bluuebunny/crossref_metadata_2025 huggingface dataset:
Positive Effects of Pollination on Subsequent Size, Reproduction, and Survival of Primula Veris
Authors: Lehtila Kari , Syrjanen Kimmo
Published: May 2006

We conducted three experiments in which we applied additional hand pollination, flower removal, and leaf removal treatments in various combinations to Primula veris, a perennial spring—flowering rosette species. The purpose of the study was to determine whether the seed set of Primula veris was limited by pollen availability or by other resources, and whether there were measurable cost of reproduction. Hand pollination in the beginning of experiments significantly increased current seed set in only one of the three experiments. It also increased the next—year fruiting probability in that first experiment. In the second experiment, hand pollination did not significantly affect current seed set, but we nevertheless observed enhanced leaf growth in the treatment year and the two following years, and increased flowering frequency, fruiting frequency, and survival in the two following years. In the third experiment, after hand pollination we observed a higher net photosynthetic capacity of the leaves and, again, increased leaf growth in the treatment year and a higher flowering probability in the following year. The positive effect of hand pollination was even clearer when the leaves of the plants were removed at the beginning of the experiment. However, the treatment in which all the flowers were removed had effects on subsequent performance similar to those of the hand—pollination treatment, suggesting trade—offs. Thus, we did not observed any costs associated with reproduction after supplemental hand pollination; on the contrary, hand pollination resulted in increased survival, size, and reproduction of the plants in the subsequent years.
Predator Interference across Trophic Chains
Authors: McCarthy Michael A. , Ginzburg Lev R. , Akcakaya H. Resit
Published: May 2006

Conflict between ratio—dependent views of trophic interactions finds its simplest resolution in the comparison of steady—state responses of trophic chain to increases in primary productivity. We analyze data on trophic abundances of lake ecosystems with a general trophic—chain model that is intermediate between prey dependence and ratio dependence, and can describe either of the two extremes, depending on parameter values. We estimate, for all trophic levels, the set of interference coefficients that predicts the observed statistical relationship between biomasses of adjacent trophic levels. This constitutes a test of two competing theories, since the model we use is a prey—dependent model if all interference coefficients are °0, and a ratio—dependent model if they are °1. The results show that the observed relationships among trophic levels in lake ecosystems are compatible with a ratio—dependent parameterization of this model, with interference distributed relatively evenly across trophic chains, and are incompatible with a pure prey dependent parameterization. We suggest that approximate ratio dependence applied uniformly across trophic chains is a more plausible description of lake ecosystems than either pure prey dependence (non—interference) or "concentrated interference" (prey dependence at some trophic levels and partial interference in others).
Effects of Basal Resources, Predation, and Alternative Prey in Microcosm Food Chains
Authors: Balciunas Dalius , Lawler Sharon P.
Published: May 2006

Ecological theorists propose that the species composition of trophic levels can influence the relative strengths of top—down (predation) or bottom—up (nutrient) effects in food chain. We tested this by constructing two— and three—level food chains of bacteria and protists. Bacteria made up to first trophic level. The second level contained Chilomonas paramecium alone, Colpidium cf. striatum alone, or both together. Predatory Euplotes patella occupied the third trophic level. These assemblages were cultured in microcosms containing either low— or high—nutrient medium. Manipulating nutrients and predation produced comparable changes in the abundance of bacteria. In the second trophic level, Chilomonas was usually driven extinct by predation, but Colpidium was affected more by nutrients than predation because it had a partial size refuge from predation. Both species survived more poorly with predatory Euplotes if the other was present, because the predator was more abundant and persistent when both prey were available. The predator was less persistent in high—nutrient microcosms, because additional nutrients boosted the proportion of Colpidium populations within the size refuge. This type of mechanism could limit trophic cascades in food chains where resources affect prey vulnerability.
Determinants of Host Range In Bruchid Beetles
Authors: Siemens David H. , Johnson Clarence D. , Woodman Robert L.
Published: May 2006

We asked what factors keep the seed beetles Stator limbatus and S. pruininus (Bruchidae) restricted to different species of Acacia (Leguminosae) in sympatry. Factors assessed were plant microenvironment, interspecific competition, suitably of seeds for food, and enemy impact. Females selectively oviposited on seeds of their normal host when given a choice of acacia seeds in their normal host microenvironment. This result occurred whether seeds of the other acacia were offered with or without potential competitors in them. Host suitability was determined by comparing full—siblings on both acacias. Three performance variables were measured: (1) emergence per egg laid, (2) time to emergence, and (3) size of females. Stator limbatus performed best on its normal host in all three variables measured, while S. pruininus performed best on its normal host in emergence time but showed no difference in percent emergence or female size. We also assessed the impact of the egg parasite Uscana semifumipennis (Trichogrammatidae) on the two species of bruchids when the bruchids occurred in their normal hosts. Uscana attacked both bruchids at the same level (20% of eggs parasitized). Thus, the proximate determinant of locality restricted use of hosts is oviposition behavior, which we suggest relates best to differences in the suitability of hosts for larvae.
Environmentally Induced Differences in Plant Traits: Consequences for Susceptibility to a Leaf‐Cutter Ant
Authors: Nichols-Orians Colin M.
Published: May 2006

