Modelling populations Flashcards
(6 cards)
Define a closed population
A closed population is one that has no migration or dispersal. In this case, change in population is equal to births minus deaths. These can be useful when modelling island populations where there is no ongoing migration.
How is population growth represented in a simple model for an open population?
N(t+1) = N(t) + B + I - D - E
Where N is population size, B is number of births, I is immigration, D is number of deaths, E is emigration and t is a relevant unit of time.
When can exponential population growth occur?
Exponential population growth tends to occur when a species is introduced to a novel environment with “unlimited” resources and no other predators or competitors e.g. microbial populations in a new culture, pest populations on an uninfested plant, animals introduced to an island with no predators.
Why can’t exponential population growth continue indefinitely?
Density-dependence processes mean that exponential population growth cannot continue indefinitely. Populations may respond differently in different cases e.g. crashing, stabilising, fluctuating cyclically or chaotically.
Define ‘R’ when modelling population change
R is the fundamental net reproductive rate; it can be calculated as N(t+1)/N(t), and therefore is always positive. It is the per capita net change in population size per unit time.
How is exponential population growth represented in a model using R?
N(t) = N(0) * R^t
Where N(0) is initial population size, R is the fundamental net reproductive rate, t is a relevant number of time-step units, and N(t) is population size at time t.
