bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Grazing by the Limpet, Acmaea Insessa, on the Kelp, Egregia Laevigata, in the Intertidal Zone
Authors: Black Robert
Published: May 2006

The limpet Acmaea insessa lives on and east only the kelp Egregia. In the intertidal zone around Santa Barbara, California, USA the grazing activities of this limpet caused extensive and conspicuous damage to the majority of the larger Egregia. Severe damage weakened the main axis of the algae and was associated not only with loss of parts of Egregia, but also with one—third of the individuals found cast ashore; the remaining two—thirds suffered detachment from the substratum. The distribution of Acmaea insessa among Egregia was not uniform. Settlement of the limpet on experimental groups of algae was greater on old, post—reproductive Egregia than on new Egregia, was greater on crowded algae than on isolated algae, and was greater on individuals with adult limpets already on them than on individuals without limpets. The density of limpets increased with increasing algal length. Results of these settlement patterns were that crowded algae suffered limpet—related mortality than isolated algae, and loss of parts of individuals was more prevalent among large algae. These risks associated with loss and mortality of Egregia were countered by better survival and faster growth of small limpets in grazing scars than on intact surfaces. Experimental tests of other effects of limpet on Egregia revealed that damage by the limpet did not affect growth rate of algae or the timing and numbers of reproductive sporophylls. However, Egregia did respond to loss of parts by producing more branch rachises than those plants remaining intact. Evidence from this and other studies suggests that, although isolated Egregia suffered less mortality from limpets and had several other advantages over crowded algae, their large size was associated with mortality by detachment which may have balanced or outweighed the advantages of isolation. Loss of rachises because of grazing damage, a form of pruning by the limpet, could have served the beneficial function of preventing an Egregia from becoming so large that it was susceptible to detachment. Egregia has several escape mechanisms from the prudent predator Acmaea insessa.
The Production and Standing Crop of Litter and Humus in a Forest Exposed to Chronic Gamma Irradiation for Twelve Years
Authors: Armentano T. V. , Woodwell G. M.
Published: May 2006

Continuous exposure since 1961 of an oak—pine forest at Brookhaven National Laboratory to chronic gamma irradiation has shown: (1) progressive reduction in litter production from the first year through 1965; (2) greater litter production in 1973 compared to 1965 at exposure rates below 9 R/day primarily because of the prolific sprouting of the oaks, especially Quercus alba; (3) further reduction in litter production in intermediate zones (14—49 R/day) from 1965 to 1973 as a result of replacement of the forest by a Carex pensylvanica mat; (4) increased litter production in the high exposure zone (125 R/day) in 1973 as a result of colonization by adventive species; (5) reduction in the standing crop of litter by 1973 at the lowest exposure rate studied (3.5 R/day) although in 1965 there was no reduction at exposure rates up to 15 R/day; (6) decline in humus content at 46 R/day and above with the standing crop in the Carex zone exceeding that of the shrub and damaged forest zones of lower exposures. Both further losses and partial recovery in the production and storage of organic matter have occurred since 1965. These changes constitute a portion of the long—term response of the forest to chronic disturbance. The pattern of response is the result of ecosystem processes that are still not in equilibrium with the chronic disturbance and which are not predictable from short—term studies, even those spanning as much as 4 yr.
Economics of Feeding Territoriality in the Golden‐Winged Sunbird
Authors: Gill Frank B. , Wolf Larry L.
Published: May 2006

Feeding territories of Golden—winged Sunbirds contain enough energy to support an individual's daily energy requirements, and the amount of nectar per flower inside a territory tends to average higher than in adjacent undefended flowers. When undefended nectar levels are low (especially below 2 @ml per flower) the costs of territorial defense can easily be offset by energy saved from shortened foraging time budgets made possible by feeding at the higher average nectar levels. At higher undefended nectar levels the costs of territorial defense should no be recoverable. The balance between these costs and gains appears to define the conditions when territorial defense in this species is advantageous.
Thermal Biology of a Solitary Lizard: Anolis Marmoratus of Guadeloupe, Lesser Antilles
Authors: Huey Raymond B. , Webster T. Preston
Published: May 2006

To describe the thermal biology of Anolis marmoratus, a species living without congeners, we obtained 29 samples of air and body temperatures. Mean body temperatures (range 9.9°) differ from locality to locality, among habitats within localities, and during the day. Strong correlation of mean body with mean air temperatures among samples suggests that these lizards are routinely passive to ambient conditions. Indeed, short—term thermoregulatory behaviors such as basking and regulation of times of activity are rarely used by individuals in most populations. Nonetheless, evidence of habitat selection at one locality suggests that these anoles have long—term thermal preferences. The broad thermal niche of A. mamoratus seems primarily due to individual eurythermy rather than to populational differentiation. The general passivity of this and some other anoles may be an adaptation to life in tropical forests, where careful thermoregulation is disadvantageous.
Net Growth Rate through Time as an Indicator of Ecological Similarity Among Phytoplankton Species
Authors: Lewis William M.
Published: May 2006

