WEWeb EcologyWEWeb Ecol.1399-1183Copernicus PublicationsGöttingen, Germany10.5194/we-16-47-2016Using niche models of indicator species to predict the distribution of
xerophytic shrub dune communitiesChefaouiR. M.rosa.chef@gmail.comChozasS.CorreiaO.SantosA. M. C.HortalJ.CCMAR, Centro de Ciências do Mar, Universidade do Algarve,
Campus de Gambelas, Faro, 8005-139, PortugalCentre for Ecology, Evolution and Environmental Changes, Lisbon,
1749-016, PortugalNational Museum of Natural History (MNCN-CSIC), Madrid, 28006, SpainR. M. Chefaoui (rosa.chef@gmail.com)9February201616147497October201527January20162February2016This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://we.copernicus.org/articles/16/47/2016/we-16-47-2016.htmlThe full text article is available as a PDF file from https://we.copernicus.org/articles/16/47/2016/we-16-47-2016.pdf
Dune plant assemblages are affected by severe conditions, which
makes them excellent models for studying the effects of species interactions
and environmental conditions on community structure. We evaluate the
relationship between the structure of dune communities, local environmental
conditions and the suitability of climatic conditions for their
characteristic species. Using data from an extensive survey of xerophytic
inland sand dune scrub communities from Portugal – one of the most
threatened habitat types of Europe – we identify the main gradients of
vegetation composition, the different types of communities and their
indicator shrub species. Then, we model the geographical responses of these
species to the environment. Soil organic matter, isothermality and the
habitat suitability for Stauracanthus genistoides defined the distribution of three shrub
communities in the study area.
Introduction
Species distributions are affected by scenopoetic and biogeographical
factors at large scales, with biotic interactions and community dynamics
becoming more important at smaller scales (Soberón, 2007; Hortal et al.,
2010). Xerophytic shrub communities growing on inland sand dunes constitute
an excellent system for studying the scaling of the effects of species
interactions, for they are subject to strong environmental filters and
present diverse community compositions (Chozas et al., 2015). In an attempt
to integrate the different processes affecting the distribution and
co-occurrence of the shrub species inhabiting these habitats, we assessed
whether the distribution of these communities can be predicted by the
suitability of the environmental conditions for their indicator species.
Methods
We developed an extensive field survey of xerophytic shrub communities
growing on inland dune habitats in southwestern Portugal. The composition and
cover of shrub species was assessed in 115 plots (10 × 10 m) randomly
distributed within sandy soil areas with forest and semi-natural land use
cover along a total extent of 1700 km2.
The most characteristic species of the xerophytic shrub communities
previously described in the study area (Neto et al., 2002) were identified
through the indicator value, using the indval function of “labdsv” package
in R (Roberts, 2015).
We modelled the responses of these indicator species to environmental
conditions (i.e. soil and climate) using occurrence records from the whole
Iberian Peninsula. First, we used Ecological Niche Factor Analysis (ENFA;
Hirzel et al., 2002) to model the climatic niche of each indicator species
and determine the contribution of each environmental predictor to their
marginality (i.e. the direction of maximum difference between the species
niche and the conditions of the study area). Mahalanobis distance (MD; Clark
et al., 1993) was used to identify the optimum for each species in the
multivariate environmental space. Habitat suitability was calculated as the
environmental distance to such an optimum and mapped to infer the potential
distribution of the species.
Indicator species of each community. The indicator value
(IndVal) is maximum when all individuals of a species occur in a single
group and in all the sites of that group.
Marginality values for the climatic predictors used in the
three keystone species analyses, according to an Ecological Niche Factor Analysis (ENFA). Most relevant variables (values beyond |0.4|) in bold.
Habitat suitability maps for the three keystone indicator
species, computed using Mahalanobis distance. Habitat suitability ranges
from 0 (low suitability) to 1 (high suitability). Orange circles represent
species occurrence data.
Non-metric multidimensional scaling ordination of
study sites based on shrub cover. Dots and crosses represent study sites
with the presence of the three main indicator species.
The main gradients of vegetation composition were identified with a
non-metric multidimensional scaling (NMS) ordination of the shrub cover data
(Legendre and Legendre, 1998; McCune and Grace, 2002), using “vegan”
package in R (Oksanen et al., 2015). The relationships between variations in
community structure and the environmental variables were assessed with a
vector fitting analysis. These variables include those that maximize the
marginality of indicator species, soil organic matter content and aridity.
The latter two were identified by Chozas et al. (2005) as the main factors
acting on xerophytic shrub communities in a small region in the north of the
study area. Both NMS and vector fitting were performed using “vegan”
package in R.
Results
Four species were identified as indicators (Table 1). Three of them,
Stauracanthus genistoides, Stauracanthus spectabilis and
Ulex australis, are known to play keystone roles in their respective communities, so
they were selected for the niche analyses. ENFA identified six significant
predictors (Table 2), from which annual mean temperature, isothermality and
temperature seasonality were able to explain most of the marginality of
these species in the study area. All three species occur in localities with
higher annual mean temperature and isothermality, and lower seasonality of
temperature than the rest of the Iberian Peninsula. According to MD analyses
their suitable habitats are restricted to the southwestern quarter of the
peninsula (Fig. 1).
NMS based on shrub cover and vector fitting between gradients of vegetation
and environmental variables identified two main gradients in community
structure: one defined by soil organic matter and another by habitat
suitability of S. genistoides and isothermality (Fig. 2). These two gradients confirmed the
occurrence of three types of shrub communities in the study area, dominated
by either S. genistoides, S. spectabilis or U. australis, defining also an intermediate stage within the succession
between S. genistoides and U. australis communities.
Discussion
Our results show a gradient between S. genistoides and U. australis communities for which soil organic
matter is the main driver throughout southern Portugal. These results
coincide with those of Chozas et al. (2015) at a local scale, although at
this regional scale this community gradient is also related to the habitat
suitability for S. genistoides in several parts of the study area. ENFA revealed that the
occurrence of the three keystone species of the xerophytic shrub communities
is constrained by the same climatic factors in the Iberian Peninsula,
restraining the distribution of the communities associated to them to the
south-west. However, S. spectabilis shows a highly restricted potential distribution due to
its high dependence of isothermal habitats (i.e. places with smaller daily
variations in temperature). In contrast, S. genistoides and U. australis show much larger potential
distribution, as well as a remarkably coincidence in their marginality.
Given such similarities, the origin of the relationship between S. genistoides' habitat
suitability and community structure remains elusive and may be related to
geographical changes in the factors determining the dynamics of these
communities. Therefore, further research is needed to determine whether
there is a geographical coherence in the successional gradients between
these communities, and whether there are regional differences in their
responses to different environmental gradients.
Acknowledgements
We thank Adrián Escudero, Mariana Vale and one anonymous referee for their valuable comments on the manuscript. This study was funded by the Portuguese FCT project
COMDUNES (EXPL/BIA-BIC/2311/2013). R. M. Chefaoui was supported by the FCT postdoctoral
fellowship SFRH/BPD/85040/2012, S. Chozas by the FCT PhD grant SFRH/BD/65659/2009,
and afterwards by a FCT BI grant funded by the project COMDUNES
(EXPL/BIA-BIC/2311/2013), A. M. C. Santos by a Marie Curie Intra-European Fellowship
(IEF 331623 “COMMSTRUCT”), and J. Hortal by a Spanish DGCyT Ramón y Cajal
grant.
Edited by: S. Navarrete
Reviewed by: A. Escudero, M. Vale, and one anonymous referee
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