bluuebunny/crossref_metadata_2025 huggingface dataset:
Habitat Choice and Phenotype‐Limited Feeding Efficiency in Bluegill: Individual Differences and Trophic Polymorphism
Authors: Ehlinger Timothy J.
Published: May 2006

Individual variation in the foraging behavior of bluegill sunfish (Lepomis macrochirus) was studied in laboratory aquaria containing vegetated and open water habitats. In general fish chose to search for prey in the habitat that provided the highest foraging return, but individuals differed markedly in the degree of habitat selection. Vegetation and open water habitats require different searching techniques for efficient prey detection and individual bluegill differed in their levels of behavioral adjustment to each habitat. Fish using slower searching tactics had the highest foraging rates in the vegetation, whereas individuals searching rapidly fed more effectively in the open water. These behavioral differences in searching rates were found to be correlated with the size of the pectoral fins. Bluegill with longer pectoral fins consistently searched more slowly and spent more time in the vegetation habitat compared to bluegill with shorter pectoral fins. These results indicate that behavioral and morphological variation among individuals can influence habitat—specific feeding efficiency and habitat selection, and may also have direct consequences for models of density— and frequency—dependent habitat selection.
Population Cycles of Western Tent Caterpillars: Experimental Introductions and Synchrony of Fluctuations
Authors: Myers Judith H.
Published: May 2006

To test several of the hypotheses to explain population cycles of forest Lepidoptera, it must be known if the decline phase is related to the local history of the insect population, and if population declines are synchronous among populations in a geographic region. To determine if out—of—phase population cycles could be initiated experimentally, egg masses of western tent caterpillars, Malacosoma californicum pluviale, were introduced to seven sites of low caterpillar density during the increase and peak phases of population fluctuation. The beginning of the decline phase occurred in 1986 in most introduced and source populations, but was delayed until 1987 in three populations initiated from egg—mass introductions in 1984 or 1985. Regardless of the history of the population, or the size and species of food—plant trees, all populations were very low by 1988. In 1986, the year of peak density at most sites, early larva
Hunting Social Wasp Interactions: Influence of Prey Size, Arrival Order, and Wasp Species
Authors: Richter Monica Raveret
Published: May 2006

To determine the effects of wasp species, nest affiliation, arrival order, and prey size on choice of and access to prey and on agonistic behavior among hunting wasps, I observed interactions among Polybia occidentalis and Polybia diguetana (Hymenoptera: Vespidae) prey foragers in Guanacaste, Costa Rica. Wasps were trained to forage on Bagisara repanda (Lepidoptera: Noctuidae) larvae at a test site, and trained wasps were used in experiments. The presence of another forager influenced the choice of an access to prey by hunting wasps. In choice tests, both species preferentially hovered near prey occupied by another Polybia forager rather than unoccupied 0.5—cm pieces of prey, but their subsequent responses differed. Polybia occidentalis foragers tended to land with other Polybia foragers of either species and to gain access to the occupied prey. Polybia diguetana foragers did not land preferentially with other Polybia. In intra— and interspecific tests of wasp pairs, tolerance among wasps varied with prey size. The greatest percentage of highly agonistic activity occurred when the resident was on the largest piece of prey that she had a chance of being able to carry away. As the size of prey increased above that, the percentage of highly agonistic behavior decreased. In intraspecific tests, P. occidentalis foragers did not treat nestmates preferentially. In cross—species tests, both prey availability and the arrival order of wasps affected the tolerance of wasps. There was a lower overall percentage of agonistic behavior in tests where the slightly larger wasp, P. occidentalis, arrived first. Hunting Polybia foragers behaved as if using the following rules: (1) If a forager was able to fly off with prey and avoid conflict, she picked up the prey and fled. (2) She fought if she had a chance of excluding others and monopolizing the prey. (3) If the prey was large, the two foragers split it. Both the defensibility of the prey and the ability of the wasps to take advantage of this defensibility structured the interactions among hunting wasps. These interactions influenced the hunting success of wasps and are therefore determinants of nest productivity. Interactions among foragers thus may bear on the diversity and abundance of social wasps.
Spatiotemporal Differences in 15N Uptake and the Organization of an Old‐Field Plant Community
Authors: McKane Robert B. , Grigal David F. , Russelle Michael P.
Published: May 2006

We investigated the hypothesis that spatial and temporal differences in nitrogen uptake facilitate species' coexistence in a nitrogen—limited, old—field plant community at Cedar Creek Natural History Area, Minnesota. Differences among the six most abundant species were assessed by measuring aboveground uptake of 15N injected at two soil depths at each of three times during the growing season. As described by 15N uptake, species were spatially and, to a greater extent, temporally differentiated into three groups. Differences in species' abundance between and within these groups suggest that spatiotemporal partitioning of nitrogen in a major determinant of community organization. Dominant species (Schizachyrium scoparium and Poa pratensis) were well differentiated and the abundances of subordinate species (Artemisia ludoviciana, Solidago nemoralis, Ambrosia coronopifolia, and Panicum oligosanthes) were positively related to the degree of differentiation from dominant species. A discriminant analysis of the data showed that subordinate species occupy "peripheral" spatiotemporal niches relative to Schizachyrium and Poa. This may promote coexistence by reducing diffuse competition. These results suggest that spatiotemporal resource partitioning slows the rate of competitive displacement among co—occurring plant species. Other research at Cedar Creek corroborates that this is an effective mechanism for coexistence on a successional time scale.
Reproductive Pattern and Mode in the Brine Shrimp
Authors: Browne Robert A.
Published: May 2006

