bluuebunny/crossref_metadata_2025 huggingface dataset:
Human Disturbance and the Historical Development of Linsley Pond
Authors: Brugam Richard B.
Published: May 2006

Paleolimnological techniques were used at Linsley Pond, North Branford, Connecticut, USA to compare changes in the biota with changes in watershed land use as documented by municipal land records. Fossil diatoms, midges, zooplankton, and chemical composition were examined in a core 238 cm long, which was dated by (210)Pb, (14)C, and changes in fossil pollen assemblages. The beginning of farming in 1700 caused only minor changes in the lake biota. In 1915 changes in agricultural activity at a nearby farm caused a rapid shift to eutrophic diatom and midge assemblages. In 1960 major changes occurred in the zooplankton community in response to the hypereutrophication caused by the construction of a suburban housing development. Fluxes of Fe, Mn, Ca, Cu, and P to the lake sediment seem to be controlled by changes in soil erosion–not by changes in the trophic status of the lake.
Microhabitats in a Forest‐Floor Small Mammal Fauna
Authors: Dueser Raymond D. , Shugart H. H.
Published: May 2006

This study examines microhabitat configurations for 3 small mammal species occupying second—growth mesic forest on Walker Branch Watershed in eastern Tennessee. Small mammal populations were sampled in oak—hickory, chestnut oak and pine forest types, with three 0.36—ha live—trapping grids per forest type. There were 255 total captures for 4 forest—floor species during 9,696 trap nights between 1 May and 16 August 1973. These captures included 2% Blarina brevicauda, 66% Peromyscus leucopus, 5% Ochrotomys nuttalli and 27% Tamias striatus. Blarina was captured most frequently in the pine forest type, Peromyscus and Tamias most frequently in the oak—hickory, and Ochrotomys exclusively in the pine. Twenty—nine variables describing proximate habitat structure were measured at each sample mammal capture site. There were significant overall species differences on 18 of these variables. A subset of variables was identified for each of the 3 most frequently observed species, consisting of only the variables of particular significance for distinguishing the capture sites of that species from those of the other species collectively. Discriminant analysis of these few variables both described the average microhabitat configuration, for a species and indicated the relative importance of each variable for characterizing or describing that configuration, subject to the assumptions of the analysis. The observed differences between species microhabitat configuration are consistent with both the composition by forest type of each species sample and the literature information for each species. Microhabitat segregation among these species is discussed with reference to recent theories of habitat selection, ecological, specialization and resource partitioning in equilibrium faunas.
Distribution and Production of Sago Pondweed (Potamogeton Pectinatus L.) on a Northern Prairie Marsh
Authors: Anderson Michael G.
Published: May 2006

Physical and Chemical parameters of soils and water, measured on 140 sites in the Delta Marsh, Manitoba between May 1973 and September 1974, were compared with presence and dry—weight standing crop of sago pondweed (Potamogeton pectinatus L.) on those sites. Mean comparisons and discriminant function analyses identified water depth, soil texture and maximum and directional exposure to wave action as important variables affecting plant distribution. Multiple regression analyses suggested that water depth, available soil K, available soil P, soil texture and directional exposure, were important factors affecting growth on colonized sites. A greenhouse experiment demonstrated that sago pondweed grew better on Delta Marsh soils that normally supported the plant, suggesting that some specific edaphic adaptations might exist. Within the euphotic zone of the Delta Marsh, sago pondweed distribution was probably most effected by prevailing winds through their influence on soil distribution and turbulence.
A Log‐Linear Model Approach to Estimation of Population Size Using the Line‐Transect Sampling Method
Authors: Anderson D. R. , Burnham K. P. , Crain B. R.
Published: May 2006

The technique of estimating wildlife population size and density using the belt or line—transect sampling method has been used in many past projects, such as the estimation of density of waterfowl nesting sites in marshes, and is being used currently in such areas as the assessment of Pacific porpoise stocks in regions of tuna fishing activity. A mathematical framework for line—transect methodology has only emerged in the last 5 yr. In the present article, we extend this mathematical framework to a line—transect estimator based upon a log—linear model approach.
A Statistical Test of the Accuracy and Consistency of Ordinations
Authors: Wilson Mark V.
Published: May 2006

A nonparametric statistical test of the performance of ordinations is adapted and extended from the work of Feigin and Cohen (1978). Two measures of ordination performance are accuracy (the tendency of ordination results to mirror correctly the true community structure) and consistency (the ability of the ordination to produce concordant results). Statistical estimates of accuracy and consistency are given and tests are developed for choosing among ordination techniques.
The Effects of Grazing by Snow Geese on Coastal Salt Marshes
Authors: Smith Thomas J. , Odum William E.
Published: May 2006

