bluuebunny/crossref_metadata_2025 huggingface dataset:
Litter Decomposition in a Red Maple Woodlot Under Natural Conditions and Under Insecticide Treatment
Authors: Weary G. C. , Merriam H. G.
Published: May 2006

A coring technique was used to intensively sample the litter layer of a red maple (Acer rubrum) woodlot in the vicinity of Ottawa, Canada. Monthly changes in the litter standing crop provided an accurate estimate of the decomposition rate of red maple litter during 2 summers and 1 winter both under natural conditions and when treated with the insecticide Carbofuran®. The Standing crop of litter ranged annually between °275 and 700 g/m2 and decomposed at a rate between 1.48 and 2.19 g°m(—2)°day(—1) under natural conditions between May and November. A common carbamate insecticide (Carbofuran®) applied at recommended rates reduced the decomposition rates to between 0.99 and 1.26 g°m(—2)°day(—1) resulting in an increase in standing crop.
Life History Responses to Resource Variation in a Sessile Predator, The Ciliate Protozoan Tokophrya Lemnarum Stein
Authors: Kent Elaine B.
Published: May 2006

To identify the responses of a Predator to resource variation, age—specific fecundity and survivorship were measured at several food levels for the sessile, predatory ciliate protozoan Tokophrya lemnarum Stein. The major life history characteristics identified were: (1) a direct relationship exists between net reproductive rate and food level, (2) age—specific fecundity closely follows food intake rate (3) each embryo is endowed with a nutrient supply upon birth and (4) an inverse relationship exists between net reproductive rate—food level and life span. Totally starved individuals had the longest mean life spans. Increased survival time at low food levels probably results from low metabolic rate between meals and a slowed accumulation of toxic waste products. Fecundity is directly related to prey number and prey size. It is postulated that this set of adaptations acts to decrease variability of population size in a predator with cannot control its hunting rate and in which prey density must vary greatly during the lifetime of an individual.
Heated Taxidermic Mounts: A Means of Measuring the Standard Operative Temperature Affecting Small Animals
Authors: Bakken G. S. , Buttemer W. A. , Dawson W. R. , Gates D. M.
Published: May 2006

The theory and procedures for using electrically heated taxidermic mounts to measure the standard operative temperature, Tes, of natural habitats have been examined using the American Goldfinch, Carduelis tristis, Tes is a thermal index directly related to the metabolic requirements of a specific endothermic animal. Tes may be calculated from a thermal energy budget analysis. However, direct measurement of Tes using heated mounts as “environmental temperature thermometers” is simpler and allows measurements in confined spaces, such as nocturnal roots, which are inaccessible to conventional instrumentation. For the goldfinch, heated mounts predict metabolic heating less evaporative cooling with an uncertainty of ±5% for temperatures below the thermal neutral zone and winds of 0−1.5 m/s.
Factors Influencing the Distribution of Species of Californian Coastal Sage Scrub
Authors: Westman Walter E.
Published: May 2006

The distributions of species and species groups of southern coastal sage scrub in Alta and Baja California are examined in relation to structural and environmental variables. Variables examined include vegetative structure, geographic and topographic position, soil physical characteristics and macronutrient levels, substrate, temperature, precipitation, and factors of disturbance (fire, light grazing, air pollution). Evapotranspirative stress during summer months seems to be a major factor influencing species distributions. Mean temperature of the warmest month appears to be a better predictor of this stress than seasonal or annual precipitation levels. Many of the dominant species also respond sensitively to differences in soil fertility and parent material, with 18 of the 21 dominant species examined showing significant preference for a single substrate among seven classes. Among soil nutrients, levels of organic and nitrate nitrogen appear as particularly useful predictors of species distributions. Of disturbance variables, regional levels of air pollutants are correlated most strongly with floristic differences. Multiple linear regression equations are presented permitting prediction of species' foliar cover levels from levels of environmental variables. Geographic segregation of floristic associations within the sage scrub flora is most marked along a northwest—southeast axis paralleling the Pacific coastline, although southern inland (Riversidian) associations show affinities with the northern coastal flora. Medium—scale patchiness (° 0.1 ha) in floristic composition occurs within the sage scrub due to local dominance by one or a small number of shrub species. The possible ecological significance of this is briefly discussed.
Population Density and the Economics of Territorial Defense in a Coral Reef Fish
Authors: Warner Robert R. , Hoffman Steven G.
Published: May 2006

