bluuebunny/crossref_metadata_2025 huggingface dataset:
The Distribution of Solar Radiation within a Deciduous Forest
Authors: Hutchison Boyd A. , Matt Detlef R.
Published: April 2006

Solar radiation was measured within and above an east Tennessee deciduous forest over a 2—yr period. Diurnal patterns of within—forest radiation follow the temporal variation in incident radiation but become more irregular with depth in the forest because of the highly variable penetration of beam radiation in space and in time. Seasonally, radiation in the forest increases substantially from winter to its annual maximum in early spring as solar elevations increase. Although solar elevations continue to rise each day until the summer solstice, amounts of total radiation and its beam component drop sharply in the forest with the advent of leaf expansion. Diffuse radiation in the forest continues to increase slowly following the onset of leaf expansion but reverses as the forest approaches a fully leafed state. Following the summer solstice, forest structure remains essentially static until abscission while solar elevations decrease. In summer and early autumn, total radiation and both its beam and diffuse components decrease slowly in the forest to their annual minimum in autumn. With leaf abscission and subsequent fall, radiation increases slightly in the forest but soon declines again as solar elevations approach their annual minimum of the winter solstice.
Field Metabolic Rate and Food Requirement Scaling in Mammals and Birds
Authors: Nagy Kenneth A.
Published: April 2006

Field metabolic rates (FMRs or HF), all measured using doubly labeled water, of 23 species of eutherian mammals, 13 species of marsupial mammals, and 25 species of birds were summarized and analyzed allometrically (log10—log10 regressions). FMR is strongly correlated with body mass in each of these groups. FMR scales differently than does basal or standard metabolic rate in eutherians (FMR slope = 0.81) and marsupials (FMR slope = 0.58), but not in birds (FMR slope — 0.64 overall, but 0.75 in passerines and 0.75 in all other birds). Medium—sized (240—550 g) eutherians, marsupials, and birds have similar FMRs, and these are ≈17 times as high as FMRs of like—sized ectothermic vertebrates such as iguanid lizards. For endothermic vertebrates, the energy cost of surviving in nature is enormous compared with that for ectotherms. Within the eutherians, marsupials, or birds, FMR scales differently for the following subgroups: rodents, passerine birds, herbivorous eutherians, herbivorous marsupials, desert eutherians, desert birds, and seabirds. Equations are given for use in predicting daily and annual FMR and food requirement of a species of terrestrial vertebrate, given its body mass.
Population Dynamics of Weddell Seals (Leptonychotes Weddelli) in McMurdo Sound, Antarctica
Authors: Testa J. Ward , Siniff Donald B.
Published: April 2006

Population dynamics of Weddell seals in McMurdo Sound, Antarctica, were studied from 1970 to 1984 using mark—recapture estimation, aerial surveys, age structure and magnitude of harvests, and direct counts of pup production. Similar data from earlier studies were used to reconstruct the history of the population during the period of human presence after 1956. Jolly—Seber estimates of population size indicated a general decline from 1970 to 1976, low numbers in 1976 and 1978, and relative stability from 1979 to 1984 at ≈1500 adult seals. From 1970 to 1983, mean annual survival of adult female and male Weddell seals was estimated at 0.85 and 0.76. Counts made in aerial surveys in the summers of 1982/1983 and 1983/1984 were substantially below similar survey counts in the 1960s. Pup production in the breeding colonies also declined from 1967 to 1976, but has recovered and been stable since 1979. Collections spanning 28 yr indicated significant shifts in age structure characteristic of populations undergoing a rapid increase and then decline. The age structure of both sexes indicated a constant age of recruitment to the adult population at 5 yr, which corresponds closely with age of maturity in females. Generalized least squares and standard regression analyses failed to detect any correlation of adult survival or female reproductive estimates with population size or ice conditions, but there were significant trends in survival estimates from 1970 to 1983 that may be due to shifting age structure. The most plausible interpretation of these data is that heavy harvests of seals to feed dog teams in the mid—1950s severely depleted the resident population of adult Weddell seals. When population studies began in the early 1960s the population was expanding rapidly, probably as a result of immigration by juveniles. The population declined to low levels in 1976—1978 and has been fairly stable since 1979, probably at a level lower than before harvesting began. Survival and reproductive parameters of these Weddell seals are low relative to other pinnipeds, suggesting that the adult population is at an equilibrium with its environment.
Interactions Among Subtidal Australian Sea Urchins, Gastropods, and Algae: Effects of Experimental Removals
Authors: Fletcher W. J.
Published: April 2006