The influence of grazing by the Snow Goose (Anser caerulescens subspecies atlantica) was studied in three distinctly different North Carolina salt marshes. One marsh was dominated by Spartina alterniflora, one by a mixture of Spartina patens and Distichlis spicata, and one by Scirpus robustus. Snow Goose grazing consists principally of removal of roots and rhizomes to a depth of 20—25 cm. Exclosures were utilized to compare (1) belowground biomass and net production, (2) aerial plant cover and (3) detritus availability between grazed and ungrazed plots. Ungrazed portions of all study had significantly more biomass (P <.001) than grazed areas in the year following grazing. Belowground net production was less in the grazed portions of two of the sites (P < .10). Grazing intensity, measured as percent biomass removed, was 58.1 ± 7.4% at all sites. Plant cover was reduced at all sites in the spring following grazing. The Scirpus robutus marsh recovered more rapidly than the other marshes and appears to be a more stable grazing system. Finally, at South Pond and Salt Flats, more uprooted root—rhizome material was found in grazed areas than in ungrazed (P < .001, P < .05 respectively). This strongly suggests that Snow Geese make belowground net production available for transport to nearby estuarine waters where it could be used by estuarine consumers.
Vegetation Organization and Dynamics of Lichen Woodland Communities in the Northwest Territories, Canada
Authors: Johnson E. A.
Published: May 2006

The variances of species abundances from 141 upland stands are partitioned into habitat and fire frequency. Principal components analysis is then performed on each of these partitions. The habitat ordination has a topographic—canopy coverage gradient and a nutrient gradient. The fire frequency ordination has one gradient which orders species according to their temporal response after fire, from shorter lived, faster growing, competitively poor species to longer lived, slower growing, competitively effective species. The fire frequency ordination interacts with the habitat ordination by changing a site's canopy cover for approximately 10 yr after fire. The nutrient gradient is only slightly affected by the fire frequency. The recovery of vegetation after fire is explained by using the information on the adaptation of species as shown in the two ordinations and from existing life—history information. Most species found in older stands are present in the first years after fire. Recovery by vascular plants, mosses and lichens is by vegetative reproduction and invasion by propagules. Buried viable seeds play little role in recovery. Lichen abundance is best explained by different habitat requirements rather than successional sequences or caribou grazing. Feather mosses are most abundant in specific sites which develop closed canopies and have greater soil nutrients. The habitat and fire frequency ordinations represent two environmental complexes for which species are adapted, and consequently these are also the two predominant levels of vegetation dynamics. The fire frequency ordination represents shorter term dynamics which cause changes primarily in abundance but not species composition. The habitat ordination represents longer term dynamics which cause major changes in species composition.
Pattern and Biological Microsite Effects in Two Shrub Communities, Southern California
Authors: Shmida A. , Whittaker R. H.
Published: May 2006

Strip transects of 100 contiguous, aligned quadrats were sampled during the spring blooming in a creosotebush (Larrea tridentata) semidesert and a chamise (Adenostoma fasciculatum) chaparral, with species covers in quadrats recorded. Techniques of pattern analysis included reciprocal averaging ordination of quadrats, measurements of pattern diversity and pattern periodicity, and species association and contagion. In both communities the first ordination axis expressed a strong pattern of differentiation of the herb flora from shrub centers to openings; second and third axes expressed other responses of herb species to shrub species and shrub cover. The pattern axis represents a principal direction of niche difference to which most species responded and along which several pairs of congeners were separated. Pattern periodicities were 6 m (weakly defined) in the semidesert and 9 m in the chaparral; pattern diversities were 1.4 and 1.8 half—changes. Quadrat species richness was highest in the transitions between shrub clumps and openings in the semidesert, but higher in the openings and lower under the shrubs of the chaparral. Overall alpha diversity resulted from roughly comparable contributions of point or small—quadrat diversity, pattern diversity of more common species, and rare species. The importance of biological modification of microsites for population function and niche relationships is suggested by species responses to the primary pattern axis, the responses of some herb species to particular shrub species, and the indicated allelopathic effects in the chaparral.
Divergence in the Foraging Responses of Birds on Two Bahama Islands
Authors: Emlen John T.
Published: May 2006

Pine Warblers and Blue—gray Gnatcatchers forage extensively on bark in the pine forests on Andros Island, while on neighboring Grand Bahama Island they forage largely on foilage. The two islands are very similar in physiography, climate, and vegetation, but differ in the number of insect—gleaning species sharing the arboreal foraging substrates. Andros has only the two species mentioned above; Grand Bahama has five, and to of the additional species are bark specialists. Summed densities and consuming biomasses (masses adjusted for size variation in metabolic rate) of the birds in these arboreal insectivore communities were found to be roughly equal on the two islands, but the distribution of total foraging activity as measured in these same units was clearly unequal; foraging biomass on bark was 2.6 times as great on Andros as on Grand Bahama, on foliage it was 1.7 times as great on Grand Bahama as on Andros. When food (insect) abundance and distribution between bark and foliage was found to be similar on the two islands, I concluded that food abundance was probably not the deciding proximal factor behind the dissimilar bird distributions. Alternatively I speculated that some form of interference competition from the bark specialists on Grand Bahama could be inhibiting Pine Warbelers and gnatcatchers from visiting the bark on that island, while in the absence of bark specialists on Andros the birds were free to forage on both substrates. Since bark avoidance is characteristics of Pine Warblers and gnatcatchers throughout Grand Bahama, however, even where the presumptive competitors are scare or absent, I tentatively ruled out interference as the overall proximal factor. With the two most obvious extrinsic factors essentially eliminated, I propose that the proximal or immediate determinant of substrate distribution in these birds is substrate preference–an innate response tendency to select foliage and avoid bark in the one case, and to accept a balance of foilage and bark in the other. Further, since bypassing a rich and readily accessible food source would be clearly maladaptive under ordinary circumstances, I suggest that populations are currently maintained below carrying capacity and that the foliage preference trait of the Grand Bahama population arose under special circumstances of intensified interference competition during an environmental crisis or series of crises in the past. Individuals which avoid the competition from bark specialists at such times by preferring substrates other than bark should theoretically be favored in natural section and emerge numerically dominant from the evolutionary bottleneck created by the crisis. Similar food crises on Andros would, in the absence of bark—gleaning specialists, produce no comparable selective pressures and permit the resident populations to retain broad general responses to all profitable substrates.
The Importance of Regenerated Nitrogen to Phytoplankton Productivity to Phytoplankton Productivity in a Subalpine Lake
Authors: Axler Richard P. , Redfield Garth W. , Goldman Charles R.
Published: May 2006

