bluuebunny/crossref_metadata_2025 huggingface dataset:
Local Specialization of Phoretic Mites on Sympatric Carrion Beetle Hosts
Authors: Brown Jonathan M. , Wilson David Sloan
Published: May 2006

Wide—ranging but ecologically variable species and their close relatives provide the best opportunity to analyze the role of trade—offs in specialization. Poecilochirus carabi Can. is a holarctically distributed mite that rides between patches of carrion on the bodies of carrion beetles (Silphidae, Nicropohorus). Using behavioral tests, we demonstrated differences in local host specialization of P. carabi at two sites in Michigan, the Kellogg Biological Station (KBS) and the University of Michigan Biological Station (UMBS). At KBS, Nicrophorus orbicollis and N. tomentosus each supported a strict host specialist. These KBS "orbicollis— and tomentosus—specialists" differed significantly in both body size and a measure of dorsal setal lengths. Laboratory crosses between specialists were not successful, suggesting that the specialists are distinct species. At UMBS, in contrast, such strong specialists were not found. Mites preferred two beetle species, N. tomentosus or N. defodiens (a species not found at KBS), over all others, but moved between these two species readily. UMBS mites all resembled the KBS tomentosus—specialist in morphology. No orbicollis—specialist mites were found at UMBS, despite the high relative abundance of N. orbicollis in the beetle community. We raised mites from each site on all available hosts to test whether preference for a host species was associated with higher fitness in association with that host species. Although P. carabi were able to reproduce in association with any Nicrophorus species, mites at UMBS had the highest reproductive success on the two species that they preferred. Each KBS specialist mite was raised in association with N. tomentosus and N. orbicollis. While the tomentosus—specialist had significantly higher reproductive success in association with its preferred host species, the orbicollis—specialist showed no difference in reproductive success between the two host species. However, when the pattern of dispersal on beetles was considered, a difference in fitness between the two hosts was apparent. This difference in dispersal pattern was due to an interaction between the parental behavior of the two host species and mite generation times. We discuss the evidence for trade—offs in this system and the use of interspecific comparisons in the analysis of specialization.
Early Stage of Host Range Expansion by a Specialist Herbivore, Euphydryas Phaeton (Nymphalidae)
Authors: Bowers M. Deane , Stamp Nancy E. , Collinge Sharon K.
Published: May 2006

We examined whether larval and adult behavior, physiology, and chemical defense were altered as a result of host range expansion by the Baltimore checkerspot (Euphydryas phaeton, Nymphalidae) from the native host plant, turtlehead (Chelone glabra, Scrophulariaceae), to the introduced weed, plantain (Plantago lanceolata, Plantaginaceae). We found that newly hatched larvae from eggs collected from a population using plantain were heavier than those from a population using turtlehead. Nonetheless, both the prediapause and postdiapause larvae derived from the turtlehead population and fed turtlehead in a laboratory experiment gained more mass than those from the plantain population fed plantain. Collections of diapausing larvae from field sites corroborated that pattern. Regardless of the population source (i.e., those using either turtlehead or plantain), postdiapause larvae reared on turtlehead exhibited higher relative growth rate (RGR), efficiency of conversation of digested food (ECI), and efficiency of conversion of digested food (ECD) than those fed plantain, even though approxi_kw checkerspot butterflies
Adaptive Significance of Ipomopsis Aggregata Nectar Production: Pollination Success of Single Flowers
Authors: Mitchell Randall J. , Waser Nickolas M.
Published: May 2006

Floral nectar rewards are expected to contribute to plant fitness by influencing several aspects of pollinator behavior. For example, when flowers have large standing crops of nectar, pollinators may take longer to probe them, thereby increasing the amounts of pollen deposited and removed. In addition, pollinators may return more often to rewarding plants and/or probe more of their flowers during each visit. We experimentally investigated how each of these behaviors influences pollination success of the hummingbird—pollinated herb Ipomopsis aggregata (scarlet gilia). Captive hummingbirds were trained to probe flowers containing known volumes of artificial nectar (25% mass/mass sucrose solution). Increasing the nectar standing crop of a flower from 1 to 5 μL significantly increased probe duration, but this had no detectable effect on pollination success through the female sexual function (pollen deposited on stigmas) or male sexual function (pollen removed from anthers and number of fluorescent dye particles exported to other flowers). In contrast, both male and female pollination success increased with the number of times a hummingbird probed a flower. For male function, there was at best a weak tendency for pollen export to diminish with successive probes, in contrast to strongly diminishing returns reported for bee—pollinated flowers. This difference may reflect foraging mode; hummingbirds hover and remove a small fraction of available pollen with each floral probe whereas bees land and remove most pollen with the first probe. For plants such as I. aggregata whose pollination success is most sensitive to the number of probes per flower, selection on nectar production may be strongest when there are cues pollinators can use to identify rewarding plants, such as phenotypic correlations between nectar production and floral morphology.
Alternative Outcomes of Natural and Experimental High Pollen Loads
Authors: Young Helen J. , Young Truman P.
Published: May 2006

