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Organisms in natural populations experience environmental heterogeneity over a range of temporal and spatial scales, and this heterogeneity has significant evolutionary implications. By affecting patterns of selection and the expression of genetic variation, environmental heterogeneity can play an important role in determining the evolutionary dynamics of phenotypic traits and the maintenance of genetic variation. Although mapping quantitative trait loci (the loci that underlie continuously varying quantitative traits) has a long history in agricultural and applied studies, the technique has only recently been applied to evolutionary studies. This application has made it possible to identify the specific loci underlying trait variation in different environments, to measure environmental variation in natural selection on those loci, and to test assumptions of models regarding the maintenance of genetic variation under environmentally heterogeneous selection. Here we review recent studies that have examined interactions between quantitative trait loci and ecologically relevant environments to address evolutionary questions.
Nontarget risk assessment for transgenic crops should be case specific, depending on the plant, the transgene, and the intended release environment. We propose an ecological risk-assessment model that preserves the strengths and avoids the deficiencies of two other commonly used models, the ecotoxicology and nonindigenous-species models. In this model, locally occurring nontarget species are classified into groups according to their ecological function. Within each group, ecological criteria are used to select the species that are most likely to be affected by the transgenic crop. Initial experimental assessments are conducted in the laboratory and consist of two kinds of test: toxicity tests using purified transgene product, and whole-plant tests using intact transgenic plants. For nontarget natural enemy species, it will also be important to evaluate both direct bitrophic impacts and indirect tritrophic impacts.
A profusion of fruit forms implies that seed dispersal plays a central role in plant ecology, yet the chance that an individual seed will ultimately produce a reproductive adult is low to infinitesimal. Extremely high variance in survival implies that variations in fruit production or transitions from seed to seedling will contribute little to population growth. The key issue is that variance in survival of plant life-history stages, and therefore the importance of dispersal, differs greatly among and within plant communities. In stable communities of a few species of long-lived plants, variances in seed and seedling survival are immense, so seed-to-seedling transitions have little influence on overall population dynamics. However, when seedlings in different circumstances have very different chances of survival—in ecological succession, for example, or when dispersed seeds escape density-dependent mortality near parent trees—the biased survival of dispersed seeds or seedlings in some places rather than others results in pervasive demographic impacts.
Understanding the relative influence of fuels and climate on wildfires across the Rocky Mountains is necessary to predict how fires may respond to a changing climate and to define effective fuel management approaches to controlling wildfire in this increasingly populated region. The idea that decades of fire suppression have promoted unnatural fuel accumulation and subsequent unprecedentedly large, severe wildfires across western forests has been developed primarily from studies of dry ponderosa pine forests. However, this model is being applied uncritically across Rocky Mountain forests (e.g., in the Healthy Forests Restoration Act). We synthesize current research and summarize lessons learned from recent large wildfires (the Yellowstone, Rodeo-Chediski, and Hayman fires), which represent case studies of the potential effectiveness of fuel reduction across a range of major forest types. A “one size fits all” approach to reducing wildfire hazards in the Rocky Mountain region is unlikely to be effective and may produce collateral damage in some places.
Plant invasions are widely recognized as significant threats to biodiversity conservation worldwide. One way invasions can affect native ecosystems is by changing fuel properties, which can in turn affect fire behavior and, ultimately, alter fire regime characteristics such as frequency, intensity, extent, type, and seasonality of fire. If the regime changes subsequently promote the dominance of the invaders, then an invasive plant–fire regime cycle can be established. As more ecosystem components and interactions are altered, restoration of preinvasion conditions becomes more difficult. Restoration may require managing fuel conditions, fire regimes, native plant communities, and other ecosystem properties in addition to the invaders that caused the changes in the first place. We present a multiphase model describing the interrelationships between plant invaders and fire regimes, provide a system for evaluating the relative effects of invaders and prioritizing them for control, and recommend ways to restore pre-invasion fire regime properties.
As public and scientific interest in black-tailed prairie dogs has grown, views about their ecological role have become polarized. We evaluated three claims frequently made concerning the status of black-tailed prairie dogs and their interactions with other species: (1) that black-tailed prairie dogs historically occupied 40 million to 100 million hectares (ha) and now occupy only 1 to 2 percent of their former range, (2) that large ungulates preferentially forage on prairie dog colonies, and (3) that prairie dogs do not reduce carrying capacity for large herbivores. The conclusion that prairie dogs historically occupied up to 100 million ha is not supported by the literature, and the more conservative figure of 40 million ha is based on estimates from the early 20th century, when prairie dog populations were artificially high as a result of human activities. Prairie dog activity is not unique in facilitating grazing by large herbivores; and selection of prairie dog colonies for foraging is limited to specific conditions, including colony age, proximity, and season of the year. Finally, prairie dogs reduce carrying capacity for large herbivores by consuming forage, clipping plants to increase visibility, building mounds, and changing plant cover and species composition.