Transcript 18 Lecture 2006

OUR Ecological Footprint - 5
1. Recycle; pay tax for it.
2. Live near work;
Ride bike; minimize car use.
3. Buy energy-efficient furnace.
4. Programmable thermostat: winter/summer
5.
Turn in notes from movie for EC
Opportunities
• IB 390 Introductory Research
• IB 490 Independent Study
• See Website for IB Majors
www.life.uiuc.edu/sib/390_490.htm
Next week:
• Lab
•
Homework 10 ANOVA
•
5 Abstracts for SDP2
•
Group Proposal WS - 3 days before lab
• Exam 2
• Formulae will be provided.
• BRING calculator.
• Practice ?s: on web on Exam 2 date
Ch 21: Community Structure
Ch 21 +23 Community Ecology
Species Abundance and Biodiversity
Objectives
• Species at regional vs. local scale
• Species sorting ---> local composition
• Species richness (# species)
Local + regional components
• Species relative abundance
Patterns
Controls
• Species-area relationship
• Species diversity
Hypotheses to explain variation in SD
Sample Exam ?
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1)
2)
3)
4)
5)
A 100-yr experiment tested the effect of fertilizer
on species diversity (H’) in a grassland.
RESULTS: H’ of unfertilized remained steady.
H’ of fertilized decreases through time.
Summarize the major result of the study.
What 2 components of a community does the
Shannon-Wiener Index (H’) incorporate?
What combination of these components yields
the greatest value of H’?
Explain the results in terms of competition and
niche theory.
Do the results support the hypothesis that the
superior competitor can exist at lower resource
levels than its competitors? Explain.
Local communities are assembled from the
regional species pool.
• Species sorting = processes that determine
local community composition.
Experimentally-composed communities show
species sorting. What caused the sorting?
Fertility:
low
high
Environmental filters eliminate species that
can’t tolerate conditions---> species sorting
Many factors influence regional and local
species richness.
Local communities contain a subset of
the regional species pool.
•
***What determines whether a species can
be a member of a given community?
1 Adaptations of species to environmental
conditions (habitat selection)
2 Persistence in face of competitors,
predators, and parasites
H1:Species sorting (and beta diversity)
should be greatest where regional species
pool is largest.
• When species pool is smaller, competition
should be relaxed--->
•
ecological release = species expand into
habitats normally filled by other species and
increase in population density
• Ecological release provides evidence for
hypothesis of local interactions controlling
species diversity.
•
(e.g. competition for resources structures
communities and limits # species)
Species richness (# species) has both local
and regional components.
•  (alpha) = local # species in small area of
homogeneous habitat
•  (beta) = # species turnover between
habitats
•  (gamma) = (landscape) regional: total #
species in all habitats within a barrier-free
geographic area
Above species richness measures
determined by ecology and regional
pool
•  (delta) = available pool of species
within dispersal distance (up to
continental scale)
• determined evolutionarily
Species in communities vary in relative
abundance. Most species are rare; few are
common.
What is the likelihood of sampling a rare
species? A common species? How
accurate are the data for rare species?
Species abundance (dominance diversity)
curves…Which community has greatest evenness in
abundance?
Log scales…
Most
Least
Rank order of abundance
Number of species increases with area
sampled.
log
log
Species - area relationship:
• S = c Az
• S = # of species
• A = area
• c and z = fitted constants
• log S = log c + z log A = linear
• z (slope) = usually 0.2 to 0.35
• z = less for continental areas, greater for islands
• Rapid dispersal within continental areas prevents
local extinction within small areas
***Why do larger areas have more species?
• in part because…
• larger areas give larger samples
but also…
• greater habitat heterogeneity (sample
more types of habitats)
• larger islands---> bigger target for
immigrants
• larger populations --->
– greater genetic diversity
– broader distributions over habitats
– numbers large enough to prevent stochastic
extinction
Area and habitat diversity both contribute to
the species-area relationship.
Spatial variation in woody species richness
Hypotheses to explain variation in species
richness
1
2
3
4
5
6
Heterogeneity in space and time
(Vegetation and food complexity)
Predation
Competition/niches
Disturbance
Equilibrium models
1 Heterogeneity in space and time
hypothesis
• Interacts with production hypothesis
• Relates to niche arguments (see below)
2 Vegetation (structural complexity) overrides
primary production in determining local
richness.
Communities with simple vegetation
structure have lower richness, yet can have
very different levels of productivity.
Bird richness increases with greater
structural complexity.
Species richness increases as a stream
becomes larger and has more habitat and
food diversity.
