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Transcript
Competition
Coastal sage scrub – note bare spots near shrubs
Rabbit grazing – source of apparent competition
Species Coexistence
Serengeti National Park
Species Coexistence
Competition is a common feature of species
interactions, yet often we find very similar species
coexisting in nature, species that seem to need the
same resources. How do they coexist?
• Refuge from competition
• Predation keeps populations of each species low
enough that they do not compete
• Resources may be variable in space and time, so that
the species coexist because both do not find resource
at same time
Dung – a valuable, variable resource
Dung Beetles
Dung Fly
Predation
Great White Shark and Fur Seal
Lions hunting – True Predator
Moose Browsing – Partial Predator
Parasitoid Wasp
Specialists and Generalist Predators
Advantages to being a
specialist
1. Avoid interspecific
competition
2. Allows evolution to
overcome chemical defense
3. Allows evolution of cryptic
coloration that matches prey
- mostly for insects on
plants
4. Increases chance of mate
encounter
Advantages of being a
generalist
1. Flexibility in face of
environmental uncertainty
2. Broad diet needed to get all
necessary nutrients and
vitamins
3. Avoid overdosing on any
one toxin - mostly for
animals grazing on
chemically defended plants
Pied Wagtail
Caribou eating lichens
Edible mussel – Mytilus edulis
Black oystercatcher
Bluegill sunfish
Mink
Muskrat
Red grouse
in heather
Bank vole
Tawny Owl
Cinnabar Moth and Caterpillar on
Ragwort Tansy
Snowshoe hare and Lynx
Lynx
Ruffed Grouse
Snowshoe hare
Sea Otter
Sea Urchin
Kelp
Forest
Sea Otter eating Sea Urchin
in Kelp Forest
Comparison of kelp and urchin biomass with and
without sea otters
Kelp forest ecsystems with and without
sea otters