Transcript Invasive Species

Outline
• Community Ecology
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Indirect effects, Keystone species, Invasive species
Biodiversity: importance and evaluation
The new paradigm in ecology: communities in flux
Conservation of species interactions
• Ecosystem Ecology
– Ecosystem services
– Biodiversity and ecosystem services
– Ecosystems of special concern (Marine and Tropical)
Successful Biological Control
Is Biodiversity Important?
• Conservation Biology Perspective
– Inherently valuable
• Utilitarian Perspective
– Natural resources: Genetic libraries; natural design
• Ecological Role
– Invasibility
– Stability
– Ecosystem Function
Diversity and Invasibility
• Tilman, D. 1997. Community invasibility,
recruitment limitation, and grassland biodiversity.
Ecology 78: 81-92.
– Seeds from up to 54 plant species (native but mostly
rare) were added to patches of native grassland
– The % seeds established was negatively correlated with
species diversity
• Conclusion: Invasibility may decrease with
biodiversity
Diversity and Stability
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Year to year variability in species
abundance higher in species rich
plots
Year to year variability in total
biomass lower in species rich plots
Effect of drought lower in spp. rich
plots
Tilman, D. 1996. Biodiversity: Population versus ecosystem stability. Ecology 77: 350-363.
Diversity and Stability
• Hypothetical Mechanism: When climatic
variations harm some spp., unharmed spp.
increase. This compensatory increases
stabilize ecosystem processes (i.e.
productivity) but cause populations to be
more variable
• This was apparent for both EV (non-drought
years) and “catastrophes” (drought years)
What is “Stability”
• Historical
– Constancy of ecological communities
• Modern
– Resilience
• Operational
– Variation in community or ecosystem processes
Tentative Conclusions
• At the community level, species diversity
may . . .
– Increase stability (reduce invasibility)
– Decrease stability (year-to-year variation in
population abundance)
The “New” Paradigm in Ecology
• Clements, F. E. 1936. Nature and structure
of the climax. Journal of Ecology 24: 252284.
– Climax succession
• Gleason, H. A. 1926. The individualistic
concept of the plant association. Bulletin of
the Torrey Botanical Club 53: 7-26.
– “Random” succession
The Land Ethic and Stability
• "A thing is right when it tends to preserve
the integrity, stability, and beauty of the
biotic community. It is wrong when it does
otherwise." - Aldo Leopold
Number of species
Intermediate Disturbance Hypothesis
Disturbance rate
Community Ecology and Conservation
classical paradigm
contemporary paradigm
Natural systems
closed
open, subject to change
by natural/human events
Stable states
1
more than 1
Metaphor
balance of nature
flux of nature
Conservation
implication
any natural unit is
conservable; keep
humans out
manage process and
context, not species;
humans included
Community Ecology and Conservation:
Nested Communities
Community Ecology and Conservation:
Nested Communities
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