The subtidal region at Cape Banks, New South Wales, Australia, is characterized by large areas covered solely by encrusting coralline algae in association with large densities of invertebrate grazers. Orthogonal removals of these grazers: the sea urchin Centrostephanus rodgersii; the limpets Patelloida alticostata, P. mufria, and Cellana tramoserica; and the turbinids Australium tentiforme and Turbo torquata, were done at two sites and two times to investigate the interactions among these species and their effects on the algal community. These manipulations had large effects on both the algal and animal communities, although the type and intensity of these interactions altered at different temporal and spatial scales. Initially, the removal of urchins and/or all species of limpets resulted in a rapid increase in the amount of noncrustose algae in these areas. Removal of turbinids, however, had no significant effect. Where both limpets and urchins had been removed, the cover of foliose algae continued to increase quickly and was ≈80—100% after 12 mo. In areas where only urchins were removed, the increase in the cover of algae was slower, and only approached 100% after 18—24 mo. Where only limpets had been removed, 3 mo after an initial increase in the cover of filamentous algae the cover declined to be only slightly more than in control areas. These results were similar at all sites and times. In one series of removals, the effects of some of the species of limpets were separated. In this case, the increase in the cover of algae was found to be fastest when only P. mufria was left (the urchins and other limpets removed), than when all limpets and urchins had been removed. Initially, the removal of the urchins generally resulted in a large increase in the recruitment and density of the limpets. Approximately 1 yr following the removal of the urchins,however, the density of adult and juvenile limpets of all species had declined to near zero. Removal of the larger species of limpets, P. alticostata and Cellana, also increased the rate of recruitment of the smaller species, P. mufria. Thus, these invertebrate grazers, especially the sea urchins, appeared to be necessary for the maintenance of the areas of crustose algae. Similarly, the sea urchins were found to be necessary for the continued presence of the limpets within these areas. The strong effects of the urchins on this community, and the application of the situation to theories concerning keystone species and facilitation, are discussed in relation to the important but more subtle effects of the limpets.
Meiofauna‐Macrofauna Interactions in a High Salt Marsh Habitat
Authors: Bell Susan S.
Published: April 2006

Biological interactions between meiofauna and macroepifauna were studied in a high salt marsh habitat using manipulative techniques. When macroepifauna were excluded from experimental cage sites, meiofauna densities increased significantly compared to open, noncaged areas. Meiobenthic polychaetes and copepods displayed consistent, seasonal increases in abundance inside cages, although their patterns of response were notably different. The dominant meiobenthic copepods, Stenhelia (D.) bifidia, Microarthridion littorale, Enhydrosoma propinquum, and Schizopera knabeni, responded to macroepifauna exclusion by rapidly (within weeks) increasing in density inside cages and, subsequently, crashing to control field levels. Polychaetes, represented mainly by Manayunkia aestuarina, increased more slowly than copepods inside cages, and unlike copepods, showed no signs of density limitation inside macroepifauna—excluded areas. In cage sites reopened to macroepifauna influences, copepod densities decreased to values intermediate between cage and open control areas, while polychaetes were quickly reduced to open field densities. The exclusion of macroepifauna not only produced changes in densities of polychaetes, but also resulted in increased survival of large size classes. My experimental results support the hypothesis that acroepifauna predation/disturbance has an important effect on meiofaunal assemblages, thus providing insight into possible competitive associations between meiofauna taxa. The significance of meiofauna—macrofauna interactions in benthic systems is discussed.
Simulation of the Diagenesis of Carbon, Sulfur, and Dissolved Oxygen in Salt Marsh Sediments
Authors: Gardner Leonard Robert
Published: April 2006

A steady—state numerical model has been developed for simulating vertical profiles of the concentrations of organic matter, pyritic sulfur, dissolved oxygen, and the carbon isotope composition of organic matter in marsh sediments.In the model organic matter enters the sediment via sedimentation, belowground production of roots, and chemoautotrophic fixation of interstitial CO2 associated with pyrite oxidation. Pyrite is formed by sulfate reduction and consumed by oxidation with dissolved oxygen in the interstitial water. Exchanges of organic matter, carbon isotopes, pyrite, and dissolved oxygen between the sediment and surface environment occur via fiddler crab bioturbation. Aeration of the sediment is caused by diffusion of oxygen into the interstitial water from air cavities assumed to be present in roots and in desaturated sediment pores formed in the upper part of the sediment by drainage and/or evapotranspiration. Sensitivity experiments with the model suggest that the accumulation of pyrite and organic matter in marsh sediments is governed in large part by the turnover time of roots and by the mean diameter of roots. The isotopic composition of the sediment was most sensitive to the rate of belowground production and to a lesser extent to the intensity of fiddler crab bioturbation. The model also indicated that fiddler crab burrowing can account for the observed isotope composition of creekbank sediments but not back (mid) marsh sediment. In both back and creekbank marshes, intense aeration of the sediment by roots is required to prevent the buildup of pyrite to unrealistically high concentrations at depth.
Fire and Climate Change During the Last 750 Yr in Northwestern Minnesota
Authors: Clark James S.
Published: April 2006

