Transcript Levels of Ecological Organization in Freshwater Systems Population

Levels of Ecological Organization
in Freshwater Systems
Population
Community
Ecosystem
Population Biology in
Freshwater Systems
Lecture Goals
• To discuss basic controls on population
size and population dynamics in freshwater
systems.
• To use the primary literature to explore
specific mechanisms regulating population
size and population dynamics in freshwater
systems.
What is a population?
• A group of interacting individuals of
the same species in a particular place,
at a particular time.
Population regulation: What determines the
size of a population?
Population dynamics: How does population
size change over time?
• A group of interacting individuals of
the same species in a particular place,
at a particular time.
• A group of interacting individuals of
the same species in a particular place,
at a particular time.
The Fundamentals
Nt+1 = Nt + B – D + I – E
“local”
“spatial”
I and E
Along streams and rivers…
Among ponds and lakes…
Lecture structure
• Life history and Reproduction (B)
• Mortality (D)
Lecture structure
• Life history and Reproduction (B)
Life History: Changes experienced by an
individual between birth and death that
determine habitat requirements, ecology,
and reproductive output.
Life History: Changes experienced by an
individual between birth and death that
determine habitat requirements, ecology,
and reproductive output.
Intrinsic differences in life history

Extrinsic ecological factors acting on stages
Variation in population size
over space and time
Lecture structure
• Life history and Reproduction (B)
> Reproductive strategies
> Variation in vital rates with life history
- Density dependence
> Abiotic controls on life history
Lecture structure
• Life history and Reproduction (B)
> Reproductive strategies
Reproductive Strategies
• Semelparity: Reproduce once in
lifetime, then die.
• Iteroparity: Reproduce multiple
times in lifetime.
• Semelparity: Reproduce once in
lifetime, then die.
Implications of Semelparity
• To contribute to B, just need to survive to
reproduce.
• Females can invest everything they have in
reproduction once they reach some “threshold”.
• If reproduce in bad year, then fitness can go to 0
(i.e., all eggs in one basket).
***Dead bodies go right back into food web***
Implications of
Semelparity
• Iteroparity: Reproduce multiple
times in lifetime.
Implications of Iteroparity
• To have a significant impact on B, need to
survive to reproduce multiple times.
• Current investment in reproduction may
reduce future reproductive potential.
• If reproduce in a bad year, then can still have
high fitness over lifetime (i.e., eggs are in
multiple baskets).
Cladoceran Life Cycle
Prop. of offspring over lifetime
Fine-tuning Iteroparity
(Dubycha 2001)
Lecture structure
• Life history and Reproduction (B)
> Reproductive strategies
> Variation in vital rates with life history
Variation in vital rates with life history
• Births
Stage (i.e., juvenile vs. adult)
Size
B and Stage
VS.
VS.
log Egg Number
B and Size
(Bruce 1978)
log Snout-Vent Length
Variation in vital rates over life history
• Births
• Deaths
Age (i.e., senescence)
Stage / Size
Stage-specific effects on D
Larvae
Brook Trout
Embeddedness
Adults
Gyrinophilus
Adults
(Lowe et al. 2004)
Variation in vital rates over life history
• Births
• Deaths
• Dispersal
Stage
Size
The colonization cycle of
freshwater insects
What is the demographic importance of
drifters?
> “Excess” individuals
> Low-fitness individuals
If drifters ARE demographically
important…
If drifters ARE NOT demographically
important…
How are we quantifying dispersal?
Dispersal and Drift
15N
(MacNeale et al. 2005)
15N
(MacNeale et al. 2005)
Sticky Traps
(MacNeale et al. 2005)
Lecture structure
• Life history and Reproduction (B)
> Reproductive strategies
> Variation in vital rates with life history
- Density dependence
Density
Dependent
Recruitment
• Brown trout (Salmo
trutta) in two streams
in UK
• Egg density ≈ Density
of reproductive adults
• May depend on range
of observations
(Elliott 1987)
Lecture structure
• Life history and Reproduction (B)
> Reproductive strategies
> Variation in vital rates with life history
- Density dependence
> Abiotic controls on life history
Abiotic controls on life history
Abiotic controls on life history
Broader implications
 Mediates exposure to other factors (e.g.,
predators)
 Regulates how closely a population can
track resources
 Affects the rate at which populations can
respond to natural selection
Lecture structure
• Life history and Reproduction (B)
• Mortality (D)
Important controls on mortality
in freshwater systems
• Drying of ephemeral pools and streams
• Flooding and bed movement
• Rapid changes in chemical or physical
conditions
• Predation
• Others…
Predation in freshwater systems
Prey mortality
Prey mortality
The “rules”:
Predator density
Prey density
…but there are important and interesting
exceptions to this rule that have been shown
in studies of freshwater organisms.
Predation in freshwater systems
• Predator functional response
• Interactions among predators
• Prey refuges
Predation in freshwater systems
• Predator functional response
Predator functional response
Prey mortality
How does predation rate (or prey mortality)
change with prey density?
Prey density
Predator functional response
How does predation rate (or prey mortality)
change with prey density?
Time spent
searching for prey
Predation Rate
Time spent
“handling” prey
Predator functional response
(Begon et al. 1990)
Predator functional response
Broader implications
 Even at high predator densities, prey
mortality is limited by handling time.
 There will always be a maximum
predation rate that prey can offset with
reproduction.
 Creates the opportunity for predator
swamping.
Individual
predation risk
Predator swamping: Reduction in
individual predation risk by aggregating.
Prey density
Assumptions:
• Predator density is fixed
• Search time is low and independent of prey density
(i.e., aggregations no more likely to be found that
individuals)
Predator swamping: Reduction in
individual predation risk by aggregating.
Examples:
• Fish schools in lakes
• Synchronous emergence in aquatic insects
• Zooplankton patches in lakes
Predation in freshwater systems
• Predator functional response
• Interactions among predators
Interactions among Predators:
Interference
With Interference
Prey mortality
Prey mortality
Without Interference
Predator density
Predator density
Interactions among Predators:
Feeding Frenzy!!
With Frenzy
Prey mortality
Prey mortality
Without Frenzy
Predator density
Predator density
Predation in freshwater systems
• Predator functional response
• Interactions among predators
• Prey refuges
 Refuge in size
 Refuge in protection
 Refuge in space
 Refuge in time
Prey mortality
Prey mortality
Prey refuges
Predator density
Prey density
Refuge in
Protection
(Boyero et al. 2006)
Potamophylax latipennis
Refuge in
Protection
(Boyero et al. 2006)
Refuge in Space
Ambystoma barbouri
(Sih et al. 1992)
Refuge in Space
(Sih et al. 1992)
Refuge in Time
STRESS
(e.g., fish predation)
Refuge in Time
Family Taeniopterygidae and Capniidae
(Winter Stoneflies)