Download The Bumblebee Metric on Nose Hill

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).
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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.
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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.
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