camphor. Of these, camphor is most toxic, followed by 1,8—cineloe. Artemisia ketone is least toxic. Terpenoids found in minor amounts include β—pinene, borneol, and the sesquiterpene hydrocarbon caryophyllene. These are intermediate in toxicity. Amount and composition of the essential oil change according to a seasonal pattern. A greater amount of essential oil is extractable in fall than in winter. Isothujone largely replaces α—thujone, and camphor becomes more abundant in late summer and fall. The soil and litter in stands of A. californica contain many of the same volatile substances as are in Artemisia foliage.
Estimation of Food Consumption in the Dingo, Canis Familiaris Dingo, by Means of ^(22)Na Turnover
Authors: Green Brian
Published: May 2006

Ten captive dingoes were injected with radioactive NaC1 and the turnover of radio—sodium was compared with the measured intake of sodium in the diet, which consisted of rabbit carcasses. A close correlation was established between food intake and (22)Na turnover (r = .95). The possible uses of the (22)Na turnover technique in measuring food intake in free—living animals are discussed.
Biomass and Production in Three Contiguous Forests in Northern Wisconsin
Authors: Crow T. R.
Published: May 2006

Biomass and net primary production were measured in 3 forest communities in northern Wisconsin comprised mainly of Populus tremuloides, Betula papyrifera, Acer rubrum, and Acer saccharum. The estimated total aboveground biomass and production for living plants in the 3 stands, designated as (1) aspen, (2) aspen—maple—birch, and (3) maple—birch—aspen types, were 94.8, 95.6 and 119.0 t/ha [=103 kg/ha] and 10.43, 8.45, and 8.69 t°ha(—1)°yr(—1), respectively. Shrub and ground vegetation accounted for minor portions of the total standing crop. The tree:shrub:ground biomass ratios were 1:.019:.015 for aspen, 1:.009:.006 for aspen—maple—birch, and 1:.003:.006 for maple—birch—aspen. The contribution to stand production by shrubs and ground vegetation ranged from 17% of the total aboveground production in the aspen type to 9% in the other stands. Inputs to the production equation often neglected in stand analysis, i.e., plant losses by death, shedding, and consumption, amounted to a maximum of 4.5% of total aboveground production. A comparison of biomass data from forests in the lake states suggests that 100 to 200 t/ha (above—ground dry weight) is inclusive of most second—growth forests. The upper and lower bounds for mature forests were projected to be °600 and 60 t/ha. Estimates of aboveground productivity for a variety of forest ecosystems within the lake states had a narrow range from 7.1 to 10.4 t°ha(—1)@?year(—1).
Activity Patterns, Body Temperature and Thermal Ecology in Two Desert Caterpillars (Lepidoptera: Sphingidae)
Authors: Casey Timothy M.
Published: May 2006

The activity patterns, body temperatures, microhabitat characteristics and feeding behavior of larvae of two sphinx moths which inhabit the Mojave desert were investigated. Hyles lineata occurred in association with and fed upon a variety of desert annual plants; Manduca sexta was associated with only one plant species, Datura metalloides, a perennial. Body temperatures of H. lineata were relatively constant over a wide range of air temperatures; body temperatures of M. sexta approximated the air temperature for most of the day. Elevated T_b was associated with exposure of the larvae to direct solar radiation and high ground temperatures. Hyles lineata regulated T_b by orienting with respect to solar radiation and exploiting thermal heterogeneity in its microhabitat. Manduca sexta was shielded from solar radiation and thermal reradiation by its foodplant and never voluntarily spent time on the ground. Feeding and locomotor activity in both species were reduced during periods of both high and low air temperatures but were not related to time of day. Upper lethal temperature in saturated air was 45 degrees C for both species. Feeding rates were strongly dependent on body temperature in both species. Hyles lineata is a generalist, utilizing a variety of energy resources; the occurrence of M. sexta in the desert may depend on the presence of a single plant species, the jimson weed.
Effects of Interspecific Competition on Fitness of the Hermit Crab Clibanarius Tricolor
Authors: Bach Catherine , Hazlett Brian , Rittschof Dan
Published: May 2006

