Transcript How species interact

Fundamental question
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How do species interact?
–Direct and indirect effects
Kinds of interactions
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Predation
Competition
Parasitism
Mutualism
+/-/+/+/+
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/E
urope%20c.jpg
How did zebra mussels get here?
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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
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
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
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.
Parasitism
• Also +/• Parasite weakens host, rarely kills it. WHY?
– Endoparasites – internal. eg: tapeworm
– Ectoparasites – external. eg: tick
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
Intraspecific competition
• Imagine:
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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
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
Mutualism
• Interaction benefits
both: +/+
• Examples?
• Picture: ants
tending aphids.
aphids protected
from predators,
ants get honeydew
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??
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’’
Differences in niche
• Specialists: organisms with a relatively
narrow niche. Specific requirements to
thrive.
• Generalists: organisms with broad
tolerances
• EXAMPLES??
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?
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
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
Resource partitioning
• Natural selection may lead species that use
the same limiting resources to evolve to
LESSEN competition.
• = resource partitioning
Resource partitioning
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
Ecological levels
• Individual organism
• Population
• Species: fundamental unit of biology. A
group of interbreeding (or potentially
interbreeding) organisms
• Community
• Ecosystem
• Biosphere
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
Feeding relationships
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• Producers = green
plants = autotrophs
• Consumers =
heterotrophs
– Primary 1°
– Secondary 2°
– Tertiary 3°
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
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)
Resource Partitioning
Closely related warbler species can occupy the same tree if they partition resources.