The main four reasons of biodiversity loss are habitat loss and fragmentation, over-exploitation, alien species invasion and co-extinction. 'The Evil Quartet' is the sobriquet used to describe them. Natality refers to the number of births during a given period in the population that are added to the initial density. Competition is a biological interaction between two or more organisms of the same or different species where the species compete with each other for different resources. The rapid increase in human population over a relatively short period of time is called population explosion.