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Comparison of yellow and white pan traps in surveys of bee fauna in New South Wales, Australia (Hymenoptera: Apoidea: Anthophila)

Sat, 01 Jan 2011 00:00:00 GMT

Comparison of yellow and white pan traps in surveys of bee fauna in New South Wales, Australia (Hymenoptera: Apoidea: Anthophila) Gollan John; Ashcroft Michael; Batley M Pan trapping is a standardised and commonly used method for collecting bees, but characteristics of the trap may influence its effectiveness or bias results. The effect of trap colour on the species and numbers caught has been studied in the Northern Hemisphere, but not in the Australian region. Australia has a unique bee fauna and colour preferences, if any, may differ from those found in other continents. In four separate surveys across a wide area of New South Wales, it was tested whether there was a difference in the abundance or species richness captured by yellow- and white-coloured pan traps. In total, 1267 bees were collected, comprising 66 species, 50 of which are in the family Halictidae. In all surveys, yellow pan traps collected a significantly larger number and greater diversity of bees. Eight of the thirteen most common species were observed significantly more frequently (P < 0.01) in yellow pan traps, while the European honey bee (Apis mellifera) was found in larger numbers in white traps. Our results demonstrate that differently coloured traps collect different components of the Australian bee fauna. Therefore, a variety of pan colours should be used when sampling overall bee biodiversity, but specific colours may be more effective when targeting certain groups or species.

Density-dependent facilitation cascades determine epifaunal community structure in temperate Australian mangroves

Sun, 01 Jan 2012 00:00:00 GMT

Density-dependent facilitation cascades determine epifaunal community structure in temperate Australian mangroves Bishop Melanie; Byers James; Marcek Benjamin; Gribben Paul Co-occurring foundation species can determine biological community structure via facilitation cascades. We examined the density dependencies of facilitation cascades, including how the density of a basal foundation species influences the density of secondary foundation species, and how the density of secondary foundation species influences community structure. The system in which we assessed density dependencies was a temperate mangrove forest in which pneumatophores trap the fucoid alga Hormosira banksii and provide substrate for the oyster, Saccostrea glomerata. The alga and oyster in turn determine benthic community structure. In the field, algal biomass was positively correlated with pneumatophore density. Oysters, by contrast, were highly over-dispersed and correlated with the presence/ absence of pneumatophores. Epifaunal abundance and species richness were positively correlated with algal and oyster abundance, but their effects were independent. The positive effect of pneumatophore density on epifauna was primarily an indirect effect of trapping more algae. Pneumatophores did not directly influence invertebrate communities. Experiments revealed that, at very low pneumatophore densities, algal retention was insufficient to facilitate epifauna above that found on pneumatophores alone. At higher densities, however, increasing the density of pneumatophores increased algal retention, and the density and diversity of associated invertebrates. Shading by the mangrove canopy reduced algal biomass but did not modify the density-dependent nature of the cascade. Our results extend facilitation theory by showing that the density of both basal and secondary foundation species can be critical in triggering facilitation cascades. Our study also reveals that, where foundation species cooccur, multiple, independent cascades may arise from a single basal facilitator.

Bayesian Conjoint Choice Designs to Measure the Willingness to Pay

Sat, 01 Jan 2011 00:00:00 GMT

Bayesian Conjoint Choice Designs to Measure the Willingness to Pay Vermeulen B; Goos P; Scarpa Riccardo; Vandebroek L. In this paper, we propose a new criterion for selecting efficient conjoint choice designs when the interest is in quantifying willingness to pay (WTP). The new criterion, which we call the WTP-optimality criterion, is based on the c-optimality criterion which is often used in the optimal experimental design literature. We use a simulation study to evaluate the designs generated using the WTP-optimality criterion and discuss the design of a real-life conjoint experiment from the literature. The results show that the new criterion leads to designs that yield more precise estimates of the WTP than Bayesian D-optimal conjoint choice designs, which are increasingly being seen as the state-of-the-art designs for conjoint choice studies, and to a substantial reduction in the occurrence of unrealistically high WTP estimates

Do Respondents' Perceptions of the Status Quo Matter in Non-Market Valuation with Choice Experiments? An Application to New Zealand Freshwater Streams

Sat, 01 Jan 2011 00:00:00 GMT

Do Respondents' Perceptions of the Status Quo Matter in Non-Market Valuation with Choice Experiments? An Application to New Zealand Freshwater Streams Scarpa Riccardo; Marsh Dan; Mkwara L Many issues relating to the sustainability of environmental resource use are informed by environmental valuation studies with stated preference surveys. Within these, researchers often provide descriptions of status quo conditions which may differ from those perceived by respondents. Ignoring this difference in utility baselines may affect the magnitude of estimated utility changes and hence bias benefit estimates of proposed environmental policies. We investigate this issue using data from a choice experiment on a community¿s willingness to pay for water quality improvements in streams. More than 60% of respondents perceived streams¿ water quality at the status quo to be better than the description we provided in our scenario. Results show that respondents who could provide details of their perception of the status quo displayed stronger preferences for water quality improvements¿and hence higher marginal willingness to pay¿than their counterparts. However, respondents who referred to their own status quo description displayed a higher inclination to prefer the status quo, while other respondents tended to prefer the proposed improvements. We argue this might be linked to the amount of knowledge each group displayed about the status quo: a kind of reluctance to leave what one believes he/she knows well.