Transcript Lecture 8: Community ecology

Community ecology
Outline:
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Community structure: attributes
Factors influencing the structure of communities
Community dynamics
Chapter 16-18
Community attributes
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# of species
Relative abundance of species
Nature of species interactions (food webs)
Physical structure
Community structure
• Species richness (# of species within
community)
10
Community structure
• Relative abundance (% each species
contributes to the total number of
individuals)
Stand one
Stand two
Simpson’s diversity index
• D=0-1
– 0: high diversity
– 1: low diversity
• Stand one (Table 16.1): D=0.13
• Stand two (Table 16.2): D=0.36
Dominance
Yellow-poplar
Food webs
Keystone species
Functional groups
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Feeding level
Exploitation of common resources (guilds)
Photosynthetic pathway
Shade tolerance
Life history
Physical structure
Zonation
supratidal
intertidal
subtidal
Association
• Relatively consistent species composition
• Uniform general appearance
• Distribution that is characteristic of a
particular habitat
Organismic concept of communities
Continuum concept of communities
Factors controlling community structure
Fundamental niche
Species interactions
Keystone predation
Apparent competition
Indirect commensalism
Top-down vs. bottom-up control
The number of trophic levels regulates plant,
herbivore and carnivore numbers
# trophic levels:
B/comp: numbers limited by availability of resources (bottom-up regulation).
Competition strong, predation weak.
T/pred: numbers limited by predation (top-down regulation).
Competition weak, predation strong.
Stress tolerance and competition
Smooth cordgrass
Salt meadow
cordgrass
Black needle
rush
Environmental heterogeneity
Relationship between the number of plants per 300m2 plot beside the
hood river, NWT, and an index (ranging from 0 to 1) of spatial
heterogeneity in abiotic factors associated with topography and soil.
More spatially heterogeneous plots had higher species richness.
Environmental quality
Plant species diversity in a control plot and a fertilized plot in the Parkgrass experiment
in Rothamstead, England. Fertilized plots have lower species diversity. The Parkgrass
experiment, which began in 1856, is the longest running ecological experiment.
Community stability
Types of stability:
1. Resilient community: returns to former
state after disturbance
2. Resistant community: changes little in
response to disturbance
Community
dynamics:
Succession
Primary
succession
Pioneer
species
Late
successional
species
Secondary
succession
beach grass
shrubs
pines
oak
Primary
succession:
newly exposed
substrate
Dryas sp.
An early succession species on glacial moraines in Glacier bay.
Dryas is a symbiotic N-fixing plant
Populus trichocarpa
Salix arctica
After Dryas, cottonwood and willows become established
Alnus incana
Alders become the dominant tree after 50 years
“Climax”: mixed spruce-hemlock forest
Picea sitchensis
Tsuga mertensiana
Secondary succession:
after disturbance
Density
Autogenic vs. allogenic change
Allogenic environmental change
Species diversity during succession
Oak-pine forest
Intermediate disturbance hypothesis
Intermediate disturbance hypothesis
High
Low
In New Zealand streams, less disturbed sites support more complex
communities (i.e., communities with larger, more connected food
webs)
Succession of heterotrophs
Bark
beetle/woodboring beetle
Fungi/bacteria
Predatory
insects
Moss and
lichen
Invertebrates/
mice/
salamanders
Changes over geologic time
Concept of community revisited
Concept of
community
revisited