bluuebunny/crossref_metadata_2025 huggingface dataset:
Ecological Convergence of Lizard Communities in Chile and California
Authors: Fuentes Eduardo R.
Published: May 2006

Convergence in community structure, under similar long—term climatic conditions, were investigated using taxonomically unrelated lizard communities in Mediterranean climatic areas in central Chile and southern California. The hypothesis of convergence, i.e., physiognomically similar sites in the two continents should have lizard community structures that are more similar to each other than to the structure of lizard communities in nearby areas in the same transect, was tested by comparing the structure of lizard communities in an altitudinal–vegetational transect in each continent. Each transect consisted of a coastal sage, chaparral, and forested montane site. Structure of the lizard communities was characterized by the patterns of habitat, food, and time of activity of the lizard species. For each of these dimensions the total range of resources used by the community as a whole was determined, as well as the utilization pattern of individual species. Utilization patterns of individual species were expressed in a multidimensional vector in which the angle between vectors representing these patterns was used as a measure of ecological similarity between species. The vector method allowed determination of species pairs exhibiting the most similar patterns of resource utilization. The comparison strongly supports the convergence hypothesis. For habitat and time of activity, range of resources used as well as utilization functions of individual species were more similar in equivalent sites in the two continents than in nearby sites in the same continent. Thus, on the average the most similar species (species analogue) is on the equivalent site in the other transect and not in the same continent. Also, in general, the proportions of lizards found, irrespective of species, are the same on analogous resources in the two continents. Habitat species analogues found by comparing sites also similarly partitioned food resources. However, there are some differences in food categories used, since two of the Chilean species eat some vegetation (fruits), but their Californian size—habitat counterparts do not. In addition, the two chaparral sites show very similar mechanisms of generation replacement such that adults go into aestivation by the time hatchings appear. Evidence supporting the hypothesis of a seasonally shrinking food supply as the cause for this pattern is also given.
Energetic Aspects of the Intertidal Oyster Reef Community at Sapelo Island, Georgia (USA)
Authors: Bahr Leonard M.
Published: May 2006

The total daily O_2 consumption rate of the intertidal oyster reef community in Georgia, USA was found to range between 0.6 x 104 and 5.0 x 104 mg O_2/m2 of reef surface, corresponding to a seasonal range of ambient water temperature from 9 degrees C to 30 degrees C. Oysters, nonoyster macrofauna, microbiota, and chemical oxidation were estimated to account for 48.1%, 10.0%, 21.9%, and 20.0%, respectively, of total O2 consumed. Reef macrofaunal biomass averages 1,108 g/m2 (ash—free dry weight) of which Crassostrea virginica comprises 87.5%. Growth of individual reef oysters, and, therefore, entire reefs, appears to be extremely slow, probably due to high maintenance costs and limited inundation time characteristic of the intertidal zone. The oyster reef community occupies only 0.06% of total marsh—water surface area in a salt marsh estuary unit (the Duplin River marsh—estuary system), but it can theoretically degrade 1% of the estimated excess annual net primary production in the system.
A Model of Stand Photosynthesis for the Wet Meadow Tundra at Barrow, Alaska
Authors: Miller Philip C. , Stoner Wayne A. , Tieszen Larry L.
Published: May 2006

A model of radiation, air temperature, and vapor density in the vegetation canopy, plant water relations, and photosynthesis, developed in the primary production research program of the U.S. Tundra Biome, IBP, is described and results for the years 1970 through 1973 presented. The model calculates daily courses of direct and diffuse solar radiation; infra—red radiation; wind; air temperature and humidity; leaf temperatures; convectional and transpirational exchange by leaves, stems, and dead material; leaf H_2O content, leaf water potential; leaf resistance to H_2O loss; internal resistance to CO_2 diffusion; and net photosynthesis. Climate varied from year to year: 1970 and 1971 were similar, 1972 was relatively warm and dry, and 1973 was relatively cold and wet. Plant parameters were obtained for Carex aquatilis, Dupontia fischeri, Eriophorum angustifollium, and Salix pulchra. Leaf area indices varied by species and by year. Leaf areas of all species were lowest in 1973. Of the incoming solar radiation ° 20% is reflected back and 32%—53% absorbed by the canopy, increasing with leaf area index. In the canopy 5—10 times more heat is lost by convection than by evaporation. Total seasonal vascular plant CO_2 uptake ranged from 400—627 g CO_2 m_G(—2) (subscript G refers to ground). In 1971 cuvette estimates for total seasonal vascular plant CO2 uptake were 602 while the model predicted 627. Individual species incorporated about 4 g CO_2 m_G(—2) day(—1) at most. The daily CO_2 incorporation was larger than the downward CO_2 flux from the atmosphere, implying that soil respiration is a source of CO_2 for the vascular plants. Photosynthesis increased with solar radiation, air and ground temperatures, and air vapor density and decreased with increasing infrared radiation for the sky and root resistance to water uptake. Factors increasing transpiration without directly affecting photosynthesis tend to decrease photosynthesis because of the effect on water stress. Net photosynthesis is higher at the top of the canopy, in spite of more favorable temperatures within the canopy, because of light limitation. Total accumulated carbon dioxide, after subtracting growth costs of leaves, becomes positive late in the season and is highest at the lower levels because of the longer duration of leaf area these levels. Photosynthesis seems adjusted to maximize carbon gain under the most frequent conditions but not under all conditions or extreme conditions.
Foliage‐Height Profiles and Succession in Northern Hardwood Forests
Authors: Aber John D.
Published: May 2006

