Highly invasive species are more dependent on mutualisms: evidence from tree invasions and mycorrhizal fungi

JAIME MOYANO; MARIANO A. RODRIGUEZ-CABAL; MARTIN A. NUÑEZ

Birmingham

Congreso; British Ecological Society (BES) 2018 annual meeting; 2018

British Ecological Society (BES)

The question why some plant species become invasive while others do not remains elusive. The high dependency on mutualistic interactions may limit the ability of spreading for some species. It has been proposed that invasive species should have low dependency on mutualisms. Evidence from many cases of invasion support this general pattern of increasing invasiveness with decreasing dependency on mutualisms, however no study has quantified yet the degree of dependency on mutualisms along a gradient of pant invasiveness. We tested this idea with Pinus since this genus includes numerous invasive and non-invasive species and form a highly specific mutualistic interaction with ectomycorrhizal fungi (EMF). Importantly, there is great variation between Pinus species dependency on EMF at the seedling stage, when they are most vulnerable. We performed a literature search on the effect of EMF on Pinus seedling growth to evaluate the level of dependency to EMF at the seedling stage. Then we matched this degree of dependency with data on Pinus species invasiveness. For Pinus species, invasiveness is highly and negatively correlated with seed size. Our database included 641 observations on 27 Pinus species from 93 papers. Our results show that Pinus species that are more invasive are more dependent on EMF. Seedling growth of Pinus species with smaller seeds was more benefited from EMF. Tolerance of big seeded species seedlings to stressful conditions during establishment may explain their lack of dependence on EMF. The limited dispersal of larger seeds may limit the spread of these species. For small seeded species, a higher survival rate of seedlings aided by this mutualism with EMF may result in a higher population growth rate. Our results contradict the idea that highly invasive species are less dependent on mutualists, and suggest that a higher dependency may increase their invasive capacity.