bluuebunny/crossref_metadata_2025 huggingface dataset:
Body Size in Island Lizards: A Cautionary Tale
Authors: Dunham Arthur E. , Tinkle Donald W. , Gibbons J. Whitfield
Published: May 2006

Samples of lizards of the genus Uta were collected from many of the islands in the Gulf of California. Other species of lizards coexisting with Uta were collected simultaneously. These samples provided data for a detailed analysis of body size and degree of sexual dimorphism in each island uta population and the correlation of body size with numerous independent variables such as the number and abundance of potentially competing species. This study tested the null hypothesis that competiting species had no significant influence on the body size or sexual dimorphism of the utas on particular islands. Various corollaries of the general hypothesis were also tested. The results not only supported the null hypothesis of no competitive effect, but demonstrated that independent variables not obviously associated with competition explained at least much of the variance in Uta body size as did variables directly related to competition. Previous studies on the evolution of body size in insular lizards have become paradigms of a presumed causal relationship between both size and intensity of interspecific competition. Our study invites caution to the indirect type of approach to the study of competition used in these previous studies. The weaknesses of past approaches are discussed at better approaches to the study of competition are suggested. Selective pressures that might have at least as great an effect on body size of organisms as does competition from other species are identified.
Neighborhood Effects on Fruit Removal by Birds: A Field Experiment with Viburnum Dentatum (Caprifoliaceae)
Authors: Sargent Sarah
Published: May 2006

The foraging behavior of fruit—eating birds can have important effects on the fitness of plants whose seeds they disperse. An important factor influencing the pattern of fruit consumption by birds may be the amount of friut in the immediate vicinity of a plant. I experimentally examined the effects of neighborhood fruit density and fruit crop size on the rate, proportion, and temporal pattern of removal of northern arrowwood (Viburnum dentatum) fruits by birds in central New York. I manipulated V. dentatum fruit densities in 100 10 X 10 m plots, then monitored fruit removal by birds during 14 wk in the fall of 1985. Each plot had either high or low fruit density in a central 1 m diameter "crop" area, and either high or zero "neighboorhood" fruit density in the rest of the 100—m2 plot. I counted marked fruit in the center of each plot weekly. Fruits in high density neighborhood plots were removed significantly faster than fruits in plots with zero density neighborhoods. A significantly lower proportion of marked friut was removed from plots with both low crop size and zero density negihborhoods. Forty—three percent of all removal of marked friut by birds took place during a 2—wk period early in the friuting season. Birds feeding in flocks were observed feeding in high density neighborhood plots almost exclusively, presumably causing the greater removal from these plots. Fruit abscission accelerated after week 9, and by week 14 no fruits were left on plants. White—tailed deer (Odocoileus virginianus) consumed 400 of the 750 marked infructescences during the 14 wk, but destroyed rather than dispersed seeds. These results indicate that the amount of fruit in the area surrounding a fruiting plant, as well as the size of the plant's own fruit crop, can influence fruit removal by seed dispersers. Thus, disperser—mediated plant fitness is affected by neighboring plants. In contrast to previous studies, I found that high fruit density in the area surrounding a plant enhanced friut removal rather than inhibited it.
Patterns of Insect Herbivory, Growth, and Survivorship in Juveniles of a Neotropical Liana
Authors: Aide T. Mitchell , Zimmerman Jess K.
Published: May 2006

Patterns of insect herbivory, growth, and survivorship were studied for 3 yr in the shade—tolerant liana Connarus turczaninowii. The percent damage to young leaves (°2 mo) ranged from 2.9% in 1981 to 7.5% in the census following an El Nino event (January 1984). Although the median leaflet lifetime was 2.5 yr, °33% of the lifetime damage by herbivores occurred during the first 2 mo. Annual rates of insect damage to mature leaves varied from 2.8% in 1982 to 6.0% in 1984. The most common herbivore observed on mature leaves was the beetle Demotispa sp. nov. The proportion and actual quantity of damage by this species was minimal on young leaves, but increased with leaf age. Compared with leaves in extremely low light, leaves from plants in extremely high light had lower concentrations of water and nitrogen, and more condensed tannins. Leaves from high light environments were also tougher. Although these charateristics have been shown to affect host choice or feeding in other species, no differences in rates of insect damage were detected among plants that occurred across a continuum of light environments. Plant growth increased with canopy openness, and, in one year, decreased with an increase in insect herbivory. Even though damage rates were high folowing El Nino, growth was high. We hypothesize that juvenile growth responded positively to the duration of the previous dry season because of increased light in the understory and a decrease in water loss from the soil due to the increased level of deciduousness of large canopy trees.
Responses of the Common Sooty Wing Skipper to Patches of Host Plants
Authors: Capman William C. , Batzli George O. , Simms Laura E.
Published: May 2006

