Suchergebnisse

The United States chose an approach to global warming that came to be viewed by much of the international community as a barrier to effective action. In explaining why, this article analyzes the interaction of the domestic political process and international negotiations. It argues that—while external pressures brought to bear through the negotiations leading up to UNCED pushed the domestic agenda on global warming—the nature of the political process, in combination with the nature of the global warming issue itself, set the general limits for U.S. participation in cooperative international arrangements to manage global warming. That is, given the broad set of interests activated by global warming concerns and the ready access those interests had to decision-making bodies through a pluralist policy process, consensus on an approach to global warming proved impossible. The U.S., unwilling to accept international commitments that obligated it to domestic actions, thwarted efforts to get an international treaty containing firm targets and timetables.

Context
Management of wildlife that may simultaneously be of conservation concern and pose problems for humans is difficult, particularly when knowledge of their population dynamics is elusive. Culling of southern hairy-nosed wombats (Lasiorhinus latifrons) is often carried out in agricultural areas, with no understanding of potential impacts on the species as a whole. Monitoring fossorial species via non-invasive means (that do not adversely impact animals by damaging their burrows) has always represented a challenge for wildlife researchers.

Aim
The aim of this research was to map the areal extent of different types of L. latifrons warrens to gain a better understanding of the relationship between the external warren signs and its subterranean structure. The findings will be used in the development of more accurate indices of population abundance to better inform management decisions.

Methods
Ground penetrating radar (GPR) was used to map warrens at four locations in the western regions of South Australia. Radar data were collected using a Mala X3M GPR system with 250 MHz and 500 MHZ antennas. 3D models of each site were then produced using the ReflexW GPR software processing package.

Key results
Subterranean warren structure varied from a mix of tunnel types in sandy-loam soil to a complex array of tunnels and caverns under sheet calcrete limestone.

Conclusions
This was the first non-invasive mapping of wombat warrens and the first mapping of a warren under a layer of calcrete limestone. In sandy-loam soil, the size and extent of the external spoil mound provided some indication of warren complexity. However, there were no external signs of the extent of the calcrete warren.

Implications
The lack of external cues regarding the extent of the calcrete limestone warren suggests that the current method of estimating population abundance based on a single index of wombats per active burrow is flawed. As a result, any management decisions in regard to culling may be based on inaccurate information. It is apparent that further research needs to be undertaken to develop a range of abundance indices that take into account local conditions such as soil type.

Fish populations globally are susceptible to endangerment through exploitation and habitat loss. We present theoretical simulations to explore how reduced adult survival (age truncation) might affect short-lived freshwater fish species in human-altered contemporary environments. Our simulations evaluate two hypothetical "average fish" and five example fish species of age 1 or age 2 maturity. From a population equilibrium baseline representing a natural, unaltered environment we impose systematic reductions in adult survival and quantify how age truncation affects the causes of variation in population growth rate. We estimate the relative contributions to population growth rate arising from simulated temporal variation in age-specific vital rates and population structure. At equilibrium and irrespective of example species, population structure (first adult age class) and survival probability of the first two adult age classes are the most important determinants of population growth. As adult survival decreases, the first reproductive age class becomes increasingly important to variation in population growth. All simulated examples show the same general pattern of change with age truncation as known for exploited, longer-lived fish species in marine and freshwater environments. This implies age truncation is a general potential concern for fish biodiversity across life history strategies and ecosystems. Managers of short-lived, freshwater fishes in contemporary environments often focus on supporting reproduction to ensure population persistence. However, a strong focus on water management to support reproduction may reduce adult survival. Sustainability management needs a focus on mitigating adult mortality in human-altered ecosystems. A watershed spatial extent embracing land and water uses may be necessary to identify and mitigate causes of age truncation in freshwater species. Achieving higher adult survival will require paradigm transformations in society and government about water management priorities.