Biological Diversity: Differences between Land and Sea [and Discussion]

This paper begins with a brief survey of the numbers of species that have been named and recorded on land and in the sea. It then assesses how many species there may be in total, giving particular attention to recent suggestions for dramatic upward revision of species totals for tropical invertebrates, fungi, benthic macrofauna, and microorganisms in general. Against this background, I comment on patterns of diversity on land and in the sea at higher taxonomic levels - orders through phyla - and on the possible causes and consequences of these patterns. I conclude with some estimates of impending extinction rates.