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.

The Fundamentals N t+1 = N t + 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.

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 > Abiotic controls on life history - Density dependence

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

Fine-tuning Iteroparity Prop. of offspring over lifetime (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.

B and Size log Egg Number log Snout-Vent Length (Bruce 1978)

Variation in vital rates over life history Births Deaths  Age (i.e., senescence)  Stage / Size

Stage-specific effects on D Larvae Gyrinophilus Adults Adults (Lowe et al. 2004) Embeddedness Brook Trout

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 (MacNeale et al. 2005) 15 N

(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 > Abiotic controls on life history - Density dependence

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 The “rules”: Prey mortality Predator density …but there are important and interesting exceptions to this rule that have been shown in studies of freshwater organisms. Prey mortality Prey density

Predation in freshwater systems Predator functional response Interactions among predators Prey refuges

Predation in freshwater systems Predator functional response

How does predation rate (or prey mortality) change with prey density? Prey mortality Prey density

Predator functional response How does predation rate (or prey mortality) change with prey density? Predation Rate Time spent searching for prey 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.

Predator swamping: Reduction in individual predation risk by aggregating. 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) Individual predation risk Prey density

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 Predator density Prey mortality Predator density Without InterferenceWith Interference Prey mortality

Interactions among Predators: Feeding Frenzy!! Predator density Without FrenzyWith Frenzy Prey mortality

Predation in freshwater systems Predator functional response Interactions among predators Prey refuges  Refuge in size  Refuge in protection  Refuge in space  Refuge in time

Without refuges Prey mortality Predator density Prey mortality Prey density With refuges Without refuges With refuges Prey refuges

Refuge in Protection Potamophylax latipennis (Boyero et al. 2006)

Refuge in Protection (Boyero et al. 2006)

Refuge in Space (Sih et al. 1992) Ambystoma barbouri

Refuge in Space (Sih et al. 1992)

Refuge in Time STRESS (e.g., fish predation)

Refuge in Time Family Taeniopterygidae and Capniidae (Winter Stoneflies)