bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Fish Predation and Spatial Heterogeneity in Determining Benthic Community Structure
Authors: Gilinsky Ellen
Published: May 2006

The effects of predation and spatial heterogeneity on the benthic macroinvertebrates in the littoral zone of a pond were investigated in a year—long caging experiment. Bluegill sunfish stocked at three densities within the cages were used as the predator. Heterogeneity was manipulated using artificial macrophytes. The presence of plants led to increases both in species richness and in density of most macroinvertebrates. Uncovered benthic sediments had greater species richness and higher macroinvertebrate densities than did sediments covered by macrophytes, suggesting that certain benthic species, notably several chironomid groups, migrate onto the macrophytes when this habitat becomes available. Fish predation had a significant impact on both the number of benthic species and the densities of certain benthic macroinvertebrate groups. The predatory chironomid Clinotanypus pinguis showed a strong negative response to bluegill predation, with fish exclusion resulting in higher densities throughout the year. A group of herbivorous chironomids exhibited a response to fish predation that varied over the year, with predation resulting in elevated densities in the fall and winter but reduced densities in the summer. Many of the other species found in the littoral zone showed no significant response to bluegill predation. In addition, fish predation had no significant effect on densities of most macroinvertebrates occurring on the macrophytes. These complex responses of the various macroinvertebrates to fish predation are explainable in terms of seasonal changes in predation intensity and the importance of invertebrate vs. vertebrate predation. In the fall and winter bluegill feeding is often reduced. By concentrating on a few preferred prey (predaceous chironomid species), their feeding might alleviate competitive or predatory relationships among the macroinvertebrates and thus lead to increased densities of many species. The high bluegill feeding intensity known to occur during the summer is severe enough to limit the numbers of most invertebrate prey. As fish predation was not effective on invertebrates in the macrophytes, it seems that the added physical complexity serves as a refuge from predation.
Depth Distributions of Armored Catfish: Predator‐Induced Resource Avoidance?
Authors: Power Mary E.
Published: May 2006

Four species of armored catfish (Loricariidae) have size—specific depth distributions in a Panamanian stream, with larger fish in deeper water. Depth distributions do not change from the dry to the rainy season, despite a two— to three—fold increase in habitat area for larger loricariids. Throughout the year, standing crops of the loricariids' attached algal food are relatively high in shallow water, but decrease rapidly with depth. Over 2.1 yr, large Ancistrus spinosus, the most common pool—dwelling loricarriid, showed significant seasonal changes in somatic growth rates, with maximum rates in the early rainy season and minimum rates in the late dry season. Significant seasonal changes in mortality rates, estimated from rates of disappearance of marked individuals, were not detected. These data are consistent with the following hypothesis: small loricariids are limited, perhaps by predation, at densities below those necessary to deplete algae in shallow water. Larger loricariids avoid shallow water where they are vulnerable to fishing birds, even in the dry season when food is in short supply in deeper areas.
Predation by Shorebirds, Fish, and Crabs on Invertebrates in Intertidal Mudflats: An Experimental Test
Authors: Quammen Millicent L.
Published: May 2006

An experimental tests, using exclosures, of the effects of different guilds of predators (shallow—feeding shorebirds, benthic—feeding fish, and a crab) on the invertebrate populations of three mudflats differing in sand concentration is reported. The effects of predation at these three sites on similar species of prey depended on the seasonality of the important predator species, which changed with sediment composition. Predation did not appear to affect the species composition of the infaunal community. The experimental treatments were designed to separate out effect of different groups of predators and to try to assure that observed differences were not caused by modifications in the physical environment inside the exclosures. Effects of fish were separated from those of shorebirds by comparing changes in infaunal densities in (1) exclosures with sides that floated up during high tide, which excluded only birds, and (2) in exclosures with rigid sides, which excluded both fish and birds. There were no detectable artifactual effects of the experimental manipulations. Fish appeared to be of minor importance. The effects of shorebird predation were very different among the three mudflats and depended upon subtle differences in sediment composition among sites. Shorebirds were most abundant at the muddiest site, and infaunal densities at this site were lowest in the winter when birds were present. The exclosure experiments demonstrated that the birds significantly reduced infaunal densities during that period. In contrast, shorebirds were least abundant at the sandiest mudflat, and infaunal densities were highest in the winter when birds were present. Excluding birds had no demonstrable effect on infaunal densities. However, the lined shorecrab, Pachygrapsus crassipes, was present only at the sandiest mudflat and only in the summer. Exclusion of crabs at this site demonstrated that the crabs reduced infaunal densities during the summer when they are active on the mudflats.
Energy Utilization by Free‐Ranging Sceloporus Virgatus Lizards
Authors: Merker Gerold P. , Nagy Kenneth A.
Published: May 2006

