Functional connectivity is a key factor for the persistence of many specialist species in fragmented landscapes. However, connectivity estimates have rarely been validated by the observation of dispersal movements. In this study, we estimated functional connectivity of a real landscape by modelling dispersal for the endangered natterjack toad (Bufo calamita) using cost distance. Cost distance allows the evaluation of 'effective distances', which are distances corrected for the costs involved in moving between habitat patches in spatially explicit landscapes. We parameterized cost-distance models using the results of our previous experimental investigation of natterjack's movement behaviour. These model predictions (connectivity estimates from the GIS study) were then confronted to genetic-based dispersal rates between natterjack populations in the same landscape using Mantel tests. Dispersal rates between the populations were inferred from variation at six microsatellite loci. Based on these results, we conclude that matrix structure has a strong effect on dispersal rates. Moreover, we found that cost distances generated by habitat preferences explained dispersal rates better than did the Euclidian distances, or the connectivity estimate based on patch-specific resistances (patch viscosity). This study is a clear example of how landscape genetics can validate operational functional connectivity estimates.

SummaryThe standard method of measuring pollen limitation is to add pollen to a number of flowers, preferably to a whole plant, and to compare fruit and seed set with that of naturally pollinated flowers on other plants. In 25 yr of research, this method has yielded valuable data, but it is difficult to use in large plants. This has caused a bias in the available data towards smaller, herbaceous plants with relatively few flowers. I argue that, in order to widen our knowledge of how pollen limitation affects plants, we should go beyond whole-plant pollen addition and change our concept of how a flowering plant functions. The traditional method does not take into account the variation in and dynamics of resource allocation and pollen availability. The concept of integrated physiological units (IPUs) does, but, although it has been applied to pollination biology, it has not received the attention it deserves. I use this article to present its merits again, to propose a step-by-step methodology for studying pollen limitation, and to examine factors influencing possible plant strategies.

For organisms with indeterminate growth, life history theory predicts that in environments where organisms experience high survival rates or gain fecundity with age or size, natural selection favors delayed maturity. In semelparous perennial plants the onset of reproduction is regulated by a threshold size for flowering. We tested this prediction by comparing sand dune populations of the facultative biennial herb Cynoglossum officinale. We collected data on flowering probability, survival, and growth rate in relation to plant size in two habitat types, open areas and poplar thickets, in Meijendel, The Netherlands, and in Holkham, England. Survival of established rosettes was highest in Holkham and lowest in open areas in Meijendel. Relative growth rates in Holkham were about three times as high as those in Meijendel. These findings agreed with the differences in threshold sizes found among the sites: the Holkham field population harbored higher threshold sizes than the Meijendel sites. We used the field data to compare optimal threshold sizes for flowering predicted by three existing models. All three models gave the same rank order for threshold sizes as found in the field: Meijendel open < Meijendel poplar thicket < Holkham. One model, which maximized population growth rate λ, predicted optimal threshold sizes that agreed very well with threshold sizes found in the field. The predictions of the two other models, both maximizing R0, were consistently lower than the threshold sizes observed in Meijendel, while their predictions for Holkham were too high.

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