Leaf area index (LAI) and foliage—height profiles were determined for 13 northern hardwood stands ranging from 3 to 57 yr since clearcutting and for 1 uncut stand. Leaf litter collection and stratified clipping were used to measure LAI which showed no relationship to total canopy height or foliage—height distribution, and recovered quickly to near mature forest levels following cutting. A camera and telephoto lens were used to measure the distribution of heights to lowest leaf in the 12 oldest stands (7 / yr). Distributions were converted to foliage—height profiles using equations from MacArthur and Horn (1969). Profiles in the 2 youngest stands (3 and 4 yr) were determined by stratified clipping. Total canopy height varies predictably with age and is the major determinant of foliage—height diversity calculated using data in 1—m intervals by height. The concentration of foliage into a definable stratum occurs early in succession and persists through year 30. An associated lack of understory in this period results in a reduced foliage—height diversity using data normalized to a 4 strata per profile. Beyond year 30, canopy structure is variable but mature stands generally have leaves evenly distributed by height.
Time‐Energy Budget of the Semipalmated Sandpiper Calidris Pusilla at Barrow, Alaska
Authors: Ashkenazie Shoshana , Safriel Uriel N.
Published: May 2006

The time—activity budget of breeding Calidris pusilla was studied at Barrow, Alaska USA, in 1973 by observing several individually marked birds. Feeding, incubating and young—attending were the most time—consuming activities: °70% and 80% of the time was spent feeding by the female during laying period by both sexes prior to southbound migration, respectively. Up to 50% of the time was spent incubating or attending young during the incubation the young—attending periods. The time—activity budget was converted into an estimate of energy requirements by using available estimates for energetic cost of activities. Although both environmental conditions and activity patterns changed throughout the season, the daily energetic cost fluctuated between only 159 kJ/d during the prelaying stage and 222 kJ/d during the laying stage for the female, and between 155 kJ/d during the prelaying stage and 167 kJ/d during the territorial stage for the male. But because females leave the area about the time of hatching, a female requires less energy from the tundra than a male; on the average, °7.1 x 103 and 8.0 x 103 kJ were required during the whole season by female and male, respectively. Energy uptake was estimated by: (a) using available data on diet composition, the energy content of prey items and their digestibility, and (b) combining them with observed feeding rates and estimated capture rates. The resultant energy budget was generally negative for the whole season and, indeed, female weights declined significantly. We conclude that either energy uptake was underestimated or the birds rely heavily upon resources obtained at wintering grounds and during migration prior to arrival at Barrow. We suggest that females, having an average daily energy requirement 15° higher than males, and entering the young—attending stage with an accumulated energy deficit, increase their fitness by deserting to better feeding grounds rather than staying with the young after they hatch. Thus females enhance their own survival to the next season. A preliminary comparison of the time—activity budget of C. pusilla with that of two rather unrelated species revealed a remarkable similarity in the pattern of time allocation.
Some Comments on the Measurement of Niche Metrics
Authors: Hanski I.
Published: May 2006

The problem of weighting resource states to make them equally distinct from each other, and thereby improving measures of niche width and overlap, is discussed on the basis of the Colwell—Futuyma (1971) weighting factors. A drawback of their approach appears to be that the distinctness of resource states is not separated from their production in the physical environment. Therefore, a new factor D/P is suggested instead of D, where D stands for the (Colwell—Futuyma) distinctness and P for the production of a resource state. The P value may be approximated by the total number of individuals associated with the resource state, assuming that resources are utilized proportionally to their availability. Information gathered in a study of the community of dung—inhabiting beetles is used in an evaluation of the "summation"and "product" approaches to the estimation of multidimensional niche metrics from unidimensional data. Niche width was measured with the Shannon—Wiener measure, niche overlap with the index of percentage similarity. The multidimensional niche width was well approximated by the summation measure, but the product measure yielded a much better estimate of the multidimensional niche overlap.
Decomposition Rates and Nutrient Contents of Arthropod Remains in Forest Litter
Authors: Seastedt T. R. , Tate C. M.
Published: May 2006

Decomposition rates and amounts of calcium, magnesium, potassium, and phosphorus were measured for dead millipedes and crickets buried in forest litter in North Carolina and Georgia. An average of 30% of the original mass of millipedes and 14% of the original mass of crickets was recovered after 1 yr in the litter. Elemental losses generally followed the pattern: K @> P > Mg > Ca; however, elemental amounts occasionally stabilized and in one experiment calcium increased in amount over time. Decomposition of arthropod carcasses was described by a two—component, negative exponential decay model. Decay coefficients were used with literature estimates of arthropod standing crops to estimate standing crops of mass and elements of arthropod remains in forest litter and soil. Estimates of standing crops of mass, calcium, and magnesium of arthropod remains were greater than those of living forest floor arthropods.
Uncertainty and Pollinator‐Plant Interactions: The Foraging Behavior of Bees and Wasps on Artificial Flowers
Authors: Real Leslie A.
Published: May 2006

