BIOE 20C Lecture Notes - Lecture 16: Trophic Cascade, Commensalism, Intermediate Disturbance Hypothesis
12 Sep 2016
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Lecture 16 11/24/2015 8:59:00 PM
Commensalism
• +/0
• One species gains in fitness
• Other species is unaffected
Remoras and large fish/whales
• Remora gets protection, food scraps, free ride
• Host not affected
Fat Innkeeper Worm and Guests
• Worm creates safe, well ventilated burrow for
o Goby (fish)
o Pea crab
o Scale worm
• “borders have no fitness impact on worm
Indirect Interactions
• Two spp that do not directly interact exert influence on each other
• Influence is indirect
• Consequence of interaction with another species
• Ex. Trophic cascade
Trophic Cascade in Yellowstone
• Wolves removed in 1925, restored in 1995
• Elk culled until 1968—afterwards population grows rapidly
• Aspen grazing by elk increases in absence of wolves, no new
recruits until the wolves return
• It gets even more complicated as other species are affected by the
absence of wolves
Keystone Species
• Spp with effects on communities that are disproportionate to their
biomass
• ie. Small part of the ecosystem but play a major role in structuring
the community
• Tend to be top level predators
find more resources at oneclass.com
find more resources at oneclass.com
Species Diversity
• Key feature of communities
• Can be measured in two ways
o Species richness=total number of spp
o Species diversity=weighted measure that includes both spp #
and abundances
Cause/Role of Species Diversity
• Why are some communities more diverse than others?
• What effect does spp diversity have on community
structure/function?
Global Patterns of Spp Diversity
• Many terrestrial ecosystems show pattern of decreasing diversity
with latitude
• No such distinct global patterns in marine ecosystems
Factors that Influence Community Diversity
• Productivity
• Disturbance
• Habitat size
Productivity Hypothesis
• High productivity supports more spp
• Supported by natural patterns
• Contradicted by experimental studies
Intermediate Disturbance Hypothesis
• Frequent disturbance=few species
o r selected species dominate
• Rare disturbance=few species
o K selected species dominate
• Intermediate disturbance=higher spp #
o Mix of r and K selected species
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Commensalism: +/0, one species gains in fitness, other species is unaffected. Remoras and large fish/whales: remora gets protection, food scraps, free ride, host not affected. Fat innkeeper worm and guests: worm creates safe, well ventilated burrow for, goby (fish, pea crab, scale worm, borders have no fitness impact on worm. Indirect interactions: two spp that do not directly interact exert influence on each other, influence is indirect, consequence of interaction with another species, ex. Keystone species: spp with effects on communities that are disproportionate to their biomass ie. small part of the ecosystem but play a major role in structuring the community, tend to be top level predators. Species diversity: key feature of communities, can be measured in two ways, species richness=total number of spp, species diversity=weighted measure that includes both spp # and abundances. Global patterns of spp diversity: many terrestrial ecosystems show pattern of decreasing diversity with latitude, no such distinct global patterns in marine ecosystems.