Demographic data on 30 phytoplankton species of Lake Lanao, Philippines, are used to test some specific hypotheses relating ecological similarity of species to their phylogenetic relationship, mean abundance, size, surface: volume ratio, and morphology. Ecological similarity is quantified in terms of the correlation of weekly growth rates for species pairs over a 65—week period. About ⅓ of all 435 unique species pairs produce significant positive correlations. The frequency distribution of the correlation values is displaced to the right of zero to the extent that there are no significant negative correlations. This is interpreted as evidence against strong interspecific antagonisms such as those which might be produced by heteroantibiosis. The incidence of significant positive correlations is significantly higher among pairs belonging to the same taxonomic division or among pairs having the same morphotype than among pairs chosen at random. Species grouped by size, S/V ratio, or mean abundance are not significantly more similar to each other than the species chosen at random. On this basis phylogenetic relationship and morphotype appear to be of general (i.e., strategic) significance in community organization, whereas size and S/V ratio are of specific (i.e., tactical) significance because they are relevant in the reaction of species to certain environmental variables but not to others. Mean abundance, which is itself a manifestation of such specific characters as S/V ratio and morphology, fails as agrouping criterion because succession proceeds by shifts in both dominant and rare species. The greater similarities observed between species of common phylogenetic relationship or morphology, while statistically detectable, are quantitatively weak and thus suggest relatively poor coherence of species groups.
Density‐Dependent Aspects of Growth and Metamorphosis in Bufo Americanus
Authors: Wilbur Henry M.
Published: May 2006

Larvae of Bufo americanus (Anura: Bufonidae) were reared at controlled densities and food levels in laboratory populations and at controlled densities in enclosures in a farm pond in one— and two—species populations. Survival during the larval period was independent of population density however, the proportion of the population that successfully metamorphosed was a negative, exponential function of density. This outcome is interpreted as the result of the effect of density on the growth rate of larvae. In high density populations, a few individuals grow at the expense of smaller members of the cohort, which then have a lowered probability of metamorphosis. In spite of the strong effect of environmental heterogeneity in field experiments, the mean size at metamorphosis was significantly decreased as the initial density of either Bufo (—0.00031 g—body wt per unit increase in density) or Rana palustris (—0.00020 g—body wt per unit increase) was increased. Rana palustris frequently breeds at the same time and in the same ponds as B. americanus in the Piedmont of the Carolinas. At low densities there is an Allee effect in which body size increases with population densities between 1 and 20 individuals. As food becomes limiting, body size decreases with density in crowded populations.
Selection for Optimal Life Histories: The Effects of Age Structure
Authors: Schaffer William M.
Published: May 2006

The theory of optimal reproductive strategies has traditionally been studied in two ways: formal analysis of simple models that neglect the effects of age structure, and computer studies of complex life histories. Each of these approaches has disadvantages. The consequences of simple models sometimes dependmore on the nature of the simplifying assumptions than on the biological issues in question. On the other hand, computer simulations are only as general as the examples considered. The present study seeks to extend the formal analysis of optimal life histories to complex cases. I show that an optimal life history maximizes for each age class the expected fecundity at that age plus the sum of all future expected parameters. This result enables us to determine, at least inthe case of a three—stage life history, the manner in which the optimal reproductive effort at each age depends on the efforts made at the other ages, and thus, the coevolution of the various age—specific efforts. Three cases are distinguished: (1) If fertility and post—breeding survival and growth are concave functions of reproductive effort (i.e., have second derivatives that areeverywhere negative) there is a single set of age—specific reproductive rates towhich the system evolves regardless of initial conditions. This set of reproductive rates corresponds to an iteroparous life history (repeated breeding at different ages). (2) On the other hand, if fertility and subsequent growth and survival are convex functions of effort (positive second derivatives), semelparity (a single, herculean reproductive effort, followed by death) will most often evolve. However, an alternative, iteroparous life history sometimes exists, although stability considerations suggest that it may be transitory. (3)More realistic fertility and growth survival functions can generate alternative reproductive strategies that are stable since each represents a local maximum infitness. Often one of these alternatives corresponds to semelparity, the second to repeated reproduction. In such cases, the evolutionary outcome depends on initial conditions. This suggests that related species, with similar ecologies, may have very different life histories, the differences resulting from historical accidents that have trapped each on a different adaptive peak. The Salmonid genera, Salmo and Oncorhynchus, are suggested as possible examples.
Effects of Urbanization on the Salamander Desmognathus Fuscus Fuscus
Authors: Orser Paul N. , Shure Donald J.
Published: May 2006

