bluuebunny/crossref_metadata_2025 huggingface dataset:
Avian Predation Risk Modifies Breeding Bird Community on a Farmland Area
Authors: Suhonen Jukka , Norrdahl Kai , Korpimaki Erkki
Published: May 2006

In farmland areas of western Finland more than four—fifths of breeding birds are migratory species, mostly small passerines. Migrants arrive at their breeding areas later than their main avian predators, European Kestrels (Falco tinnunculus). We provide evidence that avian predators are a major factor modifying the breeding bird assemblage of a large field. The distribution of kestrels (hence, predation) was manipulated using nest boxes, which are the only nesting places in open farmland. We counted birds on nine 25—ha plots in which a kestrel pair bred, and on nine control areas situated > 1000 m from the nearest kestrel nest in large agricultural fields during early summer 1992. We also counted birds on 15 transect lines (length 1000 m, width 100 m) radiating away from kestrel nests. Observations of the hunting behavior of breeding kestrels showed that kestrels mostly captured their prey items < 1000 m from their nest. Breeding bird density was higher on control areas than on areas close to a kestrel nest. In particular, densities of migratory and small birds (body mass < 140 g), which are potential prey of kestrels, were lowest near the predator nests. In contrast, the densities of nonmigratory and large—sized birds (body mass > 140 g) were independent of the presence of kestrel nests. Skylarks (Alauda arvensis), the most abundant migratory species in the study area, bred less often near kestrel nests than farther away. The results of line transect counts corroborated results of area counts. Our conclusion is that predation risk influences habitat selection of small migratory species in open habitats where scarce vegetative cover gives little protection.
Pitcher‐Plant Midges and Mosquitoes: A Processing Chain Commensalism
Authors: Heard Stephen B.
Published: May 2006

Larvae of the midge Metriocnemus knabi and of the mosquito Wyeomyia smithii are found only inside the water—filled leaves of the carnivorous pitcher plant, Sarracenia purpurea, where they feed on decaying invertebrate carcasses. I examined the interaction between the two species in a natural population in western Newfoundland, Canada. Experimental manipulations of rates of prey capture by pitcher—plant leaves indicated that both insect species are limited by carcass supply. However, the interaction between them is commensal rather than competitive. Midge growth was unaffected by experimental quadrupling of mosquito density in otherwise unmanipulated leaves. Mosquito growth, on the other hand, increased with midge density in both natural leaves and artificial leaf microcosms. This interaction is an example of a processing chain commensalism. Although both species feed on carcass material, they use it in different stages of decay; midges feed by chewing on solid material, while mosquitoes filter—feed on particles derived from the decaying matter. Consumption of particles by mosquitoes does not affect resource availability for midges, but feeding by midges does influence particle availability. In artificial leaf microcosms, high bacterial densities occurred sooner in artificial leaves with midges present than in identical leaves without them. Bacteria are a direct food source for mosquitoes, and high bacterial densities also indicate that other organic material is being comminuted, providing particles for mosquitoes and surface area for bacterial growth. Although midges remove some of the carcass resource that also limits mosquitoes, their net effect on mosquitoes in positive because they accelerate conversion of the remaining resource to particles.
Role of Tannins in Defending Plants Against Ruminants: Reduction in Dry Matter Digestion?
Authors: Robbins C. T. , Mole S. , Hagerman A. E. , Hanley T. A.
Published: May 2006

Polyphenolic allelochemicals, such as tannins, are widely thought to reduce the digestibility of plants consumed by herbivores by binding to digestive enzymes and dietary proteins. While the apparent digestibility of protein and, therefore, cell solubles is reduced in mule deer (Odocoileus hemionus) and white—tailed deer (O. virginianus) consuming tanniferous forages, digestion of the plant cell wall is not reduced beyond that predicted from its content of lignin, cutin, and silica. The lack of a tannin effect on cell wall digestion in deer is in contrast to studies with domestic sheep and numerous in vitro studies. Herbivores adapted to consume tanniferous forages may defend against such allelochemicals by producing salivary proteins that bind tannins in a highly specific manner. These tannin—salivary protein complexes would reduce apparent digestibilities of protein and cell solubles and, if completely effective, would not reduce cell wall digestion. The occurrence of such proteins in ruminants is reported here for the first time. The saliva composition of mule deer (a mixed feeder that commonly consumes browse) and domestic cattle and sheep (predominant grazers) are compared, and the higher potential of the deer saliva to neutralize tannins is related to their feeding habits. Salivary proteins that preferentially bind tannins may minimize fecal nitrogen losses by maximizing the efficiency of tannin—binding per unit of protein and may reduce the absorption of hydrolyzable tannins and the potential for tannin toxicity.
Optimal Foraging in Seed‐Harvester Ants: Computer‐Aided Simulation
Authors: Lopez Joaquin L. Reyes
Published: May 2006

This paper presents a computer—aided simulation of foraging behavior in seed—harvester ant species. The simulation is based on regression studies of running speed, net cost of transport, worker size, load mass, and distance. The results show that, as a function of its size, each worker has a maximum transport yield and an upper load limit. For yields other than this maximum, those obtained by larger workers transporting small loads are less than those obtained if the same loads are transported by smaller workers. In addition, there are two possible load sizes for the same yield.
Plant Community Diversity, Herbivore Movement, and an Insect‐Transmitted Disease of Maize
Authors: Power Alison G.
Published: May 2006

