A forest ecosystem will generally hold more species than a grassland and tropical systems will hold more species than temperate or arctic systems. In island situations immigration rates tend to balance extinction rates. The nearer an island is to a population source, the greater its immigration rate per unit time. The larger the island is, the higher its carrying capacity. In any island situation immigration of species declines as more species become established, and fewer immigrants are new species.
Stability ultimately depends on adaptive response of organisms to environmental changes.
Adaptation of an organism is simply its ability to conform through changes in physiology, behavior, and morphology. Those best adjusted to the environmental conditions make the greatest contribution to future generations - the ability of an individual to leave offspring is termed its fitness. Evolution - the net change in gene frequencies through time.