Ecosystems

Biodiversity is the variety of life on Earth — the number and variety of species, genes, and ecosystems in a given area. High biodiversity makes ecosystems more stable and resilient, and provides many resources that humans depend on.

A species is endangered when its population has declined so much that it faces a real risk of extinction. The main causes are habitat loss, hunting, pollution, climate change, and invasive species. Conservation efforts work to protect and recover threatened populations.

Decomposers are organisms that break down dead plants and animals, returning nutrients to the soil. Without decomposers, dead matter would pile up and nutrients would be locked away, making life impossible.

An energy pyramid shows how energy moves through the levels of a food chain. At each level, about 90% of energy is lost as heat, so only 10% passes to the next level. This limits the length of food chains.

A food chain shows the flow of energy from one organism to the next, starting with a producer and moving through consumers.

A food web is an interconnected network of food chains showing the complex feeding relationships within an ecosystem.

Producers make their own food through photosynthesis; consumers obtain energy by eating other organisms. Together they form the foundation of all food chains.

Deserts are dry ecosystems that receive very little rainfall, yet support a surprising variety of specially adapted plants and animals.

Forests are complex ecosystems with multiple layers of life, from the forest floor to the canopy, supporting extraordinary biodiversity.

Freshwater habitats — rivers, lakes, ponds, and wetlands — cover less than 1% of Earth's surface but support about 10% of all known species. They include still (lentic) and flowing (lotic) water environments.

Grasslands are biomes dominated by grasses, with few or no trees. They cover about 40% of Earth's land surface and include tropical savannas, temperate prairies, and steppe regions. They support huge numbers of grazing animals.

Oceans cover over 70% of Earth's surface and contain a huge variety of habitats, from sunlit surface waters to the pitch-dark deep sea.

Study of energy flow, biodiversity, species relationships, and how organisms interact within their environments.