Seasonal and sexual differences in daily energy allocation were evaluated for the striped plateau lizard (Sceloporus virgatus, Sauria: Iguanidae) from field measurements of metabolic rates (doubly labeled water), time—activity budgets, body temperatures, and energy storage rates, along with laboratory measurements of resting metabolism (gas exchange) and food utilization efficiency. In spring, males had higher field metabolic rates (FMRs) than females, but females consumed food factor while abroad and used the extra energy for producing eggs. Females were abroad about half as long as males (3.6 vs. 7.6 h/d) but an estimate of their energy metabolism while abroad was much higher than that of males (8.3 vs. 3.6 times resting metabolic rate). Males did not eat enough food to satisfy their energy and they lost body mass in spring. During summer, both sexes maintained constant body masses and steady—state energy budgets, but females had much higher FMRs and feeding rates than mules because females were abroad and active longer than males. Daily energy expenditure was positively correlated with duration of daily activity period. A lizard that was active 8 h/d had an FMR about 8 times higher than if it had remained inactive in a retreat all day. Thus S. virgatus can change its daily cost of living by nearly an order of magnitude by varying the time it spends abroad. Field behavior patterns are consistent with the hypothesis that these lizards regulate their activity in a manner that enhances survival and reproduction.
Ecology of Hatchling Sex Ratio in Map Turtles
Authors: Vogt R. C. , Bull J. J.
Published: May 2006

Incubation temperature is known to determine the sex of hatchlings in many species of turtles, including the map turtles. Graptemys ouachitensis, G. pseudogeographica, G. geographica, and painted turtle, Chrysemys picta. This paper presents a study of sex ratio and nest ecology in natural populations of these species in Wisconsin, but largely for G. ouachitensis and G. pseudogeographica. Nesting was monitored during June, and hatchlings were obtained from 236 nests during August and September 1980. The distribution of nest sex ratios samples of the two common species was bimodal, tending to be all—female or all—male within a nest, with an overall excess of females. Nests with males were located amid vegetation, with cool temperatures, and nests with females were located in open sand exposed to the sun, with high temperatures. The sex ratio differed significantly between nesting beaches, apparently because of differences in the availability of warm vs. cool nest sites. All—female nests hatched in less time than all—male nests, and the sex ratio of emerging hatchlings consequently changed from nearly all female early in August to all male in September. The data indicate major environmental influences on the hatchling sex ratio in map turtles.
Adaptations for Seed Dispersal and the Compromises Due to Seed Predation in Limber Pine
Authors: Benkman Craig W. , Balda Russell P. , Smith Christopher C.
Published: May 2006

Cone and seed morphology and phenology of the closely related limper pine (Pinus flexilis) and southwestern white pine (P. strobiformis) were studied in relation to selective seed harvesting by red squirrels (Tamiasciurus hudsonicus) and Clark's Nutcrackers (Nucifraga columbiana) on two study sites in north central Arizona. We examined possible selective influences that favor characteristics of both wind— and corvid— dispersed seeds in the limber pine. In a density forested site, red squirrels harvested >80% of the cones of both pine species before they opened. Seeds from cones harvested by red squirrels were unlikely to germinate. Harvesting of cones and seeds by red squirrels was hindered by pitch and several other cone features. Pitch was more effective in slowing red squirrel harvesting on limber pine than on southwestern white pine. When red squirrels were absent from the open study site, >70% of the cones opened on the trees. Clark's Nutcracker usually harvested seeds from open cones. Limber pine as compared to southwestern white pine was more evenly and completely harvested by nutcrackers, probably because the cones ripened synchronously within a tree and asynchronously among trees. Cones of southwestern white pine ripened synchronously within and among trees, thus saturating both nutcrackers and squirrels. Differences between the two pines are most readily interpreted as adaptations for increasing seed dispersal, hindering limber pine's main seed predator (red squirrel) and facilitating seed harvest by its most important seed disperser (Clark's Nutcracker). We conclude that squirrels in the genus Tamiasciurus are an important constraint on the development of cone characteristics that enable efficient seed harvest by birds. Furthermore, adaptations of pines for seed dispersal depend on the relative harvest by predators and dispersers during the different stages of cone—ripening phenology.
Diffusion in Fractcal Landscapes: Simulations and Experimental Studies of Tenebrionid Beetle Movements
Authors: Johnson A. R. , Milne B. T. , Wiens J. A.
Published: May 2006

