Department of Biology /Nupélia, Maringá State University, Maringá, Paraná, Brazil
Invasive aquatic macrophytes: Propagule pressure, invasibility and impacts
Invasive species are a matter of concern because they can cause severe impacts in freshwater ecosystems. In my presentation, I will address some abiotic and biotic factors that influence the invasion success of macrophytes and the main impacts caused by these plants when they become invasive. I will rely mainly on examples of tropical and sub-tropical ecosystems, which are less studied than temperate ones. Some macrophyte species disperse efficiently, have efficient vegetative reproduction and fast regeneration from disturbances, what make them successful invaders. The “propagule pressure” is one of the mechanisms related to their invasive potential. In addition to seeds, plant fragments are also dispersed by water flow, boats, aquatic birds and fish. Owning to the propagule pressure, macrophytes can spread and colonize distant habitats in the waterscape. On the other hand, stressful conditions related to environmental filters (e.g., underwater light, water and sediment nutrients, wind disturbance) limit invasion by macrophytes. Alteration of these filters by humans (e.g., construction of reservoirs and pollution) may increase the invasion likelihood. Biotic filters are also important to explain the invasion success. For example, the density and diversity of native macrophytes may confer resistance against invasions (“biotic resistance hypothesis”). Despite biotic and abiotic resistance, non-native macrophytes have successfully invaded freshwater ecosystems, where they affect individuals, populations, communities and ecosystems. Of special concern is the invasion by “engineering macrophytes”, because they may change entire ecosystems very quickly. In summary, the same main hypotheses used by invasion biologists who work with terrestrial plants can be applied to explain invasions by macrophytes. Understanding the main causes and consequences of macrophyte invasion is necessary to prevent their spread and impacts in aquatic ecosystems.