Reproductive performance variables were determined for five diverse strains of Artemia salina, two from the continental United States, two from the Indian subcontinent, and one from Puerto Rico. Significant differences were found through ANOVA for a number of variables including offspring per brood, broods per ♀, offspring per ♀, average zygotes produced per day per ♀ over her reproductive life—span, and total nauplii dry mass output per ♀. In addition, distinct distributional patterns of offspring production over time were found as well as cyst/viviparity proportion shifts with brood number. Regression analysis yielded no significant intra— or interstrain correlations between brood number and offspring survival rates, nor any relationship between the recovery time between broods and either the brood size of the number of broods per ♀. In addition, no significant correlation values were found between any of the reproductive performance variables and the length of time ♀♀ spent in adolescence or senescence. However, the length of time ♀♀ from each strain spent in the reproductive state was found to be significantly positively correlated with the number of broods per ♀, the number of days between broods, and the percentage of offspring that survived to maturity as well as negatively correlated with the percentage of zygotes encysted.
Nutrient Budget Studies for Forests Along an Elevational Gradient in New Mexico
Authors: Gosz James R.
Published: May 2006

Element budgets are presented for watersheds which differ markedly in vegetation biomass, structure, productivity, soil development and hydrology. The net organic matter increment of one of the watersheds has been estimated to be negative. The patterns in the output and net change of Ca, Mg, K and Na among watersheds are related to soil chemistry and stream discharge rates. These factors may not be related to the net organic matter increment of the ecosystem. Actual atmospheric inputs of these elements to some of the ecosystems may be an order of magnitude greater than those measured in bulk precipitation. Nitrogen outputs in stream water are strongly regulated by all of the watershed ecosystems including the one which appears to have a negative net organic increment. Low losses of nitrogen in stream water, however, do not mean a system will minimize other types of N losses (e.g., denitrification). Nutrient budgets generated from bulk precipitation and stream water discharge in the Southwest cannot prove or disprove hypotheses about nutrient regulation by net organic matter increment. Additional inputs (aerosol impaction, weathering, N fixation, NH3 absorption) and outputs (denitrification, aerosols) must be quantified before a valid test can be made of these hypotheses.
Population Biology of a Desert Scorpion: Survivorship, Microhabitat, and the Evolution of Life History Strategy
Authors: Polis G. A. , Farley R. D.
Published: May 2006

The population dynamics of the vaejovid scorpion, Paruroctonus mesaensis were studied over a 4.5—yr period. A time—specific life table is presented. The shape of the survivorship curve is intermediate between Type I and Type II curves. The survivorship of both immature and mature males was significantly lower than that of females. Density—dependent regulation is evident for both immature and mature animals. Population size is stable and fluctuates around an equilibrium point. However, density—independent events can produce severe mortality. Both the net reproductive rate and the maximum rate of increase (rmax) were very low. Population and life history characteristics indicate that P. mesaenis possesses many attributes of an equilibrium or K—selected species. It is theorized that existence in a burrow predisposed the evolution of life history traits associated with equilibrium species.
Sperm Economy in a Coral Reef Fish, Thalassoma Bifasciatum
Authors: Shapiro Douglas Y. , Marconato Andrea , Yoshikawa Tomoko
Published: May 2006

In many coral reef fishes, males face the evolutionary problems of how to allocate sperm among frequent, daily mating in order to maximize the number of eggs they fertilize. A method is developed and tested for collecting and counting the number of sperm and eggs released during separate spawns of the coral reef fish Thalassoma bifasciatum. The method was used to examine the pattern of sperm allocation for pair— and group—spawning males. The number of sperm released by pair—spawning males varied positively with the number of eggs released by their female mates and with female body size. The data suggest that males economize on sperm release by providing the minimum amount of sperm needed to fertilize the egg clutch of the female partner. Fertilization efficiency (the number of eggs fertilized by a given number of sperm) was higher with large females than it was with small females. Males differed significantly among themselves in sperm output per spawn, with some males consistently releasing more sperm than other males with same—sized females. Male—male differences were not due to differences in male body size, quality of the spawning site, or the apparent degree of water movement. The number of sperm released per spawn did not decline throughout the daily spawning period, a pattern that disproved one but not all possible patterns of sperm depletion. In group spawns, the total number of sperm released and the number released per male were respectively 50 and 6 times the number released in pair spawns, on average. Both of these measures increased significantly with the clutch size of the spawning female. Overall, sperm production is probably sufficiently costly that males have been selected to allocate sperm carefully among their frequent daily spawns.
Flexible Larval Growth Allows Use of a Range of Host Sizes by a Parasitoid Wasp
Authors: Harvey Jeffrey A. , Harvey Ian F. , Thompson David J.
Published: May 2006

