Importance of invasion mechanisms varies with abiotic context and plant invader growth form

Abstract

Many invasion hypotheses propose biotic interactions as the main mechanism to explain non-native species' success. Despite the evidence that the strength of biotic interactions varies with abiotic context, it remains unclear whether the importance of the different mechanisms proposed to explain invasion predictably varies with the abiotic context and whether this variation is consistent across different growth forms. We reviewed studies at a global scale to evaluate whether evapotranspiration, latitude, precipitation and temperature influence the importance of disturbance, enemy release, facilitation, and novel weapons mechanisms to explain non-native plant invasions. In total, we calculated 171 effect sizes for ~300 non-native plant species covering a wide range of environmental conditions and growth forms. Environmental context and plant growth form influenced the role played by each invasion mechanism. The importance of disturbance in facilitating invasion exhibited a quadratic relationship with latitude and temperature, and decreased with increasing precipitation. In mixed communities and trees, disturbance was mediated by either evapotranspiration, latitude, precipitation or temperature. Enemy release exhibited a quadratic relationship with evapotranspiration, latitude and precipitation, and it was positively related to temperature. The importance of enemy release was also contingent on growth form and was highly context-dependent. Enemy release responses for grasses, and trees were modulated by either evapotranspiration, latitude, precipitation or temperature. The importance of facilitation decreased with increasing temperature. In forbs, facilitation decreased with evapotranspiration and temperature. The importance of novel weapons was more strongly confirmed for studies conducted at lower evapotranspiration, precipitation and higher latitudes, and exhibited a quadratic relationship with temperature. Synthesis. Our results show that environmental conditions not only filter non-native species depending on physiological tolerances but may also influence the importance of invasion mechanisms.