The dispersion patterns of eggs and larvae of the common sooty wing skipper (Pholisora catullus) changed when size of patches and distance between patches of its host plant (Chenopodium album) changed. With patches widely spaced, large patches had more eggs and larvae per patch but fewer per plant than did smaller patches. Behavioral observations showed that ovipositing females in widely spaced patches encountered patches at frequencies proportional to the patch diameters plus a small detection distance. Though females laid slightly more eggs per encounter in larger patches than in smaller patches, larger patches had many more plants and, therefore, fewer eggs per plant. Egg and larval mortality rates did not differ among patch sizes, so female behavior was sufficient to account for the observed egg and larval dispersion patterns of the skipper. When we reduced the spacing between patches, female skippers laid proportionately more eggs in large patches and fewer in smaller patches. As a result, the numbers of eggs per plant no longer differed among patch sizes. This shift was due to the greater tendency of females to fly by small patches without landing when the patches were closer together. In general, our results supported the hypothesis that differnt patch spacings can alter insect behavior, which in turn can produce different concentrations of herbivores in response to host patch size.
The Effect of Invertebrate Predators on Leaf Litter Processing in an Alpine Stream
Authors: Obernborfer Reed Y. , McArthur J. Vaun , Barnes James R. , Dixon John
Published: May 2006

The effect of the predators Megarcys signata (Plecoptera: Perlodidae) and Rhyacophila sp. (Trichoptera: Rhyacophilidae) on the abundance of macroinvertebrates and on the rates of leaf processing in artificial leaf packs was studied by using manipulative field experiments. Predators were confined within artificially constructed leaf packs in an alpine stream in Utah. Both predators significantly reduced the rate of breakdown of leaves in the fall, but had no effect in late winter, when the most important shredder, Zapada cinctipes, emerges, Predation on shredders caused a reduction in breakdown rates and an increase in the residence time of the leaf litter in the stream. In experimental treatments where predators significantly reduced the numbers of shredders and decreased the rate of leaf processing, leaf pack half—life increased an average of 10.3 d. These experiments demonstrate that invertebrate shredders can contribute substantially to the rate of leaf processing in streams and suggest that one of the factors limiting the abundance of natural shredder population is predation.
The Political Economy of the Spotted Owl
Authors: Dixon Kenneth R. , Juelson Thomas C.
Published: May 2006

The economic, social, and political aspects of the Spotted Owl—old—growth issue are based on the conflict between conservation and cutting of old trees. Old—growth harvesting is made profitable by subsidies to the timber industry; without the subsidy, less old growth would be cut. Spotted Owls are undervalued in the economic debate because they are a collective good, the value of which is not being "aggregated" either in the present or in the future. There is an imbalance in the political system that favors the profit—oriented timber industry. An economic case can be made for preserving old growth, but ethical conduct requires some preservation. Dislocations of timber workers can be minimized by redirection of subsidies from industry to workers. Regulations designed to protect the Spotted Owl have not been followed. Many old—growth logs are exported to the Orient. Conservationists and the general public need to become more active in the decision—making process concerning National Forests.
Fire and the Forest History of the North Cascade Range
Authors: Cwynar Les C.
Published: May 2006

Postglacial vegetation changes are often ascribed to the direct effects of climate change. I studied pollen, plant macrofossils, and sediment charcoal in order to determine the potential role of changes in the disturbance (fire) regime in the postglacial development of local vegetation at Kirk Lake in the foothills of the North Cascade Range in northwestern Washington. Five pollen assemblage zones are recognized: a Pinus–Populus zone >12 000 BP, a Picea—Alnus sinuata zone from >12 000 to 11 030 BP, an Alnus rubra—Pteridium zone from 11 030 to 6830 BP, a Cupressaceae zone beginning at 6830 BP, and a late Holocene Pinus—Alnus rubra zone from 2400 to 900 BP. The first forests (>12 000 BP) were an open mixture of conifers and deciduous trees, chiefly Tsuga mertensiana, Abies, Pinus contorta, and Populus on a landscape subject to erosion. Just before 12 000 BP, the pioneer species Picea sitchensis, Alnus rubra, and A. sinuata became important constituents of the forest. Although pollen accumulation rates were high, the abundance of Alnus sinuata indicates an open—canopy forest. Beginning °11 200 BP, climatic warming initiated major changes in forest composition and the fire regime. Tsuga heterophylla migrated into the region, rapidly expanded, then declined shortly thereafter, while Pseudotsuga menziesii, Alnus rubra, and Pteridium expanded, and Pinus contorta, Picea sitchensis, Populus, and Alnus sinuata declined. The abundance of Pseudotsuga, Alnus rubra, and pteridium between 11 030 and 6830 BP corresponds with increased influxes of charcoal into the sediment; this zone is interpreted as a closed forest with a relatively high fire frequency and composed of a mosaic of postfire successional communities in which fire—adapted Pseudotsuga and Alnus rubra predominated over fire—sensitive Tsuga heterophylla. Pinus monticola became locally important °800 BP. Between 6800 and 6400 BP Thuja plicata arrived, Tsuga heterophylla expanded, and Alnus rubra, Pseudotsuga and Pteridium declined. These changes are accompanied by a reduced fire frequency, inferred from lower charcoal accumulation rates, and they indicate a shift to wet—temperate climate similar to today's. The late Holocene fossil record shows the development of the adjacent peatland, which Pinus contorta eventually invaded.
Extending Functional Response Models to Include a Second Prey Type: An Experimental Test
Authors: Colton Thomas F.
Published: May 2006