We propose that in some species, local population density can strongly affect the economic defendability of a mating territory. This is so because the numbers of females and potentially interfering males determine allocations of time and energy to reproduction and defense. At low densities, allocations to defense should be small and territorial mating success should initially rise with local density, reflecting the supply of females. If defense takes priority over mating, higher population densities can create a situation in which the time or energy devoted to defense against other males detracts from allocations to reproduction. Thus a point is reached where territorial mating success declines with increasing density, as a function of the number of nonterritorial males. We investigated these hypotheses by recording changes in the daily mating success of territorial males of the bluehead wrasse (Thalassoma bifasciatum) following experimental manipulations of local population size and composition. On large reefs, where mating population densities are already high, territorial mating success varied inversely with changes in overall population density and with changes in nonterritorial male numbers only; changes in female numbers had little effect. Thus at higher densities the demands of defense appear to be more important in determining mating success than the supply of available mates. Territorial mating success varied directly with population density changes only on the smallest experimental reff, where there were few nonterritorial males. The reduction of mating success at higher densities was correlated with a decreases in both the time spent in courtship and the efficiency of courtship itself. The effect of population density should be particularly important in species with short breeding periods and where the male contributes relatively little time or energy to each mating.
Spatial Patterns of Tree Growth Anomalies in the Pacific Northwest
Authors: Brubaker Linda B.
Published: May 2006

Regional patterns of ring width anomalies in Washington, Oregon, and Idaho, USA forest are examined using eigenvector (principal component) techniques. The first two eigenvectors, accounting for nearly 50% of the total variance, represent large—scale spatial patterns. Eigenvector I represents a pattern in which growth anomalies are positively correlated among all sites, and Eigenvector II one in which growth anomalies are negatively correlated between sites located on opposite sides of the Cascade Mountain crest. These patterns most likely result from two types of tree growth responses to climate variations that extend uniformly across the study area. Common responses to spring—summer rainfall probably cause the positive, region—wide correlations identified by Eigenvector I, and opposite east—west responses to summer temperature and winter precipitation may account for the negative correlations identified by Eigenvector II. No evidence supports the idea that the tree growth eigenvectors directly reflect two distinctive patterns of climate anomalies. The spatial patterns of these tree growth anomalies have remained essentially constant during the past 300 (possibly 400) yr.
Herbivory, Plant Density, and Plant Reproductive Success: The Effect of Battus Philenor on Aristolochia Reticulata
Authors: Rausher Mark D. , Feeny Paul
Published: May 2006

The pipevine swallowtail butterfly, Battus philenor, normally consumes °45% of the annual leaf crop of its primary host plant in east Texas (USA), Aristolochia reticulata. Feeding by larvae significantly increases plant mortality and decreases plant growth rate. No direct effects of larval feeding on reproduction were detected, but a substantial decrease in seed production per plant is inferred from the increased mortality and decreased growth rates. Plants grown experimentally at high density had the same probability of having eggs laid on them as did plants grown at low density. The actual number of leaves eaten per plant was also similar for plants grown at both densities. Larval feeding increased mortality and decreased plant growth rate by similar amounts at both high and low plant density. There was also no evidence that seed production was greater at one plant density than at another. The pipevine swallowtail thus does not appear to regulate the density of local patches of Aristolochia. These experimental results do not rule out the possibility of regulation by a numerical response of the butterfly to increases in host population densities throughout large areas of habitat. These results suggest that the pipevine swallowtail has exerted a potent selective pressure molding the evolution of A. reticulata. Three characteristics of this plant species may be interpreted as adaptive responses to this pressure: tough, nutrient—poor leaves; underground flowering and fruiting; and a high root/shoot ratio.
Soil Characteristics Associated with a Primary Plant Successon on a Mojave Desert Dry Lake
Authors: Vasek Frank C. , Lund Lanny J.
Published: May 2006

The playa of Rabbit Dry Lake has a fine—textured soil high in Na, Cl, and NO3 but low in K and Ca + Mg. Kochia or sometimes Suaeda plants establish in mud cracks on the playa and accumulates small mounds of silty—sandy soil. High levels of NO3, Na, Cl, K, and Ca + Mg accumulate in soil of small mounds but decrease in playa—level soil under small mounds. Atriplex torreyi invades small mounds and accumulates large mounds of wind—deposited sandy soil. Continued increase of NO3 and large increase of Na, Cl, K, and Ca + Mg occur in soil of large mounds as a result of Atriplex leaf deposition. Large mounds rapidly increase in size and coalesce to form giant mounds of sandy soil with levels of NO3, Na, Cl, K, and Ca + Mg sharply lower than those in large mounds but still higher than those in playa—level soil under the giant mounds. Soil of giant mounds is suitable for colonization by Atriplex confertifolia and Haplopappus acradenius. Following death of shrubs like Atriplex torreyi, giant mounds erode, and soil is deposited between eroding giant mounds at a level above the original playa. Such deposited soil is chemically similar to soil in giant mounds but Na and Cl are leached down to the playa level. The accumulation of soil and the redistribution of minerals by plants permit a primary plant succession to occur.
Bias and Dispersion of Overlap Indices: Results of Some Monte Carlo Simulations
Authors: Ricklefs Robert E. , Lau Michael
Published: May 2006

