bluuebunny/crossref_metadata_2025 huggingface dataset:
Fruit Choice in Neotropical Birds: The Effect of Distance Between Fruits on Preference Patterns
Authors: Levey Douglas J. , Moermond Timothy C. , Denslow Julie Sloan
Published: May 2006

The influence of distance between fruiting plants on choice patterns of four species of tanagers and two species of manakins was experimentally tested in a lowland rain forest in Costa Rica. Paired clusters of two fruit species (Miconia affinis and Urera caracasana) were presented on each of two perches separated by selected distances ranging from 0.3 to 6.4. When the two perches were closest together, all the birds ate the preferred berries, M. affinis, on both perches before eating the less preferred U. caracasana. At the extreme perch separation distance, all but one of the birds ate both species of fruits on the first perch before flying to the second perch. The distance at which each bird switched between the two feeding sequences was correlated with the strength of their preference for one species of fruit over another. Manakins switched at greater separation distances than did tanagers. Since manakins take most of their fruit on the wing, the difference in switch distance is likely related to their flight pattern, but no consistent correlation with simple morphological characteristics (wing—loading or aspect ratio) was found. The results suggest that, in the field, less preferred items may often be taken when more preferred fruits are spaced even moderately far apart. The sequence of feeding and, by implication, diet breadth appears to be a consequence of the abundance and spacing of available foods; hence, degree of generalization is a dynamic feature of a bird's foraging pattern. This result supports the prediction that travelling time is an important determinant of prey and patch choice.
Static and Dynamic Aspects of Nitrogen Cycling in the Salt Marsh Graminoid Spartina Alterniflora
Authors: Hopkinson Charles S. , Schubauer Joseph P.
Published: May 2006

Processes of nitrogen cycling including root uptake, translocation, leaching, detrital incorporation, and overwinter storage were determined for a medium—height form of Spartina alterniflora in Georgia, USA. Mean concentration of total N in live above—and belowground plant tissues was 0.60% of dry mass. Aboveground concentrations (1.05%) were more than twice the belowground N concentrations. The seasonal patterns of nitrogen concentrations were similar for aerial and subaerial Spartina tissues with maxima observed between December and May. Concentrations were highest in short, young stems and decreased as plants matured, senesced, and died. Seasonal patterns of nitrogen accumulation were out of phase for aerial and subaerial tissues. Maximum accumulation was in midsummer for aboveground plant parts and in late winter for belowground tissue. During winter ≤83% of total plant N was in roots and rhizomes. During spring, there was a large net transfer of N from belowground storage to aerial tissues; °70% of total nitrogen was in aboveground plant parts by May. A nitrogen budget for Spartina alterniflora was constructed by combining organic productivity rates with nitrogen concentrations in plant tissues. Total uptake of N by roots was 34.8 g°m—2 yr—1. Of this, 43% was lost by death or leaching from aboveground plant parts, while the rest was lost by death of roots and rhizomes. Total transfer of N from below— to aboveground tissues was 33.0 g°m—2°yr—146% of which was new nitrogen taken up from the soil. Of the N transferred aboveground, 14.4 g was lost to detritus upon culm death, 0.7g was leached from the living culm, and 17.9 g was translocated from senescing leaves to rhizomes for storage or immediate transfer to activity growing shoots. A large percentage of the total flux into and out of leaves occurred during the period of active growth. The high degree of N conservation in Spartina, low leachability, and retraction from senescent tissue are consistent with the idea that primary productivity in salt marshes is nitrogen limited.
Ecological Interpretation of Leaf Carbon Isotope Ratios: Influence of Respired Carbon Dioxide
Authors: Da Silveira Leonel , Sternberg Lobo , Mulkey Stephen S. , Wright S. Joseph
Published: May 2006

In a Neotropical moist forest at Barro Colorado Island, Panama, °13C values of CO2 in air and °13 values of leaf tissue exhibit parallel patterns of variation between the forest floor and the canopy. During the daytime, °13C values of CO2 from air sampled at 1 m and 0.5 m were significantly less than that at 25 m. Based on mass balance equations, up to 18% of the CO2 in air at 0.5 m above the forest floor is from respiration. Respired CO2 is responsible for 31 and 37% of the variation in isotope composition in leaves of two species of herbaceous bamboo grown in a well—ventilated sun treatment and in the forest understory. Respired CO2 accounts for 45—70% of the difference in °13C values between understory and canopy leaves for three species growing in large—scale irrigation and control treatments. Understory leaves of these species show °13 values consistent with higher ratios of intercellular to ambient CO2 in irrigated relative to control treatments. Estimates of water—use efficiency from leaf carbon isotope content should be corrected for the contribution of the carbon isotope composition of respired CO2 in closed—canopy forests.
Inter‐ and Intraspecific Character Displacement in Mustelids
Authors: Dayan Tamar , Simberloff Daniel , Tchernov Eitan , Yom-Tov Yoram
Published: May 2006

