Habitat Fragmentation and Habitat Alterations: Principal Threats to Most Animal and Plant Species

Many human activities, such as deforestation, urbanization, intensive agriculture, the building of roads and railways all reduce natural habitats to remnants of different size. In addition to the overall decrease in the area available for the organisms, the fragmentation of habitats leads to a division of existing populations into isolated subpopulations of small size and changes in habitat characteristics in the fragments. It is generally assumed that habitat fragmentation contributes significantly to the local extinction of animal and plant species. Unfortunately, inventories of animal and plant species in “natural” fragments do not allow a discrimination between different factors that cause local population extinction. This article outlines a long-term field experiment in which calcareous grassland in the Swiss Jura mountains is artificially fragmented into patches of different size. The experiment allows the investigation of extinction and (re)colonization processes of selected species of plants and animals in the newly-created fragments with respect to demographic traits, population sizes, levels of genetic variation and differences in mating systems.