Experiments utilizing epilimnetic water were conducted to determine the rate of ammonium regeneration, due to zooplankton excretion and microbial mineralization processes, in relation to the rate of inorganic nitrogen assimilation by phytoplankton. The euphotic zone of dimictic, meso—oligotrophic Castle Lake is characterized by a rapid depletion of both nitrate and ammonium soon after spring thaw. External inputs of nitrogen are minimal during this period and levels of inorganic nitrogen remain low until fall overturn. The rate of ammonium assimilation was high relative to nitrate assimilation, and was significantly correlated with the rate of ammonium regeneration. The importance of this rapid turnover of nitrogen to phytoplankton growth is consistent with the results of previous Castle Lake studies, and with the current conceptual model of primary production in the mixed layer of nitrogen—deficient marine ecosystems.
Interacting Influences of Density and Preference on the Emigration Rates of Some Lotic Chironomid Larvae (Diptera:Chironomidae)
Authors: Wiley Michael J.
Published: May 2006

The effects of manipulations of density and sediment type on the emigration rates of chironomid larvae (Diptera:Chironomidae) from Hunt Creek, Montmorency County, Michigan, USA, were examined in artificial stream chambers. Both basic sediment suitability and population density were found to affect larval emigration rates. Furthermore, their interaction lead to rates of emigration not predictable from an examination of either factor alone. A simple model of habitat suitability was developed and fit to the experimental data. The fitted model provided estimates of habitat carrying capacities for two important chironomid species and for a generalized chironomid assemblage. A comparison of these estimates with observed field densities indicated that competitive displacement of individuals probably occurs regularly in sand sediments. An examination of field data from 1975—1976 revealed a suppression of species diversity and of competitor standing crops by the dominant sand species. Together these results suggest that competitive interactions have an important influence on the spatial distribution of chironomid larvae in Hunt Creek.
Detrital Processing and Associated Macroinvertebrates in a Colorado Mountain Stream
Authors: Short Robert A. , Canton Steven P. , Ward James V.
Published: May 2006

Investigation of leaf litter processing in a Colorado mountain stream revealed that processing of alder (Alnus tenuifolia), willow (Salix bebbiana), and aspen (Populus tremuloides) occurred at rapid rates despite water temperatures at or near 0°C. Pine (Pinus ponderosa) was processed much more slowly. The loss rate coefficient (k) ranged from .0038 for pine to .0308 for alder. The high biomass of shredders per gram of leaf pack is a likely explanation for the rapid processing. Whereas a few large shredders per leaf pack are generally characteristic of eastern woodland streams, a large number of small—sized shredders (Capnia and Zapada) colonized leaf packs in the Colorado mountain stream. The numbers and biomass of collectors per leaf pack were directly related (P < .01) to the ash—free dry mass of fine organic particles (75—1000 @mm) indicating the importance of fine particulate organic matter in determining the suitability of leaf litter as habitat for fine particle—feeding detritivores.
A Size‐Distance Relation in Food Selection by Beavers
Authors: Jenkins Stephen H.
Published: May 2006

The relationship between sizes of trees cut by beavers and distances from the borders of their ponds was examined at three sites in central Massachusetts. For most tree genera, the beavers cut a smaller range of sizes far from shore than close to shore, and relatively more small trees and fewer large trees at greater distances. The second of these results differs from the pattern of preference found in other studies in which predators were much larger than their prey, unlike this case of beavers feeding on trees. Both kinds of results are consistent with an optimal foraging model of size—distance relations in which pursuit or provisioning time depends on size of prey as well as distance (Schoener 1979).
The Experimental Test of an Analysis of Field Distributions: Competition In Terrestrial Salamanders
Authors: Hairston Nelson G.
Published: May 2006

