1. WHAT HAPPENS TO THOSE LARVAE ANYWAY?
SUPPLY SIDE ECOLOGY
WHAT HAPPENS TO THOSE LARVAE ANYWAY?

2. DEFINITIONS
Metapopulation • • • • • • • • • • • • • • • • • • • • • •
Local populations • • • • • • • •

3. • • • • •
Closed populations •
Open populations

4. Some Basic Population Theory
Population size can change due to 4 factors
1. births
local
2. death
3. immigration
regional
4. emigration
Most ecological theory – population dynamics are a function of local processes

5. 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

6. Growth equations
Closed populations
Open populations
s = rate of settlement
A = total area available
µ = death rate

7. 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

8. 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 space
Free space
Ay = total area
ay = size of adult
Change in larval pool

10. Population Connectivity
- Exchange of individuals among geographically separated subpopulations
- Similar to larval dispersal
Reproductive Population Connectivity
- Number of individuals that survive to reproduce

12. Supply side ecology
If a patch of habitat opens up
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

13. 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

14. What causes variation in recruitment?
2) Dispersal
1. Transport by currents
2. Period of transport
3. Mortality
-difficult to measure

15. Measure of dispersal
Genetic
- Can tell closed populations but not open

16. 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

17. Density kernel

18. What causes variation in recruitment?
3. Larval mortality
Pelagic predators
- hydromedusae
- scyphomedusae
- ctenophores

19. 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

20. 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

21. 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

22. Indirect Indirect Direct Mixed Kinds of Development Patterns
Free spawning
Free spawning
Planktotrophic, free-swimming larvae
Planktotrophic, free-swimming larvae
Weakly isolecithal egg
Strongly/moderately telolecithal egg
Indirect
Indirect
Maturation
Settlement and metamorphosis
Maturation
Settlement and metamorphosis
Juvenile
Juvenile
Mating
Mating
Brooding of embryos
Brooding of embryos
Strongly telolecithal egg
Moderately telolecithal egg
Direct
Mixed
Hatch as free-swimming larvae
Maturation
Maturation
Hatch as juveniles
Juvenile
Settlement and metamorphosis

23. One attempt at modeling