Functional response models based on Holling's disc equation allow the use of one—predator/one—prey experiments to predict the feeding rates of a predator when more than one prey type is available. Single—prey trials at six densities of each prey were used to measure the functional responses of 10th—instar naiads of the damselfly Enallagma aspersum to a copepod, Diaptomus spatulocrenatus, and a cladoceran, Simocephalus serrulatus. Rogers' random predator equation, a modification of Holling's type 2 functional response equation, described the data well. The predictions of a one—predator/two—prey model based on the random predator equation were tested by performing all 36 pairwise combinations of densities of the two prey species in a factorial design. The model predicts that naiads should show a preference for Simocephalus over Diaptomus, and that Diaptomus should experience a greater reduction in predation in the presence of Simocephalus than should Simocephalus in the presence of Diaptomus. The two—prey trials show that the reverse is true; the model fails to predict these results adequately. Preference varied slightly with the density of Diaptomus, but not with the density of Simocephalus, total prey density, or the ratio of the two prey types. The "attack" and "handling time" parameters that describe predation on Diaptomus both increased significantly with increasing density of Simocephalus, and the "handling time" parameter for predation on Simocephalus decreased significantly with increasing density of Diaptomus. There was no evidence of switching behavior in this system. Clearly, the outcome of this three—species interaction cannot be predicted by studying only the component two—species interactions. A modified random predator model, which incorporates changes in the "attack rate" and "handling time" parameters with alternate prey density, provided a better fit to the two—prey data. The factorial design, which requires experiments involving all three species, permits the use of other, less mechanistic, models as well.
Within‐Habitat Spatial Separation of Two Notonecta Species: Interactive vs. Noninteractive Resource Partitioning
Authors: Streams Frederick A.
Published: May 2006

Two aquatic insect predators, Notonecta undulata and N. insulata, partitioned space in a small (< 0.25 ha) Connecticut pond. Spatial separation was established during recruitment and persisted throughout the breeding season. Over 70% of the N. undulata population developed in shallow (< 0.3 m) water near the pond margin, while > 70% of the N. insulata population occurred in deep (> 0.5 m) water in the center of the habitat. Mutual predation did not appear to play an important role in separating the populations. Although species size relationships in the pond favored predation by N. insulata on N. insulata showed little inclination to prey on N. undulata in laboratory aquaria. Cage experiments and temperature tolerance tests suggested that spatial separation reflects fundamental niche differences between the species. The survival rate of N. insulata nymphs in shallow—water cages was significantly poorer than in deep—water cages and was not significantly affected by interaction with N. undulata. N. insulata is intolerant of high water temperatures and appears to be poorly adapted for survival in shallow water exposed to solar heating. N. undulata, on the other hand, is tolerant of high temperature and, except during the fifth instar, survived as well or better in shallow—water cages than in deep—water cages. Second— and third—instar N. undulata survival rates were depressed by interaction with N. insulata in population cages, but fourth— and fifth—instar survival rates were not. Although the cage results indicated that N. insulata can depress early instar N. undulata survival rates, the hypothesis that N. insulata was responsible for the low N. undulata densities recorded in deep water is weakened by evidence that N. undulata prefers densely vegetated microhabitats during oviposition and early nymphal development. Aquatic vegetation was abundant in shallow water but sparse in deeper parts of the pond. This study reveals how the coexistence of potential competitors in a particular habitat can depend upon the interplay between the unique features of that habitat and physiological and behavioral traits of the species involved.
Substrate Selection and Use by a Deposit‐Feeding Crab
Authors: Zimmer-Faust Richard K.
Published: May 2006

Foraging by the deposit—feeding crab Scopimera inflata was examined for 1 yr at three sandy beaches in southeastern Queensland, Australia, in order to determine which factors influence foraging paths, substrate selection, and substrate use. Crabs emerged from burrows only on the ebb tide in daylight and remained close to their burrows (< 30 cm radius). The initial position and direction in which foraging crabs moved were random relative to cues provided by biotic (substrate biomass concentration) and physical (wind direction, sun position, beach slope, magnetic north, landmarks) factors. Each crab foraged in a systematic fashion along a unidirectional, radial path around its burrow entrance. This minimized distances traveled and reduced the chances of reharvesting areas already grazed. Because crabs feed on a wide range of micro—flora and —fauna, biochemical assays (chlorophyll a, ATP, and ash—free dry mass) were used to estimate the abundance of food on the substrate. Biomass concentrations were always low and unpredictable in space within the foraging areas of individual crabs. Crabs did not prefer to feed where biomass was most abundant and instead foraged in an even manner. Experiments demonstrated that foraging crabs distinguished among organic and inorganic materials, but that the threshold concentration for substrate rejection was lower than that normally encountered in the natural habitat. Crabs did not sample local distributions of biomass. They exhibited stereotyped, all—or—nothing responses to feeding stimuli even when habitat quality was varied experimentally. A model was developed for a forager that harvests substrates in order of descending biomass concentration but is otherwise identical to Scopimera. Total daily ingestion by the model forager was <10% greater than that by Scopimera, even though costs of searching and sampling were ignored in the model. The benefits potentially gained by selective grazing are small. Foraging crabs need water and refuge, which are typically provided only by the burrow. Consequently, grazing by Scopimera must balance conflicting demands. The foraging behavior of this crab approaches an optimal trade—off in which: (1) path lengths and distances traveled from burrows are minimized, and (2) use of substrates immediately adjacent to burrows is nearly maximized.
Ecological Systems in Hierarchical Perspecitive: Breaks in Community Structure and Other Consequences
Authors: Kolasa Jerzy
Published: May 2006