Seed production is usually assumed to be a positive monotonic function of pollen deposition and/or pollinator visitation. If this assumption were correct, there would be only two outcomes of excess pollen levels: an increase in fruit or seed set, or no increase. However, a substantial minority of the studies reviewed here has found that seed production declines with increased pollen loads, both under experimental and natural conditions. To explain this decrease, we propose the following mechanisms: pollen tube crowding, pollen removal or stigma damage by pollen thieves or pollinators, stigma damage during hand—pollination, application of low—diversity or local pollen, effects of bagging flowers, missed stigma receptivity, and the application of inviable pollen. These mechanisms can be distinguished through more complete and more careful experimental designs and incremental pollen supplementation.
A Method for Reciprocal Scaling of Species Tolerance and Sample Diversity
Authors: Thioulouse Jean , Chessel Daniel
Published: May 2006

The method and the associated graphical representations proposed in this paper facilitate the interpretation of the correspondence analysis (CA) of a samples/species data table. By using the "reciprocal discrimination" model of CA, this method introduces directly and on the same graph the notions of niche width and within—sample diversity. We propose two Macintosh programs for computing conditional means, variances, and covariances of factor scores for species and samples, and for drawing ellipses and Gaussian curves from these values. Two examples of ecological interest show how resulting graphics help in understanding the results of multivariate analyses.
Biological Responses of a Tundra River to Fertilization
Authors: Peterson Bruce J. , Deegan Linda , Helfrich John , Hobbie John E. , Hullar Meredith , Moller Bernie , Ford Tim E. , Hershey Anne , Hiltner Allison , Kipphut George , Lock Maurice A. , Fiebig Douglas M. , McKinley Vicky , Miller Michael C. , Vestal J. Robie , Ventullo Roy , Volk Gregg
Published: May 2006

Phosphorous fertilization of a pristine tundra river for four consecutive summers dramatically changed biological processes and populations at all trophic levels. At the primary producer level, both algal biomass and productivity increased and cholorophyll accumulated on the river bottom in the first two summers. Diatom community composition changed little in spite of large chorophyll changes. However, an increase in grazing insects prevented chlorophyll buildup in the third and fourth summers. Some microbial processes were also stimulated by the increased photosynthesis caused by fertilization. Total respiration of the epilithon, acetate uptake, and decomposition of lignin monomers were all stimulated but only in light—grown epilithon. When epilithon was grown in the dark in the fertilized region of the river, there was no increased respiration. Also, phosphorous did not stimulate the decompostition of Carex litter. Although insects grew more rapidly in the fertilized section of the river, there were community interactions that kept total insect production from appreciable change. The four most abundant large insects did increase their growth rates in response to phosphorus addition and there were increases in populations of Baetis lapponicus and Brachycentrus americanus. These increases were offset by the decline in abundance of the dominant species, the black fly Prosimulium martini, perhaps caused by competition for space from Brachycentrus. Growth of both young—of—the—year and adult grayling (Thymallus arcticus) was strongly stimulated by phosphorus addition in years 3 and 4 (not tested in years 1 and 2). Carbon and nitrogen stable isotope tracers indicated that the measured increases in insect and fish growth were largely attributable to increases in the production of epilithic algae. Overall, the results indicate a strong "bottom—up" response of the riverine food web to additions of the limiting nutrient, phosphorus. The response was modified in later years, however, by a strong "top—down" feedback of insects grazing on epilithic algae and by competitive exclusion of black flies caddisflies.
An Energetic Model of Microhabitat Use for Rainbow Trout and Rosyside Dace
Authors: Hill Jennifer , Grossman Gary D.
Published: May 2006

We constructed an energetic model to determine the optimal focal point current velocity (i.e. microhabitat) for rainbow trout (Oncorhynchus mykiss) and rosyside dace (Clinostomus funduloides) in Coweeta Creek, a fifth—order stream in North Carolina, USA. Energetic costs were evaluated by quantifying the metabolic expenditure associated with swimming at a given velocity. We estimated bebefits by measuring potential energetic gains of feeding at a given velocity. This included estimates of the ability of the fish to capture prey at different current velocities as well as etimates of the frequency and the energy content of drifting prey at various velocities. We derived separate models for small (53—70 mm SL [standard length]) and medium (71—125 mm SL) trout, and medium (47—52 mm SL) and large (53—70 mm SL) dace for all seasons, deriving net energy gain as a function of current velocity. We predicted fishes would occupy velocities at which net energy gain was maximized. Predicted velocities were compared with those utilized by fishes inhabiting Coweeta Creek. Optimal velocities predicted by energetic models ranged from 7.7 to 22.1 cm/s, and closely matched actual velocity use (average deviation = 2.6 cm/s). Prey capture success appeared to be the most important component in the models. Consequently, we constructed models based solely upon aspects of capture success; the average deviation from veolocity use with these models was only 1.8 cm/s. Thus, the ability of dace and trout to capture prey at varying velocities appears to be the dominant factor affecting microhabitat selection in these species.
Web Relocation and Habitat Selection in Desert Widow Spider
Authors: Lubin Yael , Ellner Stephen , Kotzman Mandy
Published: May 2006