Clibanarius tricolor overlaps strongly in shell utilization with the other common species of intertidal hermit crabs found in the Florida Keys. Laboratory observations indicated C. tricolor can dominate Clibanarius antillensis in shell fights, while Calcinus tibicen dominates C. tricolor. In micro—areas of sympatry with C. antillensis, C. tricolor's shell fit is better and egg production parameters not affected when compared to adjacent areas where only C. tricolor occurs. Sympatry with Calcinus tibicien in a poorer shell fit, a smaller shell size for a given size crab, a smaller mean size of crab, and a disruption of the relationship between clutch size and crab size:shell weight ratio. A strong effect of shell species on the probability of ♀ ♀ being ovigerous was noted. It is suggested that the ecological separation which characterizes these species over most of their ranges was an evolutionary response, in part, to the effects of interspecific shell competition.
A Temperate Region Plant‐Ant‐Seed Predator System: Consequences of Extra Floral Nectar Secretion by Helianthella Quinquenervis
Authors: Inouye David W. , Taylor Orley R.
Published: May 2006

Helianthella quinquenervis (Asteraceae), the aspen sunflower, secretes sugar and amino acid rich nectar from involucral bracts during bud and flowering stages. The nectar is usually collected by ants as fast as it is secreted. H. quinquenervis is subject to predispersal seed predation by larvae of several insect species, primarily tephritid flies, an agromyzid fly, and 3 Lepidoptera. When present, ants interrupt oviposition efforts by the female flies but do not appear to be effective against lepidopteran or mammalian herbivores. The degree of protection by ants conferred upon plants was investigated by excluding ants from some plants and by correlating ant density with subsequent damage to ovules and developing seeds. At higher elevations (2896 and 3091 m) damage to plants with ants was significantly reduced compared with plants without ants. At a lower elevation (2734 m) where seed predator and ant densities were highest, the ants were less effective as deterrents and predation on ovules and seeds usually exceeded 60%. Flowers of some other composite species in the same habitats appear to be more effectively protected from predation by chemical deterrents, raising questions of the relative benefits of chemical deterrents compared to ants as a means of protection.
Habitat Constraints on the Behavior, Morphology, and Community Structure of Anolis Lizards
Authors: Moermond Timothy C.
Published: May 2006

A conceptual model of Anolis—habitat interactions is proposed to explain the existence of the series of Anolis ecomorphs in the Greater Antilles. The use of perches, type of movement among perches, and the morphology of 7 species of Anolis lizards from 2 sites in Haiti were compared. Movements of anoles through the habitat are assumed to be constrained more by the dispersion of perches rather than the characters of the perches themselves. The habitat is viewed as consisting of three—dimensional structural matrices of perches differing primarily in the diameters, lengths, and distances apart of the perches. Species occupying divergent types of perch matrices are shown to differ in: (1) the rapidity of moves on surfaces, (2) the frequency of jumps between surfaces, and (3) the distances jumped between surfaces. These species can be separated into jumpers, runners, and crawlers based on movement type and various body and limb proportions. The horizontal and vertical distribution of each species within a habitat gradient coincides with the distribution of the particular perch matrices to which the species is adapted. The varying degree of restriction imposed by perch matrices may have important evolutionary implications, particularly for the dispersion of size classes within the habitat and hence for species' exploitation strategies. Applications of this approach to aboreal primates and foliage—gleaning birds are suggested.
The Hubbard Brook Ecosystem Study: Forest Nutrient Cycling and Element Behavior
Authors: Whittaker R. H. , Likens G. E. , Bormann F. H. , Easton J. S. , Siccama T. G.
Published: May 2006

