Invasional meltdowns occur when one invasive species promotes the fitness and spread of another non-native species, which results in ecosystem level state changes. These species interactions can easily shift ecosystems away from the way they once functioned. Before humans had the ability to introduce non-native species across Earth’s habitats, some exotic species still did make it to new habitats, but the rate of introduced species has skyrocketed since the dawn of our time. In a paper published in the Journal of Ecology, Jamie R. Wood and his team show how mammals from two continents and ectomycorrhizal fungi from North America promote the invasion of an invasive pine in New Zealand.
New Zealand
Pines are highly dependent on their mycorrhizal counterpart. Without pairing with their fungal mutualists, these trees become limited by water and nutrients, and their invasion in novel habitats may become impeded. Unfortunately for ecosystems with invasive pines, many ectomycorrhizal fungi disperse easily via wind. It has been shown that once invasive fungi infiltrate a new habitat, mammals can also disperse their spores through mycophagy. That’s right, mammals that consume fruiting bodies associated with pines, pass some fungal spores through their digestive system unperturbed, dispersing the fungi across the landscape. Prior to human establishment until 750 years ago, New Zealand was constrained to just three mammals-three species of bats to be exact. Two ecosystem altering mammals have since then been introduced; the European red deer (Cervus elaphus) and Australian brushtail possum (Trichosurus vulpecula).
Australian brushtail possum (Trichosurus vulpecula)
By using fecal analyses, video monitoring and a bioassay experiment, the scientists in this paper have uncovered some quite interesting results. The droppings from each mammal contained the DNA from both native and non-native fungi, showing a limited fungal feeding preference. Surprisingly, the invasive pine, Pinus contorta, became inoculated by North American ectomycorrhizal genera Rhizopogon and Suillus through the fecal pellets of the two exotic mammals. Oppositely, the native beech trees (Lophozonia menziesii) did not become inoculated with invasive fungal mutualists through the non-native mammalian vector.
Ultimately, this paper showed how introduced mammals can enhance the spread of non-native fungi, that improve the fitness of non-native plants. The native fungi and plants over time may be outcompeted by the advancing non-natives, because this tripartite interaction benefits the invasive species. The mammals get a meal, the fungi gain a dispersal agent, and the plants acquire their fungal mutualist. The native fungi did not germinate after being consumed, so there is likely going to be a shift in the fungal community, as the species that do germinate past a mammalian gut will be selected for. Invasional meltdowns like these are occurring across Earth’s landscape, and are shifting ecosystems away from how they once functioned. In New Zealand, invasive fauna and flora are flourishing as their interactions facilitate one another. The forest floor as a result is changing.
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