Peter - Density dependent growth

Question 1

Three regions of density-dependent regulation

Answer 1

1. Density independant mortality. Number surviving increase as mortality rate is constant.
2. Undercompensating density-dependent mortalty. Mortality increase, but population still grows.
3. Overcompensating density-dependent mortality. Mortality increases further, and population declines.

Question 2

Two ways to compete for resources

Answer 2

1. Scramble or exploitation competition
2. Interference or contest competition

Question 3

Scramble or exploitation competition

Answer 3

The most common one.
Individuals compete for a food source without fighting each other. Mortality because the resource goes down. No direct interaction between contestants. Food source is reduced evenly
Example: the flour beetle. Food is evenly distributed, availabe to all individuals, and each beetle eats as much as they can.
Cows grazing on field.
Birds eating breadcrumbs.

Question 4

Interference or contest competition

Answer 4

Individuals fight for resources.
Example: birds feeding on whole bread pieces.
The contest competition often involve fighting for territory, mates or food, even though there may be enough of the resources for maximum growth.

Question 5

Scramble competition model

Answer 5

R is modifier, food source is taken into account.
Nt+1 = Nt x Rmax^(1xN/K)
K = carrying capacity.
If parenthesis becomes 1, R is at max. N is big and K is low.
N is low and K is high, population does not grow.

Question 6

Contest competition model

Answer 6

Some individuals monopolise get all the resources, some are left without. Not shared equally. Individuals fight for different resources.
Modelling is more complicated, check ppt.

Question 7

Scramble competition over time

Answer 7

Gets closer and closer to zero growth. Starts with big growth, then bigger growth, then big decline, small growth, small decline, smaller growth, smaller decline, and so on.
Closer and closer to K.
Higher Rmax gives bigger variation.

Question 8

Allee effect

Answer 8

Example: common guillemost. As population size decreases, the breeding success is also reduced. This is in contrast to what density dependent competition would predict.
They learn fishing tactics and techniques from each other. More individuals are better at detecting danger.
In other species, the reason could be that they can’t fins mates if they are too few.