bluuebunny/crossref_metadata_2025 huggingface dataset:
A Nonequilibrium Marine Predator‐Prey Interaction
Authors: Katz Clifford H.
Published: May 2006

The assumptions and predictions of equilibrium predator—prey theory were tested in a southern New England intertidal community. Responses of the predatory snail Urosalpinx cinerea and the prey population dynamics of the barnacle Balanus balanoides were examined with field experiments and observations. The functional response, developmental responses, intraspecific competition, and species preference response of U. cinerea were destabilizing. Instantaneous and exploitative models revealed the functional response of U. cinerea to be a type II response. Increases in the size of U. cinerea did not affect the feeding rate per individual predator or the type of functional response. Experimental analysis of competition among U. cinerea and estimates of predator densities in the field indicated that intraspecific interactions do not cause a significant reduction in the consumption of barnacles. Presented with several frequencies of B. balanoides and the mussel Mytilus edulis, the predator showed a distinct preference for barnacles. As a result of predation, substrate cover of B. balanoides on the lower shore was transient and local extinction occurred within the years between 1977 and 1980. The evidence of destablizing predator response and prey extinction strongly suggest that the interaction between U. cinerea and B. balanoides is best explained by nonequilibrium theory.
Dynamics of the Epifauna of the Bivalve Pinna Bicolor: Interactions Among Recruitment, Predation, and Competition
Authors: Keough Michael J.
Published: May 2006

The epifauna on the shells of a subtidal population of the bivalve Pinna bicolor is composed mainly of encrusting bryozoans and serpulid polychaetes, with tunicates and sponges relatively uncommon. Only a small subset of the observed interactions between sessile organisms were capable of changing the patterns of abundance on individual Pinna shells. Didemnid tunicates were capable of excluding most other species, but the most common competitive interactions, those between encrusting bryozoans, had variable outcomes and frequently did not result in the exclusion of the loser from a patch (shell). Sponges were also capable of excluding bryozoans and serpulids, although at slower rates than tunicates. Serpulids were overgrown by all other species, although overgrowth usually did not result in their exclusion from patches. Predators were, in general, not capable of influencing the abundance of any species greatly. The exception involved two species of monacanthid fish, juveniles of which ate newly metamorphosed didemnid ascidians. These fish thus could prevent monopolization of some patches by tunicates. The effects of predation by juvenile fish and overgrowth by tunicates were variable in space and time. The interaction between variable tunicate recruitment and predation was important. Didemnids recruited in low numbers and, even in a year of high recruitment, did not colonize a large number of patches; in addition, most recruits were eaten by fish. Predation by fish played no role in another year, because few tunicates recruited. It is likely that the abundance of fish was also variable, since their recruitment is also likely to be variable in time. The combination of these factors has resulted in few patches being colonized by tunicates. In the 2 yr of the study, none of the fifty patches under observation was colonized successfully by didemnids, and observations on other Pinna shells suggest that no substantial establishment occurred in the 2—3 yr preceding this study. Thus, in most patches, predation and competition did not strongly influence the abundance of sessile organisms. The patterns of occupation of individual patches, and the overall abundance of sessile species in the community, could be explained adequately by the observed patterns of recruitment. This situation contrasts with the occupation of patches on the pilings of a nearby pier, where competitive interactions between occupants of a patch are the most important factor. The results of these experiments provide a mechanism to explain the previously noted difference in the abundance of sessile invertebrates on the shells of Pinna bicolor and on the pilings of the pier.
Why Nudibranchs are Partial Predators: Intracolonial Variation in Bryozoan Palatability
Authors: Harvell Drew
Published: May 2006

Intraindividual variations in morphology as well as variations in population density of bryozoan (Dendrobeania lichenoides) affect foraging patterns of their nudibranch predators in the field and laboratory in Puget Sound, Washington. Three nudibranch species characteristically graze Dendrobeania lichenoides colony perimeters and leave the center unconsumed: °50% of surveyed colonies showed evidence of nudibranch predation. The proportion of a colony consumed is density dependent. When prey density was low, nudibranchs could consumed entire colonies, but ate less per colony as prey density increased in laboratory experiments. Nudibranchs apparently assess intracolonial variations in quality, and when prey are abundant, select the preferred parts (perimeter) of each colony. In paired palatability tests, nudibranchs rejected strips cut from colony centers, yet readily ate pieces from other regions. Three features of the colonies were associated with the nonpalatable center of the colony: attachment rhizoids, brown bodies, and embryo. The attachment rhizoids do not account for the decreased palatability observed, which thus may result from either distasteful embryos of brown bodies, which both occur in highest numbers in the colony center. Brown bodies are products of degenerated polypides retained within zooecia in some bryozoan taxa. The function of brown body retention has never been established, despite considerable debate among invertebrate biologists. This study indicates that colonial invertebrate colonies are not necessarily homogeneous resources. Intracolonial palatability may generally vary with ontogeny which, in a colonial animal (or plant) results in intracolonial variation. Nudibranchs primarily eat colonial invertebrates (coelenterates, ascidians, and bryozoans), and consequently their foraging patterns may generally reflect intracolonial variations in the palatability of their resources.
Alpine Annual Plants: Phenology, Germination, Photosynthesis, and Growth of Three Rocky Mountain Species
Authors: Reynolds Douglas N.
Published: May 2006