In a search for possible community—wide character displacement (manifested as equal size ratios between adjacent morphospecies in a size—ranking), we examined the weasels (Mustela) of North America and also the mustelid—viverrid guild of Israel. We measured condylobasal skull length (CBL) and maximal diameter of the upper canine (Csup L) on museum specimens of the two or three weasel species sympatric at each of eight North American sites. We found substantial geographic variation and, at each site, pronounced sexual dimorphism of each species, as well as geographic variation in the degree of sexual dimorphism. With conspecific males and females viewed as separate "morphospecies," we found little variance about the mean measurement for a morpho—species at each site, and almost no overlap of distributions between sympatric morpholo—species. In site of the geographic variation, at seven of the eight sites the size ratios for CsupL between adjacent morphospecies in a size—ranking were remarkably equal, while the analogous analysis for CBL showed ratios tending towards equality at only four sites. Indications of equal ratios were largely absent for both variables when sexes were analyzed separately. For a more taxonomically diverse "mustelid—viverrid" guild of five species in Israel, the 10 ranked morphospecies had extraordinarily equal size ratios for CsupL but not for CBL, a result maintained if sexes were analyzed separately. These results, plus information on feeding behavior of mustelids, seem consistent with a hypothesis of competitive character displacement, but many critical data remain uncollected. There is no direct evidence that prey are limiting to either guild, data are scant on what the morphospecies actually eat, and there is no functional analysis for these species of the role of canine or skull size in ability to kill prey of different sizes and types. Sexual selection based on canine display or fighting might well contribute to sexual dimorphism. Though direct observation is lacking, it is also possible that canines may be used in threats or fighting in interspecific encounters. However,it seems unlikely that such canine use could account for the entire pattern of size ratio equality, as it would be quite coincidental that size ratios sexually selected between sexes within species should happen to equal those, however selected, between the male of each species and the female of the next larger species.
Cohabitation of Competing Territorial Damselfishes on a Caribbean Coral Reef
Authors: Robertson D. Ross
Published: May 2006

Individual adults of three Caribbean damselfishes defend feeding areas that do not overlap with those of conspecific adults. The feeding areas of adults of the two smaller species, Stegastes dorsopunicans and S. Planifrons, do not overlap interspecifically. However, feeding areas of adults of the largest species, Microspathodon chrysurus, are superimposed on feeding areas of adults and juveniles of the two Stegastes species. The large species aggressively dominates its smaller interspecific cohabitants. Cohabitant individuals of each species eat the same types of benthic microalgae. M. Chrysurus has the same daily cycle of feeding activity as the two small species, uses the same feeding microhabitats as they do, and feeds almost exclusively in their feeding areas. Cohabitants defend their feeding areas against the same set of other herbivorous fishes, but M. Chrysurus is involved in defensive actions much less frequently than is either of its small cohabitants. M. Chrysurus also is much less effective at such defense than at least one cohabitant, S. Dorsopunicians. S. Dorsopunicans on a reef from which M. Chrysurus were removed increased their body mass more and had larger fat deposits than conspecifics on a control reef. Thus adults of M. chrysurus appear to be dependents that use their size—based dominance ability to obtain food from their cohabitants. Juveniles of M. Chrysurus and S. Dorsopunicans exhibit small—scale habitat segregation and segregated use of feeding substrates in a shared microhabitat, which may facilitate the recruitment of both species.
Life History and Dispersal Patterns in a Dense Infaunal Polychaete Assemblage: Community Structure and Response to Disturbance
Authors: Levin Lisa A.
Published: May 2006

The effects of differing life histories on the dynamics of dispersal, recruitment,and population maintenance were investigated for a dense infaunal polychaete assemblage on the Kendall—Frost mudflat in Mission Bay, California. Polychaete life history features provided the framework for investigations of small—scale dispersal mechanisms, infaunal response to disturbance, and the spatial and temporal predictability of species' abundances. Field and laboratory studies revealed that Rhynchospio arenincola Hartman, Streblospio benedicti Webster, Exogone lourei Hartman, Fabricia limnicola Hartman, and Capitella spp. shared many life history traits which limited the range of dispersal. These included small adult size, brood protection, small brood size, and planktonic larval stages which were reduced or absent. Pseudopolydora paucibranchiata Okuda, and Polydora ligni Webster exhibited initial brood protection but had larger brood sizes and longer lived larvae. Small—scale dispersal was examined by studying patterns of larval availability, recruitment into settling cartons, and colonization of defaunated sediments. The role of dispersal in response to disturbance was examined for two levels of perturbation. Small—scale disturbance, commonly generated on the mudflat by ray foraging and human digging, was studied by artificially defaunating small (0.4—m2) sediment patches. A severe storm and consequent raw sewage spill created an episodic large—scale perturbation in the middle year of the 3—yr study. Analyses of species' responses revealed colonization ability at recruitment to be distinct from dispersal (migratory) ability. Rates and mechanisms of colonization were governed by larval development, settlement, and mobility patterns and varied with the scale of perturbation. For R. Arenincola, S. benedicti, E. Lourei, and F. Limnicola, factors such as brood protection, reduced planktonic larval phases, and postlarval movements, particularly by brooding adults, confer small—scale dispersal abilities which permit rapid colonization of disturbed patches and result in maintenance of high infaunal densities (>200,000 individuals/m2). P. Paucibranchiata and P. Ligni possess long—lived larvae whose planktonic abundances are highly seasonal and variable from year to year. The timing of disturbance must coincide with periods of peak larval availability for successful colonization by these species. In general, the annual life cycles and flexible small—scale mobilities of most species enable persistence in the face of frequent fine—grained disturbance.
Testing a Paleoecology Matrix Model: Estimates for a Sphaerium Population in Equilibrium with Its Death Assemblage
Authors: Green R. H. , McCuaig J. , Hicks B.
Published: May 2006

