for the phytophagous, but for the carnivorous forms; a good year, an increased output of cultivation, the introduction of a new or alien crop, is followed by an increase of vegetable feeders, an increase of their natural enemies, and of the creatures which subsist upon them. What is the result? The numbers are raised above the normal, and when the normal food supply returns, famine follows as surely as when the supply was short; there are too many months to be filled. Thus, taking an average of years, the necessary average is maintained, and this is nature's balance.
It is fair to say that there cannot be in any civilised, indeed in any, country populated by man a real natural balance; man is the great disturber of nature. But in a country like Britain, where civilisation has been working for the ends of man for ages, there is what we may call a human or artificial natural balance; a point at which, under the present artificial system, the interrelation of plants and animals, cultivated and domestic as well as wild, remains more or less constant. It is our duty to maintain that present-day balance so far as we can consistently with our actual requirements, for if we fail mankind as well as the lower animals will suffer. It is with this end that economic zoology and botany should be studied.
The increase beyond the normal proportions of any species of bird, due to protection which has not taken into consideration consequences, may be a tragedy. It may, probably will, affect our life interests; it certainly will have influence upon the relative numbers of other forms. Need I mention as problems of the day the extraordinary increase since 1880 of the black-headed gull and the sterling, two species wholly valuable in their proper proportions, but threatening other forms, actively or passively, now that they have become so numerous.
