Ecological applications of niche theory - Ecological Applications: Toward a Sustainable World - page 37

2.1 Introduction Kelly is a really keen angler. His friends have to smile at the sign on the door of his

room: 'Fish worship - can it be wrong?'. Kelly knows as much about the habits and
habitats of river fi sh as many experts, and enjoys both the solitude of being in a
quiet backwater and the challenge of landing the big one. But he sometimes fi nds
himself in situations where others denigrate his sport. ' They tell me that angling is
cruel - and I say so is killing stock at the slaughterhouse. ' Then they switch to a con-
servation argument, pointing out how exploitation can put species at increased risk
of extinction. ' I say that I fi sh for introduced fi sh - brown trout in my case - and they
should be pleased because this takes the pressure off native species that have been dwin-
dling in numbers. (I know this is a bit dishonest - I would fi sh for trout even if they were
native to my part of the USA!) How can people hold such contrasting views? Isn't there
some middle ground? I can't fi nd it, and it bugs me. '
Members of society are certainly not unanimous in the way they value the natural
world - the spectrum of opinions is broad, with zealots at both extremes. On the
one hand, there are some industrialists, fi shers, farmers and foresters who accept
none of the conservationist case and are not prepared to look objectively at the sci-
entifi c evidence; while on the other side are the environmental zealots - preserva-
tionists who seem unwilling to accept any exploitation of the natural world. The
middle ground is occupied by both exploiters and conservationists whose basic
philosophy holds that natural resources can be used, but this should be in a sustain-
able and balanced manner. A good understanding of ecology can provide the scien-
tifi c basis for what, in its broader context, is a question of ethics.
A successful species invasion (of Kelly's introduced brown trout, for example)
depends on the ability to establish and maintain a population in a new location. To
do this, individuals must tolerate the abiotic conditions they encounter, fi nd suffi -
cient resources (nutrients, water, food, nest sites and so on), and persist in the face
of enemies (competitors, predators, parasites). This is the domain of niche theory
(Box 2.1). Niche information is crucial not only when predicting the spread of invad-
ers (Section 2.2), but also to design reserves for endangered species (Section 2.3), as
well as for species recovery in habitat restoration projects (Section 2.4). In fact,
whenever there is a focal species - an invader, an endangered species or one crucial
to habitat recovery - the better our understanding of its ecological niche, the more
likely the success of a management strategy.

Box 2.1 Essential niche
theory

Conditions and resources - what's the difference?
Before explaining the term 'niche', it is important to distinguish between two kinds of ecological
factor - conditions and resources.
Conditions are physicochemical features of the environment such as temperature, humidity and
pH - these may be altered by the presence of organisms but cannot be consumed. Extreme condi-
tions (e.g. high and low temperatures) may be lethal, with a continuum of more favorable values
between the extremes. In some cases, the timing and duration of extremes may be more important
to an organism's success than absolute values. Species differ in the shapes of their response curves
- some, for example, because of particular metabolic effectiveness or enzyme structures, can toler-
ate higher or lower temperatures (or greater temperature ranges) than others.
Resources, in contrast to conditions, are consumed by organisms so that availability to others
may be affected - plants consume photons, nutrients, water and carbon dioxide; animals consume
water, food (whether plant or animal, living or dead) and may also be said to consume nest sites
and hiding places (making them unavailable while occupied). The fact that resources can be