The effects of different light and soil nutrient conditions on foliar chemistry and acceptability of Inga oerstediana seedlings to leaf—cutter ants were investigated. I determined differences among (1) leaves that were initiated and matured under identical conditions but subsequently were subjected to different light and fertilization treatments and (2) leaves that were initiated and matured under different soil, light, and fertilization treatments. I also assessed the relationship between environmentally induced differences in plant growth and the production of carbon—based secondary chemicals (specifically, tannins). Finally, I determined whether increases in tannins corresponded to decreases in the acceptability of leaves to leaf—cutter ants. Once a leaf matured the concentrations of tannins did not change as a function of light and soil nutrient conditions despite very large differences in growth rates among the treatments. Leaves that expanded to maturity under different soil, light, and fertilization treatments did differ in tannin chemistry, and treatment differences in plant growth rates appeared to dictate tannin chemistry. When growth was light limited, tannin concentrations were low, but when growth was nutrient limited, tannin concentrations were high. Only leaves that expanded to maturity under different environmental conditions differed in their acceptability to leaf—cutter ants. Decreases in tannins did not result in parallel increases in acceptability. Despite higher concentrations of tannins, leaf—cutter ants preferred the leaves of seedlings that were grown at 20% light over leaves of seedlings grown at 2% light. However, fertilization increased the acceptability of leaves when seedlings were grown at 20% light, a result consistent with the avoidance of very—high—tanning leaves. From these results I suggest that spatial variation in resource availability in lowland tropical rainforests would result in differences in tannin chemistry, and in susceptibility to leaf—cutter ants. However, temporal changes in resource availability would only be important to tannin chemistry and susceptibility if the duration of the change were long enough to allow new leaves to be produced.
Capture Success and Diet of Cottid Fishes: The Role of Predator Morphology and Attack Kinematics
Authors: Norton Stephen F.
Published: May 2006

In this study laboratory experiments were conducted to test predictions of capture performance based on an understanding of the hydrodynamics of contrasting feeding modes (ram and suction feeding) and on an observed ecomorphological pattern among marine members of the temperate fish family Cottidae. Small—mouthed species that feed predominately on grasping prey (e.g., crabs, isopods, gastropods) were predicted to have low capture success on an elusive prey (shrimp) and to use kinematics more consistent with suction—feeding mechanisms; large—mouthed species that feed predominately on elusive prey (e.g., fishes, shrimp) were predicted to have high capture success in attacks on shrimp and to use ram—feeding kinematics. Laboratory experiments in which predators were videotaped in attacks on either hippolytid shrimp or cancrid crabs tested both the attack success and kinematic predictions. Small—mouthed cottid species had significantly lower attack success on shrimp (20—41% vs. 45—56%) than did large—mouthed cottids. Both groups had similar high success rates in attacks on crabs on a sand surface: 93—100% for small—mouthed species and 85—95% for large—mouthed species. Most small—mouthed cottids used attack kinematics more typical of suction feeding (e.g., shorter predator—prey distances and slower attack velocities) than did ram feeders. One small—mouthed species, Jordania zonope, used attack kinematics similar to those used by large—mouthed cottids in attacks on shrimp, and had higher capture success than other small—mouthed species, but had significantly lower capture success than large—mouthed species. All predators showed some ability to modify their attack kinematics when attacking prey with different escape tactics, but cottids showed little intraspecific variation in attack kinematics, in contrast to several recent studies of the strike mechanics of lower vertebrates. These results emphasize the importance of both mouth morphology and attack kinematics in determining interspecific differences in capture success and, perhaps, diet. The success of the simple predictions presented here provides hope that general predictions of foraging ecology may be derived from morphological patterns when the prey are treated not by their taxonomic affinities but by the functional demands they make on their predators.
Morphology and Ecology: Functional Basis of Feeding Constraints in Caribbean Labrid Fishes
Authors: Wainwright Peter C.
Published: May 2006

