Species redundancy and coexistence: separating niche and service

Background/Question/Methods

Species redundancy, the observation that many species realize nearly identical functions in ecosystems, is a conundrum to community theory, but increasingly seen as essential to assuring ecosystem reliability. One suggested solution to the paradox is neutrality, the possibility that species coexist, not because of the fitness stabilizing dynamics of unique niches, but because of the fitness equalizing properties of demographic stochasticity. Here we investigate another potential mechanism by which functional redundancy is maintained through temporal niche processes, an explanation for which there is increasing evidence. Temporal dynamics, based on the storage mechanism of coexistence, require that life history stages fall into two categories, one environmentally sensitive, the other relatively insensitive and persistent. We observe that the persistent life stage is often the one that provides significant ecosystem functions and services, while the sensitive stage exhibits the niche differentiation necessary for stable coexistence. Thus, redundancy of functions within ecosystems are separated from the mechanisms that allow stabilizing dynamics. We examine this idea with a heuristic model and physiological and demographic data from the tropical dry forest of Mexico.

Results/Conclusions

We find that tree species nearly identical in their ecosystem functions as adults have predictable differences in seedling sensitivity to environmental conditions, likely to facilitate their stable coexistence. In addition, our model results indicate that niche neutrality does not deliver the ecosystem reliability effect of species redundancy in the context of climate change.