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For 13 years, we studied the role of biotic interactions, including predation, herbivory, and interspecific competition, in a semiarid thorn scrub community in north-central Chile. Using a large-scale field manipulation, we monitored changes in small mammals, plants, and vertebrate predators. We documented important “top-down” predation effects on some small-mammal species, and small-mammal effects on some plant species resulting from experimental exclusions. However, periodic El Niño Southern Oscillation (ENSO) events caused several high rainfall episodes during this interval, resulting in large “bottom-up” increases in both plants and animals. Therefore, we suggest that instead of exclusive top-down or bottom-up control, this system undergoes shifting control, with relatively greater importance of biotic interactions in wet years and of resource limitation in dry ones. Because intervals between ENSO events are long and responses are slow, long-term studies are essential for understanding such effects in semiarid or arid systems.
Throughout the 20th century, the Truckee River that flows from Lake Tahoe into the Nevada desert was progressively dammed and dewatered, which led to the collapse of its aquatic and riparian ecosystems. The federal designation of the endemic cui-ui sucker (Chasmistes cujus) as endangered prompted a restoration program in the 1980s aimed at increasing spring flows to permit fish spawning. These flows did promote cui-ui reproduction, as well as an unanticipated benefit, the extensive seedling recruitment of Fremont cottonwood (Populus fremontii) and sandbar willow (Salix exigua). Recruitment was scattered in 1983 but extensive in 1987, when the hydrograph satisfied the riparian recruitment box model that had been developed for other rivers. That model was subsequently applied to develop flow prescriptions that were implemented from 1995 through 2000 and enabled further seedling establishment. The woodland recovery produced broad ecosystem benefits, as evidenced by the return by 1998 of 10 of 19 riparian bird species whose populations had been locally extirpated or had declined severely between 1868 and 1980. The dramatic partial recovery along this severely degraded desert river offers promise that the use of instream flow regulation can promote ecosystem restoration along other dammed rivers worldwide.
A review of funding for conservation of threatened birds in Australia over the period 1993–2000 shows that most of the funds were spent on the taxa closest to extinction. Government conservation agencies provided the majority of funds, with 25 percent coming from the voluntary conservation sector and about 14 percent from the business sector and government agencies whose primary mission is not conservation. Taxa that are taxonomically distinct received more funds than would be expected by an even distribution, but nevertheless substantial funds were allocated even to Australian populations of taxa that are not threatened globally. The status of most taxa did not change during the study period, but those that did improve generally received more funds than those taxa that declined. Overall, funds provided to support Australian threatened birds have been used effectively, but more is required to secure all taxa, and investment in threatened species will have to continue well into the future.
Around the world, a great deal of effort is expended each year to estimate the sizes of wild animal populations. Unfortunately, population size has proven to be one of the most intractable parameters to estimate. The capture–recapture estimation models most commonly used (of the Jolly–Seber type) are complicated and require numerous, sometimes questionable, assumptions. The derived estimates usually have large variances and lack consistency over time. In capture–recapture studies of long-lived animals, the ages of captured animals can often be determined with great accuracy and relative ease. We show how to incorporate age information into size estimates for open populations, where the size changes through births, deaths, immigration, and emigration. The proposed method allows more precise estimates of population size than the usual models, and it can provide these estimates from two sample occasions rather than the three usually required. Moreover, this method does not require specialized programs for capture–recapture data; researchers can derive their estimates using the logistic regression module in any standard statistical package.
Integration of ecological principles into private land-use planning is critical to preservation of biodiversity and functional ecosystems in the United States. Ecologists need to play an active role in shaping land-use decisions to meet those goals. Four areas of action for ecologists are (1) educating members of the staff, planning board, and governing body involved in land-use decisions; (2) serving on a planning commission or governing body; (3) commenting at public hearings; and (4) participating in citizen review panels for land-use laws and policies. The most effective measures will be those that integrate ecological principles into arguments based on the existing standards for comprehensive planning and subdivision review.