Concepts and problems - Nonequilibrium Ecology - page 8

Among major recent approaches, mentioned by Paine ( 2002 ), are the
necessity to distinguish between open and closed systems (already recog-
nized by von Bertalanffy 1952 and Levin and Paine 1974 ), and that
''equilibrium may exist only in an abstract sense.'' Chesson and Case
( 1986 ) plead for a pluralistic approach: coexistence may be partly due to
differences in resource use, partly because species respond differently to
the environment, and partly because the advantage of one species over
another is very small, leading to very slow competitive displacement; (see
also the discussion in McIntosh 1987 ).
One of the clearest and most radical redefinitions of the aims of ecology
comes from Hengeveld and Walter ( 1999 , further references therein) and
Walter and Hengeveld ( 2000 , further references therein; see also Walter
1995 and Walter and Patterson 1995 ). Hengeveld and Walter distinguish
two paradigms in current ecology, which have coexisted for some time
but are mutually exclusive; they are the demographic and the autecological
paradigms. The former, which is the better developed and generally
accepted approach, accepts that different species are demographically
similar although they fulfill different functions in communities. Intra-
and interspecific competition are of paramount importance, leading to
coevolution of species by optimization processes. Optimization is
thought to be possible because the abiotic component of the environment
is on average constant. In contrast, the autecological approach accepts species
as dissimilar entities which are affected by abiotic as well as demographic
factors. Optimization cannot occur because the environment is very variable
in space and time. In the demographic paradigm, the important question
is why do so many species share the same resources, and the emphasis is on
evolution as the result of short-term ecological optimisation processes.
In the autecological paradigm, the central question relates to how species
arose and how they persist within a variable and heterogeneous environ-
ment. It focuses on the idiosyncratic nature of adaptations, species and
their spatial response to environmental circumstances. In the demo-
graphic paradigm, nature is balanced, i.e., there are population equilibria
maintained demographically by biotic processes; structured communities
exist that consist of populations of several species and are saturated with
species that optimally partition resources; and ecological-evolutionary
processes occur in a discrete locality. In the autecological paradigm,
because of the continually changing environmental (biotic and abiotic)
conditions which do not permit optimization, emphasis is on survival and
reproduction and not on quantification and comparison of differences in
reproductive outputs between species. Physiological, morphological and