Canada's most prestigious science award goes to research on habitat fragmentation

This winner of Canada's most prestigious scientific award, the Natural Science and Engineering Research Council's Gerhard Herzberg Canada Gold Medal, is ecologist Lenore Fahrig. Fahrig is Chancellor's professor of biology at Carleton University, and one of the world's most cited researchers in the field of ecology.

Her 40-year career has been focused on a topic that's only growing in urgency: how to balance humanity's growing impact on the landscape with the need to protect and conserve biodiversity.

Here is part of Professor Fahrig's conversation with Quirks & Quarks host Bob McDonald.

Much of your work looks at habitat fragmentation and habitat loss. How are those two different from each other?

Habitat loss is really the destruction of natural habitats. Most times it's removal of things like forest or draining of wetlands and habitat loss is the main cause of species declines resulting from human activities. Habitat fragmentation is really a pattern that results from the loss of habitat. So maybe the remaining habitat is in one or two big blocks, or the remaining habitat could be more fragmented.

What attracted your interest in studying this particular question of fragmentation? 

When I started my faculty job at Carleton, which is 32 years ago now, I got a a big computer with the goal of doing a simulation to see whether there were any situations where we could be fairly confident that fragmentation itself doesn't matter or is not a problem.

The thing that really surprised me was that I couldn't find situations where the fragmentation did have an effect.

The less habitat you have, the lower the likelihood of survival of the simulated population in the model. But having that habitat in a few large blocks or many little ones didn't seem to make any difference at all. This was really surprising because the idea at the time was that it should make a big difference.

Then over time there were some field tests of this and found that yes, usually there was no effect of the fragmentation itself. And when there was an effect it looked like it was more often a positive effect. So if you looked across a large number of small patches, you'd end up with a higher total abundance of the species than if you looked at a few large blocks of habitat of the same total area.

Does the kind of species you're looking at make a difference? For example, whether they're big animals like elk or small animals like salamanders?

It's interesting because a lot of people assume that a large animal with a large range needs less fragmented habitat. But actually what they need is more habitat, and they need it over a large area. So yes, the amount of of habitat makes a big difference to which species you'll find in an area, but the fragmentation, so how many patches that is actually divided into, doesn't really seem to have an effect.

It still seems counterintuitive. How is it that smaller blocks of protected areas are better for biodiversity?

So an individual small block is not. One large block is going to be better than one small block. But the question is, why do you have higher biodiversity on average when you have a large number of small blocks that add up to the same total area as that one big block? 

Every bit of natural habitat is important in some way for biodiversity... it does add up to a big impact in terms of protecting species.- Lenore Fahrig, Chancellor's professor of biology at Carleton University 

There are lots of hypothesis for this. One idea is that when you have a large number of small blocks, you pick up more of the different microhabitats in the region, and for that reason you're more likely to sample more of the species for that region.

Other things that we've known about for a long time are the effects of habitat subdivision on species interactions. Interactions like predator prey interactions or host parasite interactions can be stabilized because you have the opportunity for the host or the prey to escape temporarily from the predator or the parasite. Also, competitive interactions, competition between species can be more stable. There's also the idea that disturbances, something like a fire or a disease or something like that, will be less likely to spread and get as large across a set of several small patches, than a few large ones.

What does what you've learned about fragmentation tell us about how we should be protecting natural habitats?

What we know now is that every bit of natural habitat is important in some way for biodiversity. So what we need to do is not kind of say, well, this bit of habitat isn't big enough. Every bit of habitat is big enough in the sense that if you add it together with other little bits of habitat together, that makes a big difference. So what that means is that efforts to save small bits of habitat are really important.

We have a situation in in Canada where most of our threatened and endangered species are in the southern part of the country, where we have a lot of small patches of forest and or other habitats, and not very much in the way of large patches. And we tend to put our protected areas in the far north where we can have large protected areas, but that isn't actually helping the species in the southern part of the country, which are the most threatened and endangered species in Canada.

And so what this research says is that it's worth trying to protect the habitat that we do have in the south, because it does add up to a big impact in terms of protecting species. 

Q&A has been edited for length and clarity. Written and produced by Amanda Buckiewicz