Part 1: Understand size-spectrum modelling

Your goal in this first part of the course is to gain a thorough understanding of size spectra and their dynamics. This means that at the end of the week you will understand the parameters that shape the size spectra and how size spectra respond to changes. You will have a feel for how size-spectrum dynamics is different from usual single-species age-based dynamics.

It is worth expending effort on building this understanding in this first part of the course, because it will enable you to build more reliable models in the second part and to appropriately explore the model predictions in the third part.


The material for this part is split into 5 tutorials:

  1. Observed size spectra
    Because many of the physiological rates in fish (like growth, mortality, metabolism, reproduction) depend on the size of the individuals, a mizer model needs to keep track of the size distributions of the populations, the so-called size spectra. To get a feel for size spectra, in this first tutorial you will take observational data and make plots of size spectra. There is confusion in the size spectrum literature because there are different ways to represent the size spectra and this tutorial will introduce these, so that you can cut through the confusion.

  2. Single-species spectra
    At the community level, size spectra tend to look like power laws. But the size spectrum of each individual species making up the community will look different. In this tutorial we will investigate how the shape of the single species spectrum is determined by an interplay of growth and mortality.

  3. Predation, growth and mortality
    A particular strength of a mizer model is that growth curves and mortality rates are not fixed externally but are emergent and dependent on the availability of prey and the presence of predators. In this tutorial we explore how predation is modelled in mizer and how it effects growth and mortality.

  4. Species interactions
    In a mizer model all the species in the community interact with each other through size-based predation. So any changes in one species’ size spectrum affects the size spectra of the other species, which in turn affects that first species. In this tutorial we start investigating some of the effects this has.

  5. Dynamics of spectra
    In previous tutorials we have concentrated on the steady state of the mizer model, where for each size class and each species, the rate at which individuals grow into the size class balances the rate at which individuals grow out of the size class or die, thus keeping the size spectrum constant. In this tutorial we explore the dynamic that takes place when this balance is changed.

Video Introduction

In this video, Ken Andersen introduces many of the concepts that we will be discussing in this course. However, don’t feel that you have to take it all in at once. We will come back to these topics (and others) during the course where we hope to make them concrete by working hands-on with mizer.