Main Text:
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).