Five spring—fed streams near Atlanta, Georgia, comprise an urbanization gradient ranging from severely distributed to undistributed conditions. Population densities of the dusky salamander, Desmognathus fuscus fuscus, were estimated within these streams and were inversely proportional to the degree of urbanization. Differences in the chemical parameters among the stations, while reflecting habitat disruption, were not considered limiting factors on salamander densities. Analysis of invertebrate prey availability indicated no significant difference among the stations. Salamander populations were significantly affected by scouring caused by increased runoff and soil erosion in disturbed areas. Differences in salamander densities were also attributed to relative stability of the bank soils and availability and dispersal of protective cover. More cohesive substrates and increased availability of ground cover at the less distributed areas offered greater stability against erosion and better habitats for salamander burrowing. Urbanization thus creates physical instability within stream habitats. Such instability results in a disruption of trophic structure by a reduction or loss of this major stream predator.
Autecology of Atriplex Polycarpa from California
Authors: Sankary Mohamed Nazir , Barbour Michael G.
Published: May 2006

Atriplex polycarpa (Torr.) Wats. was a dominant, palatable shrub of the xeric Atripleto—Brometum disclimax in the San Joaquin valley of California. Overgrazing and agriculture during the past 100 years have restricted its present distribution to saline or fenced areas. Optimal germination temperatures (9—15°C) are close to those that prevail in nature in November, the month of utricle dispersal. Germination is rapid and can occur over a wide range of temperatures (3—33°C); it is reduced by light and NACl > 1%, but indifferent to temperature alternation and soil CaCO3 content. It is unlikely that the bracteoles contain inhibitors. In a field plot in the Temblor Range of California, during a growing season with 115 mm precipitation, none of the seeds sown produced an established seedling, possibly because of competition by introduced annuals. Optimal growth conditions were 18—hour photoperiod, 24 ± 4°C. Growth at 12°C was quite slow. If conditions are favorable A. polycarpa can produce a large biomass, but it possesses a long juvenile stage of > 2 years prior to flowering. The base value of shoot water potential at no moisture stress is —18 bars, but this can be modified downward by pre—exposure to minor cycles of drought. This species can endure soil moisture below that which causes ultimate wilting or sunflower plants and can recover from a shoot water potential as low as —69 bars. Plants in nature, in August, exhibited a shoot water potential as low as —58 bars. This species was compared in a number of ways to Syrian ecological equivalents Haloxylon articulatum and Salsola vermiculata var. villosa.
Phenology and Growth of Rocky Mountain Populations of Deschampsia Caespitosa at Three Elevations in Colorado
Authors: Pearcy Robert W. , Ward Richard T.
Published: May 2006

Populations of Deschampsia caepitosa (L.) Beauv., collected from 20 sites in Colorado, northwestern Wyoming and western Montana, were studied for patterns of ecotypic differentiation. Three uniform gardens in northcentral Colorado, at elevations of 1,580, 2,740 and 3,570 meters, were utilized to represent the range of environments for the populations. The populations were consistently different from each other in stature and rates of phenological development at all gardens. The patterns of response could be closely related to elevational gradients and differences in the length of the growing season of the native sites. Populations from high elevation sites with short growing seasons were earliest in development, had shorter periods of growth, and were shorter in height than those from low elevations. Survival of all populations was high in all three gardens after the effects of disease in the lowest garden were accounted for.
Fire and Manzanita Chaparral in the San Jacinto Mountains, California
Authors: Vogl Richard J. , Schorr Paul
Published: May 2006

Arctostaphylos glandulosa chaparral at 1,019 m (4,000 ft) elevation retained the same vegetational dominants after burning by producing root crown sprouts and/or seedlings. The floristic composition was changed by the appearance of annual species not found in the unburned chaparral. Most, if not all, of these herbs are considered to have arisen from seeds stored in the litter and or/soils. Post—fire succession is similar to that established for the lower elevational chamise (Adenostoma fasciculatum) chaparral, but is more rapid since the temporary herbaceous cover reaches a peak the first year following fire. Post—fire seedling mortality was most evident in Ceanothus spp. Although manzanita and chamise produced prodigious numbers seedlings with burning, these seedlings are suspected of seldom contributing to mature chaparral cover. Shrub distribution patterns and post—fire succession, particularly the appearance of shrub and herbaceous seedlings, may be determined more by the presence or absence of ash and related pH changes than by other factors. Arctostaphylos and Ceanothus seedlings were most numerous on gentle slopes and level sites where a deep ash layer persisted, while Adenostoma seedlings grew on steeper sites where little ash was deposited. Natural fire occurrences are considered to be less frequent than in the lower elevational chamise chaparral and the higher conifer communities, perhaps occurring only once or twice a century.
Mineral Cycling in Coastal Foredune Plant Communities in Cape Hatteras National Seashore
Authors: van der Valk A. G.
Published: May 2006