Organismal movement is frequently treated as a diffusion process arising from a simple random walk in a spatially uniform environment. However, anomalous diffusion may arise due to: (1) intrinsic departures from random movements of individuals; or (2) the effects of barriers that impede, or corridors that facilitate, movement. We examine anomalous diffusion in field studies of Eleodes beetles (Coleoptera: Tenebrionidae) and in simulations of correlated random walk on maps of real and artificial landscapes. We show how diffusion alternates between ordinary and anomalous diffusion depending on movement rules, landscape pattern, and the spatial and temporal scales of observation. Recent theories of diffusion in spatially complex media predict power law relations for anomalous diffusion. Over time scales of 5—500 s, Eleodes exhibited power laws for: (1) mean squared displacement with time; and (2) the mean time to travel from the center to the perimeter of circles of various radii. In grasslands, diffusion exponents changed significantly at a radius of 42 cm, which characterized the size of grass and bare soil patches. A second change in diffusion at scales of 24—600 h characterized home range activity. Marked discrepancies between the dynamics of beetles in the field and in simulations suggest a need for more comprehensive models of individual movement that use different rules for various domains of space and time. Studies of anomalous diffusion identify the relative effects of environment vs. innate behavior and reveal a range of scales over which the effects pertain.
Complex Interactions in Metacommunities, with Implications for Biodiversity and Higher Levels of Selection
Authors: Wilson David Sloan
Published: May 2006

Two common features of biological communities are (a) complex interactions among species, which make community dynamics sensitive to initial conditions, and (b) spatial heterogeneity, which fragments large—scale ecological systems into a mosaic of patches, hereafter termed a "metacommunity." This computer simulation study examines the effect of complex interaction on the global and local dynamics of metacommunities. Patches are physically identical and differ only in the initial proportion of species that colonize the patches. The random variation is then magnified by deterministic interactions that cause patches to follow different trajectories based on initial conditions. After a period of interaction, individuals from all patches join in global pool of dispersers that colonize a new "generation" of patches. Complex interactions can have at least two important effects on metacommunity dynamics. First the number of species coexisting in the metacommunity can greatly exceed the number of species coexisting in any single patch, despite the fact that the patches are physically identical, the species do not differ in colonization ability, and stochastic effects are absent after the colonization stage. Second, complex interactions provide a new source of variation upon which natural selection can operate at the patch level, providing a mechanism for the evolution of functionally organized communities.
Effects of Moose Browsing on Vegetation and Litter of the Boreal Forest, Isle Royale, Michigan, USA
Authors: McInnes Pamela F. , Naiman Robert J. , Pastor John , Cohen Yosef
Published: May 2006

Large mammalian herbivores can influence the dynamics and structure of ecosystems by selectively removing tissues of specific plant species. The plant community composition can be altered as animals feed on some species but not others, changing the biomass, production, and nutrient cycling of an entire ecosystem. We used four paired moose (Alces alces) exclosures and browsed plots (built between 1948 and 1950) on Isle Royale, Michigan, to examine the influence of moose on aboveground biomass, production, and annual litterfall of boreal vegetation in 1987. Tree biomass was significantly greater (X = 230 vs. 150 Mg/ha, df = 3, P < .05), shrub biomass was significantly less (X = 1.9 vs. 3.1 Mg/ha, P < .05), and herb biomass was significantly less (X = 0.2 vs. 0.8 Mg/ha, P < .05) in exclosures than in browsed plots. Tree production was greater in exclosures than in browsed plots (X = 7.9 vs. 5.0 Mg.ha—1.yr, P = .05), but there was no difference in the production per unit biomass between exclosures and browsed plots. Shrub production in exclosures was similar to that of browsed plots (X = 3.5 vs. 2.3 Mg.ha—1.yr—1, P < .05), despite total vegetation biomass differences between paired plots. There was significantly greater herb litter produced in the browsed plots than in the exclosures (X = 0.7 vs. 0.1 Mg.ha—1.yr—1, P < .05). Moose browsing prevented saplings of preferred species from growing into the tree canopy, resulting in a forest with fewer canopy trees and a well—developed understory of shrubs and herbs. In addition, browsing may have altered the eventual balance of white spruce (Picea glauca) was balsam fir (Abies balsamea), causing an increase in the former and a decrease in the latter. Thus, browsing by moose influences in long—term structure and dynamics of the boreal forest ecosystem, which has important implications for forest ecosystem management, especially where the population dynamics of moose are regulated.
Foraging Pattern, Colony Distribution, and Foraging Range of the Florida Harvester Ant, Pogonomyrmex Badius
Authors: Harrison Janet S. , Gentry John B.
Published: May 2006

This report describes the foraging pattern of the Florida harvester ant Pogonomyrmex badius in a high—density population of colonies. The foraging pattern has both promoted and been influenced by the colony distribution. Pogonomyrmex badius forages from short trails which extend into a surrounding foraging range. Direction of foraging trails is influenced by the location of a colony's near neighbors. Seasonal nest relocations always occur along a foraging trail, usually the main trail. Foraging ranges are not actively defended, but are used almost exclusively by foragers from a single colony. Foraging ranges will be extended into an area abandoned by neighboring foragers, indicating that forager presence may define each colony's range. Colony distribution has remained essentially the same for several years, despite seasonal nest relocations and addition of new colonies. Establishment of trials and exclusive foraging ranges by each colony minimizes encounters with neighboring foragers and guarantees access to available resources; this pattern also promotes maintenance of the existing colony distribution and partitioning of resources.
Responses in Growth Mortality, and Reproduction to Variable Food Levels by the Rotifer, Asplanchna Girodi
Authors: Robertson J. Roy , Salt George W.
Published: May 2006

