Treesearch

The idea of a metapopulation - a group of local populations in a patchy habitat - recurs in both ecology and evolutionary biology. Although the metapopulation concept is at least 50-75 years old, it has recently resurged, as natural habitats become fragmented and are lost because of humans' use of resources. However, fragmentation is not the same as habitat loss per se, and patchy habitats do not necessarily make metapopulations. Some populations may behave naturally as metapopulations and are characterized by extinction of some local populations and recolonization of empty patches from...

Recent conservation biology and environmental literature contains claims that livestock grazing has caused and continues to cause reduction in species diversity on Western rangelands, especially public rangelands. This paper present quantitative data on species richness (number of species) inside and outside 24 long-term exclosures; 8 exclosures in aspen vegetation in Utah, 8 in sagebrush and salt desert shrub vegetation in Wyoming and 8 in tall forbs and other high elevation vegetation in Montana. The areas inside and outside the exclosure were sampled in the mid 1990s and comparisons...

Above- and below-ground characteristics were measured and compared for six sets of paired trembling aspen (Populus tremuloides Michx.) clones on the Fishlake National Forest in central Utah. Three self-regenerating clones were compared with three non-regenerating clones and three pure aspen stands were compared with three mixed aspen-conifer stands. Regenerating clones had dense understories of younger aspen stems, which were not present in nonregenerating clones. Regenerating clones also had greater numbers of roots and greater total root surface area than nonregenerating clones. Abovegrou...

For rare plants, the question of whether and to what extent wild and domestic herbivores influence growth, reproduction, and survival can be critical to preservation. The sensitive species, Clematis hirsutissima var. arizonica, grows on Forest Service lands where cattle, elk, mule deer, and numerous small mammals forage. In a 3-year clipping experiment, I examined the impact of season and intensity of herbivory on reproduction and growth. Vegetative reproduction was not influenced by year, season, or intensity of herbivory; however, sexual reproduction was influenced by year and season of...

Although related taxa occur throughout the western United States, Salvia dorrii ssp. mearnsii is endemic to central Arizona. In part, its narrow distribution may be attributed to prehistoric human influences. A spatial analysis was used to determine the relationship of archaeological sites and populations of S. dorrii ssp. mearnsii. In the lower Verde Valley, approximately 89 percent of the plant populations were spatially related to archaeological sites. Plant populations from a different geographic area in the upper Verde Valley were also spatially related to known archaeological...

Tetraneuris verdiensis was first published in 1996. It appears to be closely related to Tetraneuris acaulis var. arizonica. The closest known location of T. acaulis var. arizonica is approximately 7 miles northwest of the known T. verdiensis locations, which are 5 miles east of Camp Verde. Tetraneuris verdiensis is significant in that no other entirely discoid populations, or series of populations, of Tetraneuris have been reported. Tetraneuris verdiensis populations are consistently discoid, which separates them from T. acaulis var. arizonica. The type locality is on the top of a low hill...

We examined the pollination ecology of Spiranthes diluvialis Sheviak, Ute ladies-tresses, a federally listed, threatened orchid species known only from small, isolated populations in the western United States. The pollinator composition, male and female reproductive success, and demography of S. diluvialis populations were examined in 1995,1997, and 1999. Spiranthes diluvialis sets fruit only when visited by pollinators and observations indicate that native bees, predominantly bumblebees (Bombus spp.), are the most important pollinators. Comparisons of male and female reproductive success...

Although related taxa occur throughout the western United States, Salvia dorrii ssp. mearnsii is endemic to central Arizona. In part, its narrow distribution may be attributed to its limited fruit production, low seedling establishment, and germination requirements. Heavy herbivory pressures decreased the numbers of mature fruits in populations in two different vegetation zones and soil origins, desertscrub (limestone origin) and chaparrral (sandstone origin). The percentage of mature fruits was higher in populations from soils of limestone origin in desertscrub vegetation than from soils...

Central to the conservation of the federally endangered Purshia subintegra (Arizona cliffrose) is development of an understanding of its cultivation requirements. This knowledge will enable us to augment declining or threatened populations as well as preserve genotypes impacted by human activities. We studied seed and stem cutting propagation of P. subintegra. The highest success rate for rooted stem cuttings of P. subintegra that were collected wild was 34 percent. The stem cuttings of P. subintegra survived best when they were taken in the fall, rooted in perlite with Hormex 8, and...

One of the goals of conservation biology is to maintain the integrity of natural processes in populations of rare plants. In the short term one of the main concerns is often whether the mating system of rare plants is disrupted, for example, by fragmentation. In the long term one of the main concerns is often whether small isolated populations maintain enough genetic variation to respond to selection due to human-induced environmental changes. Management of rare plant populations would, therefore, be supported by tools enabling the effective monitoring of these and similar processes....