Habitat destruction, poaching, climate change and lack of resource management have resulted in a decline in biodiversity by leading to the extinction of species. Other factors such as large body size, small population, and position at a higher trophic level also favor extinction of species. When there are no more individuals of a species (plant or animal) alive anywhere in the world, the species is said to be extinct. Extinction is also known as the process of dying out.
So, the correct answer is 'Decline in biodiversity'.