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Ecological Processes and the Spread of Non-native species
By Nicolas Viveros and Jessica Oh
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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
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Population growth Detection threshold Allee effect
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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
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Biotic interactions Predation Competition Mutualism
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
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Heterogeneity Organisms react to variation in the landscape in both biotic and abiotic factors as well as temporal variation
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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
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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
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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?
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Questions What is a detection threshold? How would you define it – number of individuals, biomass, etc. Is it species specific?
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Questions How does the Allee effect affect spread? What can cause an Allee effect?
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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?
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Questions How can invasive species spread rapidly after years of stagnant population growth? (lag time)
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Questions If predicting rates of spread, what factors/variables within heterogeneity would you look for?
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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
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Questions How would the spatial heterogeneity differ in a terrestrial model versus a marine model? More or less?
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Questions How would we factor different levels of heterogeneity (temporal and spatial)? Finer or more detailed?
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Questions What could be barriers in eradicating initial populations of known invasive species?
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