We have determined the changes in fecundity, mortality, and growth of the ploimate rotifer, Asplanchna girodi, in response to variations in food density. Rotifers were raised from birth on either fixed allotments of Paramecium tetraurelia or on allotments that varied temporally. Fecundity, growth rates, and size of the rotifer at the time of birth of the first offspring varied directly with food level. Longevity and age at the birth of the first young varied inversely with food level. The size of offspring remained constant regardless of parental food intake. Individuals switched from low to high food rations produced more offspring than those given a high ration from birth. The per capita death rate was insensitive to food level, but the birth rate varied directly with food level. Young individuals were better able to resist starvation than adults. These responses of A. girodi to varying resource densities are interpreted as being adaptive in environments with temporally varying food resources. When food levels are high, many young are produced and act to buffer the population against a decline in numbers when the food levels are reduced. The restoration of higher food levels causes the starved individuals to respond with high fecundities, which act to restore population densities to previous levels. In all resource environments, individual fecundity is adjusted to produce young with high changes of survival and reproduction.
Structural Stability and Architecture of Vines vs. Shrubs of Poison Oak, Toxicodendron Diversilobum
Authors: Gartner Barbara L.
Published: May 2006

To learn whether vine stems are less structurally stable than shrub stems, I studied the architecture, anatomy, and mechanics of western poison oak (Toxicodendron diversilobum), a plant that grows as a vine when provided with external support but otherwise as a shrub. I assessed the relative structural stabilities of vines and shrubs, and the relative importance of stem morphological vs. material properties for this structural stability using the following types of information: abovegound architecture and biomass distribution, and geometric, anatomical, and material properties of the stems. Shoots that were supported by a fence (vines) had a lower proportion of their dry mass in primary stem and had more aboveground dry mass, more leaves, and a greater total length of stem than did unsupported shoots (shrubs). Both growth forms had about the same proportion of their biomass at a given relative height above the ground. Supported shoots were taller and had lower stem taper (change in radius per unit length of stem) than did unsupported shoots, and, in a common garden, had longer internodes. Xylem of supported shoots had a higher proportion of vessel lumen and lower maximum thicknesses of fiber cell walls than did xylem of unsupported shoots. Supported stems were less stiff (had lower apparent material stiffness in bending) than unsupported stems at diameter ≤3.5 cm. A simple model showed that the lower taper and lower material stiffness of vines yielded much lower flexural stiffness in vine than in shrub stems. A second model showed that simplified shrub stems could reach almost 11 m before becoming structurally unstable. Actual shrubs from the modelled environment, however never exceeded 3.2 m in height. A simplified vine modelled for the same environment would become unstable at 1.2 m, whereas vines in the field can be over 30 m tall. These findings suggest that for poison oak (1) shrubs are overbuilt and vines are underbuilt for self—support, and (2) the higher structural stability of shrubs than vines is due mainly to differences in stem geometry, not to differences in stem material properties.
Phosphorus Availability in Acid Organic Soils of the Lower North Carolina Coastal Plain
Authors: Walbridge Mark R.
Published: May 2006

A natural landscape gradient of P—deficient pocosin (evergreen shrub bog) and bay forest ecosystems was used to test three hypotheses concerning P availability and P reabsorption efficiency: (1) that variations in vegetation height and aboveground biomass among even—aged pocosin stands are related to variations in soil P availability; (2) that microbial processes control P availability in these soils; and (3) that the proportion of P reabsorbed from senescing foliage in native plants is inversely related to soil P availability. The natural gradient from short pocosin to bay forest was found to represent a gradient of increasing P availability, as indicated by increases in: (1) total P in surface (0°15 cm) soils, from 19.6 to 118.3 kg/ha; (2) seasonal and annual PO43— supply to in situ anion—exchange resins; and (3) P concentrations in native plant foliage. Increases in P availability were accompanied by a significant decline in the N:P ratios of both plant leaves and surface soils. Microbial processes strongly influenced the supply of available P. Soil microorganisms immobilized up to 90% of added 32PO43— during laboratory incubations, but when microbial uptake was inhibited, as much as 90% of added 32PO43— remained in the available pool. A decline in the ratio of microbial: total P in surface soils, from 56.3 to 37.4%, and an increase in the ratio of net: gross P mineralization (estimated by isotope dilution), suggested that as P availability increased, microbial control decreased. Native plants reabsorbed both P and N efficiently from senescing foliage, reaching maxima of 86.6 and 80.5%, respectively; natural variations in soil P availability did not affect the proportion of either nutrient reabsorbed. In general, however, plants tended to reabsorb greater proportions of foliar P than N. Natural variations in P availability, the factors controlling P availability in these soils, and the potential for differential nutrient reabsorption by native plants have important implications for the cycling and accumulation of P and N in pocosin and bay forest soils. Landscape—Level processes may have contributed to the observed variations in vegetation and P availability along this natural gradient.
Measuring Biosphere‐Atmosphere Exchanges of Biologically Related Gases with Micrometeorological Methods
Authors: Baldocchi Dennis D. , Hincks Bruce B. , Meyers Tilden P.
Published: May 2006

