What appears patchy to a grasshopper may appear
uniform to a gnu.
(Wright et al. 1998, p. 19)In the previous two chapters we have reviewed
island ecological theories from both macroecologi-
cal and ecological–biogeographical perspectives,
tracing the development of ideas following the
appearance of the seminal work of MacArthur and
Wilson (1963, 1967). We return again to their
equilibrium theory at the outset of this chapter. The
exploration of these ideas by ecologists has pro-
duced many insights, sometimes consistent with
the original models, sometimes inconsistent.
Departures from predicted behaviours are in many
respects of greatest interest, as they show how the
models need to be modified. As a research
programme, this body of work is characterized by a
general assumption that the systems can be charac-
terized as dynamic and equilibrial: indeed we
might consider this paradigmatic. Yet, as we know,
this assumption may not be supported in all cases.
Accordingly, we will consider the alternatives in
the present chapter. In so doing we hope to recon-
cile the apparently conflicting lessons from 40 years
of research and to suggest where island ecological
theory might be heading.
Several themes run through this chapter. They
include: the need for alternatives to the dynamic
equilibrium model, recognizing the possibility of
dynamic but non-equlibrium systems, and of
largely static ecologies, which again may be equi-
librial or non-equilibrial; the issue of scale depend-
ency; and the need for models to accommodate
hierarchical links within ecological systems. Building
in such complexities may lead to more realistic
models, but we should not readily abandon the
search for simple, unifying theories and models
(Brown 1995), and therefore, we also consider some
recent attempts to develop more satisfactory simple
frameworks for island ecology.6.1 Limitations of the dynamic equilibrium model of island biogeography: a reappraisal
... the equilibrium model and its derivatives suffer from
extreme oversimplification by treating islands as func-
tional units with no attention to internal habitat diversity
and by treating species as functional units with no
allowance for genetic or geographical diversity. This is not
even good as a first approximation, because it filters out
the interpretable signal instead of the random noise. The
authors are in such a hurry to abandon the particulars of
natural history for universal generalization that they lose
the grand theme of natural history, the shaping of organic
diversity by environmental selection...
(Sauer 1969, p. 590, on MacArthur and Wilson 1967)
Brown (1981) observed that the EMIB has three
characteristics which he claimed any successful
general theory of diversity must possess.
●First, it is an equilibrium model, thus historical
factors, climatic change, successional processes,
and the like are acknowledged, but side-stepped.
The theory explains rather the ultimate limits, the
theoretical patterns of diversity.
●Secondly, it confronts the problem of diversity
directly, number of species being the primary
currency of the model. It also takes account both of
145CHAPTER 6