Field microenvironments of three annual alpine species, Koenigia islandica, Polygonum confertiflorum, and P. douglasii, were characterized over two growing seasons. Germination, photosynthesis, and growth of all three species were investigated in field and laboratory experiments. The Polygonum species occurred in warm, dry alpine sites which melted out early in the growing season but also dried out early; plants died by mid—August. Koenigia grew in sites which melted out later, but plants remained alive later in the season since their sites did not dry out. Polygonum plants experienced higher soil surface, air, and leaf temperatures than did Kogotus plants. Seeds of the Polygonum species required stratification before they germinated, and light increased germination. Koenigia seeds germinated equally well in light and dark, and stratification was not necessary, although it increased germination percentages. Photosynthetic responses to light were similar in all three species. Koenigia's photosynthetic temperature optimum was lower than those of the Polygonum species (27° vs. 32°C). Maximum net photosynthetic rates (CO2 uptake of wholeplants) of each species ranged from 12 to 17 μmol°m—2°s1. Koenigia plants grew significantly larger and produced more seeds at daytime temperatures of 15° rather than 25° in growth experiments. The reverse was true for the Polygonum species. A single extra week of growth often doubled seed production in these rapidly developing species. Differences in habitat and physiological response probably reflect the evolutionary origins of these species. Koenigia colonized Rocky Mountains from the Arctic, and it inhabits the coolest, wettest, alpine bogs. The Polygonum species appear to have originated at lower elevations in the temperate zone and to have colonized the warmest and driest alpine habitats. The species' photosynthetic, reproductive, and growth responses reflect the conditions in their respective habitats.
Catastrophic Windthrow in the Presettlement Forests of Wisconsin
Authors: Canham Charles D. , Loucks Orie L.
Published: May 2006

Presettlement survey records for the state of Wisconsin (circa 1834—1873) reveal a widespread pattern of catastrophic windthrow. From these records, we have calculated that there were 51.8 separate patches (>1.0 ha) of complete canopy windthrow covering a total of 4828 ha annually within the region of the presettlement hemlock—northern hardwood forests, in the northeastern part of the state. The estimated return time for catastrophic windthrow at a site in this region is 1210 yr. Catastrophic windthrow was much less common in the forests of southern Wisconsin. Comparisons of the presettlement disturbance regime with contemporary climatological records suggest that catastrophic thunderstorms were the principal mechanism for large—scale windthrow in northern Wisconsin.
Competition for Space, Disturbance, and the Structure of a Benthic Stream Community
Authors: McAuliffe Joseph R.
Published: May 2006

Interspecific competition for space limits the distribution and abundance of many benthic insects on stones in a western Montana stream. The sessile caddisfly larva Leucotrichia pictipes is territorial and aggressively eliminates conspecifics and other species from its foraging territories. Territoriality produces an intraspecific pattern of regular spacing and negative spatial associations between Leucotrichia and several other sessile insects: Parargyractis confusalis, Rhetanytarsus sp. and Eukiefferiella sp. Experimental removals of Leucotrichia resulted in higher densities of other sessile species and several mobile insects, including Baetis, Glossosoma, and Simulium. These insects show broad microhabitat overlap with Leucotrichia; competition with Leucotrichia limits their distributions and abundances within otherwise suitable microhabitats. Leucotrichia is the only species that monopolizes large areas of space. Physical disturbances interrupt the formation of competitive monopolies by Leucotrichia. During seasonal reduced flows, Leucotrichia is eliminated from stones and boulders in shallow water. Greater densities of a short—lived sessile species with multiple annual generations occupy this ephemeral spatial resource. On permanently submerged stones, Leucotrichia competitively affects a large part of the benthic fauna. On small stones that overturn with higher frequencies during flooding, Leucotrichia densities are reduced and species' abundance are highly equitable. Larger, more stable substrates with greater densities of Leucotrichia are characterized by lower species evenness.
A Variance Test for Detecting Species Associations, with Some Example Applications
Authors: Schluter Dolph
Published: May 2006