Charcoal stratigraphic analysis and fire scars on red pine (Pinus resinosa) trees were used to determine spatial and temporal occurrence of fire in 1 km2 of old—growth mixed conifer/hardwood forests in northwestern Minnesota. Charcoal was analyzed year by year on petrographic thin sections from annually laminated sediments of three small (≤5 ha) lakes having adjacent catchments. Dated fire scars (n = 150) from recent treefalls provided an independent record of the spatial patterns of past burns. Sedimentology of the varved sediments, water—balance models that use 150 yr of instrumental temperature and precipitation data, and published data were used to identify climate changes in separate studies, and they were used in this study to examine the possible connection between changing fire regimes and climate change. Fire—history data were used to show the changing probability of fire with time since the last fire and the effects of spatial variance (slope and aspect) on the distribution of fires through time. Over the last 750 yr, fire was most frequent (8.6 ± 2.9—yr intervals) during the warm/dry 15th and 16th centuries. Intervals were longer (13.2 ± 8.0 yr) during cooler/moister times from AD 1240 to 1440 and since 1600 (the Little Ice Age). The fire regime during the Little Ice Age consisted of periods during the mid—18th and mid—19th centuries characterized by longer fire intervals of 24.5 ± 10.4 and 43.6 ± 15.9 yr, respectively, and short—term warm/dry periods from 1770 to 1820 and 1870 to 1920 when intervals were 17.9 ± 10.6 and 12.7 ± 10.1, respectively. The probability of fire increased through time, probably in step with fuel accumulation. South— and west—facing slopes burned more frequently than did north and east aspects. Fire suppression began in 1910. During warm periods, probability of fire was sufficiently high that a continuous litter layer was all that was necessary for fire to spread and scar trees. During cool and moist times fire was most likely to occur in years with higher moisture deficits. The combined methods for fire—history analysis provided a more detailed spatial and temporal documentation of fire regimes than has previously been possible from analysis of fire scars or of charcoal counts derived from fossil pollen preparations. Results support predictions of particle—motion physics that thin sections record a local fire history. Because climate varies continuously, the responsiveness of disturbance regime to short— and long—term climatic change suggests caution in the interpretation of fire frequencies that derive from space/time analogies or extrapolation from short—term data.
Patterns, Mechanisms, Consequences of Variability in Settlement and Recruitment of an Intertidal Barnacle
Authors: Raimondi Peter T.
Published: April 2006

I examined the settlement or recruitment of the barnacle Chthamalus anisopoma at a variety of scales: temporally, over periods lasting 12 h to 1 mo, and spatially at sites separated by <1 cm to shores separated by 10 km. Both settlement and recruitment were variable at nearly all temporal and spatial scales that I examined. The majority of variability was attributable to differences in settlement or recruitment between sample periods. When only the spatial component was considered, variability decreased with scale. Large, consistent differences in settlement between geographic locations that are at approximately the same tidal height are probably the result of differential larval supply, whereas more subtle but still consistent differences in settlement between adjacent sites may, at least in part, be due to larval behavior. Differences in settlement between close sites were observed only when settlement was relatively high. This observation may be explained as follows. First, Chthamalus settle in pits or small depressions "suitable settlement sites (SSS's)" in the surface of a substrate. Second, within an SSS, space for settlement is restricted. Third, the density of SSS's differ between sites. When settlement is high, settlement differences between locations reflect differences in the number of SSS's, as all are used. However, when settlement is low, settlement will be similar between locations, since SSS's are not limiting. In a series of field experiments using both natural and artificial substrates I found that: (1) Cypris larvae of Chthamalus settled preferentially in the presence of a number of physical and biological factors. (2) Settlement was density dependent but growth and survivorship were not, which suggests exploitative but not interference intraspecific competition. (Although Chthamalus settle gregariously they space themselves out.) (3) Variability in the settlement of Chthamalus affected the ensuing adult population even at the highest settlement densities.
Hydrology, Community Structure, and Productivity Patterns of a Dystrophic Carolina Bay Wetland
Authors: Schalles John F. , Shure Donald J.
Published: April 2006

A shallow, 5.4—ha dystrophic Carolina bay wetland was studied between 1974 and 1978 to test the premise that biomass and production are constrained by the stagnant hydrology and dilute, acidic chemistry of bay wetlands. Our objectives were to evaluate: (1) surface and subsurface hydrology, (2) sources of production, (3) community change along a depth gradient, and (4) seasonal community patterns. The hydrology study compared surface water levels to groundwater levels in four adjacent wells. A cylinder enclosure and total harvest procedure and 24—h dissolved oxygen curves were used for 2 yr in a 1—ha sampling area to measure spatial and temporal biomass patterns and organic production of community components. Surface hydrology was dependent on seasonal and annual precipitation patterns. Lateral, episodic groundwater exchanges accounted for the dilute surface chemistry and apparent differences in surface gains and losses. Substrate exposure and fire oxidation in dry years promoted low detritus standing crops and a dark, clay—loam mineral soil. A depth gradient, marked by a peripheral grass/sedge zone and central water—lily zone, produced strong spatial patterns for most community components. Aquatic macrophytes had low shoot biomass and a high root to shoot ratio. Algae were light limited and even less productive. Purple photosynthetic bacteria approached algal productivity levels and may have important chemistry and trophic support functions. As predicted from the stagnant, dystrophic conditions, autotroph biomass and production were low. However, the warm climate and periodic fire rejuvenation may stimulate higher production than that generally found in northern bog wetlands. Secondary production was also low. Animal biomass was dominated by insects (especially odonates) and salamanders. High turnover of prey (largely midge larvae and microcrustaceans) was implied by the predator—dominated community structure. This study of a wetland ecosystem lacking several common dystrophic bog features (peat deposit, high dissolved organic matter, acidophilic mosses) enlarges our perspective of the dystrophic condition.
Relative Importance of Habitat Variables in Predicting the Distribution of Phytoplankton at the Ecotone of the Antarctic Upwelling Ecosystem
Authors: Walsh John J.
Published: April 2006