Recent optimality models of host—parasitoid associations have assumed that host quality varies with host size or age at parasitism. This is based on the fact that larger hosts provide more resources, making size a reliable indicator of the amount of resources available for parasitoid development. Few studies have examined this is parasitoids that allow their hosts to continue development after parasitism (koinobiont parasitoids). In this study we compared growth trajectories of the koinobiont ichneumonid endoparasitoid Venturia canescens developing in four larval instars of one of its host, the moth Plodia interpunctella. Hosts were reared with excess food and parasitized as late second, third, fourth, and fifth instars. Hosts were dissected at intervals after parasitism, and host and parasitoid dry mass determined. The survivorship, development time, and size of eclosing adult wasp were also monitored. Hosts parasitized by Venturia continued to grow and become prepupae, although their maximum masses were progressively smaller the earlier that the hosts were parasitized: second—instar (L2) hosts grew to 70% of control (unparasitized) size, while L4 and L5 hosts reached control size. The maximum larval dry mass, as well as eclosing adult size, varied with host instar at parasitism. Venturia larvae spent prolonged periods as first instars when developing from L2 hosts and grew most rapidly during early stages in L5 larvae.The data show that for Venturia, host quality is not a direct function of host at parasitism. Furthermore, the pattern of development shown by Venturia differs markedly from that shown by aphidiid koinobiont parasitoids.
A Theoretical Framework for Data Analysis of Wind Dispersal of Seeds and Pollen
Authors: Okubo Akira , Levin Simon A.
Published: May 2006

We compared a variety of models for the analysis of data on the wind dispersal of seeds and pollen. Dispersal distances from a source depend upon such factors as settling velocity, height of release, wind speed and turbulence, and specific morphological adaptations for dispersal. The dispersal curve, which describes the frequency distribution of dispersal distances, usually shows its peak at some distance from a source and falls off with distance. We used the location of that peak as a measure of dispersal, and organized data in terms of the predictions of two models for the dynamics of advection and diffusion. These data are summarized in a seed dispersal diagram in which the modal distance normalized by the height of seed release is plotted against the mean with speed normalized by the falling speed of seeds. Data from 15 studies were used to compare actual dispersal relationships.
Acorn Harvesting by Florida Scrub Jays
Authors: DeGange Anthony R. , Fitzpatrick John W. , Layne James N. , Woolfenden Glen E.
Published: May 2006

We documented number of acorns eaten, cached, and retrieved by Florida Scrub Jays (Aphelocoma coerulescens coerulescens), through one full annual cycle and part of another, in an oak scrub habitat characterized by abundant and reliable annual acorn crops. Jays consumed acorns during all months, with highest consumption from September through February and lowest in June and July. From August through December, most acorns consumed by jays were picked directly from shrubs; during the remaining 7 mo, acorns were recovered from ground stores. Acorn caching occurred throughout the fall, peaking in September and October. Data pooled across sex and age classes suggest that individual jays, on average, each cached between 6500 and 8000 acorns during fall of 1974. Only about one—third of those acorns were recovered later. Intact acorns recovered by Scrub Jays during fall usually were reburied, but by summer most recovered acorns were consumed. Acorn crops in the study area exhibit moderate annual variation but no crop failures. Acorns are available in substantial numbers every year, permitting Florida Scrub Jay territories to serve without fail as year—round warehouses of stored acorns. Those stores provide resources to carry group members through seasons of low arthropod availability, and perhaps facilitate delayed dispersal by juveniles. Use of a habitat characterized by relatively large and dependable annual acorn crops that are evenly dispersed, coupled with caching behavior, may contribute to the maintenance of permanent territoriality and cooperative breeding in this population.
Multidimensional Host Distribution and Nonrandom Parasitism: A Case Study and a Stochastic Model
Authors: Casas J.
Published: May 2006

In order to examine the spatial distribution of parasitism I recorded the tridimensional position of each leaf harboring tentiform mines of the leafminer Phyllonorycter blancardella Fabr. (Lepidoptera, Gracillariidae) in different apple trees. The great majority of mined leaves had only one mine. I also recorded which of the hosts had been parasitized and determined each parasitoid species. Using the nearest neighbor (NN) distance between hosts, I tested the hypothesis of spatial randomness of parasitism with Monte Carlo tests for nine parasitoid species. This procedure of characterizing and classifying spatial distributions is borrowed from the statistics on spatial point processes, and it relies on extensive simulations. The distribution of parasitism differs between parasitoid species and between trees, even for the same species. Aggregation of parasitism at low NN distances is by far the most common nonrandom spatial distribution of parasitism. The aggregation of parasitized hosts by the most common parasitoid species, the hymenopteran Cirrospilus vittatus, diminishes with the number of hosts parasitized. I also developed a stochastic model for the spatial distribution of C. vittatus. The model is based (i) on results obtained in the first phase of the work, (ii) on independent information on the oviposition rate, and (iii) on theoretical considerations. They key idea is that a single female produces an aggregated pattern of parasitism (i.e., cluster) during her visit to an apple tree. The combination of spatially independent clusters produces the final distribution of parasitism. The model is evaluated with Monte Carlo tests on data other than those used for its development. Finally, I discuss the statistical assessment, the biological realism, and the generality of the model.
Sources and Influences of Allochthonous Inputs on the Productivity of a Subalpine Lake
Authors: Richey Jeffrey E. , Wissmar Robert C.
Published: May 2006

