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We tested whether the presence of a predator (non-lethal effect) could produce patterns of prey distribution and abundance attributed historically to direct mortality. Sixteen experimental ponds (1,000 l cattle watering tanks) were established; eight containing seven enclosed banded sunfish, Enneacanthus obesus, and eight predator-free controls. Ponds were colonized by ovipositing squirrel treefrogs...
Chronic herbivory by the stem-boring moth (Dioryctria albovittella) alters the sexual expression of a monoecious tree, pinyon pine (Pinus edulis) by reducing female function and increasing male function. Observations and long-term moth removal experiments show that 55% of susceptible trees can lose all female function. Moth herbivory has little effect on male function in young trees, but has an important...
We studied the patterns and rates of migration among habitat patches for five species of checkerspot butterflies (Lepidoptera: Melitaeini) in Finland: Euphydryas aurinia, E. maturna, Melitaea cinxia, M. diamina and M. athalia. We applied the virtual migration (VM) model to mark-release-recapture data collected from multiple populations. The model includes parameters describing migration and survival...
We examined the size, age, and spatial structure of trees in an old Engelmann spruce (Picea engelmannii)–subalpine fir (Abies lasiocarpa) forest based on four stem-mapped, 0.25 ha plots. Dendrochronological techniques were used on basal discs of 1,190 trees to reconstruct age and growth pattern, including dates of rapid growth increases. There were no obvious age cohorts or other evidence of past...
This study investigated correlations among climatic variability, population age structure, and seedling survival of a dominant Sonoran Desert tree, Cercidium microphyllum (foothill paloverde), at Tucson, Arizona, USA. A major goal was to determine whether wet years promote seedling establishment and thereby determine population structure. Plant age was estimated from basal circumference for a sample...
Stand thinning across different soil drainage types was used to test the ecophysiological basis for the control of foliar monoterpenes in current-year foliage of balsam trees [Abies balsamea (L.) P. Mill.] the year following treatment. Photosynthetic capacity (Amax) was greater on mesic sites than on sub-hygric and hydric sites (1.81, 1.33 and 0.88 µmol m–2 s–1, respectively) and greater in mid-July...
Several components of the diversity of plant communities, such as species richness, species composition, number of functional groups and functional composition, have been shown to directly affect the performance of exotic species. Exotics can also be affected by herbivores of the native plant community. However, these two possible mechanisms limiting invasion have never been investigated together...
A soft-shelled non-indigenous clam, Nuttallia obscurata, has invaded coastal soft-sediment habitats of the northeastern Pacific. In a survey of 35 sites within the San Juan Islands, Washington, USA, Nuttallia was found almost exclusively in sandy substrates, higher in the intertidal than most native clams (>1 m above mean lower low water). The distinctive distribution of Nuttallia suggested that...
We investigated the hypothesis that hemiparasites accelerate nutrient cycling in nutrient-poor communities. Hemiparasites concentrate nutrients in their leaves, thus potentially producing high quality litter that releases nutrients that would otherwise remain in host tissues or in slowly decomposing plant litter. This hypothesis was tested using species from a European sub-arctic community where root...
Evidence concerning mechanisms hypothesized to explain species coexistence in hyper-diverse communities is reviewed for tropical forest plants. Three hypotheses receive strong support. Niche differences are evident from non-random spatial distributions along micro-topographic gradients and from a survivorship-growth tradeoff during regeneration. Host-specific pests reduce recruitment near reproductive...
The evolution of a showy floral display as an advertisement to pollinators could simultaneously advertise the availability of resources to pre-dispersal seed-predators. The hypotheses tested here are that the incidence of seed predation by bud-infesting insect larvae in capitula of Asteraceae is positively related to (1) capitulum size among species, (2) capitulum size within species, (3) capitulum...
We examined patterns of seedling root architecture, morphology and anatomy in Australian perennial plants chosen as phylogenetically independent contrasts (PICs) for rainfall in the areas they inhabit. Our objective was to assess whether there are consistent evolutionary patterns in structure of seedling root systems in species from different rainfall environments when examined across multiple evolutionary...
Trade-offs between traits are a fundamental component of life history theory. However, because individuals may differ in the amount of energy available for allocation between traits, expected negative relationships are often difficult to detect or may become positive. The latter can occur when both traits are phenotypically plastic in response to variation in environmental productivity. We tested...
Stable isotopes are often used as natural labels to quantify the contributions of multiple sources to a mixture. For example, C and N isotopic signatures can be used to determine the fraction of three food sources in a consumer's diet. The standard dual isotope, three source linear mixing model assumes that the proportional contribution of a source to a mixture is the same for both elements (e.g.,...
The selective pressures determining timing of reproduction and brood or litter size in animals remain to be clarified, despite much research. In several detailed studies of birds, selection for an early start of breeding has been demonstrated. Young born early in the season are often assumed to benefit from long experience, high dominance in flocks and/or early settlement in territories. For forest-breeding...
The occurrence of ten butterfly taxa (Clossiana eunomia dawsonii, Clossiana freija, Clossiana frigga, Clossiana titania, Coenonympha inornata, Erebia discoidalis, Incisalia augustinus, Lycaena dorcas, Lycaena epixanthe, Oeneis jutta) was analyzed within three acid peatland habitat types from the Lake Superior drainage basin of northwestern Wisconsin. Both first- (nearest-neighbor spatial analysis)...
Recently there has been considerable interest in determining the relative roles of endogenous (density-dependent) and exogenous (density-independent) factors in driving the population dynamics of free-ranging ungulates. We used time-series analysis to estimate the relative contributions of density-dependent forage competition, climatic fluctuation, and harvesting on the population dynamics of white-tailed...
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