The vertical distribution of phytoplankton standing crop, number of species, and community diversity in five transects across the ecotone of the Antarctic Convergence were studied in relation to physical and chemical habitat variables (light, temperature, salinity, density, relative stability, oxygen, phosphate, nitrate, and silicate) and to bacteria and yeasts. Two distinct phytoplankton communities were observed, one north and one south of the convergence. Within the convergence the southern diatomaceous Antarctic community sinks with the formation of Antarctic Intermediate Water and can be traced underneath the northern dinoflagellate subantarctic community by use of indicator species. Chaetoceros bulbosum, Chaetoceros dichaeta, Dactyliosolen antarctica, and Eucampia zoodiacus were used as indicators of the Antarctic community, and Rhizosolenia delicatula, Amphidinium amphidinoides, Oxytoxum variabile, and Phalacroma pulchellum represented the subantarctic community. Submergence of the Antarctic community is corroborated by the vertical distribution of phytoplankton biomass. South of the convergence in the upwelling system, biomass maxima of the phytoplankton consist of Antarctic species. Within the convergence separate subsurface biomass maxima contain the Antarctic community, and both Antarctic and subantarctic species constitute surface maxima of standing crop. In the upper water of the oceanic system north of the convergence, subantarctic species make up most of the biomass, where as small numbers of Antarctic species were observed in the aphotic zone. Surface layers of the euphotic zone in both systems were dominated by a small number of species. Maxima of species number occurred deeper than those of biomass, possibly reflecting the result of competitive exclusion. A low community diversity was observed in the upper water of each area, and a high ecotonal diversity was found at the convergence. A linear multiple regression analysis showed the relative importance of habitat variables in predicting the vertical distribution of the phytoplankton both within the oceanic and upwelling systems and within their transition zone. Water—mass structure, turbulence, light, silicate, and an index of heterotrophic conditions can be used to predict up to 66% of phytoplankton variation across the convergence. Additional prediction can only be achieved by incorporation of biological rate data and nonlinear expression of variable interaction in simulation models based on the present analysis.
Energetics and Population Dynamics of Diaptomus gracilis
Authors: Kibby Harold V.
Published: April 2006

The population dynamics and energetics of two populations of Diaptomus gracilis have been studied in two Thames Valley reservoirs. The seasonal changes in the standing crop biomass varied from a low of 0.3 Cal/m2 to a high of 7 Cal/m2. Although the population overwintered primarily as adults, reproduction was continuous throughout the year. From the mortality rate the production has been estimated to be 52 and 48 Cal/m2 for the Queen Elizabeth II and King George VI reservoirs, respectively. Feeding and respiratory rates of D. gracilis were measured both in the laboratory and in the field simultaneously with the population dynamics in the reservoir. The feeding rate and the rate of assimilation varied with the species of phytoplankton used as food. Filtering rates varied from 0.1 ml copepod—1 day—1 on bacteria to a high of 2.54 on Diplosphaeria, the latter also having an assimilation efficiency of 78% by D. gracilis. Respiratory rates varied with the season. When the metabolic rate was plotted against body weight, evidence of three regression lines during the year was found, the lowest slope in the winter and the highest in the late spring and early summer. When the regression of oxygen consumption on weight and temperature was calculated, it was necessary to calculate two lines, one for the fall—winter period and one for the spring—summer.
Life History and Energy Relationships of Hydrophyllum appendiculatum
Authors: Morgan Michael D.
Published: April 2006