We investigated web relocation and habitat selection in Latrodectus revivensis (Theridiidae), a widow spider that constructs webs on scattered shrubs in the Negev desert. We used repeated observations of individual spiders' habitat preferences, movements to new web sites, growth, fecundity, and survival under natural and manipulated habitat conditions to examine relationships between movement, habitat, and components of fitness. Our main objectives were to determine the spatial and temporal patterns of movement, and the causes, costs, and fitness consequences of shifting habitat. Repeated censuses of individually marked females showed that web relocation in L. revivensis is associated with spider growth. Spiders tended to move larger shrubs after one or two molts, and the size of web components and web—site features scaled to body size. Moves occurred mainly in Spring (March—May), and most moves (74%) were by juveniles. The main cost of web relocation was increased mortality: there was a 40% chance of death during a move. A comparison of occupied shrubs with those available in the habitat indicated strong site selection involving seasonally varying and age—dependent preferences for particular shrub species, and a general preference for taller shrubs. Prey availability at shrubs (as measured by pitfall traps, and by prey remains in nests) varied spatially and was affected by shrub species and size. However these effects were small compared to habitat—wide temporal variation in prey availability, suggesting that web—site relocations would not result in substantially higher prey capture. Nonetheless, movement to larger shrubs resulted in improved spider body condition and, ultimately, greater reproductive success. The advantages of web—site relocation in this species may relate to architectural features of shrubs that provide support for the web, and minimize exposure by thermal extremes and to predators. However, experimental manipulation of exposure by trimming shrubs did not decrease spider fitness. We suggest that web—site selection in this species is less precise than expected because of the risk of dying during a move.
Constraints of Nutrient Availability on Primary Production in Two Alpine Tundra Communities
Authors: Bowman William D. , Theodose Theresa A. , Schardt James C. , Conant Richard T.
Published: May 2006

A nutrient amendment experiment was conducted for two growing seasons in two alpine tundra communities to test the hypotheses that: (1) primary production is limited by nutrient availability, and (2) physiological and developmental constraints act to limit the responses of plants from a nutrient—poor community more than plants from a more nutrient—rich community to increases in nutrient availability. Experimental treatments consisted of N, P, and N + P amendments applied to plots in two physiognomically similar communities, dry and wet meadows. Extractable N and P from soils in nonfertilized control plots indicated that the wet meadow had higher N and P availability. Photosynthetic, nutrient uptake, and growth responses of the dominants in the two communities showed little difference in the relative capacity of these plants to respond to the nutrient additions. Aboveground production responses of the communities to the treatments indicated N availability was limiting to production in the dry meadow community while N and P availability colimited production in the wet meadow community. There was a greater production response to the N and N + P amendments in the dry meadow relative to the wet meadow, despite equivalent functional responses of the dominant species of both communities. The greater production response in the dry meadow was in part related to changes in community structure, with an increase in the proportion of graminoid and forb biomass, and a decrease in the proportion of community biomass made up by the dominant sedge Kobresia myosuroides. Species richness increased significantly in response to the N + P treatment in the dry meadow. Graminoid biomass increased significantly in the wet meadow N and N + P plots, while forb biomass decreased significantly, suggesting a competitive interaction for light. Thus, the difference in community response to nutrient amendments was not the result of functional changes at the leaf level of the dominant species, but rather was related to changes in community structure in the dry meadow, and to a shift from a nutrient to a light limitation of production in the wet meadow.
Planktonic Trophic Transfer in an Estuary: Seasonal, Diel, and Community Structure Effects
Authors: Mallin Michael A. , Paerl Hans W.
Published: May 2006

