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141.
Williams BK 《Journal of environmental management》2011,92(5):1371-1378
Adaptive management is a framework for resource conservation that promotes iterative learning-based decision making. Yet there remains considerable confusion about what adaptive management entails, and how to actually make resource decisions adaptively. A key but somewhat ambiguous distinction in adaptive management is between active and passive forms of adaptive decision making. The objective of this paper is to illustrate some approaches to active and passive adaptive management with a simple example involving the drawdown of water impoundments on a wildlife refuge. The approaches are illustrated for the drawdown example, and contrasted in terms of objectives, costs, and potential learning rates. Some key challenges to the actual practice of AM are discussed, and tradeoffs between implementation costs and long-term benefits are highlighted. 相似文献
142.
Adaptive management of natural resources--framework and issues 总被引:4,自引:0,他引:4
Williams BK 《Journal of environmental management》2011,92(5):1346-1353
Adaptive management, an approach for simultaneously managing and learning about natural resources, has been around for several decades. Interest in adaptive decision making has grown steadily over that time, and by now many in natural resources conservation claim that adaptive management is the approach they use in meeting their resource management responsibilities. Yet there remains considerable ambiguity about what adaptive management actually is, and how it is to be implemented by practitioners. The objective of this paper is to present a framework and conditions for adaptive decision making, and discuss some important challenges in its application. Adaptive management is described as a two-phase process of deliberative and iterative phases, which are implemented sequentially over the timeframe of an application. Key elements, processes, and issues in adaptive decision making are highlighted in terms of this framework. Special emphasis is given to the question of geographic scale, the difficulties presented by non-stationarity, and organizational challenges in implementing adaptive management. 相似文献
143.
Many populations of animals are fluid in both space and time, making estimation of numbers difficult. Much attention has been devoted to estimation of bias in detection of animals that are present at the time of survey. However, an equally important problem is estimation of population size when all animals are not present on all survey occasions. Here, we showcase use of the superpopulation approach to capture-recapture modeling for estimating populations where group membership is asynchronous, and where considerable overlap in group membership among sampling occasions may occur. We estimate total population size of long-legged wading bird (Great Egret and White Ibis) breeding colonies from aerial observations of individually identifiable nests at various times in the nesting season. Initiation and termination of nests were analogous to entry and departure from a population. Estimates using the superpopulation approach were 47-382% larger than peak aerial counts of the same colonies. Our results indicate that the use of the superpopulation approach to model nesting asynchrony provides a considerably less biased and more efficient estimate of nesting activity than traditional methods. We suggest that this approach may also be used to derive population estimates in a variety of situations where group membership is fluid. 相似文献
144.
The structure of food webs, complex networks of interspecies feeding interactions, plays a crucial role in ecosystem resilience and function, and understanding food web structure remains a central problem in ecology. Previous studies have shown that key features of empirical food webs can be reproduced by low-dimensional "niche" models. Here we examine the form and variability of food web niche structure by fitting a probabilistic niche model to 37 empirical food webs, a much larger number of food webs than used in previous studies. The model relaxes previous assumptions about parameter distributions and hierarchy and returns parameter estimates for each species in each web. The model significantly outperforms previous niche model variants and also performs well for several webs where a body-size-based niche model performs poorly, implying that traits other than body size are important in structuring these webs' niche space. Parameter estimates frequently violate previous models' assumptions: in 19 of 37 webs, parameter values are not significantly hierarchical, 32 of 37 webs have nonuniform niche value distributions, and 15 of 37 webs lack a correlation between niche width and niche position. Extending the model to a two-dimensional niche space yields networks with a mixture of one- and two-dimensional niches and provides a significantly better fit for webs with a large number of species and links. These results confirm that food webs are strongly niche-structured but reveal substantial variation in the form of the niche structuring, a result with fundamental implications for ecosystem resilience and function. 相似文献
145.
Becky L. Williams Vanessa Lovenburg Christine L. Huffard Roy L. Caldwell 《Chemoecology》2011,21(3):131-141
Some pelagic marine larvae possess anti-predator chemical defenses. Occasionally, toxic adults imbue their young with their
own defensive cocktails. We examined paralarvae of the greater blue-ringed octopus (Hapalochlaena lunulata) for the deadly neurotoxin tetrodotoxin (TTX), and if present, whether TTX conferred protection to individual paralarvae.
Paralarvae of H. lunulata possessed 150 ± 17 ng TTX each. These paralarvae appeared distasteful to a variety of fish and stomatopod predators, yet
food items spiked with 200 ng TTX were readily consumed by predators. We conclude that TTX alone does not confer individual
protection to paralarvae of H. lunulata, and that they possess an alternative defense. In larger doses, tetrodotoxin is a deterrent to the predatory stomatopod Haptosquilla trispinosa (mean dose = 3.97 μg/g). This corresponds to 12–13 paralarvae per predator based on the TTX levels of the clutch we examined.
Thus, the basic assumption that individual paralarvae of H. lunulata are defended by TTX alone was disproved. Instead, functionality of TTX levels in paralarvae may arise through alternative
selective pathways, such as deterrence to parasites, through kin selection, or against predator species not tested here. 相似文献
146.
