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While it is well known that the success of alien plants in new environments greatly depends on their functional traits, to date only a few other studies have tested whether coexisting alien and native species show converging or diverging functional attributes. To our knowledge, no comparative analysis between native and alien species has been carried out in the same mountain habitats. We characterized the main habitats of the Italian Alps on the basis of plant species traits and we then tested for evidence of functional axes of variation among the habitats for native and alien plants. Finally, we tested the 'try-harder' and the 'join-the-locals' hypotheses to understand whether coexisting native and alien plant species showed converging or diverging functional attributes. Ordination analysis showed a distribution of the habitats according to the Grime's CSR strategies, and associated to plant growth form and resource acquisition. Co-inertia analysis showed a significant association between native and alien plant traits at habitat level (RV = 0.73; Monte-Carlo test, p = 0.035). Across all species and habitats, the comparative analysis of individual traits showed that alien species have 25% higher plant height, 250% higher leaf mass, 19% lower leaf dry matter content, 10% higher SLA, and 17% longer flowering duration than native species. Overall, our findings demonstrated that aliens differ in many traits from native species in the Italian Alps, but that many of these differences disappear when one compares aliens and natives that co-occur in the same types of habitats.

Ecological studies often require studying the common structure of a pair of data tables. Co-inertia analysis is a multivariate method for coupling two tables. It is often neglected by ecologists who prefer the widely used methods of redundancy analysis and canonical correspondence analysis. We present the co-inertia criterion for measuring the adequacy between two data sets. Co-inertia analysis is based on this criterion as are canonical correspondence analysis or canonical correlation analysis, but the latter two have additional constraints. Co-inertia analysis is very flexible and allows many possibilities for coupling. Co-inertia analysis is suitable for quantitative and/or qualitative or fuzzy environmental variables. Moreover, various weighting of sites and various transformations and/or centering of species data are available for this method. Hence, more ecological considerations can be taken into account in the statistical procedures. Moreover, the principle of this method is very general and can be easily extended to the case of distance matrices or to the case of more than two tables. Simulated ecological data are used to compare the co-inertia approach with other available methods.

Assessing trait responses to environmental gradients requires the simultaneous analysis of the information contained in three tables: L (species distribution across samples), R (environmental characteristics of samples) and Q (species traits). Among the available methods, the so-called fourth-corner and RLQ methods are two appealing alternatives that provide a direct way to test and estimate trait-environment relationships. Both methods are based on the analysis of the fourth-corner matrix which crosses traits and environmental variables weighted by species abundances. However, they greatly differ in their outputs: RLQ is a multivariate technique that provides ordination scores to summarize the joint structure among the three tables, whereas the fourth-corner method mainly tests for individual trait-environment relationships (i.e. one trait and one environmental variable at a time). Here, we illustrate how the complementarity between these two methods can be exploited to promote new ecological knowledge and to improve the study of trait-environment relationships. After a short description of each method, we apply them to real ecological data to present their different outputs and provide hints about the gain resulting from their combined use. Read More: http://www.esajournals.org/doi/abs/10.1890/13-0196.1

Although experiencing strong anthropogenic pressures in many estuaries, the ecology of tidal freshwater areas remains largely undocumented. As part of a restoration project in the freshwater zone of the Schelde estuary (Belgium), a new tidal habitat restoration technique (Controlled Reduced Tide system, CRT) was hypothesised to successfully compensate for the impairment of contemporary habitats. The suitability of this newly-created habitat (CRT) and the estuary was investigated over a period of three years for its macroinvertebrate community development. In both the estuary and the CRT, habitats along a flooding gradient were monitored. Differences between the CRT and reference sites in community functioning were explored according to environmental characteristics and organism biological attributes using the RLQ ordination analysis together with the fourth-corner method. Frequently flooded reference sites exhibited environmental characteristics resulting from a hydrological shear stress. In the CRT, after a rapid removal of the terrestrial fauna at low and mid elevations, the low-energy hydrology led to taxonomic and functional enrichment. The RLQ analysis produced significant environmental filtering of biological attributes mainly related to the terrestrialaquatic transition and to the environmental stressors. This provides an example of life history modification via estuarine ecosystem management.