Figure 12.11 Positive density dependence in cowslip plants. At low densities, plants appear to be pollen-limited, which causes them to produce fewer seeds. At higher densities, each plant produces many more seeds.
Data from M. Kéry et al., Reduced fecundity and offspring performance in small populations of the declining grassland plants Primula veris and Gentiana lutea, Journal of Ecology 88 (2000): 17–30.