The word ‘ecology’ was first used by Ernest Haeckel in 1869.
Paraphrasing Haeckel we can describe ecology as the scientific
study of the interactions between organisms and their environment.
The word is derived from the Greek oikos, meaning
‘home’. Ecology might therefore be thought of as the study of
the ‘home life’ of living organisms. A less vague definition was
suggested by Krebs (1972): ‘Ecology is the scientific study of
the interactions that determine the distribution and abundance
of organisms’. Notice that Krebs’ definition does not use the word
‘environment’; to see why, it is necessary to define the word.
The environment of an organism consists of all those factors and
phenomena outside the organism that influence it, whether these
are physical and chemical (abiotic) or other organisms (biotic). The
‘interactions’ in Krebs’ definition are, of course, interactions with
these very factors. The environment therefore retains the central
position that Haeckel gave it. Krebs’ definition has the merit of
pinpointing the ultimate subject matter of ecology: the distribution
and abundance of organisms – where organisms occur, how
many occur there, and why. This being so, it might be better still
to define ecology as: the scientific study of the distribution and abundance of
organisms and the interactions that determine distribution
and abundance.
As far as the subject matter of ecology is concerned, ‘the
distribution and abundance of organisms’ is pleasantly succinct.
But we need to expand it. The living world can be viewed as a
biological hierarchy that starts with subcellular particles, and
continues up through cells, tissues and organs. Ecology deals
with the next three levels: the individual organism, the population
(consisting of individuals of the same species) and the community
(consisting of a greater or lesser number of species populations).
At the level of the organism, ecology deals with how individuals
are affected by (and how they affect) their environment. At the
level of the population, ecology is concerned with the presence
or absence of particular species, their abundance or rarity, and
with the trends and fluctuations in their numbers. Community
ecology then deals with the composition and organization of
ecological communities. Ecologists also focus on the pathways
followed by energy and matter as these move among living
and nonliving elements of a further category of organization:
the ecosystem, comprising the community together with its
physical environment. With this in mind, Likens (1992) would
extend our preferred definition of ecology to include ‘the
interactions between organisms and the transformation and
flux of energy and matter’. However, we take energy/matter
transformations as being subsumed in the ‘interactions’ of our
definition.
There are two broad approaches that ecologists can take at
each level of ecological organization. First, much can be gained
by building from properties at the level below: physiology when
studying organismal ecology; individual clutch size and survival
probabilities when investigating the dynamics of individual species
populations; food consumption rates when dealing with interactions
between predator and prey populations; limits to the
similarity of coexisting species when researching communities, and
so on. An alternative approach deals directly with properties of
the level of interest – for example, niche breadth at the organismal
level; relative importance of density-dependent processes at
the population level; species diversity at the level of community;
rate of biomass production at the ecosystem level – and tries to
relate these to abiotic or biotic aspects of the environment.
|
Disclaimer
