Those of us working on species’ conservation cannot help but admitting: Decision makers often don’t care as much as we do about population size, or the viability of “our” species: they want to know what are the implications for them. Especially, how much AREA do they need to leave aside so that we leave them alone?... Be it for the protection of a single species, or the area needed for a protected site, quite a few of us have already encountered the blunt question: “So: How much area do you need?”
What we are trying to say is that the Minimum Area Requirements (MAR) of species is a relevant concept for conservation planning and policy – perhaps much more than the more commonly used Minimum Viable Population size (MVP).
In a paper recently published in Biological Conservation, we compiled a comprehensive database of MAR estimates from the literature, covering 216 terrestrial animal species from 80 studies. We obtained estimates from a) Population Viability Analyses (PVAs) which explored a range of area-related scenarios, b) PVAs that provided a fixed value – either MAR or the MVP alongside other area-relevant information, and c) empirical studies of occupancy patterns in islands or isolated habitat patches across area. We then assessed the explanatory power of life-history traits (body mass, feeding guild, generation length and offspring size), environmental variables (average precipitation and temperature), research approach and phylogenetic group on MAR estimates.
What did this exercise bring us?
First, we found out that MAR estimates are not as copious as MVP, but there are already hundreds of available estimates.
Second, body mass, as simple as it is, is quite a useful predictor of the MAR, especially alongside feeding guild plus one or two additional life history traits and environmental information. Careful, though: it is a good proxy for approximation across species, but not so easily for a given species - estimates for a given species, based on alternative scenarios, could easily have a range over two orders of magnitude.
Most importantly, what we found is that it matters where the data come from. Empirical (occupancy) patterns are rather risky to use for estimating the MAR, likely because they are sensitive to transient dynamics. Based on our results, we recommend using PVA-based evaluations, because they enable considering both time horizon and extinction probability - two critical issues which one would likely want to consider before just ”giving” any fixed number to decision makers.
As we already collected these data, we are happy to share it. Our database is now freely available to anyone who wishes to examine, search, or download it.