Consequences of inter-specific competition among multiple adaptive species in Daisyworld

Summary We investigate the consequences of Darwinian selection in a daisymodel with uniform temperature, inter-specific competition and multiple daisies. The assumption of a higher competition between species than within them allows for the coexistence of more than two species in equilibrium. Thus, it is the first time that a high biodiversity with equal environment-altering traits at the same trophic level in a daisymodel is reported under stationary conditions. Adaptation in the biota occurs through mutations, leading to changes in the optimum temperature in order to achieve the maximum growth rate at the individual level. We study the planetary sensitivity (i.e. the variation of the global mean temperature due to a 1% change in solar radiation) as a function of the strength of the inter-specific competition and of the number of different species that grow in the model. We find the following: 1) by fixing the parameter that defines the strength of the inter-specific competition, the planetary sensitivity increases as biodiversity increases; 2) by keeping constant the number of different species in the planet, the planetary sensitivity also increases as competition between species increases. In any case, however, the planetary sensitivity associated with adaptive daisies is much greater than that obtained from non-adaptive species. However, the range of mean solar radiation where biota grows in the planet is substantially larger for adaptive species than for non-adaptive ones. This result suggests that adaptation of multiple species with the same environmental-altering traits may not imply a strong regulation of the mean planetary temperature, which differs with recent studies that analyse adaptation of single species. Similar results are obtained by using a constrained adaptation and non-uniform temperatures.