Field experiments were carried out in Nicaragua to examine the influence of plant community diversity, plant density, and host plant quality on the spread of an insect—transmitted plant pathogen. Population levels of the corn leafhopper Dalbulus maidis, which transmits the corn stunt spiroplasma to maize, were monitored in four experimental communities; low—density maize monoculture, high—density maize monoculture, two—species (maize/bean) polyculture, and multispecies (maize/weeds) polyculture. Leafhopper abundance per plant and the incidence of corn stunt were lower in high—density maize monocultures than in low—density monocultures. Increasing plant diversity by intercropping with nonhost species such as beans or weeds also led to lower leafhooper abundance and decreased disease incidence, but the effect was not enhanced as additional nonhost species were added to the community. Manipulating host plant quality by increasing nitrogen fertilization resulted in higher leafhopper densities at higher nitrogen levels. To explore the role of vector movement in disease spread, leafhopper movement rates and emigration were estimated by observing changes in the spatial gradients of leafhopper densities over time. This method of movement analysis requires neither marking the insects nor releasing them at a single point, and thus reduces the extreme disturbance caused by traditional mark—release techniques. The analysis indicated that leafhopper movement rates were lowest in the polycultures. In particular, across—row movement was strikingly inhibited in the bean polyculture. This polyculture also had the highest rates of emigration. These results indicate that plant quality, density, and diversity significantly affect the spread of corn stunt through their effects on the abundance and movement behavior of the corn leafhopper. These factors could be manipulated in a program of cultural control for corn stunt in maize fields in tropical America.
Ecological Consequences of an Exceptionally Strong El Nino Event on Darwin's Finches
Authors: Gibbs H. Lisle , Grant Peter R.
Published: May 2006

We studied the effects of heavy rainfall associated with the El Nino event of 1982—1983 on the demography of Darwin's Ground Finch (Geospizinae) populations and their resources on Isla Daphne Major, Galapagos. Total rainfall during this period (1359 mm) was 10 times the previously recorded wet season maximum. Most plant species responded by dramatically increasing seed production; total seed biomass increased by an order of magnitude, and small seed biomass increased in relative abundance, from 20% of total seed biomass before 1983 to >80% at the peak of the event. Caterpillars, the main food used by finches while breeding, also became extremely abundant. Ground finch species, mainly the Medium Ground Finch (Geospiza fortis) and the Cactus Finch (G. scandens), responded to the increase in food supply by breeding repeatedly. Females of both species produced up to 10 clutches of eggs; normally they produce 1—5 clutches. The most productive female fortis and scandens individuals fledged 25 and 19 young, respectively. Some birds born at the beginning of the season bred successfully before the end. Clutch sizes were scarcely larger than before and overall fledging success per nest was lower than in a normal breeding season. The large number of young produced resulted in (1) increases in population sizes of both species by a factor of four, (2) a dramatic skew in the age structure of both species, with birds born in 1982—1983 making up >75% of each population in January 1984, and (3) >50% of the lifetime fledgling production of females born in 1978 occurring in this breeding season. Individuals of both species immigrated from nearby islands, and a nonresident species, the Large Ground Finch (G. magnirostris) immigrated and bred on the island. Severe El Nino events have important ecological and evolutionary effects on these birds. For example, the high proportion of lifetime reproductive success contributed under exceptionally favorable conditions may have influenced the evolution of life history characteristics in the finches. Overall, our results support the view that rare events can have a major influence on key population processes in long—lived birds living in temporally varying environments, and that long—term studies are necessary to detect such effects.
Soil Acidity Affects Distribution, Behavior, and Physiology of the Salamader Plethodon Cinereus
Authors: Wyman Richard L. , Hawksley-Lescault Dianne S.
Published: May 2006

Censuses at two sites in Delaware County, New York from spring 1981 through spring 1985 indicated that the density and distribution of Plethodon cinereus were influenced by soil pH but not by soil temperature or moisture. Of 1044 1—m2 quadrats of forest litter searched, 284 had a pH of 3.7 or less only 25 of these (8.8%) contained salamanders. Of 760 quadrats with a pH 3.8 or more, 386 (50.8%) contained salamanders. Juvenile salamanders were never found on soils with a pH @< 3.7. Seasonal salamander density was correlated (r = 0.92) with the percentage of quadrats with a pH of 3.7 and less. Salamanders apparently were excluded from 27% of forest habitat because of low soil pH. In the laboratory, P. cinereus preferred to occupy substrates near neutral pH when given a choice among three levels of substrate acidity. The acutely lethal pH was between 2.5 and 3 and the 8—mo chronically lethal pH was between 3 and 4. Growth and respiration were reduced at low pHs. The influence of soil pH on salamander distribution might fundamentally change the forest floor decomposer food web of which P. cinereus is an upper—level consumer.
Comparative Life Histories of Holbrookia Maculata and Sceloporus Undulatus in Western Nebraska
Authors: Jones Steven M. , Ballinger Royce E.
Published: May 2006