A little—used measure of species association is provided by the ratio of the variance in total species number (or total density of individuals) in samples to the sum of the variances of the individual species. Use of this ratio allows a test of the null hypothesis that species do not covary among samples. As the test is simultaneous it is preferable to pairwise 2 X 2 contingency table analysis and pairwise correlation analysis when the number of species is large. Simulation reveals that this test is also more powerful than Pearson's g2 test for comparing observed and expected frequency distributions of species in samples. The variance test was applied to a selection of data from the literature. Results reveal that positive associations are the rule in nature and negative associations are uncommon. Invertebrate species tend to be more positively associated among samples than are vertebrates, although the difference is not significant. Examples of biological processes, especially interspecific interactions, that might produce associations among species are suggested. However one must be cautious not to infer the importance or unimportance of a specific process from the result of the test alone.
Regulation of Leaf Breakdown by Fungi in Streams: Influences of Water Chemistry
Authors: Suberkropp Keller , Chauvet Eric
Published: May 2006

We examined the influenced of stream water chemistry on relationships between fungal activity and breakdown rates of yellow poplar (Liriodendron tulipifera) leaves in eight streams that varied with respect to pH and nutrient (nitrate and phosphate) concentrations. We also performed a reciprocal exchange experiment of leaves that had been colonized by microoganisms in two streams with contrasting water chemistries. Decomposer activity varied greatly depending on the stream in which the leaves were placed. Variation in breakdown rates of yellow poplar leaves was over 9—fold maximum ATP concentrations associated with leaves varied as mush as 8—fold, and maximum sporulation rates of fungi associated with leaves varied over 80—fold among streams. Among all streams, nitrate, phosphate, and temperature were positively correlated with one another and with decomposer biomass and activity. When hardwater streams were analyzed separately, nitrate concentration was the only variable that was significantly correlated with all measures of microbial activity and leaf breakdown. Consequently, nitrate concentration appeared to explain much of the variation we detected among streams. Responses to the reciprocal exchange experiment were rapid, with significant changes occurring within the first 5 d after the transfer. Leaves transferred from the hardwater stream containing relatively high concentrations of nitrate and phosphate to the softwater stream containing low concentrations of nutrients exhibited by large decreases in both ATP concentrations and sporulation rates, whereas ATP concentrations and sporulation rates increased when leaves received the reciprocal transfer. The fungi associated with decomposing leaves in streams appear to obtain a significant portion of their nutrients (e.g., nitrogen and phosphorus) from the water passing over the leaf structure. These results indicate that the chemistry of the water can be an important regulator of leaf breakdown in streams by affecting the activity of decomposer fungi.
Diversity Patterns in Stream Benthic Invertebrate Communities: The Influence of Habitat Stability
Authors: Death Russell G. , Winterbourn Michael J.
Published: May 2006

Invertebrate diversity patterns were examined in 11 freshwater habitats (10 streams and a windswept lake shore) of similar physicochemical nature but different thermal and hydrologic stability in the Cass—Craigieburn region, New Zealand. Species richness and density were markedly higher at the more stable sites, but species evenness peaked at sites of intermediate stability. Of the 20 environmental variables examined, a multivariate instability index incorporating temporal variation in depth, temporal variation in current speed, substrate stability, the Pfankuch channel stability index, temperature range, and stream reach tractive force was the single best predictor of the number of species, whereas epilithic pigment concentration was the single best predictor of invertebrate density. The pattern in species richness did not support any of three diversity hypotheses considered. In contrast, the pattern in species evenness suggested competitive exclusion may be occurring patchily and that Hutson's dynamic equilibrium model may have some validity, at least at the level of the patch. However, the strong link between productivity and stability apparent in these habitats, and a lack of information on the effects of increased productivity on competition in stream benthic communities makes any firm assessment of the latter model difficult. The observed diversity patterns are, however, consistent with the idea that high diversity is maintained in these habitats by an interaction between low levels of disturbance and habitat patchiness.
The Joint Evolution of Diapause and Insecticide Resistance: A Test of an Optimality Model
Authors: Carrière Y. , Roff D. A. , Deland J.-P.
Published: May 2006

The goal of this study was to assess whether selection for insecticide resistance resulted in evolutionary change in diapause propensity in the obliquebanded leafroller, Choristoneura rosaceana. Caterpillars that diapause under bark in midsummer were assumed to escape exposure to insecticides. Estival larval diapause was modeled as a bethedging strategy that reduces the risk of reproductive failure in a stochastic seasonal environment and decreases mortality due to insecticides. The proportion of larvae entering estival diapause in populations within a local geographic area was predicted to increase in orchards treated with insecticides after midsummer. As predicted, insects from populations exposed to insecticides evolved a higher propensity to diapause than individuals from insecticide—free populations. A second prediction of the model was that the proportion of diapause in a population should be negatively correlated with survival of the non—diapausing larvae to insecticides applied after midsummer. This prediction was not supported; there was a positive correlation between diapause propensity and the estimated survival to the insecticides. A simulation model indicated that this unexpected correlation did not result from a non—equilibrium situation in which diapause propensity and physiological resistance evolved at different rates across orchards exposed to different insecticide regimes. A positive across—population correlation between physiological resistance and diapause suggests pleiotropic effects of the resistance allele(s). Such pleiotropic effects could result in a correlated response of diapause following strong directional selection for physiological resistance and may explain the inadequacy of the optimality model to predict the evolutionary trajectory of diapause propensity across the insecticide—treated populations.
Microclimate and Individual Variation in Pollinators: Flowering Plants are More than Their Flowers
Authors: Herrera Carlos M.
Published: May 2006

