Predicting the outcome of competition along a nitrogen gradient - a case study with Erodium cicutarium and Geranium pusillum

In order to understand the effect of a nitrogen gradient on the intraspecific and interspecific competition between plants, the two species Erodium cicutarium and Geranium pusillum were grown in a response-surface competion experiment at three different densities along a nitrogen gradient consisting of four different nitrogen levels. Seed set data were estimated from biomass measurements and fitted to a generalized hyperbolic competition model, and the probabilities of different ecological scenarios were calculated. The model predicted that E. cicutarium is competitively superior along most of the nitrogen gradient. This prediction was contrary to our prior expectations which were based on the occurance of the two species in natural habitats.