Plant dispersal strategies: a new classification based on the multiple dispersal modes of individual species
Abstract
The diaspores of vascular plants arc transported by vectors from which the dispersal modes are inferred, such as anemochory as a spread by wind. Traditionally, each species was assigned a single dispersal mode, based on the morphology of its diaspore; for example the presence of pappus indicated anemochory.
In this paper we present a different approach to plant dispersal, based on the fact that plant species are spread by multiple vectors that differ in terms of how frequently they are employed and how efficiently they work. The combinations of dispersal modes are repeated in species with similar ecology and diaspore morphology.
For example, for species in wetland and riparian habitats (e.g. those of the genera Phragmites, Typha and Salix) that have very small seeds with hairy flying apparatus, dispersal by both wind and water is important, but the seed can also attach to animal fur or human clothes and a portion of seed fall close to the parental plant. Even such less common dispersal modes contribute to species' spread and cannot be disregarded.
To characterize such combinations of dispersal modes occurring repeatedly with different frequencies, we propose here the concept of 'dispersal strategies'. We tested this approach by using the flora of the Czech Republic, excluding rare alien species and the majority of hybrids.
The data on the type and morphology of above-ground diaspores and on dispersal modes of plant species were obtained from the literature and databases, and completed by expert knowledge based on personal observations. Where the data was lacking, the taxa were assigned a dispersal strategy based on that of their relatives with similar seed.
We describe nine dispersal strategies that are defined by the combinations of dispersal modes and their relative importance, and named after representative genera: Allium, Bidens, Cornus, Epilobium, Lycopodium, Phragmites, Sparganium, Wolffia and Zea. We related these strategies to the origin status, invasion status and habitat affinities of their representatives.
The majority of the taxa in the Czech flora (92.8%) are dispersed exclusively by generative diaspores, in 4.5% generative and vegetative diaspores are combined, 0.7% rely exclusively on vegetative diaspores and the remaining 2.0% (Zea strategy) do not produce viable above-ground diaspores and spread exclusively by below-ground organs (which were not considered as vegetative diaspores in our system) or with human assistance. Native species are statistically significantly more represented in the Epilobium, Lycopodium, Sparganium and Wolffia strategies, while alien species are over-represented in the Allium, Bidens and Zea strategies.
The Allium strategy is the commonest in the Czech flora, despite being the least specialized, hence seemingly poorly equipped for successful dispersal. This indicates that morphological adaptations for dispersal by natural vectors might be less important for plants than previously thought.