bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of a Host‐Specific Herbivore to Resource Density, Relative Abundance, and Phenology
Authors: Solomon Bruce Peary
Published: May 2006

Ovipositing females of the host—specific herbivorous moth Frumenta nundinella Zeller discriminated among horsenettle (Solanum carolinense L.) plants in the laboratory and at five field populations. In laboratory experiments, the number of larvae that developed in high—density plant groups was not significnatly greater than the number that developed in low—density groups. Consequently, individual plants in low—density groups were disproportionately affected; twice as many larvae developed on them as on individual plants in high—density groups. Moths also discriminated between groups of pure horsenettle (high relative abundance) and groups of horsenettle plus another naturally co—occurring species (low relative abundance). Individual plants in high relative abundance groups had a tenfold greater infestation than did plants in low relative abundance groups. Natural horsenettle populations varied in density, relative abundance, plant size, and fruit production. Plant size, fruit production, and population density were all positively correlated, so the populations with the greatest density had the largest plants, which produced the most fruits. Despite differences in these plant parameters among sites, the extent of infestation differed little, except for one site that lacked parasitoids that attack F. nundinella. Infestation within field sites was heterogeneous among plants. Virtually all large plants (those with @> 15 fruits), but only about half the small plants (those with < 15 fruits), became infested (one or more infested fruit per plant). However, a greater proportion of the fruit crop was infested on small plants than on large plants. Large plants remained in flower an average 2.5 wk longer than did small plants, so a smaller proportion of their flowers was available during the short period of high oviposition risk. Because of the short oviposition period, plants that flowered earlier or later than the mean flowering time of their populations appeared to have lower infestations than did plants that flowered close to the population means.
Role of Organic Debris Dams in Regulating the Export of Dissolved and Particulate Matter from a Forested Watershed
Authors: Bilby Robert E.
Published: May 2006

An organic debris dam is an accumulation of organic matter in a stream which obstructs water flow. Debris dams trap sediments in the pool formed upstream from them and the dam structure itself collects particulate organic matter. This study was done at the Hubbard Brook Experimental Forest, in New Hampshire, to examine the relative importance of these structures in retention of sediment and organic matter in a small stream ecosystem. An experimental approach was used in which all organic debris dams were removed from a 175—m section of second—order stream, just above a gauging weir. The material being exported from the watershed was separated into three size categories: dissolved matter (<0.5 μm), fine particulate matter (0.5 μm to 1 mm), and coarse particualte matter (>1 mm). Export of each size fraction was monitored for at least 1 yr prior to dam removal, and for 1 yr following removal. Following dam removal, export of dissolved matter increased slightly due to an increase in the concentration of dissolved organic carbon in the stream water during periods of high discharge. Fine particulate matter export increased dramatically at high discharges following dam removal; concentrations in some instances achieved values five times higher than any observed before dam removal. Coarse particulate matter export also was greatly increase. Calculating dissolved matter and particulate matter export from the watershed, with an without organic debris dams, showed that dam removal brought about a 6% increase in the export of dissolved matter and a 500% increase in the export of both fine particulate and coarse particulate matter.
Prey Vulnerability and Size Selection by Chaoborus Larvae
Authors: Pastorok Robert A.
Published: May 2006

The planktonic larva of Chaoborus trivittatus (Diptera: Chaoboridae) feeds in an opportunistic manner on all sizes of its major prey, Daphnia pulicaria. Nevertheless, medium—sized prey constitute a greater portion of the diet than would be expected on the basis of their relative abundance in the environment alone. The differential vulnerability of food items is responsible for this apparent size—selection. Vulnerability is defined here as the product of the encounter rate between predator and prey and the capture success of the predator. The rate of encounter increases as a function of prey size, whereas the capture success of the predator decreases with prey size. This leads to a vulnerability curve that is concave to the prey size axis; hence, medium—size items should be overrepresented in the diet when the predator feeds indiscriminately. A model of foraging behavior, which incorporates this concept of differential vulnerability, is used to predict the optimal breadth of diet for Chaoborus feeding on a mixture of prey sizes. Because Chaoborus is an ambush predator, pursuit time is insignificant, and the profitability of prey size i(ei/ti) can be approximately by the joules assimilated from eating an individual of size i divided by the handling time. The energy content of Daphnia increases as approximately the third power of body length. Handling time, defined as the time taken to swallow an item, increases exponentially as a function of prey size. The profitability curve is concave to the prey—size axis, peaking in the middle of the prey size range. However, the foraging model predicts that the larva should include all sizes of Daphnia in its diet within the range of prey densities commonly found in nature. Furthermore, an analysis of the crop contents of C. trivittatus in Lake McDonald and in laboratory feeding experiments supports the hypothesis that larvae are opportunistic feeders on Daphnia; the size composition of the diet can be explained by the relative abundance of prey sizes in the environment weighted by their relative vulnerability. Since vulnerability may be correlated with profitability for many predator—prey combinations, it is possible that many apparent examples of optimal behavior can be explained simply on the basis of the differential vulnerability of prey.
Energy Allocation Patterns of the California Grassland Annuals Plantago Erecta and Clarkia Rubicunda
Authors: King David , Roughgarden Jonathan
Published: May 2006

