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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?