The influence of variability in nectar reward per flower on the foraging behavior of individual bumblebees (Bombus sandersoni Fkln.) and paper wasps (Vespula vulgaris L.) was explored during late summer 1979. The area around each colony was enclosed in mosquito netting, and an artificial floral patch, yellow and blue cardboard squares randomly mixed and fixed beneath wells in a clear sheet of plexiglass, was established within the enclosure. The nectar reward per flower (i.e., the volume) was manipulated to generate different degrees of variability within a floral type. The first set of experiments had equal quantities of nectar in all yellow and blue flowers. Individual foraging bees showed a significant preference for yellow. However, when blue flowers were kept constant (2 μL in each) and yellow made variable (6 μL in every third flower and none in the remainder), individual foragers avoided the variable yellow even though the expected reward from yellow was equal to blue. As a control, the variable floral type was reversed with yellow now constant. Individual foragers then showed an equally strong avoidance of blue flowers. In order to insure that bees were avoiding uncertainty rather than merely avoiding empty flowers, a new set of experiments was run with some nectar in every flower. The constant floral type contained 2 μL of nectar in every flower while the variable type contained 5 μL in every third and .5 μL in the remainder. Again the foragers preferred the constant floral type; however, the preference was not as great as when there were empty flowers. Analysis of the sequence of visits made by individual forages seems to indicate that bees learned to distinguish the variable floral type during the foraging bout. Similar experiments were run on the wasps. When flowers were of equal quality, the wasps preferred yellow to blue. When one floral type was variable and the other constant, the wasps preferred the constant type. For the same magnitude of variability, however, the bumblebee's avoidance of the variable floral type was more pronounced than was the wasps' response. The results of these experiments are then analyzed within the context of a more general model of foraging behavior in variable environments.
The Effect of Architectural Variation in Habitat on a Spider Community: An Experimental Field Study
Authors: Robinson James V.
Published: May 2006

Spider species acceptance of, and segregation by, architectural configuration was investigated for the spiders of Green Canyon in northern Utah, USA. Modular habitat units consisting of 30.48—cm (1—foot) cubes of chicken wire supporting internal strands of macrame jute tied in different orthogonal configurations were used. Configurations including all three axes were tested at two strand densities. The null hypothesis, that spiders use structures independent of architecture, was rejected in favor of the alternate hypothesis that spider species differentially use structures dependent upon architecture. Of the eight most abundant species, two showed preferences for horizontal substrata and one chose vertical substrata. All spiders strongly responded to the amount of jute available in each module. The two most abundant jumping spiders were biased toward modules with widely spaced jute, while the two most abundant web—builders preferred closely spaced jute.
Interactions Among Syrphid Flies and Bumblebees on Flowers
Authors: Morse Douglass H.
Published: May 2006

Interactions among bumblebees (Bombus terricola and B. vagans Smith) and small syrphid flies (Melanostoma mellinum L. and Toxomerus marginatus [Say]) were studied on pasture rose (Rosa carolina L.). Dominance interactions took the form: bumblebees > Melanostoma > Toxomerus. In the absence of bumblebees, Melanostoma foraged 41% longer, but the bees only reduced Toxomerus' foraging about 4%. The difference in bumblebee impact on the two syrphids resulted from Toxomerus rapidly returning after visits by bumblebees, while Melanostoma did not. Toxomerus used flowers most frequently when Melanostoma were not in them. Bumblebee foraging patterns appeared unaffected by either syrphid fly. Melanostoma may have a considerably greater impact than bumblebees on Toxomerus; a 14% reduction in foraging by Toxomerus was recorded in one test. This was because Melanostoma occupied flowers for several minutes at a time, while bumblebee visits lasted only several seconds. By affecting Melanostoma's activity, bumblebees inadvertently favored Toxomerus, because the latter returned quickly to flowers after bee visits; Melanostoma did not.
Modification of Bumblebee Foraging: The Effect of Milkweed Pollinia
Authors: Morse Douglass H.
Published: May 2006

Bumblebees (Bombus terricola Kirby and B. vagans Smith) rapidly accumulated pollinia after contacting milkweed (Asclepias syriaca L.), with losses soon balancing gains. Vagans carried significantly more pollinia than did terricola. Often there were more pollinia on the mouthparts than on the legs, especially on vagans, but there were always more pollinia and corpuscula (combined) on the legs than on the mouthparts. Turnover of pollinia on bees ranged from ½ to 2 d. Proportions of pollinia on the mouthparts often increased over the season. Pollinia—bearing bumblebees foraging on cow vetch (Vicia cracca) carried fewer pollinia on their mouthparts and more pollinia on their feet than did bees captured on milkweed. Bees foraging on milkweed regularly lost claws or segments of their legs. Pollinia slowed the foraging speed of both bee species about 25%. Corpuscula alone had less effect on foraging than did pollinia. Difficulties in foraging included losing footing and extricating feet or mouthparts from flowers. Pollinia—bearing bumblebees moved to new plants more frequently than unimpeded individuals, enhancing the possibility of outcrossing.
The Role of Foraging Profitability and Experience in Habitat Use by the Bluegill Sunfish
Authors: Werner Earl E. , Mittelbach Gary G. , Hall Donald J.
Published: May 2006