Ecologists are expected to play an important role in future studies of the biosphere/atmosphere exchange of materials associated with the major biogeochemical cycles and climate. Most studies of material exchange reported in the ecological literature have relied on chamber techniques. Micrometeorological techniques provide an alternative means of measuring these exchange rates and are expected to be used more often in future ecological studies, since they have many advantages over the chamber techniques. In this article we will provide an overview of micrometeorological theory and the different micrometeorological techniques available to make flux measurements.
Waterfowl Communities and Seasonal Environments: Temporal Variability in Interspecific Competition
Authors: DuBowy Paul J.
Published: May 2006

Controversy over the role that interspecific competition plays in structuring avian communities has polarized the debate into two alternative points of view. One school of thought, exemplified by Wiens (1977), de—emphasizes the role that competition plays in structuring communities, while the opposing school, exemplified by Schoener (1982), invokes competition as a driving force in resource partitioning and community structure. To test these alternative arguments, I examined a guild of dabbling ducks (Anas spp.) that co—occur throughout the year. Species—pairs exhibited significantly lower overlap values for foraging, habitat utilization, and food items during winter than summer. In addition, food resources (both relative and absolute abundances) were lower during winter than summer. From these data I infer that the intensity of interspecific competition and its effect on waterfowl community structure is seasonal, with greater resource limitation and, therefore, resource partitioning during "lean" winter months than during "fat" summer months. Consequently, on a yearly cycle, avian communities may exhibit periods of intense interspecific competition, alternating with times of resources abundance where competition may be insignificant or absent.
Sun, Slope, and Butterflies: Topographic Determinants of Habitat Quality for Euphydryas Editha
Authors: Weiss Stuart B. , Murphy Dennis D. , White Raymond R.
Published: May 2006

Thermal environments in a large, topographically diverse serpentine soil—based grassland were quantified and ranked using a computer model of clear sky insolation and shading on different slopes to determine the effects of microclimate on the rates of development of each of the life stages of the butterfly Euphydryas editha bayensis. Larvae developed to pupation earlier on warm slopes than on progressively cooler slopes. Availability of sunlight can be limiting for larvae, which bask indirect sun to raise body temperature. Larvae can disperse >10 m/d, allowing them to transfer between microclimates. Pupae on warmer slopes also developed faster than those on cooler slopes. Microclimate also affects the phenology of host plants of larvae and nectar sources of adults. Larval and pupal development and host—plant phenology determine the phase relationship between adult butterfly flight and host—plant senescence, which in turn determines mortality rates of prediapause larvae. Adult females that eclosed early in the season could have their offspring survive on almost all slopes, survivorship of offspring from adults that eclosed in the middle of the flight season was restricted to cooler slopes in the habitat. Some butterflies eclosed too late for their offspring to survive on any slope. Topographic diversity on several scales is a prime indicator of habitat quality for this butterfly. Areas of high local topographic diversity on a scale of tens of metres appear particularly important for long—term population persistence under variable climatic conditions.
Grazing History, Defoliation, and Competition: Effects on Shortgrass Production and Nitrogen Accumulation
Authors: Jaramillo Victor J. , Detling James K.
Published: May 2006

Plants of Bouteloua gracilis were collected from heavily grazed prairie dog (Cynomys ludovicianus) colonies (ON—colony) and lightly grazed uncolonized sites (OFF—colony) in Wind Cave National Park, South Dakota. Our objectives were to determine (1) how grazing history affected production, nitrogen uptake, and biomass and nitrogen allocation following defoliation and (2) how such responses were affected by competing neighbors of the same population. The growth chamber experiment was factorial with three main treatments in 12 possible combinations. Main treatments were: population (plants from lightly and heavily grazed sites), defoliation (three intensities), and competition (with or without neighbors of the same population). There were no significant interactions among treatments. OFF—colony plants produced 121% as much biomass and their N. yield was 203% as great as ON—colony plants. ON—colony plants allocated a higher percentage of biomass and N to the roots from OFF—colony plants, while the latter allocated a greater percentage of resources to leaf sheaths and reproductive structures. In response to defoliation, plants from the two populations had an average increase of 122% in N uptake per unit of root biomass and a 141% increase in total leaf—blade N yield. Heavily defoliated plants from both populations increased biomass and N allocation to blades, but total biomass production was substantially reduced. Intra—population competition reduced biomass production and N yield in individuals of both populations, but it did not affect total and aboveground N concentrations (per unit biomass) or N uptake per unit of root biomass. Our results support the hypothesis that genetically based morphological and physiological differentiation has occurred in B. gracilis as a result of strong selection pressures from grazing mammals on prairie dog colonies. We suggest the ON—colony population displays a strategy that reduces grazing severity rather than a "grazing tolerance" response to aboveground herbivory.
Relationships between Seed Fates and Seedling Establishment in an Alpine Ecosystem
Authors: Chambers Jeanne C.
Published: May 2006

