SUPPLY SIDE ECOLOGY

WHAT HAPPENS TO THOSE LARVAE ANYWAY?

DEFINITIONS

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Metapopulation

Local populations

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•Closed populations

Open populations

Some Basic Population Theory

Population size can change due to 4 factors

1. births

2. death

3. immigration

4. emigration

local

regional

Most ecological theory – population dynamics are a function of local processes

Marine populations are different

1. Many species have long-lived larvae that must disperse

-local birth rates – have no effect on local populations

2. All larvae disperse

3. Dispersal is a function of oceanographic processes

Growth equations

Closed populations

Open populations

s = rate of settlement

A = total area available

µ = death rate

Closed populations– stable equlibrium

Open populations– regulation of population growth – density dependent

- effective “birth” rate falls with density

Fluctuations in open populations depend on

1) Individual growth rate

2) Settlement rate

3) Density dependent mortality

Metapopulation models

- Scale of dispersal – large enough that larvae from many local populations interact

Cy = accessibility or larval site preference

L = number of larvae

Fy = free spaceFree space

Change in larval pool

ay = size of adult

Ay = total area

Population Connectivity

- Exchange of individuals among geographically separated subpopulations

- Similar to larval dispersal

Reproductive Population Connectivity

- Number of individuals that survive to reproduce

If a patch of habitat opens up

Supply side ecology

Supply of numbers of competitors and predators is a key element

- Need to know about local processes determining numbers

fairly easy

But if numbers of arrivals is determined by reproduction elsewhere and by dispersal

Predictions are less precise

What causes variation in recruitment?

1) Production of larvae

Previous assumption for free spawners

Most eggs are fertilized large number of larvae

- But its often < 20%

Why?

1. Sperm are short-lived

2. Sperm are widely dispersed in high energy habitats

3. Sparse distribution of donors

What causes variation in recruitment?

2) Dispersal

1. Transport by currents

2. Period of transport

3. Mortality

-difficult to measure

Measure of dispersal

Genetic

- Can tell closed populations but not open

More on dispersal

Need to determine if a site is source or a sink

Net exporter of larvae Net importer of larvae

Need to determine local (fine scale) flow patterns – very difficult

Need to determine level of self-recruitment – 1 species – 9-12 day planktotroph

-30 % settle within 0.5 km2

Density kernel

What causes variation in recruitment?

3. Larval mortality

Pelagic predators

- hydromedusae

- scyphomedusae

- ctenophores

4. Settlement

Recruitment depends on rate of supply and settlement success

Supply is either a very good or very bad predictor of settlement

Scale?

-large scale – passive transport – should be a relationship

-small scale – larval behaviour may obscure the relationship

Why is there so much waste?

- larval mortality is generally very high

What are the alternatives?

Widespread dispersal may be “bet hedging”

-dispersers can encounter suitable habitat

-non-dispersers risk loss via disturbance

Final problem with modeling population connectivity

Variable life histories in same habitat

On one patch of shore in Australia

- cloners

- direct developers

- brooders

- egg capsule planktotroph

- egg planktotroph

- egg on substrate lecithotroph

- free spawners lecithotroph

- free spawners planktotroph

Kinds of Development Patterns

Free spawning

Planktotrophic, free-swimming

larvae

Settlement and metamorphosis

Juvenile

Maturation

Weakly isolecithal egg

Indirect

Free spawning

Planktotrophic, free-swimming

larvae

Settlement and metamorphosis

Juvenile

Maturation

Strongly/moderately telolecithal egg

Indirect

Mating

Brooding of embryos

Hatch as juvenilesMaturation

Strongly telolecithal egg

Direct

Mating

Brooding of embryos

Hatch as free-swimming larvae

Juvenile

Maturation

Moderately telolecithal egg

Mixed

Settlement and metamorphosis

One attempt at modeling