Variation in pollinator composition at the individual plant level is an important prerequisite for plant specialization on pollinators that does not seem to have been investigated previously. I studied variation in pollinator composition in a southeastern Spanish population of the insect—pollinated shrub Lavandula latifolia (Labiatae) and examined its correlates, with particular reference to the distinction between factors intrinsic (flower morphology, nectar standing crop, size of floral display) and extrinsic (sunlight regime, ambient temperature, humidity) to the plants. L. latifolia shrubs differed significantly in all intrinsic variables measured, in average irradiance levels (due to site—dependent variation in timing and duration of insolation periods), and in pollinator composition at both the species and other levels. Individual variation in pollinator composition was largely due to differences among insect taxa in their foraging responses to the sunlight mosaic. While some pollinators foraged indiscriminately over that mosaic, others preferred sites characterized by high irradiance. Variation among plants in intrinsic variables was unrelated to differences in pollinator composition, which depended significantly only on the sunlight regime associated with each plant's location in the habitat. Site—specific effects in pollination will generally act to reduce the likelihood of selective pressures by animals on plant traits. Their importance should be greatest in habitats characterized by patchiness in environmental variables that affect pollinator behavior and in plants with pollinator assemblages dominated by ectothermic species.
Vegetation Dynamics in an Experimentally Fragmented Landscape
Authors: Holt Robert D. , Robinson George R. , Gaines Michael S.
Published: May 2006

In spatially heterogeneous habitats, plant community change may reflect spatially localized population—level processes that are sensitive to the size of an average habitat patch. However, local species turnover can also be determined by initial conditions and large—scale processes, in which case patch size effects may be overridden. To examine the role of patch size in directing secondary succession, we subdivided a newly abandoned agricultural field into an array of experimental patches (32, 288, and 5000 m2, grouped to sample equivalent portions of the field), and have thereafter censused the resident plant and animal communities at regular intervals. Here we report results from the first 6 yr of studies on the changing vacular plant community in an experimentally fragmented landscape. The general course of change in all patches followed a trajectory typical of old—field succession, toward increasing dominance by longer lived and larger plant species. The same group of species that dominated at the stare of the study continued to dominated after 6 yr, although in very different proportional abundances. Larger patches were more species rich than their smaller counterparts, and had a higher proportion of nonshared species, but the additional species were transient and low in abundance. Spatial heterogeneity in vegetation measured as local community dissimilarity, increased in all patches but to a lesser extent in the largest patches, where censuses of nearby permanent quadrats indicated less divergence over time. At a population level, the strongest effect of patch size was that local populations of clonal species were more prone to disappear from the smallest patches. Nevertheless, summary measures of temporal community change did not reflect significant differences in localized species turnover. We conclude that patch size does not markedly affect the rate or pattern of early secondary succession, at the scales imposed in our experiment.
Within‐Patch Dynamics in a Metapopulation
Authors: Hastings Alan , Wolin Carole L.
Published: May 2006

We formulate a single—species model to study the dynamics of a metapopulation that is composed of several subpopulations spread among distinct patches. In the case where extinction rates within a patch are a decreasing function of population size, and all disasters lead to extinction of the local population, we determine the equilibrium distribution of numbers within patches. We show that any equilibrium is stable. This model is also applicable to some systems of mutualists, such as some plant—pollinator systems, where the focus is on the dynamics of the plant species. Unlike models for obligate mutualism that do not incorporate spatial structure, our patch model always has a stable equilibrium.
Spatial Dispersion of Woody Regeneration in an Old‐Growth Forest
Authors: Ward Jeffrey S. , Parker George R.
Published: May 2006