Explanation of the patterns of species abundances is important because it may help in understanding mechanisms structuring communities. A general conceptual model is proposed and examined as an alternative to previous propositions, which focused too narrowly on specific mechanisms. According to this model, viewing the structure of an environment as a nested hierarchy of habitat units provides a general mechanism sufficient to account for empirically established regularities in species abundances. Various biotic and abiotic factors can be considered as specific mechanisms sorting biological components into respective levels and compartments of the hierarchical structure of the environment. Because "sizes" of these compartments vary in a predictable way as a function of their position in the hierarchy, so should the abundances. The model may provide a conceptual framework that allows evaluation of the relative contributions of competition, predation, and other biological interactions. The operational and highly simplified version of the model uses spatial or temporal measures of ecological ranges of species to facilitate testing of the general model. The operational model makes three qualitative and quantitative predictions: (1) although the species display a continuous gradation of properties, the nested hierarchy of habitat units should lead to clustering of species at distinct levels; (2) generalists should be relatively more successful than specialists, (3) relative abundances of species should be predictable from their position in the hierarchical structure. An analysis of eight communities, including flatworms, aquatic insects, foraminiferans, rodents, and birds, supports these predictions. The clusters, or "breaks" in community structure, appear to be a new and possibly general property. Moreover, quantitative predictions of relative abundances for these communities are in surprisingly good agreement with the actual abundances. A hierarchical structure of the environment appears promising in accounting for some poorly explained community—level phenomena, such as correlation between the species range and abundance, and differences between abundance structures of communities in rigorous and less severe environments. The model is compatible with commonly observed as well as irregular patterns of distribution of species abundances, with high local abundance of some species, with differentiation of extinction probabilities, and with scale dependence of ecological phenomena.
Host Selection and Larval Performance of Two Willow‐Feeding Sawflies
Authors: Roininen Heikki , Tahvanainen Jorma
Published: May 2006

Host selection by ovipositing females and larval performance of two willowfeeding sawflies, Nematus salicis and N. pavidus, were investigated in laboratory choice and feeding experiments. In the field N. salicis is more specialized in its host utilization than N. pavidus, which is commonly found on a great number of willow species. In the Multiple Choice Oviposition Experiment females of both sawfly species exhibited a strong preference for one of six willow species offered. In No Choice Oviposition Experiments N. salicis retained its high selectivity while N. pavidus laid eggs equally on several willows. Host utilization spectra of larvae, as measured by larval growth and survival, were noticeably wider than those of ovipositing females. In N. salicis larval performance was optimal on willows that were also preferred by females, but in polyphagous N. pavidus conformity between host selection by ovipositing females and the larval performance was negligible. Host plant spectra of these sawflies are largely determined by behavior of ovipositing females and not by food utilization efficiency or survival of larvae. We suggest that host specialization of the sawflies studied has developed from behavioral processes of adults and is guided by specific plant characteristics such as phenolic glycosides in willow leaves. The physiological specialization of larvae may proceed more slowly and be secondary. In general we emphasize the role of behavioral constraints and adaptations in the ecology and evolution of host utilization by herbivorous insects.
Variation in Insect Densities on Desert Creosotebush: Is Nitrogen a Factor?
Authors: Lightfoot David C. , Whitford Walter G.
Published: May 2006

A field experiment was conducted to assess the effects of nitrogen and water on the densities and taxonomic and trophic compositions of arthropods on the foilage of desert creosotebush (Larrea tridentata). Nitrogen and water were manipulated through a series of fertilizer and irrigation treatments applied to naturally growing creosotebush shrubs at a site in the northern Chihuahuan Desert. Water with nitrogen, and nitrogen fertilization alone, significantly increased creosotebush foliage production and foliar nitrogen contents. Water alone had less effect on foliage production and no effect on foliar nitrogen contents. Foliage production, foliar nitrogen contents, and numbers of foliage arthropods were all higher in the late spring than in the mid or late summer. Numbers of foliage arthropods increased significantly on fertilized plants in the late spring. Water treatments alone had no effect on numbers of foliage arthropods, but a positive water—fertilizer interaction effect on numbers of foliage arthropods was evident in the late spring. Overall, there were significant positive correlations between foliage production, foliar nitrogen contents, and foliage arthropod densities. Phytophagous sap—sucking insects accounted for the majority of arthropods on creosotebush, and their densities varied most in relation to foliage production and foliar nitrogen contents. Results of our study demonstrated that sap—sucking phytophagous insects are more responsive than leaf—chewing insects to increased nitrogen content of creosotebush foliage, and that much of the between—plant variation in densities of phytophagous insects within a stand of creosotebush may be due to sap—sucking insects tracking variable foliar nitrogen.
The Role of Predation in Age‐ and Size‐Related Habitat Use by Stream Fishes
Authors: Schlosser Isaac J.
Published: May 2006