This study integrates laboratory and field results to interpret habitat use and switching by individual bluegill sunfish (Lepomis macrochirus). Prey handling and search times for the bluegill were determined from laboratory feeding experiments at different prey sizes and densities in open water and sediment habitats. Relationships were then constructed to predict the expected return per unit time foraging in these habitats. Experience (learning) was found to increase foraging efficiency up to fourfold over the course of six to eight foraging bouts. A population of 225 bluegills was then introduced into a pond consisting predominantly of open water and sediment habitats. This population exhibited several habitat switches as resources declined during the 3—mo experiment; in addition, the population split over a 5—wk period, with individuals specializing on one habitat or the other. These specialists were considerably more successful than habitat generalists as measured by average amount of food in the stomachs. Return rates estimated from the laboratory experiments indicated that the two habitats were nearly equal in foraging profitability. The individual specialization indicated that learning and mutually interfering foraging mechanisms were involved in the species' use of the two habitats. The results suggest that learning and sampling are important aspects of both habitat use and the specialization of individuals within a population.
Microarthropod Response Following Cable Logging and Clear‐Cutting in the Southern Appalachians
Authors: Seastedt T. R. , Crossley D. A.
Published: May 2006

Litter and soil microarthropod populations were monitored following cable logging and clear—cutting of a forested watershed (WS 7) at the Coweeta Hydrologic Laboratory in the southern Appalachians of North Carolina. Annual mean densities of microarthropods in litter bags were reduced over 50% on the clear—cut watershed when compared with an adjacent forested watershed (WS 2), and averaged 8.4 individuals/g of litter on WS 7 vs. 20.4/g on WS 2 (P < .01). Density estimates obtained from 5 cm deep sections of litter and soil indicated a 25% reduction in densities on WS 7, with a 17—mo average of 98 900 microarthropods/m2 on WS 7 vs. 133 500 microarthropods/m2 on WS 2 (P > .001). In contrast, densities of microarthropods increased over 100% in deeper soil horizons (5—55 cm), averaging 89 800 microarthropods/m2 on WS 7 vs. 43 700 microarthropods/m2 on WS 2 (P < .001). Clear—cutting by methods that do not destroy the integrity of the litter—soil environment engenders two kinds of perturbations: (1) removal of the canopy, and (2) addition of organic matter inputs, primarily woody litter debris, to the forest floor. Without a protective canopy, temperatures at the litter—soil interface on WS 7 were increased; daily maximum summer temperatures averaged over 40°C. Thus, lethal or nearly lethal temperatures reduced microarthropod densities in the top 5 cm of litter and soil on WS 7; declines were attributed primarily to oribatid mite mortality. Increased densities below 5 cm were attributed primarily to increased prostigmatid mite abundance. The relationships between microarthropod densities, standing crops of organic matter and litter and microbial production were examined. The amount and vertical distribution and organic matter appears to be the best predictor of microarthropod densities and vertical distributions in most forest ecosystems.
The Limiting Role of Phosphorus in a Woodland Stream Ecosystem: Effects of P Enrichment on Leaf Decomposition and Primary Producers
Authors: Elwood Jerry W. , Newbold J. Denis , Trimble Ann F. , Stark Robert W.
Published: May 2006

The limiting role of phosphorus on leaf decomposition and primary producers was investigated in a second—order woodland stream in Tennessee by experimentally enriching, for 95 d, adjacent reaches with an average of 60 and 450 mg PO4—P/L, respectively, over upstream control levels of °4 mg/L. Red oak (Quercus rubra) leaf packs in the enriched sections lost mass 24% faster than control packs (P < .05). Nitrogen content of the enriched packs increased 60% more, and P content increased 83% more than the respective increases in the control packs (P < .05). Differences in mass loss and N and P levels between the low and high enrichments were not significant (P > .05). Respiration rates of subsampled leaf discs were significantly higher than control rates only at the high level of enrichment. The increased respiration rates in the low and high enrichments accounted for 10 and 34% of the increased mass loss in the respective enriched sections, suggesting that the enrichment also produced increases in mechanical breakdown through faster microbial conditioning, increases in macroinvertebrate feeding, or both. Effects of the enrichment on aufwuchs initially consisted of increased chlorophyll a levels, followed by increased aufwuchs biomass levels. Dense growth of filamentous algae, including some Oscillatoria, which may be a nitrogen fixer, developed immediately downstream of P inputs. In addition, Nostoc, a known nitrogen—fixing blue—green alga, sampled after the enrichment, was significantly more abundant in the enriched sections than the control (P < .05). Densities of the snail, Goniobasis clavaeformis, a grazer—shredder sampled after the enrichment, also were significantly greater in the enriched reaches, suggesting that the lack of a sustained response of chlorophyll a to the enrichment may have been a result of increased grazing on algal biomass. These findings indicate that nutrient limitation of detrital processing is a significant factor in natural streams. The apparent increases in densities of benthic macroinvertebrates in the enriched sections, along with reported relationships between detrital food richness and macroinvertebrate growth and survivorship, suggest that nutrient limitation in streams also has ramifications on higher tropic levels.
Fire Frequency and Subalpine Forest Succession Along a Topographic Gradient in Wyoming
Authors: Romme William H. , Knight Dennis H.
Published: May 2006