Allochthonous and autochthonous inputs of soluble reactive phosphate, dissolved organic P, particulate P, dissolved inorganic N, total N, dissolved organic C, and particulate organic C were measured seasonally over a 2—yr period in a subalpine lake of a coniferous forest. Such data have not previously been collected for this lake type. Using a new error analysis technique, nutrient budgets were constructed and analyzed for patterns and relative importance of material flow pathways. Of total annual particulate organic C inputs to the water column of 15.9 g/m2, °83% was allochthonous, mainly from fluvial and snowpack inputs in the spring and litter inputs in the fall. Annual allochthonous inputs of soluble reactive P and dissolved inorganic N averaged 0.12 g/m2 and 2.24 g/m2, respectively; spring fluvial sources provided 33%—50% of these annual incomes. Zooplankton excretion of soluble reactive phosphate was comparable to allochthonous inputs of soluble reactive phosphate, and °18% of total inputs of dissolved inorganic N was autochthonous. Particulate losses were assignable to both fluvial and sedimentation processes, whereas °70% of soluble reactive phosphate and dissolved inorganic N incomes were lost through the outflow and the rest to uptake. Allochthonous dissolved organic carbon inputs (68 g/m2) and allochthonous dissolved organic P inputs (0.21 g/m2) were mostly fluvial and °100% were lost fluvially. These data are related to those of other lakes, and patterns and apparent anomalies are discussed. These results suggest that terrestrial inputs to the sediments, and the subsequent cycling of nutrients in the sediments, have a major influence on biological activity in both benthic and water—column environments during most of the growing season.
Secondary Production, Emergence, and Export of Aquatic Insects of a Sonoran Desert Stream
Authors: Jackson John K. , Fisher Stuart G.
Published: May 2006

Aquatic insect secondary production, emergence, and export of adults to the adjacent terrestrial ecosystem were assessed in Sycamore Creek, Arizona, by means of benthic sampling, emergence traps, and catch—nets that passively sampled adults falling into the stream. Annual secondary production was 120.9 ± 18.0 g°m—2°yr—1 an emergence was 23.1 g°m6—2°yr—1 (in dry mass units). The ratio of annual emergence to annual production (E/P) varied among taxa and ranged from 2 to 29%. Chironomids comprised 48.2% of production and 59.7% of emergence and mayflies accounted for 45.9 and 19.2%, respectively. Approximately 3% of emergent insect biomass returned to the stream; thus 22.4 g°m—2°yr—1 was transferred to the adjacent terrestrial ecosystem. The transfer of a significant portion of aquatic insect biomass to the terrestrial habitat reduced insects available to stream insectivores while providing prey for insectivores in neighboring terrestrial ecosystems.
Granivory in a Desert Ecosystem: Experimental Evidence for Indirect Facilitation of Ants by Rodents
Authors: Davidson D. W. , Inouye R. S. , Brown J. H.
Published: May 2006

Two major groups of desert granivores, ants and rodents, coexist as permanent residents of local desert habitats in southwestern North America. At our Sonoran Desert Study site, both of the major taxa exhibited short—term increase in density when the other taxon was experimentally removed. Over the longer term, density compensation continued at a relatively constant level for rodents in the absence of ants. In contrast, beginning 82 yr after initiation of experiments, ant populations on rodent removal plots showed a gradual but significant decline relative to densities on control plots. Indirect interactions, mediated through ant and rodent resources, may account for these differences. Removal of harvester ants leads to higher annual plant densities only in small—seeded species. These plants are relatively poor competitors and do not displace the large—seeded annuals, on whose seeds rodents specialize. In contrast, rodent removal leads to a differential increase in large—seeded annuals, which competitively displace the small—seeded resource species of ants. The decline of ant populations on rodent removal plots preceded by several years the first detectable evidence for competitive suppression of small—seeded annuals. Because ants do not excavate buried seed, they probably experienced resource depression before buried seed reserves were exhausted through germination and subsequent competitive inhibition.
A Model of Competition for Space
Authors: Slatkin Montgomery , Anderson D. John
Published: May 2006

