same spatial scale for species drawn from the same
species pool of bacterivorous microorganisms, it is
clear that factors like history of community coloni-
zation can also influence the form of productivity–
diversity patterns.
At much larger spatial scales, the causes of diver-
sity patterns remain contentious. The well-known
latitudinal gradient in species richness (Pianka
1988) has been attributed to a host of factors, none
of which seems to be easily tested. Ricklefs (2004,
2008) has proposed that the causes of these large-
scale patterns are unlikely to be revealed by small-
scale studies that focus on local ongoing ecological
interactions, and that the patterns instead represent
the end result of long periods of evolution and diver-
sification within biotas. If so, the most conspicuous
community-level pattern in ecology will not be ex-
plained by the kinds of ongoing interactions that
community ecologists usually dwell on. Other expla-
nations invoke a purely statistical explanation for the
apparent peak in species richness along geographical
gradients. The mid-domain effect suggested by Col-
well and his colleagues (e.g. Colwell and Hurtt 1994;
Colwell and Lees 2000) provides a null model expla-
nation for a humped diversity pattern along any
geographic gradient, just as a consequence of the
way that species ranges will overlap along any gra-
dient. This idea, while elegant in its simplicity, also
has its critics (J.T. Kerret al. 2006; Storchet al. 2006).
Just as evolution may ultimately provide a viable
explanation for large-scale diversity patterns, evo-
lutionary processes have been invoked with increas-
ing frequency to explain phenomena including the
population dynamics of interacting species
(Yoshidaet al. 2003) and the structure of food webs
(Drosselet al. 2001; Loeuille and Loreau 2005; see
Chapter 12). Although the need to integrate ecologi-
cal and evolutionary perspectives has long been
recognized, in reality this integration remains tenta-
tive and incomplete. A couple of examples point to
ways that an understanding of evolutionary pro-
cesses can provide insights into ecological patterns.
Yoshidaet al. (2003) used a simple laboratory
chemostat system to study the dynamics of herbiv-
orous rotifers feeding on the algaChlorella. Both the
rotifers and the algae reproduce clonally, but large
differences in dynamics materialized depending on
whether algal populations consisted of single or
multiple clones (Fig. 14.1). A simple model of the
dynamics also predicts that predator–prey oscilla-
tions will have a longer period when rotifers are
feeding on multiple algal clones, if the clones differ
in susceptibility to predation or nutritional value
(Fig. 14.1). This study makes the point that the
dynamics observed in communities can be modi-
fied by dynamic shifts in the genetic composition of
prey populations–a feature seldom included in sim-
ple models of predator–prey dynamics. Similar
results emerge from other chemostat studies of in-
teractions between the bacteriumEscherichia coli
and various types of bacteriophage that act as pre-
dators. Although bacteriophages initially have a
large effect on bacterial abundances, these effects
rapidly diminish as mutant genotypes arise in the
bacterial population that are resistant to attack by
bacteriophage (Chaoet al. 1977).
Other possible roles for evolution in creating
community patterns are suggested by recent mod-
els of evolving predators and prey in food webs.
These models (described further in Chapter 12)
make few initial assumptions about food web struc-
ture, and begin with a single model species that is
allowed to evolve in size over time. Organisms that
are similar in size are assumed to compete for re-
sources, while those that diverge sufficiently in size
come to interact as predators and prey. Depending
on the intensity of competition among species and
the range of prey size that can be consumed (analo-
gous to niche width), systems evolve to have many
of the main attributes of real food webs. Whether
food webs display these properties because they are
a consequence of evolution within the context of the
web, or because webs simply assemble from species
that have evolved in various food web contexts to
have certain sets of traits, remains uncertain.14.1.6 Applied community ecology
Several contributions to this volume make it abun-
dantly clear that any boundaries between basic and
applied community ecology are artificial and not
particularly helpful. Community ecology has
much to offer to society, through an enhanced un-
derstanding of the mechanisms and consequences
of exotic species invasions, sustainable restoration,
resource management in multispecies systems andEMERGING FRONTIERS OF COMMUNITY ECOLOGY 195