Biology Reference
In-Depth Information
Figure 6.2. Species diversity of marine invertebrates correlated with rock area
available for sampling. Rosenzweig interprets these findings as evidence that the
apparent increase in diversity over geologic time is in fact an area effect. Data from
Raup and Sepkoski after Rosenzweig (
1995
). From Rosenzweig (
1995
). Reprinted
by permission of the author and Cambridge University Press.
mentioned (see, e.g., Benton and Pearson
2001
). Rosenzweig's (
1995
)
emphasis is on these steady states and on equilibrium in the past and now.
He admits that diversity rose somewhat over hundreds of millions of
years. One of the reasons for this is colonization of new habitats, such as
the muddy ocean bottom. There may also be an increase in ''versatility''
leading to diversification, for which, however, there is no definitive
evidence, but overall, these increases are thought to be relatively minor.
However, the objections of Rosenzweig and others can be rejected on
the basis of a recent study by Jablonski et al.(
2003
), who shows that the
so-called ''pull of the Recent'', i.e., possibly inflated diversity estimates
resulting from sampling bias (more complete sampling of Recent biota)
account for only 5% of the Cenozoic increase in bivalve diversity; 906 of
958 living genera and subgenera have existed in the Pliocene and
Pleistocene. Bivalves represent a major component of the marine record,
and it can be safely assumed that there has been a strong increase in
diversity throughout the Cenozoic.
How has diversity of parasites and other ''dependent'' species, such as
symbionts or commensals, evolved? Parasites comprise a very high pro-
portion of all animal species. One quarter of the 40 000 animal species in