We have used computer simulations to determine the sampling distributions of four indices of overlap or similarity: the coefficient of community, Morisita's index, Horn's information theory index, and Euclidean distance. Estimates of overlap were systematically biased downward when sample size was small and when expected values were close to 1. The standard deviations of samples of indices were greatest when expected values were intermediate between 0 and 1, and sample sizes were small. In studies having sample sizes of 25, 50, or 100, one could expect the standard error of an estimated index of similarity to fall between 0.05 and 0.10, provided that samples were truly drawn from homogeneous populations. We suggest that simulations be used to estimate confidence limits on similarity and overlap indices where hypothesis testing is required. In addition, efforts should be made to develop indices of overlap for which statistical measures of dispersion and bias can be derived analytically.
Density Effects on the Survival, Growth Rate, and Metamorphosis of Rana Tigrina Tadpoles
Authors: Dash Madhab C. , Hota Ashok K.
Published: May 2006

Rana tigrina larvae were reared in isolation, at various densities and controlled food levels, and with Bufo melanostictus larvae in laboratory populations. Growth is sigmoid in isolated individuals and mass reaches a maximum just before metamorphosis. In laboratory populations, survival during the larval period was independent of initial population density, but the proportion of the population that successfully completed metamorphosis was a negative exponential function of density. This is interpreted as the result of the slower growth rate in high—density populations arising from the competition for food. The individuals in high—density populations with slower growth rate take a longer time to reach a threshold size and have a lower probability of completing metamorphosis. In higher densities, the threshold size for metamorphosis decreases in comparison to lower density populations.
An Experimental Study of Interference Competition Among Terrestrial Salamanders
Authors: Wrobell David J. , Gergits William F. , Jaeger Robert G.
Published: May 2006

Previous studies showed that the terrestrial salamander Plethodon cinereus competitively excludes a sibling species, P. shenandoah, from optimal habitats in Virginia. However, the mode of competition (interference or exploitation) was not well understood. In the present study, pairs of congeners and pairs of conspecifics were maintained in experimental enclosures in the laboratory food—limited conditions. Mass changes and behavioral interactions during feeding periods were monitored over 20 mo. Behavioral data were compared both between species and between "winners" and "losers." (The winning salamander gained more or lost less mass than the cohabiting loser.) Winners exhibited more aggressive activity than losers among interspecific pairs, suggesting that aggressive superiority and foraging superiority are associated. However, P. cinereus did not win more often than P. shenandoah, although it was on the average more aggressive. Males of both species were more aggressive than conspecific females. The data suggested that interference competition occurs both within and between the two species. We suggest that interference may be involved in competition for space, rather than for food items per se.
The Role of Parthenogenesis and Female Aptery in Microgeographic, Ecological Adaptation in the Fall Cankerworm, Alsophila Pometaria Harris (Lepidoptera: Geometridae)
Authors: Schneider John C.
Published: May 2006

The larval stage of the fall cankerworm, Alsophila pometaria Harris, feeds on several species of deciduous trees in North America. The ecology of the fall cankerworm parallels the ecology of the winter moth, Operophtera brumata: (1) hatching too long before host tree foliation results in hatchling dispersal and mortality and (2) late hatch results in low fecundity due to deteriorated nutritional quality of the leaves. Certain adaptations by a few moth species have increased synchrony between hatch and foliation in the face of spatial variation in the latter. First, female flightlessness has reduced the effect of intrastand variation in time of foliation. Second, at least in the fall cankerworm, parthenogenetic clones in a gynogenetic system specialize on different tree species as hosts. Since the clones differ in hatching time in the appropriate way, they match interstand differences in time of foliation. Clones specializing on an early foliating tree species eclosed earlier to lay eggs than did clones on a later foliating species. It is hypothesized that increases in the population density of the fall cankerworm should tend to occur during series of years with similar spring phenologies. Under these conditions the frequency of asexuals should increase relative to the sexuals.
Vegetation of the Boreal Forests South of James Bay: Non‐Centered Component Analysis of the Vascular Flora
Authors: Carleton T. J. , Maycock P. F.
Published: May 2006

Results from an extensive vegetation survey of 1971 boreal forest stands, encompassing a full spectrum of succession and site types in the regions of Ontario and Quebec south of James Bay, are reported. Non—centered principal component analysis plus varimax rotation (nodal component analysis) is applied to overstory and understory data in order to detect vegetational noda. The overstory data are inherently more structured (i.e., contain more distinct subgroups) than those of the understory. An exception is seen with groups in which Abies balsamea plays a prominent role. These are interpreted as stages in various successions of which only one, a Betula papyrifera to A. balsamea sequence, represents the complete transition from one canopy dominant to another. The understory noda are summarized in terms of the compositional and environmental features of stands belonging to each nodum. Relationships among the understory noda are summarized in a multidimensional scaling ordination which is derived directly from similarity values (conjunction coefficients) representing the overlap between pairs of noda. Two major environmental gradients seem to affect understory composition. These are a site moisture—nutrient concentration gradient and a general fertility—productivity gradient. Canopy composition and understory vegetation are compared by nodal conjunction between the two analyses. Groups of noda, representing wet bog forests and also upland mesic forests, show moderate to good coincidence but beyond this little canopy specificity emerges. These results indicate that overstory—understory coincidence is due primarily to similar site requirements. Understory species' response to an overstory succession is examined. Many abundant herbs seem indifferent to dramatic canopy change. This observation and results from nodal component analysis are discussed with respect to forest fire.
Differential Habitat Utilization by Sexes of the Deermouse, Permomyscus Maniculatus
Authors: Bowers Michael A. , Smith H. Duane
Published: May 2006

