fundamental question
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Fundamental question. How do species interact? Direct and indirect effects. Kinds of interactions. Predation+/- Competition-/- Parasitism+/- Mutualism+/+. Zebra mussels. Arrived in U.S. 1988: Great Lakes - PowerPoint PPT PresentationTRANSCRIPT
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Fundamental question
• How do species interact?
–Direct and indirect effects
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Kinds of interactions
• Predation +/-
• Competition -/-
• Parasitism +/-
• Mutualism +/+
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Zebra mussels• Arrived in U.S. 1988: Great Lakes
• Native to Caspian and Black sea area of eastern Europe http://www.nuigalway.ie/freshwater/zebra/Europe%20c.jpg
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How did zebra mussels get here?
• Ballast water: what is it?
• BW full of marine creatures
• Most don’t survive sea crossing; some do
• mid-ocean exchange; problems
http://invasions.si.edu/nbic/forms/NBICReportingForm.pdf
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Why are zebra mussels so successful?
• Larvae: adapted for long-distance dispersal
• Few natural predators in North America– Fish and ducks in native range– Native and introduced fish don’t control them
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Zebra mussel interactions
• Predation +/-– ZM natural predators missing (fish, ducks)– ZM are filter feeders, preying on phytoplankton
(bad for phytoplankton; also bad for other phytoplankton feeders COMPETITION)
• BUT: water with ZM much clearer, so more sunlight reaches bottom: good for large, rooted aquatic plants AND also good for some fish that use these plants for cover
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Other aspects of predation• Carnivore: eat other animals• Herbivore: eat plants• Evolutionary arms race
– As predators evolve better ways to catch prey, their prey evolve better defenses
– eg: milkweeds and insects that feed on them• Milkweed contains compounds poisonous to most insects
• A few insects tolerate milkweed poisons. As a result, they avoid competition from other insects and gain a defense.
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Parasitism
• Also +/-
• Parasite weakens host, rarely kills it. WHY?– Endoparasites – internal. eg: tapeworm– Ectoparasites – external. eg: tick
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Competition • Competition -/-• intraspecific (Same Species) or
interspecific (Different Species)• What do individuals compete for?
RESOURCES
• Eg: food, mates, nesting spots, roosting spots, shelter from predator, sunlight
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Intraspecific competition
• Imagine:– Plants growing in a field – If low density: low seed production. WHY?– If medium density: increasing seed production.– But, high density: at some density, seed
production crashes. WHY? sketch how this would look on a graph
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Zebra mussel interactions
• Interspecific competition
• 1000 ZM can settle on a native bivalve, smother it– ZM compete with other phytoplankton eaters– One ZM can filter a liter or more of water a day
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Mutualism
• Interaction benefits both: +/+
• Examples?• Picture: ants
tending aphids.
aphids protected
from predators,
ants get honeydew
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Commensalism
• Taking without harming +/0
• Common in tropical forests: epiphytes– Small plants, live on or
attached to trees
– Mosses, ferns, orchids
•
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Overall impact of species interactions
• Can be hard to estimate
• eg: Flowering shrubs live in pine forest. – Both compete for resources such as soil
moisture, minerals– BUT the flowers produce nectar that is eaten by
insects that prey on other, needle-eating insects.
• SO, if removed flowering shrub, would impact on pine be positive or negative??
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Food web
•
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NICHE
• = ``ecological niche’’
• Loosely: organism’s role in ecosystem
• Includes where it lives, what it eats, what eats it, what organisms it interacts with, even interactions with abiotic components.
• NOT synonym for ``habitat’’
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Differences in niche
• Specialists: organisms with a relatively narrow niche. Specific requirements to thrive.
• Generalists: organisms with broad tolerances
• EXAMPLES??
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Fundamental vs. Realized niche
• A species may be capable of using wider range of resources than it actually does: fundamental niche
• Actual role and lifestyle of organism is its realized niche
• Q: what leads
to smaller realized
niche?
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Limiting resources
• Any resource that is scarce (compared to need)
• Can restrict ecological niche
• Examples:– Mineral content of soil may limit plants– Nest sites may limit breeding population of
birds
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Competition
• When 2 or more species overlap in fundamental niche, they compete.
• If one species competes for a limiting resource better than the other, it can entirely replace that species in the habitat.
• = COMPETITIVE EXCLUSION
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Resource partitioning
• Natural selection may lead species that use the same limiting resources to evolve to LESSEN competition.
• = resource partitioning
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Resource partitioning
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Fundamental vs realized niche
• Brown anole & green anole in FL.
• BA is introduced• Initially, large niche
overlap• BA outcompetes GA,
restricts its niche• Competition is KEY
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Ecological levels
• Individual organism• Population• Species: fundamental unit of biology. A
group of interbreeding (or potentially interbreeding) organisms
• Community• Ecosystem• Biosphere
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Community ecology
• How do species interact and coexist?• How do communities change through time?• What determines the makeup of a community
(species identity and number)?
• Community = all populations that live in the same place at the same time
• Population = all members of one species in one place at one time
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Feeding relationships
• • Producers = green plants = autotrophs
• Consumers = heterotrophs– Primary 1°
– Secondary 2°
– Tertiary 3°
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Trophic levels and energy relationships
•
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Key understandings
• What is the source of energy in ecosystems?
• How is energy transferred between trophic levels?– Rule of thumb:– How is energy lost?
• Pyramid of biomass
• Pyramid of numbers
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Keystone Species
Removing the sea star (the top predator) greatly reduced species diversity.
Similar removal of other species had little effect on community structure.
(sea star)
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Resource Partitioning
Closely related warbler species can occupy the same tree if they partition resources.