4.15—Variety of life and human threats

Biodiversity includes genetic diversity within species, species diversity and the variety of habitats or ecosystems. It supports resilience, but human activities can reduce all three levels.

Habitat destruction and fragmentation remove living space and isolate populations; overexploitation and hunting remove organisms faster than they recover; intensive agriculture can reduce diversity through monoculture, pesticides and fertiliser loss; climate change shifts conditions.

A fragmented forest may lose species directly and also increase inbreeding in small isolated populations. A disease affecting a dominant species can then cause a larger ecosystem change when genetic and species diversity are low.

Species richness is only a count; species diversity also considers relative abundance. A single threat rarely explains every change, so distinguish the measured level of biodiversity from the proposed human cause.