The importance of a relative shortage of food in animal ecology

Abstract

It is proposed that for many if not most animals — both herbivore and carnivore, vertebrate and invertebrate — the single most important factor limiting their abundance is a relative shortage of nitrogenous food for the very young. Any component of the environment of a plant, by varying the amount of adequately nutritious plant tissue available to herbivores, may consequently affect the abundance of food through all subsequent trophic levels; in this regard weather may be important more often than is immediately obvious. The hypothesis proposes that animals live in a variably inadequate environment wherein many are born but few survive, and leads to a concept of populations being “limited from below” rather than “controlled from above”. And it may lead to a reappraisal of the role of predation, competition and social and territorial behaviour as factors likely to influence the numbers of animals in the environment, the response of “pests” to manipulation of populations of their food plants by Man, and the likely effectiveness of agents of biological control.