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Community Interactions
• Community – all the species in a given
location at a given time
• Habitat the physical environment they live
in : Redwood forest
• Niche – how a species uses the resources
in its habitat
– Builds nest in tree top vs. lower branches
• Similar species coexist by Niche
specialization.
Paramecium caudatum
Paramecium aurelia
Competitive exclusion
Competitive Exclusion
• The more similar two species’ niches
the more they compete.
• No two species can share the exact
same niche- one dies out.
• Species evolve to diverge their
niches by Resource Partitioning
Competition for space on the rocks
Weak competitors stuck higher up in the intertidal
Resource Partitioning
Bristly
foxtail
Indian
mallow
Smartweed
Character
Displacement
Two species with same
Beak size can not
Coexist on same island
One adaptive result of
resource partitioning
Types of Interspecific Interactions
Species A Species B
Commensalism
+
0
Mutualism
+
+
Competition
-
-
Predation
+
-
Parasitism
+
-
Predator & Prey
a Mutualism?
Canadian lynx (dashed line)
Snowshoe hares (solid line)
Caulerpa taxifolia suffocating
a marine ecosystem
Do not
post on
Internet
Number of species of ants
Number of species of breeding birds
Number of colonizing species of mosses and vascular
plants recorded on Surtsey between 1965 and 1973
Mosses
Vascular Plants
Keystone species
• Pisaster (Sea Star) defends tide pool from
being taken over by mussels, barnacles.
Sea Otters maintain Kelp forest
• Otters are a Keystone
species
• Kelp are the base of the
kelp forest community
• Urchins eat kelp at their
base
• Otters eat urchins,
keeping their numbers
low.
• Otter numbers along
California are dropping.
• Alaska- Orcas starting to
eat otters, because seal
numbers are dropping
• No fish for seals
Succession:Community
Structure changes over time
• Primary Succession: starts with no
soil, just bare exposed rock
– Progresses in stages until long term
climax stage
• Secondary Succession starts with
the climax vegetation type
– Disturbance (fire) resets timeline
– Progresses in stages back to climax.
2-Barren Rock
1-Glacier Retreats
3-Moss and Lichen
4-Cottonwood and Alders
5-Spruce moves in
6-Spruce and Hemlock
Climax Vegetation
Fire Cycle in Chaparral
Fire poppies in burn area
Madrones sprouts from burl
Ceanothus seedlings sprout after fire
1 month
post fire
Schmidts, M.J., D.A.
Sims,
J.A. Gamon
California State
University,
Los Angeles, CA
http://vcsars.calstatela.edu/eas_00/miriam/miriam_esa_00.html
First spring
3 years post fire
20
and 40 years post fire
Mosaic of ages burns