The life histories of the iguanid lizards Holbrookia maculata and Sceloporus undulatus were studied in western Nebraska during 1978—1984. The two species differ in their reproductive strategies and age—specific survival. The reproductive strategy of H. maculata is invariant from year to year. Yearlings consistently produced a single clutch and older females (≥2 yr) consistently produced two clutches. The reproductive strategy of S. undulatus is opportunistic. Clutch frequency of S. undulatus varied among years, ranging from 1—3 for yearlings and 2—3 for older females. This variation in clutch frequency was a function of the length of the breeding season. Significant differences in the age—specific survivals of H. maculata and S. undulatus were found for juveniles and yearling females. In both cases, survival of H. maculata was greater. Despite differences in their life histories, H. maculata and S. undulatus are exposed to similar selective pressures in western Nebraska. Food does not appear to be limiting and mortality due to predation is low. Mortality is density—independent and is highest during the overwintering period. Differences in the reproductive strategies of H. maculata and S. undalatus are most likely due to their phylogenetic histories rather than to adaptation to different environments. The different reproductive strategies of the two species may account for differences in their age—specific survival. The high fecundity of yearling S. undulatus may explain its lower survival relative to H. maculata. Evidence for a cost of reproduction is provided by a negative relationship between clutch frequency of yearling S. undulatus and postreproductive survival. Because the response of lizards to specific environments may be constrained by their phylogenetic histories, comparison of life history strategies among syntopic species may not provide adequate tests of life history models. We conclude that identification of the mechanisms underlying variation in life history traits will most likely come from intraspecific comparisons.
Habitat Selection Under Predation Hazard: Test of a Model with Foraging Minnows
Authors: Gilliam James F. , Fraser Douglas F.
Published: May 2006

Animals commonly choose among habitats that differ both in foraging return and mortality hazard. However, no experimental study has attempted to predict the level of increase in resources, or the decrease in mortality hazard, which will induce a forager to shift from a safer to a more hazardous (but richer) foraging area. Here we present and test a model that specifies the choice of foraging areas ("habitats") that would minimize total mortality risk while allowing collection of some arbitrary net energy gain. We tested the model with juvenile creek chubs (Semotilus atromaculatus) in an experimental field stream in which the foragers could utilize a foodless refuge and choose between two foraging areas that differed in experimentally manipulated resource densities (Tubifex spp. worms in sediments) and mortality hazard (adult creek chubs). For the case tested, the model specified a simple rule: "use the refuge plus the site with the lowest ratio of mortality rate (μ) to gross foraging rat (f)," i.e., "minimize μ./f." Independent prior measurements of mortality hazard (as a function of predator density) and gross foraging rate (as a function of resource density) allowed us to predict the resource level in the more hazardous foraging site that should induce a shift from the safer to the more hazardous site. The chubs' preferences in subsequent choice experiments agreed well with the theoretical predictions. The "minimize μ/f" rule (deaths per unit energy), perhaps in modified form, provides a simple alternative to the "maximize f" (energy per unit time) criterion that applies to long—term rate maximization when predation hazard does not differ among choices.
The Effects of Herbivorous Snails on Submerged Macrophyte Communities in Minnesota Lakes
Authors: Sheldon Sallie P.
Published: May 2006

The influence of herbivorous snails on freshwater macrophytes was examined both in the laboratory and the field. In the laboratory, 14 macrophyte species grown in the absence of herbivores had growth rates ranging from 1—10%/d. When grown with four densities of herbivorous snails, species that grew fastest in the absence of herbivores were, in general, most negatively influenced by grazing. In food choice tests, snails typically preferred the plant species that grew fastest in the absence of herbivores. Snail densities were manipulated in a small mesotrophic lake, Christmas Lake. In areas where high snail densities were maintained, macrophyte species richness decreased, and the plants remaining were the species least preferred in laboratory choice tests. In surveys of eight additional lakes having a range of snail densities, the relationship between snail density and macrophyte species composition and diversity was consistent with the laboratory and Christmas Lake results. The levels of herbivore damage in the lake were measured for one macrophyte species. For the leaves examined, from 6 to 13% of the total leaf area was lost to herbivores. These results demonstrate that herbivorous snails can strongly influence the distribution, abundance, and diversity of freshwater macrophytes, and suggest that the role of herbivores in freshwater macrophyte communities may be similar to their role in terrestrial and marine communities.
A Large‐Scale Comparison of Factors Influencing Phytoplankton Abundance in Rivers, Lakes, and Impoundments
Authors: Soballe D. M. , Kimmel B. L.
Published: May 2006

