Species-rich temperate grasslands on five continents show consistent community assembly patterns

ANTONIO GAZOL ; JODI N. PRICE ; RIIN TAMME ; JOHN W. MORGAN ; STEVE LEONARD; CLAIRE WAINWRIGHT ; GISELA C. STOTZ ; JAMES F. CAHILL ; CANTERO, J.J.; CÉSAR NÚÑEZ ; RICARDO IBÁÑEZ ; INGA HIIESALU ; ÜLLE REIER ; MEELIS PARTEL

Brno

Simposio; 58thAnnual Symposium of the International Association for Vegetation Science; 2015

Vegetation Science Group and Mire Ecology Group Department of Botany and Zoology Masaryk University, Brno, Czech Republic

Temperate grasslands can be very diverse at small spatial scales and this raises questions about how species coexist given that all plant species are competing for the same limiting resources. We aim to discover if there are limits to the number of co-occurring species in temperate grass- lands (i.e. communities are saturated) and to determine potential biotic limitations generating such limits. We sampled ecologically similar species-rich temperate grasslands in seven floristic regions on five continents with different evolutionary histories. We collected data in 48 grass- land sites in Canada, Estonia, Spain, Mongolia, Argentina, Western Australia and South Eastern Australia (Tasmania and Victoria). In each site, we established a transect (0.1 x 10 m), consisting of 100 quadrats (10 x 10 cm). We estimated quadrat- and transect-scale species richness (i.e. alpha and gamma diversity, respectively) and their relationships (community completeness - ra- tio between species present and absent in each quadrat). The relationship between community completeness and gamma diversity indicates whether species richness is limited in different regions. We applied assembly tests and compared the observed patterns of richness variance, C-scores (species segregation within communities) and guild proportionality (proportion of forbs and grasses) to that expected from null models to further explore richness patterns and potential limitations to species coexistence. The largest values of alpha diversity were found in grasslands near the Mediterranean region in Spain with an average of 15.3 species in 10 x 10cm quadrat, and a maximum value of 23. Highest gamma diversity was found in Argentina (59 species per transect). We found that with increasing gamma diversity, communities became more saturated, i.e. had a higher proportion of available species present in the small-scale quadrats. Richness variance and guild proportionality were lower than expected at random in all of the regions (ex- cluding Western Australia and Spain), indicating some limits to the number of species occurring in a quadrat, and deviations in the relative proportion of forbs and grasses. Additionally, we found significant species segregation patterns at most sites. Our study suggests that small- scale species richness is limited and differs from random. Despite high variation in species rich- ness values, similar processes may be influencing patterns of diversity in temperate grasslands around the globe.