A paleoecologist may wish to estimate the age—specific mortality rates and fecundity rates of the population that generated the death assemblage under study. We report the result of an analysis for this purpose applied to a living bivalve mollusk population which can be assumed to be in equilibrium with its death assemblage. A Leslie matrix model that includes age—specific rates of generation, and of decay, of the death assemblage is applied to grab—sample data from a Sphaerium striatinum population in an artificial hard—water lake, Minnedosa Lake, Manitoba, Canada. The samples yielded both live clams and empty shells. Shell length was used as a measure of relative age. Mortality rate in the living population were estimated from the death assemblage, and then compared with direct estimates of the mortality rates for the living population. Close agreement was obtained, providing some validation of this approach to estimation of life history parameters of ancient populations.
Trophic Response of Fishes to Habitat Variability in Coastal Seagrass Systems
Authors: Livingston Robert J.
Published: May 2006

Shallow coastal areas of the northeast Gulf of Mexico are physically unstable in terms of short—term, seasonal, and year—to—year changes in temperature, salinity, nutrient concentration, and other water quality features. A 9—yr comparison was made of two estuaries, one polluted and one in the natural state, to determine the response of fish assemblages to habitat alteration in space and time. During the study period, extreme natural habitat changes due to storm water runoff and low winter temperatures were superimposed over water quality changes (increased color, turbidity, nutrients; reduced dissolved oxygen) associated with release of pulp mill effluents. Various grassbed fishes followed regular seasonal, age—specific feeding patterns, which did not change substantially in terms of qualitative food composition in the unpolluted estuary over a 7—yr period of observation. Such feeding behavior helped to explain temporally conservative cycles of relative abundance despite extreme (natural) habitat change. Anthropogenous habitat alterations, though seemingly slight, were associated with reductions in benthic macrophyte distribution, enhanced phytoplankton productivity, and changes in the relative dominance and numerical abundance of associated fish assemblages. Grassbed species were replaced by plankton—feeding fishes, and disruption of feeding habits of various species was apparent in the affected area relative to the unpolluted estuary. Those fishes dependent on specific benthic food organisms altered their feeding habits during the years of pollution in the affected estuary. Subsequent water quality improvement over time was associated with shifts in the age—specific dietary patterns of various species toward those observed in the unaffected estuary, although such recovery varied from species to species according to habitat utilization and trophic needs. From these results, it is clear that a relatively complex coastal seagrass system exposed to periodic, extreme natural disturbance is relatively resilient to such changes in terms of relative dominance and food web structure. However, apparently slight water quality changes due to pollution, which are outside the evolutionary experience of the biotic components, can cause serious disruptions of the basic habitat structure, energy flow, and community composition of the grassbed assemblages at various levels of biological organization.
Effects of Leaf Removal on Reproductions vs. Belowground Storage in Trillium Grandiflorum
Authors: Lubbers Anne E. , Lechowicz Martin J.
Published: May 2006

We investigated the joint and separate effects of partial defoliation and pollination on components of reproduction and rhizome carbohydrate reserves in Trillium grandiflorum, a perennial spring ephemeral frequently abundant in the herbaceous understory of deciduous forests in eastern North America. To disrupt annual net production maximally, defoliation treatments were applied during flowering just as the year's flush of leaves matured. Natural pollination limited seed set in one year but not another at our study site near Montreal, Quebec; it is likely that year—to—year variation in pollinator availability is the norm. Removal of leaf or floral bract tissues did not affect mean seed set, but leaf removal did reduce allocation of biomass and nonstructural carbohydrates to rhizomes. As the level of defoliation increased, the correlation between reproduction and storage within plants became increasingly negative. Although the mean seasonal leaf conductance of partially defoliated plants was greater than that of intact plants, any compensatory increases in photosynthesis that may have occurred were apparently insufficient to prevent the reduced allocation to belowground storage. The allocation of resources to current reproduction at the expense of survival and future reproduction possibly reflects the selective effects of unpredictable availability of pollinators for this spring ephemeral.
Population Characteristics, Growth, and Survival of the Halophyte Salicornia Europaea
Authors: Ungar Irwin A.
Published: May 2006

