Understanding the impacts of global change on ecological communities is a major challenge in modern ecology. The gain or loss of particular species and the disruption of key interactions are both consequences and drivers of global change that can lead to the disassembly of ecological networks. We examined whether the disruption of a hummingbird–mistletoe–marsupial mutualism by the invasion of non‐native species can have cascading effects on both pollination and seed dispersal networks in the temperate forest of Patagonia, Argentina. We focused on network motifs, subnetworks composed of a small number of species exhibiting particular patterns of interaction, to examine the structure and diversity of mutualistic networks. We found that the hummingbird–mistletoe–marsupial mutualism plays a critical role in the community by increasing the complexity of pollination and seed dispersal networks through supporting a high diversity of interactions. Moreover, we found that the disruption of this tripartite mutualism by non‐native ungulates resulted in diverse indirect effects that led to less complex pollination and seed dispersal networks. Our results demonstrate that the gains and losses of particular species and the alteration of key interactions can lead to cascading effects in the community through the disassembly of mutualistic networks.

Understanding the impacts of global change on ecological communities is a major challenge in modern ecology. The gain or loss of particular species and the disruption of key interactions are both consequences and drivers of global change that can lead to the disassembly of ecological networks.We examined whether the disruption of a hummingbird-mistletoe-marsupial mutualism by the invasion of non-native species can have cascading effects on both pollination and seed dispersal networks in the temperate forest of Patagonia, Argentina. We focused on network motifs, subnetworks composed of a small number of species exhibiting particular patterns of interaction, to examine the structure and diversity of mutualistic networks. We found that the hummingbirdmistletoe-marsupial mutualism plays a critical role in the community by increasing the complexity of pollination and seed dispersal networks through supporting a high diversity of interactions. Moreover, we found that the disruption of this tripartite mutualism by non-native ungulates resulted in diverse indirect effects that led to less complex pollination and seed dispersal networks. Our results demonstrate that the gains and losses of particular species and the alteration of key interactions can lead to cascading effects in the community through the disassembly of mutualistic networks.

Many invasion hypotheses propose biotic interactions as the main mechanismto 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.2. 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.3. 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 nonnative species depending on physiological tolerances but may also influence the importance of invasion mechanisms.