Spatial pattern and density for woody regeneration were examined in relation to canopy structure for an old—growth forest in east—central Indiana. All woody stems ≥2 cm diameter at 1.37 m were recorded by species and diameter on a 4—ha area gridded into 10 x 10 m quadrats. Canopy structure was inventoried using a 5 x 5 m grid. Canopy structure was divided into three classes: canopy gaps, secondary canopy, and primary canopy. The nonparametric dispersion index was used to examine spatial patterns of woody species and the Clark—Evans nearest neighbor index was used to examine spatial pattern of canopy gaps. Canopy gaps covered 9.0% of the 4 ha area, averaged 52.4 m2 in area, and were randomly dispersed. Most species were aggregated at scales >400 m2. While overall regeneration density did not vary significantly with canopy structure, densities for some individual species were significantly different under different canopy structures. The current disturbance regime of this forest, primarily single—tree gaps, has created a canopy structure which favors the regeneration of shade—tolerant species.
The Seed Bank of a Freshwater Crustacean: Copepodology for the Plant Ecologist
Authors: De Stasio Bart T.
Published: May 2006

The spatial and temporal aspects of dormancy in a freshwater copepod, Diaptomus sanguineus, were investigated during three consecutive years in Bullhead Pond, Rhode Island. Patterns of diapausing egg production and deposition were monitored with plankton sampling and settling traps. Vertical and horizontal distributions of diapausing eggs in sediments were investigated by taking core samples. Diapausing eggs removed from sediments were tested in the laboratory for hatching ability. The long—term spatial and temporal patterns of emergence from the diapausing egg stage were documented in the field using inverted plastic funnel traps sampled weekly. The field data along with an estimated annual budget for diapausing eggs in the pond suggest that D. sanguineus has an egg bank, analogous to the seed banks of plants, that allows it to survive through harsh environmental periods.
Bivalve Growth and Higher Order Interactions: Importance of Density, Site, and Time
Authors: Peterson Charles H. , Beal Brian F.
Published: May 2006

Field experiments were conducted from 1980 to 1982 to test how shell growth of the suspension—feeding bivalve Mercenaria mercenaria within a single estuarine system around Cape Lookout, North Carolina, varied with (1) year, (2) density within enclosed 1—m2 plots, (3) the presence of enclosure walls, (4) the source of the clams, (5) site, and (6) various two—way interactions between these factors. Growth rates generally did not change between years, although occasional interactions between site and year were caused by specific sites exhibiting significant temporal changes in growth rate. Mercenaria at densities of 80 individuals/m2 tended to grow less than at densities of 10 individuals/m2, with a significant average reduction of 18% for 6—cm clams and a nearly significant 10% reduction for 3—cm clams, presumably because of enhanced local food depletion in benthic boundary layers at higher densities. The presence of enclosure walls enhanced Mercenaria growth by 15—21%, perhaps because hydrodynamics roughness of projecting walls increased mixing into the otherwise depleted bottom waters. Clams taken from a single common source grew an average of 43—86% faster than locally collected clams at each of five other sites scattered throughout the estuarine system. This effect of clam origin did not diminish in the 2nd yr, suggesting that the difference was more likely to have a genetic than a physiological basis. Mercenaria growth differed by as much as threefold among sites within the estuarine system and even among habitats within a single localized water mass. Despite this substantial growth variation among sites and occasional site x year interactions, the effects of manipulating local density, clam origin, and presence/absence of enclosure walls did not vary significantly with site. A simple additive model serves to describe how site effects combined with experimental effects to explain Mercenaria growth rate (defined as ln[final size/initial size]).
Sex‐Specific Mortality in Nestling Great‐Tailed Grackles
Authors: Teather Kevin L. , Weatherhead Patrick J.
Published: May 2006

The growth and survival of male and female Great—tailed Grackles (Quiscalus mexicanus) was monitored between 1985 and 1987 to test the hypothesis that, because of their large size, sons are more likely than daughters to suffer when food is limited. Larger egg and clutch sizes, as well as lower levels of starvation, indicated that food was more abundant in 1985 than in 1986 or 1987. Fledgling sex ratios were 1:1 in 1985 but female—biased in the latter 2 yr, suggesting that males suffered higher mortality during years of food shortage. Biased fledging sex ratios were due primarily, but not exclusively, to higher male starvation among last—hatched nestlings. Indirect evidence suggests that sex ratio bias in other than last—hatched eggs could be a consequence of predation not being independent of starvation. The fledging sex ratio (males: females) in individual nesting colonies was negatively correlated with the level of starvation in those colonies. Finally, an experiment that subjected male and female nestlings to a similar and potentially food—stressed situation suggested that males were affected more severely than females. Together, these observations provide strong evidence of differential mortality among sons and daughters of a dimorphic species. Although these data are qualitatively consistent with Fisher's (1930) hypothesis of biased sex ratios balancing investment in sons and daughters, the data are also consistent with the hypothesis that biased sex ratios are a nonadaptive consequence of one sex being more costly to produce and of a 1:1 primary sex ratio.
Seasonal Abundance and Pattern of Chydorid, Caldocera in Mud and Vegetative Habitats
Authors: Whiteside M. C. , Williams J. B. , White C. P.
Published: May 2006

