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The Landscape Ecology of Invasive Spread

The Landscape Ecology of Invasive Spread. Question: How is spatial pattern expected to affect invasive spread? Premise: Habitat loss and fragmentation leads to spread of invasives

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The Landscape Ecology of Invasive Spread

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  1. The Landscape Ecology of Invasive Spread • Question: How is spatial pattern expected to affect invasive spread? • Premise: Habitat loss and fragmentation leads to spread of invasives • Definition: Landscape ecology: not regional level but the study of spatial pattern of resources, habitat, etc. on ecological processes

  2. History • Reaction Diffusion Models • Theory by Skellam (1951) • Tested by Andow et al (1990)(animal) and Higgins and Richardson (1996 and others) (plants) • Parameters: population density, population growth rate and diffusion coefficient across a heterogeneous landscape

  3. From: Andow et al 1990

  4. Integrodifference equation models • Parameters: population growth at each spatial point and the ease of movement between points (dispersal kernel). • Stage structured dispersal important. Long distance dispersal, though rare, determines spread • Problem: As in Reaction-diffusion, assumes the landscape is homogeneous

  5. Neubert and Caswell (2000):Traveling Invasion Wave

  6. Neutral Landscape Models • Theory: Invasive Spread occurs above a threshold limit of disturbance, which depends on the spatial pattern of the disturbance • Definition: Connectivity: The ability of organisms to move among patches • Implication: To reduce invasive spread, reduce the extent and connectivity of disturbances.

  7. A: RANDOM: Spread in a random landscape B: FRAGMENTED: Spread across a fragmented fractal landscape C: CLUMPED: Spread across a clumped fractal landscape with spatially autocorrelated disturbance

  8. A: An invasive species with poor dispersal ability able to move only to adjacent cellsB: Invasive spread for a species with better dispersal. Low levels fo disurbance, fragmentation limits spread, but at intermediate levels, species able to spread farther by using fragments as stepping stones.C: Invasive species in fragmented fractal landscapes that vary with dispersal ability. Good dispersers less influenced by fragmentation

  9. Landscape transformation is the final stage of a terminal invasion

  10. Dispersal success declines as lacunarity thresholds, especially on clumped landscapes

  11. Bergelson et al 1993: Senecio disperse well when a landscape is fragmented but population growth rates higher when a landscape is not fragmented!

  12. What about landscape structure leads to invasive spread? Exotics travel along edges

  13. Facilitation? Invasibility of Systems • Parasitism (e.g. Cowbirds) • Enhanced Competition • Population Sinks are more vulnerable • Edge Effects • Lower genetic diversity of native species

  14. Questions • Habitat fragmentation in order to stop invasives: Is this practical? • How can we manage for both spread of invasives as well as keeping the native populations healthy? • Which parameters are needed in a model predicting spread of invasives? • Dispersal vs. Demography: which is more important in invasive spread?

  15. Higgins and Richardson 1998

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