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The 2022 United Nations Biodiversity Conference (COP 15) addressed five
“horsemen of the biodiversity apocalypse”: climate change, pollution,
invasive species, overexploitation, and land use change. Policies to
regulate land use are especially important because habitat loss and
degradation continue (Riva et al. 2022) and contribute the most
to ongoing biodiversity loss (Haddad et al. 2015; Fahrig 2017).
At the same time, such policies are especially delicate because the
complexity of species responses to habitat change has spurred a heated
debate regarding the importance and influence of habitat fragmentation
(Fletcher et al. 2018; Fahrig et al. 2019). Unanswered
questions include how often does habitat fragmentation exacerbate or
interact with the effects of habitat loss on biodiversity?
Because different contexts can determine different answers to such
questions, deciding which habitat is most valuable based on its pattern
and amount has proven difficult. Managers and policy makers might
therefore believe that scientists cannot agree on how biodiversity
should be preserved in the face of widespread and increasing global land
use. We contend that ongoing debates should not distract from shared
principles based on decades of research in biodiversity conservation. To
identify and articulate such principles, we intentionally brought
together researchers from both sides of the habitat fragmentation debate
(Fletcher et al. 2018; Fahrig et al. 2019). The three
resulting principles relate to the geographic coverage, abundance, and
connectivity of native habitat areas (or “patches”) (Fig. 1):
1) To protect Earth’s biodiversity, we must protect and restore native
habitats in all biomes and ecoregions (Fig. 1.1). This will safeguard
the unique contribution of each biome and ecoregion to the Earth’s
biological heritage (Olson et al. 2001). Widespread geographic
cover of native habitats is a prerequisite for any effort in global
biodiversity conservation.
2) Protecting as much native habitat as possible is our best way to
safeguard biodiversity (Fig. 1.2). This requires protecting both the
remaining large native ecosystems and the many small native patches in
human-dominated regions. Considering the socio-economic costs of habitat
restoration, effort should be focused on preserving native habitats.
Restoration is an important tool in regions that are already extensively
transformed by humans.
3) Habitat patches must be functionally connected (Fig. 1.3).
Connectivity ensures access to sufficient and complementary resources
when remnant habitat patches are too small for a single patch to sustain
a species. Connectivity is also fundamental when patches are larger, as
migration between them decreases population extinction risk, facilitates
re-colonization, and may allow species to shift their ranges in response
to shifting climate.
These principles are not exhaustive. For instance, they do not cover
issues of habitat quality (Betts et al. 2022) or overexploitation
within protected areas (Plumptre et al. 2014). Furthermore, when
detailed information is available, the principles might be superseded by
actions tailored to a well-known system. Still, biodiversity is poorly
understood across most of the Earth (Hortal et al. 2015), such
that the design of ad hoc actions in most ecosystems and/or for
most species is not possible. Given the dominant role of habitat change
in the current biodiversity crisis, and unresolved biodiversity
knowledge shortfalls, the application of effective, “coarse-filter”
(Schwartz 1999) general principles will largely benefit biodiversity.
Therefore, we argue that the three simple principles we propose should
be at the core of conservation action in response to the recent Global
Biodiversity Framework, complementing the broader Targets and Goals
identified in the Kunming-Montreal meeting of the Conference of the
Parties (COP 15).