Allocation models for annual plants predict that reproductive yield is maximized by an instantaneous switch from vegetative to reproductive growth. The switch is timed so that final reproductive yield is equal to the vegetative mass at the time of the switch, provided vegetative and reproductive growth efficiencies are equal. Measured allocation patterns for Plantago erecta and Clarkia rubicunda show a gradual shift from vegetative to reproductive growth in both species. This graded patter results in a 5.5% decrease in reproductive yield for Plantago relative to the theoretical maximum. The timing of that graded pattern appears optimal.
Indian‐Set Fires in the Forests of the Northeastern United States
Authors: Russell Emily W. B.
Published: May 2006

The historical evidence for the Indians' burning the forests of the northeastern United States is reevaluated. Of 35 documents that describe vegetation or Indian life in the 16th or 17th centuries, only half mention any use of fire except for cooking. Only six purportedly first—hand accounts might refer to purposeful, widespread, and frequent use of fire. These six are all consistent with use of fire only locally near camps or villages, or with accidentally escaped fires. It is concluded that the frequent use of fires by the Indians to burn the forests was probably at most a local occurrence. The Indians' presence in the region and their use of fire for many purposes did, however, increase the frequency of fires above the low levels caused by lightning, and thus had some effect on the vegetation; for example, grasses characterized the ground cover at small, local, frequently burned sites.
Resource Enhancement by Indirect Effects of Grazers: Armored Catfish, Algae, and Sediment
Authors: Power Mary E.
Published: May 2006

Armored catfish (Loricariidae) are the major grazers of attached algae in pools of the Rio Frijoles, Panama (9°9' N, 79°44' W). In the dry season, sunny pools were inhabited by °6 individuals loricariids per square metre of grazeable substratum. At these densities, armored catfish depleted algae and cleared sediment from bedrock substrata, leaving sparse standing crops of small, adnate diatoms (primarily Achnanthes spp.). To study the effects of armored catfish at 1/6 their natural density, I stocked four 6—7 cm (SL), 10—g Ancistrus (the most common size class of the most common species in stream pools) in each of five stream pens. Pens enclosed 4 m2 of bedrock substratum, and were alternately stocked or left empty during three consecutive periods of 29, 11, and 11 d. At the end of each period, standing crops of sediment and attached algae, and rates of photosynthesis by attached algae, were measured. The attached algae that developed with sparse Ancistrus had higher standing corps with larger cells or colonies, and higher primary productivity, than did periphyton subjected to heavy grazing by unconfined armored catfish. Even heavy grazing, however, was less deleterious to attached algae than prolonged sedimentation on substrata in enclosures left empty for 11 or 29 d. The net effect of Ancistrus on their algal food changed from depletion at high grazer densities to enhancement at low grazer densities, as sedimentation became more limiting to algae than grazing.
Nutrient Spatial Heterogeneity: Effects on Community Structure, Physiognomy, and Diversity of Stream Algae
Authors: Pringle Catherine M.
Published: May 2006

Nutrient—diffusing substrata (sand—agar plates) were combined with an in situ, flow—through bioassay system to experimentally separate effects of substratum and water enrichment on algal communities in a phosphorus—poor stream in northern Michigan, USA. Glass slides and both control and fertilized sand—agar substrata (N:P ° 16) were exposed to low ambient nutrient levels in a phosphorus—limited stream (N:P ° 40) and to water amended with nitrogen and phosphorus (N:P ° 16). Quantitative cell counts of periphyton taxa and microscopic examination of intact communities on sand—agar substrata indicated that motile biraphid diatom taxa (e.g., Navicula and Nitzschia spp.) responded to nutrients in both the water and substratum, attaining spatial dominance in the upper canopy. These upperstory taxa comprised > 50% total algal biovolume on sand—agar substrata and appeared to interfere with the response of sessile understory taxa (e.g., Achnanthes minutissima, Cocconeis placentula) to inorganic nutrient amendments to the water. Sessile taxa did respond to inorganic nutrients added to the water when growing on glass slides, where algal communities lacked a dense motile upperstory, indicating that substratum type can influence the nature of periphyton taxon response to nutrients. Periphyton community physiognomy and interactions between taxa are interrelating factors regulating algal response to nutrients from different sources. In addition, the form of phosphorus enrichment (inorganic vs. organic) influenced algal growth, physiognomy, and taxon composition. Algal response to the form of phosphorus was dependent on the source of the nutrient (water vs. substratum) and substratum type. Taxon diversity was greater on all nutrient treatments relative to controls on both substratum types. Diversity and species richness were highest on enriched substrata exposed to low ambient nutrient levels, relative to more homogeneous nutrient regimes where communities on enriched substrata were exposed to water amended with nutrients. Results indicate that nutrient spatial heterogeneity between substratum and water is a mechanism maintaining the species diversity of periphytic algae.
Arthropod Prey‐Predator Ratios in a Sagebrush Habitat: Methodological and Ecological Implications
Authors: Lockwood Jeffrey A. , Christiansen Tim A. , Legg David E.
Published: May 2006