At two sites on the front (oceanside), top, and back of the foredune, measurements were made of salt spray deposition and the quantity of cations (K, Na, Ca, and Mg) present on the surface and 20, 40, and 60 cm below the surface of the soil. Cationic inputs in salt spray were calculated by partitioning the cation content of bulk precipitation collected on the back of the fore dunes into salt spray and rainfall components. The biomass and cationic content of the dominant grasses and forbs were determined in all three zones from a combination of field measurements and estimates of the standing crop and from samples of each dominant species analyzed for their cationic content. On the average 55%, 34%, and 11% of the salt spray deposited on a foredune falls on the front, top, and back respectively. In all three zones Na (250—1,300 kg/ha°yr) was the most abundant cation input in the salt spray. It is followed by Mg (37—120 kg/ha°yr), Ca (19—120 kg/ha°yr), and Kg (13—77 kg/ha°yr). In rainfall, the annual input of cations was calculated to be 1.3, 26, 2.3 and 3.9 at Bodie Island and 1.0, 21, 3.4, and 3.0 kg/ha°yr at Ocracoke for K, Na, Ca, and Mg respectively. It appears that the total annual input of cations exceeds slightly their calculated annual outputs through leaching for all cations in all zones. Subsurface cation levels were very low: K (2—5 kg/ha), Na (17—88 kg/ha), Ca (5—17 kg/ha), and Mg (2—9 kg/ha). Estimates of the total standing crop of cations in the vegetation of a zone and inputs of cations in salt spray and rainfall indicate that the annual inputs of Na and Mg exceed their standing crops, while the annual input of K, and sometimes Ca, is smaller than its standing crop on the back.
Food Limitation of the Spider Linyphia marginata: Experimental Field Studies
Authors: Wise David H.
Published: May 2006

Field experiments were performed to determine whether the spider Linyphia marginata C. L. Koch is food limited, and, if so, whether a shortage of prey acts as a density—independent or density—dependent limiting factor. The experiments uncovered the effects of food supply, spider density, and the interaction of food and density upon survival (combined effects of migration and mortality), rate of increase in weight, and fecundity. Replicate, unenclosed spider populations were established at two densities, and natural food levels were supplemented by fruit flies added to the spider webs in one—half of the populations at each density. Adding food to the webs of immature spiders did not improve survival at either low or high spider density. Survival was lower in the high—density populations. Supplementing the food supply of immatures did increase the rate at which they gained weight. Density, however, had no negative effect on growth rate, indicating that though a shortage of food limits growth, immature spiders are not competing for food. Hence, for immature L. marginata, food supply acts as a density—independent limiting factor. For mature ♀ ♀, supplementing the food supply improved survival and increased fecundity. Spider density had a negative effect upon both survival and fecundity. There were no statistically significant interactions between food supply and density, probably because not enough food was added. It appears that mature L. marginata compete for food; hence, for them, food supply acts as a density—dependent limiting factor.
Breeding and Postlarval Migrations of the Redspotted Newt, Notophthalmus Viridescens, in Massachusetts
Authors: Healy William R.
Published: May 2006

Intrapopulation variation in migrant size and number was observed during a 2—yr study of the movement of efts and postlarval metamorphs at a pond in Charlton, Massachusetts. Rainfall strongly influenced the timing of both migrations and increased the growth rates of efts. In the wetter of the 2 yr efts were larger and more numerous, and the proportion of female migrants increased. Sex differences among efts in timing and magnitude were attributed to differences between males and females in the minimum size required for migration. Annual differences in larval density were associated with variation in the duration of the migration and mean size of emigrating metamorphs.
Some Notes on Estimating the Competition Matrix, a
Authors: May Robert M.
Published: May 2006

Recent theoretical and field work on communities of interacting species has employed various forms for estimating the competition matrix elements, αij, from utilization coefficients pia (which measure the relative utilization of the path resource category by the ith species). Some little—known properties of these forms are discussed. When more than one resource dimension is involved, there is in general no substitute for measuring the species' full multidimensional utilization functions; a critical discussion is given of the estimation of such multidimensional competition coefficient αij by products of one—dimensional coefficients.
The Role of the Territory in the Ecology of the Intertidal Limpet Lottia Gigantea (Gray)
Authors: Stimson John
Published: May 2006

The marine mollusk Lottia gigantea, a large grazing limpet of the upper intertidal zone, grazes algal film from a territory which it defends against intrusions by conspecifics and other grazers as well as the gradual encroachment of sessile organisms. The areas of the territories are correlated with the length of the resident Lottia, but for a given size of Lottia the areas vary greatly at different study sites. The thickness of the algal film charcteristic of the territory fluctuates, being greatest in spring. Experimental removal of abundant algal film from some territories in spring was followed by enlargement of these territories relative to controls. Growth rates of Lottia are positively correlated with the thickness of the algal film in their territories. The smaller limpets (1—2 cm in length) of the genus Acmaea are able to crop the algal film more closely than Lottia and will remove almost all the algal film from a territory if the territory—resident is removed. Experiments to determine whether territorial behavior sets a limit to the abundance of Lottia showed that removal of large individuals from the smooth surfaces they characteristically graze allowed smaller Lottia to move from less suitable sites and establish territories on the smooth surface. Experimental reduction of abundant algal film in enclosures where Lottia were living at high densities was followed by a decrease in the numbers of Lottia relative to controls. The decline in numbers of Lottia over 3 years in a population at the principal study site was due to a decrease in recruitment from the plankton or a low rate of survival of newly settled animals but was not a result of mortality induced by territorial defence. Territorial behavior of Lottia apparently evolved as an adaptation that allows the defence of a thick algal film necessary for growth of such a large grazing limpet. Defense of territories also keeps the grazing area free of sessile organisms that compete for space.
Competition in Cladoceran Communities: The Cost of Evolving Defenses against Copepod Predation
Authors: Kerfoot W. Charles
Published: May 2006

