Are differences in seed mass among species important in structuring plant communities? Evidence from analyses of spatial and temporal variation in dune-annual populations (original) (raw)
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Annals of botany, 2014
Simultaneous formation of aerial and soil seed banks by a species provides a mechanism for population maintenance in unpredictable environments. Eolian activity greatly affects growth and regeneration of plants in a sand dune system, but we know little about the difference in the contributions of these two seed banks to population dynamics in sand dunes. Seed release, germination, seedling emergence and survival of a desert annual, Agriophyllum squarrosum (Chenopodiaceae), inhabiting the Ordos Sandland in China, were determined in order to explore the different functions of the aerial and soil seed banks. The size of the aerial seed bank was higher than that of the soil seed bank throughout the growing season. Seed release was positively related to wind velocity. Compared with the soil seed bank, seed germination from the aerial seed bank was lower at low temperature (5/15 °C night/day) but higher in the light. Seedling emergence from the soil seed bank was earlier than that from th...
Evidence for community assembly constraints during succession in dune slack plant communities
2005
Community assembly during succession can be constrained by both local and regional factors. Despite an increasing regional species pool size during succession, we found a limit on the number of species in 1× 1 m plots in dune slacks. Three alternative hypotheses (habitat heterogeneity, dispersal limitation and niche limitation) explaining this community saturation were tested.
Geographical shifts in the successional dynamics of inland dune shrub communities
Aim: Species’ environmental requirements and large-scale spatial and evolutionary processes are known to determine the structure and composition of local communities. However, ecological interactions and historical processes also have major effects on community assembly at landscape and local scales. In this work we evaluate whether two xerophytic shrub communities follow fixed ecological assembly dynamics throughout large geographical extents, or their composition is rather driven by species individualistic responses to environmental and macroecological constraints. Location: SW Iberian Peninsula (Portugal and Spain) Taxa: Stauracanthus genistoides agg. and Ulex australis agg (Fabaceae). Methods:Inland dune xerophytic shrub communities were sampled in 95 plots distributed within their potential area of occurrence. Then, we described the main gradients of vegetation composition and assess the relevance of biotic interactions. We also characterized the habitat suitability of the domi...
Plant Ecology, 2002
Many studies have investigated the density-dependent regulation ofannual-plant populations on coastal sand dunes, but few have explored theconsequences of competition for the coexistence of plants in these simplecommunities. We used neighbourhood techniques to parameterize competition anddispersal functions from field data collected for two species of dune annual(Aira praecox and Erodium cicutarium)over three successive years, and then combined these functions into spatiallyexplicit simulation models. The population size of Airavaried enormously between years, while Erodium remainedsteady. Competition with neighbours reduced the spike length ofAira plants only in one of the three years (when itspopulation density was highest), while competition with neighbouringErodium plants appeared to result in the local death ofAira plants. However, these density-dependent effects werefar too weak to generate the observed changes in the population size ofAira among years, or to maintain populations below theupper limits observed. The large-seeded Erodium wasaffected by intraspecific competition but was unaffected by small-seededAira plants. Therefore, the larger-seeded species wascompetitively superior to the smaller-seeded species, an affect that couldpromote coexistence (albeit weakly) by a competition-colonisation trade-off.Modal dispersion distances of Aira andErodium were 45 and 60 mm respectively,greater than the radius within which competitive interactions occurred (40mm). Theoretical studies suggest that under these conditions thespatial arrangement of plants should be nearly random. In factAira was spatially aggregated, especially when rare,suggesting that patchy mortality across the dunes was important in generatingspatial structure. The study suggests that density dependence only weaklyregulates dune annual communities, while year-to-year environmental variationexert major influences on population sizes and spatial structures.