We analyzed two large data sets (the National Stream Water Quality Accounting Network and the National Eutrophication Survey) to compare quantitatively the ecological structure and function of rivers, river impoundments, and natural lakes on a broad scale. Discriminant analysis with physical—chemical variables separated these three types of aquatic systems along a composite gradient that correlated with water residence time (r = 0.7), drainage area (r = 0.7), water depth (r = 0.6), stream flow (r = 0.6), and water clarity (r = 0.4). Natural lakes and rivers occupied opposite ends of this gradient, and reservoirs, on average, were intermediate, but natural lakes and impoundments overlapped extensively and did not form a useful dichotomy. Regression analysis showed algal abundance per unit phosphorus increasing in the sequence: rivers < impoundments < natural lakes, which paralleled intergroup differences in residence time. Algal abundance per unit phosphorus did not differ significantly among these three system types when systems with similar residence times were compared. Our results indicate that water residence time is a useful system—level index that has similar ecological implications for rivers, lakes, and reservoirs.
Chihuahuan Desert Annuals: Importance of Water and Nitrogen
Authors: Gutierrez Julio R. , Whitford Walter G.
Published: May 2006

We examined the effects of water supplementation and nitrogen amendment on biomass, cover, and density of annual plants on a termite—free and a termite—present area in the Chihuahuan Desert. Soil moisture was higher in the termite than in the termite—free plots, and in the watered than in the unwatered plots during the spring and summer. There were no differences in soil moisture among plots during the winter. Soil nitrogen was higher in the termite—free than in the termite plots. There were no differences in total plant biomass produced in termite and termite—free areas. There were significant differences in relative abundances of species among treatments. natural rainfall was sufficient for maximum spring—annual biomass development on all plots except for the termite—free unfertilized, unwatered plots. These were the driest plots but had high soil nitrogen. Most of the herbaceous species responded to the water amendments by lengthening growing seasons, increasing density, or increasing biomass. When there was sufficient water for most of the spring annuals, high soil nitrogen levels favored increased densities and biomasses of Descurainia pinnata and Lepidium lasiocarpum. The absence of C4 summer annuals in the high—nitrogen plots suggests that relatively high soil nitrogen adversely affected the summer annuals. Termite—free watered plots had higher soil moisture than the termite—unwatered plots, but summer annuals were relatively abundant on the latter. Water amendments had a greater effect on the species abundances in the termite—free area than in the one with termites. In the area with termites, nitrogen amendments had a greater effect on species abundances. Species diversity and richness were affected by fertility as was species composition. This study demonstrates that we must understand patterns of soil nitrogen availability and processes affecting nitrogen availability in addition to water availability, in order to understand productivity and species composition of Chihuahuan Desert annual plants.
Anova for Unbalanced Data: An Overview
Authors: Shaw Ruth G. , Mitchell-Olds Thomas
Published: May 2006

Ecological studies typically involve comparison of biological responses among a variety of environmental conditions. When the response variables have continuous distributions and the conditions are discrete, whether inherently or by design, then it is appropriate to analyze the data using analysis of variance (ANOVA). When data conform to a complete, balanced design (equal numbers of observations in each experimental treatment), it is straightforward to conduct an ANOVA, particularly with the aid of the numerous statistical computing packages that are available. Interpretation of an ANOVA of balanced data is also unambiguous. Unfortunately, for a variety of reasons, it is rare that a practicing ecologist embarks on an analysis of data that are completely balanced. Regardless of its cause, lack of balance necessitates care in the analysis and interpretation. In this paper, our aims is to provide an overview of the consequences of lack of balance and to give some guidelines to analyzing unbalanced data for models involving fixed effects. Our treatment is necessarily cursory and will not substitute for training available from a sequence of courses in mathematical statistics and linear models. It is intended to introduce the reader to the main issues and to the extensive statistical literature that deals with them.
Indirect Effects of Predation in a Freshwater, Benthic Food Chain
Authors: Bronmark Christer , Klosiewski Steven P. , Stein Roy A.
Published: May 2006

Theories of cascading trophic interactions provide specific predictions regarding the forces that regulate populations across trophic levels. Reducing predators in a food chain with three trophic levels should permit herbivores to increase, thus reducing primary producers. In a manipulative experiment involving a mulluscivorous fish (pumpkinseed sunfish, Lepomis gibbosus), freshwater snails, and periphytic algae, we tested this prediction. With 10 cages (3 ° 3 ° 2 m) in each of two lakes in northern Wisconsin, we generated three treatments: exclosures (fishless), enclosures (three pumpkinseed sunfish), and cageless controls, both in Mann Lake, which had high natural densities of pumpkinseed sunfish (HDP), and in Round Lake, which had low densities (LDP). During a 16—mo experiment, we quantified snail and periphyton biomass on plastic flagging within treatments during summer at 3— and 6—k intervals in 1986 and 1987, respectively. Predation by pumpkinseed sunfish reduced snail biomass on flagging, permitting periphyton biomass to increase, as compared to exclosures. As expected, periphyton biomass in cageless controls in Mann Lake (HDP) mirrored periphyton biomass in enclosures, whereas cageless controls in Round Lake (LDP) differed from exclosures. The periphyton assemblage changed dramatically with increasing grazing pressure. In enclosures (low grazing), filamentous algae and large, stalked diatoms dominated the periphyton assemblage, whereas in exclosures (high grazing), assemblages were dominated by small, adnate diatoms and a colonial, filamentous bluegreen alga (Gloeotrichia). In laboratory trials, snails preferentially fed on periphyton from enclosures (where grazing pressure had been low). Predation reduced snail density, but indirectly increased periphyton biomass, dramatically modifying species composition of the assemblage. Thus, in mesotrophic Wisconsin lakes, top—down interactions regulate the benthic, freshwater food chain.
The Effect of Silica in Grasses on the Feeding Behavior of the Prairie Vole, Microtus Ochrogaster
Authors: Gali-Muhtasib H. U. , Smith C. C. , Higgins J. J.
Published: May 2006

