Introduction
Human societies are under increasing pressure to halt unprecedented
biodiversity loss (Caro et al. 2022; Cowie et al. 2022).
Given the magnitude of current environmental impacts, this will require
quickly protecting a considerable portion of the Earth’s biomes, moving
from the currently protected ~ 17% of the planet
surface to 30% before 2030 (Dinerstein et al. 2019; Maxwellet al. 2020). Yet, our understanding of natural phenomena remains
at best partial across most of the planet (Hortal et al. 2015;
Hughes et al. 2021). There is, therefore, an urgent need to
identify general conservation principles that would allow the most
effective habitat protection in the face of limited knowledge about
particular ecosystems (Currie 2019; Arroyo-Rodríguez et al. 2020;
Fahrig et al. 2022).
One of the most widely applied such general principles for biodiversity
conservation, first proposed by Diamond (1975), is the SL >
SS principle that a single large
patch (or a few large patches) has higher conservation value than
several small patches. Although the SL > SS principle seems
intuitive, both historical (Simberloff & Abele 1976; Quinn & Harrison
1988) and recent (Deane et al. 2020; Fahrig 2020; Hammill &
Clements 2020; Riva & Fahrig 2022) evidence support the opposite SS
> SL pattern, that a
set of many small patches usually
harbors more species than a set of few large patches totaling the same
area. In addition, many studies suggest high potential of small patches
for conservation of rare species, provision of ecosystem services, and
optimal reserve design (Bennett & Arcese 2013; Tulloch et al.2016; Hunter et al. 2017; Deane & He 2018; Wintle et al.2019; Valdés et al. 2020; Yan et al. 2021). Nevertheless,
the idea that habitat in large patches is disproportionately important
for biodiversity is strongly entrenched in conservation research and
practice (Wintle et al. 2019; Fahrig et al. 2022).
Persistence of the SL > SS principle over more than four
decades despite evidence to the contrary is largely due to the
assumption that the SL > SS principle is valid for species
of conservation concern, many of which are habitat specialists that
require large expanses of continuous habitat. The SL > SS
inference is also expected to hold when the matrix separating habitat
patches is hostile to those species. Nevertheless, recent tests do not
support these ideas. Species richness of habitat specialists and of
threatened or declining species is generally higher across several small
than few large patches, and the direction of this relationship does not
change when the matrix is hostile (Fahrig 2017, 2020; Riva & Fahrig
2022). Thus, it seems reasonable to ask – should the SL
> SS principle be reversed ? In other words, when a choice
must be made, should the default principle be to protect many small
patches, i.e., SS > SL? The evidence to date supports such
a shift, but science is conservative, erring on the side of the status
quo unless and until the evidence is overwhelming.
Here we bring the evidence to that tipping point by adding analyses of
76 metacommunities, including 4401 species and 1190 patches, from the
database compiled by Chase et al. (2019). Implementing a novel
resampling algorithm, we synthesize the largest unbiased (rarefied)
metacommunity dataset generated to date for the “SLOSS” question: for
the same total area, is biodiversity higher in several small patches or
in one or a few large patches? Based on the results, we propose a new
principle for biodiversity conservation – for a given total
area, protecting the largest possible number of patches,
including very small ones, will maximize biodiversity for most taxa .
This is opposite to current strategies that typically target for
protection patches orders of magnitude larger than the smaller patches
in the database we analyzed. Immediate recognition of the value of small
patches is therefore fundamental to global biodiversity conservation.