Biogeography and climatic differentiation of two annual species of Teesdalia R. Br. (Brassicaceae)

Aim The two annual species of Teesdalia R. Br. occupy nearly exclusive ranges. Autecological data on T. nudicaulis (L.) R. Br., taken from the literature, are compared with data obtained from a climatic analysis of the general distributional range of the species. This paper addresses the question of whether the observed autecological characteristics of the species (local scale) are reflected in the data obtained from the climatic analysis (global scale). Furthermore, the marked biogeographical differentiation of the two annual species of Teesdalia R. Br. is investigated. Location The genus Teesdalia is naturally distributed in Europe and North Africa. Methods The number of occurrences of the species along climatic gradients is calculated. The data are primarily presented in frequency diagrams (FDs) exhibiting the number of occupied grid cells along the climatic gradients. The temperature-precipitation diagrams (TPDs) are derived from the FDs to illustrate the monthly climate spaces of the species. The climate spaces of the species in the course of the year are shown in the climatic mean diagram (CMD). Each type of diagram illustrates distinctive characteristics of the species' ranges. Results Autecological studies of T. nudicaulis show that distinctive thermal and hydric (autumn and spring) conditions are necessary for optimal germination and fruit set. The significance of these two seasons is also reflected in the climatic analysis of the species' range. Despite their importance, the results of the autecological study are not sufficient to explain the whole range of the species. It seems that additional factors, such as low temperatures, but also higher or lower amounts of precipitation at temperatures similar to those observed locally, may be limiting in other parts of the range. The three types of diagram shed light on factors affecting the geographical differentiation of the two annual species. However, the biology and ecology of T. coronopifolia (J. P. Bergeret) Thell. are not well enough known to trace evolutionary pathways of this biogeographical differentiation. Main conclusions Local ecological or biological studies are necessary for a better understanding of the species' ranges. Results of local studies concerning the influence of climate on the species' ranges may be tested at a global level using the methodology presented here. The diagrams provide a framework for analyses of geographical differentiations of species and the formulation of locally testable hypotheses for comparative biogeographical studies.