It is often argued that ecosystems with greater species diversity are more stable. In
practice, many variables are involved in determining ecosystem stability, and in a given
situation the path of succession can be unpredictable (Figure 3.7). In a stable ecosystem
each species is assumed to have found a position, primarily in relation to its functional
needs: food, shelter and so on. This position, or niche, is where a given organism can
operate most effectively. Some organisms have very specialised demands and so occupy very restricted niches (e.g. the water-filled hollow of a particular bromeliad plant, itself
with a restricted niche), while others can exist in a wide range of niches. A species may
be using only a portion of its potential niche, and alteration of a single parameter
affecting competition with other organisms may suddenly open, restrict or deny a niche
for an organism.