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Species abundance and
diversity (Ch. 16)
New Unit:
Communities/Ecosystems
• Community: Interacting species in defined area.
• Functional groups: subdivide organisms based on
life history
– Guild: Organisms living in same fashion
• Animal Ex.: granivore guild
Harvester ants
K-rat
New Unit:
Communities/Ecosystems
• Growth form: Combination structure + growth
pattern.
• Ex.: tree, shrub, graminoid, forb, climber
Species Abundance
• How express?
• Log abundance (x-axis), number species in
abundance category (y-axis)
– Ex, plant species (% cover measures abundance)
– Ex, bird species (counts measure abundance)
Curve?
Species Abundance
• Normal (bell-shaped) curve
– x-axis log scale: lognormal distributions
Species Abundance
• Often only part curve seen.
– Why? Sample size.
• Ex, moth community & sample size
Tiger moth
(Arctiidae)
Sphingid moth
(Sphingidae)
Species Diversity
• Two factors:
– 1) Species Richness
• Number species
Species Diversity
• Two factors:
– 2) Species Evenness
• Relative abundance of species
Species Diversity
• How integrate?
• Diversity Index. Gives single number
Species Diversity
• Common: Shannon Wiener Index
– Fish diversity lab!
Ecology
SU 2005
Species Diversity
• Shannon Wiener Index:
s
H´ = - pi logepi
i=l
•
•
•
•
H´ = Value of index
pi = Proportion individuals of ith species
loge = Natural log
S = Number species in community
Species Diversity
• Ex: b greater
diversity (same
richness)
Rank Abundance Curves
• Rank abundance curves:
– Relative abundance (proportional abundance: y-axis, log
scale) vs. abundance rank (x-axis)
• a vs. b
Rank Abundance Curves
• Ex: reef fish communities (Gulf of California)
Rank Abundance Curves
• Which more diverse? (Richness, evenness)
Environmental Complexity
• In general: diversity increases with environmental
complexity (heterogeneity)
• Ex, warblers (eat insects on trees)
Environmental complexity
= foliage volume
Environmental Complexity
• Foliage height diversity correlates positively
bird species diversity
Environmental Complexity
• Hutchinson (1961):
– Phytoplankton: simple environments, compete
same nutrients
– But many species coexist
Environmental Complexity
• Algal niches.
– Ex, Diatoms (Protists,
Phylum Bacillariophyta)
– Photosynthetic
– Cell walls: silicate
Environmental Complexity
• Coexistence depends on ratio silicate:phosphate
• Different niches: different diatoms dominate
Environmental Complexity
• Do nutrients vary in “real world?”
• Ex, Pyramid Lake, Nevada
Environmental Complexity
• Ex, Pyramid Lake, Nevada
Environmental Complexity
• Tropical rain forest diversity?
• Amazon: 1 hectare (2.47 acres) up to 750
tree species
USA has
850 native tree
species!
Environmental Complexity
• Diversity due to:
– 1) many species per community
– 2) many communities per unit area
• Complexity helps explain diversity
Environmental Complexity
• Relationship nutrients and rainforest richness?
– Negative!
– Competitive exclusion by best competitors
Environmental Complexity
• Reducing environmental complexity
– When humans add nutrients (intentionally or
not!)
• Reduces diversity
– Reduces limiting nutrients
Environmental Complexity
• Ex, English grassland fertilized since 1856!
Environmental Complexity
• Ex, N fertilization & ectomycorrhizal fungi
diversity
– N aerial pollutant (Alaska factory)
Environmental Complexity
• Contributes to diversity
• But so does…disturbance
• Define??
Disturbance and Diversity
• Disturbance: departure from “average?”
• Sousa:
– Discrete, punctuated, killing, displacement, or damaging
of individuals that directly or indirectly creates an
opportunity for new individuals to establish.
• White and Pickett:
– Relatively discrete event that disrupts ecosystem,
community, or population structure and changes
resources, substrate availability, or physical
environment.
Disturbance and Diversity
• Two major characteristics:
– Frequency (how often)
– Intensity (how severe)
• Abiotic: fire, hurricanes, ice storms, flash
floods
• Biotic: disease, predation, humans
Intermediate Disturbance
Hypothesis
Intermediate Disturbance
• Ex: intertidal zone
– Disturbance depends on boulder size.
Intermediate Disturbance
• Richness greater medium boulders
Temperate Grasslands
• American prairie dog disturbance….
Disturbance
Disturbance
• Prairie dog control: reduced populations 98%
Humans as disturbance
• Human disturbance & diversity
– Ex, chalk grasslands (Europe)
– Graze livestock, cut hay
– What happened when “protected”?
Humans as a disturbance
• Diversity dropped (Brachypodium dominated)