A Resource-based Approach to Mapping Habitat

Defining the habitat of an organism is key to understanding its role in the environment and how it interacts with other species. In a general sense, habitat is the space in which an organism or group of organisms lives. More finely, habitat is often defined based on the dominant vegetation of an area. However, defining habitat in this way does not always accurately represent species densities or even their overall presence or absence. Another approach to defining habitat is the resource based model, which accounts for species-specific essential resources and environmental conditions rather than general vegetation type alone. For mapping species’ local distributions, this approach may be more accurate than the vegetation-based model.

In their study, Vanreusel and Van Dyck tested the resource-based approach against the vegetation-based approach using green hairstreak butterfly (Callophrys rubi) populations in a heathland landscape. The researchers generated both a vegetation map and a resource map including variables such as nectar plants, mate-locating sites, shelter, microclimate, and host-plant availability (fig. 1). Observations of C. rubi were recorded in two consecutive years using GIS. The proportion of observations explained by the resource-based approach was significantly larger than in the case of the vegetation type approach (1466/1724 versus 954/1724, Fisher’s Exact Test, p < 0.0001). Even for highly mobile organisms on a landscape scale, the resource-based model can more successfully define the actual habitat of a species.

Figure 1) (a) Vegetation map (dark green and pale green: pine forest; bright green: broad-leaved forest; pink: dry heathland; purple: wet heathland; yellow: Molinia dominated moorland; orange: Myrica shrubland; blue: open water. (f) Habitat suitability zones for larva and adult C. rubi based on resources. Figure courtesy of https://doi.org/10.1016/j.biocon.2006.10.035.

            A resource-based, rather than a vegetation-based, model for defining habitat is useful in urban environments. Urban environments are highly fragmented, so using vegetation alone as a determinant of habitat is too coarsely grained to define habitat. In our urban Ecology project, we will use vegetation/substrate type as an explanatory factor to the distribution of fungi on Grinnell’s campus. However, we also need to consider other essential resources for fungi, such as moisture availability or shelter from disturbance to fully be able to explain variation in fungal density. We believe this resource-based approach would best explain fungal density variation because of the highly fragmented nature of Grinnell's campus.

Reference:

Vanreusel, W., Van Dyck, H. (2007). When functional habitat does not match vegetation types: A resource-based approach to map butterfly habitat. Biological Conservation, 135(2), 202-211. https://doi.org/10.1016/j.biocon.2006.10.035.