Download Lecture 19: Intro to Predation Facilitation vs. Inhibition Pumice Plains

Lecture 19: Intro to Predation
But first…
Back to Mount St. Helen’s
Two studies:
a) Morris & Wood 1989
b) Bishop 2002
Facilitation vs. Inhibition
• Lupines: nitrogen-fixing pioneer species
• Anaphilis: later invader
• Epilobium (fireweed): later invader
Pumice Plains
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True Primary Succession
Covered in debris
Then lava flows
Low in nutrients (especially nitrates) &
pyroclastic flows hold water poorly
• Summer: high surface temperatures & low
water availability
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Introduction of Invaders Species
• Seeds survival:
Barren Areas > Dead Lupines > Live Lupines
• Seedling growth & flowering:
Best in areas with Lupines
What Explains Seed Survival?
1) More pathogens or herbivores
2) Competition with Lupines
3) Allelopathic substances produced by
Lupines
Likely a combination…
What Explains Seedling Growth?
1. Increased nitrate availability
2. Increase in water availability (mulching)
3. Amelioration of microclimate
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What happened after first 10
years?
• Originally very high population growth of
lupines
• But, expansion rates decreased 10 fold in
1991-1995 time period
• Not a reflection of habitat availability
• Early explanation: poor dispersal of heavy
seeds (but, they managed to get there)
Impact of Insect Herbivores?
• Lots of Lepidopteran larvae & Anthomyiid
flies
• Feed on stems, leaves & seeds
• Other populations: may or may not have
effect on populations, succession or
colonization
Core Patches
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More effect at the edge
Effect not significant to population growth
Competition appears to be more significant
Fewer insects in core?
Likely a result of presence of insectivores,
parasitoids, vertebrate predators
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Edge Patches
• Strong effect of insects
• Especially in relation to seed loss, but also
serious effect on adult survival
Conclusions
Small Scale:
• Aids succession by opening up spaces &
decreasing inhibitory effects
Large Scale:
• Decreases colonization by lupines, therefore
decreases site amelioration, eventually
slows succession
Now, back to predation
What is a predator?
• An organism that consumes all or part of
another living organism.
• Interaction is positive for predator &
negative for individual prey
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Predator-prey interactions
Many trophic levels:
• Herbivores on plants
• Carnivores on herbivores
• Carnivores on carnivores
• Parasites/Parasitoids on host
• Disease on victim
Effects of Predation
• Obvious direct effects
• Less obvious indirect effects
• Influence on energy flow & nutrient cycling
(affects movement through trophic levels)
• Effects are obvious through antipredator
adaptations.
Competition vs. Predation
• In terms of adaptations:
• Tend to be more complicated/sophisticated
for predation
(mimicry, crypsis, chemical defenses,
behaviours, mechanical defenses)
• Competition (size, morphology, behaviour)
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Biological Control
• Good way to find effect of predators on
prey populations
• Prickly pear cactus
• St. John’s wort
• Salvinia molesta
• Rabbits
Prickly Pear Cactus
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Australia
Rangeland problem: sheep can’t graze
Control: Cactoblastis cactorum
Larval moths specific to this cactus
Low density of predator & prey
St. John’s Wort
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California
Rangeland: phototoxic to cattle, can’t sell
Chrysolina beetle
Only survives in shade (beetle survives poorly)
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Salvinia molesta
• Aquatic fern
• Introduced from Brazil, weed in tropics
(boats, fishing, ecosystem function)
• Cyrtobagus singularis (weevil)
• Originally wrong species so worked poorly
• Very effective now
Rabbits
• Australia
• Myxoma virus (vertebrate predators would
& have seriously affected native species)
• Did a decent job but evolved decreased
virulence & rabbits evolved resistance
Biological Control Examples
Show:
• Predators can directly limit populations well
below that attained without native predators
• Suggests that they are important in
structuring communities.
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Effect of Predation
• Varies with type of community (e.g.
freshwater vs. terrestrial)
• Varies with strength of competition
• Varies with specificity of predator
• Varies with density & distribution of prey
• +++
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