The phenology of marked Hydrophyllum plants in five permanent 1—m2 plots in Brownfield Woods near Urbana, Ill., was observed from March 1966 through August 1966 and from June 1967 through July 1968. The first—year plant which appears above the soil surface in early spring persists during the entire summer under the closed canopy with two to four erect, solid—colored, palmately shaped leaves. In autumn, mottled, palmately shaped leaves are formed which then overwinter in the form of a basal rosette. The upright, first—year leaves die back with the advent of heavy frosts. The plants break dormancy in early spring with subsequent formation of a large basal rosette of mottled, pinnately shaped leaves. As the forest canopy closes, solid—colored, palmately shaped leaves and an erect stem are formed. Floral buds soon appear. Flowering and seed set take place under a closed canopy with plant senescence occurring approximately 2 months after canopy closure. Carbohydrates are the major form of food reserves (82% of ovendry weight) in Hydrophyllum seed. At least a year is needed after seed dispersal before germination. Accumulated degree—hours and the floral bud and flowering stages are closely related in Hydrophyllum. Low temperatures are important in rosette formation in both greenhouse and field plants, but photoperiod apparently is not important if temperatures remain moderate. Plants will not flower unless they first develop a basal rosette. Although only a relatively short vernalization period is essential, longer periods of low temperature will decrease the length of time needed to flower after the plants have broken dormancy. Floral buds appeared in photoperiods ranging from less than 12 to over 13.5 hr, but longer photoperiods shortened the time interval between breaking dormancy and floral bud initiation. Hydrophyllum is adapted photosynthetically to canopy closure by producing different types of leaves for different light regimes. Plants with only solid—colored, palmately shaped leaves (first—year stage and seed—set stage) are present only under closed canopy conditions Light—compensation point of these plants is 60—80 ft—c, and light—saturation intensity is approximately 700 ft—c. their maximum net photosynthetic rates are about 2.4 mg CO2/dm2 per hour. Mottled, pinnately shaped leaves are present on second—year vegetative plants which grow under an open, spring canopy. These plants have a light—compensation point of 100 ft—c and light—saturation intensity of 2,500 ft—c. Their net photosynthetic rate at light saturation is 8.5 mg CO2/dm2 per hour. Flowering plants, which occur under a closed canopy and usually have both types of leaves, have net photosynthetic rates and light—saturation intensities at intermediate levels between the solid—colored and mottled groups of plants. All phenological stages except the seed—set stage demonstrated small but significant decreases in photosynthesis with increasing temperatures in the 15°—27°C range.
Origin, Composition, and Flux of Dissolved Organic Carbon in the Hubbard Brook Valley
Authors: McDowell William H. , Likens Gene E.
Published: April 2006

The concentration, composition, and flux of dissolved organic carbon (DOC) were measured in the Hubbard Brook Valley, New Hampshire. Data on precipitation, throughfall, soil solution, streamside seeps, stream water, and lake water are presented for 1976—1980. Characterization of DOC included analysis of phenolics, monomeric and polymeric carbohydrates, carboxylic acids, primary amines, and aldehydes. DOC concentrations increased with passage of water through the forest canopy and forest floor, decreased due to abiotic sorption in the mineral soil, and remained relatively low in most "downstream" ecosystems (streamside seeps, streams, and Mirror Lake). Average flux of DOC is estimated as 16, 47, 263, 54, 23, and 20 kg · ha—1 · yr—1 in precipitation, throughfall, soil solution (E, upper B, and B horizons), and streamflow, respectively. The composition of DOC, in particular the relative proportions of carbohydrates, appears to be related to the degree of biological activity at a given site in the landscape. Carbohydrates are particularly high in both absolute and relative terms in throughfall and lake water, which are the areas of highest photosynthetic activity within the terrestrial and aquatic ecosystems, respectively.
Biogeochemical Diversity Along a Riverside Toposequence in Arctic Alaska
Authors: Giblin A. E. , Nadelhoffer K. J. , Shaver G. R. , Laundre J. A. , McKerrow A. J.
Published: April 2006

Nitrogen and phosphorus pool sizes, distribution, and cycling rates were described and compared for six different ecosystem types occurring along a single toposequence in northern Alaska. The toposequence was located on a series of old floodplains of the Sagavanirktok River, in the northern foothills of the Brooks Range. From tussock tundra in the uplands, the toposequence passed through a relatively dry hilltop heath zone, a hillslope shrub/lupine/Cassiope zone, a footslope Equisetum zone, a wet sedge tundra, and a riparian shrub zone. A late—melting snowbank covered the hillslope site in early June of each year, and the sites consistently varied in soil temperature, soil moisture, thaw depth, and the seasonal pattern of soil thaw. The standing stocks of N, P, and C in soils of these six ecosystem types varied dramatically but not monotonically along the toposequence, as did the turnover rates of these elements. Several measures were used in comparisons of N and P availability, including soil solution concentrations, in situ accumulation on ion—exchange resins, and levels of KCI—extractable N and P. Annual rates of net N mineralization were assayed using a buried bag method, and ecosystem respiration was measured by trapping CO2 in soda lime [NaOH + Ca (OH)2]. Soil P pools were characterized by sequential extraction methods into four major pools, including loosely bound P, Al— and Fe—bound P, primary mineral P, and organic P. Both N and P availability were low in all six ecosystems when compared with temperate forests or wetlands. Among ecosystems, however, there was considerable variation in the relative availability of N vs. P, and in the apparent relative importance of nitrate as a nitrogen source.
An Experimental Study of Competition Between Two Species of Dasyurid Marsupials
Authors: Dickman Chris R.
Published: April 2006