A simple model of competition among individuals for space is defined and analyzed. Each individual is assumed to occupy a certain area and grow at a specified rate. When two individuals attempt to occupy the same area, one or the other dies. An analytic approximation for the model is developed and tested against computer simulations. The implications of the model for the self—thinning of even—aged stands, for the generation of overdispersed spatial patterns, and for the generation of bimodal size distributions are discussed.
The Effects of Low‐Level Consumption by Canopy Arthropods on the Growth and Nutrient Dynamics of Black Locust and Red Maple Trees in the Southern Appalachians
Authors: Seastedt T. R. , Crossley D. A. , Hargrove W. W.
Published: May 2006

The effects of low—level consumption by canopy arthropods on foliage nutrient content, canopy leachates (throughfall), and biomass of 4—yr—old black locust (Robinia pseudoacacia) and red maple (Acer rubrum) were studied in the southern Appalachians of North Carolina. A carbaryl insecticide was used to reduce foliage consumption from °10 to °2% in black locust and from °4 to °1% in red maple. Phosphorus concentrations in untreated black locust foliage were significantly lower than those of insecticide—treated foliage early in summer, but equalled concentrations of treated foliage by late summer. Potassium concentrations in untreated red maple foliage were significantly reduced during late summer; calcium concentrations in untreated red maple foliage were significantly higher later in the summer. Potassium in throughfall from black locus trees (amount of K collected below the canopy minus bulk precipitation inputs) increases from 5.7 kg/ha for insecticide—protected trees to 9.8 kg/ha for unprotected trees (P < .05). Potassium lossesw from unprotected red maple also increased. Black locust lost 0.3 kg/ha of sulfate—S from untreated trees, but adsorbed 0.4 kg/ha of sulfate—S in insecticide—treated trees (P < .05). Total biomass production (net primary production per kilogram of preseason biomass) was unaffected by the low levels of herbivory observed here. Such nominal herbivory did not stimulate biomass and nutrient accretion by these tree species but did increase the cycling of K and perhaps other elements within these systems.
Treefall Pits and Mounds, Buried Seeds, and the Importance of Soil Disturbance to Pioneer Trees on Barro Colorado Island, Panama
Authors: Putz Francis E.
Published: May 2006

In mature forest on Barro Colorado Island (BCI), Republic of Panama, 0.09% of the ground surface is covered by pits and mounds created by uprooted trees as compared to 14—60% of the ground surface in temperate forests. Newly formed treefall pits on BCI rapidly filled with soil at an average rate of 8 cm/yr. Although pits and mounds rapidly disappeared on BCI, pioneer (gap phase or forest nomad) trees were more concentrated on mineral soil associated with freshly uprooted trees than elsewhere in treefall gaps. There was a large population (742 seeds/m2) of viable buried seeds, primarily of common pioneer tree species, in the top 10 cm of soil in closed forest; these seeds may give rise to many of the pioneers colonizing the disturbed soil. Large treefall gaps are more frequently colonized by pioneer trees than are small treefall gaps, partially because large gaps are more often caused by uprooted, thus soil—disturbing, trees.
Grazing Minnows, Piscivorous Bass, and Stream Algae: Dynamics of a Strong Interaction
Authors: Power Mary E. , Matthews William J. , Stewart Arthur J.
Published: May 2006

Striking differences in pool—to—pool distributions of an algae—grazing minnow (Campostoma anomalum), attached algae (predominantly Spirogyra sp. and Rhizoclonium sp.), and bass (Micropterus salmoides and M. punctulatus) are known to occur in some small Oklahoma streams. This study evaluates the complementarity of bass, Campostoma, and algae at different seasons, and uses in—stream experimental manipulations of bass and Campostoma to determine if the patterns resulted from strong interactions between predators, herbivores, and algae. In a 1—km reach of Brier Creek (south—central Oklahoma), bass and Campostoma distributions in 14 consecutive pools were inversely related in six of seven censuses conducted from 8 November 1982 to 5 September 1983. Bass and Campostoma co—ocurred in more than two pools only on two occasions, following the largest floods of the year. Campostoma and algal abundances were inversely related during late summer and in both autumns of this study. This relationship did not hold during the spring, when floods strongly affected algal distributions. During autumn of 1983, we removed bass from a pool, fenced it longtidinally, and added Campostomata to one side (1.4 individuals/m2). Over the next 5 wk, standing crop of algae decreased significantly on the Campostoma side but increased on the control side. In a nearby unmanipulated Campostoma pool, standing crop of algae was consistently low. We added three free—swimming bass to a Compostoma pool to evaluate presumptive predator—prey interactions. Within 3 h, the Campostoma moved from the deepest part of the pool to shallow areas. Over the next 5 wk, numbers of grazing Campostoma declined due to behavioral changes, emigration, and (presumably) predation. The standing crop of algae increased significantly 10—13 d after bass addition. In a second bass—addition experiment in June 1984, Campostoma responses were almost identical, and algal standing crop in deeper areas increased significantly after 1 wk. Collectively, our censuses and the experiments indicate that in Brier Creek, biotic interactions strongly influence the pool—to—pool distributions of Campostoma and algae, particularly during long periods of constant low discharge.
Cellulose Digestion and Assimilation by Three Leaf‐shredding Aquatic Insects
Authors: Sinsabaugh R. L. , Linkins A. E. , Benfield E. F.
Published: May 2006

