Population DynamicsPopulation dynamics is the study of the long

term changes in population sizes and the factors that cause a change.

The current focus is on human populations (ageing studies, population booms or declines), but biologists use population dynamics to study competing species and predator-prey relationships as well.

Examples

Examples

Population DynamicsIt has been around for

210 years which was when Thomas Malthus proposed the first mathematical equation to characterize human population growth.

This lead to the equations for both exponential and logistic growth which we will examine later in this unit.

Factors affecting population growth

There are four factors affecting population growth:1) Births (natality)2) Deaths (mortality)3) Immigration4) Emigration

They can all be put into a neat little equation…

N1 = N0 + (B – D) + (I – E)

If you simply want to look at the change in population from one time interval to the next simply look at:

(B – D) + (I – E)

Population DispersionPopulation Dispersion is how individuals are arranged in their habitat.There are 3 types of population dispersion:

1) Uniform Dispersion (usually due to competition between individuals)2) Clumped Dispersion (usually due to uneven distribution of resources)3) Random Dispersion (usually due to an even distribution of resources)

Population DensityPopulation Density is a measure of how many

individuals of a given species are found in a given area.

Two types of density:1) Crude density: total number of individuals

divided by the total area2) Ecological density: total number of

individuals divided by the total useable area

Equation is D = N/S

(D is density, N is population size and S is area)

Density Sample Questions1) A backyard measuring 3.0 m by 4.0 m contains 215

dandelions. Determine the population density of the plants.

2) A small field having an area of 1.5 ha contains a pond with a surface area of 0.3 ha and is home to 300 field mice. Calculate their ecological density.

3) Researchers want to relocate some nuisance black bears into a forest in Northern Quebec that is 750 km2. If each bear requires 40 km2 of forest to live successfully, how many bears can be successfully relocated here?

Population DensityIt is found differently

depending on whether the species being studied is mobile or stationary.

Quadrat studies are used for non-mobile populations like plants.

Mark-Recapture studies are used for mobile populations like animals.

Quadrat StudiesThese are used to study

non-mobile populations.A quadrat is simply a

small, known area (usually a square or rectangle) that is placed in a larger ecosystem at random and all the species in question that are located in that quadrat are counted and recorded.

More practical than counting every individual in a given ecosystem!

Quadrat StudiesAll the quadrats and

their individuals are added together in the following equation to figure the population density in a given area.

Estimated Population Density (EPD) = total number of sampled individuals / sample area

Basically a density equation.

Quadrat Study Example4) Scientists are studying the distribution of

Trilliums in a section of Lemoine Point covering 100m by 100m. They place four 1.0m X 1.0m quadrats randomly in this area and count the number of trilliums in each to be 5, 2, 1 and 3. What is the estimated trillium population density? What is the estimated trillium population size? What is one source of error in this method?

Mark-Recapture StudiesFor mobile populations

we use mark and recapture analysis.

On day one, traps are laid out in the study area and any subjects that are captured are marked and returned to the environment.

On the right is a Longworth trap… standard small mammal capturing material.

Mark-Recapture StudiesSometime later in time,

usually no more than a day or two, the traps are set again and individuals are captured.

This time it is noted how many individuals were recaptures and how many were new captures.

All this data can be plugged into an equation to figure out population density.

Mark-Recapture StudyM/N = m/n

M is the number of individuals marked the first day

m is the number of marked recaptures on the second day

n is the total number of captures on day twoN is the estimated population size

Mark-Recapture Example5) On day one, 20 warblers are captured in

mist nets. The birds are then marked with leg bands and released. One week later, the nets are reset and 50 warblers are captured. Of these 50, 10 of them were banded from the week before. Estimate the warbler population size.

Transect StudiesA transect is a straight line (or rectangle) chosen by

researchers along which they will travel counting the species being monitored.

Both mobile and stationary species can be counted this way.Size of the transect depends on the species monitored.Works best when the expected density is low or when the

individuals are very large (i.e. Douglas Fir Trees).