How abiotic context affects plant invasions mechanisms

Mariana Chiuffo discusses her recent paper: ‘Importance of invasion mechanisms varies with abiotic context and plant invader growth form‘.

You can also read this blog post in Spanish here.

Human activity has caused an unprecedented geographic reorganization of non-native plants. At a global level, 3.9% of vascular plants have become naturalized somewhere else (van Kleunen et al., 2015). In this context, understanding the underlying processes influencing non-native species invasions is crucial to predicting and controlling future invasions. Intentionally or unintentionally, humans influence the geographical distribution and composition of the species being transported (Gallien & Carboni, 2017; van Kleunen et al., 2015).

However, only those overcoming the environmental filtering will be able to thrive (Gallien & Carboni, 2017). Those environmentally adapted species lose enemies, competitors and mutualists from their native range, and gain novel interactions with native species of the recipient community (Colautti et al., 2004; Mitchell et al., 2006).

The balance of those biotic interactions gains and losses may limit or facilitate non-native species establishment. Indeed, many of the biological invasion hypotheses propose biotic interactions as the main mechanism to explain non-native species success (Mitchell et al., 2006). Despite the evidence that the strength of biotic interactions varies with the abiotic context, we lacked a clear understanding about the importance of invasion mechanisms across abiotic gradients.

I first got interested in this topic when I was still a PhD student working on the response of non-native and native ruderal species to disturbance in caldén (Prosopis caldenia) woodland of central Argentina.  At the time I was reading a lot about the discrepancy amongst studies evaluating the relationship between plant invasions and disturbance, and, very influenced by classic papers such as Bertness & Callaway (1994) and Grime (1977), I started to conceive the idea of this study.  Contradictory results in these relationships may be explained by context differences, namely importance of invasion mechanisms may vary across space, i.e. they may be context dependent.  In nature, one factor that explains the context dependency of biotic interactions is the environmental context (i.e. the set of abiotic conditions such as light, precipitation, temperature) (Chamberlain et al., 2014; Maron et al., 2014; Thompson, 1988). 

With this idea and theoretical background in mind, I wrote a proposal and applied for a postdoc scholarship – that I got! – to work with Martin Nuñez and Mariano Rodriguez-Cabal research group in Bariloche (Patagonia, Argentina).  It was during my postdoc in Bariloche, where I still live, that I started to explore this idea.  I live literally surrounded by amazing abiotic gradients (e.g. in Patagonia precipitation increases from about 300 mm in the east to 3000 mm in the west due to the Andes’ rain shadow (Paruelo et al., 1998) which are both a great source of inspiration and amazing systems to study the context-dependency of biotic interactions -and a place of endless beauty!

Abiotic gradients in Andes mountains in northwestern Argentinean Patagonia. In the area, temperature varies with altitude, and precipitation varies with longitude. Photo by Mariana Chiuffo.

What we did, what we found, and why it matters!

As a first step towards exploring the context dependency of invasion mechanisms, with my new – at the time -lab mates, we conducted a revision to evaluate whether evapotranspiration, latitude, precipitation and temperature influence the importance of four common mechanisms used to explain the success of non-native species: disturbance, enemy release, facilitation, and novel weapons.  We found evidence showing that abiotic context influenced the importance of invasion mechanism.  Responses also vary depending on growth form.  Understanding the context dependency of invasion mechanisms across environmental gradients is important as it may help to provide a unified conceptual framework that integrates different invasion mechanisms. 

Our results show that abiotic conditions influence the importance of plant invasion mechanisms.

Results seemingly contradictory regarding the importance of an invasion mechanisms may be in fact explained by differences in the environmental context or specific species traits such as growth form.  Our results suggest that climate change may influence plant communities’ composition by affecting the invasion mechanisms that facilitate non-native species establishment.  We suggest to include both the direct effects of shifting climate conditions and the indirect effects, through modifications of biotic interactions, when predicting the effects of climate change on non-native species performance.

Mariana Chiuffo National University of Comahue, Argentina

Read the full article online: Importance of invasion mechanisms varies with abiotic context and plant invader growth form.

You can also read this blog post in Spanish here.

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