Exotic Mammals Disperse Exotic Fungi That Promote Invasion by Exotic Trees

Abstract

Biological invasions are often complex phenomena because many factors influence their outcome. One key aspect is how non-natives interact with the local biota. Interaction with local species may be especially important for exotic species that require an obligatory mutualist, such as Pinaceae species that need ectomycorrhizal (EM) fungi. EM fungi and seeds of Pinaceae disperse independently, so they may use different vectors. We studied the role of exotic mammals as dispersal agents of EM fungi on Isla Victoria, Argentina, where many Pinaceae species have been introduced. Only a few of these tree species have become invasive, and they are found in high densities only near plantations, partly because these Pinaceae trees lack proper EM fungi when their seeds land far from plantations. Native mammals (a dwarf deer and rodents) are rare around plantations and do not appear to play a role in these invasions. With greenhouse experiments using animal feces as inoculum, plus observational and molecular studies, we found that wild boar and deer, both non-native, are dispersing EM fungi. Approximately 30% of the Pinaceae seedlings growing with feces of wild boar and 15% of the seedlings growing with deer feces were colonized by non-native EM fungi. Seedlings growing in control pots were not colonized by EM fungi. We found a low diversity of fungi colonizing the seedlings, with the hypogeous Rhizopogon as the most abundant genus. Wild boar, a recent introduction to the island, appear to be the main animal dispersing the fungi and may be playing a key role in facilitating the invasion of pine trees and even triggering their spread. These results show that interactions among non-natives help explain pine invasions in our study area.

The unnoticed effect of a top predator on complex mutualistic ecological interactions

“…), contributing to the relatively high success of the genus. Furthermore, this interaction facilitates long-distance dispersal of this exotic plant in the lowland xeric habitats of the Canaries, together with the native Raven (Corvus corax) (Nogales et al 1999), and is a good example of how exotic species can aid each other in their dispersal (see complex interactions between invasive species in Nuñez et al 2013 and references therein).…”

Mutualistic Interactions and Biological Invasions

“…Invasion complexes are probably more common and influential on islands where ecosystems are simpler than they are on mainland, but more work is needed to test this hypothesis. Wild boar and deer on Isla Victoria (Argentina) enhance the invasion of alien pine trees by dispersing via their feces the ectomycorrhizal fungi needed for the establishment of the pines (Nuñez et al 2013). …”

Non-native and native organisms moving into high elevation and high latitude ecosystems in an era of climate change: new challenges for ecology and conservation

“…Plants and their associated fungi disperse independently; therefore dispersal limitations for mycorrhizae (e.g. lack of dispersal vector such as large herbivores, Nuñez et al 2013) may hamper the rate of plant movement.…”