I examined the effects of age and body size on intra— and interspecific habitat relationships for 15 species of fishes in a natural second—order warmwater stream. Juveniles (age 0) of all taxa and adults (>age 0) of taxa with small maximum body size (darters and cyprinids) were at high densities predominantly in shallow riffle and raceway habitats. Adults of taxa with large maximum body size (catastomids and centrarchids) were at low densities predominantly in deep pool habitats. Based on the complementarity in depth distribution of large and small fishes, controlled experiments were conducted in a semi—natural experimental stream to assess (1) the effect of large centrarchid piscivores in pools on the habitat use of small fishes, (2) the influence of structural complexity of pool habitats on the interaction between centrarchid predators and their prey, and (3) the effectiveness of centrarchid predators at capturing small fishes when shallow refugia exist. In the experiments, juvenile hornyhead chub, white sucker, and smallmouth bass were allowed to select one of four physical habitats in the presence and absence of adult smallmouth bass: riffle, raceway, structurally simple pool, or structurally complex pool. Predators were restricted to pool habitats so that riffles and raceways were effective refugia. Predation by bass occurred even though effective refugia were present. However, the taxa exhibited considerable variation in susceptibility to predation; white suckers were most vulnerable and smallmouth bass least vulnerable. In the absence of bass, juveniles of all taxa preferred structurally complex or structurally simple pools, even though benthic insect densities were higher in riffles than pools. In the presence of bass, juveniles of all taxa were largely restricted to shallow riffle or raceway refugia, with the extent of the shift in distribution to shallow habitats related to the vulnerability of the taxa to predation. If juvenile fishes occurred in pools with centrarchid predators, juveniles were at low densities and only in pools with high structural complexity. These results suggest that the high density and extensive overlap in habitat use of small fishes in shallow habitats of small warmwater streams is related to the increased risk of predation by centrarchids in pools.
Effect of Food Supply on the Breeding Biology of Western Kingbirds
Authors: Blancher Peter J. , Robertson Raleigh J.
Published: May 2006

We studied the breeding ecology and behavior of Western Kingbirds in relation to abundance of flying insects in an area of sympatry with Cassin's Kingbirds in southeastern Arizona. Day—to—day variation in abundance of flying insects was related to date and temperature, while annual differences appeared to reflect precipitation during the previous year. Western Kingbirds nesting in study sites with relatively high insect biomass had earlier clutch initiation dates, larger clutch sizes, higher nestling growth rates, shorter time between foraging flights, and shorter time between nestling feedings, compared to birds nesting where food supply was lower. Annual differences in insect biomass were also reflected in kingbird clutch initiation dates, clutch sizes, and nestling growth rats. Fledgling survival was related to rate of mass gain as a nestling. Indications were that food was not superabundant, yet no detectable effects of kingbird density on clutch size or nestling growth rate existed. Kingbirds did not appear to reduce significantly the local abundance of flying insects, which calls in question the importance of competition for food in determining local habitat separation.
Nitrification, Nitrate Reduction, and Nitrogen Immobilization in a Tidal Freshwater Marsh Sediment
Authors: Bowden William B.
Published: May 2006