On exposed soils relationships between soil surface characteristics and seed morphological attributes the microsites of seed entrapment and influence patterns of seedling establishment. I examined seed and seedling fates of alpine species with varying morphology over a range of uniform— and mixed—particle—size soils on the Beartooth Plateau, Montana. Physical relationships between seeds and surface soils determined entrapment and retention within the zone of potential emergence (0—1 cm depth). Seed size (length or mass), the presence or absence of specialized appendages or seed coats, and the nature of the appendage or seed coat influenced numbers of seeds trapped and seed distributions among the particle sizes. Antrorse hairs, hygroscopic awns, pappuses, and mucilaginous seed coats all resulted in higher entrapment over the range of particle sizes. The effectiveness of different seed morphologies was decreased by prolonged exposure (1 yr) to the environment. In contrast to seed entrapment and retention, seedling emergence and survival depended on the ability of the different particle—size soils to meet the biological requirements of the species. Although some seedling emergence occurred in particle sizes that ranged from < 0.5 to 4—8 mm, almost no seedlings survived in particle sizes larger than 1—2 mm. In particle sizes in which emergence occurred, a higher percentage of the total seeds trapped survived the first growing season as seedlings for large—seeded than for small—seeded species. For most species, the highest entrapment and retention occurred in particle sizes in which there was little or no emergence. Seedling emergence and survival were related to seed entrapment only for species with reasonably high emergence, and the R2 values were often low. Understanding seedling establishment patterns in different—particle—size soils requires knowledge of how relationships between seed morphology and soil characteristics affect entrapment patterns, and knowledge of soil particle size thresholds for seedling establishment.
Natural Distribution and Abundance of Forest Species and Communities in Northern Florida
Authors: Schwartz Mark W.
Published: May 2006

Quantitative estimates of the distribution and abundance of trees in northern Florida prior to extensive land development are summarized from Public Land Survey (PLS) records. The PLS data on 127 653 trees at 48 831 sample locations, collected between 1822 and 1854 and tabulated from original field notes, are summarized here to examine the abundance and distribution of major tree species and plant associations. These results are compared to another early, quantified estimate of vegetation published in 1914. These two records of vegetation were compared within 20 vegetation zones in northern Florida. Both data sets describe the vegetation of northern Florida as strongly dominated by pine and similarly describe regions more heavily represented by upland hardwood or forested wetland trees. The data sets differ predominantly in that the PLS data indicate: (1) more pine; (2) less cypress, gum, and sweetgum than the early 20th—century survey; and (3) that, in contrast to major upland hardwood taxa, the representation of major taxa typical of pinelands and forested wetlands is only loosely correlated between data sets. The PLS records were used to map the distribution of species and community types across northern Florida. The PLS data support, and quantify, previously published accounts of the overwhelming dominance of pine in the presettlement vegetation of northern Florida. This abundance of pine refutes various hypotheses that mixed hardwood vegetation dominated upland habitats in northern Florida.
Metapopulation Structure and Migration in the Butterfly Melitaea Cinxia
Authors: Hanski Ilkka , Kuussaari Mikko , Nieminen Marko
Published: May 2006

We describe a spatially realistic metapopulation model and parameterize it for a metapopulation of the butterfly Melitaea cinxia, residing in a network of 50 discrete habitat patches within an area of 15 km2. Parameter values that are difficult to estimate independently are obtained by fitting the model to patterns of patch occupancy and local density. There is no large "mainland" population, and the metapopulation appears to survive at an extinction—colonization equilibrium. Empty patches were smaller than the occupied ones, indicating the extinction proneness of especially small local populations; population turnover was 16% between 2 yr. Density in the occupied patches increased with decreasing isolation and with decreasing patch area, suggesting that migration plays an important role in local dynamics. Mark—recapture results confirmed that migration between local populations was common, in contrast to what is frequently assumed for butterflies with well—defined local populations in discrete habitat patches. The modelling results demonstrate that it is possible to have empty habitat patches in a metapopulation in spite of frequent migration, as we observed for M. cinxia. Colonization rate of empty patches may be low for several reasons, including difficulties in mate location at low density (not likely to be important here), conspecific attraction (possibly important), stepping—stone and other forms of nonrandom migration (likely to be important), and weak density dependence (likely to be important). Our results support the assumptions of structured metapopulation models, which demonstrate the possibility of alternative stable equilibria for metapopulations in which migration significantly affects local dynamics.
A Stable Isotope Study on Seasonal Food Web Dynamics in a Eutrophic Lake
Authors: Yoshioka Takahito , Wada Eitaro , Hayashi Hidetake
Published: May 2006