This study describes an experimental investigation of the hypothesis of interspecific competition between the dasyurid marsupials Antechinus stuartii and A. swainsonii, conducted between May 1978 and December 1979. Antechinuses were live—trapped, marked, and released in five natural enclosures (four experimental, one control), each established in dense forest along a valley floor in the Brindabella Range near Canberra, Australia. The enclosures were similar in size, shape, vegetation, and climate, and semi—isolated from one another by creeks or by dry, open habitat unsuitable for the marsupials. Antechinus stuartii was removed from two enclosures in July 1978 and later reintroduced to one, whereas A. swainsonii was removed from two other enclosures and later returned to one. Neither species was manipulated in the control enclosure. Comparisons of the population parameters and resource use were made for each species when it occurred in the presence and in the absence of the other. Removal of the larger and more terrestrial species, A. swainsonii, produced several effects on A. Stuartii that were consistent with the interpretation of competition. These included increased numbers; enhanced survival of newly weaned young; increases in extent of movements, home range areas, and use of structurally complex terrestrial habitat; and decreased arboreal activity. The proportion of large, terrestrial invertebrate prey in the diet also increased. The experimental reintroduction of A. swainsonii after ≈8 mo produced reciprocal shifts in most of these parameters. An anomalous finding was that the mean body mass of A. stuartii declined when A. swainsonii was excluded. This was probably due to increased levels of intraspecific interference, since the decline coincided with unusually high population densities in A. stuartii. Competition with A. swainsonii had little evident effect on the time of activity of A. Stuartii. In contrast, manipulations of the numbers of A. stuartii produced no changes in the population parameters of the pattern of resource use of A. swainsonii; hence it was concluded that the competitive effects of A. stuartii on its larger congener are small. Predation, the presence of a superfluous third species (a eutherian rat) during the experiments, and genetical differences between the enclosure populations of Antechinus were rejected as possible alternative explanations of the results; none was as convincing as that of interspecific competition. probably occurs for food, and is therefore most intense in winter, when surface litter invertebrates are scarce. This study demonstrates that competition has asymmetrical effects on the two study species, and challenges the notion that competitive interactions are weak or absent in marsupial communities.
Mechanical Consequences of Size in Wave‐Swept Algae
Authors: Gaylord Brian , Blanchette Carol A. , Denny Mark W.
Published: April 2006

The intertidal zone of wave—swept rocky shores is characterized by high velocities and exceedingly rapid accelerations. The resulting hydrodynamic forces (drag, lift, and the accelerational force) have been hypothesized both to set an upper limit to the size to which wave—swept organisms can grow and to establish an optimal size at which reproductive output is maximized. This proposition has been applied previously to intertidal animals that grow isometrically, in which case the accelerational force is the primary scaling factor that constrains size. In contrast, it has been thought that the size of wave—swept algae is limited by the interaction of drag alone with these plants' allometric pattern of growth. Here we report empirical measurements of drag and accelerational force in three common species of intertidal algae (Gigartina leptorhynchos, Pelvetiopsis limitata, and Iridaea flaccida). The drag coefficients for these species decrease with increased water velocity, as is typical for flexible organisms. For two of these species, this decline in drag coefficient is dramatic, leading to small drag forces with concomitant low drag—induced mortality at plant sizes near those observed in the field. However, all three species have surprisingly large inertia coefficients, suggesting that these plants experience large accelerational forces in surf—zone flows. Preliminary calculations show that these accelerational forces combine with drag to act as a size—dependent agent of mortality, constraining the size of these algae. This study further models the interplay between size—dependent survivorship and reproductive ability to predict the size at which reproductive output peaks. This "optimal size" depends on the strength distribution and morphology of the algal species and on the flow regime characteristic of a particular site. This study shows that the optimal size predicted for G. leptorhynchos, calculated using velocities and accelerations typical of the moderately protected location where this species was collected, closely matches its observed mean size. Similarly, the predicted optimal sizes of P. limitata and I. flaccida at the exposed site where these plants were sampled also match their mean observed sizes. These data, although preliminary, suggest that mechanical factors (in particular the accelerational force) may be important in limiting the size of intertidal macroalgae and that attention solely to biological constraints may be inappropriate.
Diving Behavior and Energetics During Foraging Cycles in King Penguins
Authors: Kooyman G. L. , Cherel Y. , Maho Y. Le , Croxall J. P. , Thorson P. H. , Ridoux V. , Kooyman C. A.
Published: April 2006

