Transcript No Slide Title

A brief introduction to ecosystem
modeling using Ecopath with Ecosim
Daniel Pauly and Villy Christensen
Fisheries Centre,
University of British Columbia, Vancouver, Canada
United Nations University Fisheries Training Programme
Institute of Marine Science,
December 17, 2002
Reykjavik, Iceland
The software: Ecopath with Ecosim
• The Ecopath with Ecosim software package includes
mass-balance (Ecopath), time-dynamic (Ecosim) and
spatial simulation (Ecospace) models, and can be used
to:
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Evaluate biomasses and fluxes;
Address ecological questions;
Evaluate ecosystem effects of fishing;
Evaluate effects of environmental changes.
Explore management policy options;
Evaluate impact and placement of marine protected areas;
Quantify bioaccumulation, and more.
Ecopath Master Equation (I)
Production =
predation
+ fishery
+ biomass accumulation
+ net migration
+ other mortality
Ecopath Master Equation (II)
Consumption
=
production
+ unassimilated food
+ respiration
Mass balance: cutting the pie
Harvest
Predation
Harvest
Predation
Other
mortality
Other
mortality
Unassimilated
food
Respiration
Predation
Unassimilated
food
Predation
Predation
Other mortality
Unassimilated
food
Respiration
Respiration
Ecopath Master Equation (I):
How it is actually implemented
Bi * P/Bi * EEi =
Catchi
+ j Bj Q/Bj DCji
+ Net migrationi
+ Biomass accumulationi
•
Most common input: B, P/B, Q/B, Catch, Net migration (NM), biomass
accumulation rate (BA), and diet compositions (DC).
•
B, P/B, Q/B, EE, NM or BA is estimated by Ecopath.
•
DC’s are usually modified as required to ensure that EE’s are  1.
Key data requirements for Ecopath
• Biomass
(t·km-2)
• Production / Biomass
(t·km-2 ·year-1)
• Consumption / Biomass (t·km-2 ·year-1)
• Ecotrophic efficiency
(proportion)
• Diets
(proportion)
• Catches (by fleet)
(t·km-2 ·year-1)
• Growth parameters for PSD & Ecosim
It is possible to use ranges for all parameters
(see Ecoranger).
Addressing uncertainty:
• Pedigree for input data and overall index of model
quality;
• Sensitivity analysis for documenting the effect of
inputs on estimated parameters;
• Ecoranger routine for explicit consideration, in a
Bayesian context, of the uncertainty inherent in all
input;
• Closed-loop policy simulations for evaluating the
effect of uncertain inputs on the management
process.
Ecoranger
• Semi-Bayesian parameter estimation for Ecopath
Input
ranges
Acceptable
inputs
Selection of
possible models
Resampling
(S I
R
)
ampling
mportance
Mass balance
&
physiological
constraints
esampling
Selection of
‘best’ model
Accepted inputs
‘Priors’
Outputs
‘Posteriors’
EwE can incorporate all functional
groups (100+) and all fisheries (20+)
Key Ecopath routines
• Ecopath routines for entry of key data on the biology
and exploitation of ecosystem groups, and for
establishing mass-balance in semi-automatic fashion;
• FishBase bridge (www.fishbase.org) established for
input data;
• Econet: network analysis for study of ecosystem form
and functioning, incl. particle size distribution (PSD);
• Ecowrite routine for documentation of data and
assumptions used when constructing and validating
models. Incorporates reference database;
• Ecoempire module with empirical relationships, etc.
To get started with Ecosim
• Ecosim builds on Ecopath
• First step is to construct an Ecopath model
using the constraints offered by mass-balance
and thermodynamics to ensure that parameters
are compatible and realistic
Representing limited prey vulnerability in Ecosim
Predator
P
aVP
Unavailable prey
B-V
v(B-V)
vV
B = Total prey biomass;
V = Vulnerable prey biomass;
v = Behavioral exchange rate;
P = Total predator biomass;
a = Predator rate of search.
Available prey
V
Fast equilibration
between B-V and V
implies
V=vB/(2v+aP)
Data requirements for Ecosim
1. Flow-control: (top-down to bottom-up);
– Incorporates five methods for evaluating this
sensitive parameter (sensitivity analysis, time
series fitting, two-model comparison, Bunfished/B0 ,
Fmax/M);
2. Feeding time adjustment rate;
3. Predator effect on feeding time;
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Ecological interpretation of all parameters;
Monte-Carlo routine linking to Ecoranger.
