Future threats to biodiversity and pathways to their prevention — study notes
Introduction and scope
Topic: Future threats to biodiversity focusing on terrestrial mammals and birds over the next 50 years; explore how extinction risks may change under rising population and economic development.
Key message: While threats are substantial, proactive actions (agricultural intensification to raise yields, reducing land clearing and habitat fragmentation, protecting natural lands) can improve food security in developing nations and preserve biodiversity.
Authors and source framing: Review synthesizes IUCN assessments and regional analyses to project extinction risks and discuss prevention pathways.
IUCN framework and data used
IUCN Red List categories and encoded risk values used in this work:
Metrics used for countries:
the percentage of all species that are threatened with extinction; and
the mean extinction risk value for all species in a country.
Data exclusions: data-deficient and not evaluated species were excluded from calculations (see Supplementary Methods).
Scale and scope: IUCN assessed ~61,000 animal species (mammals and birds largely covered in this review).
Major drivers of biodiversity loss
Primary direct threats to terrestrial mammals and birds (habitat loss/degradation and fragmentation) account for the most common declines.
Major mechanisms of threat (as shown in Fig. 1a):
Habitat loss and degradation (driven by land-use change, agriculture, logging, urbanization, mining, transport corridors) — the most frequent direct threat.
Direct mortality (hunting and persecution) — approximately 40–50% of threatened bird and mammal species (larger effect on large herbivores).
Bushmeat exploitation: notable for threatening many species; Ghana case (1970–1998) shows a 76% biomass decline across 41 mammal species; bushmeat hunting is a key nutrition source in some areas.
Invasive species: relatively few terrestrial mammals are threatened by invasives, but island birds are heavily impacted by introduced predators; invasive species threaten ~21% of terrestrial birds (26% if seabirds included).
Disease and climate change: exotic diseases can threaten amphibians and some birds/mammals/plants; climate change not yet a major threat but expected to pose challenges in the future.
Bushmeat and local livelihoods: in many regions, hunting is intertwined with nutrition, economic activity, and governance; reducing reliance on bushmeat requires alternative protein sources and protection enforcement.
Large-bodied species are disproportionately vulnerable: in both mammals and birds, larger species are ~3x more likely to be threatened than small-bodied species.
Geographic focus and regional patterns
Regions analyzed: SAIC (South and Southeast Asia, India, China cluster), Sub-Saharan Africa, and Tropical South America.
Global biodiversity patterns: most diversity in the tropics for both mammals and birds.
Current threats show region-specific intensities:
SAIC: highest share of large mammal diversity and highest proportion of large mammals threatened; almost two-thirds of mammals >10 kg threatened here.
Sub-Saharan Africa: substantial threat to large mammals but generally lower mean extinction risk than SAIC and Tropical SA; 34% of its large mammals threatened (vs 40–90% in SAIC for large mammals).
Tropical South America: high diversity; 50% of large mammal species threatened; 25–40% of large birds threatened.
Mammal diversity by region (current): SAIC ~1,500 species; Sub-Saharan Africa ~1,200; Tropical South America ~900.
Bird diversity by region (current): Tropical South America ~3,100; SAIC ~3,100; Sub-Saharan Africa ~2,100.
Regional extinction risks and regional leadership (current status)
Large mammals in SAIC: 62% threatened (96 of 155 species); mean extinction risk ≈ 2.1 (i.e., average species status around Endangered-into-Vulnerable boundary).
Large mammals in Sub-Saharan Africa: 34% threatened (42 of 125 species); mean extinction risk ≈ 0.7 (between Least Concern and Near Threatened).
Large mammals in Tropical South America: 50% threatened (19 of 38 species); mean extinction risk ≈ 1.2 (Near Threatened).
National-level insights: Countries with higher growth in cropland since 1961 and higher GDP per capita by 2010 show higher mean extinction risks for mammals and birds; strong positive relationships with cropland expansion, GDP per capita growth, and body-mass of species.
Regression results (current state):
Mammals: R^2 = 0.69,
F_{12,110} = 20.6,
N = 123,
P < 0.0001.Birds: R^2 = 0.84,
F_{12,110} = 48.5,
N = 123,
P < 0.0001.These models are reported in Supplementary Table 1.
Cross-country relation: national mean extinction-risk values for mammals and birds are highly correlated with the percentage of a country’s species that are threatened (across the three regions): R^2 = 0.97,
F_{1,250} = 8{,}599,
P < 0.0001.
