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

• Native to Caspian and Black sea area of eastern Europe http://www.nuigalway.ie/freshwater/zebra/Europe%20c.jpg

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

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:– 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

•

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

•

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

• • Producers = green plants = autotrophs

• Consumers = heterotrophs– Primary 1°

– Secondary 2°

– Tertiary 3°

Trophic levels and energy relationships

•

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.