Foreword

Alas, the poor ecologist who is expected to follow the laws of scientific inference that have arisen from physics and chemistry. Erect hypotheses, make predictions, see if they are supported by evidence obtained by observations or manipulative experiments. Perhaps it would be easier if, instead of 30 million species, we had only 118 elements in the periodic table to study or only a few forces in physics to design hypotheses around. So how do we cope? We can deal with autecology or the ecology of individual organisms because we have a strong base in physiology and simple things like metabolic rates are constrained by how evolution has proceeded. We can deal with populations because they typically have a restricted nexus of interactions, as Andrewartha and Birch (1984) told us. But things are getting more complicated since the interactions can involve competition, predation, disease, food supplies, climate, and social effects. Perhaps we can cope with this amount of complexity, but it is certainly complex enough to allow many ecologists to argue extensively about the factors causing populations to rise or fall. In principle we can sort out these arguments at the population level by field or laboratory experiments, and this approach will often work to provide evidence-based explanations. But when we move up to community and ecosystem ecology problems multiply if only because experimental manipulations become more difficult and certainly more expensive. It is partly a reflection of why aquatic community ecology has progressed more than terrestrial community ecology – large-scale experiments in rivers and lakes are more prevalent than they are in terrestrial ecosystems. But it may also be partly a reflection of hypotheses that are not operational.

In an ideal universe we might be able to work out some of these problems but the arrival of human influences has added yet more complexity. Invasion biology is now one of the leading fields of community ecology both because of its intrinsic interest as a test case of how much we understand community interactions and even more because many species invasions have consequences written very large in dollars and cents.