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?”
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| "Sol y MAR?" - shedding some Light over the Minimum Area Requirements of species |
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.
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