Ecosim incorporates:
• Ontogenetic changes (juvenile/adult life history, variable
stage, growth/reproduction allocation strategy, seasonal
egg production);
• Food related behavior changes (diets, feeding time,
handling time)
• Trophic effects (predator/prey dynamics);
• Mediation effects, (e.g., tuna/small pelagics/birds);
• Forcing functions (seasonal/long-term; environmental,
productivity, …) ;
• Fisheries effects (bioeconomic model);
• Density-dependent catchability; …
Ecosim predicts ecosystem effects
of changes in fishing effort
Biomass/original biomass
Fishing effort over time
Building on the past: time series
• Ecosim can incorporate (analyses indeed benefit from)
time series data on:
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Relative or absolute biomasses;
Mortality rates, F, Z, catches;
Effort data;
Forcing factors (notably primary productivity)
• Incorporates goodness of fit measure (weighted SS)
• Incorporates anomaly fitting (productivity, recruitment);
• Sensitivity of the crucial Ecosim parameters can be
evaluated, and the model fitted to data;
• Ecosim thus incorporates much of the information
commonly obtained through single species assessment.
North Sea
time series
from
MSVPA (•)
compared
to Ecosim
(line)
Ecosim
interface for
evaluating
trends
over
time
Ecospace
Ecospace is a spatial
simulation tool for
prediction of spatial
patterns
and impact
of protected areas
To get started with Ecospace
• Ecospace builds on
Ecopath and
Ecosim
• Use Ecosim to check model behavior
• Build an Ecospace scenario (map, habitats, …)
Ecospace:
a spatial, meso-scale version of Ecosim
• Replicates Ecosim dynamics over spatial grid of
‘homogeneous’ cells;
• Links cells through dispersal of organisms, and
fishing effort movement/allocation;
• Incorporates an advection model.
• Accounts for spatial variation in productivity
and cost of fishing;
• Represents habitat ‘preferences’ by differential
dispersal, feeding and predation rates;
Ecospace dispersal linkage
Bij
mi,j+1Bij
Equal m’s (symmetrical mixing,
except at shores, toward preferred habitats)
Ecospace: basemap
Ecospace can consider advection
Ecospace predicts spatial distributions and
impact of protected areas & habitat changes
Ecoseed
• A routine of
Ecospace for optimal
location and sizing of
MPAs;
• Ecoseed evaluates
one seed cell for each
run;
• The ‘best’ seed cell is
selected as an MPA
cell;
• Adjacent cells
become seed cells;
• Process continues
until all cells are
MPAs.
Ecoseed: results from test model
2.5
Relative
Rent of rent
fishery
2.0
1.5
1.0
0.5
Non-market
value
Existence value
0.0
0 10 20 30 40 50 60 70 80
% MPA
0.2
0.1
0.0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
Documentation of methods
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Ecopath:
Ecol. Modelling (1992) 61: 169-185;
Ecosim:
Fish Biol. Fisheries (1997) 7:139-172;
Ecosim:
Ecosystems (2000) 3: 70-83;
Ecospace:
Ecosystems (1999) 2: 539-554
EwE overview:
ICES J. of Marine Science (2000)
‘EwE Methods, capabilities and limitations:’ Fisheries Centre
Research Report (2001) and Ecol. Modeling (in press)
• ‘EwE: A User’s Guide’ (2000);
• Ecopath –Autobalance routine: Ecol. Modelling (in press);
• Also EwE incorporates complete context-sensitive help.
Dissemination
• Distributed free-of-charge
• 2000+ users in some 150
countries (half in the
tropics);
• Present rate: 2 new users a
day;
• 20+ international
workshops/training
courses;
• 150+ published models;
• 50+ models known to be
in preparation;
• 90 peer reviewed papers,
incl. some high profile;
• 40 other publications;
• 12+ universities offering
courses;
• 13 PhD’s completed;
• 10 MSc’s completed;
• On average 100 visitors
per day to
www.ecopath.org.
Models are not like religion
you can have more than one…
and you don’t have to believe them.
Thank you.