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Transcript
Ecological Processes and the Spread of Non-native species By Nicolas Viveros and Jessica Oh Chapter Overview Possible factors that affect spread • Population growth • Dispersal • Biotic interactions • Spatial and temporal heterogeneity Complex patterns of spread • Lag times • Boom and bust Population growth • Detection threshold • Allee effect Dispersal • Long-distance portion is most important factor in dispersal • Generally unable to find long-distance dispersal estimates – Methods – seed traps, radio collars • Different dispersal vectors – Wind, water – Animals – seeds – Humans Biotic interactions • Predation – Positively affect spread – Predators remove competitors – Negatively affect spread – Reduce the invasive species’ population and number of individuals able to disperse • Competition – Negatively affect spread – reduce access to resources, generally reduce reproduction • Mutualism – Positively affect spread – mutualist increases the number of individuals able to disperse – Negatively affect spread - absence of a mutualist Heterogeneity • Organisms react to variation in the landscape in both biotic and abiotic factors as well as temporal variation Lag time • Definition: time from initial establishment to subsequent spread • Lag times vary widely Potential sources of lag time • Nature of population growth trajectories • Thresholds to detection • Allee effect • Dispersal • Biotic interactions • Heterogeneity • Genetic augmentation Boom and bust • Non-native populations increase dramatically in their numbers and geographic extent after initial establishment and then dramatically decline in numbers and extent • Can be due to a variety of ecological reasons – mechanism is unclear Questions • How can we distinguish between species appearing at new locations and species merely increasing in numbers at these locations? How is spread different from population growth above a detection threshold? Questions • What is a detection threshold? How would you define it – number of individuals, biomass, etc. Is it species specific? Questions • How does the Allee effect affect spread? What can cause an Allee effect? Questions • Figure 8.6 p. 170 • What could potentially explain the greater distance in lower temperature counties than the higher temperature counties at the start of the graph. What you think is happening in the middle of the graph? Questions • How can invasive species spread rapidly after years of stagnant population growth? (lag time) Questions • If predicting rates of spread, what factors/variables within heterogeneity would you look for? Questions • Do pathogens and parasites have a slower or faster dispersal than wildlife species? Why? What kind of dispersal curves do they have? • Table 7.1 p. 143 Questions • How would the spatial heterogeneity differ in a terrestrial model versus a marine model? More or less? Questions • How would we factor different levels of heterogeneity (temporal and spatial)? Finer or more detailed? Questions • What could be barriers in eradicating initial populations of known invasive species?