Experimental removal of the terrestrial salamander Plethodon jordani from marked plots in the Great Smoky Mountains and the Balsam Mountains of North Carolina, USA resulted in statistically significant increases in the abundance of P. glutinosus in both areas. The increase appeared earlier in the Smokies, where the two species overlap by only 70—120 m. Removal of P. glutinosus the less abundant species, did not result in a statistically significant increase in P. jordani, but did increase the proportion of young in that species. Again, the effect was more pronounced in the Smokies than in the Balsams, where the altitudinal overlap is 1220 m (4000 ft). Stronger competition in the narrow zone of overlap had been predicated on the basis of field distributions, but a measurable level of competition in the wide zone of overlap was surprising. The experiments permitted the direct calculation of coefficients of competition and carrying capacities for both species in both areas. Competition coefficients were higher in the Smokies, but carrying capacities were very similar in the two areas. The experimental approach eliminated the assumptions required for calculating competition coefficients by resource partitioning, and since the experimental design was published before the experiments were begun, the circularity implicit in retrospective analyses was avoided.
Litterfall, Stemflow, and Throughfall Nutrient Fluxes in an Alluvial Swamp Forest
Authors: Brinson Mark M. , Bradshaw Hansel D. , Holmes Russell N. , Elkins Joseph B.
Published: May 2006

Nutrient deposition to the forest floor of an alluvial swamp in the North Carolina Coastal Plain was measured and compared with other wetland and upland forests. For the alluvial forest, annual litterfall was 6428 kg dry mass/ha of which 63% was Nyssa aquatica leaves. Nutrient flux to the forest floor in kilograms per hectare per year for litterfall and aqueous sources (stemflow plus throughfall), respectively, was 2779 and 91.5 for organic carbon, 72.77 and 10.31 for N, 5.38 and 1.55 for P, 7.19 and 921 for S, 21.1 and 11.96 for K, 45.1 and 15.31 for Ca, and 17.0 and 7.60 for Mg. Most of these values are near the upper range or higher than those reported for mature upland temperate forests and still—water swamps. The particularly high values for nitrogen and phosphorus in the alluvial forest may be a consequence of fluvial sources, whereas nutrient sources for upland forests and still—water swamps are restricted to atmospheric inputs and weathering.
Migration in Heterogeneous Environments: Differences in Habitat Selection Between the Wing Forms of the Dimorphic Planthopper, Prokelisia Marginata (Homoptera: Delphacidae)
Authors: Denno Robert F. , Raupp Michael J. , Tallamy Douglas W. , Reichelderfer Charles F.
Published: May 2006

The planthopper, Proklisia marginata, feeds selectively on the intertidal grass, Spartina alterniflora. Populations contain two adult wing forms that vary in proportion from one local area to the next. There are short—winged flightless individual (brachypters) and individuals with fully developed wings (macropters) that fly. Differences in the ability of the two wing forms to select high quality habitats in a heterogeneous environment are measured to elucidate further the advantages of migration (macroptery). Adult planthoppers (both wing forms) occur most abundantly on the parts of individual plants, seed heads in particular, that contain the highest percent crude protein. The percent crude protein in stands of S. alterniflora and the frequency of flowering plants are used as measures of habitat quality and vary considerably over the marsh surface. There is a significant positive relationship between the densities of both wing forms and habitat quality. However, the slope of the regression line for macropters is significantly steeper than for brachypters suggesting that macropters are better able to move from low— to high—quality patches. The relative mobility of wing forms is further documented by the inability of brachypters to colonize small defaunated plots of grass compared to macropters. We suggest variation in habitat quality is unpredictable, that high—quality patches of vegetation may be separated by distances greater than the ambit of brachypters, and that macropters can more effectively track spatial oscillations in habitat quality.
Competitive Interactions between California Reef Fishes of the Genus Embiotoca
Authors: Hixon Mark A.
Published: May 2006

Embiotoca lateralis and E. jacksoni are very similar morphologically and exhibit the greatest dietary overlap within a guild of microcarnivorous subtidal reef fishes off Santa Barbara, California. Within this zone of sympatry, they segregate by depth: E. lateralis numerically dominates shallow reef areas covered by various algae, from which it picks its prey; E. jacksoni dominates and forages over deeper areas covered by a relatively food—poor "turf" of sessile invertebrates and small algae. E. lateralis rarely fed from turf—covered substrates experimentally translocated from deep water, while E. jacksoni frequently fed from translocated shallow algae. In allopatry, however, each species occupies all reef depths and commonly forages over both food substrates. When E. lateralis was experimentally removed from a reef inhabited by both species, E jacksoni entered shallow areas and foraged over algae. However, removing E. jacksoni from another reef did not affect the distribution of E. lateralis. E. lateralis aggressively dominated E. jacksoni, and E. jacksoni avoided foraging near E. lateralis. E lateralis eventually entered and foraged over deep reef ares only when all shallow algae and E. jacksoni were removed. Sympatric population densities of E. lateralis, here at the southern margin of its geographical range, are much lower than those of allopatric populations elsewhere. Hence, shallow food sources may be sufficiently abundant that marginal E. lateralis populations occupy only this richest end of the bathymetric reef food gradient. This situation may provide a competitive refuge for E. jacksoni in less productive deep reef areas, thus maintaining the coexistence of these species within the same habitat.
Predator‐Prey Interactions between Stoneflies and Mayflies: Behavioral Observations
Authors: Peckarsky Barbara L.
Published: May 2006