This study examines the role of functional morphology of the feeding apparatus in constraining the food habits of Caribbean wrasses (Labridae) in the genus Halichoeres. Like other wrasses, these fishes crush prey with powerful pharyngeal jaws. Estimates of pharyngeal jaw crushing strength were made, based on muscle size and architecture, for an ontogenetic series of fish from each of six species. The resultant scaling relationships indicated that, at any given body length, the six species differed in crushing strength. The ability to crush prey items was, therefore, predicted to vary among species. The relative importance of crushing strength and pharyngeal jaw gape in constraining predation was examined in laboratory feeding trials using three species that differed in estimated crushing strength: H. garnoti, H. bivittatus, and H. maculipinna. The feeding trials determined the largest individuals of three prey species that fishes could eat. Two hard—bodied prey species (a gastropod and a crab) and a softer bodied crab species were offered to wrasses. Feeding ability on the two hard—shelled prey was predicted best by crushing strength; fishes of equivalent crushing potential were able to eat the same maximum size prey, in spite of considerable interspecific variation in pharyngeal jaw gape and body length at any given crushing strength. The consequences of ontogenetic and interspecific differences in crushing ability for feeding habits were explored by analyzing the intestinal contents of fishes collected from the Belizean barrier reef. Crushing strength appeared to play a central role in constraining diets of these fishes. Ontogenetic diet analysis of three species revealed that fishes switched from soft—bodied to hard—shelled prey at °3—5 N crushing strength, even though this crushing strength occurred at a different body size and pharyngeal jaw gape in each species. This switch was followed by a reduction in dietary breadth as fishes specialized on hard—bodied prey. Few other Caribbean coral reef fishes are capable of crushing molluscs effectively. Wrasses thus utilize a relatively unexploited trophic niche on the prey—hardness resource dimension.
Thermal Biology of Anolis Lizards in a Complex Fauna: The Christatellus Group on Puerto Rico
Authors: Huey Raymond B. , Webster T. Preston
Published: May 2006

To describe the thermal biology of the three trunk—ground species of the Anolis cristatellus group on Puerto Rico, an island with 10 species of Anolis, we obtained samples of air and body temperatures of A. gundlachi (shady perches, montane forests), A. cristatellus (shady or sunny perches in open or closed forests, lowlands to mid—elevations), and A. cooki (sunny perches in open, xeric lowlands). Average body temperatures parallel altitudinal and habitat association (lowest for A gundlachi, highest for A. cooki). Within a species, body temperatures are strongly correlated with air temperatures and thus vary with altitude, time of day, habitat, and weather. Observed differences between sympatric species in body temperatures and habitat probably reflect physiological requirements, but may be magnified by competition. Relative thermal niche breadth of individuals of these species is approximated and compared with data on species from simple anole faunas to evaluate hypotheses on the evaluation of thermal niche breadth. Extent of basking behavior is inversely related to associated costs for these species. In closed forests where costs of raising body temperatures are high, A. gundlachi and A. cristatellus rarely bask and seemingly are routinely passive to ambient conditions. In open habitats where costs are low, A. cristatellus and A. cooki frequently bask.
Herbivory and Tree Stand Composition: Moose Patch Use in Winter
Authors: Danell Kjell , Edenius Lars , Lundberg Per
Published: May 2006

Foraging decisions by large herbivores in a heterogeneous environment with several available plant species are a scale problem. If, for example, the foraging decisions primarily occur at the stand level, then stands of trees might be regarded as patches within a habitat of several stands over which intake rate is to be maximized. The food consumption within a stand should be in proportion to the availability of different food types. If, on the other hand, food selection occurs at the tree level within a stand, then the individual trees are regarded as "patches"; total stand exploitation should then be the result of foraging decisions made within the stand. We tested these two hypothesis in field experiments in winter with free—ranging moose (Alces alces) having access to artificial stand of trees. In these stands Scots pine (Pinus sylvestris) was mixed with either aspen (Populus tremula) or alder (Alnus incana). In experiment A, where the total available pine biomass per stand was much greater than any of the additional species, total stand consumption did not differ between stand types. In experiment B, where pine biomass did not dominate to the same extent, pine + aspen stands were more heavily used than pine + pine and pine + alder stands. The within—stand consumption of different species appeared to be nonrandom, i.e., the tree biomass was not consumed in proportion to availability. The mean pine biomass consumption per tree did not differ between stand types in either experiment. We conclude that the food selection appears to occur primarily at the tree level within stands. The level of decision might also be important for the performance of the plant species exploited. The results from this study question the general validity of recent hypotheses regarding "associational protection" in plant communities. We suggest that the optimal patch use approach taken in this study might give better insight in these kinds of plant—animal interaction problems.
The Productivity of the C_4 Grass Echinochloa Polystachya on the Amazon Floodplain
Authors: Piedade M. T. F. , Junk W. J. , Long S. P.
Published: May 2006

