Evolution__3rd_Edition

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present. Biotic pollination, in particular, is associated
with enhanced diversity in flowering plant taxa.
5 The level of virulence of parasites can evolutionarily
decrease or increase. It can be understood in terms
of the parasite–host relationship: two factors that
influence it are kin selection and the mode of transmission
of the parasite between hosts.
6 Some parasites speciate simultaneously with their
hosts, in a process called cospeciation. Cospeciation is
particulaly likely if the parasites have limited powers of
dispersal independently of the host. Cospeciation is
tested for by: (i) cophylogenies; and (ii) the molecular
clock.
7 Coevolutionary “arms races” between predators
and prey produce escalatory long-term evolutionary
trends; they can be seen in the evolution of brain sizes
Further reading
CHAPTER 22 / Coevolution 641
in mammals and of armor and weapons in mollusks
and their predators.
8 The extinction rates of species are independent of
how long the species has existed for: a species does
not become more likely to go extinct as time passes.
Taxonomic survivorship curves are logarithmically
linear.
9 Van Valen explained the log linearity of survivorship
curves by his Red Queen hypothesis. It suggests
that: (i) each species’ environment deteriorates as
competing species evolve new, superior adaptations;
(ii) the competing species improve at a constant rate
relative to each other; and (iii) the constant deterioration
in the environment causes the chance of
extinction of any one of them to be probabilistically
constant.
Thompson (1994) is a general book on coevolution. This chapter began by distinguishing
mutualistic from antagonistic coevolution. A further point to note is that the two
processes can be mixed within a single interaction, in different parts of a geographic
range. Thompson & Cunningham (2002) describe a recent example. Bronstein (1994)
reviews mutualism. Page (2002) is a multiauthor book on cophylogenies.
On plant–animal, and particularly plant–insect, coevolution, see the book by
Schoonhoven et al. (1998) and the special issue of Bioscience (1992), vol. 42, pp. 12–57.
Rausher (2001) reviews plant resistance to herbivores. On plant-pollinator evolution,
see Waser (1998), Johnson & Steiner (2000), and the newspiece in Science October 4,
2002, pp. 45–6. Mant et al. (2002) is a further study of the topic by cophylogenies. They
analyze the relation between orchids and their specialist wasp pollinators, finding a fair
amount of congruence but some oddities in the branch lengths. The evolutionary
forces at work are uncertain. Machado et al. (2001) describe another emerging case
study in cophylogenies, between figs and fig wasps.
On the grand pattern of relations between plants and insects, see also Dilcher (2000),
who puts the topic in the big picture of angiosperm evolution. Labandeira (1998)
argues that pollinator evolution preceded angiosperm evolution, which would at least
complicate (and might refute) the coevolutionary story.
On parasites and hosts, Clayton & Moore (1997) is a multiauthor book, concentrating
on avian examples. Ebert (1998) reviews experimental work. See Ebert (1999) and
his references for the evolution of virulence, and Ewald (1993). On the influence
of number of infections, see also Chao et al. (2000). Moreover, increased rates of