Darwinian evolution by natural selection is driven primarily by differential survival and reproduction among individuals in a population. When the evolutionary interest of an individual is in conflict with the interests of the population, the genes increasing individual fitness at the cost of population performance will increase in frequency.
Yield, one of the fundamental agronomic variables, is not an individual, but a population characteristic. A farmer wants a high yield per hectare; he is not interested in the performance of individual plants. When individual selection and population performance are not in conflict, it is unlikely that plant breeding can radically improve the results of millions of years of evolution through natural selection. However, efforts to improve crops can be very successful, when breeding is directed towards goals diverging from natural selection. The potential difference between optimal individual and optimal population performance increases with strong competition among individuals. Thus dense populations make ideal environments to exert forms of selection pressure deviating from natural selection.
The first part of this study investigates the central hypothesis of Evolutionary Agroecology that the highest yielding individuals do not necessarily perform best as a population. The investment of resources into strategies and structures increasing individual competitive ability carries a cost. If a whole population consists of individuals investing resources to compete with each other, it will have a negative impact on the population performance.
While high density results in strong competition, it also increases the potential for cooperation. The other aspect of this study has been to investigate the possibility of improving the yield and weed suppression potential of cereal crops in dense uniform cultivation systems, by reducing phenotypic plasticity in shade avoidance. Shade avoidance is an elongation response of plants to perceived vegetative shade, enhancing individual survival and fitness. By reducing the strength of this response we hope to develop plants that instead of optimizing their individual light foraging capacity, cooperatively shade and suppress weeds.
The last part of this work reviews empirical evidence for the law of constant final yield, the phenomenon that total biomass production levels off at high densities. This robust pattern represents the maximum biomass for a genotype in an environment after a period of growth. As some of the most sustainable natural plant communities are those with the highest biomass, predicting and utilizing constant final yield can be a useful tool for developing dense, sustainable high productivity cropping systems.