Masting promotes individual- and population-level reproduction by increasing pollination efficiency.

Masting is a reproductive strategy defined as the intermittent and synchronized production of large seed crops by a plant population. The pollination efficiency hypothesis proposes that masting increases pollination success in plants. Despite its general appeal, no previous studies have used long-term data together with population- and individual-level analyses to assess pollination efficiency between mast and non-mast events.

Masting in ponderosa pine: comparisons of pollen and seed over space and time.

Many plant species exhibit variable and synchronized reproduction, or masting, but less is known of the spatial scale of synchrony, effects of climate, or differences between patterns of pollen and seed production. We monitored pollen and seed cone production for seven Pinus ponderosa populations (607 trees) separated by up to 28 km and 1,350 m in elevation in Boulder County, Colorado, USA for periods of 4-31 years for a mean per site of 8.7 years for pollen and 12.

Contrasting cascades: insectivorous birds increase pine but not parasitic mistletoe growth.

1. Intraguild predation occurs when top predators feed upon both intermediate predators and herbivores. Intraguild predators may thus have little net impact on herbivore abundance.

A chemical polymorphism in a multitrophic setting: thyme monoterpene composition and food web structure.

We investigated the effects of chemical variation in thyme (Thymus vulgaris L.) on its interactions with competitors, herbivores, and herbivore predators. Four different thyme monoterpene phenotypes (chemotypes) were grown in a 4x2x2 factorial of chemotype, caging (sham half-cages vs.

Qualitative and quantitative variation in monoterpene co-occurrence and composition in the essential oil of Thymus vulgaris chemotypes.

Thymus vulgaris has a chemical polymorphism with six different chemotypes that show marked spatial segregation in nature. Although some populations have a single chemotype in majority, many have two or three chemotypes. In this study we analyze the quantitative variation among T.

Plant diversity, herbivory and resistance of a plant community to invasion in Mediterranean annual communities.

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.

DIRECT AND INDIRECT ESTIMATES OF SEED VERSUS POLLEN MOVEMENT WITHIN A POPULATION OF PONDEROSA PINE.

We examined the spatial distribution of maternally inherited mitochondrial DNA and paternally inherited chloroplast DNA polymorphisms in a permanently marked stand of ponderosa pine (Pinus ponderosa Laws). Movement of maternally inherited mtDNA occurs only via seed dispersal, and mtDNA haplotypes showed significant patch structure. Moreover, individuals within patches identified by mtDNA haplotypes were related approximately as half-sibs based upon analysis of allozyme genotypes.

Path analysis of natural selection on plant chemistry: the xylem resin of ponderosa pine.

We analyzed the pattern of correlations among fitness components, herbivory, and resin characteristics in a natural all-aged stand of ponderosa pine, to infer the strength and mechanism of natural selection on plant chemistry. Male and female cone production were monitored yearly for 15 years, and levels of herbivory for 9 years in 165 trees. Resin flow rate and monoterpene composition were determined for these same trees.

Terpene-based selective herbivory by Helix aspersa (Mollusca) on Thymus vulgaris (Labiatae).

In natural populations of Thymus vulgaris in the south of France, six genetically different chemical "chemotypes" occur, each differentiated by a single dominant monoterpene that gives individual plants a characteristic smell and taste. Individual populations may contain all six chemotypes, but are often dominated by one to three chemotypes. We tested the hypothesis that this chemical polymorphism was associated with selective herbivory by the snail Helix aspersa, which feeds upon T.

Intra-specific variation in the inhibitory effects of Thymus vulgaris (Labiatae) monoterpenes on seed germination.

The ecological role of plant secondary compounds has received a great deal of attention yet little is known regarding variation in the ecological significance of different compounds produced by a single species. This is particularly pertinent to species where variation in compound presence is under genetic control. In this study we have quantified variation in the inhibitory effects of the six dominant monoterpene oils produced by different genotypes (or chemotypes) of Thymus vulgaris on achene germination of an associated species (Brachypodium phoenicoides), and seeds of T.

Differential host utilization by two parasites in a population of ponderosa pine.

We compared phloem characteristics of individual Pinus ponderosa attacked by the dwarf-mistletoe Arceuthobium vaginatum (Viscaceae) or by the beetle Dendroctonus ponderosae (Scolytidae) or by neither species. We quantified total nonstructural carbohydrates and a broad range of chemical elements for these three categories of trees. There were significant differences between trees parasitized by Arceuthobium, trees parasitized by Dendroctonus, and non-infected trees.

GENETIC VARIATION IN ALETES ACAULIS AND ITS RELATIVE, THE NARROW ENDEMIC A. HUMILIS (APIACEAE).

We compared the organization of genetic variability in Aletes humilis, a species restricted to seven populations in north-central Colorado, with A. acaulis, a closely related widespread species. Genetic variability was scored at 11 electrophoretically detectable protein loci.

INTRAPOPULATION DIFFERENTIATION IN ANNUAL PLANTS. III. THE CONTRASTING EFFECTS OF INTRA- AND INTERSPECIFIC COMPETITION.

The roles of intraspecific and interspecific competition in producing differentiation within populations of Veronica peregrina were studied in two populations under controlled, greenhouse conditions. In nature, each population spans an environmental gradient across the center and sides of a temporary, vernal pool in California. Individuals at the center are subjected to intense intraspecific competition produced by high densities (to 30 seedlings/cm ) generated by quasi-simultaneous germination (90% of seeds germinate in one week).

Seed dispersal by nutcrackers causes multi-trunk growth form in pines.

We present a unique example of a seed disperser determining the basic growth architecture of two species of plants. Clark's Nutcracker (Nucifraga columbiana) is the primary disperser for Pinus flexilis and P. albicaulis, caching clusters of seeds in the process.