Phytoplankton, zooplankton, benthic invertebrates, and pond smelt were collected in a eutrophic lake (Lake Suwa, Japan) from spring to autumn in 1986 and 1987. Their stable carbon and nitrogen isotope ratios were analyzed together with conventional examination of the gut contents of pond smelt. Temporal variations in isotope rations were similar among the organisms other than benthic animals. The @d15N values of diet for several animals in the pelagic food web were estimated, assuming a stepwise enrichment in 15N with increasing trophic level. A calanoid copepod, Eodiaptomus japonicus, seemed to feed on the predominant phytoplankton, including Microcystis spp., while Microcystis did not seem to be important as an organic source for other zooplankton and pond smelt. The temporal variation of the isotope ratios of pond smelt was well explained by visual gut content analysis. It is suggested that intensive measurements of carbon and nitrogen isotope ratios of each species serve to effectively assess the yearly dynamics of the food web structure in eutrophic lakes when productivity and species composition of plankton change seasonally.
Habitat and Area Effects on Forest Bird Assemblages: Is Nest Predation an Influence?
Authors: Martin Thomas E.
Published: May 2006

The ability of nest predation to explain patterns of covariation in species numbers with area and habitat was examined for forest birds. Numbers of individuals and species of birds were counted in 23 drainages in high elevation (2300 m) forest in central Arizona for 3 yr. Variation in bird species numbers was compared to variation in area and habitat structure among drainages. Birds were grouped into foraging (bark, understory foliage, canopy foliage, aerial) and nesting (cavity, understory foliage, canopy foliage) guilds based on heights and substrates used. Numbers of species increased with area for all guilds, but species—area slopes differed among nesting guilds. Differences in slopes cannot be explained by passive sampling because source pool size was the same or similar between guilds compared. Differences in slopes are consistent with a prediction that slopes should be greater for guilds that are more susceptible to nest predation. Variation in numbers of species among drainages was positively correlated with variation in the density of foraging and nesting substrates. However, correlations were greater when based on nesting than foraging heights and substrates. The results are consistent with a prediction that birds are selecting habitat sites based in part on the availability of nest sites that minimize risk of nest predation, and that these nest sites increase with density of foliage at nest height. These results ar also consistent with a hypothesis that availability of suitable nest sites is one of the bases for the relationship between species numbers and foliage density for foliage—nesting species. This conclusion is supported by a re—analysis of the data of Willson (1974), where foliage—nesting birds were grouped into nest—height guilds using data from the Cornell Nest Record Program; more of the birds that were added with vegetation layers tended to nest in those layers than forage in them. In short, multiple activities (foraging and nesting) can allow multiple processes to act simultaneously.
Reproductive Correlates of Breeding‐Site Fidelity in Bobolinks (Dolichonyx Oryzivorus)
Authors: Gavin Thomas A. , Bollinger Eric K.
Published: May 2006

To investigate the relationship between reproductive success (RS) and breeding—site fidelity in a transequatorial migrant, we studied two populations of marked Bobolinks (Dolichonyx oryzivorus) in upstate New York during 1982—1985. At these sites, 44% of the males and 25% of the females resident in one year returned in one or more subsequent years. There were more nests built, eggs laid, eggs hatched, and young fledged in territories of returning males in this polygynous species than in territories of males that did not return in subsequent years (P < .04). For females that returned, the number of eggs hatched, young fledged, young fledged on last nest attempt, and young fledged per egg laid were higher than for females that did not return (P < .02). Discriminant function analysis and data from 1982—1984 were used to predict correctly the return behavior of 30 to 42 individuals (sexes combined) in 1985, based on their reproductive success (RS) in 1984 (P < .01). Using data on RS and return rate for all years, the best single—variable model for males based on the number of young fledged from each territory classified correctly 59 of 85 individuals (69%) as returning or not (P < .005). The best single—variable model for females based on the number of yound fledged on their last nest attempt classified correctly 61 of 86 individuals (71%; P < .005). Using all data for 1982—1985, sex—specific models that included only whether an individual fledged one or more young classified correctly the same proportion as the best single—variable models above. However, among males that fledged one or more young, those that returned had fledged significantly more young the previous year than those that did not return (P < 0.5). Not all individuals that failed to return were dead, because five individuals that did not return to our study sites were captured in a subsequent year at another site. We concluded that male and female Bobolinks used information on their breeding success in one year to influence their choice of breeding site in the next year.
Time and Size at Metamorphosis Related to Adult Fitness in Ambystoma Talpoideum
Authors: Semlitsch Raymond D. , Scott David E. , Pechmann Joseph H. K.
Published: May 2006

