Demographic Processes Underlying Population Growth and Decline in Salamandra salamandra

Abstract:  Human activity commonly has negative impacts on wildlife. Often, however, only a single element of the life cycle is affected, and it is unclear whether such effects translate into effects on population growth. This is particularly true for research into the causes of global amphibian declines, where experimental research focuses primarily on the aquatic larval stages but theory suggests these stages have only minor importance for population growth. We used data from long-term mark-recapture studies of two natural populations of the salamander Salamandra salamandra to confirm the predictions of population models. One population remained stable (i.e., stationary) throughout the 20 years of the study whereas the other declined to local extinction. We used mark-recapture models to break down population growth rate into its two main components, recruitment and adult survival. Survival of postmetamorphic salamanders was constant over time in the stable population, whereas the declining population was characterized by a decrease in survival and constant recruitment. Population growth was most sensitive to variation in adult survival. Current amphibian research focuses on preadult stages, and researchers assume recruitment is the most important determinant of population growth. This may not be the case. A better understanding of amphibian population dynamics is possible only through the integration of experiments, theory, and data from natural populations. Our results also suggest that amphibian conservation efforts should focus on all stages of the life cycle and their associated habitats.     

Avoidance Behavior by Prairie Grouse: Implications for Development of Wind Energy

Abstract:  New wind-energy facilities and their associated power transmission lines and roads are being constructed at a rapid pace in the Great Plains of North America. Nevertheless, little is known about the possible negative effects these anthropogenic features might have on prairie birds, one of the most threatened groups in North America. We examined radiotelemetry tracking locations of Lesser Prairie-Chickens ( Tympanuchus pallidicinctus ) and Greater Prairie-Chickens ( T. cupido ) in two locations in Oklahoma to determine whether these birds avoided or changed movement behavior near power lines and paved highways. We tracked 463 Lesser Prairie-Chickens (15,071 tracking locations) and 216 Greater Prairie-Chickens (5,750 locations) for 7 and 3 years, respectively. Individuals of both species avoided power lines by at least 100 m and Lesser Prairie-Chickens avoided one of the two highways by 100 m. Prairie-chickens crossed power lines less often than expected if birds moved randomly ( p < 0.05) but did not appear to perceive highways as a movement barrier ( p > 0.05). In addition, home ranges of Lesser Prairie-Chickens overlapped the power line less often than would be expected by chance placement of home ranges; this result was supported by kernel-density estimation of home ranges. It is likely that new power lines (and other tall structures such as wind turbines) will lead to avoidance of previously suitable habitat and will serve as barriers to movement. These two factors will likely increase fragmentation in an already fragmented landscape if wind energy development continues in prairie habitats .     

MINING AGREEMENTS IN DEVELOPING COUNTRIES-ISSUES OF FINANCE AND TAXATION

This article continues a Forum series on recent trends in mining contracts between host countries and foreign investors begun in the April 1977 issue. Based on intensive research carried out for the preparation of a book on Mining Ventures in Developing Countries , published recently in the Federal Republic of Germany, the authors discuss sources of finance, institutions, exchange controls and special accounts, royalties, income taxation, and equity participation. They conclude that taxation is most likely to remain the principal source of income; equity participation should be evaluated carefully as it does not automatically guarantee maximum benefits. The combination of taxes and royalties provide a steady flow of income. An increase of the total tax burden beyond a certain percentage may be counterproductive for the host country, as it encourages the investor to look for less controllable means of shifting profits or discourages investment for exploration and development.     

Setting Priorities for Research on Pollution Reduction Functions of Agricultural Buffers

The success of buffer installation initiatives and programs to reduce nonpoint source pollution of streams on agricultural lands will depend the ability of local planners to locate and design buffers for specific circumstances with substantial and predictable results. Current predictive capabilities are inadequate, and major sources of uncertainty remain. An assessment of these uncertainties cautions that there is greater risk of overestimating buffer impact than underestimating it. Priorities for future research are proposed that will lead more quickly to major advances in predictive capabilities. Highest priority is given for work on the surface runoff filtration function, which is almost universally important to the amount of pollution reduction expected from buffer installation and for which there remain major sources of uncertainty for predicting level of impact. Foremost uncertainties surround the extent and consequences of runoff flow concentration and pollutant accumulation. Other buffer functions, including filtration of groundwater nitrate and stabilization of channel erosion sources of sediments, may be important in some regions. However, uncertainty surrounds our ability to identify and quantify the extent of site conditions where buffer installation can substantially reduce stream pollution in these ways. Deficiencies in predictive models reflect gaps in experimental information as well as technology to account for spatial heterogeneity of pollutant sources, pathways, and buffer capabilities across watersheds. Since completion of a comprehensive watershed-scale buffer model is probably far off, immediate needs call for simpler techniques to gage the probable impacts of buffer installation at local scales.     

