Bernard Campbell, Human Ecology. Aldine Publishing Co., 1985.

TYPES OF RELATIONSHIP

Fig 1.8. If we examine energy flow from the point of view of a particular animal or plant species we soon realize that the food chain is an unrealistic simplification. Most animals consume more than one species of organism and are consumed in turn by many other species. The inter-relationships of organisms as herbivore or carnivorous predator must be supplemented by the phenomenon of parasitism. When we try to analyse the situation in detail we discover, not a linear food chain but a systemic food web. The [diagram at right] illustrates only the more abundant 50 species which directly or indirectly derive their energy resources from the cole plant Brassica oleracea (after D. Pimental, 1966). Altogether 210 species are involved in this incredibly complex food web. The wide interdependence of these species is clear. The complexity of a food web is such that non one to date has worked out the complete pattern of food relationships in any natural community.