Sources of Diversity in a Grassland Metacommunity: Quantifying the Contribution of Dispersal to Species Richness

Abstract

Metacommunity theory suggests a potentially important role for dispersal in diversity maintenance at local, as well as regional, scales. In addition, propagule addition experiments have shown that dispersal often limits local diversity. However, actual dispersal rates into local communities and the contribution of immigrants to observed local diversity are poorly known. We present a new approach that partitions the diversity of a target community into dispersalmaintained and dispersal-independent components. Specifically, we quantify distances through space and time to the nearest potential seed source for naturally occurring recruits in target communities by using hierarchical data on species pools (local, site, region, and seed bank). Using this "recruit tag" approach, we found that dispersal contributed 29%-57% of the seedling diversity in perennial grasslands with different successional histories. However, both dispersal and seedling mortality remained remarkably constant, in absolute terms, over succession. The considerable loss of diversity over secondary succession (66%), therefore, could be understood only by considering how these processes interact with the decreasing disturbance rate (i.e., frequency of gaps) in later-successional sites. We conclude that a metacommunity perspective is relevant and necessary to understand the diversity and community assembly of this study system.

Patterns of seed dispersal syndromes on serpentine soils: examining the roles of habitat patchiness, soil infertility and correlated functional traits

“…The observed dispersal syndrome differences among soil types were not consistent with patterns expected under habitat patchiness as an ecological filter (Levine and Murrell 2003;Vandvik and Goldberg 2006). Overall, longdistance dispersal (wind, water and vertebrate) was neither more nor less common on serpentine.…”

“…Dispersal among patches can enable species to persist in unfavourable 'sink' habitats as a result of dispersal from more favourable 'source' 2 M.J. Spasojevic et al habitats ; however, the effect of dispersal in influencing the structure of communities in patchy habitats is dependent on the dispersal ability of the species present within those patches (Leibold et al 2004;Holyoak et al 2005). Species found in patchy habitats may be those that have longer-distance dispersal syndromes (vertebrate, water and wind dispersal syndromes) allowing them to disperse to and maintain populations in isolated habitat fragments (Levine and Murrell 2003;Vandvik and Goldberg 2006).…”

Metacommunity patterns in larval odonates

“…Even in permanent ponds, relatively few species were found to be consistently present in these sites. Although a solid body of theory indi cates that dispersal is important to maintaining species diversity in local and regional systems (Tilman 1994;Leh man and Tilman 1997;Loreau and Mouquet 1999), empiri cal evidence for this has been limited (Vandvik and Goldberg 2006). Results from this system suggest that dis persal between Xuctuating source and sink ponds are criti cal to maintaining diversity regionally, including in sites not subjected to regular disturbance.…”

“…If dispersal is important in determining community structure, we would predict that species will regularly colo nize habitats which are at least intermittent sinks, resulting in a breakdown between species life-history requirements and their distributions. Dispersal thus may have an impor tant role in maintaining diversity both locally and region ally (Vandvik and Goldberg 2006), and we examine the eVects of dispersal on both aspects of diversity. The neutral community perspective (Hubbell 2001) pro vides an alternative null model to the three models above which assumes that species respond diVerently to aspects of the habitat gradient (Bell 2001).…”

Dormancy in metacommunities

“…Across a 40-year successional gradient in a subalpine birch forest, dispersal played a consistently strong role in community assembly, but the importance of dormancy declined with 206 increasing time since disturbance (Vandvik and Goldberg 2006). As a result, recently or frequently disturbed plant communities tend to have the highest compositional similarity to the 208 seed bank, but this is not always the case (Hopfensperger 2007;Saatkamp et al 2014).…”