The capacity of three leaf—shredding aquatic insects, Pteronarcys proteus (Plecoptera: Pteronarcidae), Tipula abdominalis (Diptera: Tipulidae), and Pycnopsyche luculenta (Trichoptera: Limnephilidae), to digest and assimilate cellulose was investigated. Pteronarcys numphs collected from two second—order woodland streams over a 14—mo period exhibited high levels of cellulolytic activity in their alimentary tracts, especially in the anterior gut. Similar though slightly lower activity levels were measured in Pycnopsyche guts. Cellulolytic activity in Tipula larvae collected from the streams during the same period was low to absent, and when present, was concentrated in the hindgut. General proteolytic activity was activity was similar in the alimentary tracts of all three species. Assimilation of uniformly labelled 14C—cellulose was determined by a dual—label technique, and assimilation efficiencies were estimated at 11.2% for Pteronarcys, 18.5% for Tipula, and 12.0% for Pycnopsyche. Confirmation that labelled digestion products passed the gut wall in two species was obtained by in vitro label transport experiments. Ion exchange fractionation of labelled digestion products crossing the gut wall showed >90% of the label was transported as organic acid and amino acids in Tipula, while >40% of the label crossing the gut wall in Pteronarcys was neutral sugar. Based on the label experiments and published information, we hypothesize that Tipula relies mainly on microbial endosymbionts for cellulose hydrolysis, while Pteronarcys accomplishes hydrolysis largely by means of acquired microbial enzymes obtained through ingestion of microbially conditioned detritus. This study demonstrates the potential for certain leaf—shredding stream insect to derive nutritional benefit from plant polysaccharides, although not without microbial mediation.
Macroinvertebrate Production in a Southeastern United States Blackwater Stream
Authors: Smock Leonard A. , Gilinsky Ellen , Stoneburner Daniel L.
Published: May 2006

Macroinvertebrate production was studied by replicated monthly sampling of five different substrate types at three sites in a second—order South Carolina blackwater stream. Both community—level and species—specific production in the major habitats found above, within, a below a swamp were determined. In addition, total stream production at the three sites was determined using data on habitat availability and habitat—specific production. Production varied among habitats at each site. Production on snags was at least twice as high as that found in any other habitat. Production in the muddy stream banks was higher than in sandy, main channel sediments, but was similar to levels found in the silty main channel sediments within the swamp. Production in leaf packs caught on snags was the lowest found in any of the habitats. High production on the snags was due to filter—feeders and collector—gatherers. The hydropsychid caddisfly Macronema carolina (dry mass of 4.90 g°m—2°yr—1) dominated upstream production on the snags, while the chironomid Tanytarsus sp. was the main filter—feeder on snags within and downstream of the swamp. Collector—gatherers dominated production in the other habitats. Highest production in all habitats was found above the swamp. Filter—feeder production, which was lower within and below the swamp, exhibited the greatest site differences. Total annual stream production, incorporating production from all habitats adjusted according to habitat availability, dropped from 4.11 g/m2 at the upstream site, to 3.09 g/m2 within the swamp, to 1.96 g/m2 below the swamp. The main channel sediments, which accounted for 44, 39, and 42% of production at the three sites, respectively, supported the greatest proportion of total macroinvertebrate production of any habitat. Snag production contributed 32, 35, and 28% of total production at the three sites. Total production from this habitat and from the main channel sediments decreased within and below the swamp. From 40 to 53% of total stream macroinvertebrate production was due to collector—gatherers (especially Polypedilum digitifer, Eurylophella doris, and Tubificidae), while filter—feeders accounted for 13—34% of total stream macroinvertebrate production. Shredders accounted for <5% of total production at each site within this fully canopied, deciduous forest headwater stream.
Energy Costs of Subduing and Swallowing Prey for a Lizard
Authors: Pough F. Harvey , Andrews Robin M.
Published: May 2006

We measured the oxygen consumption (aerobic energy cost) and lactic acid production (anaerobic energy cost) of scincid lizards, Chalcides ocellatus, eating domestic crickets. Aerobic metabolism accounted for 90% or more of the total energy cost of subduing and swallowing prey. The time required to subdue and swallow a cricket was linearly correlated with oxygen consumption. Oxygen consumption increased as a power function of cricket mass, but the maximum size of crickets swallowed by the lizards was set by morphological rather than by energetic constraints. The energy cost of subduing and swallowing was 0.2—0.4% of the utilizable energy of the cricket eaten. Net energy gain per unit time spent subduing and swallowing prey (e/t) declined monotonically with increasing cricket mass. Because the energy cost of eating is trivial, the shape of the e/t curve is determined by the function relating prey mass to the time required for subduing and swallowing; the energy value of prey was proportional to prey mass, whereas the time required for subduing and swallowing increased faster than prey mass. The energy value of anthropods is so high, relative to the costs for a lizard of pursuring, subduing, and swallowing, that these costs can be ignored for most ecological purposes.
Experimental Manipulation of a Desert Rodent Community: Food Addition and Species Removal
Authors: Brown James H. , Munger James C.
Published: May 2006