The morphological characteristics of plants from three populations of Salicornia europaea along a salinity gradient are described. Plants from these populations differed in a number of characteristics including plant height, dry mass, branch number, flowering branch number, and flowering internode number. Reciprocal transplants were made between the Edge and Tall populations, and at the fruiting stage these transplants still resembled plants from their source more closely than those in the new site. Greenhouse transplants from the Tall, Very Tall, and Edge populations proved to be plastic in their growth responses depending on their time of transplant. Mortality was greatest in the Pan Zone, which had the highest soil salinity stress. Density—dependent factors did not explain a significant portion of mortality, indicating that abiotic stress was the primary factor determining mortality in this system. A persistent seed bank of small seed of S. europaea plays a significant role in maintaining plant populations in this highly stressful salt marsh habitat.
A 6000‐Year Record of Forest History on Mount Rainier, Washington
Authors: Dunwiddie Peter W.
Published: May 2006

Sediments in three ponds between 1300—1500 m on the south side of Mt. Rainier were examined for plant macrofossils and pollen. Macrofossils of seral species such as Abies lasiocarpa, Pseudotsuga menziesii, Pinus monticola, Abies procera, and Pinus contorta are conspicuous from 6000 to 3400 BP. These species suggest a climate that was warmer/drier than today and favored frequent fires. Neoglacial cooling may have begun 3700—3400 BP, as species typical of higher elevations became prominent; a decline in seral species after 3400 BP suggests less frequent fires. In the last 100 yr, Tsuga heterophylla became abundant and then declined at the highest elevation site. General trends in pollen percentages are similar to the macrofossil curves. Tephra deposition from Mt. Rainier and Mt. St. Helens did not produce conspicuous changes in forest composition. Few major fires are evident from charcoal and macrofossils at these sites.
Nitrogen Cycling as Affected by Interactions of Components in a Georgia Piedmont Agroecosystem
Authors: Groffman P. M. , House G. J. , Hendrix P. F. , Scott D. E. , Crossley D. A.
Published: May 2006

Patterns of nitrogen cycling were studied in N—fertilized (N: 95 kg/ha, P: 45 kg/ha, K: 135 kg/ha) and “unfertilized” (no N, but the same levels of P and K) agroecosystems with heavy weed infestations. To calculate monthly standing crop nitrogen levels, nutrient concentrations were multiplied by biomass values for each month. Soils were also sampled monthly at three depths; precipitation was sampled weekly and analyzed for N inputs. Nitrification and denitrification enzyme activities were measured, as well as rates of denitrification from unaltered soil cores. Nitrate leaching was measured with porous cup lysimeters. Weeds completed more vigorously with the crop in fertilized treatments than in unfertilized treatments, resulting in greater crop growth in unfertilized treatments. Nitrification, denitrification, and leaching losses of N were greater in fertilized treatments than in unfertilized treatments, especially after residue input following harvest of the summer crop. Soil organic nitrogen tended to be lower in unfertilized treatments than in fertilized treatments after summer cropping, whereas soil organic carbon showed an opposite trend. As a result the carbon: nitrogen ratio of soil organic matter was significantly higher in unfertilized treatments than in fertilized treatments. Fertilized treatments showed a positive N balance (47 kg/ha) while unfertilized treatments showed a net loss of N (57 kg/ha). Nitrogen use efficiency by plants was higher in unfertilized treatments than in fertilized treatments, but was low relative to many unmanaged ecosystems.
Benefits of Host Plant Specificity in Uroleucon (Homoptera: Aphididae)
Authors: Moran Nancy
Published: May 2006

Benefits of host specificity for Uroleucon nigrotibium (Homoptera: Aphididae) include not only improved physiological efficiency but also enhanced success of dispersal and defense tactics. I tested the physiological efficiency hypothesis, which predicts a higher reproductive rate for this specialist that for the generalist U. gravicorne when each is reared on their shared host, Solidago nemoralis. Between—species comparisons of developmental times and fecundities of individuals reared on naturally occurring and potted screenhouse host plants supported this prediction for the spring but not in summer, when most reproduction occurs. Greater physiological efficiency of the specialist is also supported by its greater size, which may aid in dispersing and in escaping enemies by walking. Field colonies of the specialist were found to produce few winged forms and to disperse frequently via apterae walking between hosts; consequently, U. nigrotibium infestations are larger and longer lived and are attacked more by enemies than those of its generalist congener. In experiments using potted host plants, the specialist was better able than the generalists to escape predation by walking to nearby hosts. This strategy of persistence depends on specificity to a long—lived, clumped, bushy host such as S. nemoralis.
Mechanism and Adaptive Significance of Substrate Selection by a Sessile Rotifer
Authors: Wallace Robert L. , Edmondson W. T.
Published: May 2006