To study the importance of silica as an anti—herbivore defense, two brome grasses were grown hydroponically to control silica, nitrogen, phosphorus, and potassium content and subsequently offered to the prairie vole, Microtus ochrogaster, in food choice experiments. Feeding experiments used two designs. In the first design, voles were presented a choice of a standard grass having intermediate silica content, and another grass with high or low silica and nitrogen content. In the second design, voles were presented with one of eight pairwise combinations of grasses. Voles consumed less grass of high silica content in both experiments, suggesting that silica acts as an effective deterrent to mammalian herbivores.
Mutualism with Pollinating Seed Parasites Amid Co‐Pollinators: Constraints on Specialization
Authors: Thompson John N. , Pellmyr Olle
Published: May 2006

The genus Greya is closely related to the yucca moths, and Greya species interact with their host plants in many of the same ways as yucca moths. Females both pollinate and oviposit in the flowers of their host. Unlike yucca moths, however, pollinating Greya species share flowers with co—pollinators that do not oviposit on the host. We studied the interaction between Greya politella (Walsingham) (Lepidoptera: Prodoxidae) and Lithophragma parviflorum (Hook.) Torr. & Gray (Saxifragaceae) to evaluate the effect on seed output of a pollinating seed parasite against a background of co—pollinators. Flowers were visited and pollinated mostly by bombyliid flies, solitary bees, and G. politella. Bombyliid flies alone composed 68—88% of the 5522 visits recorded over 2 yr. Although both male and female G. politella visited the flowers and probed for nectar, pollination by this species occurred only as females oviposited through the corolla tube, thereby passively transferring to the stigma pollen adhering to the abdomen. Visitation to flowers by all pollinators averaged 0.3—1.9 visits/h during daylight hours. Consequently, most flowers were visited multiple times during the several days that stigmas were receptive, and 77% of the flowers tagged during the 4 yr had some developing seeds. Pollination did not depend upon visitation by G. politella. Flowers receiving G. politella eggs had the same probability of producing some seed and the same mean number of developing seeds as flowers visited only by other insects. Most flowers received the eggs of only one G. politella female, and the larvae ate 15—27% of the developing seeds. The final number of mature seeds remaining in attacked flowers did not differ from unattacked flowers except at one site in 1 yr, in which the values for attacked plants were marginally lower. Other sources of variation affecting seed output masked the effects of seed consumption by Greya. Overall, G. politella females have the potential to be mutualistic with L. parviflorum: they are effective pollinators, generally visit most plants and about half the flowers in the populations, and impose a fairly small cost on seed output. Nonetheless, the abundant and effective co—pollinators, which do not eat the developing seeds, swamp Greya's mutualistic effects. Under the current conditions at Granite Point, the relationship between G. politella and L. parviflorum may be mostly commensalistic. The evolution of specialization to G. politella as an exclusive pollinator would seem to be possible only in L. parviflorum populations in which effective co—pollinators were either rare or unpredictable. That is, the potential for the evolution of specificity in this mutualism appears to depend upon the community context in which the interaction takes place rather than upon the simple outcome of the pairwise interaction between Greya and Lithophragma.
Population Dynamics of Bacteriophage and Bacillus Subtilis in Soil
Authors: Pantastico-Caldas Marissa , Duncan Kathleen E. , Istock Conrad A. , Bell Julia A.
Published: May 2006

The dynamics of the interaction of populations of Bacillus subtilis and a temperate bacteriophage in soil microorganisms were examined. The purpose of the study was to investigate these dynamics in a structured habitat approaching that of their natural habitat in soil, in contrast to previous investigations in broth or chemostats. We addressed three main questions. What are the population dynamics of a phage—bacteria interaction in soil? What role might the heterogeneity of the soil play in shaping the interaction? Are the dynamics controlled more by the population biology of the phage or of the bacteria? The phage used was isolated from Arizona desert soil in which B. subtilis is common. Phage and bacteria were grown separately or together in sterile soil microcosms consisting of autoclaved soil rich in organic material. Densities of phage and bacteria were estimated through repeated sterile sampling of the microcosms by spreading precise dilutions of sampled soil suspensions onto plates of microbiological media. The plates for estimation of phage densities contained in addition a lawn of host bacteria. While the principal focus is on temperate phage ecology, the dynamics of a single example of interaction between B. subtilis and virulent phage is also presented. In all cases an initial epidemic of phage occurred, followed by stable equilibria lasting weeks to months. A threshold host density for phage outbreak occurs at °5 x 106 colony—forming units per gram of soil. At equilibrium the phage, both temperate and virulent, were much less abundant than the bacteria. The temperate phage did not depress the equilibrium host density, while the virulent phage lowered it by a factor of ten. The acidic soil of these experiments caused rapid and permanent inactivation of free phage, making the continuous interaction of phage and host essential for persistence of phage. Low levels of phage resistance (superimmunity or genetic) were typical of host populations. Most properties of the interaction between B. subtilis and phage in soil are quite different from those observed with chemostat populations of Escherichia coli and virulent phages. Potential doubling times and rates of increase in soil for phage and B. subtilis were calculated. At equilibrium, soil slows the interaction of phage and host relative to population growth in broth culture, and possibly also makes it heterogeneous in space and time. The life—history features of B. subtilis and temperate phage are considerably more complex than those of non—sporeforming bacteria and virulent phage. The biotic relationship of temperate phage and host may be distinct from predation or parasitism. Patterns in the ecology and evolution of temperate and virulent phage were explored, leading to the expectation that temperate forms will be more common among the phages of soil bacteria.
Hierarchical Mechanisms of Fruit Selection by an Avian Frugivore
Authors: Sallabanks Rex
Published: May 2006