A 3—yr study of arthropod prey—predator ratios, based on species richness and density, was conducted in undisturbed and in intensively managed sagebrush habitats in southeastern Wyoming. Using simulated data sets, Bartlett's regression generated significantly more accurate prey—predator ratios than either simple ratios or ordinary least squares, so Bartlett's regression was used for analysis of field data. Both richness and density ratios were generally constant across taxonomic groups (insects, arachnids, and all arthropods) in both undisturbed and managed habitats. Prey—predator richness ratios ranged from 1.18 to 2.36 and were considered temporally and spatially constant in undisturbed habitats. The more sensitive density ratios ranged from 2.23 to 7.77, and showed significant variation in time and space. Herbicide application significantly decreased the prey—predator richness ratios in the treatment year, but the ratios increased the following year. Mowing also decreased richness ratios, but the changes were not significant. Although spatial and temporal heterogeneity prevented determination of valid control for assessing the impact of disturbances on most density ratios, the management practices appeared to have increased prey—predator ratios in the treatment and post treatment years.
Stem‐Growth Periodicity of Trees in a Tropical Wet Forest of Costa Rica
Authors: Breitsprecher A. , Bethel J. S.
Published: May 2006

Stem—growth periodicity of several tree species was investigated in a tropical wet forest of eastern—lowland Costa Rica. The climate of the region is moderately wet and only weakly seasonal. The forest in which the study was conducted is luxuriant, mainly evergreen, and apparently free of recent significant human disturbance. Two sites with differing soil drainage were utilized: a well—drained area and a fresh—water swamp. Radial dendrometers were installed on 27 trees comprising 12 species, and hourly readings were automatically recorded for 20 and 24 mo, respectively. Daily rainfall, air temperature, and relative humidity were monitored; day—length and sun—elevation values were calculated. Five of the eight species studied in the well—drained habitat showed periodic behavior. Their seasonality was mainly annual, but two of four Pentaclethra macroloba had semi—annual rhythms. The periodic trees were well synchronized with one another and with the climatic cycle. All of them exhibited growth cessations that were associated with the drier portion of the year. Each of the two semiannual Pentaclethra underwent an additional interruption during the wet season. All of the trees monitored in the swamp displayed intermittent stem growth. Only one or possibly two trees (both Pentaclethra) had annual periods. The remainder showed cycles that were either longer or shorter than a year. The Pentaclethra were fairly well synchronized with one another and with the drier time of year. Cambial activity of the synchronized trees was inversely related to day length, insolation angle, and air temperature at both sites.
Survival and Mortality in a Population of Adelie Penguins
Authors: Ainley David G. , DeMaster Douglas P.
Published: May 2006

Life table and survivorship estimates were calculated for Adelie Penguins (Pygoscelis adeliae) of known age, sex, and breeding status. Fledglings had been banded and web—punched in nine consecutive breeding seasons at Cape Crozier, Ross Island. During four later seasons the returns of 2— to 14—yr—olds were recorded. Adjustments for band loss and emigration were made in the data. Survivorship estimates were also calculated for the Yellow—eyed Penguin (Megadyptes antipodes) using Richdale's (1949, 1957) data. Results indicate that breeding is risky, especially in the Adelie Penguin and particularly among younger breeders. In both species, females breed at younger ages than males and in any mature age class a greater proportion of females than males breed. These factors result in higher mortality among females and a sex ratio that changes to favor males in the older age groups. The oldest individuals tend to be those that are habitually inept breeders or nonbreeders. The higher annual mortality and shorter life—span in the Adelie Penguin compared to the Yellow—eyed Penguin are probably due in part to heavier predation pressure.
Formulation and Validation of a Mathematical Model of Phytoplankton Growth
Authors: Collins Carol Desormeau
Published: May 2006

A submodel for internal nutrients, critical to prediction of phytoplankton growth dynamics, is described. Process equations were developed to represent storage of nutrients with separate mechanisms for nutrient uptake and assimilation, multiple—nutrient limitation by the threshold hypothesis, and light—dependent photorespiration. These have been incorporated into the ecosystem model MS.CLEANER and calibrated for @Avre Heimdalsvatn, Norway, an ultra—oligotrophic, subarctic lake. The model has been validated for Vorderer Finstertaler See, Austria.
Effects of an Omnivorous Crayfish (Orconectes Rusticus) on a Freshwater Littoral Food Web
Authors: Lodge David M. , Kershner Mark W. , Aloi Jane E. , Covich Alan P.
Published: May 2006

