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Coexistence with Stochastic Dispersal in a Nearshore Multi-Species Fishery

Coexistence with Stochastic Dispersal in a Nearshore Multi-Species Fishery. Heather Berkley & Satoshi Mitarai. Competitive Exclusion Principle. Two species with similar ecological traits competing for a limited resource cannot coexist – one will drive the other to extinction. (Volterra-Gause)

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Coexistence with Stochastic Dispersal in a Nearshore Multi-Species Fishery

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  1. Coexistence with Stochastic Dispersal in a Nearshore Multi-Species Fishery Heather Berkley & Satoshi Mitarai

  2. Competitive Exclusion Principle • Two species with similar ecological traits competing for a limited resource cannot coexist – one will drive the other to extinction. (Volterra-Gause) • This does not occur often in nature • Several different theories explain why coexistence occurs • Niche differentiation • Intermediate disturbance • Storage effect • We will focus on temporal & spatial variability in settlement & recruitment

  3. Simple Two Species Example • Consider two similar species A & B • Species A has a slightly better ability to utilize resources • Recruits compete for limited resources at settlement sites • Spawning timings are separated by weeks • Compare cases with i) smooth dispersal kernel & ii) packet model for connectivity • Smooth dispersal kernel: spawning timing does not matter • Packet model: species A & B “catch” different eddies & can settle at different sites

  4. Diffusion Case IC’s: A = 100, B = 100 On their own, both species can persist If they are put together, species B becomes extinct, species A thrives Note: this is what eddy-diffusion model predicts Time (years)

  5. Packet Model N larval packets • Larval settlement as arrival of N packets • L = domain size • l = eddy size (50 km) • T = Spawning time • t = eddy turnover rate (14 d) eddy size (l)

  6. Packet model case • Completely different spawning timing leads to coexistence IC’s:A = 100, B = 100 Generations

  7. Time-space variations Species A Species B Generations Generations Alongshore Location (km) Alongshore Location (km) Coexistence with Species A more abundant at most (but not all) locations

  8. Spawning Window Overlap • Specify how many days of overlap between spawning times for both species • Makes some packets perfectly correlated for both species and others independent Packets will have same settlement locations Species A Spawning Window Species B Spawning Window TIME

  9. Connectivity • ~half of packets perfectly correlated Species ASpecies B

  10. Parameters • Tsp (spawning time) = 30 days for both • Vary amount of overlap • Fecundity of Sp.A = 0.5 • Fecundity of Sp.B = 0.45 • Adult Mortality = 0.09 • Run time = 500 yrs; • Patch size = 5 km; • Domain size = 500 km; • Larvae on larvae DD (total # of both sp) • Averaged over 10 simulations

  11. 0 days of overlap Species ASpecies B

  12. 10 days of overlap Species ASpecies B

  13. 20 days of overlap Species ASpecies B

  14. 25 days of overlap Species ASpecies B

  15. 30 days of overlap Species ASpecies B

  16. Correlation between Connectivity Matrices for Sp A & B

  17. Correlation between Connectivity Matrices for Sp A & B Mean Correlation Coefficient # of Independent Packets

  18. Spawning Window Overlap • SpA has its entire spawning window the same as SpB • Only Sp B has independent packets Vary this amount of time Species A Spawning Window Species B Spawning Window TIME

  19. Tsp = 30 days Tsp = 30 days Species ASpecies B

  20. Tsp = 30 days Tsp = 36 days Species ASpecies B

  21. Tsp = 30 days Tsp = 42 days Species ASpecies B

  22. Tsp = 30 days Tsp = 48 days Species ASpecies B

  23. Tsp = 30 days Tsp = 54 days Species ASpecies B

  24. Tsp = 30 days Tsp = 60 days Species ASpecies B

  25. Tsp = 30 days Tsp = 66 days Species ASpecies B

  26. Tsp = 30 days Tsp = 72 days Species ASpecies B

  27. Tsp = 30 days Tsp = 78 days Species ASpecies B

  28. Correlation between Connectivity Matrices for Sp A & B

  29. Correlation between Connectivity Matrices for Sp A & B

  30. Spatial Patterns of Adults • Look at spatial covariance in Adult densities for SpA and SpB • Are these spatial patterns Adult densities strengthening coexistence?

  31. Mean Cov(A,B) through time Overlap (days)

  32. Species ASpecies B

  33. Next Steps • Compare packet model results with particle tracking simulations • Graphs of Correlation vs. Days of overlap in Tsp for 2 scenarios presented • Shorten lifespan to see how much is due to the temporal vs spatial storage effect or buffering

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