ABSTRACT
The absence of an organism from an area might be due to competition, poor dispersal capability, or perhaps because of some behavioural mechanism such as habitat selection. This chapter examines the biogeographical implications of these so-called intrinsic limiting factors. Plant ecologists, entomologists, ornithologists, and biogeographers frequently use the terms in different contexts and sometimes as if they meant one and the same thing. It is probably impossible to satisfy all biologists and biogeographers, but the definitions given by L. R. Taylor are very interesting. In contrast, migration relates to geographical coordinates, although, as Taylor notes, it may be done in company or alone. A typical example of random dispersive behaviour was the large immigration of the grey and diamond-back smudge moth along the coasts of eastern and north-eastern Britain in June 1958. In marine environments planktonic larvae drift in water currents and can migrate successfully if the characteristics of the water body or substrate are suitable.