Field experiments were conducted at two streams to determine the mechanisms by which mayfly prey detect and avoid stonefly predators, and to quantify the effect of stonefly predators upon mayfly behavior, distribution, and activity levels. Direct observations of the interactions between stoneflies and mayflies were made at Otter Creek, Sauk County, Wisconsin, USA and the East River, Gunnison County, Colorado, USA using plexiglass boxes with screen ends and an artificial substrate. Ephemerella subvaria and Stenonema fuscum, Otter Creek, avoided the stonefly predator Acroneuria lycorias given only noncontact chemical stimuli. Ephemerella infrequens and Baetis bicaudatus, East River, Responded to long—range chemical stimuli from Megarcys signata and Kogotus modestus, East River. Baetis phoebus and Heptagenia hebe, Otter Creek, and Cinygmula sp., East River, did not respond to stonefly predators given long—range chemical cues along. Differences among responses of different mayflies may be due to differential predation pressure or effectiveness of predator evasion tactics. None of the species of mayflies tested responded to the presence of stonefly predators given only visual stimuli. The Ephemerella species assumed a "scorpion"—like display posture upon encounter with the stoneflies. This posture may increase the apparent size of the mayflies which are then rejected by the tactile predators. The Baetis species characteristically swam or drifted in response to contact with the stonefly predators. Predator evasion could partially explain the high incidence of this genus of mayflies reported in stream drift. The remaining mayflies, of the family Heptageniidae, showed an effective crawling evasion upon contact with stonefly predators. Ephemerella infrequens and B. bicaudatus differentially responded to contact with three different stonefly predators in the East River. Both species of mayflies evaded contact with Pteronarcella badia, a large omnivorous stonefly which morphologically resembles M. signata, significantly less frequently than they evaded M. signata and K. modestus upon contact. The mechanism by which this differentiation occurs could be chemotactile. Cinygmula sp. avoided all stoneflies equally regardless of size or relative threat of consumption. Tactile stimuli are probably responsible for this behavior.
Nutrient Variation in Beach Grass in Relation to Beach Vole Feeding
Authors: Goldberg Mark , Tabroff Norman R. , Tamarin Robert H.
Published: May 2006

The beach vole (Microtus breweri), found only on Muskeget Island, Massachusetts, consumes different parts of its main food plant, beach grass (Ammophila breviligulata), at different times of the year. Blades are consumed in spring and summer, roots in the late summer and fall, and stems from the late fall through the winter into early spring. This feeding behavior, assessed by food choice experiments, was highly correlated with the fiber, water, and phosphorous content of the plant part. We confirm also the general observation that overall nutritional content (N, P, Mg, Ca) of the blades is high in the spring and early summer when the blades are preferred. This is the period of breeding, and hence maximum nutritional stress.
Energy Flow and Grazing Behavior of Conocephaline Grasshoppers in a Juncus Roemerianus Marsh
Authors: Parson Keith A. , De La Cruz Armando A.
Published: May 2006

At least three species of conocephaline grasshoppers (Tettigoniidae) from the major grazing herbivores on the leaves of the marsh black needlerush Juncus roemerianus Scheele. They ingested 105 kJ/m2 of the 31.62 MJ/m2 net annual aboveground production of Juncus. Assimilation of ingested Juncus tissue was 60.7 kJ°m—2°yr—1 and production of new tissue by the grasshoppers was 9.6 kJ°m—2°yr—1, which represents 0.03% of the net annual primary production. A secondary effect of grazing was manifested by the premature death of portions of the Juncus leaf distal to the grazed area. Subsequent mechanical breakage resulted in early deposition of broken—off leaf tips into the detrital mat on the marsh. This represented a maximum input into the decomposer trophic level of 246 kJ°m—2°yr—1 prior to the death and deposition of the entire Juncus leaf. The addition of Juncus to the diet of the conocephaline post—nymphal and adult stages is discussed in the light of the hypothesis that C4 plants are nutritionally inferior to C2 plants, based on comparisons of amino acid concentrations within different parts of the Juncus leaf and in comparison with Spartina cynosuroides.
Foraging Specialization in Orb‐Weaving Spiders
Authors: Olive Cader W.
Published: May 2006