Data from dimension analysis of forest biomass and production are combined with analyses of plant tissues, soil, and precipitation to describe nutrient cycling in a cool—temperate deciduous forest on a podzol. Mean concentrations of nutrient elements measured (N, P, S, Ca, K, Mg, Mn, Na, Fe, Zn, Cu) in tissues are relatively low, and nutrient stocks in vegetation are low compared with other forests because of the low concentrations and the relative youth of the forest (cut in 1909—17). The largest fractions of nutrients in aboveground net primary production (NPP) go into leaves–58—78% of all nutrients except Na (45%)–although leaves are only 40% of aboveground NPP. Net community (woody) growth included °30% of aboveground NPP, but smaller fractions of nutrients (7% of N and K to 21% of Ca and 28% of Na). Nitrogen, P, and some other elements are retracted from dying leaves; but concentrations of Ca, Mn, and Na increase from living to dead leaves, branches, and stem wood. Return to the soil from aboveground is primarily by leaching for K and Na but by litterfall for other elements. "Throughflow" is defined as nutrient uptake needed beyond that in NPP to provide for both leaching and increase in dead tissues before they fall. For Na, throughflow exceeds uptake into NPP; but negative throughflows for N and P reflect conservation of these elements. Belowground plant nutrient stocks are 0.25 to 0.5x and belowground uptake rates into NPP are 0.1 to 0.2x aboveground values for most elements, but belowground values are higher for N, P, Na, and Fe. Significant amounts of some elements, especially S, Ca, K, and Na, are exuded from roots as part of the total, above— and belowground throughflow. Behaviors of nutrient elements can be characterized by ratios expressing concentration into leaves vs. woody tissues and relative leachability and throughflow vs. conservation. Relative turnover rates compare litterfall plus leaching with aboveground stocks or with nutrient contents of NPP. Turnover rates increase in the sequence: N and P; Ca; Mg, K, Fe, and Mn; S; and Na. Means and coefficients of variation of foliage nutrient concentrations express some differences between ecosystems. Comparing different ecosystems, coefficients of variation are low for N and P, intermediate for Ca, K, Mg, and Al, and high for Si, Mn, Fe, Cl, and Na. Differences in these and other expressions of element behavior can be interpreted on the basis of function in plants.
Likelihood Measures of Niche Breadth and Overlap
Authors: Petraitis Peter S.
Published: May 2006

Currently used niche measures of overlap and breadth are shown to be inappropriate for analyzing field data. Previously proposed measures assume resources are equally available, but this assumption is unwarranted in field studies. Comparisons of different measures of either breadth or overlap are also not valid. A measure of niche breadth is derived by asking how likely it is that a species' utilization of resources could have been drawn from the available resources in the environment. An overlap measure is derived in a similar manner and represents the likelihood that the utilization of resources by one species is identical to the utilization by another species. Tests for comparing different measures are given.
Primate Social Groups as Biological Islands
Authors: Freeland W. J.
Published: May 2006

The intestinal protozoan faunas of 11 social groups of Cercocebus albigena, 3 groups of Ceropithecus mitis, 3 groups of Cercopithecus ascanius, 2 groups of rain forest and 4 groups of savannah Papio anubis are documented. All individuals in a particular social group exhibit identical protozoan faunas. All social groups of each species, except the savannah P. anubis, exhibit intergroup differences in the composition of their protozoan faunas. The number of intestinal, protozoan species in Cercocebus albigena social groups is a function of group size. The similarity between the protozoan faunas of different C. albigena groups is related to the density of the social groups and types of land tenure in particular localities. Past social history of C. albigena groups may have some influence on the level of similarity of different groups' faunas. Entrance of a nongroup member into a group of Cercopithecus mitis resulted in an increase in the species richness of the group's protozoan fauna. Group fission may result in reduction of a group's protozoan species richness. All groups of savannah Papio anubis exhibit identical protozoan faunas. I argue that this is because savannah P. anubis has a higher rate of exchange of individuals between groups than has been recorded for the rain forest primates under consideration. I hypothesize that the differing rates of exchange are due to disease—related selection against traits which result in high rates of individual exchange among rain forest primate groups. Primate social groups are functionally biological islands; the species of their protozoan faunas changes according to group size and levels of protozoan migration between groups.
An Experimental Analysis of Dispersal in Fluctuating Vole Populations: Demographic Parameters
Authors: Gaines Michael S. , Vivas Antonio M. , Baker Crystal L.
Published: May 2006

Demographic attributes of dispersers from Microtus ochrogaster populations in eastern Kansas, USA, were characterized by three experimental methods: (1) voles were trapped and removed from two grids every 2 wk from 1973—1977 and voles that colonized these vacuums were compared to residents on neighboring control grids; (2) two grids were burned in the springs of 1976 and 1977; voles colonizing grids during a 6—wk period after the fire were compared to resident voles before the fire; (3) ten virgin male and female voles from a laboratory colony were introduced in 1975—1976 and again in 1976—1977 into three fenced enclosures equipped with exit doors. After breeding populations were established, voles emigrating through exit doors were compared with voles remaining inside the enclosures. In the removal—grid and fenced—enclosure experiments, more dispersal occurred when resident populations were increasing or at peak densities than during phases of declining density. The loss from control grids attributable to dispersal onto removal grids was 22% higher during phases of increasing density than during phases of declining density. In all experiments, fewer dispersing adult females were in reproductive condition than residents, and subadults showed the greatest dispersal rates of all age classes. Subadult female dispersers were in reproductive condition more frequently than residents in the removal experiment but less frequently than residents in the burning experiment. In all experiments there were no consistent differences between residents and dispersers in breeding activity of adult or subadult males. More males than females dispersed in the removal experiment but not in the burning or enclosure experiments. Density data for populations in fenced enclosures with exit doors indicated that immigration as well as emigration are necessary for multiannual cycles in numbers.
Metabolism, Critical Oxygen Tension, and Habitat Selection in Darters (Etheostoma)
Authors: Ultsch Gordon R. , Boschung Herbert , Ross Martha J.
Published: May 2006

