Larval dispersal in reef fishes: biology, ecology, economics Michael - PowerPoint PPT Presentation

Larval dispersal in reef fishes: biology, ecology, economics Michael Bode ARC Centre of Excellence for Environmental Decisions, University of Melbourne mbode@unimelb.edu.au

Early research into tropical fish communities

Population dynamics on a single patch Nonlinear dynamics in the absence of dispersal: i

Population dynamics on a single patch Recruitment limitation: Doherty (1991) Ecology of Fishes on Coral Reefs

Population dynamics on multiple patches

Dispersal is essentially a linear coupling of a multidimensional nonlinear system • Dispersal is defined by connectivity matrix C • Matrix elements are the proportion of larvae from reef i that travel to reef j 1 2 3

Dispersal is essentially a linear coupling of a multidimensional nonlinear system • Dispersal is defined by connectivity matrix C • Matrix elements are the proportion of larvae from reef i that travel to reef j 1 2 3

Measuring dispersal P. maculatus. Harrison et al. (2012) Current Biology

• Resource intensive • Invasive – individual & species level • Scale limited – (temporal and spatial)

Part 1: Modelling dispersal

Modelling dispersal

Connectivity patterns ( d ) 14 Source reef 16 18 14 16 18 Destination reef

Inter-annual variation

Inter-specific variation

Part 2: Dispersal and coexistence

Coexistence needs differences

Reef fish community theory

Metacommunity simulation • Real distribution of reefs ( P = 110) • Variable dispersal matrices ( t = 1, …, 32 years) • Multiple species ( S = 5) – Identical competitors – Identical niches – Different dispersal behaviour Normally we would expect monodominance

(%)

Dispersal differences and coexistence • Same model • Two species, identical at a local scale • Larval dispersal stages of slightly different lengths. • Three identical patches

Dispersal differences and coexistence

Dispersal differences and coexistence

Coexistence is possible if each species is a superior disperser over one of the inter-patch distances

Coexistence is possible if each species is a superior disperser over one of the inter-patch distances Mechanism has high predictive power for larger simulations

Dispersal differences support coexistence that: • Is simple and intuitive • Driven by common factors • Can create quite complex patterns • Creates stable geographic replacement

Mechanisms ¡ are ¡not ¡locally ¡ observable. ¡

Part 3: Economic perspectives on dispersal

Measuring dispersal on Manus Island Mbunai Locha Pere Timonai Tawi Plectropomus areolatus. Source: FAO

Bioeconomic scales on Manus

Bioeconomic scales on Manus Community tenure areas Spawning aggregation source areas

Management question • What is the maximum annual equilibrium harvest rate from each spawning aggregation? • How do dispersal externalities affect the harvesting decision?

Harvested population model Plectropomus areolatus. Source: FAO

Harvested population model

Harvested population model Simulation model Population estimates

Independent communities • Each community chooses: – a harvest rate on each of their aggregations, – that maximises total equilibrium harvest. – given that other communities act rationally.

Harvests under different coalitions • Communities are highly heterogeneous • Describe coalition structures using partitions e.g., C 0 = {{1} {2} {3} {4} {5}} C 1 = {{1} {2},{3} {4,5}} C 2 = {{1,2,3} {4,5}} C G = {1,2,3,4,5} – 52 unique coalition structures

Harvest coalition size • Non-cooperative groups remove 12-25% / FSA / yr • Cooperative harvests remove 10-17% • Grand coalition improve overall catch (by 15%) and equilibrium population levels (by 70%)

Harvest coalition size • The current scale of management on Manus could lead to undesirable outcomes. • A grand coalition would result in an increase in catches in every community, for much lower effort

Grand coalition stability Group 2 leaves coalition

Grand coalition stability • The grand coalition surplus is insufficient for a set of side-payments to yield rational cooperation.

Smaller coalitions • The coalition between Locha and Pere is the only Nash equilibrium (internal & external stability). • Almost all the resultant benefits are captured by the adjacent communities: Tawi and Mbunai Mbunai Locha Pere Timonai Tawi

Economic impacts of larval dispersal • The scale of larval dispersal creates interconnections between communities • The dissonant scales causes problems. – Too much dispersal to ignore each other – Too much dispersal to want to cooperate – Not enough dispersal to provide necessary surplus

Collaborators Maurice James • Paul Armsworth • Glenn Almany • Lance Bode • Rick Hamilton • Luciano Mason • Geoff Jones • David Williamson •