The fluffy, feel-good news story relates how a rail company in Scotland responded to a resident’s request to take into account access past the rail line for a hedgehog when performing maintenance on a wall. The company responded with a hedgehog-sized throughway in the new wall.
COLIN Seddon, manager of the Scottish Society for the Prevention of Cruelty to Animals’ wildlife centre at Middlebank, said it was becoming increasingly important to consider the effect on animals of human developments.
“We are moving further and further out into their territory so we have to do everything we can to make life easier for them,” he said. “We are invading their land, so we have to give something back.”
Well, the fact is that human development subdivides more than just lots in residential areas. As humans work out the most economical ways to connect things up, we arbitrarily restrict the movement of wild animals, and even plants. For each one-off solution to a noticed problem, we tend to overlook building in solutions to lots of unnoticed ones. This is a one-two punch for wildlife; first, there is the outright loss of habitat claimed by humans in development. Each time a home goes up, that plot of land is no longer available for the endemic wildlife to use. Second, when we connect together our separated developments with roads, pipelines for water and sewer services, rail lines, or separate apart property with fences, walls, ditches, mounds, and the like, we curtail the usual and normal means of access that wildlife has with other parts of the same population. “Habitat loss” is the usual term for the first, and it is easily remembered. The second part, though, comes under the daunting rubric of “vicariance biogeography”. Even though the term is a bit on the clunky side, the results from the science are pretty easily comprehended.
Vicariance refers to the events that split taxa. Vicariance biogeography takes as its field the geographical splitting of populations and the resulting patterns of phylogeny. A 1967 book by Edward O. Wilson and Robert MacArthur, “The Theory of Island Biogeography”, got things rolling, and a generalized appreciation for how barriers to intermixing of populations across geographical ranges impacts diversity followed. The short version is that introducing effective barriers that create non-mixing subpopulations reduces diversity and increases the likelihood that populations will go extinct.
On small scales, we see things like “mouse islands”, where interstate clover-leaf engineering puts small patches of green-space within a zone that is effectively lethal to mammalian predators that take rodents. Other than the occasional raptor, the rodents are fairly safe within the confines of a clover-leaf circle. But transfer of genetic material is strictly curtailed; even getting to the “mouse island” in the next clover-leaf over is a highly risky endeavor. These small micro-environments tend to support only depauperate diversity of wildlife, perhaps a couple of rodent species and whatever grass and plant species the road landscapers permit.
But there’s a lot of land that is not next to things like interstate highways. However, at the scale of highways, we see the same pattern emerging. Crossing those barriers is abnormally risky, so they create subpopulations with reduced gene flow on either side. These make for ready application of vicariance biogeography. In wildlife, it isn’t “divide and conquer”, it’s “divide and lose diversity”.
I’m sorry to put a damper on the holiday cheer for the resolution of the plight of Hamish the Hedgehog. The problems for wildlife created by both habitat loss and ignoring the lessons of vicariance biogeography are not the sort that have win-win solutions. Addressing either requires that humans do things that are costly to do. Fixing the problems we are experiencing is going to require addressing both. Making accommodations for an individual family of hedgehogs is a good thing, but we shouldn’t lie to ourselves that we have come to terms with our relationship with wildlife with these small gestures of limited scope.