Biology Reference
In-Depth Information
a subset of those species with characteristics that permit their coexistence
(Roughgarden
1989
). Elton (
1933
) subscribed to the latter view, whereas
Gleason (
1926
) subscribed to the former. (For a discussion of the concept
of community see also Brown
1995
, further references therein.)
Comparing the individualism of species composing communities advo-
cated by Gleason, Whittaker and others, with the structured approach of
MacArthur, Hutchinson, and others, Brown emphasizes that both
approaches are not incompatible. He points out that it is not correct to
equate Gleason's individualism with the influence of abiotic conditions,
and structure with the effects of biotic interactions. Both interactions and
reactions to abiotic factors are individualistic, depending on unique
features of the species; and the environment can impose patterns of
community structure, as indicated by convergent structural and func-
tional features of only distantly related organisms in different continents.
Brown discusses some examples.
There has been much discussion about how communities should be
defined, on the basis of palaeontological evidence (see the controversy of
Anderson
1995
and Walter and Patterson
1994
,
1995
). Anderson stresses
that interactions between species in addition to their co-occurrence,
define a community. The latter authors come to the conclusion that
palaeoecological evidence supports the view that species have associated
individualistically and have not co-adapted to other species in the extant
community, which - however - does not mean that they have evolved
independently of other species. They point out that, in order to demon-
strate co-adaptation, conclusive evidence for resource partitioning has to
be given, and that no studies of purported cases of local character dis-
placement have satisfied the minimum criteria outlined by Connell
(
1980
). Emphasis should instead be placed on the study of individuals
and their adaptations, and a community should be viewed as a level of
organization and not as an entity. One looks for repeated patterns and
such patterns occur most consistently where adaptive mechanisms exist.
Species that form extant communities have evolutionary histories that are
independent of other species in extant communities, which - however -
does not imply that the species have evolved in a vacuum. Lawton
(
1984a
) considers that, with regard to herbivore communities, coevolu-
tion should be ignored as an explanation ''until the data absolutely force us
to do otherwise.'' And, based on his study of insects of bracken fern,
''Chance may have played a large part in determining which species
colonized the plant over evolutionary time.'' Bracken insects use their
own locations on the plant and their own mode of feeding, and are
