Biodiversity is what lets ecosystems absorb shocks and keep supplying the food, clean water and stable climate people depend on. This unit covers the levels of biodiversity, the services ecosystems provide, why islands are special, how species tolerate and adapt to change, and how communities rebuild after disturbance.
Biodiversity includes genetic, species and habitat diversity. Genetically diverse populations handle stress better, and bottlenecks erase that diversity. Species-rich ecosystems recover more easily. Habitat loss removes specialists first, then generalists, and hits species that need large territories.
Ecosystems provide four categories of services: provisioning, regulating, cultural and supporting. Human activities can disrupt them, with both economic and ecological costs.
Island biogeography studies how species colonize and persist on islands, or habitat "islands" like isolated parks. Larger islands and islands closer to the mainland hold more species. Many island species evolve into specialists, which makes them vulnerable to invasive generalists.
Ecological tolerance is the range of conditions, such as temperature, salinity, flow rate and sunlight, that an organism can endure before injury or death. It applies to individuals and to whole species.
Natural disruptions can be as damaging as human ones. They happen on many timescales: periodic, episodic or random. Climate and sea level have changed over geological time, reshaping habitats and sending wildlife migrating.
Natural selection acts on heritable traits, so populations adapt over generations through small genetic changes. When the environment changes, individuals must change behavior, move, or perish.
Primary succession builds a community on bare rock with no soil; secondary succession rebuilds where soil remains. Keystone species shape community structure, and indicator species reveal ecosystem conditions. Succession changes total biomass, species richness and net productivity over time.