<P> Some plants and animals are generalists, and their habitat requirements are met in a wide range of locations . The small white butterfly (Pieris rapae) for example is found on all the continents of the world apart from Antarctica . Its larvae feed on a wide range of Brassicas and various other plant species, and it thrives in any open location with diverse plant associations . The large blue butterfly is much more specific in its requirements; it is found only in chalk grassland areas, its larvae feed on Thymus species and because of complex lifecycle requirements it inhabits only areas in which Myrmica ants live . </P> <P> Disturbance is important in the creation of biodiverse habitats . In the absence of disturbance, a climax vegetation cover develops that prevents the establishment of other species . Wildflower meadows are sometimes created by conservationists but most of the flowering plants used are either annuals or biennials and disappear after a few years in the absence of patches of bare ground on which their seedlings can grow . Lightning strikes and toppled trees in tropical forests allow species richness to be maintained as pioneering species move in to fill the gaps created . Similarly coastal habitats can become dominated by kelp until the seabed is disturbed by a storm and the algae swept away, or shifting sediment exposes new areas for colonisation . Another cause of disturbance is when an area may be overwhelmed by an invasive introduced species which is not kept under control by natural enemies in its new habitat . </P> <P> Terrestrial habitat types include forests, grasslands, wetlands and deserts . Within these broad biomes are more specific habitats with varying climate types, temperature regimes, soils, altitudes and vegetation types . Many of these habitats grade into each other and each one has its own typical communities of plants and animals . A habitat may suit a particular species well, but its presence or absence at any particular location depends to some extent on chance, on its dispersal abilities and its efficiency as a coloniser . </P> <P> Freshwater habitats include rivers, streams, lakes, ponds, marshes and bogs . Although some organisms are found across most of these habitats, the majority have more specific requirements . The water velocity, its temperature and oxygen saturation are important factors, but in river systems, there are fast and slow sections, pools, bayous and backwaters which provide a range of habitats . Similarly, aquatic plants can be floating, semi-submerged, submerged or grow in permanently or temporarily saturated soils besides bodies of water . Marginal plants provide important habitat for both invertebrates and vertebrates, and submerged plants provide oxygenation of the water, absorb nutrients and play a part in the reduction of pollution . </P>

Name two small animals that have their homes in the soil