PATTERN AND PROCESS IN COMPETITION
21
of competition (Brown and Wilson, 1956; Hutchinson, 1959; Mayr, 1963);
the species composition of natural communities may reveal fewer repre
sentatives of a genus than would otherwise be expected in the absence
of competition (Elton, 1946); and MacArthur’s (1957) model of nonoverlapping niches has been advanced as a test for competitive exclusion
(Hutchinson, 1957; Slobodkin, 1961). In each case we are left, however,
with the question of whether the observed phenomena are in fact due
to competitive exclusion, or whether they cannot be explained instead
by ecological differences which have arisen through some other agent
of natural selection (Elton and Miller, 1954).
A. DISTRIBUTION PATTERNS
Figure 3 shows the relationships that may exist in the spatial distributions and fundamental niches of two populations. For simplicity
SPATIAL DISTRIBUTION
Allopatry
Syrnpatry
Contiguous Allopatry
FUNDAMENTAL NICHE
1
B
N1
C
N1
FIU. 3. Distribution patterns of two species (S, and S, ) and their possible niche relationships (N, and N2).
the niches are represented by single variables. They illustrate (A)
non-intersection; (B) intersection corresponding to Case 2, Fig. 2; (C)
intersection corresponding to Case 1, Fig. 2; and (D) contiguous nonintersection. Even though it is unlikely that the critical variables in
B