Plants utilizing the C4 photosynthetic pathway show higher potential efficiencies in the use of intercepted radiation, water, and nitrogen for the production of dry matter than do other photosynthetic types. C4 species are most numerous in tropical and warm, temperature semi—arid zones, where their greater water—use efficiency appears to be a key selective advantage. This fails to explain the dominance of a few C4 grasses in floodplain communities of the wet tropics. One such species, Echinochloa polystachya, occurs along the fertile white waters of the Amazon region. In this habitat, where neither water nor nitrogen supply are likely to be limiting to production or survival, a C4 species may realize its high productivity potential. This possibility was examined by monthly measurements of stand demography, biomass, and radiation interception at a site in the central Amazon. The maximum standing crop of 80 Mg/ha and annual net primary production of 99 Mg/ha of dry matter are among the highest values recorded for natural vegetation. The mean rate of dry—matter production per unit of solar radiation intercepted by the stand was 2.3g/MJ, an efficiency close to the considered maximum for C4 species. The significance of this high productivity to the carbon budget of the region is discussed. Despite the investment of most of its high productivity into stem material, growth of E. polystachya was only just sufficient to keep pace with the 8 m rise in water level that occurs as part of the annual cycle in river discharge. In this unusual environment, the high productivity potential conferred by C4 photosynthesis may be essential, in allowing this rooted macrophyte to produce a stem which is of sufficient rigidity and length to hold the canopy above the rising flood waters.
The Size Structure of Theoretical Plant Populations: Spatial Patterns and Neighborhood Effects
Authors: Bonan Gordon B.
Published: May 2006

The role of neighborhood competition in the formation of size hierarchies was investigated using an individual—plant, spatially explicit growth model of annual plant population dynamics. Neighborhood effects were varied by having plants grow individually and in random and hexagonal spatial patterns. Resources shared between two individuals were allocated symmetrically or asymmetrically. The effect of genetic variability was controlled by first assigning constant initial masses and growth rate coefficients for all individuals and then drawing these parameters from normal frequency distributions. Size hierarchies formed when relative growth rates were positively correlated with plant mass. Neighborhood effects were an important means of inducing this relationship. When plants competed for resources, individuals had the same relative values of available growing space, relative growth rate, and mass so that size differences were enhanced over time. However, genetic variation in growth rates also caused a positive correlation between plant mass and relative growth rate. In this case, regardless of the type of resource allocation, neighborhood competition increased the variability in growth rates beyond that expected from genetic variation. These theoretical results suggest the importance of neighborhood effects in the formation of size hierarchies and imply that size structure is in part an expression of the spatial distribution and availability of resources within a stand.
Bats and Gaps: Microchiropteran Community Structure in a Queensland Rain Forest
Authors: Crome F. H. J. , Richards G. C.
Published: May 2006

We examined how a community of insectivorous bats in upland rain forest differentially used closed canopy areas and artificial gaps produced by selective logging. Bat foraging activity was monitored at paired canopy and gap sites using ultrasonic detection equipment. The data supported the prediction that gap use was related to morphology and bat species were classifiable as closed canopy specialist, gap specialists, and gap incorporators. Closed canopy specialists were species with low aspect ratio and wing loading, whereas gap specialists had high values for these two measures. Gap incorporators, which used both canopy areas and gaps, were intermediate in morphology. The closed canopy species were presumed to forage more readily in a cluttered environment. In this community there were no strict gap specialists, but instead the gap specialists were also recorded in other, more open habitats. The community consisted of two distinct subcommunities: four species in closed canopy areas and five in gaps. Three other species were incorporators, but the incorporation rate was very low; only 8% of the activity in gaps and 27% in closed canopy areas was due to these species. There was no relation between patterns of gap use and gap vegetation cover or age up to 6 yr, suggesting that exclusion of gap specialists from a regenerating gap is a slow process. There is tight phenetic packing in the two subcommunities, indicating that vegetation structure is more important than competition in constraining the structure of this community.
Field Tests of the Size‐Fitness Hypothesis in the Egg Parasitoid Trichogramma Pretiosum
Authors: Kazmer David J. , Luck Robert F.
Published: May 2006

The hypothesis that fitness following dispersal from the natal host increases with body size was tested under field conditions in the egg parasitoid Trichogramma pretiosum. In one experiment, size distributions of males and females at emergence were compared to those of males successful in locating mates and females successful in locating hosts. Mate and host location success increased with size in smaller parasitoids but were constant with respect to size in larger parasitoids. Selection intensities were 3.5—5.4 times greater in males than females possibly reflecting the small contribution of postdispersal matings to total male fitness in this partially sibmating species. In a second experiment using field releases of genetically marked lines, the number of trap hosts parasitized by "large" females reared from Helicoverpa zea eggs and "small" females reared from Sitotroga cerealella eggs was compared. Large females parasitized more hosts than small females in one trial but the reverse was observed in a second trial. Acceptance and suitability of the trap host species were not influenced by marker line or rearing host. We hypothesize that a genotype—environment interaction based on host age, host species, and wasp genotype accounts for the heterogenous results of the second experiment. Our main conclusion is that average postdispersal fitness of adult T. pretiosum increases with size in smaller wasps and is constant with respect to size in larger wasps. Contrary to general expectation, average wasp fitness does not increase linearly with size. Most importantly, wasp size is not a reliable predictor of individual or average cohort fitness; consistent size—fitness relationships emerge only when fitness is averaged over many genotypes and environments. Systematic factors such as host age and wasp genotype can have a strong influence on wasp fitness without strongly affecting size. The implications of these results for progeny and sex allocation in Trichogramma and for the mass production of parasitoids in biological control programs are discussed.
Leaf Damage Decreases Pollen Production and Hinders Pollen Performance in Cucurbita Texana
Authors: Quesada Mauricio , Bollman Krista , Stephenson Andrew G.
Published: May 2006