The dominant microbial transformations of ammonium and nitrate in the sediments of a tidal freshwater marsh estimated from measured rates of isotope dilution of ammonium [15N] added to sediment and litter samples, reduction of nitrate[15N] to ammonium[15N] in fresh sediments, and net exchange of ammonium and nitrate between the marsh and river water in flumes built in the field. In two separate laboratory experiments, nitrification in mixed, fresh, surface sediments was 2.8 and 3.4 nmol°cm—3.h—1. In undisturbed field sediments, nitrification rates are probably ≤1 nmol°cm—3°h—1. Additions of nitrate[15N] to fresh sediments showed that nitrate produced from ammonium by nitrification was reduced very quickly. Less than 10% of this nitrate was reduced back to ammonium by dissimilation. The net transfer of nitrate in this marsh is to the sediments, and since nitrate does not accumulate in these sediments, the remaining nitrate produced by nitrification must be reduced by denitrification or by assimilatory nitrate reduction. Ammonium was removed quickly from filtered and aerated river water that was mixed with plant litter in laboratory incubations. Ammonium—N removal from experimental flasks (215 nmol°g—1°h—1) was dependent on the presence of litter and was biologically mediated, but was not due to nitrification since nitrate concentrations were constant in the same experiments. Under anaerobic conditions, ammonium—N was released from litter to river water (93 nmol°g—1°h—1). The estimated total rate of ammonium—N immobilization by microbes on aerobic litter (130 μmol°m—2°h—1) agrees well with measured losses of ammonium from river water in field flume studies (156 μmol°m—2°h—1). An aerobic litter layer may enable marshes to regulate the loss of ammonium that is regenerated in reduced, subsurface sediments and that would otherwise be lost by diffusion or advection. For example, during portions of the year, excess ammonium may be immobilized on plant litter in aerobic surface layers. Some of this litter is incorporated into reduced subsurface sediments where, later, microbial mineralization may regenerate the immobilized nitrogen. The importance of the nitrogen recycling process in a particular marsh will depend on the degree to which litter is mineralized in place or exported from the marsh before it is incorporated into the reduced sediment, as well as the extent to which plant roots can take advantage of the regenerated nitrogen. If conditions are favorable (low export fraction, low litter C:N ratio, and advantageous root distribution) then mineralization may supply a major portion of the annual plant requirement for nitrogen in excess of that stored in perennial tissues. Both internal recycling and translocation make the plant community less dependent on nitrogen imported from the river.
Cost of Benefits of Territoriality: Behavioral and Reproductive Release by Competing Aphids
Authors: Whitham Thomas G.
Published: May 2006

Colonizing stem mothers of the gall—forming aphid Pemphigus betae defend galls sites on narrowleaf cottonwood, Populus angustifolia. Kicking—shoving contests are used to establish microterritories 3—5 mm in length. The largest stem mothers usually win in competitive bouts. Small differences in body size (i.e., a 3.4% difference in prothorax widths) are more importantly associated with territorial interactions than with fecundity. Stem mothers that win the superior basal position of a leaf produce an average of 56% more progeny than stem mothers displaced to inferior distal positions. Differences in reproductive performance within a leaf result from microhabitat variation in leaf quality. A change of only a few millimetres in the position of the gall on the leaf blade affects aphid reproduction. Experimental removal of either member of a competing pair allows the remaining stem mother to cross the former territorial boundary and enlarge her own territory. The impact of competitive release on reproductive success is asymmetrical. The distal stem mother of a competing pair achieves an average 48.5% increase in number of progeny, whereas the basal stem mother achieves an 18.5% increase in number of progeny. Because both members of a competing pair suffer reduced success from competitive interactions, selection favors stem mothers that occupy leaves singly. The largest stem mothers are solitary; their despotic behavior prevents smaller competitors from settling.
Habitat Use by Insular Small Mammals: Relative Effects of Competition and Habitat Structure
Authors: Dueser Raymond D. , Porter John H.
Published: May 2006

This study tests two predictions about habitat use by the small mammal species of Assateague Island, the largest of the Virginia barrier islands: (1) habitat segregation between species should be conspicuous, with centers of species abundance located in different plant associations, and (2) competition should exert a strong influence on habitat use by each species, with the effects of the other species at least as great at the effects of habitat structure. Prediction 1 was supported by analyses of mammal species abundances (based on live—trapping) in five vegetation types. Habitat segregation was pronounced and species' distribution reflected coarse—grained habitat patchiness. However, prediction 2 was not supported by analysis of the independent effects of competition and habitat structure on the local abundance of each species. Despite the apparent ubiquity of competition, all of the interaction coefficients were °1.00 in absolute value, suggesting that the competition was relatively “weak”. Furthermore, for most species the effects of other species were found to be relatively less important than those of habitat structure. Only Mus musculus, and to a much lesser extent Zapus hudsonius, appear to be affected more strongly by competition. These findings impugn an earlier suggestion that competition plays a significant role in promoting the strong positive relationship between rodent diversity and habitat complexity on the Virginia barrier islands. Although no data on turnover rates are available, there is no compelling reason to invoke a dynamic equilibrium to explain the biogeography of small mammals on the Virginia barrier islands. The number and combination of species found on an island may simple represent a sample drawn from the pool of available species, weighted primarily by island area and habitat complexity and by the colonizing abilities of the species.
Heterothermy in Free‐Ranging Abert's Squirrels (Sciurus Aberti)
Authors: Golightly Richard T. , Ohmart Robert D.
Published: May 2006