Differences in fire frequency and the rate of secondary succession following fire have had a major effect on the present composition of forest vegetation in a 4500—ha undisturbed watershed in the subalpine zone of the Medicine Bow Mountains, southeastern Wyoming. USA. Periodic fire coupled with slow secondary succession has perpetuated lodgepole pine forest on the upland, while mature Engelmann spruce—subalpine fire forests have developed in sheltered ravines and valley bottoms where fire is less frequent and succession following fire is more rapid and/or more direct. A graphic model is presented showing the relationship between topographic position, fire—free interval, and the occurrence of mature forests dominated by spruce and fire.
Energy Flow, Nutrient Cycling, and Ecosystem Resilience
Authors: DeAngelis D. L.
Published: May 2006

The resilience, defined here as the speed with which a system returns to equilibrium state following a perturbation, is investigated for both food web energy models and nutrient cycling models. Previous simulation studies of food web energy models have shown that resilience increases as the flux of energy through the food web per unit amount of energy in the steady state web increases. Studies of nutrient cycling models have shown that resilience increases as the mean number of cycles that nutrient (or other mineral) atoms make before leaving the system decreases. In the present study these conclusions are verified analytically for general ecosystem models. The behavior of resilience in food web energy models and nutrient cycling models is a reflection of the time that a given unit, whether of energy or matter, spends in the steady state system. The shorter this residence time is, the more resilient the system is.
Populations Dynamics and Role of Two Species of Lepidostoma (Trichoptera: Lepidostomatidae) In an Oregon Coniferous Forest Stream
Authors: Grafius E. , Anderson N. H.
Published: May 2006

The aim of this study was to gather quantitative field and laboratory data on the role of Lepidostoma cascadense (Milne) and Lepidostoma unicolor (Banks) in the processing of conifer needles in a stream ecosystem. Samples were collected monthly in a riffle—pool section of Mack Creek, Lane County, Oregon, USA. For L. cascadense, maximum larval density was 812/m2 and instantaneous growth rate was 1.5%/d. The larvae grew slowly throughout the winter and pupation occurred in May and June. In contrast, L. unicolor increased very little in size during the winter and grew very rapidly during June and early July, reaching a maximum larval density of 320/m2 and with an instantaneous growth rate (March through July) of 2.7%/d. Production of L. cascadense was estimated as 0.31 g°m—2°yr—1 and that of L. unicolor was 0.23 g°m—2°yr—1. In addition to temporal separation in periods of maximum growth, the two species occurred in different microhabitats. L. cascadense larvae were found within the sediments and debris while L. unicolor occurred on the surface of the debris. Laboratory studies were conducted with L. unicolor larvae. Consumption and fecal production rates (measured gravimetrically) increased with higher temperature, greater food density, or longer conditioning time of the food, and decreases with increased size of the larvae. Production and biomass of L. cascadense and L. unicolor in Mack Creek are minor in relation to other insects in the system. However, because of high consumption rates and low assimilation efficiency, the processing of large particulate organic matter by these two species contributed significantly to the food available to collectors in the study area.
A Physiological Basis for Niche Separation Between Agropyron Smithii (C3) and Bouteloua Gracilis (C4)
Authors: Kemp Paul R. , Williams George J.
Published: May 2006

Agropyron smithii (a C3 species) and Bouteloua gracilis (a C4 species) occur in the same habitat of the shortgrass prairie ecosystem in northeastern Colorado. The hypothesis tested in this study was that the two species differ in their fundamental niches partly as a function of their different physiological responses to temperature and moisture gradients. Growth and gas exchange patterns were measured on plants grown in controlled—environment chambers at cool (20°/15°C) and warm (35°/15°C) temperatures. Total dry mass growth of A. smithii was approximately two times greater when grown at cool compared to warm temperatures, whereas total dry mass of B. gracilis was 2.7 times greater when grown at warm compared to cool temperatures. The temperature for maximal growth was correlated with the temperature response patterns for gas exchange of leaves and roots. A smithii had maximal rates of net photosynthesis when grown at cool temperatures, while B. gracilis had maximal rates when grown at warm temperatures. In plants not water stressed, net photosynthesis was limited primarily by stomatal aperture in B. gracilis and internal leaf factors in A. smithii. Rates of net photosynthesis of both species from both growth temperatures were very sensitive to leaf water potential and decreased exponentially with decreasing leaf water potential. Root respiration, measured simultaneously with leaf gas exchange in hydroponically grown plants, was greater in A. smithii grown at 20°/15°C and in B. gracilis grown at 35°/15°C, and decreased with decreasing solution water potential. Root respiration of warm—grown A. smithii and cool—grown B. gracilis was lower than that of plants grown at more nearly optimal temperatures and did not decrease with decreasing solution water potential. These finding suggest that the temporal displacement of growth between A. smithii and B. gracilis in their native habitat is partly a function of the differential temperature responses of photosynthesis and related metabolic processes. The differences in the temperature responses of photosynthesis appear to be a consequence of the species having different photosynthetic pathways. The similarities between the species in their physiological responses to water stress suggest that seasonal moisture gradients are not as important a parameter along which niche separation has occurred as are seasonal temperature gradients.
Energy and Nitrogen Relation for a Macrosiphum Liriodendri (Homoptera: Aphididae) Population in an East Tennessee Liriodendron Tulipifera Stand
Authors: Van Hook R. I. , Nielsen M. G. , Shugart H. H.
Published: May 2006

