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Ecological Impacts of Invasive Species Marieke and Ann Genetic Level • Defined as alterations to the native gene pool through hybridization and introgression – Easy definition is backcrossing, producing gene flow between the native and invasive New Zealand grey duck Australian black duck Hawaiian duck Individual Level • Defined as alterations to the fitness or traits of individuals, including changes in morphology or behavior Population Level • Competition: non-natives outcompete natives • Predation: most discussed because of devastating impacts on evolutionarily naïve natives • Physical: physical attributes of the invader Community Level • Mass extinctions: evolutionary isolated systems receive a novel predator or herbivore • Community alterations: whole community changes, especially on islands Ecosystem Level • Altering the flow of materials through the ecosystem or the disturbance regime Landscape, Regional and Global Level • Endemic species most affected, naïve • Homogenization: the idea that the world will eventually look the same across all continents Questions?! • Think of some examples not in the chapter and classify their impact (genetic, individual, population, community, ecosystem, global). • Do you agree with the following statement: “…impacts will generally only result from species that have moved through all previous stages.” • What is the role of humans in the struggle to maintain “genetically pure” native populations? How do we stop hybridization? • In the Species Survival Plan for tuataras three options for recovery are listed: – Do nothing – Eradicate the kiore – Captive breeding program for tuataras, with reintroduction • Which option(s) would you choose? • Which, if any, of the different levels discussed are the most “insidious”? – (The authors believe the genetic level impacts are most destructive.) Figure 9.3 Fecundity (fruits/plant) of Arabis fecunda individuals through time, in control and treatment plots. The treatment was the removal of spotted knapweed (Centaurea maculosa), an invasive plant in the northwestern USA. Although fecundity was influenced by annual climatic events (i.e. rainfall), the removal of the invasive consistently resulted in higher rates of reproduction for the rare native. From Lesica and Shelly 1996. Figure 9.4b Size-class frequency distribution (SVL = snout-to-vent length) for tuatara on kiore-free (uninvaded) and kiore-inhabited (invaded) islands. The distributions differ significantly, with a noticeable absence of small juvenile tuatara on invaded islands. Figure 9.5 Histograms of total ant species richness in sites with and without the imported red fire ant (Solenopsis invicta). Figure 9.6 Histograms of native ant abundance over sites with and without the imported red fire ant.