Students

Anne Hoschuied [Niche conservatism in invasive plants] University of Groningen – Netherlands

Explanations for the success of alien species have frequently been based on their degree of niche overlap with native species. In order to predict and understand future invasions, we thus need to know if ecological traits/requirements of aliens remain similar [niche conservatism (NC)] or change [niche lability (NL)] in their novel habitat.  Here we review the evidence for either NC or NL and the importance of these concepts for the further development of the field of invasion biology. For this we first discuss different views of the niche, and their implications for NC versus NL. Building from this, we address three key topics relevant to this discussion: evolutionary divergence vs. convergence of traits, conservation vs. adjustment of the bioclimatic niche, and the phylogenetic stasis vs. evolution of the niche. We emphasize the importance of the use of an appropriate niche concept for the accurate description and prediction  of the fate of introduced aliens. In a meta-analysis, we find that NC in aliens is much more frequent than NL, making the concept of NC useful in predicting future invasions.  In contrast, we find traits to be more flexible, which suggests that aliens change their traits in order to conserve their niche.

Summary of 70 studies showing direct or indirect support for or against the idea of niche conservatism (NC) or lability (NL) in natural and invaded communities. Each section of the bar shows percentages of significant results showing support of NC or NL. Inside each bar, the number of studies corresponding to each category is presented.

Evey Jongepier  [Savannah woody species distribution is interactively driven by environmental filters, stochastic disturbances and clonal ability ] University of Groningen – Netherlands

Recruitment, persistence and dispersal ultimately determine the distribution and abundance of plants across the landscape. Their relative role in shaping African savannahs is however poorly understood. This study examined how the importance of recruitment, persistence and dispersal for local and regional woody species dynamics varied along environmental gradients. Hereto, we assessed differences in the distribution and abundance of clonal and seeder species. Since clonality provides benefits in terms of local recruitment success and persistence, factors that impose recruitment limitation would favour clonal species in terms of abundance, whereas environmental conditions that increase local extinction risk would favour clonal species community membership.  However, environmental conditions that promote dispersal assembly would support seeder species community membership on account of their superior dispersal ability. Our results showed that drought helped the relative abundance but not the relative number of clonal species present. Consequently, clonality, as a community-level trait, decreased along the rainfall gradient. Fire frequency had a positive effect on the relative abundance of clonal species but an opposite, negative effect on clonal species community membership. Therefore, community clonality was independent of fire frequency. Finally grazing pressure did not affect clonal species abundances but had a non-linear effect on the relative number of clonal species and consequently on community clonality. These results imply that both drought and fire frequency impose recruitment limitation whereas intermediate grazing pressure favours persistence. In conclusion, we find that high water?/grazing pressure as well as frequent fire favour superior colonizers.

Model estimates of the effect of environmental factors on clonality in Hluhluwe iMfolozi park. Effect sizes represent the proportional change for clonal-species relative to seeders (i.e. zero-centred relative rates and odds ratios for the Poisson model and the logistic models, respectively). Non-zero-overlapping 95% CI indicate significant differences between clonals and seeders in their relationship with standardized environmental factors. Models were based on 35 species (23 seeders and 12 clonals) and 721-770 plots (see text for details). Analyses of species abundances, richness and clonal abundances were performed using zero-inflated Poisson MCMCglmm, multiple logistic regression and logistic MCMCglmm, respectively.

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