Habitat destruction and habitat fragmentation
- Most of the grasslands and forests of the Northern Hemisphere were destroyed by the end of the nineteenth century, the grasslands of the southern hemisphere are now vanishing, and tropical forests are disappearing at a rate of about 2% per year. This type of destruction has become the norm for most biological communities, as the human population expands our economic needs require resources from more and more land. The remaining habitat is often broken into many small fragments, which are separated by large areas of land under cultivation or other human uses, effectively reducing a single "continent" into many "islands".