Since 1977 we have been conducting experiments in which we add supplemental seeds or remove certain combinations of species of seed—eating rodents and ants from 0.25—ha plots in the Chihuahuan Desert of southeastern Arizona. These experiments evaluate the extent to which food availability and interspecific competition influence rodent populations. Monitoring with live traps revealed that: (1) the addition of seed at the rate of 96 kg°plot—1°yr—1 resulted in an increased density of the largest granivorous rodent species (Dipodomys spectabilis), decreases in the densities of the two next—to—largest species (D. merriami and D. ordii), and no detectable changes in the densities of other rodents; (2) the removal of D. spectabilis, as well as other experimentally induced changes in the abundance of this species, resulted in reciprocal shifts in the densities of the two congeneric species, D. merriami and D. ordii, and no significant changes in densities of other rodents; and (3) the removal of all three Dipodomys species resulted in large increases in density of four of the five species of smaller seed—eating rodents, but had no effect on two species of insectivorous rodents. Taken together, these results indicate that limited food resources and interspecific competition pay major roles in regulating the density of rodent populations and determining the organization of desert rodent communities. However, the responses of the rodent populations to our manipulations were unexpectedly complex; they included long time lags, asymmetrical interactions, and little compensation in energy consumption. This indicates how much remains to be learned about the processes that determine the structure and function of even this relatively simple and well—studied community.
Optimal Foraging by Largemouth Bass in Structured Environments
Authors: Anderson Owen
Published: May 2006

The effects of different densities of vegetation on the foraging behavior of largemouth bass, Micropterus salmoides, were examined in the laboratory. Prey encounter rates and handling times and the swimming velocities of the bass while searching for and handling prey were significantly influenced by changes in the amount of vegetation. An optimal—foraging model was then used to predict prey selection by the bass in two environment with identical prey communities but different densities of macrophytes. Consumption of prey by the bass corresponded closely with the predictions of the model. Diet breadths differed between environments, with bass in the sparse—vegetation habitat being more specialized. There was less variance in the foraging behavior of bass in sparse vegetation, and such fish adopted a particular diet more quickly than did their counterparts in dense vegetation.
Plant Fitness Variation Caused by Different Mutualist Genotypes
Authors: Parker Matthew P.
Published: May 2006

This study examined whether mutualism with different genotypes of nitrogen—fixing symbionts affected relative plant fitness in a natural environment. Amphicarpaea bracteata (Leguminosae) plants from eight populations were paired and transplanted into 86 small plots at a field site. Each 16 cm diameter plot contained three plants from each of two populations, and was inoculated with an isolate of Bradyrhizobium from the native site of one of the two host populations (chosen at random). The total seed biomass produced by plants from each host population within a plot was used as a measure of lifetime reproductive success. For three out of the four sets of paired competitors there was a highly significant increase in relative fitness when plants grew in the presence of a Bradyrhizobium isolate from their native population. On average, substituting a native for a non—native bacterial genotype caused a 39% increase in seed biomass per plant (range among eight population, —13% to +182%). These results indicate that differential compatibility of host and symbiont genotypes can be a significant factor controlling the fitness of competing plants in nature.
Diel Pulses of O_2 and CO_2 in Sandy Lake Sediments Inhabited by Lobelia Dortmanna
Authors: Pedersen Ole , Sand‐Jensen Kaj , Revsbech Niels Peter
Published: May 2006

Lobelia dortmanna is a common representative of the small isoetid plants dominating the vegetation on sandy sediments in nutrient—poor softwater lakes in North America and Europe. We report here the discovery of pronounced depth profiles and pulses of dissolved O2 and CO2 in the pore—water of vegetated sediments between light and darkness. Pulses of O2 and CO2 were extensive in the upper sediment layers of high root density, because Lobelia roots absorb CO2 and release O2 during photosynthesis but absorb O2 and release CO2 during respiration, whereas fluxes across leaf surfaces are impeded by a cuticle of low gas permeability. Release of most O2 from the roots during Lobelia photosynthesis leads to O2 concentrations close to saturation in the root zone and O2 penetration to great sediment depth because of low microbial O2 consumption rates. The CO2 concentrations in the root zone of the most nutrient—poor sediments examined here (0.37—0.71 mmol/L) were below the levels required to saturate Lobelia photosynthesis (>3 mmol/L), and experimental enrichment with CO2 stimulated the development of higher O2 concentrations in the root zone. Cycles of O2, CO2 and nutrients are, therefore, intimately coupled in the Lobelia—sediment system, in contrast to terrestrial and other aquatic plants, where gas and nutrient fluxes are physically separated between leaves and roots and their respective surrounding media. The release of O2 from the roots should ensure efficient aerobic degradation or organic matter, lead to oxidized forms of Fe, Mn, and N, and can supply O2 to mycorrhizal fungi and an aerobic fauna associated with the roots.
The Effect of Disturbance Scale on Sand Dune Colonization by Lithospermum Caroliniense
Authors: Weller Stephen G.
Published: May 2006