Six species of darters (Etheostoma) were studied in the field and laboratory to relate respiration to habitat selection. The species ranged in habitat preference from a fast—water form (Etheostoma rufilineatum) to a slow—water form (Etheostoma fusiforme). Field measurements showed that winter O_2 tensions were not limiting the distribution of the darters when these tensions were compared with the critical O_2 determinations made in the laboratory at a low temperature (10 degrees C). However, summertime ambient O_2 levels were as low as 3.3 ppm [= 7.33 kilopascals or 55 mm Hg], a level that was 1.0—1.7 ppm below the wintertime critical O_2 tension (P_c) of several of these species. The fishes compensated for this by lowering P_c in the summer. This finding is contrary to previously reported results on the relationship between P_c and temperature. While not all darters selected habitats such that the downward shift of P_c in the summer was of ecological consequence, this was the case in 1 of the slow—water stream forms (E. boschungi) which inhabits waters in the summer that would be uninhabitable without such a shift in P_c. Additionally, one of the darters that typifies fast—water habitats (E. rufilineatum) had a P_c of 6.1 ppm [= 14.0 kilopascals or 105 mm Hg), which prevented it from occupying slow waters in the summertime. However, such respiratory exclusion from available habitats is not the case in the other stream forms studied (Etheostoma flabellare, Etheostoma squamiceps, and Etheostoma duryi), nor do these other stream forms occupy waters as slow as they are capable of on the basis of respiratory abilities. Therefore, a limited tolerance to low O_2 levels at summertime temperatures is not the general cause of the preference of Etheostoma for streams, although this is the case in some specific instances. In addition, the stillwater from (E. fusiforme) does not have any respiratory advantage over many of the stream forms in terms of a low metabolic rate or low P_c. However, darters as a group do show a rather low metabolic rate when compared to freshwater fishes in general.
The Weibull Distribution: A New Method of Summarizing Survivorship Data
Authors: Pinder John E. , Wiener James G. , Smith Michael H.
Published: May 2006

Survivorship data can be effectively summarized using the shape and scale parameters of the Weibull frequency distribution. The shape parameter controls the rate of change of the age—specific mortality rate and, therefore, the general form of the survivorship curve. Estimates of shape and scale parameters and their confidence intervals can be easily calculated and used to compare survivorship curves of different populations.
Foraging in Seed‐Harvester Ants Progonomyrmex SPP
Authors: Whitford Walter G.
Published: May 2006

Pogonomyrmex rugosus, a group forager, foraged preferentially on seeds of plant species with shed large quantities of seeds at 1 time. Pogonomyrmex desertorum, an individual forager took seeds in relation to their availability but concentrated on grass seeds late in the growing season. Pogonomyrmex californicus selected seed species which allowed it to avoid contact with its congeners. During a dry year, P. rugosus exhibited little selectivity, supporting the idea that selectivity should be decreased under conditions of low food abundance. Pogonomyrmex spp. removed a significant fraction of the seed production of only 1 species, Boutleoua barbata. It is suggested that Pogonomyrmex foraging may affect the relative abundance of plant species.
Sexual Reproduction in Agaves: The Benefits of Bats; The Cost of Semelparous Advertising
Authors: Howell D. J. , Roth Barbara Schropfer
Published: May 2006

The pollination success of Agave palmeri is strongly dependent on nectar—feeding bats. In areas with very low or nonexistent bat populations, Agave seed set is <5% of its maximum potential. A 30 yr trend of declining seed set parallels a decline in bat numbers during that period. We speculate that habitat destruction and an increase in human use of Agave are causal factors. Over half of the measurable energy in the plant biomass is allocated to advertising and reproduction. We discuss the costs and risks involved in the semelparous strategy when pollinators decline. Where bats remain, agaves in dense patches show higher seed set than do outlying plants, suggesting that the pollinators favor grouped plants. This behavior may reinforce the plants' colonial tendencies.
The Guild of Myrmecochores in the Herbaceous Flora of West Virginia Forests
Authors: Beattie Andrew J. , Culver David C.
Published: May 2006

