Page 1 Community ecology I. Structure A. Diversity B. Trophic structure C. Species with big impacts II. Dynamics and interactions A. Succession B. Food web dynamics C. Complex interactions Community ecology What’s a community? Assemblage of populations co-occurring in space and time • the diversity of species in a habitat • interactions among these species At the largest scale, communities are often characterized by the dominant vegetation. Example: Pinyon- juniper community of parts of the Mojave What is biological diversity? 1) Species Richness = number of species in a given area Community structure A. Diversity (who’s there in a community) What is biological diversity? 1)The number of species in a given area, also called species richness 2) Relative abundance of species in a given area
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Community Ecology 2006 - University of Arizona Ecology 2006 handout.pdfC. Complex interactions Community ecology II. Community interactions Communities are dynamic in time A. Ecological
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Page 1
Community ecology
I. StructureA. DiversityB. Trophic structureC. Species with big impacts
II. Dynamics and interactionsA. SuccessionB. Food web dynamicsC. Complex interactions
Community ecology
What’s a community?
Assemblage of populations co-occurring in space and time
• the diversity of species in a habitat
• interactions among these species
At the largest scale, communities are often characterized by the dominant vegetation.
Example:Pinyon-juniper community of parts of the Mojave
What is biological diversity?
1) Species Richness = number of species in a given area
Community structureA. Diversity (who’s there in a community)
What is biological diversity?
1)The number of species in a given area, also called species richness
2) Relative abundance of species in a given area
Page 2
2) The relative abundance of species in a given areaImagine that in each of two communities,
A and B, there were 10 species, and a total of 100 individuals
Do they have the same species richness?
What other information might you want to know about them?
How are the individuals distributed among species?
Imagine:
In Community A: 10 individuals of each species
In Community B: 91 individuals of one species and 1 individual of all of the other 9 species
In Community A:
In Community B:
Which do you think is more diverse?
In Community A:
In Community B:
Various measures, e.g. the Shannon-Wiener Diversity Index, measure the spread of individuals across species
Community A would score higher
I. Community structureB. Food webs (the trophic structure, or the “Who’s eating who” of a community)
At its simplest, a food chain:
Secondaryconsumer (predator)
Primary consumer (herbivore)
Producer (plant)
TrophicLevelsSee Table 55.1
I. Community structureB. Food websA more realistic example from the tropics
Lots of interactions between species. Many leafminers feed on more than one plant, many wasps attack more than one leafminer.Many species don’t feed on just one trophic level
Parasiticwasps
Leaf-miners
Plants
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I. Community structureC. Species with large impacts1. Dominant species – most abundant or
have the highest total biomass
Exert controls over the distribution of other species
e.g. Sugar maples in eastern forests –impact soil and shades other plants
2. Example: a sea star maintains intertidalanimal diversity
Treatments: Predatory sea stars removed from some tidal pools for several years, not from others
pool with sea stars
(eco beaker)2. The predatory sea star maintains animal diversity in the intertidal zone
‘63 ‘65 ‘67 ‘69 ‘71 ‘73Year
Control
Sea stars removed
20
15
105
0No.
of s
peci
es
Mussels(dominantcompetitor)take over
2. Example: a sea star maintains intertidalanimal diversity
The experimenter called the sea star a keystone species
The keystone keeps the arch from falling apart
In communities, a keystone species is one thatIs especially important in maintaining speciesdiversity
I. Community structureC. Species with large impacts
3. Ecosystem engineers – organisms that maintain diversity by create, modify, and maintain habitat
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3. Ecosystem engineers – organisms that create, modify, and maintain habitat