Stage-dependent Demographic Modelling at Your Finger Tips


Soay sheep: an organism that can be modelled with two-sex dynamics. ©Julian Paren

Soay sheep: an organism that can be modelled with two-sex dynamics. ©Julian Paren

Typically, ecology courses contain at least a day of matrix population models. So most ecologists are somewhat familiar with how simple life cycles (and complex ones) can be depicted and analysed using matrix models. Briefly, these models represent what happens to individuals over a certain time interval (do they die? do they reproduce? if so, how much?). What individuals do in the context of these models can then be used to study the dynamics of a population.

Often, individuals are classified by size in matrix models, as small individuals tend to have different survival, growth and reproduction rates than large ones. But how many classes do you need to model the dynamics of a size-structured population properly? Instead of choosing arbitrary size class boundaries, Easterling, Ellner and Dixon (2000) came up with the idea of using continuous size variables and integrals to define a population model… and that’s how the first Integral Projection Model (‘IPM’ for us friends) came to be.

Naturally, for the development of a new demographic tool to prove useful to the scientific community, it must be flexible enough to be ‘one-size-fits-all’… and the needs of ecologists, evolutionary biologists and conservation biologists – who have to date used extensively size-based matrix models – are rather variable in size, colour and shape. Continue reading