On Valuing Information in Adaptive‐Management Models

Abstract: Active adaptive management looks at the benefit of using strategies that may be suboptimal in the near term but may provide additional information that will facilitate better management in the future. In many adaptive‐management problems that have been studied, the optimal active and passive policies (accounting for learning when designing policies and designing policy on the basis of current best information, respectively) are very similar. This seems paradoxical; when faced with uncertainty about the best course of action, managers should spend very little effort on actively designing programs to learn about the system they are managing. We considered two possible reasons why active and passive adaptive solutions are often similar. First, the benefits of learning are often confined to the particular case study in the modeled scenario, whereas in reality information gained from local studies is often applied more broadly. Second, management objectives that incorporate the variance of an estimate may place greater emphasis on learning than more commonly used objectives that aim to maximize an expected value. We explored these issues in a case study of Merri Creek, Melbourne, Australia, in which the aim was to choose between two options for revegetation. We explicitly incorporated monitoring costs in the model. The value of the terminal rewards and the choice of objective both influenced the difference between active and passive adaptive solutions. Explicitly considering the cost of monitoring provided a different perspective on how the terminal reward and management objective affected learning. The states for which it was optimal to monitor did not always coincide with the states in which active and passive adaptive management differed. Our results emphasize that spending resources on monitoring is only optimal when the expected benefits of the options being considered are similar and when the pay‐off for learning about their benefits is large.     

Changes in Forest Use Value through Ecological Succession and Their Implications for Land Management in the Peruvian Amazon

Abstract:  Research on local use values of forests across an ecological succession informs land-use decisions and conservation planning. I evaluated use values of three age classes of secondary forest: fallow fields (<5 years old, $8.20/ha/year), young secondary forest (5–20 years old, $20.60/ha/year), and old secondary forest (>20 years old, $6.80/ha/year). I quantified daily forest product use and calculated use values in dollars per hectare per year for three communities in the northern Peruvian Amazon. I made three comparisons between forest types: number of useful species, value based on different use categories, and overall use values. Old secondary forest had the greatest number of total species present and species collected. Wood, food, and medicine were the three most valuable use categories. The value different families extracted from local forests varied enormously, but median forest values were lower for all forest types than potential gains from agricultural land use (e.g., coffee $167/ha/year). Values of different-aged stands on privately owned lands in two communities did not differ significantly, whereas in the third community, young secondary forest had a significantly greater value than other forest types. Old secondary forests were the most valuable source of wood products, and wood was the only use category in which there was any difference in the value of products extracted from different-aged forest stands. The value of all three forest types on open-access (nonprivate) lands was minimal (mean in each forest type, $0/ha/year). Local people can utilize the valuation results to develop land-use strategies that balance forest product use, agricultural productivity, and biodiversity conservation.     

Site‐Occupancy Distribution Modeling to Correct Population‐Trend Estimates Derived from Opportunistic Observations

Abstract: Species’ assessments must frequently be derived from opportunistic observations made by volunteers (i.e., citizen scientists). Interpretation of the resulting data to estimate population trends is plagued with problems, including teasing apart genuine population trends from variations in observation effort. We devised a way to correct for annual variation in effort when estimating trends in occupancy (species distribution) from faunal or floral databases of opportunistic observations. First, for all surveyed sites, detection histories (i.e., strings of detection–nondetection records) are generated. Within‐season replicate surveys provide information on the detectability of an occupied site. Detectability directly represents observation effort; hence, estimating detectablity means correcting for observation effort. Second, site‐occupancy models are applied directly to the detection‐history data set (i.e., without aggregation by site and year) to estimate detectability and species distribution (occupancy, i.e., the true proportion of sites where a species occurs). Site‐occupancy models also provide unbiased estimators of components of distributional change (i.e., colonization and extinction rates). We illustrate our method with data from a large citizen‐science project in Switzerland in which field ornithologists record opportunistic observations. We analyzed data collected on four species: the widespread Kingfisher (Alcedo atthis) and Sparrowhawk (Accipiter nisus) and the scarce Rock Thrush (Monticola saxatilis) and Wallcreeper (Tichodroma muraria). Our method requires that all observed species are recorded. Detectability was <1 and varied over the years. Simulations suggested some robustness, but we advocate recording complete species lists (checklists), rather than recording individual records of single species. The representation of observation effort with its effect on detectability provides a solution to the problem of differences in effort encountered when extracting trend information from haphazard observations. We expect our method is widely applicable for global biodiversity monitoring and modeling of species distributions.     

Predicting Offenses and Crashes from Young Drivers' Offense and Crash Histories

Previous research has indicated that offenses are better predictors of subsequent crashes than crashes themselves. We examined this hypothesis for 13,800 young beginning drivers in Michigan for up to nine years during the initial years of driving. Our analyses indicated that previous-year offenses are better predictors of both subsequent-year offenses and crashes than either previous-year crashes or at-fault crashes. This finding also held for the apparently higher-risk subset of subsequent-year serious offenses and at-fault crashes. Although there were no gender differences in the predictive power of crashes, it was found that the predictive power of previous offenses to subsequent serious offenses was significantly stronger for women than for men. The predictive power of incidents appeared to increase somewhat with increasing driving experience, suggesting that early incidents may be more attributable to inexperience, a characteristic of all beginning drivers, while later incidents may be more attributable to individual differences.