Cascading trophic interactions are important in many freshwater pelagic food webs, but their importance in more complex, omnivore—rich littoral—zone food webs is less well known. We tested the existence of a trophic cascade involving omnivorous crayfish (Orconectes rusticus), macroinvertebrates, periphyton, and macrophytes using 9—m2 cages in the littoral zone of Plum Lake, Wisconsin, USA. Treatments in the replicated (N = 4) experiment were crayfish enclosures, crayfish exclosures, and cageless references. During June—September, we measured macrophyte shoot numbers, macroinvertebrate numbers, and periphyton (on plastic strips) chlorophyll a, and dry mass (DM). We expected that crayfish foraging would directly reduce abundance and change species composition of macrophytes and macroinvertebrates and would indirectly enhance periphyton abundance by reducing the abundance of grazing snails. In enclosures, macrophyte and snail (but not nonsnail macroinvertebrate) densities declined significantly throughout the experiment, whereas densities of macrophytes, snails, and nonsnail macroinvertebrates increased in exclosures and cageless references. Some of the reduction in macrophytes resulted from nonconsumptive fragmentation of macrophytes by crayfish. Consistent with the cascading trophic interactions model, periphyton chlorophyll a per unit surface area increased in enclosures, but declined in exclosures. Periphyton quality (as indexed by chlorophyll a/DM) also increased in enclosures relative to exclosures and cageless references. However, because of large reductions in macrophyte surface area (which periphyton colonizes) in enclosures, total amount of periphyton chlorophyll a in enclosures (relative to exclosures) probably declined while periphyton quality per unit surface area and periphyton quality increased. Thus, the impacts of crayfish omnivory on periphyton, expressed in two conflicting indirect effects, confirm the possibility that omnivory can complicate cascading trophic predictions. Overall, results support the existence of strong trophic interactions in the littoral zone, in which omnivorous crayfish control abundance of macrophytes, snails, and periphyton.
Construction of Multidimensional Clustered Patterns
Authors: Mangel Marc , Adler Frederick R.
Published: May 2006

Ecological processes often depend upon the patterning, as well as the absolute density, of resources. In this paper, we develop methods for describing pattern from the perspective of the organism encountering and exploiting the resources, and for reconstructing pattern from the description. The essence of our description is the “structure function,” which is the probability that a point r units away from the current point contains resources, conditional on the resource state of the current point. We first show how the structure function is determined from pattern and then describe an algorithm (the method of the “Force to be Full” for constructing pattern in any number of dimensions from a given structure function. We illustrate our ideas with empirical data for krill surveys and with simulated but complex three—dimensional patterns.
Interspecific Interactions Among Phytophagous Insects of Tallgrass Prairie: An Experimental Test
Authors: Evans Edward E.
Published: May 2006

Densities of the grasshopper Phoetaliotes nerbrascensis (Acrididae) were manipulated in native tall grass prairie at Konza Prairie, Kansas, to measure competitive and facilitative effects on densities of co—occuring phytophagous insects. In late June 1987, P. nebrascensis nymphs were transferred among enclosed plots (each 550—900 m2) to produce three pairs of plots with grasshoppers either removed or added. Pretransfer densities in the six plots were estimated at °5 nymphs/m2, 2—2.5 nymphs/m2 were then removed or added. Densities of the manipulated species and other abundant phytophagous insects were subsequently monitored (by sweep net) through mid—August. The manipulations in late June resulted in mean densities of P. nebrascensis nymphs 1.5–4 times as large on addition plots as on removal plots; these differences persisted through mid—August. No significant differences between treatments were found, however, in the numbers of individuals of other Acrididae or Tettigoniidae on four post—transfer sampling dates (July to mid—August). Significant differences were also not found in the numbers of individuals of Phasmatidae, Homoptera, or phytophagous Hemiptera and Coleoptera, or in the biomasses of live grass, dead grass, or forbs present in mid—August. 1987 was year of moderate primary production on Konza Prairie. The manipulations produced experimental treatments that mimicked intermediate vs. relatively high natural densities of P. nebrascensis. The results indicate that under these conditions, changes in P. nebrascensis density have little net short—term impact, competitive or otherwise, on the population dynamics of co—occurring grasshoppers or other phytophagous insects.
Suspended Clay and the Population Dynamics of Planktonic Rotifers and Cladocerans
Authors: Kirk Kevin L. , Gilbert John J.
Published: May 2006

The direct and indirect effect of suspended clay on the population dynamics of several species of planktonic rotifers and cladocerans were investigated using long—term laboratory experiments. Life table and population growth experiments showed that high, but naturally occuring, concentrations (50—100 mg/L) of coarse, suspended clay (<2—μm particle size) caused large reductions in the population growth rates (rm) of four cladoceran species (Bosmina longirostris, Ceriodaphnia dubia, Daphnia ambigua, and D. pulex). Juveniles were more susceptible than adult to suspended clay. Low concentrations (10 mg/L) of coarse clay, and high concentrations of fine clay (<1 μm), did not decrease, and sometimes increased, cladoceran population growth rates. Both the inhibitory effects of high concentrations of coarse clay and the stimulatory effects of low concentrations of clay were greater at limiting food (Cryptomonas) concentrations. The population growth rates of four rotifer species (Brachionus calyciflorus, Keratella cochlearis, Polyarthra vulgaris, and Synchaeta pectinata) were not affected by high concentrations of coarse or fine clay, even at very low food levels. The population growth rates of the rotifer K. crassa was decreased by coarse clay. The threshold food concentration (the food concentration, measured as dry mass, at which population growth rate equals zero) of the cladoceran D. ambigua was increased from 0.15 to 0.40 mg/mL in the presence of 50 mg/L coarse clay, indicating a reduced ability to compete in exploitative contests. The threshold food concentration of the rotifer K. cochlearis (0.05 mg/mL) was unaffected by suspended clay. Suspended clay reversed the outcome of two rotifer—cladoceran competition experiments, between K. cochlearis and D. ambigua, and between K. cochlearis and C. dubia. In the absence of clay, the cladocerans dominated; in the presence of clay, the rotifer dominated. The presence of suspended sediments in natural ecosystems, such as turbid lakes and reservoirs, should favor rotifers over cladocerans and thus influence the structure of zooplankton communities.
Microbial Production and Consumpution of Nitrate in an Annual Grassland
Authors: Dividson E. A. , Stark J. M. , Firestone M. K.
Published: May 2006

