A habitat is not just a place. It is a set of conditions — temperature, moisture, food sources, shelter, predators, competitors — that make a place habitable for a particular species. Habitat loss is the dissolution of these conditions.
The primary cause is human land use. Forests are cleared for agriculture. Wetlands are drained for development. Grasslands are ploughed for crops. Rivers are dammed, diverted, or polluted. The habitat dissolves not because the land disappears but because it changes into something the species cannot use.
The dissolution is often incremental. A forest is not cleared all at once but fragmented — a road here, a field there, a settlement somewhere else. The fragments are too small to support viable populations. The edges are different from the interior — more light, more wind, more predators. The habitat dissolves from the edges inward.
Habitat loss is the leading cause of species extinction. A species can survive many things — predation, disease, competition — but it cannot survive the dissolution of the place where it lives. When the habitat goes, the species follows. The dissolution of place is the dissolution of life.