King Penguins are the second largest of all diving birds and share with their congener, Emperor Penguins, breeding habits strikingly different from other penguins. Our purpose was to determine the feeding behavior, energetics of foraging and the prey species, and compare these to other sympatric species of subantarctic divers. We determined: (1) general features of foraging behavior using time—depth recorders, velocity meters, and radio transmitters, (2) energetics by doubly labeled water, (3) food habits and energy content from stomach lavage samples, and (4) resting and swimming metabolic rate by oxygen consumption measurements. The average foraging cycle was ≈6 d, during which the mass gain of 30 birds was ≈2 kg. When at sea, the birds exhibit a marked pattern of shallow dives during the night, whereas deep dives of >100 m only occurred during the day. Maximum depth measured from 34 birds and 18 537 dives was 304 m, and maximum dive duration from 23 birds and 11 874 dives was 7.7 min. The frequency distribution of dive depth was bimodal, with few dives between 40 and 100 m. Overall, swim velocities when a bird was at sea averaged 2.1 m/s (N = 5), while descent and ascent rates of change in depth averaged 0.6 m/s for dives <60 m (N = 74) and 1.4 m/s for dives >150 m (N = 90). Night feeding dives occurred at a rate of ≈20 dives/h, and deep dives occurred at a rate of ≈5 dives/h. The energy consumption rate while resting ashore was 3.3 W/kg (N = 3) or 1.6 times the predicted standard metabolic rate (SMR). The average energy consumption rate while away from the colony was 10 W/kg (N = 8) or 4.6 x SMR, compared to 4.3 x SMR estimated from a time—energy budget. The latter value is based on an average metabolic rate of 4.2 W/kg for three birds while resting in 5°C water and 9.6 W/kg while swimming at 2 m/s, which was extrapolated from the average of three birds swimming at 1 m/s. The average energy intake based on 9 stomach content samples was nearly 24.6 kJ/g dry mass. The main prey by number are myctophid fish of the species Krefftichthys anderssoni and Electrona carlsbergi. It was concluded that: (1) feeding begins ≈28 km from the colony, (2) prey is pursued night and day through its vertical movements, (3) vertical distribution of the prey is reflected closely by diving habits of the birds, (4) deep—diving, for unknown reasons, is an important component of foraging success, (5) diving capacities of King Penguins are remarkable compared to other birds and many pinnipeds, and (6) calculated foraging energetics can be closely estimated from time—energy budgets.
Variation of Dispersal Phenology in a Bird‐Dispersed Shrub, Cornus Drummondii
Authors: Willson Mary F. , Whelan Christopher J.
Published: April 2006

Variation in the timing of seed dispersal among individuals of Cornus drummondii was marked at two sites in east—central Illinois. Individuals whose fruit crops were removed most quickly shared few characteristics. Fruit removal rates, dispersal efficiency (percent of total crop removed), and dispersal success (estimated percent of dispersed seeds attributable to each individual) were not closely related to characteristics of the fruits or the immediate environment of the parent plant. Although small fruit crops were often depleted proportionately faster than large crops, dispersal success relative to others in the population was positively related to crop size; i.e., plants with larger crops contributed more seeds to the total pool of dispersed seeds than plants with smaller crops. Over the 4—yr study, individual plants often exhibited between—year differences in ripening time, crop size, and pulp characteristics, but between—year correlations of traits were only sporadically significant. Crop size showed the most consistent between—year correlation (i.e., plants with large crops tended to make large crops in all years), but even this trait was not always correlated between years. Dispersal success was usually correlated between years, but dispersal efficiency was not. Annual (and sometimes site) differences in most dispersal—related plant traits and in dispersal efficiency and dispersal success were common. No plant traits except crop size had consistent effects on dispersal success, although we found some evidence of selective foraging. We suggest that fruit removal may be more a function of avian biology (flocking and social behavior, frequency of foraging interruptions, sun—seeking in cold weather, etc.) than of most characteristics of the fruiting plant. The ecological consequences of differences in dispersal phenology were variable between years. Postdispersal seed predation and germination success showed no consistent seasonal trends. The most important consequence of failure of early fruit dispersal may be a high probability of nondispersal (falling, rotting, being eaten by a predispersal seed predator or poor dispersal agent). Great variation in space and time in the outcome of bird/fruit interactions means that studies directed at the evolution of the interactions need to have both larger samples sizes and longer duration than has been feasible so far.
Nitrogen in West Africa: The Regional Cycle
Authors: Robertson G. Philip , Rosswall Thomas
Published: April 2006

We have calculated a nitrogen cycle budget for West Africa south of the northern Sahara that quantifies biologically important pools of nitrogen in the region and major fluxes associated with these pools. Major compartments of our model include noncultivated systems broken down by vegetation zone, successional status, and plant components; annual and perennial crops each broken down by crop species and plant and harvest components; wetlands; anthropic systems; and soils and sediments. Base reference year is 1978. Biological nitrogen fixation and precipitation fluxes dominated nitrogen inputs to West Africa in 1978. Approximately 12 × 109 kg were fixed in noncultivated systems; about half of this was fixed in early successional (0—6 yr) rain forests, and much of the rest in grazed or fallow savanna grasslands and woodlands. Less than 0.7 × 109 kg were fixed in cultivated systems; legumes accounted for ≈25% of this. Total anthropic sources (fossil fuel combustion, fertilizer production, and agricultural commodity imports) were minor (<0.3 × 109 kg). Precipitation inputs to the region were ≈0.4 × 109 kg. Most nitrogen leaving West Africa did so volatilized by fire (≈8.3 × 109 kg), principally in non—cropped systems. Major losses also occurred via hydrologic export to the Atlantic Ocean (1.5 × 109 kg) and via denitrification (1.1 × 109 kg). Total N losses from West Africa exceeded 11.0 × 109 kg. The nitrogen immobilized in growing woody vegetation appeared to have amounted to ≈5.6 × 109 kg. Most was immobilized in forested regions by vegetation regrowth during the fallow phase of the bush fallow crop rotation cycle, the dominant cropping system in West Africa. A very small amount was immobilized by perennial crops such as cacao and rubber. Net immobilization in soil was not estimated; total soil N was assumed to be in steady state for the region as a whole. Our overall budget balances within 1%, despite independent calculations of all major fluxes. The balance portrays a nitrogen cycle dominated by pools and fluxes in noncropped systems. In contrast to N balances in developed regions, direct anthropic fluxes are a minor part of the West Africa cycle. Indirect human influences, however, mainly through effects on vegetation cover, appear to be a major determinant of both the rates at which nitrogen is cycled in West Africa and the relative importance of most pools and fluxes.
A Predator‐Prey Interaction between Two Physically and Biologically Constrained Tropical Rocky Shore Gastropods: Direct, Indirect and Community Effects
Authors: Garrity Stephen D. , Levings Sally C.
Published: April 2006

