Many plant communities show strong fine-scale spatiotemporal dynamics due to frequent natality and mortality events. This process is often non-random, implying that the community can be broken into groups within which species mutually replace each other in time and are distinct from the other such groups. We examined whether such groups fill separate niches and are functionally complementary in a species-rich mountain grassland.
We used cluster analysis of fine-scale spatial data time series to discern which species were more likely to replace each other in space. Next, a four-year removal experiment (removing one group in each experimental treatment, or similar amount of biomass across all groups) was used to determine whether simultaneous occurrence of all these groups would maintain a greater total biomass than if an entire group were eliminated.
The results do not support the hypothesis that the simultaneous presence of groups of species that replace each other in space is necessary for the community to attain its maximum biomass. However, the experiment showed strong differences among the replacement groups in their capacity for opportunistic behaviour: some groups responded quickly to space made available by removal while others did not. Furthermore, there were strong differences between groups composed primarily of grasses and groups composed primarily of dicots. In spite of the large differences among these groups, they are not functionally complementary. We therefore conclude that replacement processes in this grassland community more closely resemble a neutral process with sets of species differing in the speed at which they fill empty spaces.