Pattern sampling (Whiteside and Williams 1975) was employed to study the population changes, habitats and spatial arrangements (pattern) of littoral cladocera in Lake Itasca, Minnesota during 1974. Population dynamics of the 19 most abundant species of chydorids had changes similar to other populations studied in north—temperate lakes. All species had either spring or fall maxima, or both, a mid—summer low in numbers. Population trends were the same for vegetative and mud habitats. In a comparison of Chara vs. mud habitat we found Chydorus piger, Leydigia leydigi, Alona quadrangularis, Pleuroxus aduncus, and Alona circumfibriata to live mainly in littoral mud. Kruzia latissima, Camptocerus rectirostris and Chydorus faviformis were most restricted to the vegetative habitat, while other species were more ubiquitous. Pielou's (1974) terms describing pattern, phase, mosaic, grain, and intensity are discussed. We redefined intensity as describing the visual effect of density. The changes of intensity accompanying changes in density typified 1974 patterns, while no changes in the other parameters were evident. Preliminary experiments exploring the behavior of chydorids suggest that visual stimuli are very important in directing movements, followed by tactile and chemical clues.
Some Relationships between Systematics and Trophic Ecology in Nearctic Aquatic Insects, with Special Reference to Trichoptera
Authors: Wiggins Glenn B. , Mackay Rosemary J.
Published: May 2006

Based on the general premise that the genus represents an ecological, as well as a morphological type, a number of generalizations are developed concerning the use of food resources in fresh waters by Trichoptera and some other aquatic orders of the Nearctic fauna. There are more genera of the Nearctic order Trichoptera (144) than in the orders Ephemeroptera (59), Odonata (84), or Plecoptera (88). Trichoptera have a wide range of habitats and a broader range of trophic categories than any of these other wholly aquatic orders. This relatively high ecological diversity is attributed to the many uses of silk by trichopteran larvae. Genera of 3 families of filter—feeding Trichoptera show differences in distribution which are correlated with the type of food particle. Most of these genera are found in the eastern deciduous forest biome and all sizes of organic particles are filtered. In the western montane forest biome, generalist filter feeders are absent or underrepresented; predacious genera or those filtering very fine particles have been more successful. Possibly there are differences in the quality and quantity of fine particulate detritus between eastern and western forest which account for the above distributions. In the trichopteran family Limnephilidae, genera of the detritivorous shredders have exploited lotic, lentic, and even terrestrial habitats; grazer genera are mostly confined to cool lotic habitat. Grazers in other families of Trichoptera are also more diverse in upstream areas, and grazer genera are particularly well—represented in the western montane forest biome. In streams of the eastern deciduous forest biome, the relative proportions of feeding categories shown by trichopteran genera appear to agree with a general trophic model of benthic invertebrate communities in that dominance of shredder—collector genera in upstream sections gives way to grazer—collector dominance downstream. In western montane streams, trichopteran generic distributions conform to the model downstream, but show relatively more grazers than the model would predict for upstream areas. Periphyton growth, and thus food for grazers, may be more abundant in the western coniferous forest than in the shaded streams of the eastern deciduous forest. In general, an ecological analysis of Nearctic Trichoptera at the generic level appears to provide a reasonable indication of the energy resources available in aquatic habitats.
Organization of an Assemblage of Early Successional Species on a Soil Moisture Gradient
Authors: Pickett S. T. A. , Bazzaz F. A.
Published: May 2006

To determine to roles of prior evolutionary divergence and competitive displacement of species in successional community organization, and aspects of the colonizing strategy, 6 co—occuring annuals were grown together and alone on a soil moisture gradient. The species had similar board vegetative and reproductive responses to the gradient. Interspecific competition reduced the niche breadth and similarities of the species. Competitive and gradient stresses were generally absorbed through plasticity, although Polygonum pensylvanicum and Chenopodium album showed some mortality. Response centers of Polygonum, Ambrosia artemisiifolia, and Chenopodium, competitively subordinate species, shifted due to interspecific competition. Amaranthus retroflexus and Setaria faberii, the leading competitors, already slightly offset from each other when grown alone, did not shift response centers. Competition delayed the start of flowering in Setaria, Chenopodium, Polygonum and Ambrosia. Competitive success did not correlate with response breadth or overlap. Polygonum and Abutilon behaved differently in different competitive environments, indicating the existence of competitive refugia. Refugia may be shifted, reduced, or maintained depending on the competitors present. Coexistence may depend on: (1) differences in response to the moisture gradient and other niche dimensions previously investigated, and (2) on heterogeneous and unpredictable distributions of neighbors. Thus, competitive refugia will be unthreatened at some times and places.
Timing of Autumn Migration and Its Relation to Winter Distribution in Dark‐Eyed Juncos
Authors: Nolan Val , Ketterson Ellen D.
Published: May 2006