Gross nitrification rates (calculated by 15N pool dilution) ranged from 12 to 46% of gross mineralization rates during the growing season of annual grasses. Pools of NH4/ and NO3— (measured as N) remained below 7 and 4 mg/g soil, respectively, but turned over about once a day. Microbial assimilation of NO3— occurred at rates similar to previous estimates of plant uptake. hence two common assumptions, that nitrifying bacteria are poor competitors for NH4/ and the microbial immobilization of NO3— is insignificant, are not correct for this grassland system. Soil heterogeneity probably results in NH4/ availability to NH4/ oxidizers at some microsites, while NO3— assimilation by heterotrophic microorganism occurs at other microsites where NH4+ is not available. Relatively high rates of NO3— production and consumption in an ecosystem with an annual mean hydrologic loss of NO3——N of only 3.3 kg/ha indicate the importance of NO3— in the internal N cycle of this ecosystem. Nitrification potential rates, which are an index of population size, declined during the dry season. However, a significant population remained viable when soil water potential was below —9 MPa, indicating that nitrifying bacteria can tolerate severe desiccation. A simple diffusion model demonstrates the dependence of NH4/ availability on soil moisture. Population decline during the dry season may result from both desiccation stress and a lack of substrate availability for maintenance energy of the population. Spatial compartmentalization of sites of production and consumption of inorganic—N, along with diffusional constraints among such microsites, appear to be critical factors affecting N—cycling characteristics of the ecosystem.
Factors Affecting Tissue Nutrient Concentrations in a Scirpus‐Equisetum Wetland
Authors: Auclair Allan N. D.
Published: May 2006

The influence of community and edaphic variables on tissue nutrient concentration was assessed for 6 species occupying a Scirpus—Equisetum emergent wetland in southern Quebec, Canada. Potassium and nitrogen (12.0—23.5 mg/g) had by far the highest tissue concentrations followed by Ca > Na > P > Mg. Micronutrient concentrations (Fe > Mn > Zn > Cu) ranged from .003—.532 mg/g. Macronutrients were 1.3—6 times and micronutrients 2—20 times as great as reported in Carex, Fagus, and Quercus dominated ecosystems. Mean tissue concentrations of N, P and K were consistent between species. Variation was 1/3 (24%) that observed in Ca, Mg and the micronutrients (74%). All elements except Cu, Na, and Zn had closely similar patterns of interspecies variation. Chelation, ion antagonism and increased solubility of micronutrients in flooded soils were possible mechanisms accounting for the unique patterns of Cu, Na, and Zn accumulation. Equisetum fluviatile had the highest level of total nutrients in green tissue. This was over twice that in Phragmites communis which had the lowest level. Moderate tissue nutrient concentrations were observed at both pioneer and mature extremes of a species primary successional gradient. However, compared to the community average, element concentrations were 22.3% higher in pioneer species and 21.9% lower in mature species. Species ordinated by principal components analysis showed wide differences between species. No species occupied a median position in the model. Edaphic parameters were 4 to 5 times important than community structural attributes in varying tissue element concentrations. Soil potassium concentration was the foremost or second most important parameter in 9 to 12 elements tested by multiple regression. It was concentrated in plant tissue 79—fold over levels measured in the soil. This was 4 times the enrichment noted for phosphorus and 12—34 times the enrichment of other micronutrients. Among soil elements, potassium had the highest correlation with tissue P, K, Ca and Mg concentration. Soil calcium had the highest correlation with tissue nitrogen and the micronutrients Cu, Fe and Mn. The concentration of any soil element, however, never explained more than 64% of the variation in any tissue element.
Ecological Relations Among Space, Time, and Thermal Niche Axes
Authors: Tracy C. Richard , Christian Keith A.
Published: May 2006

While the physical environment is often viewed as that with which an organism must contend, and the biotic environment as including resources that may be exploited, interactions occurring between the physical and biotic portions of animal niches suggest that animals also exploit their physical environments. The space and time required for physiological optimal interactions with the environment represent units with which the thermal environment can be quantified as an ecological resource. Characteristics of the thermal environment that an animal experiences within its home range have been incorporated into measures to quantify the quality of the home range with respect to temperature relations, to evaluate the importance of thermal transients to an animal, and to assess temporal aspects of habitat exploitation. Since the thermal environment is physiologically important to animals, and since there can be competition for space and time, this approach provides a bridge between physiological and population/evolutionary ecology.
Inverse Density‐Dependent Parasitism of Cornus Amomum Fruit by Rhagoletis Cornivora
Authors: Borowicz Victoria A. , Juliano Steven A.
Published: May 2006