We examined the nature and adaptive significance of substrate selection by larvae of the sessile rotifer Collotheca gracilipes. In a small artificial pond the preferred substrate was the anatomical undersurfaces (abaxial) of Elodea canadensis leaves, although four other macrophytes were present (Ceratophyllum demersum, Lemna minor, Myriophyllum spicatum, and Nymphaea odorata). Density of adults on Elodea at times reached >6 individuals/mm2, with >98% attached to abaxial surfaces. However, larvae offered plants in pairwise combinations selected substrates in the following order; Lemma > Elodea > Myriophyllum > Nymphaea. No larval loyalty to parental substrate was exhibited. Larvae preferentially selected abaxial over adaxial surfaces of Elodea leaves (91% on abaxial) in continuous illumination experiments, but the larvae did not discriminate between the two surfaces in total darkness (48% on abaxial). In the absence of a plant substrate, cell debris from any one of four aquatic and two terrestrial plant species induced larval settlement on the bottom of plastic well—depressions. Activity could not be attributed to carbohydrate, lipid, nucleic acid, or protein moieties within these extracts. However, alpha—amylase induced rapid larval settlement in the depressions. In the presence of this calcium chelator, larvae did not distinguish between ad— and abaxial leaf surfaces to the same degree as without the enzyme. Phospholipase—C and EDTA induced similar effects. Larval preference for abaxial surfaces could be reduced slightly when PH was stabilized at <7.0. Because living Elodea in neutral—to—alkaline water can remove Ca+2 from beneath its leaves and release it from adaxial surfaces while photosynthesizing, we hypothesized that larvae initiate substrate selection activities on any surface when they are in microhabitats having ambient Ca+2 concentrations below a threshold concentration. Short—term, in vitro growth experiments showed that rotifers attached to abaxial surfaces of Elodea leaves grew significantly taller and produced more eggs per female than those which had been induced to settle on adaxial surfaces.
Effects of Reduced Interspecific Competition on Resource Utilization in Perch (Perca Fluviatilis)
Authors: Persson Lennart
Published: May 2006

The effects of a reduction in the size of a roach (Rutilus rutilus) population on a perch (Perca fluviatilis) population were studied. The population size of roach was reduced by 70% and the biomass by 40%. The biomass of the perch population increased by 140%, which was a result of an increase in young—of—the—year (0+) perch. The consumption of the adult perch population increased more than two—fold compared to the situation before the removal experiment. 0+ perch did not switch in August from a diet of zooplankton to a diet of macroinvertebrates, as was the case before the removal experiment, and they also expanded their habitat. This resulted in a reduced age class competition, and the limitations set by the macroinvertebrate bottleneck phase in the life period of perch were reduced. Though the removal experiment lacked a control, the considerable response of both the zooplankton community and the perch population strongly suggests that roach greatly influenced the resource intake and resource utilization of perch.
Arthropod Community Responses to Manipulation of a Bitrophic Predator Guild
Authors: Hurd L. E. , Eisenberg Robert M.
Published: May 2006

We used replicated field enclosures to manipulate population densities of two species of bitrophic predators in a terrestrial old—field community: a mantid (Tenodera sinensis), and a wolf spider (Lycosa rabida). The treatments consisted of adding mantids alone (8 individuals/enclosure), lycosids alone (10 individuals/enclosure), and lycosids and mantids together (8 + 10 individuals). A control consisted of enclosures to which no predators were added. The impact of these predators on numbers and biomass of other arthropods in the community was examined on several levels: overall community, different size (body length) categories, and major taxa. We asked whether the impact of these predators in combination could be predicted from their separate effects. Mantids depressed total numbers (10—15%) and biomass (50%), in the arthropod community over the course of 10 d. This effect was confined to the largest size categories in the community. Lycosids had no measurable effect at this level of resolution. Mantids depressed abundance of acridids in both mantid and mantid/lycosid enclosures, but again lycosids had no impact. Lycosids alone enhanced abundance of gryllids, but not in the presence of mantids. Both mantids and lycosids depressed numbers of small spiders (also members of this guild), but this effect was not additive. Interactions among members of bitrophic generalist predator guilds may contribute to the commonness of nonadditive and higher order effects in manipulative experiments. Depending upon the level of resolution, it may be impractical to predict the impact of the whole guild from summing the individual effects of single predator species on terrestrial arthropod communities.
Facilitation of Reproductive Synchrony by Gestation Adjustment in Gregarious Mammals: A New Hypothesis
Authors: Berger Joel
Published: May 2006

Among gregrious, plaental mammals, breeding synchrony usually occurs by adjustment of the timing of estrus, not births, and it has been suspected that the former process govern synchronized parturition. Gestation length data gathered on wild plains bison (Bison bison) over a 5—yr period demonstrate:(1) females in good body condition who were mated after the seasonal peak shortened gestation by °6 d, synchronizing births with other females; (2) no similar adjustments occurred among females in poor condition; and (3) those females that shortened gestation incurred a cost because their neonates were, on average, °20 kg lighter when 6 mo old. Reproductive synchrony may also be achieved by a less radical tactic; unmated females use olfactory cues to explore the status of other females prior to their own estrus but not after. These data suggest that there is adaptive variation in gestation length in bison cows in good condition and that assumptions about the constancy of gestation are unwarranted.
Cumulative Effects of Plant‐Animal Interactions on Seed Production by Bauhinia Ungulata, A Neotropical Legume
Authors: Heithaus E. Raymond , Stashko Edward , Anderson Pamela K.
Published: May 2006

