Poor dispersal destines many grassland species to dark diversity

Hyper-diverse ecosystems can be even richer: poor dispersal destines many grassland species to dark diversity

When counting plant species within a few square meters, northern European grasslands are among the most species-rich communities in the world. An international team of ecologists examined how many ecologically suitable species are still absent from these grasslands and what causes such absences. The team’s findings, published in Ecography, revealed that even if a square meter of dry calcareous grassland supports 30-40 plant species, there are an even larger number of species suitable for these ecosystems in the region that are currently absent. “This set of potentially suitable but absent species has been called dark diversity – an analogy to dark matter in cosmology”, explained the leader of the team, Professor Meelis Pärtel from University of Tartu, Estonia. The team used more than 1000 descriptions of plant community composition (each description was of 1 square meter spanning the entire distributional range of northern European dry calcareous grasslands. Using species co-occurrence patterns from this large data matrix, they were able to estimate the dark diversity for each individual sampled location.

“Given the high diversity, the high number of suitable absent species of these ecosystems was surprising, so we examined reasons why those species are absent”, said Kersti Riibak, the first author of the study and PhD student of professor Pärtel. “We analysed functional traits of both present and absent species and found that absent species dispersed shorter distances and produced fewer seeds than the species which were present”. A century ago, these calcareous grasslands were widespread throughout the region but now only small isolated patches remain. These findings suggest that nature conservation activities should promote species dispersal between the grassland patches. “Many plant seeds disperse by livestock or even by hay cutting devices. It would be helpful if grazing animals and cutting machines are moved from one site to another without cleaning,” suggested Riibak.

“As a general message, our study demonstrates that understanding the ecological processes shaping biodiversity may require knowledge of the species absent from suitable habitat patches, not only observed diversity”, concluded Pärtel.

Full article here: http://onlinelibrary.wiley.com/doi/10.1111/ecog.01312/abstract

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