Leaf damage is known to adversely affect reproductive output through the female (fruit and seed) function, but little is known about the effects of leaf damage on the male function of plants. This study simulates the timing, location, and pattern of natural herbivory by diabroticite beetles and shows that leaf damage reduces male reproductive success in Cucurbita texana. Partially defoliated branches of C. texana produced significantly fewer staminate flowers and fewer pollen grains per flower than undamaged branches on the same plant. Moreover, pollen from staminate flowers on partially defoliated plants was less likely to sire seeds than pollen from undamaged plants when deposited onto a stigma with pollen from a tester line, indicating that leaf damage not only decreases pollen production but also adversely affects pollen performance.
On the Evolution of Host Specificity in Phytophagous Arthropods
Authors: Bernays Elizabeth , Graham Michelle
Published: May 2006

We argue that generalist natural enemies of herbivorous insects provide a major selection pressure for restricted host plant range. The significance of plant chemistry is discussed in terms of regulating behavior, while the chemical coevolutionary theories are considered to be of limited value.
Sexual Differences in Biomass and Nutrient Allocation in the Dioecious Rubus Chamaemorus
Authors: Agren Jon
Published: May 2006

I compared the seasonal pattern of biomass distribution and amounts of N and P in male and female ramets of the dioecious perennial herb Rubus chamaemorus L. Two populations, one in an open and one in a shaded habitat, were studied for 2 yr. The cost of fruit production in terms of reduction in vegetative growth was estimated in a field experiment. Ramets were larger, but the proportions of aboveground biomass, N, and P that were allocated to reproduction were lower at the shaded site than at the open site. The annual aboveground shoot of R. chamaemorus is either single—flowered or nonfloral. Female flowers had a lower dry mass and nutrient content than had male flowers. However, the ripe fruit had a dry mass, and a content of N and P, several times as great as those of male flowers. Fruit production interfered with vegetative growth; fruit—producing female ramets produced smaller leaves, and began producing rhizome branchlets later, than male ramets and than female ramets whose flowers had been excised to prevent fruit development. Fruit—producing female ramets had a higher mortality, and a lower probability of flowering in the subsequent year, than had male ramets. The sexual differences in vegetative growth and ramet mortality were smaller in the shaded than in the open habitat. In the shaded habitat, $\approx$50% of the ramets on male clones, and $\approx$30% of the ramets on female clones, were floral. The results suggest that male reproductive effort is greater than female up to the time of flowering, but that the total female allocation to reproduction is greater than the total male even at relatively low levels of fruit set. The predominance of R. chamaemorus populations with male—biased floral sex ratios is proposed to be the result of males having both a greater competitive vigor and a higher flowering propensity than females.
Fertility and Disturbance Gradients: A Summary Model For Riverine Marsh Vegetation
Authors: Day R. T. , Keddy P. A. , McNeill J. , Carleton T.
Published: May 2006

Although freshwater shorelines occupy extensive areas of the temperate zone, we still have few conceptual models for pattern and process in shoreline vegetation. This study uses multivariate vegetation data to describe vegetation—environment relationships in a set of riverine wetlands and then explores general relationships between pattern and process. Samples were collected from five marshes along the Ottawa River (eastern Canada) (n = 94 sample units). Detrended correspondence analysis was used to described major gradients, and TRWINSPAN was used to classify vegetation types. TWINSPAN produced four major classes dominated by Sparganium eurycarpum, Eleocharis smallii, Scirpus americanus, and Typha latifolia. Within each class, two associations could be recognized, differing in the degree to which one species managed to dominate the vegetation. Ordination showed that these vegetation types were arranged along two major axes: a standing crop and litter gradient, and a water depth gradient. Species richness was greatest just above the late August waterline in Eleocharis smallii vegetation that had low fertility, intermediate total biomass (250g/m2) and low littermass (30 g/m2). Very high biomass (>400g/m2) was observed where indices of high fertility and low disturbance coincided. Low species richness in this Typha—dominated vegetation is thought to be a result of competitive exclusion. Exposure to waves, ice, and flowing water produced a fertility gradient. The least fertile sites had small evergreen species such as Eriocaulon septangulare and Ranunculus flammula. These species possessed traits associated with Grime's "stress tolerator" strategy. The three main factors controlling vegetation competition were water depth, the effects of spring flooding in removing litter, and the fertility gradient produced by waves and flowing water. These were incorporated into a conceptual model including both patterns and processes observed along the Ottawa River.
Tropical Wet Forest Treefall Gaps and Distributions of Understory Birds and Plants
Authors: Levey Douglas J.
Published: May 2006