To examine behavioral mechanisms of fruit selection, American Robins (Turdus migratorius) were studied foraging on Crataegus monogyna fruits in western Oregon. Robins faced a hierarchical decision—making process of fruit selection: (1) in which shrub to feed (decisions among shrubs); (2) which fruits to pick (visual decisions among fruits); and (3) which fruits to shallow once picked (within—bill decisions). Field observations of natural and experimentally manipulated populations of C. monogyna shrubs demonstrated that choices made by robins among shrubs were correlated with three plant traits (decision cues):fruit abundance, fruit size, and fruit pulpiness. These cues were themselves used hierarchically, so that when higher—ranking cues were held constant by manipulating shrubs, the next available cue became important. Once shrubs were selected, field and aviary work revealed that robins then made visual choices among fruits correlated with fruit size. However, no evidence was found to suggest that robins made within—bill decisions; once fruits were picked, additional discrimination did not occur. I suggest that a hierarchical process of fruit selection may have evolved to enable frugivores to cope with environmental uncertainty that is typical of fruiting systems. Such flexibility in foraging behavior may, in itself, promote variability within and among fruiting plants and therefore help to explain why so few general patterns have been identified in fruiting plant—frugivore relationships.
Food Quality Controls Sexual Selection in Mormon Crickets by Altering Male Mating Investment
Authors: Gwynne Darryl T.
Published: May 2006

Populations of several katydid species (Orthoptera: Tettigoniidae) show large differences in mating system; in some species males compete and females choose mates, whereas in others these courtship roles are reversed. Male katydids feed their mates during mating with a large, nutritious spermatophore. I hypothesized that courtship role reversal and increased sexual selection on females was a result of limitation in nutritious food items causing a decrease in the number of males available for mating (and thus in the spermatophore meals available). This hypothesis was tested by varying diet in field cages of Mormon crickets, Anabrus simplex. Results showed that, in contrast to a diet supplemented with proteinaceous food items, a poor diet resulted in: (1) a decrease in the number of sexually active males, (2) an increase in sexual selection for female body size, and (3) a reversal in the typical courtship roles. The experiment ruled out alternative explanations for variation in the mating system of this species,such as differences in population density and age. The conclusion from this study is that increased sexual selection on females due to such a change in diet is a result of an increase in the relative importance of male parental investment.
Life and Death in Moving Fluids: Hydrodynamic Effects on Chemosensory‐Mediated Predation
Authors: Weissburg Marc J. , Zimmer-Faust Richard K.
Published: May 2006

Previous studies in taxonomically diverse marine animals have established the general existence, and importance, of the olfactory sense in a wide variety of behavioral processes. Evidence suggests that the sense of smell mediates predatory search in many marine animals. Past investigations have not, however, been designed to link either the degree of successful olfactory—mediated search or guidance mechanisms with the hydraulic environment in which predatory activities naturally take place. In an effort to examine the interaction between hydrodynamics and chemoreception, we investigated predatory success and search strategies of blue crabs foraging in controlled hydrodynamic environments generated in a flume. Hydrodynamics were characterized by quantifying boundary layer shear velocity (°) and roughness Reynolds number (Re°), two measures that describe the structure of boundary layer flows. Flow properties affected the ability of crabs to orient to odor plumes emanating from actively pumping infaunal bivalves (Mercenaria mercenaria). High flow speed or large sediment particle size increased boundary layer turbulence, thereby decreasing the success of crab chemo—orientation ability. In addition, high flow speed also lessened the probability that crabs contacted odor plumes. Thus, habitats with high flows can provide hydrodynamic refuges from olfactory—mediated predation. Because search ability is contingent on the magnitude of boundary layer turbulence, olfactory—mediated predation may also be ineffective in slow flows, if bottom roughness elements can generate sufficient turbulence. Further, search ability in blue crabs is extremely sensitive to small changes in benthic boundary layer structure. The presence of a thick viscous sublayer, dominated by quasilaminar flow, seems especially critical for successful location of an odor source by crabs. Benthic estuarine crustaceans inhabit an environment where flows are transitional between smooth—and rough—turbulence conditions. Accordingly, chemosensory systems appear geared primarily to extracting information from hydraulically smooth flows. These results indicate that mechanisms governing the physical transport of odor signals can have profound influences, not only on the development of sensory and behavioral mechanisms, but also on biotic interactions such as predation, which, in turn, can mediate community structure.
Pod‐Specific Demography of Killer Whales (Orcinus Orca)
Authors: Brault Solange , Caswell Hal
Published: May 2006

