Geographical shifts in the successional dynamics of inland dune shrub
communities
Abstract
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 dominant species, S.
genistoides and U. australis, to map the potential distribution of the
xerophytic shrub communities. Finally, to identify the relative
importance of each factor driving changes in community composition, we
examined the relationships between the vegetation gradients and a broad
set of explanatory variables. Results: Our results show that xerophytic
shrubs follow uniform successional patterns throughout the whole
geographical area, but also that these communities respond differently
to the main environmental gradients in each region. Soil organic matter
is the main determinant of community variations in the northern regions,
Setúbal Peninsula and Comporta, while in the South/South-Western region
most of the variation between both types of communities is explained by
temperature seasonality. Main conclusions: The relative importance of
the main factors causing community-level responses varies according to
regional processes and the suitability of the environmental conditions
for the dominant species in these communities. These responses are also
determined by intrinsic community mechanisms that result in a high
degree of similarity in the gradient-driven community stages in
different regions.