Biomass and density of all instars of a Liriodendron aphid population on three mature trees in an east Tennessee yellow "poplar" stand were determined for the 1971 growing season. Concurrently, laboratory studies were carried out to ascertain rates of each aphid instar's metabolism, growth, reproduction, and honeydew production. Similarly, whole body caloric content and concentrations of N were determined for each instar. Results from these studies were utilized in estimating ingestion of sap by the aphid population, and in developing a mathematical model of aphid population dynamics. These estimates were used in preparing annual budgets of dry matter, energy, and N for the population. Maximum aphid biomass of 169 mg dry mass/m2 ground area (Leaf Area Index = 4.7) occurred in early June coincident with maximum nitrogen concentrations in phloem sap and favorable canopy temperature. There was a second peak in population biomass in September, just prior to leaf abscission when nitrogen compounds were again mobile in the phloem streams. Reproduction and honeydew production were functions of temperature and followed a Q10 = 2 relationship. Metabolism and growth were also functions of temperature but increased exponentially (Q10 relationship) up to an optimum temperature, °22°C, and them declined rapidly. Values observed for these parameters were well within ranges reported in the literature for numerous aphid species. Energy budgets calculated for both laboratory and field populations of this aphid species indicate that M. liriodendri consumes ca. 400% of its dry body mass per day, or 185 kcal/m2 annually. Of this ingestion, 65% goes into honeydew production (egestion), 6% into respiration, and 27% into production of biomass. Similar budgets prepared for nitrogen indicate that 970 mg N/m2 are consumed annually, and of this, 27% goes into honeydew and 73% is incorporated into aphid biomass. Comparison of these data with standing pools of energy and nitrogen in the Liriodendron stand shows that this aphid population consumes 1% of annual photosynthate production and an amount equivalent to 17% of the annual standing crop of foliar N. The impact of this consumption on primary production is not presently known.
Phenology and Ecophysiology of Tropical Trees: Erythrina Poeppigiana O. F. Cook
Authors: Borchert Rolf
Published: May 2006

Under the climatic conditions of San Jose, Costa Rica, leaf fall, flowering, and shoot emergence of Erythrina poeppigiana O. F. Cook were markedly asynchronous among trees of the same population, suggesting strong endogenous control of the tree's development. During 1 yr, trees passed through two cycles of leaf shedding and shoot emergence. The endogenous periodicity of leaf shedding appeared to be primarily the result of leaf senescence. During the dry season, leaf senescence and hence leaf shedding were enhanced by tree water deficits. As a consequence of leaf shedding, water stress was alleviated and shoot emergence occurred, even under continued drought. The degree of water stress, reflected in stem shrinkage, was affected by tree size, soil moisture availability, and seasonal changes in evapotranspiration. Large trees at dry sites water deficits and hence passed through leaf change early in the dry season, while smaller trees and trees at humid sites did so up to 3 mo later. The phenology of Erythrina along an altitudinal gradient of increasing atmospheric water stress showed a transition from an evergreen to a deciduous habit. At permanently humid sites, all phenological phases occurred simultaneously on the same tree. With increasing drought, consecutive developmental stages tended to be more separate in time and more synchronized. In humid tropical climates, characterized by the absence of significant environmental stress, the periodic development of Erythrina is thus primarily determined by variables such as leaf age and tree size, which affect the tree's internal functional balance. Increasing environmental stress, in tropical environments most likely drought, may secondly synchronize certain phases of the basic endogenous rhythmicity with seasonal climatic changes.
Importance of Organic Debris Dams in the Structure and Function of Stream Ecosystems
Authors: Bilby Robert E. , Likens Gene E.
Published: May 2006

