Measuring levels of biological invasion
It is all very well having an academic definition of novel ecosystems, but how do we identify them in practice?
In reality, ecosystems and communities are always in a state of flux – they are never stable – so there will be constant, continuous changes in species assemblages. Species will flicker in and out, and their relative abundances can be as dynamic as environmental conditions are. In Australia, with its great environmental variability, ecosystems can be very dynamic. Consequently, quantifying ecosystem novelty and determining whether a change in community composition is meaningful or not can be a little tricky.
Some colleagues and I grappled with this issue in the context of biological invasions (Catford et al. 2012). As simple as it may seem, there is no standard way to quantify the extent or severity of invasion: people use all sorts of different measures, which makes comparisons really difficult. If two ecosystems are invaded by a different suite of species, for example, how can management resources be prioritized objectively if the net impact of invasion on the ecosystems is unknown?
To help answer this question, we identified the best way to quantify the level of invasion by non-native animals and plants by assessing the advantages and disadvantages of different metrics…