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Workshop 1
Zooplankton Individual Based Models


Harold P. Batchelder (Oregon State University, USA)
Douglas C. Speirs (University of Strathclyde, UK)

Invited Speaker:

Wendy C. Gentleman (Dalhousie University, Canada)

This workshop will review the use of individual-based models (IBMs) in zooplankton ecology, and the ongoing debate between those favouring density-based population models and those favouring more flexible, but more complex, simulation approaches. Individual-based models are population models in which individual organisms, or quasi-individuals representing homogeneous groups of individuals, are explicitly represented as discrete elements of a computer simulation. Individuals have their own state variables (or i-state configuration), such as age, size, developmental stage, and physiological condition; population-level dynamics arise as emergent properties of the interactions among individuals and between individuals and their environment. This approach contrasts with population-level models (PLM), or aggregated mathematical models, in which population processes are described by relationships between densities of individuals. Although PLMs can represent individual properties, they do so through an i-state distribution over a population rather than explicitly representing individuals.

One of the main appeals of IBMs is that they provide an easy way of capturing population heterogeneity, or inter-population variability, because stochastic processes impacting individuals can readily be incorporated into simulations. When non-linear rate processes, the functional feeding response for example, determine population growth, the mean behaviour need not necessarily correspond to that predicted by using the underlying mean rates in a deterministic PLM. Because corresponding IBMs represent population heterogeneity explicitly and the population level outcomes emerge from this, such difficulties are side-stepped. A second advantage is that is much easier to introduce behavioural rules, especially those relating to movement, which can be extremely hard to represent in PLMs in a mathematically compact way. The inclusion of diel vertical migration in IBMs of marine zooplankton, for example, has helped to demonstrate the importance of such behaviour in the retention of populations in productive coastal upwelling zones.

The most fundamental difference between IBMs and PLMs is the continuum assumption underlying PLMs. At high trophic levels, when individual organisms are sparse, the concept of density becomes problematic, and IBMs are a natural tool. By contrast, for abundant and relatively homogeneously-distributed organisms the computational cost of representing individuals over large areas can be prohibitive. Many zooplankton populations, with complex life-histories and behaviours, and widespread but often patchy distributions, fall somewhere in the centre of this spectrum, thereby making the choice of modelling approach particularly problematic. Computational costs, and the large number of often un-measurable parameters, also mean that IBMs are not practical tools when moving away from single species zooplankton models to include coupling to higher and lower trophic levels. The workshop will focus on new methods and current challenges in the unification of individual level and population level approaches.

March 16, 2011
Wendy C. Gentleman (Invited)
Thinking outside the Z-box: How Individual-Based Models (IBMs) can advance zooplankton ecology (W1-7328)
(pdf, 1.1 Mb)
Gaël Dur, Sami Souissi and Jiang-Shiou Hwang
Individual Based Model for the phenology of Eurytemora affinis from the Seine Estuary, France (W1-7240)
(waiting for permission)
Douglas C. Speirs and Michael R. Heath
Modelling Calanus finmarchicus in the Irminger Sea: From individuals to populations (W1-7340)
(pdf, 0.7 Mb)
Matteo Sinerchia, Wes R. Hinsley, Anthony J. Field and John D. Woods
Using an Individual Based Model with four trophic levels to model fisheries recruitment (W1-7124)
(pdf, 0.8 Mb)
Jeffrey G. Dorman, Thomas M. Powell, William J. Sydeman and Steven J. Bograd
Modeled krill distribution in the California Current from 1990-2005 (W1-7309)
(pdf, 1.1 Mb)
Brie Lindsey and Harold P. Batchelder
North Pacific krill production: A bioenergetic model for Euphausia pacifica in the California Current System (W1-7307)
(waiting for permission)
Harold P. Batchelder and Brie Lindsey
Comparison of IBM and concentration based approaches to modeling krill growth and population dynamics (W1-7288)
(pdf, 1 Mb)
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    November 5 , 2010
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    December 15 , 2010
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