Seed production was studied in Bauhinia ungulata, a neotropical, perennial legume. Our goals were to identify the biotic factors influencing seed output, the magnitude and variability of their effects, and whether these effects were density dependent. We measured predispersal reproductive success in five stands, ranging in size from 18 to 175 ramets. Pollination success and flower herbivory were evaluated for 1375 flowers. Other sources decreasing seed output were observed by examining 1714 seedpoints. Six factors led to reduction in potential seed—set. In order of the magnitude of their effects, these factors were lack of pollination, incomplete development of ovules in flowers that formed seedpods, herbivores that damaged flowers that could have been pollinated, bruchids that destroyed developing seeds, herbivores that damaged pistils, and herbivores that ate developing pods. Density dependence was observed for three of the factors: level of pollination success, seed predation, and herbivory on developing seedpods. There was significant variation among stands for the six factors that were measured in all stands. Key factor analysis was used to estimate the influence of these factors on variation among stands in seed—set. Seed predators and pollinators accounted for most of the observed variation. We conclude that pollinators and predators on seeds are potentially important to the population dynamics of this plant.
Evolution of Fruiting Strategies Among Fleshy‐Fruited Plant Species of Eastern Kansas
Authors: Stapanian Martin A.
Published: May 2006

Seed dispersal of fleshy—fruited plants by birds in Kansas riparian forests was investigated from an energetic point of view. Energy invested in fruit represents a reward to birds, but to plants it is a cost that is necessary to attract birds to eat the fruit and disperse the seeds. Seed volume (proportional to seed energy) in fruit represents a cost to birds in terms of digestive processing and mass carried, but a benefit to plants in terms of offspring dispersed. Increasing the fleshy energy per fruit would make the fruit more attractive to birds, but this would result in a decrease in the number of seeds a plant can make for a given reproductive energy budget. None of the birds in the study are fruit "specialists"; their preferred food is insects. An energetic model is presented: it hypothesizes that plants species fruiting when a preferred food (caterpillars) is abundant should have a high ratio of fleshy energy: seed energy: those fruiting when caterpillars are less abundant should have a lower ratio of fleshy energy: seed energy. This hypothesis was supported from phenology and calorimetry data for 16 species of fleshy—fruited plants. Frugivorous birds were found to be most numerous but very unpredictable in fall (migration season), moderately numerous and fairly unpredictable in winter, and least numerous but very predictable in their breeding season. The trade—offs among fruiting season of plants and the energetic cost of fruit, the number of interspecific competitors, the energy and nutritional requirements of birds, and the predictability of birds as a resource over time are discussed.
An Experimental Analysis of Social Spacing in Tamias Striatus
Authors: Mares Michael A. , Lacher Thomas E. , Willig Michael R. , Bitar Nancy A. , Adams Richard , Klinger Alan , Tazik David
Published: May 2006

We report on a series of experiments performed on a population of free—living eastern chipmunks, Tamias striatus, inhabiting a forest in northwestern Pennsylvania. The experiments were designed to examine, via pertubations of food supply and/or population density, the relationship between home range size, food availability, and population density. When food levels were increased within an area, a simultaneous effect was noted: mean home range size decreased and population density increased through recruitment from neighboring habitats. Whether the cause of the decreased patterns of movement was the increased food supply or the elevated population density was determined in subsequent experiments. When population density was held constant and food supplies were experimentally increased, there was a significant reduction in mean home range sizes when compared to the normal (control) situation. When food supplies were undistributed, put population density was greatly reduced, there was no change in the mean home range size over that determined at higher mean home range size, whereas population density, at least at the levels we examined experimentally, has no effect on movement patterns. These results are in accord with those theories relating movement patterns to resource abundance, but are not in accord with hypotheses suggesting that the home range sized and population density and inversely associated.
Species Diversity and Phasing of Disturbance
Authors: Abugov Robert
Published: May 2006

This study provides evidence that the temporal patterning of disturbance may play an important role in determining the effects of disturbance on species diversity. To describe this temporal patterning, a "phasing parameter" is developed, and mechanisms by which this parameter affects the relative abundances of fugitive and competitively dominant species are discussed.
A Question of Taste: Crypsis and Warning Coloration in Freshwater Zooplankton Communities
Authors: Kerfoot W. Charles
Published: May 2006

Visual predation by fishes appear to have driven prey towards divergent extremes, with two of the alternative avenues dependent upon initial palatability. On the one hand, selective predation upon initially large—bodied, strongly pigmented, and highly palatable zooplankton has selected for reduced conspicuousness (smaller body size at maturity, increased transparency of tissues). On the other hand, selective predation upon initially pigmented, yet mildly unpalatable groups (e.g., water mites), has selected for enhanced conspicuousness and increased distastefulness. At the basis of these two diverging selective responses lies the initial mouthing experiences of the predator, i.e., whether the image of the prey is associated with pleasure (reward) or with pain (punishment). While aposematic coloration seems limited among zooplankters to special cases, chemical defenses appear to be more widespread than commonly believed.
Do Stonefly Predators Influence Benthic Distributions in Streams?
Authors: Peckarsky Barbara L. , Dodson Stanley I.
Published: May 2006