I examined the patch dynamics of understory birds and fruiting plants in treefall gaps and intact forest sites to determine the importance of gaps in structuring a Costa Rican tropical wet forest community. Understory birds and fruiting plants were censused monthly for 12 mo in 13 gaps and 13 intact forest sites. Of species with adequate sample sizes, 40% of bird species (17 of 42) and 30% of fruiting plant species (10 of 33) were found significantly more often in gaps than in intact forest. In contrast, only 5% of the bird species (2 of 42) and no plant species were found significantly more often in intact forest sites. Frugivorous and nectarivorous bird species were especially common in gaps. Birds of second—growth and forest edge were proportionately more abundant in gaps than were birds of forest interior. Canopy birds were not prevalent in gaps. Plants in gaps tended to produce more fruit over a longer period of time than conspecifics fruiting under a closed canopy. Also, large gaps had higher densities of fruiting plants and fruit—eating birds than small gaps. The high diversity and long fruiting periods of plants in gaps suggest that gaps may be important sources of fruit during periods of fruit scarcity. Given the high density of fruit—eating birds in gaps, seed deposition patterns generated by these birds are probably nonrandom. In particular, seeds may be dispersed into or around the periphery of gaps more often than into closed understory sites. Thus, the distributional patterns of understory fruits and frugivores may reinforce each other; fruiting shrub density affects the distribution of fruit—eating birds, which then influences the distribution of fruiting plants and birds in the next generation.
The Comparative Feeding Rates of North American Sparrows and Finches
Authors: Benkman Craig W. , Pulliam H. Ronald
Published: May 2006

Data on the seed profitabilities (mass of seed ingested per unit time) of captive emberizine sparrows and cardueline finches were used to interpret the underlying factors promoting differences in their ecologies. Sparrows consume seeds that the approximately an order of magnitude smaller in size that those consumed by finches of similar body mass. Because sparrows consume such small seeds and because finches are much more efficient at handling large seeds, sparrows need to encounter seeds at rates that are one to two orders of magnitude greater than that required by finches. As a result, sparrows have to spend much more time foraging than do finches, and sparrows are not able to go for as long periods of time searching for new food patches as are finches. Consequently, sparrows are relatively sedentary and restricted to areas of dense seed concentrations, whereas finches are extremely vagile and move over very large geographic areas in search of new patches of food. Furthermore, resource partitioning is more pronounced among finches. Small and large finch species eat very different seed sizes, whereas the diets of small and large sparrows overlap greatly.
The Effect of Shading by the Table Coral Acropora Hyacinthus on Understory Corals
Authors: Stimson John
Published: May 2006

Field surveys at Enewetak Atoll, Marshall Islands, show that coral density and diversity is much lower beneath Acropora table corals than in adjacent unshaded areas. Additionally, the understory community is predominantly composed of massive and encrusting species, while branching Acropora and Pocillopora predominate in unshaded areas. Results of experiments in which coral fragments were transferred to the shade of table Acropora and to adjacent unshaded areas show that shading slows the growth and leads to higher mortality of branching species, while massive and encrusting species are unaffected. Light measurements made beneath table Acropora show that illumination and irradiance values fall to levels at which most hermatypic corals do not occur. The fast—growing but fragile table Acropora are abundant in a wide variety of atoll habitats and grow rapidly to form a canopy °50 cm above the substrate. However, table Acropora also have high mortality rates, so that there is continuous production of unshaded areas. The growth and death of tables thus create local disturbances, and the resulting patchwork of recently shaded and unshaded areas may enhance coral diversity in areas of high coral cover.
Nestling Eastern Kingbird Growth: Effects of Initial Size and Ambient Temperature
Authors: Murphy Michael T.
Published: May 2006

Growth, defined in terms of mass gain and increase in lengths of tarsus and ninth primary wing feature, was studied in nesting Eastern Kingbirds in relation to a suite of environmental variables. These data indicate that many factors influence survival probabilities and final size attained by nestlings, though initial mass (egg size) seems of primary importance. The impact of weather variables was, however, nearly as important. Mass gain throughout the first half of the nestling period depended most on initial mass on the day of hatching. During the latter half of the nestling period, variation in ambient air temperature was the variable best able to explain mass variation. Nestlings lost mass on days with high air temperatures. Nestling mortality due to heat stress was also high on hot days, but only for nestlings with poorly developed powers of thermoregulation, i.e., those <10 d of age. Tarsal and primary lengths at fledging were directly correlated with hatching tarsal length and mass at day 14. Primary growth was also directly correlated with ambient air temperature.
Morphology as a Predictor of Flower Choice by Bumble Bees
Authors: Harder Lawrence D.
Published: May 2006