We tested the prediction that decreased fruit density would lead to decreased parasitism of Cornus amomum fruits by Rhagoletis cornivora flies in a field manipulation. Fruit density following manipulation ranged from no reduction to 88% reduction. We found no evidence of parasitism decreasing with fruit density. Instead, the relationship was inversely density dependent. Although individual tephritid fruit flies concentrate attacks on fruits in areas of high fruit densities, the searching behavior of individual flies apparently does not result in a density—dependent pattern of parasitism at the population level.
Detachment of Egg Masses of a Polychaete: Environmental Risks of Benthic Protective Development
Authors: Wilson W. Herbert
Published: May 2006

Females of the maldanid polychaete Axiothella mucosa attach gelatinous egg masses to the surface openings of their vertical tubes. This study assessed the risks to the embryos due to environmental stresses. In Florida, embryonic development takes 7—8 d, after which the embryos crawl free from the egg mass and assume a benthic existence. Contrary to earlier suggestions, diatoms growing within and on the egg masses do not contribute significantly to embryonic nutrition. By marking cohorts of egg masses , it was shown that most egg masses become detached from the parental tube before natural release of the juveniles. A caging experiment established that water currents, rather than predators or other biological disturbances, are the cause of detachment. Detached egg masses often become abraded, resulting in the early release of embryos, prematurely released embryos showed significant reductions in survivorship relative to late—stage embryos released artificially. On average, detached egg masses produced less than half the number of juveniles released from egg masses that developed entirely in the laboratory in the absence of environmental stresses and from egg masses that remained attached in the field to the parental tubes. Thus, physical factors that cause detachment impose a significant reduction in the number of juveniles released. Encapsulation of embryos does not guarantee high survivorship of those offspring.
Interactions in Microhabitat Use between Dipodomys Ordii and Onychomys Leucogaster
Authors: Rebar Cindy , Conley Walt
Published: May 2006

Hypothesis attempting to explain structure in desert rodent assemblies have emerged primarily from studies dealing with heteromyid interactions. Little attention has been given to the cricetid elements in the community, despite their often high densities and year—round activity in close association with heteromyid species. This study extends the understanding of desert rodent assembly dynamics by examining interactions in microhabitat use between Dipodomys ordii (Heteromyidae) and Onychomys leucogaster (Cricetidae). Research was designed to test the hypothesis: in a two species (experimental) enclosure, microhabitat use by each species will not differ from that in one species (control) enclosures. Results indicate that D. ordii shifts microhabitat use when co—occurring with O. leucogaster, while the reverse does not occur. This outcome shows that interactions are operating between these two species. Further, studies and aimed at determining presumed structure among desert rodent species may be lacking information on significant nonheteromyid elements of the community.
Species‐ and Age‐Specific Differences in Bacterial Resource Utilization by Two Co‐Occurring Cladocerans
Authors: Pace Michael L. , Porter Karen G. , Feig Yvette S.
Published: May 2006

The trophic interaction between zooplankton and bacteria was examined to determine how this food web linkage varied with resource abundance and consumer species and age. Life table experiments and feeding—rate measurements were conducted with two species of co—occurring cladocerans, Daphnia parvula and Ceriodaphnia lacustris. Cohorts of these cladocerans were followed from birth to death and fed either no food (particle—free lake water), natural bacteria only (1—μm filtrate of lake water), whole lake water, or lake water enriched with 104 cells/mL of the green algae Chlamydomonas reinhardi. By comparing cohorts grown in lake water to those grown in enriched lake water, we also determined the extent of food limitation in the natural populations of these two potentially competitive species. As bacterial densities increased from winter through summer, the ability of the larger species, Daphnia parvula, to grow and reproduce on the bacterial fraction also increased. Bacteria, however, were never a primary resource for Daphnia. The rate of population increase (r) was always negative even at the highest in situ concentrations of bacteria (1—2 ° 107 cells/mL). The smaller species, Ceriodaphnia lacustris, was able to increase (° K 0.070) on bacteria alone at lower bacterial concentrations (5 ° 106 cells/mL). Ceriodaphnia juveniles had the highest age—specific survival rates (lx) on bacteria. The improved survivorship was not due to higher feeding rates on bacteria by Ceriodaphnia. Neither age nor species when adjusted for the effect of body mass accounted for a significant portion of the variance in filtering rates on bacteria. Natural field food concentrations were always suboptimal, based on comparisons of growth rates, reproduction, and ° values for the cohorts grown in lake water vs. enriched lake water. Rates of increase (°), however, were always substantially greater than zero in the lake water treatment for both species, indicating that food is not the primary factor that causes seasonal declines of the cladoceran populations in this lake. These results demonstrate a differential utilization efficiency of the smallest resource size—classes by these two zooplankton species. The experiments also indicate the dynamic nature of the trophic interaction between zooplankton and bacteria. The strength of this food web pathway varies with both the seasonal abundance of bacteria and the age, size, and type of zooplankton consumer.
Application of Genotype‐Environment Interaction Analysis to Niche Quantification
Authors: Garbutt K. , Zangerl A. R.
Published: May 2006

