Wildlife in the city – a new way of perceiving habitat (part 1)

A lot of the way we manage native flora and fauna is about remnants – those tiny (or not so) patches of land that are still usually relatively undisturbed. We take care of those and map them, survey them, try and keep them suitable preserves for the things we think we probably shouldn’t lose. But, as a recent article across my desk pointed out, while that’s all well and good, we can have a greater effect if we look at the space around those patches. The researchers make the convincing argument that the patches are mostly set, now. Particularly in urban areas we’ve already taken away most of the native vegetation and protected most of the tiny bits left, we simply can’t clear any more. The main option for change is the matrix, the area around the patches. That’s quite an important concept. The article’s called “Conceptual domain of the matrix in fragmented landscapes”, which basically means “Here’s a way of thinking about how the land around the patches affects everything and what we can do with it”. And the way they’ve suggested thinking about it is quite interesting – it’s the beginnings of a roadmap to increase the survival of our native species without having to take away the houses and turn our cities back into bush. The abstract I’ve linked to is a bit impenetrable, so the researchers have kindly made a video that explains it. I’ll go through their “way of thinking about it” below to look at how this can influence our urban gardens and urban farming practices.

First, they identify three main impacts that affect the species living in those little patches. They are movement and dispersal, resource availability and the abiotic (non-living) environment.

Movement and dispersal is about the question “can native species move between the patches?” This depends on what’s between them (it’s easier the more similar the matrix is to the remnants), the distances between patches, and “fence” effects at boundaries making it impossible for some species to cross.

Providing the right resources means a species can live throughout the matrix as well as in the remnants, which increases their numbers. But they have to live in the matrix – there’s only limited evidence to suggest that you can have a high population in a patch that forages outside a patch to support itself. A matrix without suitable resources obviously isn’t going to support any extra animals or plants outside their safety patch.

The abiotic environment looks at microclimate variations such as light, heat, wind penetration, which vary a lot at the edge where a patch meets the matrix. It also includes disturbance regimes such as fire and logging in the matrix. This effect is a big driver of invasion of feral species into a patch.

Then the researchers describe five “dimensions” which are interacting with these three effects. There’s spatial scale and spatial variation – the matrix is not homogenous. More so in an urban environment, but still variable. Some patches are more isolated than others not because of distance between them but because of what’s between them. Though, there’s findings that what’s between them only matters at intermediate distances. Large distances still don’t get crossed, and small distances can get crossed regardless. So the scale matters.

The next two are temporal scale and temporal variation. These are easily overlooked but quite important. The matrix doesn’t stay the same with time. There are seasonal and years-long changes which can be quite important. Take a look at photos of the land around the Rabbit-Proof Fence in winter, spring and summer and you’ll see what I mean. Resources might only be available in the matrix during a certain season, but that might be long enough for some species to cross through it to repopulate patches. Then there’s temporal scale – some changes are much longer-term, such as the succession of plant species in edge areas, climate cycles of droughts and floods, or a plantation growing from seedlings, forming canopy, and then being logged and restarted. At different stages of that plantation’s life different species will be able to move through it or find resources in it. Not all species will react the same to temporal variation so scale does matter – some (often small animals) are better set for short pulses of resource abundance, others such as lichens need much longer times to be able to recolonise.

The last “dimension” is adaptation – a species can change how it copes with the matrix over time, sometimes quite short times such as in the case of insects with short generational cycles. This isn’t something you can rely on though because there’s no guarantee we’ve built a matrix within the range that a species is able to adapt to.

So, if you start viewing our suburbs as the new habitat, how does this start making our cities and our gardening and farming habits look? Part 2, discussing this, tomorrow.

This post has been largely based on the paper DRISCOLL, D. A., BANKS, S. C., BARTON, P. S., LINDEMAYER, D. B. & SMITH, A. L. (in press). Conceptual domain of the matrix in fragmented landscapes. Trends in Ecology and Evolution. Links to the published article, an approved preprint and the video are also available at lead author and researcher Don Driscoll’s website.

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