Previous studies indicate prey—specific attack behaviors in orb—weaving spiders. This study explored functional relationships between the morphology of contrasting orb—weaver species and their prey—specific attack capabilities. Araneus trifolium and Argiope trifasciata were observed attacking acridid Orthoptera, calyptrate Diptera, and Lepidoptera in the laboratory. Diets and habitat use of spiders in the field were determined by surveys. Distributions of prey types were determined by trapping. Araneus captured Orthoptera more quickly than did Argiope, but Argiope was more successful in capturing this prey type. There were no attack time differences between spider species on dipterans and lepidopterans, but Araneus captured these types more successfully. Attack times do not appear to limit prey intake rates in the field. Spider morphology and web design appear to interact in causing the above behavioral differences. Araneus builds its web in high, open sites, usually in herbaceous vegetation. Argiope tends to build its web in low sites in both grassy and herbaceous vegetation. Prey distributions are such that each spider species is found most often in sites where its more successfully captured prey type is relatively more abundant. Predation and physiological stress may also select for these differences in habitat use. If these results are extended to other species, the following predictions arise. Spiders with relatively short, stout legs, large fangs, and high, simple, open—meshed webs (such as Araneus) should specialize on innocuous, rapidly escaping prey types (Diptera and Lepidoptera). Spiders with relatively long legs, small fangs, and low, densely meshed, ornamented webs (such as Argiope) should specialize on dangerous, slowly escaping insects (Orthoptera, Homoptera, Hymenoptera).
The Role of Rhus Copallina in the Dynamics of the Forest‐Prairie Ecotone in North‐Central Oklahoma
Authors: Petranka James W. , McPherson James K.
Published: May 2006

The functional role of Rhus copallina in the tension zone between forests and prairies and the mechanisms which allow clones of this species to replace climax tallgrass prairie were studied in the cross—timbers region of north—central Oklahoma. Measurements and observations indicated that bottomland forest trees were unable effectively to invade climax tallgrass prairie without the prior invasion of R. Copallina or other shrubs. Upland forest tree species, however, were frequently able to invade climax prairie, but these invasions were enhanced by the prior invasion of shrubs. The entry and growth of clones of R. copallina into climax prairie was characterized by a reduction in the density of prairie vegetation and a concomitant increase in tree seedlings, shrubs, and herbs which comprised the nearby hardwood forests. Growth ring counts of nine clones revealed an average rate of encroachment of 1.25 m/yr. The reduced fire frequencies (relative to primeval prairies) on the study area tended to favor the growth of R. copallina clones. Laboratory tests demonstrated that the rhizomes, flowers, fruits, senescent leaves, and leaf litter of R. copallina contain toxins which significantly inhibit either seed germination or seedling growth in both climax prairie and weedy test species. Lighe intensities were found to reach critically low levels in mature, well—formed clones. Seedling response in experimentally manipulated study plots further indicated that both allelopathy and competition for light significantly reduce the number of prairie seedlings underneath clones of R. copallina. Soil moisture and macronutrient content generally were higher within clones so that competition for these factors appears to be insignificant in excluding prairie species from clones.
Genecology of Douglas‐Fir in a Watershed in the Oregon Cascades
Authors: Campbell Robert K.
Published: May 2006

To gain insight into genetic microstructure of subregional populations of coastal Douglas—fir (Pseudotsuga menziesii [Mirb.] Franco var. menziesii), genetic variability in a population found on a 6100—ha, central Oregon watershed is described. Genotypic values of 193 parent trees located throughout the watershed were estimated from progeny grown in a common garden. Then, genetic variation was partitioned into components attributable to parent—tree location and to differences among trees within locations. Within—location variation appeared to be homogeneous in the watershed; between—location variation was related to topography, but the patterns of trait variation differed depending on the trait measured. Growth traits exhibited strong gradients with elevation, but the relationship varied depending on position within the watershed. Based on estimates of proportions of nonadapted seedlings in hypothetical transfers of seed from one part of the watershed to another, genetic differentiation within the watershed was surprisingly large. In one transfer of 3.5 km between north— and south—facing slopes at the same elevation, °80% of seedlings were estimated to be poorly adapted. Although other possibilities exist, the topoclinal variation in traits probably results from selection as does the large within—location variation. Both kinds of variation are due to high selection intensities in the seedling stage, the former to selection by average environmental differences along gradients, the latter to microenvironmental heterogeneity. The combination of high within— and between—habitat variation is suited to a species which episodically colonizes an environment that is extremely heterogeneous in time and space.
Grazing Effects of Four Marine Intertidal Herbivores on the Microflora
Authors: Nicotri M. E.
Published: May 2006

The impact of 4 species of intertidal gastropods (3 limpets and 1 periwinkle) on microalgal species composition and biomass has been evaluated and the degree of overlap of grazer diets has been examined. A series of clay pipes set in a mud flat became artificial substrates for diatom assemblages; grazers were added to the outside of these pipes after an initial period during which the flora developed. The mud proved to be an effective barrier to both immigration and emigration. All 4 gastropods selectively removed 3 diatom species from the pipes: Melosira moniliformis, Melosira nummuloides, and Fragilaria striatula var. californica. These species consist of long chains of moderate—sized cells that form an overstory within the diatom mat; a total of 130 additional species may be found within the diatom community. Selective removal may be facilitated by the chain morphology, by the location of these diatoms in the outermost portion of the mat, and by loose adhesion of these species to the rock surface. Diatoms with potentially tighter adhesion such as the stalked Achnanthes spp. are less affected by grazers. The abundance of 3 species of blue—green algae was little changed by grazing. All 4 grazers had remarkably similar diets, apparently using the same resource in about the same way. Data on the amount of chlorophyll a per m2 on natural rock surface indicate that grazers greatly reduced microalgal standing crops. Differences in grazer zonation and use of macroalgae, coupled with increased food availability during reproductive seasons (winter and spring), allow continued coexistence of these very similar herbivores.
Population Growth Rates and Age Versus Stage‐Distribution Models for Teasel (Dipsacus Sylvestris Huds.)
Authors: Werner Patricia A. , Caswell Hal
Published: May 2006