Demography, home range size, and sexual dimorphism of the common deermouse (Peromyscus maniculatus) were examined in three xeric communities of the West and Pacific Northwest. In heterogeneous communities, female mice inhabited the more favorable, moist microhabitats. Males were found in the less favorable, more exeric areas. The intersexual difference in home range size and body weight is positively correlated with habitat heterogeneity. Differential sex distribution with female dominance is a strategy that maximizes reproductive effort and survival of the young.
Litter Fall From Shrubs in the Northern Mojave Desert
Authors: Strojan Carl L. , Turner Frederick B. , Castetter Richard
Published: May 2006

Plant litter was collected in traps from 8 to 10 replicates each of Ambarosia dumosa. Ephedra nevadensis, Krameria parvifolia, Larrea tridentata, Lycium andersonii, and Lycium pallidum in Rock Valley, southern Nevada, USA. Collections were made at biweekly to monthly intervals from 1975 to 1977 and handsorted into leaves, stems, flowers, and fruits. Lycium pallidum produced the most litter, with annual means ranging from 52 to 173 g per shrub. Annual means per shrub for other species ranged from 39 to 89 g (Lycium andersonii), 27 to 77 g (Larrea tridentata), 20 to 29 g (E. nevadensis), 6 to 18 g (K. parvifolia), and 3 to 21 g (A. dumosa). Litter fall was generally correlated with annual rainfall, which was low in 1975 (62 mm), high in 1976 (223 mm), and close to the long—term mean in 1977 (141 mm). Leaves were generally the largest litter category, followed by stems, fruits, and flowers. Large sample variations were found, particularly for reproductive parts. Aboveground litter fall from the six species, which comprise °82% of perennial plant biomass and °81% of shrub cover in Rock Valley, was about 117 kg/ha in 1975 and 318 kg/ha in 1976. Total aboveground litter fall for Rock Valley (all perennial and annual plants) was estimated to be 194 kg/ha in 1975 and 530 kg/ha in 1976. Distinct litter fall patterns occurred for shrub species and litter categories. Most litter fell during the summer months, with individual species peaks reflecting particular phenologies. Significant amounts of live aboveground biomass were shed as litter. Amounts of litter from the six species ranged from 7 to 83% of their respective live aboveground biomass.
Bird Species Diversity on an Andean Elevational Gradient
Authors: Terborgh John
Published: May 2006

This paper analyzes patterns of bird species diversity on an elevational transect of the Cordillera Vilcabamba, Peru. Major changes in climate and vegetation are encompassed by the transect which extended from the Apurimac Valley floor at 500 m to the summit ridge of the range at >3,500 m. Four vegetation zones are easily discerned–lowland rain forest, montane rain forest, cloud forest, and elfin forest. In progressing upwards there is a monotonic trend toward decreasing canopy stature and reduced number of plant strata. The vegetation gradient provided the opportunity to examine the relation between bird species diversity and habitat complexity in an entirely natural setting. The decrease in forest stature with elevation was closely paralleled by decreasing avian syntopy (the total number of bird species cohabiting the forest at a given elevation). Bird species diversity was shown to be highly correlated with foliage height diversity, using either four or five layers in the foliage height diversity calculation (r = .97), and less well correlated using three layers, as defined previously by MacArthur (r = .84). At this superficial level the trend in bird species diversity seemed to be adequately explained as a response to the vegetation gradient. This preliminary conclusion was found to be illusory when the elevational trend in syntopy was reexamined separately for three major trophic subdivisions of the fauna. The number of insectivores decreased 5.2—fold from the bottom to the top of the gradient, frugivores decreased by a factor of 2.3, and nectarivores showed no change. It was now clear that the diversity in each of these trophic categories was responsive to environmental influences other than, or in addition to, the gradient in habitat structure. Additional factors implicated by the available evidence are competitive interactions with other taxa at the same trophic level, changing composition of the resource base as a function of elevation, and declining productivity at high elevations. Analysis of netted bird samples revealed an unexpected diversity maximum in the lower cloud forest zone. The immediate cause of this was a relaxation of the vertical stratification of foraging zones, such that an anomalously large fraction of the species present entered the nets. The excess diversity was found to consist almost entirely of insectivores. Several factors appear to contribute to the ultimate causes of the diversity maximum: greater patchiness of the montane forest due to the rugged topography, a higher density of foliage near the ground, and possibly increased resource productivity. A correlation between diversity and density in the netting results suggested a causal connection mediated via resource levels. The conclusion in that diversity is a complex property that is responsive to many types of influences beyond simply the structure of the habitat.
Seasonal Variation in Thermoregulatory Behavior and Body Temperature of Diurnal Kalahari Lizards
Authors: Huey Raymond B. , Pianka Eric R.
Published: May 2006

