Marine biology: the role of accommodation in shaping marine biodiversity

A review of evidence from two kinds of studies conducted in the marine environment suggests a species relationship not previously recognized as being consistent and widespread. In the first instance, observations on species invading from a more diverse ecosystem into a less diverse ecosystem indicate that successful colonizations take place because space is yielded by their ecological equivalents. In the second instance, widespread studies show that any community, rich or poor, located in tropical or cold waters, is vulnerable to invasions by species from a larger, more diverse region. Furthermore, the species richness of a community apparently depends upon that of the region to which it belongs. Together, these observations indicate the existence of a general rule which states that if an invader becomes established, it is permitted to do so by an accommodation on the part of the species that occupies the preferred ecological space. Paleontological data on invasions provide evidence of speciation following accommodation. This leads to the recognition of a three-step process: invasion to accommodation to speciation (IAS). This process, which may be called the IAS mechanism, may have contributed to historical rises of global biodiversity.