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SUPPLY SIDE ECOLOGY WHAT HAPPENS TO THOSE LARVAE ANYWAY?

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Presentation on theme: "SUPPLY SIDE ECOLOGY WHAT HAPPENS TO THOSE LARVAE ANYWAY?"— Presentation transcript:

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 2. death 3. immigration 4. emigration local regional 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 C y = accessibility or larval site preference L = number of larvae F y = free space Free space Change in larval pool a y = size of adult A y = total area

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

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12 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

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 larvaeNet 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 km 2

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 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

23 One attempt at modeling

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