We discuss seasonal variation in thermoregulatory behavior and its consequences on body temperature for 12 species of diurnal lizards in the southern Kalahari semidesert of Africa and also evaluate several methods of attempting to document thermoregulatory behavior using a descriptive data base. Lizards vary time of activity among seasons, which limits the variation in ambient conditions actually experienced. Ground—dwelling lizards and probably arboreal lizards move nonrandomly with respect to sun and shade; thus the percentage of lizards in sun in inversely proportional to air temperature. Arboreal lizards shift to higher perches at midday in summer and to logs or ground in winter thus decreasing and increasing incident heat loads, respectively. Both juveniles and adults of 3 species, only juveniles of 2 species, and only adults in 1 species are active in winter: both adults and juveniles of 6 species brumate [= hibernate]. Mean body temperature (Tb) varies within days and among months and is positively correlated with corresponding mean air temperature (Ta) in almost all species. Nonetheless, correlation and regression analysis suggests that thermoregulatory behaviors reduce the impact of variations in ambient conditions on Kalahari lizards. The mean Tb of different species reflect evolutionary relationships. In summer, mean Tb is proportional to the percentage of lizards in sun and with the tendency of lizards to be active only in summer. Thus, lizards with inferred low optimal temperatures are active during more months of the year.
Nutrient Concentration Patterns in a Stream Draining a Montane Ecosystem in Utah
Authors: Bond Hedley W.
Published: May 2006

The concentrations of several nutrients in a stream draining a large montane ecosystem in northern Utah, USA were monitored over a 2—yr period. Stream discharge (cubic metres per day) accounts for much of the variation in the concentration of the most common nutrients. When the concentration of each nutrient is plotted logarithmically against stream discharge and the points are joined in a time sequence, a locus or trajectory is obtained which varies more between ions than between years for the same ion. These patterns of nutrient flux appear to be controlled largely by the magnitude of stream discharge and the relative contributions of groundwater flow, overland flow, and interflow. Plant uptake, supply of exchangeable ions, and equilibrial dynamics of the calcium carbonate system also influence the shape of the trajectories and give rise to much of the differences between trajectories for different ions. The trajectories for less common ions are more variables than those for abundant entities. Available data indicate that trajectories are observed in other ecosystems but are only seen clearly in watersheds with a simple annual pattern of streamflow. These patterns of nutrient flux occur for each significant rise and fall in stream discharge and are not observed distinctly in ecosystems with frequent changes in streamflow. The characteristic and recurring form of trajectories suggests that these patterns represent an important and general property of some ecosystem and that they may provide a basis for a theoretical approach to ecosystem nutrient dynamics.
Dominance and the Acquisition of Superior Home Ranges in the Lizard Uta Stansburiana
Authors: Fox Stanley F. , Rose Elizabeth , Myers Ronald
Published: May 2006

Natural home range features of juvenile Uta stansburiana were measured and compared between socially dominant and subordinate individuals of size— and sex—matched pairs. Dominance was determined via paired encounters in laboratory, neutral arenas. Dominants originated from home ranges with significantly less dense croton and grass vegetation. Dominants showed a slight tendency to inhabit larger home ranges. Dominants' home ranges were significantly more diverse than subordinates' home ranges. A survivorship—based multivariate index of home range quality showed that dominants originated from home ranges of higher overall quality than those subordinates. Home ranges of dominant juveniles resembled home ranges of oversummer survivors of a previous study, and home ranges of subordinates resembled those of nonsurvivors. Subjects were introduced by pairs into outdoor pens with halves of disparate habitat quality. Dominants showed significantly greater occupation of the superior half than subordinates. Dominant juveniles, then, appear to inhabit home ranges different from subordinates; features of these home ranges may convey increased survivorship. The same dominant juveniles are more apt than subordinates to secure superior habitat in a novel situation.
Treefalls and the Distribution of Understory Birds in a Tropical Forest
Authors: Schemske Douglas W. , Brokaw Nicholas
Published: May 2006

Monthly mist—net censuses were conducted in central Panama to contrast the species richness and composition of the understory avifauna in treefall gaps to that of adjacent, intact forest. We compiled 826 captures of 73 species over a 9—mo period. Species richness was greater in gaps than forest (66 vs. 53 species), but capture rates were nearly identical (gap, 409; forest, 417). Of the 31 species with adequate sample sizes, 5 displayed significant habitat preference (P ° .05): 3 in gaps and 2 in forest. Ordination of all nets by Bray—Curtis analysis indicates that gap and forest bird assemblages are quite distinct. We suggest that treefall gaps contribute to the structural heterogeneity of the forest and influence the composition and richness of the bird community.
Floral Convergence and Pollinator Sharing in Two Bee‐Pollinated Tropical Herbs
Authors: Schemske Douglas W.
Published: May 2006

