British bird species distributions and the energy theory

Abstract

The steep decline in the number of species from Tropic to Pole may possibly be explained by 'the weather', that is, the latitudinal decline in the input of solar energy. This explanation, often obvious to the lay person, is dismissed or even ignored by most ecologists1–3. Only J. H. Brown and colleagues have proposed a direct 'species–energy' relationship4–6, an excellent scientific theory which implies simple tests that would refute the theory if it failed them. One such is the change in species numbers according to the seasonal fluctuation in the distribution of available energy: we will show that the varying distribution of small insectivorous birds in Britain in summer and winter corresponds well with the predictions of the species–energy theory; it also provides support for the theoretical model which explains it6,7. We find no support for the alternative 'historical' and 'habitat' theories.