An intimate relationship is apparent between fecudity and predator resistance in clones of the parthenogenic cladoceran Bosmina longirostris. Young of certain clones possess spines slightly larger bodies, the thicker carapaces, all of which frustrate the handling tactics of predatory copepods. During periods of abundant resources, the resistance is purchased at considerable cost, since eggs and developing young are carried n a restricted space, a special brood chamber formed from the dorsal portion of the carapace. The energy used in the development of protective defenses comes from the egg yolk supply, leading to larger eggs and small broods. During the spring algal bloom in Union Bay, Lake Washington, long—featured lines carry few large eggs, while short—featured lines fill their pouches with many small lines in the inshore regions after fisher remove predatory copepods.
A Grassland Nitrogen Flow Simulation Model
Authors: Reuss J. O. , Innis G. S.
Published: May 2006

A dynamic simulation model of nitrogen flow in a grassland ecosystem has been developed. State variables in the model include the nitrogen in the following major components; soil ammonium, soil nitrate, live roots, dead roots, soil organic matter, live tops, and litter. Belowgrown components are subdivided into four depth layers. The model includes a simple producer—decomposer submodel, but the nitrogen sections have also been incorporated into the ELM 73 ecosystem model. Temperature and soil H2O driving variables are supplied from external sources. Nitrogen flows, plant growth, and plant decomposition are controlled by temperature, soil H2O, phenological stage of plant development, and the nitrogen status of the various components of the system.The interaction of the nitrogen components with production and decomposition rates allows nitrogen status to act as a control variable in ecosystem processes, an important feature in a grassland model. Test conducted to date indicate that the model performs in a realistic manner. Simulation of fertilizer effects has been satisfactory, and the model has been useful in identifying critical processes where further research is necessary for an understanding of the system.
Generalized Models of Two Species Interactions: A Graphical Analysis
Authors: Vandermeer John H.
Published: May 2006

A qualitative approach to modeling non—linear two—species systems is presented. The construction of isoclines of the equations dX_1/dt = 0, dX_2/dt = 0, where the X_1 are the population densities of two interacting species, is described intuitively. An analysis of singularities using graphical methods only is described. This is followed by a description of the behavior of various combinations of non—linear interactions, using the graphical techniques explained earlier.
Shift in the Structural Habitat of Anolis Opalinus Due to Congeneric Competition
Authors: Jenssen Thomas A.
Published: May 2006

The Jamaican Anolis opalinus has different perch height characteristics depending on locality. Toward the center of the island, around Mandeville, A. opalinus characteristically perches low, being classified as a trunk—ground species. In Kingston, however, A. opalinus perches high, classified as a trunk—crown species, Evidence indicates the Kingston A. opalinus would also perch low except that interaction with Anolis I. Lineatophus forces A. opalinus into perch sites higher than appear to be the species' preference.
Pollen Influx to Laminated Sediments: A Pollen Diagram from Northeastern Minnesota
Authors: Craig Alan J.
Published: May 2006

A pollen diagram is presented from Lake of the Clouds, Lake County, Minnesota, in the Boundary Waters Canoe Area. Of the 5.6 m of sediment analyzed, almost 5 m are laminated. The 9,349 laminations counted, composed of alternating dark organic and light layers, are annual varves which provide a time scale for study of vegetational history and calculation of pollen influx. The pollen concentration in each sample was determined by a technique involving the addition of microspheres. The pollen influx was calculated from the pollen concentration and varve count. Pollen concentration was very low in the herb pollen zone of late—glacial time. During postglacial time the pollen influx was generally 2—4 x 104 grains cm‐2 years‐1. The pollen diagram has been divided into six zones. Zone 1 records tundra—like vegetations; most of the pollen rain, which was sparse, was probably blown in from a great distance. Zone 2 records spruce forest, with some pine and thermophilous deciduous trees, succeeded in zone 3 about 9,200 years ago by forests dominated by jack or red pine or both. With the start of zone 4, dated about 8,300 years ago, alder migrated into the area, followed about 7,000 years ago by white pine, concurrently with the maximum eastward extension of prairie in the state. In the period represented by zone 5, commencing about 6,500 years ago, white pine was very important, spruce was at a minimum, and the climate was probably relatively dry. Environmental changes brought about increases of spruce and cedar and a decline of pine in zone 6, commencing about 3,000 years ago. The diagram is truncated at 200 years or more before the present.
Mapping Individual Plants with a Field‐Portable Digitizer
Authors: Mack Richard N. , Pyke David A.
Published: May 2006

