Keystone species are species which have significant and disproportionately large influence on the community. Removal or decrease in their number causes disruption in structure and function of community. For example in intertidal regions starfish feeds on mussels. Removal of starfish leads to dominance of mussels that excludes algae and browsing species. In tropical rain forests, fig trees function as keystone species as they provide fruits to a number of animals during the period of food scarcity.