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SUPPLY SIDE ECOLOGY WHAT HAPPENS TO THOSE LARVAE ANYWAY?

SUPPLY SIDE ECOLOGY WHAT HAPPENS TO THOSE LARVAE ANYWAY?. DEFINITIONS. Metapopulation. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. Local populations. •. •. •. •. •. •. •. •. •. •. •. •. •. Closed populations. •. Open populations.

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SUPPLY SIDE ECOLOGY WHAT HAPPENS TO THOSE LARVAE ANYWAY?

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  1. 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

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

  10. 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

  11. 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

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

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

  14. 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

  15. Density kernel

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

  17. 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

  18. 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

  19. 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

  20. 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

  21. One attempt at modeling

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