This paper examines whether the use of 14 plant species as nectar sources by eight species of bumble bees related systematically to differences in bee morphology. I predicted that a particular bee should have fed from a given plant species if the bee was physically more similar to the other bees visiting that plant species than to bees on any other species. Glossa (=tongue) length, body mass, and wing length all influence a bumble bee's foraging ability and its choice of flowers and were therefore included in the analysis. Morphological differences between bees were associated with use of different plant species; however, the role of bee morphology in flower choice was most evident when preferred plant species bloomed abundantly. The interaction between morphology and flower choice was also influenced by plant species richness, season, the plant species visited, and the species of bee; but was not affected by the time of day that the bee was foraging, overall bee density, or the bee's caste. Bee species with long glossae had access to nectar in a greater variety of flowers than those with short glossae, and they tended to feed from a larger number of plant species. Also, their use of a particular species was less predictable. Discrimination between bees using different plant species depended on joint consideration of several morphological characters: no character alone accurately separated the bees.
Death Stars, Ecology, and Mass Extinctions
Authors: Quinn James F. , Signor Philip W.
Published: May 2006

The appeal of a simple, extrinsic (sensu Gould 1977) physical mechanism for all or even one mass extinction in undeniable. But it now seems unlikely that extraterrestrial impacts provide the ultimate cause of more than a single mass extinction. At the Cretaceous–Tertiary (K–T) boundary there is ample evidence for unusual astrophysical or geophysical events, but the link between those events and the extinction of terrestrial and marine faunas and floras remains uncertain. One means of understanding the demise of clades during the K–T and other mass extinctions lies in the paleoecology of the survivors compared to causalities, in temporal, geographical, and ecological patterns. Likewise, similarities in patterns provide a means to test mechanisms common among extinction events (Jablonski 1986a). Extinctions are biological events. Evidence for extrinsic influences on the biosphere will certainly aid in comprehending the nature of biohistorical events, such as mass extinctions, and may well be responsible for those events, but the ecology of fossils is the crucial link to understanding these events.
Hot Rocks and Not‐So‐Hot Rocks: Retreat‐Site Selection by Garter Snakes and Its Thermal Consequences
Authors: Huey Raymond B. , Peterson Charles R. , Arnold Stevan J. , Porter Warren P.
Published: May 2006

Studies of behavioral thermoregulation of ectotherms have typically focused only on active animals. However, most temperate—zone ectotherms actually spend more time sequestered in retreats (e.g., under rocks) than active above ground. We documented retreat—site selection during summer by gravid garter snakes (Thamnophis elegans) at Eagle Lake in northeastern California, USA. To explore the thermal consequences of retreat—site selection, we measured potential body temperatures in retreats and combined these with data on thermal tolerances, thermal preferences, and thermal dependence of metabolism and digestion. Garter snakes at Eagle Lake usually retreated under rocks of intermediate thickness (20—30 cm) even though both thinner and thicker rocks were available. Empirical and biophysical analyses of temperatures under rocks of various sizes and shapes demonstrated that rock thickness had the dominant effect on potential Tb available to snakes and in turn on thermal physiology. Snakes selecting thin rocks (<20 cm thick) or very shallow burrows would die of heat stress in midafternoon and would have strongly impaired physiologial capacity from cold at night. Snakes selecting very thick rocks (>40 cm thick) or remaining at the bottom of deep burrows would not experience such extreme Tb, but neither would they warm to Tb in their preferred range. However, snakes selecting intermediate—thickness rocks would never overheat but would achieve preferred Tb for long periods–far longer than if they remained on the ground surface or moved up and down within a burrow. Interestingly, snakes selecting burrows or intermediate—thickness rocks may be able to have either the highest energy gain or the lowest overall metabolic rate, depending on the particular Tb they select. Medium—thickness rocks, the size rocks normally selected by the snakes, offer them a variety of suitable thermoregulatory opportunities.
Aggregation in Aphis Varians: An Effective Strategy for Reducing Predation Risk
Authors: Turchin P. , Kareiva P.
Published: May 2006

It has been suggested that by clumping together, even defenseless prey may reduce their chances of being consumed by a predator. However, the advantage of clumping to prey may be negated by a strong aggregative response of predators to prey clusters. We studied the balance of forces that determine the advantage or disadvantage of clumping to prey in one particular case: the interaction between the aphid Aphis varians (Homoptera: Aphididae) and its predator Hippodamia convergens (Coleoptera:Coccinellidae). Aphid movement was congregative, i.e., aphids tended to stay within clumps of conspecifics. Furthermore, by quantifying the per capita population growth rates for aphid colonies of differing sizes, we found that individual aphids benefited by being clumped together. However, a predator—exclusion experiment indicated that clumping was beneficial to aphids only in the presence of predators. To gain a mechanistic understanding of why aphid congregation reduced predation risk to individuals, we examined the behavioral response of predators to aphid density. Predators exhibited a strong aggregating response: large colonies of aphids were attacked by more predators than were small colonies. In addition, ladybird feeding rate increased with increasing colony size. The total number of prey taken from colonies by predators, however, could not keep pace with the increase in aphid colony size, and thus the risk of predation to individual prey was "diluted" by prey numbers.
Seasonal Variation in the Intensity of Competition and Predation Among Dragonfly Larvae
Authors: Wissinger Scott A.
Published: May 2006

