Succession is a change in the mix of species in an area over time. Primary succession begins on a surface lacking developed soil, such as newly exposed rock. Secondary succession follows disturbance where soil or biological legacies remain. Communities need not follow one fixed pathway or reach an identical final state. Species richness counts species; abundance counts individuals. These measures are related but are not interchangeable.
Habitat destruction, introduced species and rapid environmental change can increase extinction risk. Populations with low genetic diversity may be vulnerable to new pressures and random events. Conservation can protect habitat, reduce damaging pressures and reconnect populations to support gene flow. A wildlife corridor is different from simply increasing the number of captive individuals. Extinction is permanent loss of a species, not just local movement.
Example 1
Plants recolonise after a fire while soil remains. Classify the succession.
This is secondary succession because the disturbance left soil and biological legacies.
Example 2
A reserve contains species A:20 individuals, B:15 and C:5. Find richness and total abundance.
Richness =3 species. Total abundance =20+15+5=40 individuals.