Conservation efforts to date
Historical conservation impact: at least 31 bird species saved from extinction in the last century; 16 of these saves occurred between 1994 and 2004, and these efforts are estimated to have prevented ~20% of threatened vertebrates from moving closer to extinction.
Protected areas: now cover about 14% of Earth's terrestrial surface and help reduce habitat conversion, hunting, and extinction risks inside their boundaries.
Other protections: legal protections reducing hunting, control of invasive species (notably on islands) enabling population recoveries; captive breeding and reintroductions have saved species such as Arabian oryx (Oryx leucoryx) and California condor (Gymnogyps californianus).
Remaining biodiversity declines: biodiversity continues to decline globally; example provided: African lion populations have fallen due to human pressures, poor infrastructure, and underfunded protected-area management.
Overall implication: need accelerated and proactive conservation (beyond traditional approaches) to address present and future threats.
The geography of future extinction risks: projections to 2060
Drivers of future risk: continued population growth, rising per-capita income, and corresponding increases in cropland demand and animal-protein consumption; these factors drive habitat loss and fragmentation.
Land-demand projections:
The country-level land demand ratio (LDR) is defined as the forecasted cropland area in 2060 divided by cropland area in 2010 under BAU assumptions (increasing cropland to meet rising demand with observed yield trajectories).
Regions with the largest projected 2060 LDRs: Sub-Saharan Africa; 13 SSA countries have LDRs > 4 (e.g., Mozambique, Zambia, Angola, Chad, Côte d'Ivoire, Cameroon, Tanzania, Mali, Guinea).
Under BAU, an estimated 710 million hectares of cropland worldwide would be cleared by 2060 to meet demand; about 430 million hectares of this would be in SSA (roughly half the area of the continental United States).
Total cropland expansion and biodiversity risk: higher GDP per capita and cropland expansion are associated with higher extinction risks; the authors use regression models with projected 2060 GDP per capita and cropland growth to forecast BAU extinction risks for SAIC, SSA, and Tropical South America.
Magnitude of projected risk increases (2060, BAU) by region and taxon:
Across all body-mass classes, extinction risks are predicted to rise in all three regions.
Sub-Saharan Africa: greatest expected increases for mammals; medium and large mammals may experience extinction risks much higher than current large-mammal risks in SAIC.
SAIC: mean extinction-risk increases for large and medium mammals by about 1.5$-$2 Red List categories by 2060.
Tropical South America: increases for large mammals and all birds by roughly 1$-$1.5 Red List categories.
Interpreting a 1.5-category increase:
Current status of large mammals in SAIC vs. SSA illustrates potential changes: lions in SAIC reduced to a few populations (≈400 in one population) and cheetahs extirpated in many areas, whereas SSA maintains larger populations (≈20,000–30,000 lions; ≈7,500 cheetahs).
In Bovidae, 10 of 11 SAIC species are threatened vs 1 of 10 SSA species threatened.
Some groups (primates, elephants, rhinoceroses) are globally threatened but rarer or more severely threatened in SAIC than in SSA at present.
Population, yields, and future food security context (Figure 4 context)
Population trajectory to 2060: UN projections indicate global population rising, with SSA bearing a large portion of new people; by 2060, global population expected to rise by about billion, with the majority of new people (about billion) in Sub-Saharan Africa.
Crop yields and caloric production: 2010 yields for nutritious crops are used to establish a baseline in order to assess future yield gaps and food security implications (see Supplementary Methods).
Relation to extinction risk: as cropland expands to meet food demand, habitat loss and fragmentation intensify, feeding into elevated extinction risks, especially for large-bodied species in regions with rapid cropland expansion.
Red List categories and regional extinction-risk patterns (Figure 5)
Current vs. projected mean extinction risk for mammals and birds (by region and body-mass class):
SAIC, SSA, Tropical SA regions show rising mean extinction-risk values from 2010 to 2060 for large, medium, and small species across both taxa.
Specifically, for mammals: SSA shows the largest relative rise in mean extinction risk for medium and large mammals by 2060; SAIC and Tropical SA show substantial increases as well.
For birds: increases are predicted across all three regions, with variation by body size.
Summary of regional trends:
Mammals: SSA likely to experience the greatest future elevations in extinction risk for medium and large mammals; SAIC also shows notable increases; tropical SA shows increases, particularly among larger mammals.
Birds: increases in extinction risk across all regions, with some regional nuances tied to body mass categories.