Killer whales live in stable social groups, called "pods." It has been suggested that the structure of such groups may influence the vital rates, and hence the fitness, of their members. To test this suggestion we used data from a long—term study of killer whales in the Pacific Northwest (Bigg et al. 1990). We constructed stage—classified matrix population models for the entire population, two sub—populations, and individuals pods. The population growth rate for the entire population is λ = 1.0254, with 90% bootstrap confidence interval from 1.0178 to 1.0322. The mean female population stage distribution is not significantly different from the predicted stable stage distribution. Population growth rate is most sensitive to changes in adult and juvenile survival, followed by fertility Factors that cause even small changes in survival will thus have a large impact on population growth. Pod—specific growth rates range from λ = 0.9949 to λ = 1.0498. Most of the interpod variance in growth rate is due to variance in adult reproductive output. Randomization tests show that this variance is not significantly greater than expected on the basis of variation in individual life histories within the population. We conclude that there is no evidence for an effect of social structure on pod—specific population growth rate. The restriction of population growth rates to such a narrow range suggests, but does not prove, a possible role of density—dependent processes.
Genotype, Fish‐Mediated Chemical, and Phototactic Behavior in Daphnia Magna
Authors: De Meester Luc
Published: May 2006

Clones were isolated from natural populations with contrasting fish predation pressure and were tested for their phototactic behavior in the presence and absence of fish and/or fish—mediated chemicals. The presence of fish—mediated chemicals induced a more negatively phototactic behavior in all clones tested. This response was observed within 24 h after exposure to these chemicals. Release from the presence of the fish—mediated chemicals resulted for most clones in a gradual change back to control behavior, which took several days. There was no indication of a maternal effect. The response was not enhanced by a more direct exposure to the presence of fish, suggesting that the stimulus is a chemical. The results indicated genetic differences in responsiveness to fish—mediated chemicals in Daphnia. Clones isolated from habitats in which fish were present were on average more responsive than clones isolated from a fishless habitat. Significant genetic differences in phototactic behavior between the clones tested could be observed in the presence as well as in the absence of fish—mediated chemicals.
Ecology and Energetics of Sandlerlings Migrating to Four Latitudes
Authors: Castro Gonzalo , Myers J. P. , Ricklefs R. E.
Published: May 2006

We examined ecophysiological responses of Sanderlings (Calidris alba) to their nonbreeding environments in New Jersey (USA), Texas (USA), Punta Chame (Panama), and Puerto Viejo (Peru). Daily energy expenditure (DEE; measured using doubly labeled water) was strongly influenced by the thermal environment, being higher at colder locations, and equivalent to 4.2 times the basal metabolic rate of New Jersey, 2.8 in Texas, 2.1 in Panama, and 2.7 in Peru (200, 135, 100, and 129 KJ/d; n = 10, 5, 10, and 16, respectively. Time budgets varied among locations, but in all cases feeding and roosting accounted for °90% of daylight hours. Feeding times were 55% in New Jersey, 90% in Texas, 40% in Panama, and 45% in Peru, suggesting that Sanderlings required more time to satisfy their food requirements in Texas than in the other locations. Total body mass and body fat increased linearly with decreasing long—term mean January air temperature but, because of the synchronous increase in energy expenditure, predicted survival times during food deprivation increased only slightly. Individual Sanderlings experience different living conditions throughout their non—breeding distribution, with DEE and nutritional reserves being determined primarily by temperature. Time budgets vary accordingly to accommodate these demands.
Dispersal in a Monogamous Rodent, Peromyscus Californicus
Authors: Ribble David O.
Published: May 2006

In view of theoretical interest in the relationships between mating systems and dispersal patterns and the paucity of empirical data on dispersal in monogamous mammals, I studied natal dispersal in the monogamous rodent Peromyscus californicus. Genealogical relationships were determined using fluorescent pigment transfer and DNA fingerprinting, and dispersal distances were determined using dispersal fences and intensive trapping. Minimum dispersal distances were greater for females than for males. Philopatric males (those settling within one home—range diameter of their birth site) tended to be from smaller litters than non—philopatric males. Minimum dispersal distances of males were positively associated with natal litter size at weaning, whereas minimum dispersal distances of females were positively associated with number of sisters in the natal litter. These results suggest that intrasexual mate competition drives female dispersal, while resource competition drives male dispersal. Males remain closer to their natal range than females, most likely to acquire and defend resources to attract females. Peromyscus californicus is unusual among mammals in displaying both a monogamous mating system and female—biased dispersal.
Lotic Macroinvertebrate Production in Three Dimensions: Channel Surface, Hyporheic, and Floodplain Environments
Authors: Smock Leonard A. , Gladden James E. , Riekenberg Jayne L. , Smith Lane C. , Black Cheryl R.
Published: May 2006