A field—portable sonic digitizer has been developed for use in conducting rapid censuses of large numbers of small plants through time. The x, y coordinates of all plants (to the nearest 1 mm) within a 6.5 x 6.5 dm quadrant can be rapidly recorded onto a paper tape. Additional information for each plant may be recorded simultaneously onto the paper tape with a numeric keyboard. The unit also may be used to measure plant canopy coverage and map soil surface features.
Bird Versus Bats: Behavioral Interactions at a Localized Food Source
Authors: Shields William M. , Bildstein Keith L.
Published: May 2006

During June and July 1976, we investigated the foraging behavior and interactions of bats and common nighthawks (Chordeiles minor) at a localized food source in Columbus, Ohio. The patch consisted of insects attracted to a cone of light produced by six large (1000 W) spotlights illuminating a sign. While foraging in the light cone members of both taxa engaged in both intra— and interspecific chases. Seventy—five percent of the bat—initiated and 94% of the nighthawk—initiated chases had nighthawk targets. The smaller bats appeared to dominate the larger birds in all individual aggressive encounters. Members of both taxa foraged differently while using the patch. When either birds or bats foraged in the absence of members of the other taxon, they foraged low in the light cone. When birds and bats were present simultaneously, the aggressive interactions conditioned their foraging behavior. When together, bats remained in the lower zone of the light cone, while some nighthawks rose into the upper zones. When foraging in these upper zones, nighthawks suffered a decrease in foraging efficiency based on energetic considerations. They missed more prey per attempted capture, and either increased the time between captures or increased their foraging speed in the upper zones. In any case, more energy was expended by nighthawks foraging in the presence of bats than when they were alone. The expanded pattern of patch used by the larger yet socially subordinate nighthawks in the presence of bats supports Morse's (1974) hypothesis. Morse predicted that social dominance would be more important than body size in determining resource use in communities where interspecific aggression and dominance is important in resource partitioning.
Energy Metabolism and Food Consumption by Wild Howler Monkeys (Alouatta Palliata)
Authors: Nagy Kenneth A. , Milton Katharine
Published: May 2006

Rates of CO2 production in free—living and captive howler monkeys were measured using doubly labeled water, and assimilation of energy from natural foods was determined. Results permit construction of a field energy budget, and estimation of the feeding rate of these arboreal, plant—eating primates. Field metabolic rates averaged 355 kJ kg—1 day—1 (°2 x basal metabolic rate). Assimilation of the energy in a fruit and leaf diet was °40%. Feeding rate in the field is estimated to be °54 g dry matter kg— day—1, or °90 kg dry matter ha—1 yr—1.
Foraging by Cave Beetles: Spatial and Temporal Heterogeneity of Prey
Authors: Kane Thomas C. , Poulson Thomas L.
Published: May 2006

This study assesses the effect of temporal and spatial heterogeneity of preferred prey on the foraging strategies of two carabid cave beetles, Neaphaenops tellkampfii and Pseudanophthalmus menetriesii. Neaphaenops tellkampfii prefers the eggs and nymphs of the common cave cricket (Hadenoecus subterraneus) which are patchy in time but not in space. Cave cricket eggs are laid in sandy habitats which support few alternate prey. As a result N. tellkampfii is forced to switch diet, habitat, and foraging mode in the fall when cricket eggs and nymphs become rare. Pseudanophthalmus menetriesii preys on collembola that are confined to habitats with organic matter. These items are patchily distributed but continuously available. In sand or mud habitats collembola are rare and P. menetriesii appears to incur higher foraging costs in these habitats than in litter areas. As a result P. menetriesii shows restricted habitat preference and tracks its prey between various organic patches.
Plants Bearing Extrafloral Nectaries and the Associated Ant Community: Interhabitat Differences in the Reduction of Herbivore Damage
Authors: Bentley Barbara L.
Published: May 2006

Field experiments, designed to imitate the role of extrafloral nectaries, demonstrate that ants attracted to sugar droplets on plants can reduce the level of herbivore damage. This protection is more effective in disturbed habitats, such as forest clearings and edges, where ant—forager abundance is high. Natural nectary—bearing plants are more abundant in these same habitats. Other forms of disturbance such as annual flooding and fire, reduce ant abundance, reduce protection levels, and alter the frequency of natural nectary plants.
The Relationships of Locomotion to Differential Predation on Pseudacris Triseriata (Anura: Hylidae)
Authors: Wassersug Richard J. , Sperry David G.
Published: May 2006