The effect of varying levels of natural sand deposition on emergence and survival of seedlings of Lithospermum caroliniense (Boraginaceae) was investigated experimentally at four different distances from Lake Michigan. Nutlet mass was varied in the experiments to test for potential interactions between nutlet mass and the degree of sand deposition. On the two rapidly accreting sand dunes closest to Lake Michigan, substantial sand deposition prevented emergence of all but a few seedlings. In two other sites located in stable areas farther from the lake, emergence averaged from 55 to 72.5%. The main effect of nutlet size on emergence was significant, although no interaction with distance from the lake was noted because of the lack of sand deposition at sites distant from the lake. Survival through the first season of seedlings located in one of the stable areas was only 9%, due to desiccation and the burrowing activity of mammals. Survival of seedlings in the other stable area, located on the first dune where naturally established L. caroliniense is found, averaged 36%. Most of these individuals survived to 1985, and fared far better than naturally established individuals located at greater distances from the lake, where lake climatic effects diminish. In a separate experiment, located at the periphery of a localized disturbance known as a blowout, 2—4 cm of sand deposition favored the emergence of seedlings in the two areas closest to the edge of the disturbance. There, seedlings produced by larger nutlets had a disproportionate advantage because of their ability to emerge from greater depths. In the third site, located further from the center of the blowout in a stable area, larger nutlets had no advantage during emergence. These experiments indicate that sand deposition has favored the evolution of increased nutlet mass in L. caroliniense. It appears that a combination of lake climatic effect and moderate sand deposition is most favorable for growth and establishment of this species.
Spatial Heterogeneity and Clonal Structure in Arctic Populations of Apomictic Daphnia
Authors: Weider Lawrence J.
Published: May 2006

Allozymic surveys of obligately parthenogenetic Daphnia pulex from a Canadian high—arctic island revealed high levels of clonal richness in these populations. The present study was conducted to elucidate the underlying spatial patterns of clonal distributions. Three—way G tests of independence indicated significant within—pond spatial and temporal heterogeneity of clones. In addition, spatial autocorrelation analysis indicated significant between—pond patterning of clones,although distributions were patchy. Generally, clones found at low frequencies in a given pond showed restricted distributions, while the most abundant clones were widespread across the island. Principal components analysis revealed that certain clones were distributed differentially in ponds, which varied in size, relative age, and location on the island. The present clonal composition on the island is most likely the result of multiple colonization events during the period of deglaciation. Between—pond clonal distributions are influenced strongly by the probability of passive dispersal of resting eggs (ephippia) via any number of dispersal vectors (e.g., avian, human). Elucidation of the underlying mechanisms that maintain clonal diversity and influence clonal distributions in this Daphnia assemblage requires further study of both deterministic (e.g., selection) and stochastic (i.e., historical) factors.
Seasonal Variation in Feeding Habits of Darwin's Ground Finches
Authors: Smith James N. M. , Grant P. R. , Grant B. R. , Abbott I. J. , Abbott L. K.
Published: May 2006

We investigated the effects of seasonal variation in food abundance on food partitioning among Darwin's ground finches of the genus Geospiza. Finch populations, the availability of seed of fruits, and finch feeding habits were measured during 2 visits to each of 4 study sites on 3 Galapagos islands. Our 1st visit was made near the end of the 1973 rains at a time of seasonal food abundance and the 2nd, 6—8 mo later, when food was scarce. If interspecific competition prevails, finch populations should decline from wet to dry season in response to declining food availability. At 2 sites where food supplies declined sharply, so did an index of finch numbers; at the other 2 sites, both food supplies and finch numbers remained high. Total finch biomass at 5 dry—season study sites was correlated with food abundance but was not at 8 wet—season study sites. If interspecific competition is stronger, diets of finch species should diverge as food becomes scarce, but if intraspecific competition is stronger, diets should expand and overlap among species increase. At all 4 sites, finch species diverged in their diets and took a narrower range of foods in the dry season. All species shifted from a common wet—season diet of soft, easy—to—handle seeds and fruits to different diets reflecting the morphological specializations of each species. The results are consistent with interspecific competition for food occuring at all sides, but other explanations cannot be ruled out. Even where food remained relatively abundant, species diets changed and overlapped less. Intense competition was not, therefore, a necessary condition for seasonal diet changes; these may have been simple proximate responses to food availability. Existing foraging theory does not predict these results or others, because the assumption that available foods do not change qualitatively between seasons is violated. Where food greatly decreased, inter— and intraspecific competition may have caused the death or dispersal of most of the finches in the wet—season populations and diet divergence minimized interspecific competition are probably complemented by year—to—year differences caused by the unpredictable Galapagos rainfall.