1. 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
See for more details on the EwE approach and software, numerous application examples, and the publications documenting them.

2. 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:
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.
The software can be freely downloaded from the website whose address was given in the previous slide.

3. Ecopath Master Equation (I)
Production = predation
+ fishery
+ biomass accumulation
+ net migration
+ other mortality
Contrary to a widespread opinion, Ecopath does not require ‘equilibrium’ conditions, but only mass-balance, as achieved, e.g., over the course of a year. Over that period, however, the two mass-balance equations of Ecopath must apply, for each of the groups in a model. This slide presents the first of these two equations, which pertains to mass balance between groups, i.e., to predation, fishery and migratory losses.

4. Ecopath Master Equation (II)
Consumption = production
+ unassimilated food
+ respiration
The second of the two mass-balance equations in Ecopath refers to the fluxes within a group, i.e., to the physiology of organisms.

5. Mass balance: cutting the pie
Other
mortality
Harvest
Unassi-
milated
food
Predation
Harvest
Respi-
ration
Respi-
ration
Predation
Predation
Other mortality
Unassi-
milated
food
Consumption
This slide is meant to explain how the two mass-balance equations link groups, and explain what happens to the food they consume.
Other mortality
Unassi-
milated
food
Predation
Predation
Respi-
ration

6. 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.
This is the only equation that you really need to deal with when constructing an Ecopath model. Also note that net migration and biomass accumulation usually take values of zero.

7. 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).
The data requirements of Ecopath models are easily met, as demonstrated by the large number of published models. Indeed, these requirements are for data that fisheries scientists and marine biologists commonly gather.

8. 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.
Issues of uncertainty can be explicitly addressed. Again, contrary to a widespread notion, the uncertainty inherent in species-specific parameter estimates does not ‘explode’ models that include numerous species.

9. Selection of possible models Selection of ‘best’ model
Ecoranger
Semi-Bayesian parameter estimation for Ecopath
Input ranges
‘Priors’
10,000 x
Acceptable inputs
Mass balance & physiological constraints
Selection of possible models
Resampling
(Sampling Importance Resampling)
In fact, parameter uncertainty is usually reduced when the interactions between species are considered, as these constrain the values that their parameters can take. This idea is here illustrated in a Bayesian framework.
‘Posteriors’
Selection of ‘best’ model
Accepted inputs
Outputs

10. EwE can incorporate all functional groups (100+) and all fisheries (20+)
The largest Ecopath models so far constructed included about 55 functional groups.

11. 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 ( 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.
The key Ecopath routine is obviously that which solves the system of linear equations linking the functional groups in a model (Master Equation II), though a robust matrix inversion routine which, in the process, estimates the missing parameters (one per functional group).

12. 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
Earlier attempts to construct simulation models useable for fisheries research had one major handicap: that of obtaining reasonable parameter estimates for the the underlying system of differential equations. Ecopath resolves this through its system of linear equations.

13. Representing limited prey vulnerability in Ecosim
Predator P
aVP
v(B-V)
Unavailable prey
B-V
Available prey V vV
Ecosim also addresses the issue of top-down vs. bottom up control. Users can choose a wide range of settings, rather than having to use only one form of control.
B = Total prey biomass;
V = Vulnerable prey biomass;
v = Behavioral exchange rate;
P = Total predator biomass;
a = Predator rate of search.
Fast equilibration between B-V and V implies V=vB/(2v+aP)

14. Data requirements for Ecosim
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);
Feeding time adjustment rate;
Predator effect on feeding time;
Ecological interpretation of all parameters;
Monte-Carlo routine linking to Ecoranger.
For all its versatility, Ecosim has very limited requirements beyond the data required for Ecopath.

15. 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; …
Though essentially simple, Ecosim incorporates a sizeable number of capabilities normally built in other models.

16. Ecosim predicts ecosystem effects of changes in fishing effort
Biomass/original biomass
The purpose of all this, obviously, is to explore policies…
Fishing effort over time

17. Building on the past: time series
Ecosim can incorporate (analyses indeed benefit from) time series data on:
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.
The most important recent development of Ecosim, however, has been its ability to ‘fit’ time series data.

18. North Sea time series from MSVPA (•) compared to Ecosim (line)
This made it possible to engage in formal validation exercises

19. Ecosim inter-face for evalua-ting trends over time
And it is not only the fit to biomass trends that can be evaluated, but also to mortality, and size series.

20. Ecospace
Ecospace is a spatial simulation tool for prediction of spatial patterns and impact of protected areas
Now of all the things that are missing in Ecosim-type simulations, space is the dimension that is most lacking…

21. To get started with Ecospace
Ecospace builds on Ecopath and Ecosim
Again, the data incorporated in, and validated through Ecopath provide the foundation for the next step.
Use Ecosim to check model behavior
Build an Ecospace scenario (map, habitats, …)

22. 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;
Obviously, the ‘space’ included in Ecospace has a few restrictive features, relative to the space spanned by a real ecosystem.

23. Ecospace dispersal linkage
mi,j+1Bij
Bij
One of these features is that the Ecospace ‘basemap’ consists on a number of homogenous cells, linked with each other by (generally) symmetrical exchanges.
Equal m’s (symmetrical mixing,
except at shores, toward preferred habitats)

24. Ecospace: basemap
By defining the features of these cells, users can define the basic structure of an ecosystem.

25. Ecospace can consider advection
Physical oceanographers can even add one of their favorite processes.

26. Ecospace predicts spatial distributions and impact of protected areas & habitat changes
Once an Ecospace model runs, it predicts the distribution of the functional groups, with each cell mass balanced (i.e., with an Ecosim model running in it).

27. 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.
Ecospace can also be used to explore one of the most important aspects of ecosystem-based fisheries management, i.e., the size, shape and placement of marine reserves.

28. Ecoseed: results from test model
Non-market value
Relative rent
% MPA
Rent of fishery
Existence value
The results, e.g. for the North Sea, are very much in line with what might have been expected: about 40% of it should be closed to maximize rent from the system as a whole.
This seems a lot, but let’s not forget that presently, a 100% closure of the North Sea is being considered (if only for a key species such as cod), due to the desperate situation of its fisheries.

29. Documentation of methods
Ecopath: Ecol. Modelling (1992) 61: ;
Ecosim: Fish Biol. Fisheries (1997) 7: ;
Ecosim: Ecosystems (2000) 3: 70-83;
Ecospace: Ecosystems (1999) 2:
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.
Ecopath with Ecosim is rather well documented in the literature, in addition to being illustrated through numerous published case studies, most emphasizing one or the other aspect of the approach and software.

30. 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
Here are some of the indicators of the wide dissemination of Ecopath with Ecosim, attesting, among other things, of it ease of use.

31. Models are not like religion
you can have more than one…
This does not mean other approaches or models should not be used.
and you don’t have to believe them.
Thank you.