Mathematical models are developed to examine the population—level response of an herbaceous plant species (teasel, Dipsacus sylvestris Huds.) which was experimentally introduced into several habitats and monitored for 5 yr. Models based on morphological stages (size) rather than chronological age give more satisfactory results. Populations growth rates (λm) range from 0.63 to 2.60, which are likely typical for fugitive plants. Values are interpreted as responses to both external and internal factors. Grass litter, and the presence of other dicotyledonous species, and the overall primary productivity of the rest of the community are important factors determining the success or failure of an attempted colonization by teasel. Individual plant and population—level growth rates seem to be determined independently.
Uptake of Cadmium and Lead by a Rooted Aquatic Macrophyte (Elodea Canadensis)
Authors: Mayes Roger A. , MacIntosh Alan W. , Anderson Virgil L.
Published: May 2006

The role of roots in the uptake of nonessential trace metals by aquatic macrophytes was investigated Elodea canadensis. Plants were grown in 2 lakes in which metal concentrations in the water differed. Specimens in each lake were anchored in either control sediment or in sediment contaminated with Cd and Pb. Plants grown in the same water but in sediment from different sources had significantly different concentrations of the 2 metals. Elodea samples rooted in sediments from the same source but grown in water with different levels of metals also accumulated significantly different amounts of Cd and Pb. Thus the importance of both sediment and the surrounding water as sources of metals for aquatic plants was demonstrated. Samples grown in water and sediment containing low levels of metals had minimal concentrations of 0.32 mg/g Cd and 5.2 mg/g Pb, while plants grown in metal—contaminated water and sediment accumulated up to 32.33 mg Cd/g and 160.9 mg Pb/g.
Ecosystem Dynamics and a Phosphorus Budget of an Alluvial Cypress Swamp in Southern Illinois
Authors: Mitsch William J. , Dorage Carol L. , Wiemhoff John R.
Published: May 2006

Annual patterns in hydrology, phosphorus circulation, and sediment dynamics were studies in a southern Illinois, USA floodplain swamp dominated by bald cypress (Taxodium disyichum) and swamp tupelo (Nyssa aquatica). The study emphasized the swamp's interactions with the adjacent river. For the year, major inputs of water to the swamp were throughfall (74.3 cm) and runoff (69.4 cm) with minor contributions due to groundwater (21.6 cm). Outflows were by evapo—transpiration (72.3 cm), surface outflow (56.5 cm), and groundwater (21.0 cm), with the latter two draining primarily to the river. A flood occurred during the study period, passing 1.6 x 107m3 of river water over the swamp and depositing 0.06 cm of sediments. An annual phosphorus budget was developed for the swamp from field measurements. The greatest input of phosphorus to the swamp was 3.6 g P.m—2.yr—1, due to deposition of high—phorsphorus sediments during the flood. This was 10 times greater than the outflow of phosphorus to the river, 0.34 g P.m—2.yr—1, and 26 times greater than the throughfall input of 0.14 g P.m—2.yr—1. Total tree uptake from sediments was estimated to be 0.87 g P.m—2.yr—1 of which 0.77 g P.m—2.yr—1 returns as litterfall to the swamp sediments. Duckweed productivity was estimated to take 3.3 g P.m—2.yr—1 from the water column and deposit this in the sediments during die—off. For the period 1937—1967, cypress growth, based on tree ring analyses, was closely correlated with several measurements of flooding frequencies and magnitude, all obtained from past river data. Three ring data prior to 1937 showed poor correlation with flooding, probably because of logging activity. Cypress growth has decreased dramatically in recent years, corresponding to the rise in water level caused by beaver activity.
Transport and Transformation of Phosphorus in a Forest Stream Ecosystem
Authors: Meyer Judy L. , Likens Gene E.
Published: May 2006

