Isabel Pérez Postigo¹, Jörg Bendix², Heike Vibrans Lindemann³ and Ramón Cuevas Guzmán¹

¹Universidad de Guadalajara, Centro Universitario de la Costa Sur, Av. Independencia Nacional #151, C.P. 48900, Autlán, Jalisco, Mexico
²Philipps-Universität Marburg, Germany
³Colegio de Postgraduados Texcoco, Mexico

e-mail: perezpostigo@gmail.com

Disturbed areas are particularly prone to invasion by alien species (Espinosa-García & Villaseñor 2017). Though various hypotheses exist on the factors that influence invasive plant distribution, little is known about the relationship with environmental conditions, especially in the tropics (Pyšek & Richardson 2006, Rejmánek et al. 2005). In Mexico, a megadiverse country, studies on invasion ecology have been restricted mainly to central Mexico and to floristic comparisons between states (Espinosa-García et al. 2004, Espinosa-García & Villaseñor 2017, van Kleunen et al. 2015, Villaseñor & Espinosa-García 2004). In order to shed some light onto regional patterns we ask: (i) what is the floristic composition of alien and native herbaceous species in the ruderal vegetation in western Mexico?, and (ii) which environmental variables influence species distribution and abundance patterns of the alien and native herbaceous species?

We worked along an elevational gradient from the Jalisco state coast up to 2150 m in the Sierra de Manantlán, located in the northern part of the Southern Sierra Madre. Alien and native herb richness and abundance was documented in the field using 37 plots of 5 × 1 m² along with various environmental factors; other variables were obtained from databases. Floristic composition, species richness, abundance and their relation to 17 selected environmental variables were analysed using random forest modelling methods.

We registered 353 herbaceous species, of which 9% are introduced. The family Poaceae was richest in species for aliens and natives, with taxa present in all plots and among the most abundant. We found a positive correlation between native and introduced species richness but no correlation between abundances. Species composition formed clear clusters along the elevation gradient with variation in species composition, especially in plant families and a significant positive correlation between alien species abundance and elevation. For the behaviour of alien species richness along the elevation gradient no pattern was found.

This indicates the dominating influence of other environmental variables for species richness. The most important variables returned by the random forest modelling for alien species richness were distance to roads and highways, mean and maximum temperature and slope. Variable importance analysis for alien abundance patterns in general was not significant. Single species abundance patterns of Melinis repens, one of the most abundant taxa, showed good model performances. Pattern identification helps us to understand the factors shaping present and future distributions of exotic herb species.

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