Exotic wild boars and native wild guinea pigs maintain plant diversity in Argentinean coastal grasslands by decreasing plant dominance.

Question: In productive grasslands highly dominated by a single plant species, herbivores can promote overall plant diversity. Wild boars (Sus scrofa) often decrease species diversity, alter regeneration and change community composition in their native and invader ranges while digging and uprooting vegetation for feeding. In addition, wild guinea pigs (Cavia aperea), a small vertebrate herbivore native to South America, concentrate their feeding activities in open patches where they also affect plant diversity, biomass and composition. In this context, can wild‐boar disturbances promote plant diversity in herbaceous systems characterized by a highly dominant species? Can native wild guinea pigs magnify these impacts? Location: Coastal grasslands and salt marshes of the northeastern part of the temperate Argentine pampas, that are dominated by native or exotic herbaceous species. Methods: We first analyzed alpha‐ and beta‐diversity of plant assemblies in three natural coastal herbaceous areas, invaded by wild boars, through samplings (comparing disturbed and undisturbed areas) and experiments (using exclosures and control plots). Then, we analyzed whether wild guinea pigs could affect patch recovery (alpha‐ and beta‐diversity) after wild‐boar disturbances in one site. Results: Wild boars enhanced alpha‐diversity (compared to undisturbed areas) but had no significant effect on beta‐diversity. Nevertheless, wild guinea pigs feeding on wild‐boar disturbances increased between‐patch heterogeneity in species composition (i.e., beta‐diversity). Conclusion: Wild boars remove vegetation in patches that, without subsequent wild‐guinea‐pig herbivory, dominant species rapidly recover. Wild‐guinea‐pig herbivory allows different subordinate species to peak at different disturbed patches, contributing to larger species richness at larger scales in areas otherwise occupied by highly dominant plant species. In a wider context, these results imply that the joint action of different‐sized exotic and native herbivores can help to maintain plant species diversity in highly plant‐dominated grasslands. [ABSTRACT FROM AUTHOR]