Laboratory experiments, using the garter snake Thamnopphis sirtalis as predator and the chorus frog Pseudacris triseriata as prey, show that metamorphosing anurans are captured more frequently by T. sirtalis than either premetamorphic tadpoles frogs. Stomach contents of wild—caught Thamnophis have similarly revealed more anuran prey in transformation than at earlier or later stages. The high susceptibility of transforming Pseudacris to snake predation appears to be a direct consequence of a body form not conductive to effective locomotion. The sustained swimming ability of premetamorphic and metamorphic P. triseriata was examined in the laboratoy. It was found that until the eruption of the forelimbs, the larger a tadpole is, the longer it can maintain its position in a steady current. The length of the tail appears to be a positive factor in sustained swimming. Large hindlimbs do not appear to assist swimming and may increase drag. Tadpoles that have begun to metamorphose (forelimbs visible) demonstrate a greatly diminished ability to hold thei position in a current. The maximum jumping distance of metamorphic and postmetamorphic P. triseriata was also examined in the laboratory. Individuals which have just begun to metamorphose cannot hop as far as individuals which have advanced through metamorphosis and lost their tails. Amputation of the tails from early metamorphic individuals demonstrates the retarding role that the tail has on saltatory locomotion. Additional features, such as maturation of the anterior appendages, may also account for an increased jumping ability observed in P. triseriata as they progress through metamorphosis. Anurans spend a disproportionately short time in metamorphic transformation. The rapidity of this transformation appears to be an adaptation minimizing the amount of time anurans spend in this most vulnerable form.
Leaf Area of Mature Northwestern Coniferous Forests: Relation to Site Water Balance
Authors: Grier Charles G. , Running Steven W.
Published: May 2006

Leaf area of nature coniferous forest communities of western Oregon appears to be related primarily to site H2O balance rather than characteristics of tree species composing the community. Leaf areas were determined for stands in communities ranked along measured gradients of precipitation and evaporative potential. Nine coniferous and 1 deciduous tree species were found in the various stands along these gradients. Leaf areas of these stands were linearly correlated with a simple site H2O balance index computed from measurements of growing season precipitation, open pan evaporation, and estimates of soil H2O storage. Species composition had no apparent influence on the relation between community leaf area and site H2O balance.
Jackknifing An Index of Diversity
Authors: Zahl Samuel
Published: May 2006

The method of jackknifing is introduced for estimating an index of diversity and is illustrated with tree data. The method yields approximately normally distributed jackknife estimates and also gives estimated standard deviations, making possible tests of hypotheses and confidence interval estimates. These results apparently can be obtained under the usual conditions of field sampling, where associations within and between species or between quadrats or segments of a traverse may be found. Because of these associations there is no guarantee that the method works; hence an eyball and a statistical test for the approximate normality of the estimates are given and illustrated with the tree data. The tree data come from 24 quadrats arranged in two blocks of contiguous quadrats. The estimated tree—species diversity, using both indices considered, showed a smooth monotonic decrease over a 19—yr interval providing striking confirmation of the reality of this ecological parameter. The normality tests on this data showed that the normal approximations to the distributions of the jackknife estimates were justified, except in three instances, only one of which seemed to be seriously in error. A conclusion is that it seems reasonable to suppose that in many, if not most, cases, only moderate sample sizes will be needed in practice for the jackknife estimate, at least for forest data.
Processing of Leaf Litter by a Stream Detritivore: Effect on Nutrient Availability to Collectors
Authors: Short Robert A. , Maslin Paul E.
Published: May 2006

An artificial stream containing alder (Alnus rubra) leaves labeled with radiophosphorus, a shredder (Pteronarcys californica), and two collectors (Hydropsyche californica and Simulium arcticum) was used to test the processing effect shredders have on nutrient availability to collectors. The radioactivity accrued by the collector species was significantly greater (P <.01 for H. californica and P <.005 for S. arcticum) when the shredder was present. This indicates the importance of the leaf—processing activities of shredders in enhancing nutrient availability for collectors.
Vegetation of the Santa Catalina Mountains, Arizona. V. Biomass, Production, and Diversity along the Elevation Gradient
Authors: Whittaker R. H. , Niering W. A.
Published: May 2006

Measurements were taken in 15 communities along the elevation gradient from fir forest at high elevations, through pine forest, woodlands, and desert grassland, to deserts at low evelations in the Santa Catalina Mountains, Arizona, and in a Cercocarpus shrubland on limestone. Eight small—tree and shrub speices of woodlands and deserts were subjected to dimension analysis by the Brookhaven system. Aboveground biomass decreased along the elevation gradient from 36—79 dry kg/m2 in fir and Douglas—fir forest to 0.26—0.43 kg/m2 in the desert grassland and two desert samples. Net aboveground primary productivity similarly decreased from 1,050—1,150 g/m2° yr in mesic high—elevation forests to 92—140 g/m2° yr in desert grassland and deserts. Both biomass and production show a two—slope relation to elevation (and, probably, to precipitation), with a steeper decrease from the high—elevation forests to the mid—elevation woodlands, and a less steep decrease from dry woodlands through desert grassland into desert. The two groups of communities at higher vs. lower elevations also show different relations of leaf area index and chlorophyll to elevation and to productivity. The two groups may represent different adaptive patterns: surface—limiting, with low productivity in relation to precipitation but high production efficiency in relation to surface in the more arid lower elevations, vs. surface—abundant, with high productivity relative to precipitation based on high community surface area, but lower production efficiency in relation to this area, in the more humid higher elevations. Vascular plant species diversity shows no simple relation to productivity, but decreases from high—elevation fir frests to the pine forests, increases from these to the open woodlands, and decreases from dry woodlands through the desert grassland and mountain slope desert to the lower bajada (creosotebush) desert.
Energy Dynamics of Benthic Fishes in a Small Kentucky Stream
Authors: Small James W.
Published: May 2006

