Evolution__3rd_Edition

698 Answers to Study and Review Questions
tests of both. If the extinctions of species with differing
developmental modes in Figure 23.9, or in the test of
synchroneity in Figure 23.3, were pseudoextinctions, the
explanation for the trend, or synchronous pattern, would
be something to do not with nature but with the habits
of taxonomists. Lazarus-type pseudoextinction would also
suggest the results are artifacts. Pseudoextinction of type
(b) in Figure B23.1 may be less damaging. (Also, the test
of the Red Queen hypothesis by survivorship curves in
Chapter 22 may be little damaged by either of the taxonomic
causes of pseudoextinction. The hypothesis might
be recast in terms of rate of change rather than chance of
extinction.)
3. (a) The iridium anomaly (Figure 23.4), perhaps combined
with the dated Chicxulub crater. (b) The extinctions should
be sudden and synchronous in all taxa, rather than gradual,
and they should not in general be preceded by reductions in
population size. For the difficulties of testing these predictions,
look at Section 23.3.2.
4. At the end of the Cretaceous and Permian (for the top two
extinctions); plus either the end Ordovician or the end
Triassic (for the top three); plus the Devonian (for the top
five).
5. See Figure B23.2. The observed extinction rate in the earlier
interval will be (a) high, and (b) low.
6. At mass extinctions there is no relation. In background
extinctions the taxa with planktonic development have an
extinction rate that is half that of taxa with direct development.
The background extinction difference can be explained
either by bias in the fossil record (if planktonically
developing species are more likely to be preserved) or by
their being more likely to survive local difficulties by their
dispersing larval stage.
7. Two possibilities we looked at are differences in speciation
or extinction rates caused by differences in adaptations of
different species, or by differential persistency of niches (see
Section 23.6.2).
8. The heritability criterion is as relevant as ever here. In
classic group selection problems, the character (such as
altruism) is disadvantageous to individuals but advantageous
to groups. Selfish individuals can invade groups.
Once the group is infected by selfishness, it loses altruism.
The character (altruism) is not inherited by groups for
long. In classic cases of species selection, there is no question
of a species being invaded by some alternative adaptation.
Selection favors different adaptations in different
species a direct development in some, planktonic development
in others, for example. Those attributes are passed
down from ancestral species to descendant species. Species
selection is possible because there is no conflict between
individual and species selection; heritability therefore is
possible. Species selection is not a theory of the evolution of
adaptation a only of the consequences of adaptations.
9. See Figure 23.11. A double wedge pattern suggests a competitive
replacement. If one taxon goes extinct before the
other radiates, it suggests non-competitive replacement.
10. Partly by different data compilations (with different taxonomic
make ups) but mainly by different statistical corrections
for biases in: (i) the amount of rock preserved from
different times, and (ii) the amount of rock studied.
..