Body temperatures (T_b) of 7 free—ranging Abert's squirrels were monitored by intraperitoneally implanted temperature sensitive radio transmitters. Relationships between Tb, activity, solar exposure, ambient air temperature (T_a), and weather conditions were examined. T_b values ranged from 35.2 to 41.1 degrees C (° = 39.0 degrees C) and varied with behavior. A hyperthermic condition during both summer and winter developed during bouts of intense activity and the degree of hyperthermia was related to intensity of activity. Immediately following intense activity, squirrels sought shade in a tree to facilitate cooling. Squirrels exhibited hypothermia in the nest during the day and night. A diurnal rhythm of Tb was observed in free—ranging squirrels when in the nest and similar rhythms of T_b and O_2 consumption rate (V_(O_2)) were observed in laboratory squirrels. Basking was common on winter afternoons and upon emergence from the nest in the morning throughout the year, resulting in elevated Tb values. Position of the tail appeared to moderate solar irradiation striking the squirrel during basking. When positioned dorsally, the tail increased reflectance. Wind and rain significantly reduced Tb in squirrels outside the nest. The relationship between Tb and Ta was subtle and difficult to ascertain in the field. In the laboratory, Tb decreased in response to falling Ta and subsequently metabolic expenditures were depressed from the expected. The mean field Tb during summer and early fall was significantly higher than during winter or spring and may indicate seasonal acclimatization. Squirrels in the field did not cache substantial quantities of food. They foraged daily and were active during all seasons, including inclement winter weather. Fresh snow appeared to restrict movements. Squirrels were seldom outside of the nests at Ta values < —10°C. Laboratory experiments established a thermoneutral zone between 29° and 35°C. Within the zone the Vo2 was 0.69 ml O2 (g h)—1 (standard temperature and pressure, dry) or 104% of the predicted weight specific value. The curve of thermogenesis is best described by a polynomial regression due to shifts in Vo2 caused by changes in Tb in response to falling Ta. The lower lethal limit was near —20 degrees C.
Late Quaternary Pollen Record from Big Meadow, Pend Oreille County, Washington
Authors: Mack Richard N. , Rutter N. W. , Bryant Vaughn M. , Valastro S.
Published: May 2006

The pollen record at Big Meadow in northeastern Washington contains at least 5 pollen zones spanning ca. the last 12,500 yr. Initial vegetation after Pinedale deglaciation was nonarboreal. Estimates of the pollen influx and the dominance of Artemisia and Gramineae plus comparatively little pine pollen suggest a tundra—like landscape from the time of deglaciation until ca. 9,700 BP. Zone II probably lies disconformably atop this earliest zone and reveals a community dominated first by grasses plus diploxylon pines and later by diploxylon pines without prominent grasses (Zone III) between 9,700 and 3,300 BP. zone IV demarcates a short reversal of climatic conditions in which Picea and Abies are relatively prominent. Tsuga heterophylla, the present day climatic climax dominant of the area, rapidly emerged in the pollen record at ca. 2,400 BP.
Substrate Attachment by Drifting Aquatic Insect Larvae
Authors: Walton O. Eugene
Published: May 2006

A series of laboratory experiments was designed to evaluate sediment type and illumination as factors affecting substrate attachment by 3 species of drifting aquatic insect larvae. Stone or cobble sediment patches with (natural) or without (sterile) an epilithic food resource were placed in artificial stream channels. Larvae of Stenacron interpunctatum (Ephemeroptera), Acroneuria abnormis (Plecoptera), and Chimarra aterrima (Trichoptera) were drifted over these patches. Attachment was partitioned into (1) settling and (2) failure to return to the drift (delayed drift). Significant sediment effects on settling were observed with S. interpunctatum and C. aterrima, for the former only during daylight. For all 3 species, significantly fewer animals settled in darkness. Significant delayed drift occurred in both S. interpunctatum and C. aterimma, but only in darkness, off sterile sediments, for the former. These results suggest that invertebrate drift may function as a direct, one—way link between substrate specific faunal associations. A similar experiment tested the effect of a predator (A. abnormis) on substrate attachment by drifting prey (S. interpunctatum). No predator effect was observed on either settling or delayed drift of the prey. Repeating the first series of experiments with killed animals allowed an evaluation of the relative importance of behavior and morphology in substrate attachment. A sediment effect was observed only in A. abnormis, and no settling differences were observed between S. interpunctatum and C. aterrima, species of strikingly different morphology. Killed animals rarely reentered the drift after settling. For these species, settling and delayed drift were much more a function of behavior than of morphology.
Energetics of Reproduction in Peromyscus Leucopus: The Cost of Lactation
Authors: Millar John S.
Published: May 2006

Captive Peromyscus leucopus exhibited a positive relationship between weight of @V and number and size of nestlings. Size of neonates, but not size of post—neonatal young was negatively related to litter size. Ingested energy related to offspring was linearly related to litter size and varied from 899 kJ (74% of nonbreeding requirements) for 2 offspring to 2100 kJ (146% of nonbreeding requirements) for 6 offspring. Despite these differences between litter sizes, mean litter size was not different (° = 4.60 and 4.94) respectively between captive and wild females, and varied little seasonally and geographically. The relatively constant commitment to offspring may be related to the fact that conception occurs long before the period of peak energy demand.
Predation Risk and Unpredictable Feeding Conditions: Determinants of Body Mass in Birds
Authors: Lima Steven L.
Published: May 2006