Migratory Dark—eyed Juncos in eastern North America migrate southward in autumn and tend to segregate in the winter range according to sex and age. North to south, the most abundant classes are young males, adults males, young females, and adult females. Because adults tend to dominate young at winter feeding sites, this distribution appears at first to conflict with the view that dominance interactions are responsible for differential avian migrations and that dominant individuals remain nearest the breeding range. However, if young juncos establish winter residency at earlier dates than adults, a prior residence effect might make them dominant. This hypothesis requires that young arrive at wintering sites earlier than adults and that residents of all classes arrive earlier than their transient counterparts. We tested these predictions by comparing first—capture dates of juncos at Bloomington, Indiana, which is north of the latitudianal midline of the junco's winter range. During 13 autumns, individuals were classed as local residents or an transients and were sexed and aged. Contrary to predictions were not caught earlier than transients. Further, adults were caught earlier, not later, than young among transiets and probably also among residents. Thus, settlement of the winter range does not proceed from north to south, and dominance established through prior residence cannot account for the concentration of 1st—yr males in the northern part of the winter range. The fact that some sex—age classes tend to winter south of others predicts that at a northern capture site the classes that migrate farthest should be commoner among transients than among residents. This expectation was fulfilled. In addition, the median capture dates of the sex—age classes were arranged approximately according to the north—to—south order of their distribution, indicating that classes with the farthest to travel passed through (transients) or settled (residents) earliest in autumn. We conclude that comparison of autumn migration schedules of transiet and resident passerine birds at a single location can yield considerable information about the dynamics of settlement of the entire winter range, including possible information about differences in destination of subsets of transients.
Sex‐Differential Resource Allocation Patterns in the Subdioecious Shrub Hebe Subalpina
Authors: Delph Lynda F.
Published: May 2006

Vegetative growth and sexual reproduction were compared (under natural conditions and following defoliation) for the two sexual morphs of the subdioecious evergreen shrub Hebe subalpina. Under natural conditions, both morphs produced the same number of flowers, but because the flowers of the polleniferous morph (here called males) are larger males allocated almost twice as much biomass to flower production as did females. Females, by contrast, produced larger fruit as well as more fruit than males. In terms of biomass, females allocated 4.7 times as much as males on fruit production. Overall, females allocated almost twice the biomass to flowers and fruit. The morphs also differed in the timing of their growth, with each morph growing less during the phase in which its reproductive costs were highest. In spite of the greater allocation by females to reproduction, the two morphs grew the same amount over the entire reproductive cycle. This may be a result of the fact that females produced more leaves earlier in the season, which enabled them to accumulate more resources than males. The defoliation experiment substantiated the morph—differential allocation patterns. Defoliated shoots on females fruited, but did not grow relative to controls, and defoliated shoots on males grew, but did not fruit. These differences suggest that divergent selection has been operating on the morphs since the evolution of subdioecy (via gynodioecy) from cosexuality in Hebe, and may be related to differences in the relative fitness gains to the morphs through pollen vs. seeds.
Prey Exchange Rates and the Impact of Predators on Prey Populations in Streams
Authors: Cooper Scott D. , Walde Sandra J. , Peckarsky Barbara L.
Published: May 2006

We present four lines of evidence that the magnitude of prey exchange (=immigration/emigration) among substrate patches has an overwhelming influence on the perceived effects of predators on prey populations. (1) An extensive review of the literature on predation effects in benthic and littoral freshwater revealed a significant relationship between prey exchange rate and observed predator impact. In streams, studies showing significant predator effects used cages with smaller mesh sizes than studies showing nonsignificant effects. Similarly, there was a highly significant correlation between cage mesh size and the magnitude of predator impact on common prey. Large—scale stream studies indicated that prey drift and colonization rate were inversely related to predator impact on benthic prey. (2) These patterns were confirmed by field experiments and observations where mesh size was directly manipulated or where exchange rates varied among taxa. In Colorado streams we saw greater predator impacts on Baetis prey when immigration/emigration was restricted vs. when the mesh size of the cage was relatively large. Similarly, the effects of trout in California stream pools were greater when prey turnover rates were low. (3) A re—analysis of Peckarsky's (1985) data shows an inverse relationship between predator impact and prey mobility within a field experiment. (4) Finally, a model that incorporates both predation and exchange of prey indicates that we ought to expect a lower magnitude of predator effects when exchange rates are high. These results suggest that some discrepancies in past studies may be explained by differences in the exchange rates of prey, and that differences in predator effects across different systems or habitats may be related to variation in the rates of prey dispersal and colonization.
Experimental Studies on Behaviorally Mediated, Indirect Interactions through a Shared Predator
Authors: Huang Chifu , Sih Andrew
Published: May 2006

