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Traditionally, species absence in a community is ascribed either to dispersal limitation (i.e., the inability of propagules of a species to reach a site) or to habitat limitation (abiotic or biotic conditions of a site prevent species from forming a viable population); sowing experiments can then distinguish between these two mechanisms. In our view, the situation is even more complicated. To demonstrate the complexity of the problem, we designed and applied simulations based on an extension of matrix models covering effects of propagule pressure and habitat limitation, and reflecting various characteristics of a species and of a habitat. These included life history, fecundity, seed bank viability of a species, habitat carrying capacity and disturbances. All the investigated factors affected proportion of occupied habitats. Whereas they can, to a large extent, compensate for each other, simultaneous decrease of habitat suitability and propagule input can be detrimental to the survival of a population. Our model demonstrated that in many cases, the absence of a species in a community is of stochastic nature, and result of interaction of species life history and various external conditions, and thus cannot be simply attributed to a single cause. The model results are supported with examples of case studies. The results also explain some well-known ecological phenomena, as decrease of niche breadth from the center to the margins of area of distribution. Finally, the model also suggests some caveats in interpretation of the results of sowing experiments.

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