Biology Reference
In-Depth Information
Figure 6.3. Diversity (species per sample) of Ordovician marine benthos. Note rise
in diversity in the late Ordovician, and diversity of 6-8 species per sample during
the following 4 Myr. These data suggest that there has been no increase in diversity
throughout the Ordovician. Time measured as thickness of geological layer. From
Rosenzweig (
1995
). Reprinted by permission of the author and Cambridge
University Press.
Germany are parasites, not including parasites of plants (Arndt
1940
), and
more than half of the British fauna were estimated to be parasitic,
including parasites of plants (Price
1977
). Since very few fossil parasites
are known (for a list see Combes
2001
), statements on their evolution
must be based on inferences from studies of extant species.
The opportunities provided by free-living animals to parasites (and
hyperparasites, predators, symbionts, commensals) were taken into
account in the diversification equation developed by Rohde (
1980d
)
and based on the logistic equation for population growth. It is:
K
f
ð
t
Þ
S
f
þ
P
n
a
ij
ð
t
Þ
S
j
ð
t
T
Þ
dS
ð
t
Þ
dt
¼ð
b
ð
t
Þ
e
ð
t
ÞÞ
S
f
ð
t
Þ
j
;
K
f
ð
t
Þ
where dS/dt
¼
rate of species diversification, b
¼
rate of species forma-
tion, e
¼
rate of species extinction, S
f
¼
number of free-living species,
K
f
¼
carrying capacity for free-living species,
a
ij
S
j
¼
the sum of all