The hypothesis that the understory herbs Costus allenii and C. laevis (Zingiberaceae) have converged in floral characteristics to use the same pollinator was investigated in central Panama. Observations and experiments indicated that these species (1) occupy the same habitats, (2) flower synchronously, (3) are identical in flower color, morphology, and nectar secretion patterns, (4) share the same pollinator, the bee Euglossa imperialis, (5) are self—compatible, but not autogamous, and (6) have strong barriers to hybridization. Both grow in low density along streamsides and produce a single flower per day for an extended period (up to 4 mo). Flower density is depressed through extensive predation by the weevil Cholus cinctus, which damaged 31% of all C. allenii and 60% of all C. laevis inflorescences. Direct observation of foraging bees indicated that individuals regularly visit both plant species. An experimental analysis of interspecific pollen transfer using powered paint as a marker verified these results; 97% of the flowers checked had received heterospecific visits. The high probability of interspecific pollination did not affect fruiting success. I suggest that low flower density, exaggerated by extreme floral predation, has selected for floral similarity and pollinator sharing in these species. Floral convergence increases effective flower density and nectar supplies, and probably increases the regularity and rate of pollinator visitation.
Ecotypic Differentiation of Growth Processes in Carex Aquatilis along Latitudinal and Local Gradients
Authors: Chapin F. Stuart , Chapin Melissa C.
Published: May 2006

The genetic and environmental determinants of plant size, growth rate, reproduction, and survival were examined in five populations of Carex aqualtilis by reciprocal transplants to arctic, subarctic hot spring, subarctic muskeg, temperate alpine, and temperate subalpine sites. In the arctic and muskeg sites, only locally evolved populations survived 3 or more yr. In other sites, interpopulation differences in tiller density were due more to differential autumn or winter mortality than to differences in tillering rate. Shoot height of all populations was smaller when grown in arctic and alpine sites than in others. This small shoot size was genetically fixed in populations native to these sites. In contrast, the muskeg population showed compensatory adaptation to low soil temperature and produced taller shoots than the adjacent hot spring population when both were grown in any given site. All populations maintained similar numbers of green leaves, but through different mechanisms. This occurred through a high leaf production rate in warm soil populations but through enhanced leaf longevity in populations adapted to cold soils. Cold soil populations had larger root: shoot ratios and smaller tiller mass.
Seasonal Variations in Fuel and Fuel Consumption by Fires in a Bluestem Prairie
Authors: Bragg Thomas B.
Published: May 2006

Plots in an ungrazed, re—established grassland near Omaha, Nebraska, USA, dominated by little bluestem (Andropogon scoparius), were burned at 3—wk intervals from March through November 1976. The amount of vegetative biomass consumed during burning, a measure of flammability, was high throughout the study period, varying from >99% in April to 84% in mid—June. Areas burned in March were able to carry a second fire in October of the same year. High flammability throughout the growing season, in conjunction with current fire and climatic records, suggests that widespread, late—summer fires were probably common in presettlement, ungrazed, bluestem prairies.
Ecological Correlates of Insular Rodent Diversity
Authors: Dueser Raymond D. , Brown William C.
Published: May 2006

Rodent populations were censused on nine Virginia barrier islands during the summers of 1975 and 1977. The five species observed include Microtus pennsylvanicus, Mus musculus, Oryzomys palustris, Rattus norvegicus, and Sciurus carolinensis. The number of rodent species ranged from zero on a small, low—lying, sandy island to five on a large, elevated, forested island. Rodent species richness(diversity) increased directly with island area, elevation, vegetation height, and habitat complexity (i.e., the number of distinct woody plant associations). Because of strict zonation of plant associations, increased habitat complexity represents increased availability of exploitable patches of habitat. As expected from studies of mainland rodent communities, this patchiness appears to promote increased species diversity. Each species exhibits and "exploitation specialty" involving little spatial overlap with other species diversity. Each species exhibits an "exploitation speciality" involving little spatial overlap with other species. Although no direct tests have been conducted, we speculate that the rodent communities of these islands are at equilibrium. Low rates of colonization and high rates of extinction interact to produce low species diversity and a steep species—area curve.
Vegetation Structure, Food Supply, and Polygyny in Bobolinks (Dolichonyx Oryzivorus)
Authors: Wittenberger James F.
Published: May 2006

Territories of polygynous male Bobolinks averaged higher percent cover of several forb species than did those of unmated males. Some differences were also found between territories of polygynous and monogamous males, but not in all years. These differences were associated with differing soil moisture conditions on the various male territories. Vertical density of all vegetation types, vegetation biomass, and grass height were not correlated with the number of females attracted to each territory. Observed vegetation differences do not explain why some territories attracted two females while others attracted only one. Caterpillars constitute a major component of nestling diet. Caterpillar densities were higher on polygynous male territories than on adjacent, physiognomically similar monogamous male territories in mesic habitat. They were also higher on polygynous male territories than on physiognomically similar bachelor male territories in dry habitat. Grasshopper densities were higher on polygynous male territories than on monogamous male territories in mesic habitat, but not at the time second—mated females selected territories. They were lower on polygnous male territories than on monogamous male territories than on habitat. The nesting success of second—mated females was lower than that of first—mated females primarily because of higher nestling starvation. It is concluded that polygyny occurs in Bobolinks because it enables females to breed in areas with more abundant food resources.
The Biology of Viola Fimbriatula in a Natural Disturbance
Authors: Cook Robert Edward , Lyons Elizabeth E.
Published: May 2006

