Detrimental effects of anthropogenic disturbances on ant-mediated seed dispersal services: A global meta-analysis

Anthropogenic disturbances, particularly the loss of natural and semi-natural habitats, have global impacts on ecosystems, notably affecting vital ecological services like seed dispersal by ants, which are crucial for about 4.5 % of plant species. These effects depend on factors such as biogeographical origins of the biota, plant growth form, plant and seed traits, interacting ant species, and local site characteristics. In this meta-analysis, we investigated the overall trends in the impact of anthropogenic disturbances on ant-mediated seed removal rates and dispersal distances. We also explored how these services are influenced by disturbance type, environmental factors (e.g., temperature, precipitation, and biome), plant and seed traits (e.g., dispersal syndrome, its interaction with plant growth form, and seed size), and disperser species characteristics (e.g., keystone species). We analyzed 76 independent studies, comprising 430 experiments related to seed dispersal services (353 focused on seed removal rates and 77 on seed dispersal distances). Our findings revealed that anthropogenic disturbances negatively impact seed removal rates, although not consistently across all abiotic and biotic contexts, while having no significant effects on seed dispersal distances. The relationship between disturbances and seed removal was influenced by disturbance type, biome, plant and seed traits. Specifically, mining activities decreased seed removal rates, and disturbances in general reduced seed removal by ants in Mediterranean forests, woodlands, deserts and xeric shrublands. Interestingly, myrmecochorous trees were especially vulnerable in seed removal compared to other plant growth forms or dispersal syndromes, suggesting that the impacts of disturbance on ant-mediated seed dispersal could lead to major modifications in the structure of forest ecosystems. Our study highlights the importance of conserving ant-mediated seed dispersal, particularly in myrmecochory hotspots, to protect this critical ecological service.