In nature, both similar and disparate sizes of Libellula lydia and L. luctuosa larvae frequently co—occur in time and space. To determine if these larvae interact as competitors, and/or predators and prey, I used artificial ponds to manipulate density, species composition, and size range of co—occurring larvae. Detailed life history data were used to design separate fall and spring experiments. In both experiments, "competition treatments" contained only larvae similar in size, whereas "predation treatments" contained larvae disparate in size. In fall competition treatments there were no density—dependent growth responses. However, in the spring experiment, larvae of both species grew significantly faster in low density than in high density treatments. This seasonal difference in competition was attributed to fluctuations in resource abundance. Competition did not directly affect survivorship. In spring and fall predation treatments, mortality was significantly higher than it was in competition treatments. Inter—odonate predation accounted for 25—45% of total larval mortality in fall, but only 10—15% in spring. In the absence of inter—odonate predation, total mortality was lower for larger larvae than smaller larvae, suggesting the latter are more susceptible to predation by other invertebrate predators. Thus, competition, by decreasing growth rates, should indirectly affect larval survivorship. These data provide evidence that competition and predation will simultaneously affect coexistence between these two dragonfly species. Predation early in larval development should ameliorate the intensity of subsequent competitive interactions at a time when resources are most likely to be limiting. This type of mixed competition/predation interaction is analogous to predator—mediated coexistence, and might explain how such ecologically similar species can coexist at such high densities.
Habitat Separation Between Sympatric Snake Populations
Authors: Reinert Howard K.
Published: May 2006

Quantitative data consisting of 14 structural habitat variables and 5 climatic variables were obtained from 505 telemetric relocations of 21 timber rattlesnakes (Crotalus horridus) and 20 northern copperheads (Agkistrodon contortrix mokeson) in eastern Pennsylvania. Multivariate analysis of variance revealed that the habitats utilized by the two species differed significantly. The single discriminant function generated by a discriminant analysis was highly correlated with variables describing structural features of the forest floor and canopy. A. c. mokeson utilized relatively open areas with higher rock density and less surface vegetation than did C. horridus. The discriminant function correctly classified 76% of the samples. The 24% overlap consisted largely of locations from gravid C. horridus whose habitat preference closely paralleled A. c. mokeson. Measurements of habitat overlap indicated that the separation of the two species along the habitat axis was theoretically sufficient for competitive avoidance. Although the observed species separation can be interpreted as reflecting interspecific competition, an alternate explanation based upon inherent physiological differences is also presented.
Predation and Resource Partitioning in Two Sunfishes (Centrarchidae)
Authors: Mittelbach Gary G.
Published: May 2006

This study examines the diet and habitat use of two congeneric sunfishes in light of the effects of size—specific predation risk and foraging efficiency. Large bluegills (Lepomis macrochirus) and pumpkinseeds (L. gibbosus) (> 75 mm SL) exhibited distinct diet and habitat separation in three small Michigan lakes. Bluegills foraged primarily on open—water zooplankton (Daphnia), while pumpkinseeds specialized on vegetation—dwelling gastropods. These differences in resource use by large fish were directly related to differences in their functional morphology and foraging ability. In laboratory feeding experiments, pumpkinseeds had significantly lower prey handling times of gastropods than did bluegills. The bluegill, on the other hand, was the more efficient of the two species when feeding on zooplankton (Daphnia). In contrast to the large fish, the diets and habitat use of small bluegills and pumpkinseeds (@<75 mm SL) were quite similar. Small fish of both species foraged predominantly in the vegetation, and 76—91% of their average seasonal diet was vegetation—dwelling prey (nongastropods). This increase in shared resources among small fish was due to two factors: (1) piscivorous fish restrict small size—classes to the vegetation where they are less vulnerable, and (2) small pumpkinseeds are unable to feed effectively on snails, the adult resource in the vegetation. Laboratory comparisons of the foraging rate of small bluegills and pumpkinseeds on vegetation—dwelling prey, and field measures of the growth rate of each species while occupying the vegetation, indicate that the two species are nearly equal competitors in the juvenile habitat. The two species, however, were not in equal abundance across the study lakes; the ratio of bluegills to pumpkinseeds ranged from 25:1 to 1:1. The pattern in species abundance was directly related to the availability of "adult" resources (snails and zooplankton) in each of the lakes, suggesting that the volume of the competitive refuge experienced by each species at larger sizes is the predominant factor controlling their relative numbers.