The high tertiary production of estuaries is largely supported by photoplankton primary production. An important question thus concerns how much phytoplankton production enters the food web through planktonic grazing and what physical, chemical, or biological factors influence this trophic transfer. We conducted a 2—yr, diel investigation of planktonic trophic transfer and the factors influencing in the Neuse River Estuary, North Carolina. Zooplankton community grazing rates were generally lowest in winter and highest spring through late summer, ranging from 0.1 to 310 mL°L—1°h—1 . There were few significant diel differences in community grazing rates. The overall daytime mean (± 1 SE) rate was 3.30 ± 0.62 mL°L—1°h—1 while the night mean rate was 3.07 ± 0.60 mL°L—1°h—1. Post—naupliar copepods were usually more abundant at night than day, but tintinnids were often more abundant by day, while total zooplankton, copepod nauplii, and rotifers displayed no significant diel abundance differences. Community grazing was positively correlated with primary productivity and the abundance of total phytoplankton, centric diatoms, dinoflagellates, and the small diatom Thalassiosira. Community grazing was also positively correlated with upstream river flow and negatively correlated with salinity. However, there were no significant correlations with water temperature, nutrient concentrations, or grazer abundance variables. On an annual basis, the zooplankton community grazed °38—45% of daily phytoplankton production. Planktonic trophic transfer was coincidentally greatest in late spring through summer, during the period when anadromous fish larvae migrating from the open ocean reach their estuarine primary nursery areas. The fish arrive when planktonic trophic coupling is strongest and depart in fall, when planktonic trophic transfer, zooplankton abundance, and phytoplankton productivity all decrease.
Trade‐Offs in Diel Vertical Migration by Zooplankton: The Costs of Predator Avoidance
Authors: Loose Carsten J. , Dawidowicz Piotr
Published: May 2006

Diel vertical migration (DVM) of zooplankton is a behavioral antipredator defense that is shaped by the trade—off between higher predation risk in surface waters and reduced growth in deeper waters. We conducted two laboratory experiments to quantify the costs connected with DVM. In the first experiment, Daphnia magna were kept individually in thermally stratified flow—through tubes and exposed to seven different concentrations of fish—exuded kairomones. Above a threshold concentration, the strength of migration increased with increases in the concentration of fish exudates. Enhancement of migration resulted in a lower mean ambient temperature experienced by the animals and marked decreases in individual growth and reproduction rates. In order to separate costs due to low hypolimnetic temperatures in a stratified system from costs due to reduced food concentrations in deeper waters, we conducted an experiment with a 2 ° 2 factorial design (fish presence vs. absence and high vs. low food conditions). Differences in mean ambient temperature between Daphnia that performed DVM and nonmigrating animals were found to have a much stronger impact on life history parameters than food effects. A reevaluation of field data on DVM in Daphnia further supports the view that vertical gradients are more important than food gradients.
Foraging Theory, Patch Use, and the Structure of a Negev Desert Granivore Community
Authors: Brown Joel S. , Kotler Burt P. , Mitchell William A.
Published: May 2006

We tested five mechanisms of coexistence in a community of three common rodent species (two gerbils, Gerbillus allenbyi and G. pyramidum, and one jerboa, Jaculus jaculus) inhabiting sand dunes in the Negev Desert, Israel. The five mechanisms, based on foraging theory, considered various forms of habitat selection in time and space. From November 1986 until January 1988, we live—trapped to census rodent populations, counted rodent spoor in tracking plots to quantify activity, and measured the rodents' giving—up densities (GUDs: the amount of food remaining within a resource patch following exploitation by a forager) in seed trays to determine relative foraging efficiencies. The population sizes of the two gerbil species tended to fluctuate synchronously (unfortunately, we could not live—trap any jerboas). G. allenbyi biased its activity towards the stabilized sand habitat and towards the bush microhabitat. In contrast, G. pyramidum and J. jaculus biased their activity towards semistabilized sand habitats, and J. jaculus also biased its activity towards the open microhabitat. Despite divergent patterns of habitat use among species, G. allenbyi tended to be the most efficient forager and J. jaculus the least efficient forager regardless of microhabitat, sand habitat, or month. G. allenbyi's presence in the community may be assured by its higher foraging efficiency. J. jaculus's presence in the community may either result from its ability to travel greater distances and utilize rare, rich resource patches, or result from an herbivorous diet. G. pyramidum's presence with G. allenbyi in the community appears to require the less stabilized sand habitats and the ability of G. pyramidum to dominate rich patches by interference or nightly temporal partitioning.
Effects of Interannual Climate Variation on Phenology and Growth of Two Alpine Forbs
Authors: Walker Marilyn D. , Ingersoll Richard C. , Webber Patrick J.
Published: May 2006

Variations in growth, flowering, and phenology of two forbs, Acomastylis rossii and Bistorta bistortoides, were compared among six years (1983—1988) and five plant communities (fellfield, dry meadow, moist meadow, were meadow, snowbed) at an alpine site in the Front Range of Colorado. The purpose was to determine the extent to which the phenolgical patterns of these species varied among plant communities and how interannual climate variability affects phenology and growth. There were significant differences in growth among communities for both species. In B. bistortoides, there were also significant differences among years, due primarily to the influence of a single year (1983) when leaf length increased by °10% and the average number of B. bistortoides leaves nearly doubled. Key phenological events of both species (initiation of growth, date of maximum leaf length, leaf number, and flower number) were related to snowmelt patterns, resulting in differences among communities. There were also significant differences among years, again primarily related to the single year 1983, the year of a major El Nino Southern Oscillation (ENSO) event that produced high snowfall amounts at the site. The increased leaf length in a high snow year is counterintuitive to the commonly accepted notion that alpine species may be limited by season length. We hypothesize that changes in phenology related to changes in snowfall of snowmelt will cause detectable changes in growth, but that these will not be predicted simply from phenology alone. Rather, the timing of snowmelt in relation to nutrient availability, soil moisture, and air temperature will be critical in determining how individual species respond.
A Note on the Analysis of Species Co‐Occurrences
Authors: Manly Bryan F. J.
Published: May 2006

