What drives invasibility? A multi‐model inference test and spatial modelling of alien plant species richness patterns in northern Portugal

Abstract

Understanding and predicting biological invasions can focus either on traits that favour species invasiveness or on features of the receiving communities, habitats or landscapes that promote their invasibility. Here, we address invasibility at the regional scale, testing whether some habitats and landscapes are more invasible than others by fitting models that relate alien plant species richness to various environmental predictors. We use a multi-model information-theoretic approach to assess invasibility by modelling spatial and ecological patterns of alien invasion in landscape mosaics, and by testing competing hypotheses of environmental factors that may control invasibility. Because invasibility may be mediated by particular characteristics of invasiveness, we classified alien species according to their C-S-R plant strategies. We illustrate this approach with a set of 86 alien species in northern Portugal. We first focus on predictors influencing species richness and expressing invasibility, and then evaluate whether distinct plant strategies respond to the same or different groups of environmental predictors. We confirmed climate as a primary determinant of alien invasions, and as a primary environmental gradient determining landscape invasibility. The effects of secondary gradients were detected only when the area was sub-sampled according to predictions based on the primary gradient. Then, multiple predictor types influenced patterns of alien species richness, with some types (landscape composition, topography and fire regime) prevailing over others. Alien species richness responded most strongly to extreme land management regimes, suggesting that intermediate disturbance induces biotic resistance by favouring native species richness. Land-use intensification facilitated alien invasion, whereas conservation areas hosted few invaders, highlighting the importance of ecosystem stability in preventing invasions. Plants with different strategies exhibited different responses to environmental gradients, particularly when the variations of the primary gradient were narrowed by sub-sampling. Such differential responses of plant strategies suggest using distinct control and eradication approaches for different areas and alien plant groups.

A multi-scale modelling framework to guide management of plant invasions in a transboundary context

“…Vicente et al 2010Vicente et al , 2011Fernandes et al 2014). It is located within the area predicted as suitable for the study species by the regional scale model (see below), hence its choice for the fine-scale component of this work.…”

“…To allow for the identification of potentially important non-climatic predictors, a climatically homogeneous area (Fig. 2c) was selected within the region, as performed in Vicente et al (2010); see "Model Calibration" section.…”

“…SDMs have been widely used in the field of biological invasions (e.g. Peterson 2003;Broennimann et al 2007;Vicente et al 2010Vicente et al , 2011Fernandes et al 2014). Despite their usefulness, a recurrent difficulty in applying SDMs is the likelihood of model overfitting due to a high ratio between the number of environmental predictors and the often-scarce species occurrence data (Guisan and Thuiller 2005).…”

Do Landscape Structure and Socio-Economic Variables Explain the Solidago Invasion?

“…multiple interacting factors including abiotic conditions, human activity and habitat type, which may operate at different spatial scales (Kumar et al 2006;Pauchard and Shea 2006;Catford et al 2009;Milbau et al 2009;Vicente et al 2010Vicente et al , 2014González-Moreno et al 2014). Nevertheless, they can be described and understood using different kinds of simplified models.…”

“…Therefore, for modelling purposes, different characteristics of landscape diversity and habitat edges have usually been employed (e.g. Deutschewitz et al 2003;Ohlemüller et al 2006; Bartuszevige et al 2006;Ibáñez et al 2009b;Vicente et al 2010Vicente et al , 2014Catford et al 2011;González-Moreno et al 2013.…”