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2014 The Bumblebee Metric on Nose Hill AN URBAN GREEN NETWORK CONNECTIVITY ANALYSIS PETER MEADOWS – EVDS 626 The Bumblebee Metric It has been suggested that Nose Hill Park, due to its apparent physical isolation from other parks and natural areas, is of minimal importance to Calgary’s ecologies. In this report I demonstrate this assertion to be false through a connectivity analysis based on the accessibility of the city’s green network to the common bumblebee, a crucial pollinator (Kevan, 1999). It is reasonable to expect that similar connectivity analyses focusing on other small flying animals, or animals to whom urban built features would present comparable obstacles to movement, would return similar results. Regardless, the esthetic, economic, ecological, and ethical importance of the bumblebee alone, along with the pollination services it provides (Kearns, Inouye, & Waser, 1998), is more than sufficient to justify the preservation of Nose Hill Park in Calgary. As bumblebees in Southern Alberta prefer to build their nests in tunnels made in the ground by other animals (e.g. prairie dogs), or in tussock grass (Richards, 1978), Nose Hill Park presents an ideal habitat for bumblebees, in addition to functioning as a central network node for bumblebee access within the rest of Calgary’s green network for foraging and pollination. Forage Impediments and Patch Neighbourhood Bumblebee foraging range differs widely from species to species (Walther-Hellwig & Frankl, 2000), however for urban environments it is reasonable to assume that few bumblebees will forage more than 1500 m from the nest (Ahrne´, Bengtsson, & Elmqvist, 2009). Kearns, Inouye, & Waser have argued that species diversity among pollinators is necessary to prevent pollination crises (1998). Ahrné, Bengtsson, & Elmqvist have shown that impervious surfaces in urban environments are the most significant variable to bumblebee diversity, and that the “higher variability in abundance of certain species in the most urban areas may indicate a weaker reliability of the ecosystem service pollination in areas strongly influenced by human activity” (2009). I therefore developed a resistance surface for this study which assumes that urban development is an impediment to bumblebee travel (Fig. 1). Fig. 1a shows least-cost paths along the resistance surface which do not exceed 1500 effective meters, which clearly separates the natural areas in north-central Calgary into a cluster based around Nose Hill Park. On the same figure, patches consisting of parks and natural areas are coloured by the number of neighbours they are connected to by two jumps, indicating their connectivity importance in the network. Nose Hill Park stands out as not only the most important patch in the north-central Calgary cluster, but one of the most important in the entire city (Fig. 1a). Page 1 of 4 Minimum Forage Distance and Betweenness Further, there has been suggestion that bumblebees prefer not to forage close to their nests (Ahrne´, Bengtsson, & Elmqvist, 2009), which suggests that strong connectivity to an extensive green network is crucial in order to allow bumblebees enough room to thrive. Fig. 1b shows links between nodes in Calgary’s urban green network which are greater than 200 m in length, which shows Nose Hill Park as one of only three connecting nodes between the northeastern and western areas of the city. Nodes on the same figure are sized according to betweenness centrality (Fig. 1b), which again clearly illustrates that Nose Hill is not only by far the most important node bridging those two areas, but one of the most important in the entire network. Conclusions A casual understanding of green networks may lead to the belief that Nose Hill Park, because it is not directly connected by green corridors to other natural areas in the city or outside of it, does not play an important role in Calgary’s urban green network. A relatively simple analysis of the network using the model of the common bumblebee, however, shows this assumption to be false. Both for its importance to the cluster of parks and natural areas in north-central Calgary, and for its role as a connector between areas in the greater network, Nose Hill Park is a crucial component of the city’s natural facilities. Page 2 of 4 Page 3 of 4 References Ahrne´, K., Bengtsson, J., & Elmqvist, T. (2009). Bumble Bees (Bombus spp) along a Gradient of Increasing Urbanization. PLoS ONE. Kearns, C. A., Inouye, D. W., & Waser, N. M. (1998). Endangered Mutualisms: The Conservation of PlantPollinator Interactions. Annual Review of Ecology and Systematics, 83-112. Kevan, P. G. (1999). Pollinators as bioindicators of the state of the environment: species, activity and diversity. Agriculture, Ecosystems and Environment, 373-393. Richards, K. W. (1978). Nest Site Selection by Bumble Bees (Hymenoptera: Apidae) in Southern Alberta. The Canadian Entomologist, 301-318. Walther-Hellwig, K., & Frankl, R. (2000). Foraging habitats and foraging distances of bumblebees, Bombus spp. (Hym., Apidae), in an agricultural landscape. Journal of Applied Entomology, 299306. Page 4 of 4