Ecological impact and cost-effectiveness of wildlife crossings in a highly fragmented landscape:A multi-method approach

Context: Road infrastructure construction is integral to economic development, but negatively affects biodiversity. To mitigate the negative impacts of infrastructure, various types of wildlife crossings are realized worldwide, but little is known about their effectiveness, and cost-effectiveness. Objective: The paper contributes to the methodological and empirical discussion on the effectiveness of wildlife crossings for enhancing the quality of surrounding nature and its cost-effectiveness by analyzing a large-scale wildlife-crossings program in the Netherlands. Method: A multi-criteria cost–benefit analysis is applied, comprised of monetary and non-monetary measures, and a mixed-method approach is used to determine ecological effects. Ecological effects are expressed in the standardized weighted hectare measurement of threat-weighted ecological quality area (1 T-EQA = 1 ha of 100% ecological quality, averagely threatened). Cost-effectiveness is calculated comparing the monetary costs of intervention with ecological benefits (Euro costs/T-EQA), for different types of wildlife crossings and for two other nature policies. Results: The Dutch habitat defragmentation program has induced an increase in nature value of 1734 T-EQA at a cost of Euro 283 million. Ecological gains per hierarchically ordered groups of measures differ strongly: The most effective are ecoducts (wildlife crossing bridges) followed by shared-use viaducts and large fauna tunnels. Ecoducts generated the largest gain in nature value, but were also the most costly measures. In terms of cost-effectiveness, both large fauna tunnels and shared-use viaducts for traffic and animals outperformed ecoducts. Conclusions: Ecoducts deliver ecologically, but their cost-effectiveness appears modest. Purchasing agricultural land for restoration of nature appears more cost-effective than building wildlife crossings. Yet, reducing environmental pressures or their effects on existing nature areas is likely to be most cost-effective.</p

Flexible parasitoid behaviour overcomes constraint resulting from position of host and nonhost herbivores

Parasitoids face several hurdles and distractions while foraging for their hosts, one of which is the presence of nonhost herbivores. Nonhost herbivores may interfere with plant volatile-mediated location of host-infested plants and reduce encounter rates with hosts on the plant. This results in a lower foraging efficiency. In this study, we tested whether the feeding position of a host and nonhost herbivore on the same plant influences foraging decisions and parasitism efficiency of parasitoids. We confined host and nonhost herbivores to either higher positions, i.e. younger leaves (preferred by the host) or lower positions on the plant, i.e. older leaves (preferred by the nonhost). Host and nonhost herbivores fed either on separate leaves or on the same leaf. Results from laboratory experiments show that during the first phase of foraging when plant volatiles are used to locate a host-infested plant, parasitoids were misled when host and nonhost were positioned in an unnatural way on the individual plant (host on the older leaves). The positions of host and nonhost partly influenced parasitoids during the second phase of foraging, when the host is located on the plant by using host cues. Total host-finding efficiency, as tested in a semifield set-up, was not affected by herbivore position. We conclude that parasitoid foraging behaviour has enough flexibility to overcome constraints resulting from an unexpected distribution of herbivores over a plant.</p

Reversibility of the hydrogen desorption from nabh(4) by confinement in nanoporous carbon

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