The archaeogastropod Nerita scabricosta is an abundant and extremely mobile herbivore which occurs from above mean high water through the mid—intertidal zone of exposed rocky areas along the Pacific coast of Panama. It is the principal prey of Purpura pansa, a patchily distributed, high intertidal neogastropod. Both snails exhibit activity patterns and habitat preference which appear to have evolved in response to heavy predation pressure by fish and to harsh physical factors. These behavioral mechanisms restrict movement and limit foraging time for both species, but also result in a cyclic overlap of their distributions. Potential interaction between the two gastropods is thus limited to well defined, discrete periods. Purpura elicits both an escape and an avoidance response in Nerita. The intensity of predation on the nerite by Purpura is lessened by these responses and Purpura appears unable directly to control the abundance of Nerita. However, it is experimentally shown that in a heterogeneous environment, Nerita's distribution is still more restricted and its local abundance further reduced by avoidance responses to temporally stable aggregations of Purpura. These aggregations, centered on specific fish—safe microhabitat, are thus hypothesized to result in the creation of local patches of intertidal substrate which are free from herbivory or disturbance effects by Nerita scabricosta. Evidence from field observations and manipulations is presented to support the hypothesis that in this complex, four trophic level community, a predator—prey interaction between two gastropods can limit potential resource monopolization and affect primary space occupancy.
Phenology of the Drought‐Deciduous Shrub Lotus scoparius: Climatic Controls and Adaptive Significance
Authors: Nilsen Erik Tallak , Muller Walter H.
Published: April 2006

In regions of mediterranean climate drought deciduousness has been considered an important adaptation for many species. This investigation focuses on the influences of a mediterranean climate on the phenology of a drought—deciduous shrub Lotus scoparius ssp. scoparius. Two research sites were chosen in the Santa Ynez mountains northwest of Santa Barbara, California for the field investigations. Phenological progressions of leaf production, leaf composition, shoot elongation, lateral branch production, and flowering in even—aged stands of Lotus scoparius were correlated with such factors as temperature, relative humidity, soil moisture, plant water relations, and photoperiod. These correlations were determined during a characteristic and uncharacteristic growing season for this mediterranean—climate region. Field correlations were the basis for the design of laboratory experiments in which the influences of photoperiod, temperature, water stress, and total daily photon flux on the phenological development of Lotus scoparius were studied. Climatic controls over Lotus scoparius phenology are complex with water relations and photoperiod having the greatest influence. Photoperiodic control over leaf abscission during water stress, and leaf production following dormancy, were two important phenological phenomena related to the unpredictably fluctuating mediterranean climate of southern California. The complex climatic control over phenology in Lotus scoparius constitutes an adaptation to the California mediterranean climate.
The Indivisible Niche of Tamiasciurus: An Example of Nonpartitioning of Resources
Authors: Smith Christopher C.
Published: April 2006

Tree squirrels in the genus Tamiasciurus are adapted to exploit conifer seeds and fungi in boreal conifer forests. The ranges of the two species in the genus are parapatric, suggesting competitive exclusion. Where their ranges are contiguous in the Cascade Mountains of southern British Columbia, Canada, the squirrels differ in at least five characters which adapt each species to be competitively superior in its range. Two of the characters (alarm calls and fur color) adapt the squirrels to avoid predation and the other three (jaw strength, body size, and reproductive rate) adapt them to exploit the resources typical of their ranges. Two or three of these differences also allow each species to be competitively superior on its side of other sections of the species boundary in coastal British Columbia and northeastern Oregon. The two species from rare hybrids, especially where logging has created disturbed habitats. The pattern of carrying food to storage in a central cache is the basis for both the evolution of territoriality in Tamiasciurus and the absence of sympatry for the two species. In most cases where congeneric territorial species are sympatric and carry food to the center of the territory, they spend most of their time searching for and catching food and relatively little time carrying it. For Tamiasciurus, on the other hand, food is easy to locate and most of the foraging time is spent in carrying food to the cache. Splitting the food niche of Tamiasciurus would involve too large an increase in time and energy for carrying food to be balanced by any gain in feeding and digestive efficiency that could result from specializing on a narrower range of food.