Browsing by Subject "distance-decay"

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  • He, Siwen; Soininen, Janne; Chen, Kai; Wang, Beixin (2020)
    Metacommunity theory provides a useful framework to describe the underlying factors (e.g., environmental and dispersal-related factors) influencing community structure. The strength of these factors may vary depending on the properties of the region studied (e.g., environmental heterogeneity and spatial location) and considered biological groups. Here, we examined environmental and dispersal-related controls of stream macroinvertebrates and diatoms in three regions in China using the distance-decay relationship analysis. We performed analyses for the whole stream network and separately for two stream network locations (headwater and downstream sites) to test the network position hypothesis (NPH), which states that the strength of environmental and dispersal-related controls varies between headwater and downstream communities. Community dissimilarities were significantly related to environmental distances, but not geographical distances. These results suggest that communities are structured strongly by environmental filtering, but weakly by dispersal-related factors such as dispersal limitation. More importantly, we found that, at the whole network scale, environmental control was the highest in the regions with highest environmental heterogeneity. Results further showed that the influence of environmental control was strong in both headwaters and downstream sites, whereas spatial control was generally weak in all sites. This suggests a lack of consistent support for the NPH in our studied stream networks. Moreover, we found that local-scale variables relative to basin-scale variables better explained community dissimilarities for diatoms than for macroinvertebrates. This indicates that diatoms and macroinvertebrates responded to environment at different scales. Collectively, these results suggest that the importance of drivers behind the metacommunity assembly varied among regions with different level of environmental heterogeneity and between organism groups, potentially indicating context dependency among stream systems and taxa.
  • Hatakka, Tapio (Helsingin yliopisto, 2020)
    In the last few decades urbanisation has increased in Finland. Due to need for additional housing, it is necessary to compact current residential areas or develop existing green spaces into residential areas. Compact residential areas reduce water-permeable land cover and therefore increase stormwater runoff. Wetlands are increasingly being used for urban stormwater treatment as they are natural stormwater filtration systems. To assess utility of wetlands and streams it is important to identify their ecosystem services and ensuing benefits. Economic valuation methods can be applied to the valuation of small-water bodies and wetlands using either actual market information or a hypothetical market context created in a survey questionnaire. The aim of the research is to estimate the value of current and future ecosystem services provided by streams and wetlands in the drainage basin of Viikki residential area in Helsinki. The stated preferences survey was implemented to elicit resident’s benefits from wetland ecosystem services. The payment vehicle in a choice experiment was a yearly stormwater fee. This research focused on the wetlands and streams located in Viikki and the northern region of Vanhankaupunginlahti bay. Survey invitation was sent in 2016 to 1000 randomly selected residents in Viikki and nearby areas. The sample targeted the residents aged 19-79, and the shares of postal code areas were Viikki 21,6%, Myllypuro 24,4 % and Kontula-Vesala 54 % as the largest. The survey was responded partially or completely by 244 respondents. The willingness to pay for wetland ecosystem services was the highest for stormwater treatment, followed by recreational services and biodiversity. The information on wetlands did not affect the choices. Distance to wetlands and streams had negative effect on choice situations. A wealth of information and opinions were obtained from respondents about wetland ecosystem services and wetlands. Urban Oases-project have succeeded in providing wetland information to residents and in involving residents in environmental management. The feedback from the survey was essentially positive. Based on analysis, new urban wetlands projects would increase residential welfare.