Removal of all organic debris dams from a 175—m stretch of second—order stream at the Hubbard Brook Experimental Forest in New Hampshire led to a dramatic increase in the export of organic carbon from this ecosystem. Output of dissolved organic carbon (<0.50 μm) increased 18%. Fine particulate organic carbon (0.50 μm—1 mm) export increased 632% and coarse particulate organic matter (>1 mm) export increased 138%. Measurement of the standing stock of coarse particulate organic matter on streambeds of the Hubbard Brook Valley revealed that organic debris dams were very important in accumulating this material. In first—order streams, debris dams contain nearly 75% of the standing stock of organic matter. The proportion of organic matter held by dams drops to 58% in second—order streams and to 20% in third—order streams. Organic debris dams, therefore, are extremely important components of the small stream ecosystem. They retain organic matter within the system, thereby allowing it to be processed into finer size fractions in headwater tributaries rather than transported downstream in a coarse particulate form.
Age Structure and Disturbance History of a Southern Appalachian Virgin Forest
Authors: Lorimer Craig G.
Published: May 2006

The frequency and intensity of natural disturbances in a montane old—growth forest of coniferous (Tsuga) and broad—leaved deciduous trees (Liriodendron, Betula, Costanea, Fagus, Acer) were investigated by means of diameter frequency distributions, diameter—age regressions, and analysis of radial growth patterns. The seven species investigated are represented by all—aged populations regardless of the degree of shade tolerance. The age distributions of most species, however, are irregular with several prominent peaks. Apparent coincidence of these peaks among some species suggests a common underlying influence. Radial growth patterns reveal higher than average numbers of abrupt and sustained increases in growth rate in most decades of peak recruitment which, along with other evidence, suggest that disturbance was the principal causal factor. There is evidence for eight partial disturbances in the past 250 yr, each of which generally removed <10% of the overstory trees. These fairly light disturbances appear to be sufficient to cause major deviations from the theoretical equilibrium diameter distribution of the forest.
Vegetation Response to Climate and Fire in the Driftless Area of Wisconsin
Authors: Kline Virginia M. , Cottam Grant
Published: May 2006

Quantitative analysis of original land survey data was used to study the presettlement vegetation of a 681—km2 watershed at a forest—savanna ecotone in the Driftless Area of southwestern Wisconsin. Five vegetation types were found: mesic forest, white oak—pine forest, oak—aspen forest, white oak woodland, and oak savanna. Existence of the five types was attributed to gradients of fire and climate, and the discrete boundaries between the types of topographically imposed discontinuities in the gradients. The mesic forest of the study area was at the northern limit of a mesic forest "island" in the extensive oak savannas of southwestern Wisconsin. The mesic forest island is a geologically controlled meteorological island, which experiences a combination of relatively high annual rainfall and cool summer temperatures. The presence of the mesic forest is attributed to this mesoclimate. Structural analysis of the mesic forest data and other evidence suggest a climatic change in the area at °430 BP
Host‐Parasite Interaction as a Potential Population‐Regulating Mechanism
Authors: Steinwascher Kurt
Published: May 2006

Candida humicola, a parasitic yeast occuring in the gut of Green frog (Rana clamitans) tadpoles, enhanced the growth of tadpoles of this species under certain conditions. Low concentrations of C. humicola (1—10 cells per millilitre) increased the growth rate of tadpoles relative to siblings raised under identical conditions but without C. hunicola cells. Furthermore, the impact of a given concentration of C. humicola cells varied inversely with the size of the tadpole. Candida humicola appears to act as a mutualistic symbiont of the larger tadpoles and as a parasite of the small ones. Because larger tadpoles are more likely than their smaller siblings to metamorphose and reproduce, the mutualism benefits those individuals which are most likely to contribute to the continuation of the Green frog population. For this reason, resistance to the parasitism is not likely to develop. The parasite may act to regulate the adult Green frog population size by altering the probability of metamorphosis of individual tadpoles.
Intraspecific Variation in demography and Life History of the Lizard, Sceloporus Jarrovi, Along an Altitudinal Gradient in Southeastern Arizona
Authors: Ballinger Royce E.
Published: May 2006

Mark—recapture studies were conducted on a low (1675 m) and high (2542 m) altitude population of Sceloporus jarrovi in southeastern Arizona, USA from 1973 through 1976. Average age—specific mortality rates differed between altitudes only in the 0—1 yr age class. The increased mortality of neonates are low altitude was correlated with an increased number of potential predators and a significantly greater frequency of natural tail—breaks. Tail—break frequency did not differ between sites for older age classes. Survivorship and age at maturity were greater at high altitude. Low—altitude females mature in their first reproductive season. Transfer of neonates between altitudes indicate that high—altitude females do not mature in their first season even if raised at low altitude. Age at maturity appears to be adaptively adjusted by the demographic environment. Fertility schedules indicate that °40% of the replacement of low—altitude populations results from reproduction by 1st yr animals. There was a greater variation in replacement rate and population size at low than at high altitude.
The Effects of Stem Gall Insects on Life History Patterns in Solidago Canadensis
Authors: Hartnett David C. , Abrahamson Warren G.
Published: May 2006