We examined indirect interactions between two noncompeting prey species (small—mouthed salamander larvae, Ambystoma texanum, and freshwater isopods, Lirceus fontinalis) that were mediated by the prey's antipredator responses to a shared predator (green sunfish, Lepomis cyanellus). Lirceus fontinalis responded to sunfish by decreasing overall activity and by decreasing their time spent of refuges. Male isopods were more active than females; as a result, males suffered higher predation rates than did females. Salamander larvae tended to drive isopods out of refuges; as a result, female (but not male) isopods suffered higher predation rates with than without salamanders. Ambystoma texanum responded to sunfish by decreasing their time spent outside of refuges. Despite this shift into refuges. A. texanum suffered high predation rates. Isopods increased the behavioral response of salamander larvae to sunfish. A. texanum decreased their emergence rate from refuge in response to sunfish, only when isopods were present. The apparent behavioral mechanism was that with isopods present, sunfish were more active, which, in turn, elicited a stronger antipredator response from salamanders. As a result, the presence of isopods significantly increased the survival of salamanders when fish were also present. Salamander larvae negatively affected female isopod survival, whereas isopods positively affected salamander survival. These effects were caused by changes in antipredator behavior and thus in predation rate. The indirect interaction between salamander larvae and isopods can be termed @`apparent predation" or indirect antagonism."
Factors Affecting Population Fluctuations in Larval and Adult Stages of the Wood Frog (Rana Sylvatica)
Authors: Berven Keith A.
Published: May 2006

During a 7—yr population on the wood frog, Rana sylvatica, the breeding population size fluctuated by a factor of 10 and juvenile production by a factor of 100. Variation in the adult population among years was largely due to variation in juvenile recruitment. Annual net replacement rates (Ro) varied from 0.009 to 7.49. Survivorship curves (calculated using the number of eggs deposited as the initial point) showed that most variation in the proportion of individuals surviving to adulthood was due to variation on larval survival; juvenile and adult survival was relatively constant among years. Male and female survival did not differ. Because females matured a year later than males, on average 2.3 times as many males as females from a given clutch survived to breed. This difference accounted for the observed male—biased sex ratio in breeding choruses. Premetamorphic survival and size at metamorphosis were negatively correlated with the number of eggs deposited. Length of larval period was positively correlated with number of eggs deposited. Survival was higher among juveniles that metamorphosed early and were large at metamorphosis. Larger juveniles matured earlier and were also larger as adults. The population appeared to be regulated through density—dependent factors affecting larval survival, larval size, and time of metamorphosis. Adult population size also negatively affected total clutch volume. Mean monthly rainfall positively affected adult survival.
Seed Variation in Wild Radish: Effect of Seed Size on Components of Seedling and Adult Fitness
Authors: Stanton Maureen L.
Published: May 2006

Seed mass in wild radius (Raphanus raphanistrum) varies up to sixfold within single fruits. The impact of such variation on subsequent growth and fecundity was studied. Seeds from single fruits were used to minimize genetic differences among individuals. Weighed seeds were planted close together in a disturbed area typical of Raphanus habitats. Large seeds (>6 mg) were more likely to emerge as seedlings than were small seeds (<4 mg). Seed size had no effect on emergence time. Seedlings from large seeds grew more rapidly and produced more flowers than did those from related smaller seeds. Results from the field experiment contrasted with those obtained in greenhouse growth studies, where seed size had no significant effect on final plant size. This study points out two factors that have led to inconsistent results in previous studies of seed size and seedling success: (1) differences in the timing of growth measurements, and (2) the presence or absence of competitive inequities among neighbors within the experimental design.
Predation of Heterocope Septentrionalis on Two Species of Daphnia: Morphological Defenses and Their Cost
Authors: Dodson Stanley I.
Published: May 2006

Two herbivorous zooplanktonic species, Daphnia middendorffiana and D. Pulex have disjunct distributions in arctic ponds of the Alaskan north coastal plain. D. Middendorffiana co—occurs in ponds with the predaceous copepod Heterocope septentrionalis. Body size, tail spine length, and carapace strength of D. Middendorffiana are defenses against Heterocope predation. These defenses occur only in the developmental stages susceptible to predation. The morphology of Daphnia changes from generation to generation in response to the predator's annual life cycle. Daphnia pulex lacks morphological antipredator defenses and lives in the absence of Heterocope. Field samples suggest that D. Middendorffiana has a lower reproductive rate than D. Pulex. The lower rate may reflect the cost of producing morphological antipredator defenses, especially large offspring. D. Middendorffiana may be able to afford its morphological antipredator defenses only in the presence of Heterocope, which may keep the herbivore density lower and the food density higher than in D. Pulex ponds.