High Genetic Diversity:

• Grey wolves: High genetic variation allows them to thrive in diverse habitats from Arctic tundra to temperate forests
• Humans: Tremendous genetic diversity despite being a single species
• Domestic dogs: Extreme phenotypic diversity (size, shape, color) due to genetic variation

Low Genetic Diversity:

• Cheetahs: Extremely low genetic diversity due to past population bottleneck; vulnerable to diseases
• Northern elephant seals: Reduced to <20 individuals in 1890s; now recovered but with low genetic diversity
• Florida panthers: Small population with inbreeding problems (genetic defects, reduced fitness)

Estimated Number of Species on Earth:

• Total estimated: 8.7 million species (range: 3-100 million)
• Described/documented: Only about 1.5-2 million species
• That means 86% of terrestrial species and 91% of marine species remain undiscovered

Distribution Across Taxa:

• Insects: ~1 million described (estimated 5-10 million total)
• Plants: ~400,000 species
• Fungi: ~150,000 described (estimated 2.2-3.8 million)
• Vertebrates: ~70,000 species
• Bacteria and archaea: Millions (mostly unknown)

1. Habitat Loss and Destruction

The most significant cause of species extinction. When habitats are destroyed, species lose their homes, food sources, and breeding grounds.

Causes of Habitat Loss:

• Deforestation: Tropical rainforests cleared for timber, agriculture (palm oil, soy, cattle ranching)
• Agricultural expansion: Natural habitats converted to farmland for crops and livestock
• Urbanization: Cities and infrastructure replace natural ecosystems
• Mining and resource extraction: Destroys habitats and pollutes surrounding areas
• Wetland drainage: Wetlands drained for agriculture or development

2. Overexploitation (Hunting and Overharvesting)

Harvesting species at rates faster than they can reproduce, leading to population collapse.

Forms of Overexploitation:

• Hunting: For food, sport, trophies, or traditional medicine
• Poaching: Illegal hunting (ivory, rhino horn, tiger parts)
• Overfishing: Commercial fishing depletes fish stocks
• Wildlife trade: Capture for pets, zoos, or collectors
• Logging: Unsustainable timber harvesting

3. Pollution

Introduction of harmful substances into the environment that poison organisms or disrupt ecosystems.

Types of Pollution:

• Chemical pollution: Pesticides, herbicides, industrial chemicals (DDT, PCBs)
• Plastic pollution: Marine animals ingest or become entangled in plastic
• Water pollution: Agricultural runoff, sewage, oil spills
• Air pollution: Acid rain, smog, greenhouse gases
• Noise pollution: Disrupts communication and navigation in marine mammals
• Light pollution: Affects nocturnal species and migratory patterns

4. Invasive Alien Species

Non-native species introduced to new areas (intentionally or accidentally) that outcompete, prey upon, or bring diseases to native species.

How Invasive Species Are Introduced:

• Global trade: Species hitchhike in cargo ships, containers
• Pet trade: Released or escaped exotic pets
• Intentional introduction: For pest control, hunting, or agriculture
• Ballast water: Ships discharge water containing organisms from other regions

5. Climate Change

Global warming and changing precipitation patterns alter habitats faster than species can adapt.

Climate Change Effects on Biodiversity:

• Habitat shifts: Species' ranges move toward poles or higher elevations
• Phenological mismatches: Timing of life events (breeding, migration) disrupted
• Ocean acidification: Dissolves calcium carbonate shells of marine organisms
• Coral bleaching: Rising ocean temperatures kill symbiotic algae
• Extreme weather: Droughts, floods, storms destroy habitats
• Sea level rise: Inundates coastal ecosystems

Scale of Deforestation:

• 420 million hectares of forest lost between 1990-2020
• 10 million hectares lost annually (area the size of Iceland)
• Amazon rainforest: 17% deforested; contains 10% of world's biodiversity
• Indonesia: Lost 80% of original forests
• Tropical rainforests most affected

Drivers of Deforestation:

• Cattle ranching: Largest driver in Amazon (80% of deforestation)
• Soy plantations: Major crop for animal feed and oil
• Palm oil plantations: Southeast Asia losing forests rapidly
• Logging: Legal and illegal timber extraction
• Infrastructure: Roads, dams, urban expansion
• Mining: Resource extraction destroys large areas

Consequences of Deforestation:

• Loss of biodiversity (80% of terrestrial species live in forests)
• Climate change (forests store 45% of terrestrial carbon)
• Soil erosion and degradation
• Disruption of water cycles
• Loss of indigenous cultures and livelihoods
• Increased risk of zoonotic disease transmission

🔍 Impact: Intensive agriculture creates "ecological deserts" with minimal biodiversity—only crops and pests survive.

🔍 Impact: Wetlands provide flood control, water filtration, carbon storage, and nursery habitat for fish. Their loss has cascading effects on both wildlife and human communities.