Analysis of herbaceous vegetation and ant activity in random quadrats from 10 forest sites in West Virginia, USA, shows that ant—dispersed (myrmecochorous) plant species constitute about 30% of the herbaceous flora. Twenty—one such species were encountered in this study, three of which were not previously known myrmecochores: Carex jamesii, C. laxiculmis and Luzula echinata. Ant activity is a good predictor of the number of myrmecochorous species at a given site. There is also a weak correlation between ant activity and overall herbaceous species richness. A matrix of correlation coefficients and Wisconsin ordination suggest that the ant—dispersed species constitute a guild. The number of species in a guild for a given site may be limited by competition for ant diaspore vectors, and/or germination microsites. These resources are likely to be especially critical for shade—adapted forest herbs which experience nutrient stress. The ant—diaspore mutualism is viewed as a strategy to overcome nutrient scarcity, and the present study shows clearly that it is a major factor in forest herbaceous communities.
The Evolution of Coloniality in White‐tailed and Black‐tailed Prairie Dogs (Sciuridae: Cynomys Leucurus and C. Ludovicianus)
Authors: Hoogland John L.
Published: May 2006

In a 6—yr study, I investigated possible selective bases for coloniality in two species of squirrels (Sciuridae): loosely colonial White—tailed Prairie Dogs (Cynomys leucurus) and densely colonial Black—tailed Prairie Dogs (C. ludovicianus). White—tail study sites were in Wyoming and Colorado, USA; Black—tail study sites were in Colorado and South Dakota. I examined three hypotheses that might explain the evolution of coloniality: (a) shortage of suitable habitat, (b) social facilitation of foraging, and (c) reduced predation. The apparent surplus of unused suitable habitat and the absence of isolated individuals both indicated that prairie dogs are not forced to live together because of habitat shortages. An analysis of prairie dog foraging patterns indicated that there is no social facilitation of foraging in terms of either (a) group hunting of either large or elusive prey, (b) the location of large, scattered food supplies, (c) modification of the soil in order to effect the growth of vegetation that is more favorable or more abundant than that which would otherwise result, or (d) group defense of foraging grounds. Three lines of evidence indicate that reduced predation may be the most important benefit of prairie dog coloniality. First, simulated predatory attacks by badgers (Taxidea taxus) indicated that individuals in large wards (subcolonies) detect predators more quickly than do individuals in smaller wards; further, Black—tails detect predators more quickly than do White—tails. Second, individuals in large wards devote proportionately less time to alertness (i.e., scanning for predators) than do individuals in smaller wards, and Black—tails are less vigilant than are White—tails. Third, breeding synchronization and center—edge differences in individual alertness both indicate the possible importance of self herd effects. Interspecific differences in ward size and ward density may ultimately result because White—tail habitats contain significantly more protective cover than do Black—tail habitats.
Predation, Physical Stress, and the Organization of a Tropical Rocky Intertidal Hermit Crab Community
Authors: Bertness Mark D.
Published: May 2006

Predation pressure and physical stress are shown to be important selective pressures on hermit crabs in the Bay of Panama, influencing their intertidal distributions, shell preferences, and behaviors. Predation on hermit crabs by shell—crushing teleost fish and crabs is greatest in the low intertidal habitat and decreases in the high intertidal environment where physical stresses are the most intense. Pagurus sp. (undescribed) lives in the low intertidal habitat exclusively and prefers relatively heavy shells with narrow apertures which reduce vulnerability to predation while decreasing resistance to thermal stress. Calcinus obscurus is found in the middle to low intertidal environment, and Clibanarius albidigitus has a middle to high intertidal distribution, partly as a result of active competitive displacement by C. obscurus from the low intertidal habitat. These two speices prefer shells that minimize thermal stress and give relatively little defense against predators. Predation in these crabs is avoided by a behavioral escape response most acutely developed in C. obscurus, while C. albidigitus is superior to C. obscurus in withstanding thermal stress. Habitat and shell resource utilization pattern sin this tropical hermit crab community can be interpreted to represent the result of a complex interaction between predation, physical stress, and competitive pressures.