The body mass (or fat reserves) maintained by a wintering bird can be viewed as a trade—off between the risk of starvation and the risk of predation. This follows from the fact that fat reserves after survival in very different ways. From the starvation point of view, a bird should be as fat (or heavy) as possible in order to minimize its probability of starvation during weather—related food unavailability because fatter birds can survive longer without food than leaner birds. From the predation risk point of view, however, a bird should be as lean as possible to minimize its probability of being killed. Leaner birds will incur a smaller cost of existence than heavier birds and thus spend less time feeding, potentially exposed to predators. In addition, lean birds are likely to be more adept at escaping predators once attacked. If a bird is attempting to minimize its probability of death during the winter season, the fat reserves and thus the body mass it maintains will reflect a trade—off between starvation and predation risk. A simple stochastic simulation model developed to explore the nature of this trade—off indicates that body mass should: (1) increase with the frequency and/or harshness of periods of food unavailability (due to snow, ice, wind, etc.); (2) decreases with increasing predation risk; (3) decrease with increasing temperature; and (4) increase with food abundance. The analysis of the model readily explains why wintering birds maintain fat levels lower than those of which they are capable. The tendency for individuals of a given bird species to be heavier in more northerly populations and during midwinter is also readily interpreted in terms of the above trade—off. Implications for foraging behavior and population regulation in wintering birds are discussed.
Digestibility of Plant Constitutents By Canada Geese and Atlantic Brant
Authors: Buchsbaum Robert , Wilson John , Valiela Ivan
Published: May 2006

The ability of free—ranging Brant (Branta bernicla) and free ranging and captive Canada Geese (B. canadensis) to digest various constituents of marsh plants was studied using lignin as a nondigestible tracer in plant food and feces. These constituents included total organic matter, soluble carbohydrates, protein, total ether—soluble material, soluble phenolics, cell wall polysaccharides, and phenolic acids esterified to plant cell walls. The digestion of total organic matter averaged 37% in both species of geese, indicating that geese are less efficient at digesting plant material than most other vertebrate herbivores. The low total organic matter digestion was largely a result of inefficient digestion of cell wall polysaccharides. Geese digested °28% of the cellulose and 25% of the hemicelluloses present in their plant food. In contrast, the apparent digestibility of soluble carbohydrates were 69—85%, and the digestibility of protein (61—80%) was similar to that of most other vertebrate herbivores or graminoid diets. The two cells wall polysaccharides still provide up to 31% of the energy geese extract from plants despite their low digestibility, because they are present in relatively high concentrations (together, °40% of dry mass). Geese digested cellulose as efficiently as predicted by the previously reported relationship between herbivore body size (or metabolic requirement) and cellulose digestion.
Large‐Scale Management Experiments and Learning by Doing
Authors: Walters Carl J. , Holling C. S.
Published: May 2006

Even unmanaged ecosystems are characterized by combinations of stability and instability and by unexpected shifts in behavior from both internal and external causes. That is even more true of ecosystems managed for the production of food or fiber. Data are sparse, knowledge of processes limited, and the act of management changes the system being managed. Surprise and change is inevitable. Here we review methods to develop, screen, and evaluate alternatives in a process where management itself becomes partner with science by designing probes that produce updated understanding as well as economic product.
Hydrologic Influences, Disturbance, and Intraspecific Competition in a Stream Caddisfly Population
Authors: Feminella Jack W. , Resh Vincent H.
Published: May 2006

In an earlier study, exploitative intraspecific competition was demonstrated for middle instars of the caddisfly Helicopsyche borealis in Big Sulphur Creek, a stream in northern coastal California. This population is univoltine with early instars first appearing in June, growing into late instars the following spring, and emerging as adults in May. Competition occurs during the summer dry season (June—September), a period of low—flow conditions without storms or increases in stream discharge. Beginning in autumn, however, larval densities decline because of wet—season storms and high discharge. Using multiple regression, we found a strong relationship between spring (i.e., post wet season) density of late—instar H. borealis and various hydrologic parameters of the preceding wet season over a 4—yr period, 1985—1988. Of eight hydrologic parameters used as indices of disturbance, total wet—season rainfall and peak discharge together accounted for 42% (P < .0001) of the variation in H. borealis density. In contrast, densities of middle instars of the next generation in summer were unrelated either to the preceding wet—season hydrologic regime of late—instar densities of the previous generation. Field experiments conducted in enclosures using larval densities of H. borealis that correspond to harsh, moderate, and mild wet—season hydrologic regimes (low, intermediate, and high densities, respectively) indicated that: (1) increases in larval density had a strong negative effect on algal biomass (as chlorophyll a); (2) larval density was negatively correlated with the proportion of larvae that pupated, and with pupal size; and (3) the high density (mild hydrologic regime) treatment produced smaller adult males and females, and lower fecundities than intermediate and low densities (moderate and harsh regimes, respectively). In most years, storms and associated disturbance reduce late—instar H. borealis density below levels of larval competition; this counteracts earlier competition among middle instars that occurs during low—flow conditions. In drought years, however, densities may not be reduced as severely by wet—season storms and competition may continue until emergence. In this case, competition can reduce individual fitness, but because of high adult densities during these mild—disturbance conditions the reproductive capacity of the population is unaffected.