Williams AF 《Traffic injury prevention》2011,12(3):207-209
The widespread application of graduated driver licensing (GDL), starting in the mid-1990s, has greatly reduced young driver crashes. Substantial further reductions are possible by raising the licensing age to 17. This can be done indirectly, through extension of GDL policies (minimum learner age of 16, one-year holding period), or by legislation directly establishing 17 as the licensing age. Other approaches are likely to have limited impact. 相似文献
147.
148.
Abayomi A Nimmo M Williams C Olayinka KO Osuntogun B Alo B Worsfold PJ 《Journal of environmental monitoring : JEM》2011,13(7):1884-1889
Roadside soils were sampled from the Lagos Lagoon catchment during the wet and dry seasons over the period 2005-2009. Lagoon sediment samples were also collected within the same period. All samples were digested with aqua regia to determine total phosphorus and extracted with 0.5 M sodium bicarbonate to determine the bioavailable fraction (Olsen-P). A segmented flow analyser method was used for analysis and good accuracy was demonstrated for two reference soils (SO-2 from CCMET and SRM 2711 from NIST). The Lagos Lagoon is a hypereutrophic water body (1270 ± 1170 μg P L(-1)), with significant areas of anoxia and water hyacinth growth. The total phosphorus concentrations in roadside soils (16 sites; mean ± 2 S.D.) were 285 ± 279 mg kg(-1) in the wet season and 424 ± 629 mg kg(-1) in the dry season, indicating that rainwater leaching is a major source of phosphorus in the lagoon. The bioavailable fractions were 5.17 ± 3.47 mg kg(-1) (2.1 ± 1.5% of the total) in the wet season and 13.0 ± 8.7 mg kg(-1) (4.3 ± 4.5% of the total) in the dry season. 相似文献
149.
Cindy E. Hauser Katherine M. Giljohann Michael A. McCarthy Georgia E. Garrard Andrew P. Robinson Nicholas S. G. Williams Joslin L. Moore 《Conservation biology》2022,36(3):e13888
Surveys aimed at finding threatened and invasive species can be challenging due to individual rarity and low and variable individual detection rates. Detection rate in plant surveys typically varies due to differences among observers, among the individual plants being surveyed (targets), and across background environments. Interactions among these 3 components may occur but are rarely estimated due to limited replication and control during data collection. We conducted an experiment to investigate sources of variation in detection of 2 Pilosella species that are invasive and sparsely distributed in the Alpine National Park, Australia. These species are superficially similar in appearance to other yellow-flowered plants occurring in this landscape. We controlled the presence and color of flowers on target Pilosella plants and controlled their placement in plots, which were selected for their variation in cover of non-target yellow flowers and dominant vegetation type. Observers mimicked Pilosella surveys in the plots and reported 1 categorical and 4 quantitative indicators of their survey experience level. We applied survival analysis to detection data to model the influence of both controlled and uncontrolled variables on detection rate. Orange- and yellow-flowering Pilosella in grass- and heath-dominated vegetation were detected at a higher rate than nonflowering Pilosella. However, this detection gain diminished as the cover of other co-occurring yellow-flowering species increased. Recent experience with Pilosella surveys improved detection rate. Detection experiments are a direct and accessible means of understanding detection processes and interpreting survey data for threatened and invasive species. Our detection findings have been used for survey planning and can inform progress toward eradication. Interaction of target and background characteristics determined detection rate, which enhanced predictions in the Pilosella eradication program and demonstrated the difficulty of transferring detection findings into untested environments. 相似文献
150.
Masahiro Nakaoka Masatoshi Matsumasa Tetsuhiko Toyohara Susan L. Williams 《Marine Biology》2008,153(4):589-598
Eelgrass, Zostera marina, produces two types of shoots: morphologically simple vegetative shoots and highly branched flowering (reproductive) shoots,
the latter found only in summer months. We examined whether the abundance and diversity of mobile epifaunal assemblage are
affected by the presence of flowering shoots in an eelgrass meadow of Otsuchi Bay, northeastern Japan. Comparisons of epifauna
in natural vegetation revealed that density and species richness did not differ significantly between sites consisting of
both flowering and vegetative shoots, and those only of vegetative shoots. A transplant experiment, conducted to examine the
colonization rates of epifauna to defaunated eelgrass planted with different combination of vegetative and flowering shoots,
showed no obvious variation in abundance and species richness. At species level, the density of some species such as a tanaid
Zeuxo sp. and a polychaete Platynereis sp. was higher at sites and/or treatments with flowering shoots, whereas that of some gastropods, such as Lirularia iridescens and Siphonacmea oblongata was higher at sites without flowering shoots. The species-specific response led to dissimilarity of epifaunal assemblage
between sites and among treatments with different densities of vegetative and flowering shoots. Similar patterns observed
for natural vegetation and the transplant experiment suggest that the variation in assemblage structure is caused by habitat
selection of each species, for example, the utilization of flowering shoots as feeding ground and nursery by Zeuxo sp. 相似文献