Implication: without mitigations, 2060 extinction risks could surpass current regional maxima, especially in SSA and SAIC, for many large-bodied species.
Implications for conservation policy and practical action
Core policy recommendations:
Increase agricultural yields to reduce the need for cropland expansion and habitat fragmentation.
Expand and improve land-use planning at national and regional levels to minimize habitat loss and fragmentation.
Expand protected-area networks and connect them with ecological corridors to maintain metacommunity dynamics (especially for large carnivores and migratory species).
Protect biodiversity within and outside protected areas; ensure that protected areas are sufficiently large and well placed to maximize conservation gains while preserving local food security.
Strengthen enforcement of protective legislation to reduce hunting and illegal wildlife trade; address root drivers of hunting and poaching (e.g., through alternative livelihoods and protein sources).
International responsibility: economically developed countries should contribute to global biodiversity conservation (beyond their borders) due to their consumption patterns and externalities.
Practical considerations for on-the-ground action:
Link protected areas via corridors or manage them as metacommunities to support wide-ranging species (e.g., large carnivores similarly to examples in South Africa).
address data gaps and target management actions at species or locale level (national and local analyses complementary to regional assessments).
Recognize that protecting species beyond reserve boundaries is crucial; species outside protected areas still require protection efforts.
Social and ethical considerations:
Balancing food security with biodiversity protection; ensuring that local communities have access to protein and livelihoods while reducing habitat destruction.
Recognizing that social norms, governance, and incentives influence hunting and land-use decisions; policy measures should be designed with local contexts in mind.
Summary of key formulas and numbers to remember
LDR (land demand ratio):
Regression models for extinction risk (current state):
Mammals: R^2 = 0.69,\; F_{12,110} = 20.6,\; N = 123,\; P < 0.0001
Birds: R^2 = 0.84,\; F_{12,110} = 48.5,\; N = 123,\; P < 0.0001
Correlation between country mean extinction risk and proportion of threatened species: R^2 = 0.97,\; F_{1,250} = 8{,}599,\; P < 0.0001
Population and cropland growth context (illustrative): global population growth between 1960–2010: +130% population; global constant-dollar GDP (PPP) growth: +约490%.
Regional mean extinction risks (current, large mammals):
SAIC: mean ≈ 2.1 (threatened status around Vulnerable to Endangered)
SSA: mean ≈ 0.7 (between Least Concern and Near Threatened)
Tropical SA: mean ≈ 1.2 (Near Threatened)
Projections to 2060 under BAU:
Large and medium mammals in SSA expected to rise by ~1.5–2 Red List categories on average; Tropical SA and SAIC show ~1–1.5 category increases for birds and some mammals.
710 million hectares of cropland to be cleared by 2060 under BAU; SSA could account for ~430 million hectares (roughly half the area of the continental US).
Notes on figures mentioned
Figure 1: Anthropogenic threats to mammals and birds and the role of body mass. Components include habitat loss, direct mortality, invasive species, pollution, bushmeat, and climate change context.
Figure 2: Diversity and threat patterns by country with mammal and bird species counts per country, scaled by area to create biodiversity indices; regional comparisons for threat prevalence.
Figure 3: Current extent of large mammals and projected land clearing (LDR under BAU and with yield-gap reduction); country-level visibility of threat percentages.
Figure 4: Projected growth rates for human population and current crop yields; population ratio 2060/2010; 2010 crop yields across nutritious crops.
Figure 5: Current and projected regional extinction risks for mammals and birds by region and body-mass class.
Connections to broader themes and prior knowledge
Highlights the interaction between development (population and GDP growth), land-use change, and biodiversity risk—consistent with classic biodiversity and landscape ecology concepts (habitat fragmentation, edge effects, metacommunity dynamics).
Emphasizes the potential for policy interventions (land-use planning, yield improvements, protected areas, and international conservation assistance) to decouple development from biodiversity loss.
Aligns with precautionary approaches in conservation biology: proactive protection and landscape-scale planning are more effective than species-by-species interventions in rapidly changing systems.
Ethical considerations include equity (how to balance development with global biodiversity preservation) and responsibility (wealthier nations supporting global conservation efforts).
Supplementary context and caveats
All projections rely on assumptions about future population growth, income trajectories, cropland demand, and yield improvements; actual outcomes depend on policy choices, technology, governance, and unforeseen ecological feedbacks.
Regional results depend on country-level data and the countries included in each region; national policy actions can alter regional trajectories.
The Supplementary Methods contain full model specifications and country-level details not presented here.