The analysis of records of species occurrences on islands in an attempt to detect interactions between species has been an area of controversy in recent years in terms of the validity of some of the statistical methods used. In this note I make two contributions to the continuing debate. First, I advocate a generalized Monte Carlo testing procedure because this is easy to implement, is computationally efficient, and has guaranteed properties when the null hypothesis of no species interactions is correct. Second, I propose a test statistic that can be decomposed into a component for each individual species, and I demonstrate how this makes it possible to isolate species with unusual patterns of co—occurrence with other species, even after an allowance for multiple testing is made.
Seedling Crown Orientation and Interception of Diffuse Radiation in Tropical Forest Gaps
Authors: Ackerly D. D. , Bazzaz F. A.
Published: May 2006

In forest gaps, the geometry of canopy openings above a plant determines the spatial distribution of diffuse and direct radiation, which may be received from different sectors of the sky. We examined crown orientation and light interception by seedlings of four species of pioneer trees, Cecropia obtusifolia, Heliocarpus appendiculatus, Piper auritum, and Trema micrantha, transplanted into natural forest gaps at the Los Tuxtlas Tropical Biology Station, Veracruz, Mexico. The four species differed in the number and mean size of leaves, but total leaf area was not significantly different among equal age plants. The mean azimuth and zenith angle of diffuse and direct radiation were determined from hemispherical photographs taken above each plant. Mean diffuse radiation vectors were distributed around the zenith, with a significant clustering in an easterly direction, while mean direct radiation vectors were distributed along the solar track in the southern portion of the sky. The mean orientation of the crown of each seedling was determined from detailed, three—dimensional reconstruction of leaf display using a canopy architecture model. A directional correlation test indicated that seedling crowns were orientation of individual leaves. The mechanisms of this differential response to diffuse vs. direct radiation are not known. For diffuse radiation, the total light capture capacity integrated over all sky directions increased with seedling leaf area, while efficiency of capture per unit area decreased. Based on simulations, the light interception efficiency of each plant in its own microsite was 5—25% greater than would be achieved in the sites of conspecifics of in symmetric canopy openings centered on the zenith. These analyses provide a quantitative estimate of the value of nonrandom leaf and crown orientation for whole—plant light interception in natural environments.
A Spatially Explicit Test of Foraging Behavior in a Clonal Plant
Authors: Evans Jonathan P. , Cain Michael L.
Published: May 2006

Through plasticity in traits controlling clonal morphology, clonal plants possess the potential to selectively place ramets within a heterogeneous environment or "forage." Although many studies document plant responses that are consistent with foraging, few studies test directly whether plants can preferentially locate "good" patches or avoid "bad " patches when grown in a heterogeneous environment. We conducted such a test for Hydrocotyle bonariensis, a clonal dune species that inhabits soils known to be extremely patchy on both time and space. We subjected Hydrocotyle to a temporally constant but spatially variable soil resource environment created by clipped patches of grass. Clonal morphology on the patch treatment was compared to that in two homogeneous treatments: no grass and full grass. In order to predict the effect of our treatments on the long—term expansion of clones, we calibrated diffusion models of clonal growth with data on the morphological response of Hydrocotyle to our treatments. Clones of Hydrocotyle bonariensis were able to respond to the presence of patches by selectively placing ramets outside of grass patches, thus providing direct evidence of an effective foraging response. For each of the three traits identified as potentially contributing to an overall foraging response (branching, internode distance, and direction of rhizome growth), the response in and out of grass patches was substantially different from the degree of plasticity manifested by the two homogeneous treatments. For example, no difference in main rhizome internode lengths was found between the two homogeneous treatments. In contrast, ramets in the heterogeneous (patchy grass) treatment responded to their local environment by increasing internode lengths when in the unfavorable (grass patch) portion of the environment. Empirically calculated diffusion models indicate that habitat complexity has considerable impact on the long—term expansion of clones: only in the heterogeneous treatment did clones expand less rapidly in favorable habitat than they did in unfavorable habitat. In the heterogeneous treatment, Hydrocotyle rhizomes exhibited a previously undocumented behavior: they appeared to veer away from patches of grass. Finally, we discuss how the foraging response of Hydrocotyle ramets may be enhanced by its previously documented capacity for resource integration.
Nutrient Dynamics, Bacterial Populations, and Mosquito Productivity in Tree Hole Ecosystems and Microcosms
Authors: Walker Edward D. , Lawson Daniel L. , Merritt Richard W. , Morgan William T. , Klug Michael J.
Published: May 2006