Experimental manipulations were conducted within the substrate of a Wisconsin stream and a Colorado stream to measure the effect of stonefly predators on the distribution of benthic invertebrates. Screen cages containing free predators, predators restricted from foraging, or no predators, allowed prey migration but no predator migration over 3—d periods. The presence of Acroneuria lycorias (Perlidae) in the Wisconsin stream significantly depressed the establishment of prey populations within cage microhabitats. Mechanisms for reduction were consumption of prey by the stonefly, and predator—avoidance by prey using contact and non—contact cues. The presence of Mergarcys signata (Perlodidae) reduced prey colonization in the Colorado stream by the same mechanisms, but restricted predators produced less consistent effects. This results could be due to colonization of cages by prey that could not detect predators without contact. Pternarcella badia (Pteronarcidae), a large stonefly detritivore that takes occasional prey, did not affect colonization of Colorado stream cages by prey. This differential response by prey to two moprphologically similar, but functionally different, stonefly species suggests that predator avoidance was not purely tactile. Chemotactile and non—contact chemical cues are possible mechanisms by which prey differentiated these stoneflies. The presence of A. lycorias and M. signata in experimental cages significantly increased the attrition of mayfly prey, compared to that from cages with no stonefly or a restricted stonefly in each stream. This result suggests that predation and avoidance by prey of contact with foraging predators were responsible for the higher disappearance of mayflies from cages. Free P. badia had a similar effect, probably due to tactile avoidance of this large detritivorous stonefly by some prey in the Colorado stream.
Loss of Mass and Chemical Change in Decaying Boles of a Subalpine Balsam Fir Forest
Authors: Lambert Robin L. , Lang Gerald E. , Reiners William A.
Published: May 2006

Decay of balsam fir (Abies balsamea) boles was examined in an upper subalpine forest of the White Mountains, New Hampshire, USA. Fifty percent of the initial mass was los in 23 yr; 90% was lost in 77 yr. High decay rates were attributed to the small diameters of the boles, ample moisture, and a nitrogen—rich environment. Average dead woods mass in this forest was 4.9 kg/m2, representing 25% of the sum of dead wood, live plant biomass, and forest floor organic matter. Changes in density and moisture and in the concentrations and content of various chemical components of the boles were traced over the decay sequence. Changes in the content of cellulose, lignin, carbon and sodium followed loss of mass during decay. Contents of calcium, magnesium, potassium and phosphorus decreased faster than loss of mass in the early stages of decay. Much of this initial loss was ascribed to sloughing of nutrient—rich bark which in these small boles comprised 13% of dry mass. Later in decay, the loss rates of calcium, magnesium and potassium were about the same or slightly less than the loss rate of mass. After a steep initial drop, phosphorus content of the boles remained approximately constant between years 12 and 33. Thereafter the loss rate paralleled loss of mass. Nitrogen content was approximately constant in the first 33 yr after which it declined in parallel with loss of mass.
Invertebrate Drift From Predator‐Prey Associations
Authors: Walton O. Eugene
Published: May 2006

Laboratory experiments evaluated the effect of a predator, Acroneuria abnormis (Plecoptera), on the drift of two prey taxa, Taeniopteryx spp. (Plecoptera) and Stenacron interpunctatum (Ephemeroptera), from substratum patches in artificial stream channels. Drift of Taeniopteryx spp. increased significantly as its own density and the predator's density increased, but a predator density threshold was required to boost drift of the prey substantially. Drift of S. interpunctatum increased as its own density increased but was not significantly affected by the predator's density. Consumption of Taeniopteryx spp. by A. abnormis increased as the former's density increased but was not significantly affected by the predator's density. More S. interpunctatum were consumed as densities of the predator and prey increased. Both prey taxa occupied interstitial refuges in the substratum patches but Taeniopteryx spp. occupied them more successfully. Some Taeniopteryx spp. may have actively deserted the substratum patches in the presence of the predator. Drift of Taeniopteryx spp. alone was judged density independent at a current velocity of 12.5 cm/s but density dependent at 25.0 cm/s. Drift of S. interpunctatum alone (at 8.0 cm/s) was density independent. At 25.0 cm/s, drift of A. abnormis alone was density dependent, but insufficient drift of this taxon occurred at a lower velocity (8.0 cm/s) to allow such a determination. Predator satiation did not occur in these experiments. Occupation of interstitial refuges and drift by the prey combined to reduce the predator—prey encounter rate. Drift of the predator was not significantly affected by prey density.
Effects of Nutrient and Light Limitation on Mountain Hemlock: Susceptibility to Laminated Root Rot
Authors: Matson Pamela A. , Waring Richard H.
Published: May 2006