Individual plants of Viola fimbriatula which germinated from buried seed in two tree blowdowns in 1975 were censused for 6 yr. Growth, seed production, and mortality were monitored at fortnightly intervals. Only seedlings of the cohort established immediately following the disturbance grew large enough to produce seed. The performance of individuals within this cohort was highly skewed, and both reproduction and survival were correlated with individual size. After 1977 the conditions in the blowdowns which initially stimulated germination, growth, and reproduction rapidly deteriorated for V. fimbriatula, and the populations declined to extinction. We conclude that individuals of V. fimbriatula, interacting with the habitat conditions of this natural disturbance, display many of the traits characteristic of species commonly associated with disturbance. In this habitat the dynamics of the entire population are determined by the relative performance of individuals immediately following the disturbance.
Selective Pressures on Clutch Size in the Gall Maker Asteromyia Carbonifera
Authors: Weis Arthur E. , Price Peter W. , Lynch Michael
Published: May 2006

The insect Asteromyia carbonifera (Diptera; Cecidomyiidae) has a life history that entails larval development in a gall with several sibs, maturation of a single batch of gametes during pupal development, and an ephemeral adult existence that includes many ovipositional events, each of which results in formation of a gall. Ecological factors acting on both the adult and larval stages were evaluated to determine the selective pressure they exert on the number of eggs deposited per ovipositional site (i.e., clutch size). Optimal clutch size is determined by a balance between the fitness per offspring, which is dependent on clutch size, and the number of clutches mothers can deposit in their brief life—span. As clutch size increased, so did sibling competition, with the result of smaller size and lower fecundity for larvae developing in large clutches. Larval survivorship was lower in small clutches because of differential attack by parasitoids. From the offspring's viewpoint, benefits of small clutch size out—weighed the deficits, since those deposited in clutches of one enjoyed the greatest potential fitness. A model was constructed indicating that when mothers experience no risk of mortality, optimal clutch size from their viewpoint is also one. However as the risk of mortality between ovipositional events increases, females are unlikely to survive to deposit all their eggs. When fewer clutches can be formed, females will be selected to deposit several eggs per clutch, since this results in the development of many moderately fecund offspring whose aggregate fitness is greater than that of the few highly fecund offspring that would result if one egg were deposited per site.
A Comparsion of Nesting‐Ledges Used by Seabirds on St. George Island
Authors: Squibb Ronald C. , Hunt George L.
Published: May 2006

Measurements of 288 nesting—ledges of six species of seabirds on St. George Island, Alaska, revealed significant interspecific differences in the size, shape, and overhang of ledges used. Typically, Red—legged Kittiwakes used ledges 1 dm deep; Northern Fulmars, Black—legged Kittiwakes, and Thick—billed Murres used ledges of an intermediate 2—4 dm depth; Red—faced Cormorants used ledges 3—6 dm deep; and Common Murres occurred singly on shallow ledges or in groups on deeper ledges. Fulmars and murres, which did not build nests, used nearly horizontal ledges exclusively; the nest—building species occurred on a wider range of slopes. Only the Red—legged Kittiwake regularly used ledges with over 50% cover by overhanging cliff within 5 dm of the ledge. Classification of the measured ledges of the cormorant, the two kittiwakes, and the Thick—billed Murre by a discriminant function analysis revealed significantly greater overlap than expected between the species pairs of cormorant with Thick—billed Murre, Black—legged with Red—legged Kittiwake, and Black—legged Kittiwake with Thick—billed Murre. Observations of 43 interspecific exchanges of nest sites during and between three breeding seasons agreed with the predictions by the discriminant analysis of overlap or lack thereof in three of four significant cases. Exchanges occurred significantly more frequently than expected between the species pairs of cormorant with Black—legged Kittiwake, cormorant with Thick—billed Murre, and Black—legged with Red—legged Kittiwake.
Weak Competition among Spartina Stem Borers, by Means of Murder
Authors: Stiling Peter D. , Strong Donald R.
Published: May 2006

We examined co—occurrence among five species of insect larvae that bore the stems of salt marsh cordgrass, Spartina alterniflora, in northwest Florida. Statistical analysis of 5400 stems at three different sites revealed fewer empty stems, more stems containing one species, and fewer stems containing two or more species than one would expect if individuals were arranged randomly and independently. Particular interspecific co—occurrences at individual sites were significantly rarer than expected for 6 of the 10 possible species pairs. This deficiency in species co—occurrences is likely a result of direct interspecific aggression and murder of larvae within stems, as demonstrated in laboratory experiments. However, we detected no obvious decreases in population densities or alteration of stem section occupancy patterns due to competition. Thus, although interspecific competition occurs, it does not play a critical role in structuring this community.
Habitat and Seasonality As Niche Axes in an Odonate Community
Authors: Crowley Philip H. , Johnson Dan M.
Published: May 2006