The relationships among timing of metamorphosis, size at metamorphosis, and traits related to adult fitness were studied for 8 yr in the salamander Ambystoma talpoideum at a temporary pond. Among years, the modal time of metamorphosis and mean body size at metamorphosis were positively correlated with the date the pond dried. In years that the pond dried late, one group of larvae metamorphosed well before the pond dried, whereas the other group metamorphosed just before pond drying. Mean body size of late—metamorphosing individuals was not greater than that of individuals metamorphosing early. Early—metamorphosing males and females were larger at first and second reproduction than were late—metamorphosing individuals. Independent of timing of metamorphosis, larger juveniles at metamorphosis were also larger adults at first reproduction. Age at first reproduction for males was not associated with timing of or size at metamorphosis but large early—metamorphosing females reproduced at a younger age than did small early—metamorphosing females. Neither time of metamorphosis nor size at metamorphosis was associated with survival to first reproduction. These results demonstrate a direct relationship between phenotypic variation generated in the larval stage and adult traits closely associated with an individual's fitness.
Detrital Chemistry, Growth, and Food Choice in the Salt‐Marsh Snail (Melampus Bidentatus)
Authors: Rietsma Carol S. , Valiela Ivan , Buchsbaum Robert
Published: May 2006

Chemical properties of detritus including its phenolic and nitrogen contents affect its palatability to the salt—marsh snail, Melampus bidentatus (Gastropoda: Pulmonata). We determined if chemical cues that enhance palatability also promote growth. Snails were reared in the laboratory on four diets of Spartina alterniflora detritus that differed in chemical composition. Laboratory growth was highest on a diet with lowest phenolic content; an increase in phenolic content resulted in a decrease in growth. Percent nitrogen, C:N ratio, and available nitrogen were not correlated with growth. Laboratory growth rates were similar to field rates. This suggests that laboratory diets resembled what snails found in the marsh and that chemical cues that control laboratory growth have relevance for field populations of snails. Phenolic content of detritus, therefore, controlled both palatability and growth. A decrease in phenolic content enhanced palatability of detritus to snails. Feeding on the detritus with the lowest phenolic content provided adequate nutrition to support growth.
Relationships among Defoliation, Red Oak Phenolics, and Gypsy Moth Growth and Reproduction
Authors: Rossiter MaryCarol , Schultz Jack C. , Baldwin Ian T.
Published: May 2006

This research assessed (1) the relationship between defoliation and phenolic chemistry of red oak trees, and (2) the relationship between food quality, measured in terms of oak phenolic chemistry and defoliation, and aspects of gypsy moth biology that can influence population dynamics. In a field experiment, larvae were reared in mesh bags on red oaks. Measurements of phenolics were made weekly on foliage inside and outside bags of 60 trees, which experienced 7 to 58% tree—wide defoliation by the end of the larval feeding period. We found that the phenological pattern of tree phenolic concentration over 8 wk was unrelated to defoliation or bagging. Bagging itself caused no change in foliar phenolic chemistry. Greater defoliation was associated with higher levels of total phenolics, hydrolyzable tannins, and protein—binding capacity of leaves. Pupal mass and fecundity were negatively correlated with both defoliation and the concentration of total phenolics, hydrolyzable tannins, and protein—binding capacity of the host tree. Additionally, egg mass was negatively correlated with the protein—binding capacity of the mother's diet. Statistical investigation of the relationship between components of food quality (both related and unrelated to damage) and insect performance, indicated that gypsy moth pupal mass was influenced by constitutive phenolic variation (unrelated to defoliation), by damage—induced nonphenolic variation, and by damage—induced phenolic variation. Variation in defoliation and in phenolic concentrations were related to variation in fecundity and egg mass.
Laboratorary Experiments with a Mixotrophic Chrysophyte and Obligately Phagotrophic and Photographic Competitors
Authors: Rothhaupt Karl O.
Published: May 2006

Mixotrophic flagellates can compete with obligately heterotrophic flagellates for the uptake of food particles, whereas mixotrophs and obligately phototrophic phytoplankton can compete for soluble nutrients. Competition for soluble nutrients is expected when photosynthesis covers a significant portion of the mixotrophs' carbon metabolism. When heterotrophy predominates, however, mixotrophs may release soluble nutrients and facilitate phototrophs. Mechanistic resource competition theory predicts that, due to their ability to utilize substitutable C and P sources, mixotrophs should be able to coexist with their more specialized competitors under certain conditions of resource supply. In laboratory experiments, the mixotrophic flagellate Ochromonas excluded heterotrophic flagellates when only phototrophic growth was possible. However, Ochromonas was excluded by heterotrophic flagellates when only phagotrophic growth was possible. Both coexisted when food bacteria and light were supplied simultaneously. Ochromonas coexisted with a P—limited phytoplankter, Cryptomonas sp., when soluble reactive phosphorus (SRP) and bacterial phosphorus were available as alternative P sources. In nature, the mixotrophic strategy may be successful when resources are limiting. This is supported by published data on the occurrence of mixotrophic chrysophytes.