Populations of goldenrods (Solidago canadensis) were sampled to determine the effects of three stem gall insects, Gnorimoshema gallaesolidaginis (Gelechiidae), Eurosta solidaginis (Tephritidae), and Rhopalomyia solidaginis (Cecidomyiidae) on resource allocation patterns in the plants. Gall infestations were as high as 38.5% and the dominant gall insect differed from site to site. The gall insects caused significant and highly specific effects on the plants. Each of the three gall types increased stem production, decreased current rhizome production, and lowered seed reproductive allocation as measured both by inflorescence production and propagule production. Vegetative reproductive allocation (the proportion of biomass allocated to new rhizome) was unaffected. With the exception of ball gall—beaing ramets, the number of new rhizomes produced was unaffected by the presence of galls. Growth of the elliptical gall significantly reduced shoot height and significantly increased lateral branching and propagule weight. Formation of the ball significantly reduced propagule weight and the number of new rhizomes produced. Thus gall insect—plant interactions may play an important role in the evolution of plant life history patterns in certain taxa. Future studies are needed to determine the effects of galls on entire clones (genets) and the implications of gall infestation on future growth, survivorship, and reproduction.
Robust Estimation of Population Size When Capture Probabilities Vary Among Animals
Authors: Burnham K. P. , Overton W. S.
Published: May 2006

A model is given for multiple recapture studies on closed populations which allows capture probabilities to vary among individuals. The capture probability of each individual is assumed to be constant over time. Based on this model we give a nonparametric estimation procedure for population size. The estimator involves selecting one of a sequence of estimators which are each linear combinations of the capture frequencies. The individual estimators are derived from the generalized jackknife method. We also give a goodness of fit test for the model's assumption that individual capture probabilities do not change during the study. The robustness of this estimation procedure is investigated with a simulation study. By virtue of this study, and the theoretical nature of the estimator, it is judged to be robust to moderate variations in individual capture probabilities which may occur in commonly used short—term livetrapping studies.
A Technique For estimating the Size of Lizard Populations
Authors: Heckel David G. , Roughgarden Jonathan
Published: May 2006

We describe a mark—resight procedure for estimating population size which integrates field techniques with a method of statistical estimation. The field protocol consists of an efficient method of applying marks to a large fraction of the population. The statistical method provides a number of different models with which to project an estimate of the total population from the census data, and enable choice of the model giving an estimate with small error and good fit to the data. This method enables one to detect and correct for differences in the properties of marked and unmarked animals, an important consideration in mark—resight methods. We illustrate the method with our data on two species of the lizard Anolis.
Competition and Nest Spacing in a Tropical Stingless Bee Community
Authors: Hubbell Stephen P. , Johnson Leslie K.
Published: May 2006

The density and dispersion patterns of nests of 5 stingless bee species are described for a tract of Costa Rican tropical dry forest. Features of suitable nest sites are analyzed, but it does not appear that nest site availability limits colony density or determines colony dispersion. Rather, food limitation is suggested by a linear relationship between the logarithm of colony biomass and the logarithm of foraging "home range." Colonies were uniformly dispersed intraspecifically in 4 species. The pattern in a 5th species could not be distinguished from a random dispersion. Partial nest counts in 3 more species suggested a clumped dispersion in at least 1 species. The 4 species with uniform nest spacing all use pheromones for recruitment in foraging, whereas the remaining 4 species do not. The 3 most uniformly dispersed species are also intraspecifically aggressive at food sources. We propose that colony spacing is accomplished in these species by aggressive prevention of new colony establishment. The mechanism of colony spacing we propose has as essential elements: pheromone marking of potential nest sites; recruitment of workers; and aggression between workers from rival nests. This mechanism has been observed in operation in at least 1 of the species.
Energy Allocations in Annual and Perennial Lupines (lupinus: Leguminosae)
Authors: Pitelka Louis F.
Published: May 2006

The energy allocation patterns of 3 species of lupine, an annual, a perennial herb, and a shrub were investigated and related to life cycle differences as well as ecological differences among the species. All 3 species occur along the central California coast but differ in their specific environmental tolerances. The annual, Lupinus nanus, and the shrub, Lupinus arboreus, have high growth rates and photosynthetic rates when compared with the perennial herb, Lupinus variicolor. The 3 species initially have similar energy allocation patterns, but they gradually diverge during the growing season. The annual ultimately devotes up to 61% of its energy to reproductive tissues and 29% to seeds alone, while only 3%—4% ends up in the roots. Its life cycle strategy and energy allocation pattern make it a poor competitor in stable environments, and it is only found in disturbed sites along the coast. The perennial herb may not reproduce in the 1st year, and in the 2nd year devotes only 18% of its energy to reproduction and only 5% to seeds. At least 40% of its energy is invested in its large taproot system where energy for future growth can be stored. Its prostrate growth form and low investment in reproduction are related to its restriction to the climatically stable but fairly harsh environment found on cool, windy bluffs. The shrub also may not reproduce in the 1st year but later devotes at least 20% of its energy to reproduction and 6% to seeds. It typically devotes °50% to stems, and this, along with its high growth rate, makes it a superior competitor, particularly in successional habitats away from the ocean bluffs. Its unusually short life span explains its fairly high reproductive effort as well as its absence from climax coastal communities. The 3 lupines have energy allocation patterns that fall within the patterns found for other plants with similar life cycle strategies, except that the reproductive efforts are at the high ends of the respective ranges. Investments in seeds alone are more in line with previous findings and reveal that the lupines devote an unusually high percentage of their energy budgets to structures ancillary to reproduction.