Coral Reef Decline:

• 50% of coral reefs lost since 1950
• 90% threatened by 2050 under current trends
• Causes: warming waters, ocean acidification, pollution, coastal development
• Coral reefs support 25% of all marine species despite covering <1% of ocean floor

Other Marine Losses:

• Mangroves: 35% lost globally; provide coastal protection and nursery habitat
• Seagrass beds: Declining due to coastal development and water quality
• Ocean dead zones: 500+ areas with insufficient oxygen due to nutrient pollution
• Plastic pollution: 8 million tons enter oceans annually

🔸 Unprecedented Speed

Extinctions occurring at rates 100-1,000× faster than natural background rates—faster than species can evolve or adapt.

🔸 Human Dependence

Human survival depends on biodiversity (food, clean water, medicines, climate regulation, pollination). Losing biodiversity threatens human well-being.

🔸 Irreversibility

Once species go extinct, they're gone forever. We lose millions of years of evolutionary history and potential future benefits (medicines, genetic resources).

🔸 Cascading Effects

Loss of one species affects others in food webs and ecosystems. Keystone species loss can cause ecosystem collapse.

🔸 Global Scale

Unlike past extinctions (regional), this is a global crisis affecting terrestrial, freshwater, and marine ecosystems simultaneously.

1. Evolutionary Distinctiveness (ED)

Measures how isolated a species is on the tree of life:

• Based on phylogenetic trees (evolutionary relationships)
• Calculated as the sum of branch lengths from species to root of tree, divided by number of species sharing those branches
• Higher scores = fewer close relatives = more unique
• Measured in millions of years of independent evolution

2. Global Endangerment (GE)

Based on IUCN Red List status:

• Critically Endangered (CR) = highest score
• Endangered (EN) = high score
• Vulnerable (VU) = moderate score
• Lower threat categories = lower scores

Final EDGE Score Formula:

EDGE Score = ED × GE weight

Species are then ranked by EDGE score. Higher scores indicate greater conservation priority.

🐢 Yangtze Giant Softshell Turtle

Status: Critically Endangered (possibly only 3 individuals left) | ED: 120 million years of unique evolution | One of the most endangered species on Earth. Found only in China and Vietnam.

🦇 Bumblebee Bat (Kitti's Hog-nosed Bat)

Status: Vulnerable | World's smallest mammal (2g, size of a bumblebee) | Found only in Thailand and Myanmar. Unique nose structure for echolocation.

👻 Aye-aye

Status: Endangered | Bizarre nocturnal lemur from Madagascar with elongated middle finger for extracting insects from tree bark. Only member of its family. Superstition threatens its survival.

🐸 Purple Frog (Pignose Frog)

Status: Endangered | ED: 130 million years | Lives underground in India's Western Ghats. Surfaces only for 2 weeks each year to breed. Discovered in 2003. Ancient lineage separated from all other frogs.

🦔 Long-beaked Echidnas

Status: Critically Endangered | One of only five egg-laying mammals (monotremes). Found in New Guinea. Ancient lineage dating back 20+ million years. Threatened by hunting and habitat loss.

🦎 Chinese Giant Salamander

Status: Critically Endangered | World's largest amphibian (up to 1.8m long) | ED: 170 million years | Ancient lineage. Declined >80% due to habitat loss, pollution, and consumption as luxury food.

🐬 Vaquita

Status: Critically Endangered (<10 individuals left) | World's rarest cetacean (marine mammal). Found only in Gulf of California, Mexico. Deaths from gillnet fishing. May go extinct within years.

🦌 Hirola (Hunter's Hartebeest)

Status: Critically Endangered (~500 left) | Only member of its genus. Found on Kenya-Somalia border. Called "the world's most endangered antelope." Threatened by habitat loss, drought, predation.

1. Raise Awareness

Highlight forgotten species through websites, media, publications. Generate public interest and support for unusual, overlooked species.

2. EDGE Fellows Programme

Train and fund in-country conservationists (EDGE Fellows) for 2 years. Fellows conduct research, implement conservation actions, and build local capacity. Over 157 species in 47 countries supported so far.

3. Research Poorly-Known Species

Fund expeditions to find species not seen in decades. Conduct population surveys and ecological studies. Determine conservation status and threats.

4. Develop Conservation Action Plans

Create species-specific strategies. Address threats (habitat protection, reducing hunting, captive breeding). Engage local communities and governments.

5. Build Long-Term Conservation Capacity

Support EDGE Alumni to continue work after fellowship. Partner with organizations for scaled-up projects. Ensure local ownership of conservation efforts.

6. Identify EDGE Zones

Map priority areas where many EDGE species coexist. Target conservation efforts to maximize impact. EDGE Zones make up 0.7% of Earth's surface but contain 1/3 of four-legged EDGE species.