Energy dynamics of the benthic stream fishes, Etheostoma flabellare, Etheostoma spectabile, and Cottus carolinae were studied in an upper and lower section of Steeles Run, a small stream in central Kentucky. Production was estimated from the exponential model of growth and energy consumption with the use of models derived from laboratory studies on caloric intake and growth. For comparative purposes, energy consumption was also estimated with equations based on an approxiation of the metabolica rate. Both systems gave good agreement varying 2%—7%. Annual production estimates of 10.89 and 14.88 kcal/m2 were made for two upper and 3.56—2.58 kcal/m2 for two lower sections of stream. Annual consumption by these fish was estimated to be 52.22 and 67.59 kcal/m2 for the two upper and 21.83 and 17.87 kcal/m2 for two lower sections. Measurement of total fish standing crop gave 1.70—15.95 kcal/m2 for the upper and 1.15—7.83 kcal/m2 for the lower section. The three benthic species make up about 40% of this biomass. Food studies indicate benthic fish are the primary users of aquatic invertebrate production, other sampled species using mostly terrestrial production. Cottus carolinae spawns in winter and the other benthic species in spring. Caloric content varies and drops to its lowest point the season before spawning and then rises rapidly to its peak. Period of miximum growth rate differed among the benthic species; this division of resource usage may allow greater production.
The Regulation of Plant Species Diversity on an Early Successional Old‐field
Authors: Tramer Elliot J.
Published: May 2006

Patterns of plant species diversity were analyzed during the first 4 yr of succession on a small Ohio old—field. Diversity (—ϵ pi 1n pi) was calculated using both numerical abundance and biomass data. Abundance—based diversity and evenness were low during year 1 and early in year 2; they peaked quickly in July of year 2 after the disappearance of a numerical dominant and were stable at an intermediate level during years 3 and 4. Biomass—based diversity and evenness declined steadily until year 4, peaking earlier each successive year. Species richniess was highest year 1 and declined markedly during year 4. None of these patterns fit the conventional dogma that diversity increases during the early stages of succession. Changes in the life history strategies of dominants, slowing species turnover rates, and decreasing spatial heterogeneity all suggest that the observed diversity trends result from an r—K selection continuum operating during the early stages of old—field succession. Site—to—site variations in successional diversity trends may reflect differences in the land use histories of individual old—fields.
Allelochemic Effects of Petalostemon Gattingeri on the Distribution of Arenaria Patula in Cedar Glades
Authors: Turner Barbara Homan , Quarterman Elsie
Published: May 2006

Petalosdtemon gattingeri (Heller) Heller (Leguminosae) influences the distribution pattern of Arenaria patula Michx. (Caryophyllaceae) in cedar glades of middle Tennessee by means of inhibitors present at all seasons of the year in some or all parts of the Petalostemon plant. The inhibitors are leached from living plants and from litter shed in September and October and are retained by the soil. Inhibitors were neither degraded by aerobic bacteria nor leached away. Correlation of the life cycles of the two species and intraction with seasoanl precipitation ensures that inhibitors are present at the crucial time of germination and seedling establishment of Arenaria. In deeper soils, where the cover of Petalostemon, and therefore the production of inhibitors, is greater per unit area, the silt and clay fractions are sufficient to retain inhibitors that prevent germination and growth of Arenaria. In the more shallow soils, where there are coarser particles and less cover of Petalostemon, only stunting of growth occurs. It seems clear that Petalostemon affects the local distribution of Arenaria in the feild through allelochemic action on germination of seed and growth of seedlings.
A Preliminary Study of Seed Predation in Desert and Montane Habitats
Authors: Brown James H. , Grover Jill J. , Davidson Diane W. , Lieberman Gerald A.
Published: May 2006

Multifactorial experiments in which domestic seeds in shallow glass containers were distributed in desert and montane habitats provided data on identity of seed predators (whether rodents or ants), spatial and temporal pattern of their foraging activities, and their preferences for sizes and species of seeds. The results indicate that in some desert ecosystems both rodents and ants are important and efficient collectors of seeds. These two taxa overlap greatly in several parameters of seed utilization, suggesting that they are potentially close competitiors. Rodents removed much more seed than ants, perhaps because they are more efficient at locating and harvesting large clumps. This technique has considerable promise for assessing the significance of competitive interactions between distantly related taxa in natural ecosystems.
Community Diversity of Coastal Plain Forests in Southern East Texas
Authors: Marks P. L. , Harcombe P. A.
Published: May 2006

Forests on the coastal plain of southern east Texas have high within— and between—habitat diversity for woody species. High shrub diversity is responsible for high within—habitat diversity; a long topographic—moisture grandient may be responsible for at least part of the between—habitat diversity.