Water—filled treeholes provide an experimental setting for examining processes within an ecosystem, and influences of external factors on those processes. Using a limnological, experimental approach involving both natural tree holes and laboratory microcosms of the tree hole ecosystem, we identified and studied interacting, biotic processes, including dynamics of bacterial populations and variation in concentration of inorganic nutrients in tree hole water, and density—dependent competition for food among larvae of the mosquito Aedes triseriatus. We characterized the influence of external factors (inputs of leaf detritus and stemflow) on those processes. Analyses of water samples over time showed that tree hole water was rich and dynamic in nutrients (nitrite, nitrate, ammonium, phosphate, and sulfate); ammonium was the dominant form of inorganic nitrogen. Variation in nutrient concentrations in microcosms depended upon exogenous inputs (leaf detritus and stemflow water), dilution of nutrients by stemflow, nutrient cycling processes (nitrification, dentrification, and sulfate reduction), and ammonium excretion by mosquito larvae. The densities of bacteria in tree hole water, obtained using direct counts of DAPI—fluorochrome stained samples and epifluorescence microscopy, ranged from 2.0 ° 106 to 6.0 ° 107 cells/mL, and in microcosms from 4.6 ° 105 to 2.6 ° 108 cells/mL. Experimentation involving microcosms revealed that bacterial abundance was reduced by mosquito feeding and stemflow flushing. Further experiments showed that stemflow flushing increased mosquito productivity from microcosms several—fold and released mosquitoes from density—dependent competition. This effect was likely related to nutrient input and the simultaneous removal of toxic metabolites owing to inputs of stemflow water. We conclude that disturbance by a physical factor, stemflow, has a major influence on the interactions of nutrient dynamics, bacterial populations, and mosquito productivity in temperate tree—hole ecosystems.
Foraging Cyanobacteria by Copepods: Responses to Chemical Defense and Resource Abundance
Authors: DeMott William R. , Moxter Felix
Published: May 2006

We used laboratory feeding trials to examine the responses to copepods to a variety of cyanobacteria of differing size, morphology, and toxicity. Diaptomus birgei exhibited behaviors ranging from strong preferences for some taxa of cyanobacteria to almost complete rejection of other taxa when allowed to feed in low—concentration mixtures of a high—quality green alga, Chlamydomonas reinhardi, and each of 16 taxa of cyanobacteria. Our results demonstrate the overriding importance of chemical factors. Copepods exhibited very high clearance rates for some filaments and colonies but rejected morphologically similar strains shown to contain potentially toxic compounds. Responses to resource abundance exhibited three patterns, each consistent with the assumptions and predictions of an optimal diet model. First, selectivity for high—ranking cyanobacteria declined in high—concentration mixtures with Chlamydomonas relative to selectivity in low—concentration mixtures. Second, a test of the effects of time without food showed that hunger, rather than food concentration per se, was responsible for these shifts in selectivity. Finally, each toxic strain was consistently ingested at very low rates, even when offered as the sole food resource. Experiments with complex mixtures of natural seston revealed similar patterns of consistently strong discrimination against a presumably toxic cyanobacterium and concentration—dependent selectivity for presumably nontoxic taxa. Our results show how the behavioral flexibility of copepods can be adaptive in lakes with significant populations of cyanobacteria. The ability of copepods to feed size—selectively on filaments and colonies and to discriminate against toxic forms suggests that these grazers may be important in the evolution and continued success of toxic strains.
Patterns of Individual Variability in Floral Resources
Authors: Real Leslie , Rathcke Beverly J.
Published: May 2006

The distribution and presentation of floral rewards to insects has been demonstrated to influence pollinator visitation rates, pollinator movements, and consequent plant fitness. However, very little is known about the extant variation in nectar rewards among individuals in a single population. Patterns of nectar production within individual shrubs of Kalmia latifolia L. (Ericaceae) were examined during summer 1985, in a Southern Appalachian health bald in Giles County, Virginia. Five inflorescences from each of 20 shrubs at two sites in the study area were bagged to exclude insect visitors. Twenty—four hour nectar production was measured using microcapillary extractions in each open flower within each of the bagged inflorescences. For each individual we monitored arithmetic mean reward per flower and variance in reward over the flowering season. There is significant variation among individuals in the mean reward/flower at both sites, but the variance in reward/flower is significant at only one site. The mean reward and the variance in reward are positively correlated among shrubs. If the coefficient of variation is used to uncouple the intrinsic correlation between these two plant variables, then no significant differences emerge among shrubs in levels of relative variability at either site.
Differential Importance of Beetle Species Pollinating Dieffenbachia Longispatha (Araceae)
Authors: Young Helen J.
Published: May 2006