This study focuses on the coexistence of the dominant populations among 46 odonate species found in Bays Mountain Park, Sullivan County, Tennessee, USA. By monthly sampling of six aquatic habitats within the park, we established the larval biomass distributions of the 12 dominant populations across habitats and seasons and from these derive estimates of distributions along corresponding niche axes. We use an index proposed by Hurlbert (1978) to estimate niche specialization (breadth—1) and overlap on habitat and seasonal axes, both separately and simultaneously (two—dimensional analysis). This enables us to evaluate two possible mechanisms of coexistence in this community: resource partitioning (i.e., differing time—average patterns of resource utilization among competitors) and ecological shift (i.e., nonevolutionary change in resource utilization in response to competition). Three results support the resource—partitioning mechanism: 1) Competition coefficients, obtained by dividing niche overlap values by the appropriate niche specialization values, are all less than one; this indicates that each population should inhibit its own access to a limited food supply more than it inhibits the access of the other populations. 2) Though little or no complementarity between the habitat and seasonality axes is apparent when single—axis index values are examined, the two—dimensional competition coefficients are slightly smaller on average than the product of single—axis means, suggesting two—dimensional complementarity. 3) There are about the same number of consistent 3—yr trends in specialization and overlap as would be expected by chance, suggesting a relatively persistent arrangement of odonate niches in niche space. But the ecological shift mechanism may be operating within or between those populations that do exhibit consistent 3—yr trends in specialization or overlap; more of these values consistently decrease than would be expected by chance. The six populations that comprise the detritus—submersed macrophyte guild account for most of the larval biomass, and the dominant population within the guild (and the community as a whole) is the semiovoltine anisopteran Tetragoneuria cynosura. A particularly intense interaction, as indicated by the competition coefficients, is between the abundant zygopterans Enallagma traviatum and E. signantum; unusually high specializations and overlap were observed for the rush—dwelling zygopterans Ischnura verticalis and I. posita.
Availibility of Space for the Territorial Caribbean Damselfish Eupomacentrus Planifrons
Authors: Robertson D. Ross , Hoffman Steven G. , Sheldon Janice M.
Published: May 2006

Populations of coral reef fishes are often thought to saturate habitable space and to be limited by its availability, particularly those fishes that defend space. In Panama, individual adults of the common Caribbean damselfish Eupomacentrus planifrons defend permanent, all—purpose territories . A territory contains a mass of coral from which the fish derives required substrate—based resources: shelter from predators, a nest site (males only), and food (from a distinct mat of algae). Two experiments tested whether an excess of suitable substrate was present in two of the main habitats of E. planifrons. (1) Coral substrate that contained algal mats was removed from small areas (up to 45 m2) in habitats composed of Agaricia and Acropora corals. After 3 mo new algal mats were established on previously mat—free parts of the experimental areas, and the density of adult E. platnifrons increased in the experimental areas. (2) The area of habitat of three small patch—reefs was reduced by one—half through the removal of coral substrate. One year later, the density of E. planifrons adults had increased on the remaining halves of those reefs. The results of both experiments indicated that a surplus of suitable substrate existed in the experimental areas and that E. planifrons was not generally limited by the availability of habitable space. Compared to control fish of the same length, experimental E. planifrons were similar in mass, in the amounts of fat reserves, and, in the case of females, in activity of their ovaries. Both experimental and control fish were breeding at the end of the experiment. Thus the experimental increase in population density did not appear to be detrimental to the physiological condition or reproductive capacity of the fish. We conclude that E. planifrons is probably not at the carrying capacity of the habitats it occupies
Competition and Coexistence among the Grazing Snail Lymnaea, Chironomidae, and Mircrocrustacea in an Arctic Epilithic Lacustrine Community
Authors: Cuker Benjamin E.
Published: May 2006

Effects of the grazing activity of the gastropod Lymnaea elodes (arctica?) on animal community structure in the rocky littoral of an arctic lake were examined. In situ caging experiments on natural substrates with various snail densities resulted in shifts in faunal biomass abundance and distribution. Chironomids living in fixed tubes (Paratanytarsus) were greatly reduced at high snail loads. Free—living scrapers (Corynoneura, Crictopus cf. sylvestris, Zalutschia trigonocies, and others) fared only slightly better, while predators (Arctopelopia and Ablabesmyia) were relatively less sensitive to changes in snail density. Trichoptera larvae, Acari, and copepods were unaffected by the snails. Ostracoda and Cladocera biomass was significantly reduced by Lymnaea. All of the less sensitive groups were relatively more mobile. Reduced algal biomass and chlorophyll concentration were correlated with increased snail densities. Lymnaea production was limited by conspecific density and food.