A hierarchical model for zero-inflated biomass data ...

0 downloads 0 Views 709KB Size Report
A hierarchical model for zero-inflated biomass data, with a spatial structure. Jean-Baptiste Lecomte 1, Liliane Bel 1,. Hugues Benoıt 2, Eric Parent 1. ISEC.
A hierarchical model for zero-inflated biomass data, with a spatial structure

Jean-Baptiste Lecomte 1 , Liliane Bel 1 , Hugues Benoˆıt 2 , Eric Parent 1 ISEC 03-06 July 2012

1. UMR AgroParisTech/INRA 518 - Team MORSE - France 2. Gulf Fisheries, Moncton, New Brunswick, Fisheries and Oceans Canada

Introduction

Context & Objectives Context ◮

Stock management



Fisheries impact

Objectives ◮

Prediction of the abundance



Effect of global warming



Effect of political fisheries management

Hierarchical modeling for zero-inflated biomass data N

1 / 18

Dataset

Study area : Saint-Lawrence Gulf

Latitude

55

50

Study area

45

40 −75

−70

−65

Longitude

N

−60 modeling for −55zero-inflated biomass data Hierarchical

2 / 18

Dataset

Urchins in the south Saint-Lawrence Gulf 49

Latitude

48

47

46

45 −66

−64

−62

Longitude

N

−60

Hierarchical modeling for zero-inflated biomass data

3 / 18

Dataset

Difficulties





High proportion of absence of the target species Hidden spatial structure High Inter-annual variations

Mean biomass

10



8

6

4 1990

1995

2000

2005

Years

Hierarchical modeling for zero-inflated biomass data N

4 / 18

Modeling

Chosen strategy



Zero-inflated modeling



Latent spatial structure



Hierarchical modeling



Bayesian paradigm

Hierarchical modeling for zero-inflated biomass data N

5 / 18

Modeling

Model behaviour

Hierarchical modeling for zero-inflated biomass data N

6 / 18

Modeling

Zero-Inflated Latent process

Ns ∼ Poisson(Ss µs)

Ms ,i ∼ Exp(ρ)

Hierarchical modeling for zero-inflated biomass data N

7 / 18

Modeling

Zero-Inflated Latent process

Ns ∼ Poisson(Ss µs)

Ms ,i ∼ Exp(ρ)

Observation model  N Ps   Ms ,i if 

Ys =   

i =1 0

if

Ns > 0 Ns = 0

Hierarchical modeling for zero-inflated biomass data N

7 / 18

Modeling

Zero-Inflated Latent process

Ns ∼ Poisson(Ss µs)

Ms ,i ∼ Exp(ρ)

Observation model  N Ps   Ms ,i if 

Ys =   

i =1 0

if

Ns > 0 Ns = 0

Hierarchical modeling for zero-inflated biomass data N

8 / 18

Modeling

Geostatistic : Spatial structure Addition of a Spatial structure log(µs ) = α0 + vs

Hierarchical modeling for zero-inflated biomass data N

9 / 18

Modeling

Geostatistic : Spatial structure Addition of a Spatial structure log(µs ) = α0 + vs

Covariance function

Cov (v s , vs ) = σ ′

2



h

 exp(− ) Φ

h = d (s , s ′ )

Hierarchical modeling for zero-inflated biomass data N

9 / 18

Modeling

Environmental covariate : Temperature

49

Latitude

48

47

46

45 −66

−64

−62

−60

Longitude

Temperature

0

5

10

15

Hierarchical modeling for zero-inflated biomass data N

10 / 18

Modeling

Environmental covariate : Sediment type

49

25 26

27

Sediment type 48

1 : Pelite



2 : Fine sand



3 : Coarse sand



4 : Gravel with occasional sand

31 33 32

43 42 40 20 21 23

6

34 35 8

9

47

44 10 46 5963 58

19

22

62

24

39 37 38 47 11 48

3

46

45

41

29

36

Latitude



30 28 7

61

12

16 17 50 49 51 1

18 60 5756 55 54

2

53

15 14 5213

4 5

45 −66

−64

−62

−60

Longitude

Hierarchical modeling for zero-inflated biomass data N

11 / 18

Modeling

Zero-Inflated Latent process

Ns ∼ Poisson(Ss µs)

Ms ,i ∼ Exp(ρ) log(µs ) = α0 + α1 ∗ Tp s + βSeds + vs

Observation model  N Ps   Ms ,i if 

Ys =   

i =1 0

if

Ns > 0 Ns = 0

Hierarchical modeling for zero-inflated biomass data N

12 / 18

Modeling

Inference and validation

Inference ◮

MCMC methods



OpenBUGS and GeoBUGS



Convergence checking ( 30,000 burn-in + 50,000 iterations )

Validation ◮

Posterior predictive checking



Cross-validation

Hierarchical modeling for zero-inflated biomass data N

13 / 18

Results : Covariates effects

Green Sea Urchin

Hierarchical modeling for zero-inflated biomass data N

14 / 18

Results : Covariates effects

Temperature : 95% confidence intervals 0.4

0.2

0.0

−0.2

−0.4

1

α1 Hierarchical modeling for zero-inflated biomass data N

15 / 18

Results : Covariates effects

Sediment type : 95% confidence intervals

1

0

−1

−2

1

2

β

3

4

Hierarchical modeling for zero-inflated biomass data N

16 / 18

Results : Predictions

Conditional simulations Patches number

Quantity of biomass

48

48

Latitude

49

Latitude

49

47

47

46

46

45

45 −66

−64

−62

−60

−66

−64

Longitude

Predicted Observed

0

1−5

0

10

6−10

20

−62

−60

Longitude

11−20

30

20−50

40

50

51+

60

Predicted Observed

0.0

0.01−5

0

10

6−10

20

11−20

30

20−50

40

Hierarchical modeling for zero-inflated biomass data N

50

51+

60

17 / 18

Conclusions

Perspectives & Advantages Advantages ◮

Zero-inflated modeling



Latent variables with an ecological meaning



Hidden spatial structure

Perspectives ◮

Two sources of data



Temporal dimension

Hierarchical modeling for zero-inflated biomass data N

18 / 18