A phosphorus budget was constructed to examine P retention and processing during 1 yr (1974—1975) in Bear Brook, an undisturbed headwater stream in the Hubbard Brook Experimental Forest, New Hampshire, USA. Year—to—year variation in the P mass balance was also estimated for a 13—yr period using a empirical model of the annual budget. In the model, fluvial inputs and exports of P were calculated using the 13—yr record of streamflow and regressions between P concentration and discharge developed from measurements made during 1974—1976. Precipitation and streamflow were average in the 1974—75 water year, and the relative importance of P input vectors during this year were: tributary streams (62%) > falling and blowing litter (23%) > subsurface water (10%) > precipitation (5%). Geologic export of P in stream water was the only export vector of consequence. Under these average hydrologic conditions, there was no annual net retention of P in the stream: annual inputs of 1.25 g P/m2 were essentially balanced by exports of 1.30 g P/m2. However, during most days of this year inputs exceeded exports: P accumulated, was processed in the ecosystem, and was exported during episodes of high stream discharge. Because of the pulsed nature of P flux, a mass balance provides an overestimate of the P entering functional pathways of a stream ecosystem. Over the 13—yr period (1963—1975), annual mass balances calculated with the model were variable; the ratio of P exports to pinus varied from 0.56 to 1.6 and was directly related to annual streamflow. Thus monthly transport patterns or annual mass balances generated from only 1 yr of record may lead to erroneous conclusions on stream ecosystem function. Although variability characterized most aspects of P dynamics in Bear Brook, processing of P is consistent. Inputs of dissolved P (DP, <0.45 μm) and coarse particulate P (CPP, >1 mm) exceeded exports, while exports of fine particulate P (FPP, 0.45 μm—1 mm) exceeded inputs. (Thus there was a net conversion of other forms of P to the FPP fraction, which was the predominant form (62% of the total) exported downstream.
Size‐Selective Predation on Daphnia by Neomysis Mercedis
Authors: Murtaugh Paul A.
Published: May 2006

Predation on different—sized Daphnia by the crustacean Neomysis mercedis was examined in the laboratory and the field. Small mysids select the smallest prey available, while adult mysids can consume Daphnia as large as 3.0 mm. Laboratory observations and frequencies of injured Daphnia in the lake indicate that difficulty in handling prey sets the upper limit to the size of Daphnia ingested. The pattern of electivity over the manageable size range of prey is variable for large Neomysis, suggesting that the mysids may alter their feeding behavior in response to changing availability of prey. Freshwater mysids apparently consume prey of a broader size range than most other invertebrate planktivores. The opportunities for evolutionary adjustment of body size and morphology in response to mysid predation are relatively limited for zooplankton prey, especially in lakes where visual predators restrict the sizes that can be attained. This limitation may help to explain the apparent effectiveness of mysids in controlling Daphnia populations.
Communtiy Structure and Nutrient Content of Canopy Arthropods in Clearcut and Uncut Forest Ecosystems
Authors: Schowalter T. D. , Webb J. Warren , Crossley D. A.
Published: May 2006

This paper describes differences in canopy arthropod community structure, major cation content, and calculated nutrient consumption between clearcut and undisturbed hardwood forest watersheds at Coweeta Hydrologic Laboratory, North Carolina, USA, during the first two growing seasons following cutting. Although canopy arthropod biomass was about 0.08% of foliage biomass on both watersheds, aphid mass increased 23—fold and ant mass increased 6—fold per unit foliage mass following cutting. These groups in general had lower nutrient concentrations than did chewing herbivores and predators. Arthropod K concentrations were 33% lower on the clearcut; Na, K, and Mg concentrations were 20%—50% higher in 1978 than in 1977. Arthropod Mg and Ca concentrations, but not Na, and K, were reduced significantly more by the greater effect of drought on the clearcut watershed. Consumption estimates based in part on consumption rates reported by others indicated increased nutrient translocation from foliage via arthropods following cutting. These data indicated that canopy arthropod responses in nutrient availability following disturbance could have increased nutrient cycling rates and contributed to nutrient retention by the recovering ecosystem.
Resource Limitation of Larval Treehole Mosquitoes Subsisting on Beech Detritus
Authors: Carpenter Stephen R.
Published: May 2006

Mechanisms of larval population regulation in the detritivorous treehole mosquito Aedes triseriatus were explored experimentally, using laboratory microcosms of the treehole ecosystem. Quantity of beech leaf litter strongly limited growth, survivorship, and development rates of larvae. Little support was found for the hypothesis that an excreted substance causes density—dependent responses of larval A. triseriatus populations. Such an effect, if it exists, is much weaker than resource limitation.
Diversity and Seasonality of Male Euglossine Bees (Hymenoptera: Apidae) in Central PanamÁ
Authors: Ackerman James D.
Published: May 2006

Seasonal changes in species richness, composition, and abundance of male euglossine bees were determined by weekly censusing of individuals attracted to 16 chemical baits. Bee populations were monitored for >1 yr in the lowland tropical moist forest of seasonally dry Barro Colorado Island (BCI), Panama. Male euglossine bees were also censused one every 4 wk at three nearby mainland sites, two at low elevation, and one at a middle—elevation locality. Among the lowland sites the male euglossine bee communities varied little; species composition, dominance ranks, species' phenological profiles, and seasonal changes in bee abundance were similar. Male bee populations at these sites were probably influenced by factors of similar timing and magnitude. In contrast, the male bee community of the upland locality differed from lowlands in species composition and timing of seasonal fluctuations in bee abundance. At all census sites the male euglossine bee community had four genera (Eulaema, Euglossa, Eufriesia, and Exaerete), 33—44 censused species, and low evenness of species abundance. On BCI, the relative abundance of individuals in the four genera was not constant throughout the year. Species richness and bee abundance were correlated; both fluctuated seasonally, and peaked in the early wet season. However, species composition, evenness, and dominance ranks were virtually nonseasonal, so some structural continuity existed in the male euglossine bee community.