Levels of Ecological Organization
in Freshwater Systems
Population
Community
Ecosystem
Community Ecology in
Freshwater Systems
What controls species composition (aka,
diversity)?
• What causes species composition to
change over space and time?
What are the consequences of variation in
species composition?
• Why does “biodiversity” matter in
freshwater systems?
What is a community?
• A group of interacting species
occurring in a particular place, at a
particular time.
How do we describe
freshwater communities?
• Species richness
• Relative abundance
• Diversity indices
(e.g., Shannon, Simpson’s)
How do you describe a community?
• Species richness: 4
How do you describe a community?
• Diversity indices: richness weighted
by relative abundance
>
Food Webs, Functional Groups, and
Trophic Levels
Levels ~ Diversity
Sp. 10
Sp. 7
Sp. 1
Sp. 2
Sp. 8
Sp. 3
Sp. 9
Sp. 4
Sp. 5
Sp. 6
Assumptions:
• Individual species occupy one level
Sp. 7
Sp. 6
Sp. 7
Sp. 1
Sp. 7
Sp. 7
Sp. 2
Sp. 5
Sp. 3
Sp. 4
Assumptions:
• Individual species occupy one level
• These systems are rare:
Sp. 3
Sp. 5
Sp. 2
Sp. 1
Sp. 1
Sp. 2
Sp. 3
Sp. 4
Variation in community
composition over space
Variation in community
composition over time
Spring
Fall
What controls community composition
(i.e., species diversity)?
• Interactions with the abiotic environment
> Limiting resources
> Limiting conditions
Limiting Resources: Some thing a
species or group of species uses to
survive.
Limiting Condition: Some attribute of
the environment that a species or
group of species must tolerate to
survive in a particular place.
What controls community composition
(i.e., species diversity)?
• Interactions with the abiotic environment
• Interactions among species
> Predation (+ / -)
> Competition (- / -)
> Mutualism (+ / +)
Predation and Community Composition
• Trophic cascades
…and galaxiid hell.
(Flecker and Townsend 1994)
Predation and Community Composition
• Trophic cascades
No Fish
(Flecker and Townsend 1994)
Predation and Community Composition
• Trophic cascades
• Significant effect of
“fish species” on total
invertebrate density.
•Significant negative
effect of “fish” on
species richness, no
effect of “fish species”.
(Flecker and Townsend 1994)
What isn’t insect richness telling us about the
effect of trout on community composition?
(Flecker and Townsend 1994)
Predation and Community Composition
• Super predators!!
No Fish
Fish
Competition and Community Composition
Disruptive
selection
Proportion of Population
• The ghost of competition past
Diet breadth
Competition and Community Composition
• The ghost of competition past
Competition and Community Composition
• The ghost of competition past
What controls community composition
(i.e., species diversity)?
• Interactions with the abiotic environment
AND
• Interactions among species
Abiotic  Biotic effects on community composition
Dicosmoecus
“Resistant Grazer”
(Wootton et al.
1996)
Abiotic  Biotic
effects
(Wootton et al. 1996)
=
Unregulated
Regulated
Abiotic  Biotic effects
(Wootton et al. 1996)
What controls community composition
(i.e., species diversity)?
• Interactions with the abiotic environment
• Interactions among species
• Ecosystem age
What controls community composition
(i.e., species diversity)?
• Interactions with the abiotic environment
• Interactions among species
• Ecosystem age
- Successional ponds
- Ephemeral streams and ponds
What controls community composition
(i.e., species diversity)?
• Interactions with the abiotic environment
• Interactions among species
• Ecosystem age
• Disturbance
Disturbance and community composition
Good Colonizers
+
Good Competitors
Good
Competitors
Minimally
Disturbed
Good
Colonizers
Extensively
Disturbed
(Connell 1978)
Disturbance and community composition
Disturbance and community composition
Kadashan River Basin, SE Alaska
• Response of riparian
plant communities to
flood frequency.
• Frequency = number of
times per year that the
mean elevation of a site
was inundated.
(Pollock et al. 1998)
Disturbance and community composition
(Pollock et al. 1998)
What controls community composition
(i.e., species diversity)?
• Interactions with the abiotic environment
• Interactions among species
• Ecosystem age
• Disturbance
• Productivity
Productivity and community composition
VS.
Productivity and community composition
Population Size
The paradox of enrichment
Time
(Rosenzweig 1971)
The paradox of
enrichment
Low and Moderate
Productivity
Population Size
Population Size
High Productivity
Time
Time
(Rosenzweig 1971)
What controls community composition
(i.e., species diversity)?
• Interactions with the abiotic environment
• Interactions among species
• Age
• Disturbance
• Productivity
• Size and Complexity
Size and community composition
Hypothesis: As size increases, so does
habitat heterogeneity, resulting in more
“niches” that can be filled by more species.
Size and
community
composition
What controls community composition
(i.e., species diversity)?
• Interactions with the abiotic environment
• Interactions among species
• Age
• Disturbance
• Productivity
• Size and Complexity
?
Size versus Productivity
• Sampled 25 lakes in North America that
varied in size AND productivity.
• Used N isotopes in top-predators fish to
determine food-chain length leading to that
predator.
15N < 15N
Maximum
Trophic
Position
<
Maximum
Trophic
Position
(Post et al. 2000)
Size versus Productivity
(Post et al. 2000)
Size versus Productivity
(Post et al. 2000)
What controls community composition
(i.e., species diversity)?
• Interactions with the abiotic environment
• Interactions among species
• Age
• Disturbance
• Productivity
• Size and Complexity
?
What controls community composition
(i.e., species diversity)?
• Interactions with the abiotic environment
• Interactions among species
• Age
• Disturbance
• Productivity
• Size and Complexity
• Colonization and Extinction
Colonization, extinction, and
community composition
Island Biogeography Theory
(MacArthur and Wilson 1987)
Colonization, extinction, and
community composition
Island Biogeography Theory
• Effect of
increased
isolation
Colonization, extinction, and
community composition
Electric
Fishes
(Fernandes et
al. 2004)
Colonization, extinction, and
community composition
Tributary
“Isolated”
“Connected”
(Fernandes et al. 2004)
Colonization, extinction, and
community composition
(Fernandes et al. 2004)
What controls community composition
(i.e., species diversity)?
• Interactions with the abiotic environment
• Interactions among species
• Age
• Disturbance
• Productivity
• Size and Complexity
• Colonization and Extinction