A three—dimensional spatial perspective was used to determine annual macroinvertebrate production in two low—gradient, first—order stream systems on the Coastal Plain physiographic province of Virginia. Production in predominant habitats was weighted by the proportional areal abundance of each habitat to determine production in the channel surface, hyporheic zone, and floodplains of both blackwater streams. Highest production as dry mass in Buzzards Branch, a sand—bottomed stream, was in debris dams (27.4 g/m2); production on the sand sediment was lower (4.9 g/m2) and decreased with depth into the hyporheic zone, primarily as a function of decreasing oxygen concentration. Production on the floodplain varied with elevation, and hence period of inundation; it was 1.1 and 4.3 g/m2 at high and low elevations, respectively. Production, weighted for habitat abundance, was 1.7 g/m2 on the floodplain and 15.8 g/m2 in the channel (10.2 g/m2 in the hyporheic zone; 5.6 g/m2 on the channel surface). Production in the Buzzards Branch stream system, incorporating the channel and floodplain, was 2.4 g/m,2, 67% of which was on the floodplain, 21% in the hyporheic zone, and 12% on the channel surface. Production in the Colliers Creek system, with a clay and detritus sediment and no hyporheic zone, was only 2.8 g/m2 in debris dams but was 6.1—6.6 g/m2 on channel sediments and floodplain soils. Production in the stream system was 6.1 g/m2, 95% of which was on the floodplain. Primary consumers composed 72—74% of production in the channels and 80—85% on the floodplains. The predominant functional feeding groups differed between habitats, suggesting a spatial mosaic of functioning within the stream systems. The majority of production in debris dams and on the sediment was by shredders (30—46%) and predators (31—48%). Collector—gatherers composed 58% of production in the Buzzards Branch hyportheic zone and 56—61% on the floodplains of both streams. This study further emphasizes the patchy nature of lotic systems and that habitat—specific sampling is required to adequately determine invertebrate production and function in streams. It also shows the need to view streams with a three—dimensional spatial perspective. Both the hyporheic zone and floodplains can contribute a significant proportion of invertebrate production in low—gradient stream systems.
Camel Lake: A 40 000‐yr Record of Vegetational and Forest History From Northwest Florida
Authors: Watts W. A. , Hansen B. C. S. , Grimm E. C.
Published: May 2006

Camel Lake records the vegetation history of northwest Florida from °40 000 yr BP to the present. The Middle Wisconsin, from 40 000 to 29 000 yr BP, was a time of forests with abundant pine, oak, and diverse mesic tree species. Chestnut (Castanea) was an important element in the vegetation before 31 000 yr BP. The Late Wisconsin forest (29 000 yr BP to 14 000 yr BP) was a species—poor pine forest. The Wisconsin—age forests varied greatly in species composition from time to time, probably because of climatic variation. From 14 000 to 12 000 yr BP Picea (spruce) was present with northern aquatics in forest with abundant Carya (hickory) and other deciduous trees. This is believed to be the coldest phase recorded at Camel Lake, with a suggested climate of —5°C January mean temperatures, similar to southern Quebec today. After 12 000 yr BP the forest was oak—dominated with diverse deciduous hardwoods, unlike northeast Florida, which at that time had a less mesic flora with some prairie development and low lake levels with many dried—out lake basins. Sedimentation in shallow water was continuous at Camel Lake in the early Holocene, but a sudden change in sediment type and pollen composition indicates a hiatus between 10 020 and 7760 yr BP. After the hiatus modern turkey oak/long—leaf pine forests were present. There was a rise of some 4 m in the water table in the later Holocene, and cypress swamps and bayheads developed. The climates indicated by pollen data are in conflict with the simulations of published general circulation models (GCMs) for both the Late Wisconsin and the Holocene. Discrepancies may be explained by the particular boundary conditions used for the models, especially an assumption of little change in ocean temperatures at the latitude of Florida.
Defoliation, Nitrofen, and Competition: Effects on Plant Growth and Nitrogen Nutrition
Authors: Polley H. Wayne , Detling James K.
Published: May 2006

Defoliated and nondefoliated individuals of western wheatgrass (Agropyron smithii) from a prairie dog (Cynomys ludovicianus) colony were grown at two nitrogen (N) addition rates and with either a similar defoliated individual of A. smithii or with defoliated fringed sagewort (Artemisia frigida). Defoliation reduced total and residual biomass yields and increased aboveground relative to belowground investment of total biomass and N in A. smithii individuals. Elevated N—addition rate increased tillering and leaf extension rates and residual biomass yield of A. smithii. Total biomass and N yields of A. smithii individuals were reduced, and proportional investment of biomass and N in roots was increased, by association with the larger A. frigida neighbor. Defoliation increased N accumulation per unit root biomass of A. stimulii plants grown with a conspecific, but not a heterospecific neighbor. Nitrogen—accumulation efficiency of A. smithii x A. smithii and A. smithii x A. frigida combinations (proportion of available N recovered by plants) was reduced by increased input of N and by defoliation of both plants per mixture at high N input in intraspecific mixtures.