Dieffenbachia longispatha (Araceae) is pollinated by scarab beetles (Cyclocephala spp. and Erioscelis sp.) at the La Selva Biological Station, Costa Rica. The relative contributions of each beetle species to female reproductive success of D. longispatha were determined by observing inflorescences during the flowering seasons of 1982 and 1983 and recording the number of visiting beetles of each species. Fruit production was determined for each inflorescence as fruits ripened, 9 mo after flowering. The three most abundant beetle species differed in abundance, recapture rates, pollen loads carried, and behavior at inflorescences. Despite these differences, the effect of the single visit on fruit—set of D. longispatha (the "pollinator effectiveness" of each species) did not vary among the beetle species. The "importance" of each pollinator species, estimated in previous studies from the abundance and effectiveness of each species and determined in this study from examining fruit—sets of inflorescences visited by varying numbers of beetles, was not a positive, linear function of beetle abundance. In 1982, when visitation rate of all beetle species was low, fruit—set was positively correlated with the number of beetles in an inflorescence but "per visit" effectiveness decreased with increasing visitation, resulting in a saturation of fruit—set at 42%. Beetle identity (to species) did not explain a significant proportion of the variance in fruit—wet in 1982. In 1983, beetle abundance quadrupled relative to 1982 and fruit—set was positively correlated with beetle numbers up to four, but visitation by more than four beetles resulted in a decreased in fruit—set. A high proportion of Cyclocephala gravis produced higher than predicted fruit—set, while a high proportion of Erioscelis yielded fruit—sets lower than was predicted by total number of beetles. The presence of large numbers of Eriosceliis within inflorescences in 1983 and the low fruit—sets of those inflorescences explained the significantly negative slope of the regression for inflorescences fisted by more than four beetles. Previous models have predicted saturation of fruit—set with increasing pollinator visitation (as seen in 1982) but have not predicted a significant decline in fruit—set with pollinator abundance. The proportion of the variance in fruit—set explained by beetle abundance was low for both years (2—8%), suggesting that other factors contribute to female reproductive success in Dieffenbachia (i.e., number of potential mates and the distances to potential mates in the population). Use of common indices of pollinator contribution to seed set, such as pollinator abundance and the number of seeds produced as a result of a single visit, would lead to erroneous conclusions if applied to Dieffenbachia and its beetle pollinators, or to other pollination systems where there is cumulative floral damage with increasing visitation frequencies.
Genetic Variation Among Plants and Insect Community Structure: Willows and Sawflies
Authors: Fritz Robert S. , Price Peter W.
Published: May 2006

The effects of both genotype and spatial position of host plants on density, proportion, and total community structure of herbivore species were experimentally tested for a guild of gall—forming sawflies on their host plant, the arroyo willow, Salix lasiolepis. Genetic differences among individually potted stem cuttings from 6 and 12 willow plants were found to have a significant effects on the densities of each of the four sawfly species and on their proportional representation on willow clones. Analyses also showed that the total community structure (proportions of species) varied among clones. Proportional overlap values showed that two the of willow clones differed markedly from the others regarding the predominant species on them. However, phenotypic correlations showed that the sawfly species were positively correlated among plants during 2 yr. Genotypic correlations were positive and mostly significant in 1985, but were mostly nonsignificant in 1986. Estimates of broad—sense heritability indicated that between 20 and 50% of variation in the density of two species, the stem galler (Euura lasiolepiis) and the leaf folder (Phyllocolpa sp.), was due to clone genotype, whereas only 9—28% of variation in the density of the leaf galler (Pontania sp.) and the petiole galler (Euura sp.) was due to clone genotype. Environmental variation due to spatial position of plants contributed little to variation in density of species in experiments in 1985, but was an important source of variation in 1986 for three species. As a consequence species proportion for all species varied significantly among rack positions of the willow pots. In 1986, clone x position interactions were not significant for species density or for species proportion, with the exception of the leaf folder, which showed marginal significance. Thus, there was little evidence of genotype x position interactions. These studies suggest that plant genetic variation may be an important variable influencing community structure of phytophagous insects on host plants with plant populations. Plant morphological traits that are important to sawfly oviposition in the field (e.g., mean shoot length) differed significantly among willow clones in both years and were correlated with the variation in density of three of the four sawfly species among all plants in both years. In 1985, correlations between shoot length and species density based on clone means were significant for all four species, but in 1986, none of the correlations was significant, although for three of the four species correlation coefficients were similar in magnitude to those from 1985. Species density of the leaf folder, stem galler, and petiole galler were also correlated with leaf length among plants and clones in 1985. These data tentatively suggest that there are positive genetic correlations between plant characteristics and susceptibility to sawfly galling
A Consideration of the Trophic Dynamics of a Late Cretaceous Large‐Dinosaur Community (Oldman Formation)
Authors: Farlow James O.
Published: May 2006