3 Predation hypothesis
• High productivity---> high predator populations --->
reduce competition among prey and permit more to
coexist (starfish experiment)
• More predation---> more selection for escape
adaptations by prey
Crypsis to avoid predation
Pest pressure hypothesis for maintaining
tree species richness
Distance-dependent mortality is consistent
with the pest pressure hypothesis.
Soil pathogens kill seedlings near parent
trees ---> maintain species richness?
4 Competition hypothesis:
• High richness --> less competitive
exclusion?
• Why? By what means?
Niche metrics
How can more species be added to a
community?
• Increase
total niche
space
• Increase
niche
overlap
• Decrease
niche
breadth
Does increase in niche diversity --> increase
in species richness? As s.r. increases, so
does morphological diversity.
4 Competition hypothesis, cont.:
• High richness --> less competitive
exclusion?
• Why? By what means?
•
greater specialization (narrower niche)
•
greater resource availability (greater
niche space)
•
reduced resource demand (smaller
populations)
• intensified predation (populations below K)
• Are there more ecological roles in tropics?
• Greater niche space from greater number of
niche axes and length of each axis?
• relates to heterogeneity in space/time
hypothesis
Populations in regions with few species show
ecological release (and larger realized niches).
Less regional species
---> 1) less local sp. rich
2) each species
more abundant
greater habitat
breadth
3) beta diversity
(turnover of species)
decreased.
• Realized niche is always smaller than
fundamental niche,
•
but with ecological release --->
larger realized niches
5 Intermediate Disturbance Hypothesis
• Richness peaks at intermediate levels
Too low disturbance -->
competitive exclusion
Too high disturbance -->
limited number of species adapted
6 Equilibrium hypothesis
• Richness reaches an equilibrium when
factors removing species = factors adding
species.
•  more additions (e.g. speciation) or and/or
fewer deletions (e.g. extinctions) = greater
species richness.
Nile perch vs. cichlid fish in Lake Victoria
Scientific Process
• Observation: Cichlid fish populations
declined after the introduction of Nile perch.
• Question: Did the introduction of the perch
cause the decline in cichlid populations?
***Generate an ‘if…then’
hypothesis/prediction
• Hypothesis 1: If introduction of Nile perch
caused the decline of cichlid populations,
• then
•
1) lower cichlid populations in areas with
high than low perch populations.
2) then higher cichlid populations in areas
with perch removed than in control
areas.
***What are independent and dependent
variables?
• Plot each prediction.
• Which provides a stronger test of the hypothesis?
• If get no support, what do next?
***Are there alternative hypotheses?
• H1: original hypothesis
• H2: A newly introduced cichlid parasite
caused the decline.
• H3: A marked decline in aquatic
vegetation on which cichlids feed
caused the decline.
• H4: Dramatic changes in water
chemistry caused by agricultural runoff
caused the decline.
• H5….
How can community structure be quantified
and compared?
***
Which variables can be used to describe the
species diversity of a community?
Which community is more diverse?
• Species richness
• Species relative
abundance
Species richness (# of species) = S
• S varies with sample size so…
• Compare S by rarefaction:
equal-sized subsamples randomly drawn.
Measures of community structure
•
Species richness: # of species BUT
species differ in abundance and thus in role
•
Species diversity:
weight species by their relative abundance
•
Simpson’s index: D = 1 /  pi2
p = proportion of each species in total
sample
•
Shannon-Wiener index: H' = -  pi ln pi
•
Evenness = ratio observed/maximum diversity
ED = D/Dmax, where Dmax = S
or EH’ = H'/Hmax, where Hmax = ln S
Calculate Species Diversity:
Species No. Ind. pi
pi2
1
5
.25
.0625
2
4
.20
.0400
3
3
.15
.0225
4
4
.20
.0400
5
4
.20
.0400
Total (N) 20
1.00 ∑=.205
ln pi
-1.386
-1.609
-1.897
-1.609
-1.609
pi ln pi
-.3465
-.3218
-.2846
-.3218
-.3218
∑= -1.5965
• D = 1/ ∑pi2 = 1/.205 = 4.878
• H' = -∑ pi ln pi = 1.5965
• Calculate Evenness:
• ED = D/Dmax 4.878/5 = .9756
• H' = H'/Hmax = 1.5965/1.609 = .9922
(Dmax = S)
(Hmax = ln S)
Comparisons of diversity indices among
communities.
C1
C2
C3
C4
C5
•***What factors increase species diversity?
• more species.
• less difference in relative abundance
among species.
Objectives
• Species at regional vs. local scale
• Species sorting ---> local composition
• Species richness (# species)
Local + regional components
• Species relative abundance
Patterns
Controls
• Species-area relationship
• Species diversity
Hypotheses to explain variation in SD
Measures to quantify and compare SD