Current methods of calculating niche breadth are often inadequate for plant study. Classical analysis techniques of genotype—environment interaction are offered as a better method of quantifying the niches of organisms, particularly plants. The analysis which is widely used in the fields of genetics and crop and stock breeding can be used to examine ecological relationships between genotypes in a population, populations of a species, or species within a community. The analysis gives measures of the relative niche breadth (equability) and magnitude of response between organims being compared. All that is required for input into the analysis is the performance of each organism (entity) in a number of environments (states). Quantification of the environment is not necessary and different resource gradients can be lumped together in a single analysis. A step—by—step description of the analysis is given. The techniques are demonstrated with two examples, one using a hypothetical data set and the other employing data from the classic experiments of Clausen, Keck, and Hiesey on Potentialla glandulosa. This analysis has advantages over classical niche metrics in that the magnitude or level of response of organisms is measured as well as the breadth of response.
Alternative Defenses against Herbivores in Inga (Fabaceae: Mimosoideae) over an Elevational Gradient
Authors: Koptur Suzanne
Published: May 2006

Inga densiflora and Inga punctata have foliar nectaries that promote protection against herbivores by ants. Nectar—drinking ants were found to be less active at higher elevations than at lower elevations in Costa Rica, and ant defense less effective in upland populations of these trees. Herbivore damage to leaves was greater at higher elevations than at low elevation, although the abundance of lepidopteran larvae was not different. This study tested the hypothesis that lack of ant defense in Inga at high elevations is compensated for by alternative defenses. Upland I. densiflora and I. punctata had higher concentrations of phenolics in their leaves than their lowland counterparts. Extrafloral nectaries were found to be present and actively secreting nectar on plants at high as well as at low elevations. Adult wasp and fly parasitoid presence at nectar sources was greater at high elevations in the absence of ants, and parasitization o caterpillars reared from upland Inga was significantly higher than in those reared from lowland Inga. Thus, upland caterpillars on Inga are more vulnerable than those at low elevations to predators and parasitoids attracted to nectar, because at high elevations less of the nectar is taken by ants. The antiherbivore properties of upland Inga represent a novel complex of facultative defenses in the absence of protection by ants.
Using Time and Energetic Measures of Cost in Estimating Prey Value for Fish Predators
Authors: Stein Roy A. , Goodman Cheryl Gosse , Marschall Elizabeth A.
Published: May 2006

In the predator—prey interaction between redear sunfish (Lepomis microlophus) and benthic, freshwater snails (Physa, Helisoma, and Oxytrema), we document selective predation among genera and sizes of prey and use optimal foraging theory in an attempt to explain diet selection. In experiments, sunfish strongly selected against Oxytrema and weakly discriminated between Physa and Helisoma, with Physa most often chosen; size selection within any genus did not occur. Among genera, selection results were consistent with differences in shell strength and a time cost/benefit (C/B) construct operationally defined as handling time divided by prey dry mass. Within any genus, neither shell strength (smallest snails had weakest shells) nor time C/B (largest snails had minimal C/B) provided predictions consistent with results from selective—predation experiments. To explain this discrepancy, we measured metabolic costs of handling and energy content of prey. Dividing net energy of prey (E, generated by subtracting the energetic costs of handling from prey energy content) by handling time (T) yielded values of E/T that were similar for Physa and Helisoma. Within either genus, E/T was always highest for largest snails. Thus, this construct also provided predictions inconsistent with our experimental results. Only an energetic C/B ratio, in which the energetic costs of handling were divided by the energetic value of the prey, was consistent with selection of Physa over Helisoma and no size selectivity within either genus. Whether predators add prey to their diet based on this construct is unknown at present. The lack of concurrence between theoretical predictions of how prey should be ranked by predators (i.e., according to energy gained per unit time expended) and our experimental results suggests these constructs should be re—evaluated. Unless we know the discriminatory ability of our predators (in terms of how fine a difference in prey they can assess) and the currency used in making decisions, C/B or E/T constructs provide little insight into diet selection by predators.
Rates of Tree‐Island Migration, Colorado Rocky Mountains, USA
Authors: Benedict James B.
Published: May 2006

Rates of spruce (Picea engelmannii) and fir (Abies lasicocarpa) tree—island migration were estimated by radiocarbon dating the trails of dead wood left by three krummholz tree islands as they moved downwind across the forest—tundra ecotone on Niwot Ridge, Colorado Front Range. The leeward ends of the tree islands have expanded eastward at average rates of 1.5 to <2.6 cm/yr due to rooting of low horizontal branches; the windward ends of the tree islands have receded eastward at average rates of 0.9 to 1.9 cm/yr due to needle death by freezing or desiccation. The trees are in equilibrium with their environments, or are becoming elongated. Long—term movement rates determined by radiocarbon dating are lower than short—term rates estimated from annual measurements of leeward shoot growth. Changes in the direction of tree—island migration with time show no consistent trends that can be used to reconstruct past changes in winter wind direction. Errors in archaeological radiocarbon dates resulting from prehistoric use of old tree—island wood for fuel are unlikely to exceed 100 yr in the Front Range timberline environment.
Competition Between Two Spider, Species: Experimental Field Study
Authors: Spiller David A.
Published: May 2006