Mountain hemlock forests in the Oregon Cascades exhibit wave—form dieback resulting from infection by laminated root rot (Phellinus weirii). Although Phellinus remains viable in dead roots after the wave of dieback passes, many regenerating mountain hemlock forests do not become immediately reinfected. We measured at least a doubling of nitrogen availability in the dieback and regrowth zones, and thought that this increased availability could improve tree resistance to the fungus. To test this hypothesis, we grew small mountain hemlock under nutrient and light limitations in a growth room, and then inoculated them with the fungus. Trees growing without added nutrients had significantly greater foliage damage and mortality after Phellinus inoculation than did trees growing with nutrients. Shading significantly increased susceptibility whether or not nutrients were added. We believe that increased nitrogen availability and possibly increased light levels after dieback in the field act similarly to increase resistance and prevent reinfection of the regrowing stands. Foliage damage and susceptibility to infection were related to pool sizes of total nitrogen, phosphorus, and nonstructural carbohydrates. Plants with very low nitrogen, phosphorus, and nonstructural carbohydrates. Plants with very low nitrogen reserves (<10 mg per plant), or very low energy reserves (<20 mg starch per plant), were more susceptible. It appears that resistance to Phellinus occurs via a defensive pathway that requires resources of both nutrients and carbohydrates.
Opposite Density Effects of Nymphal and Adult Mortality for Periodical Cicadas
Authors: Karban Richard
Published: May 2006

In a cohort of 17—yr periodical cicadas, I measured adult density, density of newly hatched nymphs, and density of nymphs after 2 yr. I looked for density dependence by regressing the logarithms of nymphal density upon logs of adult density. Mortality during the adult and egg stages decreased as the density of adults increased, corroborating earlier observations. However, nymphal mortality during the 1st 2 yr was higher where the density of newly hatched nymphs was higher. This density—dependent nymphal mortality more than compensated for the inversely density—dependent mortality during the adult stage; the number of 2—yr—old nymphs produced per adult was greater at sites of lower than of higher adult density. I found no correlation between soil and rootlet traits and number of 2—yr nymphs recovered. Factors responsible for nymphal mortality remain unknown. There may be selection upon adults to disperse away from dense chorusing centers before ovipositing, because nymphs nearest chorusing centers suffer higher mortality during the 1st 2 yr of life. Almost all cicadas that I observed dispersing away from chorusing centers were mated females.
Floral Resource Variation, Pollinator Response, and Potential Pollen Flow in Psiguria Warscewiczii
Authors: Murawski Darlyne A.
Published: May 2006

Fluorescent dyes were used to examine several hypothesized ecological correlates of pollen flow in a natural population of a tropical, butterfly—pollinated vine, Psiguria warscewiczii. The study population consisted of monoecious, perennial vines that flower year round, have a flowering peak during the rainy season, and possess an extreme bias in proportion of flowering plants in male phase. Number of flowers on individual plants, flower density, and pollen surplus in staminate flowers at the end of the day (an indicator of visitation activity, or average resource availability) were monitored periodically over 4 yr from 1980 to 1984. Also monitored were the accumulated number of conspecific pollen grains on stigmas, and presence or absence of tephritid fly larvae (Blepharoneura sp.), which infested between 0 and 15% of the staminate flowers sampled. Local flower density (measured within 50 m of the dye—source plant) explained °50% of the variation in mean dye—dispersal distance. Visitation rate, number of individual visitors, and floral occupation rates of individually marked Heliconius butterflies were negatively correlated with average pollen surplus in staminate flowers. At very low levels of resource availability, many butterflies defended individual flowers for entire mornings against repeated attempts by other butterflies to visit the same flowers; at higher resource levels, butterfly visits were of shorter duration, and more movement among plants was observed.
Failure to Detect Senescence in Persistence of Some Grassland Rodents
Authors: Slade Norman A.
Published: May 2006

Several recent papers raise the question of how frequently senescence is detectable in survival estimates from natural populations of mammals. If animals do not age, the probability of disappearance is constant through time. This null hypothesis leads to the prediction that lengths of residence on a trapping grid, censused monthly, will follow a geometric distribution. After testing for survival differences between sexes and among seasons, I compared lengths of residence (persistence) from capture—recapture data for five species of small rodents in an old—field habitat near Lawrence, Kansas, USA to geometric distributions. Gender did not influence persistence on the grid for any species, but persistence of Microtus ochrogaster and Reithrodontomys megalotis varied significantly with season. All species showed a tendency for high rates of disappearance in the 1st mo after individuals were marked. When the analysis was limited to individuals residing on the area for at least 1 mo, neither Peromyscus maniculatus, P. leucopus, nor Sigmodon hispidus departed significantly from the geometric model. Seasonal analysis of Reithrodontomys megalotis was precluded by small samples, but data for all seasons combined seemed to indicate age— (or persistence—) specific rates of disappearance, as did M. ochrogaster, except those first captured in spring. To identify which patterns were consistent with senescence, I regressed rates of disappearance against persistence, testing for positive slope. Only those M. ochrogaster first captured in winter and autumn exhibited senescence by these criteria, despite disappearance rates of R. megalotis that increased sharply beyond persistence of 5 mo. The regression test for P. maniculatus indicated senescence even though the geometric test failed to indicate persistence specificity. The regression method alone is not a reliable test of senescence, because if does not incorporate variances of estimated probabilities of survival. Any approach derived from horizontal life tables potentially confounds seasonality with aging, making determination of senescence equivocal. In my data there is little convincing evidence that survival in the wild decreases with age in these rodents.