Jana Doudová and Jan Douda
How it is possible for many species to coexist in one habitat is still a fascinating question that re-emerges in each new generation of ecologists. This issue is all the more provocative in habitat types such as wetlands, which are characterized by the presence of dominant species that significantly exceed the size of smaller ones.
Some earlier studies have shown that large species need not operate always as competitors, but under some circumstances they may serve as nurse plants, helping to ensure biomass stability of small species. This has been observed especially under stressed conditions. Most studies have documented this phenomenon in relatively harsh ecosystems such as in arid and semiarid areas or in alpine plant communities, where water and nutrients are particularly limiting. Here, we extend this model to cover wetland plant communities that lie at the opposite extreme of the water and productivity gradient. Our results thus show that non-dominant small species may be facilitated by dominant large species in ecosystems where highly asymmetric competition for light is to be expected. Thanks to the detailed measurement of individuals’ fitness and the measurement of plant responses to water stress using functional traits, we have revealed in more detail the mechanisms of how species coexist under stress. We show that the dominant species decreased the relative performance differences among smaller plant species under conditions of permanent drought stress, which is a prerequisite for their long-term coexistence. The dominant species supressed drought-tolerant species with low competitive ability, while supporting less drought-tolerant species with relatively high competitive ability.
Our results indicate a certain resistance of wetlands to prolonged drought periods and show that wetland communities are able to survive them without major impacts on their species diversity.