The Late Cretaceous Oldman Formation comprises sediments that were deposited along the margin of a great inland sea that covered much of the western interior of North America. The environment of deposition appears to have been tracts of fluvial marshes that separated “islands” of higher, drier ground. The climate was probably warm—temperate, and it is suggested that upland plant communities were parkland—like in aspect. The large dinosaurs of this community comprised animals that were between a hippopotamus and a large African elephant in adult weight. Some workers have suggested that dinosaurs had metabolic rates comparable to those of living birds or mammals. By extrapolating from the food consumption rates of these living endotherms it is possible to obtain crude estimates of the ingestion rates of endothermic dinosaurs. Similar extrapolations from the ingestion rates of living reptiles and amphibians provide estimates of the ingestion rates of ectothermic dinosaurs. By deriving an empirical equation relating the ratio of annual secondary productivity/average annual biomass to adult weight in living mammals, and employing estimates of adult weight and biomass for the herbivorous dinosaur populations, it is possible to estimate the annual secondary production of endothermic Oldman herbivorous dinosaurs. If the body weight vs. production/biomass relation derived for mammals can be applied to ectothermic tetrapods, it is possible to estimate annual secondary production of ectothermic dinosaur populations. These calculations suggest that the annual secondary production of endothermic herbivorous dinosaurs would have been insufficient to meet the food requirements of an endothermic carnivorous dinosaur population as large as is preserved in the Oldman Formation. However, ectothermic carnivorous dinosaurs would have been easily able to make energetic ends meet. Unfortunately, the situation is complicated by the possibility that carnivores are overrepresented in collection from the Oldman. Because of this, I cannot presently decide between ectothermy and endothermy in dinosaurs on the basis of methods presented in this paper. Alternative methods that may be more successful in this regard are discussed. It is hoped that as paleontologists collect fossils from an ecological point of view the methods presented in this paper can be employed to make realistic statements about the trophic dynamics of ancient vertebrate communities.
Size‐Limited Predation: An Observational and Experimental Approach with the Mytilus‐Pisaster Interaction
Authors: Paine R. T.
Published: May 2006

In many space—limited systems, for instance forests, coral reefs, and mussel beds, the main biological component of the spatial matrix is provided by large—bodied species. At some point during their growth these matrix species surpass the ability of any single individual of a predator species to consume them, although they still may be overwhelmed by concentrated group attacks (i.e., by aphids, fungi, internal parasites). These species thus surpass through continued growth a size threshold limiting their consumers, and thereby attain a refuge in size. The implications of these refuges are discussed, with special reference to a predatory starfish, Pisaster ochraces, and its primary prey, the mussel, Mytilus californianus. The mean wet weight of Pisaster varies between localities from ° 150 g to 2,640g. Long—term (12—yr) observation indicates little annual variation and generally no trends within areas, yet consistent differences between areas. Five transplant experiments demonstrate that Pisaster is an indeterminate grower, andis capable of adjusting its body size through growth to local conditions. Limited recovery of individually marked starfish suggest that exchange between areas is restricted. Observations on the natural diet of Pisaster show a pronounced maximum body size limit to the mussels that can be consumed by intertidal starfish of a given size. This limit was explored experimentally in two ways. First, Pisaster was allowed to reinvade an area from which it had been manually excluded for 5 yr. In this interval those mussels comprising the matrix of the clump had attained shell lengths > 8—10 cm. and could not be consumed by Piaster weighing 203 g. Second, artificial clumps of known—size mussels were protected by plastic screening, allowed to attach, and then exposed to predation. Survival was significantly greater in those mussels expected to be too large to be eaten. The significance of size—limited predation is that prey and predator can coexist in very intimate proximity, that the surviving prey often attain large sizes and probably make a reproductive contribution greater than their abundance, and that these same prey diversify the spatial structure of the environment, usually by adding a vertical dimension not otherwise present.
Walking the Tight Rope: Arboreal Sprint Performance Among Sceloporus Occidentalis Lizard Populations
Authors: Sinervo Barry , Losos Jonathan B.
Published: May 2006

We document variation in the degree of arboreality among four populations of the western fence lizard (Sceloporus occidentalis), and investigate how this variation related to locomotor performance capability in an arboreal context (e.g., artificial branches). We raced lizards on four different rod diameters, measured maximum sprint speed, and also scored agility on the rods. Lizards from more terrestrial populations ran faster on thick rods, but slower on thin rods than did lizards from more arboreal populations. The terrestrial lizards experienced a greater difference in sprint speed than did the more arboreal lizards over the range of rod sizes we used. Arboreal lizards were more adept at running on all surfaces in that they stumbled and fell less often, particularly from the thinnest rods. Thus, specialization for maximizing sprinting performance on arboreal surfaces of a particular diameter entails a performance trade—off that is reflected in both speed and "sure—footedness." We investigated whether the population differences in arboreal sprinting are correlated with the significant differences in hind—limb span found among populations. We found that lizards with relatively longer limbs sprinted faster. By using juveniles reared in a common laboratory environment, we demonstrated that these among—population differences in arboreal sprint performance are probably genetically based.