To test for interspecific competition between two common orb—weaving spiders, Metepeira grinnelli and Cyclosa turbinata, I conducted a controlled competitor—removal experiment in the field. Metepeira prey—consumption rate and fecundity were higher in plots where Cyclosa were removed than in control plots. Cyclosa density and vertical distribution were higher in plots where Metepeira were removed than in control plots, but Cyclosa prey—consumption rate was not higher in the removals. A separate food—supplement experiment, conducted while the competitor—removal experiment was in progress, showed that food was a limited resource for both species. During this experiment, Metepeira often displaced and sometimes killed Cyclosa, but Cyclosa were never observed displacing Metepeira. The experiments suggest that exploitation was probably the predominant mechanism responsible for the effects of Cyclosa on Metepeira, whereas interference was probably the major mechanism responsible for the effects on Meteperia on Cyclosa. During this study, interspecific competition between spiders was significant and appeared to play an important role in structuring their community. However, other experimental studies have found no evidence of interspecific competition between spiders. Predators or abiotic sources of mortality may have been reducing the spider populations during these other studies, reducing competition. I suggest that the abundance of predators of spiders was low at this study site because of physical constraints.
The Dynamics of Chemical Elements in Forest Litter
Authors: Laskowski Ryszard , Niklinska Maria , Maryanski Maciej
Published: May 2006

Litter bags with natural mixed litter were incubated until °60—70% mass loss in two oak—hornbeam and two pine—beech forest stands in southern Poland. At the same stands the input of chemical elements with throughfall was followed. Decomposition constants k for the oak—hornbeam litters were —0.57 and —0.55, and for the pine—beech litters —0.30 and —0.27. Chemical elements (except for Cu and Mn) revealed similar relative mobility in the four litters. On average the elements could be ordered by decreasing mobility as follows: K > Mg > Ca > S > Cu > Na > Mn = N > Cd > Pb = Zn > Fe. Instead of the two presupposed factors controlling litter decomposition, biological and chemical, three factors were specified: (1) biological, dominating the decay of organic matter and the dynamics of N, Ca, Mg, Mn, and S; (2) physical, dominated by leaching and atmospheric deposition, and controlling the dynamics of organic matter, K, Na, Pb, Cd, and Zn; and (3) chemical, determining the dynamics of Fe, Zn, Pb, and Cd through the fixation of metal ions to humic substances. Potassium was the only element that decreased in concentration in all litters, while the concentrations of N, Na, Fe, Zn, Pb, and Cd increased in all litters. S. Ca, Mg, and Mn concentrations revealed different patterns in different litters, presumably due to the differences in initial concentrations and soil acidity. No clear trend was found for Cu. In all litter types, Fe, Zn, Pb, and Cd significantly increased in absolute amounts at the end of litter—bag incubation. In all four stands the input with throughfall was high enough to explain the increases in amount of elements, with the exception of Fe in the oak—hornbeam litters.
Interspecific Competition among Phloem‐Feeding Insects Mediated by Induced Host‐Plant Sinks
Authors: Inbar Moshe , Eshel Amram , Wool David
Published: May 2006

The role of interspecific interactions among herbivorous insects is considered to be limited, especially in specialist communities. In the current study we report on exploitative interspecific interaction between two closely related phloem—feeding species of gall—forming aphids (Homoptera; Pemphigidae; Fordinae), mediated by the supply of photoassimilates from the host plant. Geoica sp. forms a spherical gall on the leaflet midrib of Pistacia palaestina (Anacardiaceae), while Forda formicaria forms crescent—shaped galls on the leaflet margin of the same host plant. Using 14C labeling, we were able to trace the food supply (assimilated carbohydrates) from the leaves to galls of each species. We found that Geoica galls are strong sinks. These galls divert the normal phloem transport of the plant and reduce the amount of assimilates imported by F. formicaria, especially when they are located on the same leaflet. By the end of the season Geoica caused death of 84% of F. formicaria galls that were located on the same leaflet, and reduced reproductive success in the surviving galls by 20%. This is because the presence of Geoica causes early senescence (but not abscission) of the leaflet it is on (whether or not F. formicaria is present). The interaction is asymmetrical: F. formicaria did not affect reproductive output of Geoica nor did it cause visible damage to the leaflets. To our knowledge, this it the first demonstration of exploitation competition for plant assimilates between two insect—induced sinks. This exploitative competition, mediated by manipulation of plant phloem transport, stands in contrast to the absence of interference competition for galling sites between the two aphid species. Although their spatial distributions partly overlapped, the niche breadth of each species (measured from gall positions on leaves along the shoot axis) was not affected by the presence of the other. Moreover, when both species were located on the same leaf, they formed galls independently on the same or different leaflets, and there was no indication of interference competition over galling sites.