Propagule pools mediate community assembly and diversity‐ecosystem regulation along a grassland productivity gradient

Abstract

Summary 1The relative importance of regional species pools and local ecological processes in governing landscape variation in plant species diversity and productivity was evaluated in a Kansas grassland. 2 We examined the impact of multispecies sowing treatments and experimental canopy disturbances on plant species diversity and ecosystem processes along a complex natural gradient of plant standing crop. 3 Data collected 4 years after sowing showed that plant invasion and diversity were seed limited in unproductive sites, but microsite limited in productive sites. Effects of sowing on plant diversity along the natural landscape gradient were paralleled by significant effects of sowing on measures of local plant production and community resilience to disturbance. 4 These results support the shifting limitations hypothesis (SLH) that landscape gradients in local plant diversity should reflect shifts in the major regulating factor, from species pools to local ecological processes, as one moves from sites of inherently low to inherently high productivity. 5 Our findings also indicate that diversity at the level of the available propagule pool acts to constrain ecosystem productivity and stability by mediating local community assembly, by determining the availability of key species, and by governing opportunities for functional compensation within the community. 6 In total, our results support an emerging view that community processes and ecosystem functions are dynamically linked and act reciprocally to constrain each other.

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

“…The most common empirical approach to questions of community-level effects of dispersal has been propagule addition experiments (Burke and Grime 1996;Tilman et al 1997;Stampfli and Zeiter 1999;Shurin 2000;Fargione et al 2003;Foster et al 2004;Mouquet et al 2004). A considerable number of such experiments, conducted across a wide range of habitats and community types, show that diversity of plant communities is often limited by dispersal; that is, when propagules are added, diversity is increased (reviewed by Turnbull et al 2000;Levine and Murrell 2003;Zobel and Kalamees 2005).…”

Biodiversity and ecosystem functioning: exploring large-scale patterns in mainland China

“…Most experimental studies of constructed species assemblages determined that increasing diversity contributes to greater biomass production (e.g., Hooper et al 2005, Spehn et al 2005. Alternatively, species reduction experiments in natural systems revealed biomass was resilient to decreased biodiversity , Suding et al 2006), while Foster et al (2004) demonstrated during species addition experiments that species pools or communities were integral to increased biomass. These experiments were comparatively small.…”

Spatial variation in seed limitation of plant species richness and population sizes in floodplain tallgrass prairie

“…Grassland and savanna plant communities, especially successional ones, often may be invasible and/or unsaturated with species (Tilman 1997, Foster et al 2004, Zeiter et al 2006. Community "invasibility" means that species whose propagules are added to the community establish populations.…”

“…Rigorous evaluations of seed limitation of plant population size, community invasibility and saturation are rare because few seed addition studies have been of sufficient duration to determine whether adding seed increases numbers of reproductive individuals of the added species (reviewed in Turnbull et al 2000). However, several long-term studies have documented sustained population increases and community responses to seed addition in grasslands and savannas (Foster and Tilman 2003, Foster et al 2004, Zeiter et al 2006. One of the striking and poorly explained results of seed addition experiments in herbaceous plant communities is the large variation among sites in the magnitude of population and community response to increased density and diversity of the seed rain.…”

“…Differences between sites in mean resource availability or in the amount of spatial heterogeneity in resource availability may be proximate determinants of community invasibility and saturation (Grace 1999, Bakker et al 2003. In mesic grasslands, sites with high ecosystem productivity may not respond to seed additions either because insufficient light penetration through the canopy prevents adult recruitment (Grime 1973, Foster et al 2004 or because few species are adapted to grow under conditions of high soil resource availability (Taylor et al 1990, Safford et al 2001). Spatial homogeneity in resource levels also may limit community responses to added seed.…”