Environmental change and biological diversity: Present, past and future

Abstract

The present paper reviews the current distribution and factors determining the level of biological diversity. Past climate changes causing mass extinctions, lessons drawn from these past events and the impact of future climate change on biological diversity in its broadest sense are also considered. Large scale changes in vegetation zones and composition, over extensive parts of the globe are indicated. Displacement of isotherms due to rise in global temperatures would necessitate very rapid species shifts which may be possible only with human assistance except for plants propagated by spores or dust seeds. Rates of migration and behaviour of the migrating species will determine their range shift capabilities. Differences in migration rates may result in new combinations of species because of dissociation of communities into their component species. Species rigidly associated to a particular set of environmental conditions may well become extinct Characteristics such as large population size, broad geographical distribution and high dispersal potentials will protect species from extinction. Increased pressure from invaders, increased frequency of epidemics and alteration of productivity and species distributions are indicated. Elevated sea water temperatures may badly damage sea flora and fauna as is exemplified by present day El nino effects. Destruction of coastal habitats due to sea level rise may affect birds and fishes using sail marshes, estuaries and islets as breeding ground. Island species will be severely affected both due to reduced area and limitations of latitudinal migration. Changes in precipitation pattern may result in reduced avian and mammalian populations in many parts of the world.