Single species population dynamics

Question 1

What did Thomas Malthus write an essay on?

Answer 1

1798 an essay on the principle of population. Saw the power of population growth and inevitability of suffering. Predicted a famine as crop supply was increasing arithmetically but the population was increasing geometrically. Inspired Darwin’s theory.

Question 2

What is the demographic transition?

Answer 2

Transition from high birth and death rates to lower birth and death rates as a country or region develops from a pre-industrial to an industrialized economic system. Naturally reduces the number of offspring through education.

Question 3

What is the model for discrete population growth?

Answer 3

N(t) = N(0) λ^t

Question 4

What is the model for continuous population growth?

Answer 4

N(t) = N(0) e ^ (rt) dN/dt = (b - m) N

Question 5

Define the intrinsic growth rate?

Answer 5

Rate at which a population increases in size if there are no density-dependent forces regulating the population. Births - Deaths.

Question 6

What is the Logistic Model?

Answer 6

dN/dt = rN ( [K - N] / K ) Sigmoidal curve, which involves density dependent factors.

Question 7

Define carrying capacity (K)?

Answer 7

The maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water, and other necessities available in the environment.

Question 8

What is the Leslie/Transition matrix?

Answer 8

A discrete, age-structured model of population growth that is very popular in population ecology.

Question 9

What happens for transition matrices that are biologically sensible?

Answer 9

All populations will come to grow/decline at a constant rate. Stable age distribution.

Question 10

Which type of competition is most important for density dependence?

Answer 10

Intraspecies competition.

Question 11

What would happen in absence of density dependence?

Answer 11

Populations would grow or decline forever, which is unrealistic.

Question 12

When is equilibrium reached in a population?

Answer 12

When birth rate equals death rate. Could have more than one equilibrium. Some populations will reach equilibrium at zero if starting at a low density.

Question 13

When does a population grow?

Answer 13

When r is above zero.

Question 14

Define an unstable equilibrium?

Answer 14

When there is slight variation, the population doesn’t return to the equilibrium.

Question 15

Define a stable equilibrium?

Answer 15

When there is a slight variation, the population returns to the equilibrium.

Question 16

Where does a population stabilise on a graph?

Answer 16

Where the growth curve intercepts the y=x line, as this means the population next year equals the population this year.

Question 17

What is the Allee effect?

Answer 17

Population doesn’t necessarily grow exponentially from small sizes. At small population sizes you get a slower growth rate than logistic suggest. Positive density dependence. Low growth rate at low density.

Question 18

Example of where the Allee effect can occur?

Answer 18

Cooperative behaviours require minimum population size. Mating pairs require a certain population density. Penguins?

Question 19

What are the types of competition for resources?

Answer 19

Scramble and Contest

Question 20

What is a contest competiton?

Answer 20

Winner takes all. A situation where available resources, such as food and mates, are utilized only by one or a few individuals, thus preventing development or reproduction of other individuals. The population levels out.

Question 21

What is a scramble competition?

Answer 21

Share the resources. A situation in which a resource is accessible to all competitors. The population suddenly plummets as there aren’t enough resources to sustain any individuals.

Question 22

What is exploitation competition?

Answer 22

Occurs indirectly through a common limiting resource which acts as an intermediate. For example, use of resources depletes the amount available to others, or they compete for space. Some plant species, for example, are able to extract water and nutrients from the soil faster than surrounding species.

Question 23

What is interference competition?

Answer 23

Organisms use up resources directly. Once used, the resource is no longer available for other species to use. The two species physically interfere with one another by aggressively attempting to exclude one another from particular habitats.

Question 24

What is a search image?

Answer 24

The mental image of an object that is apparently possessed by an animal searching for that object, and whose existence is inferred from observation of the behaviour of animals. When aphids are common, birds get a search image and predate more easily. The predator becomes saturated as breeding takes time. This is an unstable equilibrium for the aphids, so the aphid population can spiral out of control.

Question 25

Do density dependent factors keep populations at a certain size?

Answer 25

No, as other factors are also involved - environmental factors.

Question 26

What factors are negatively density dependent?

Answer 26

Predation, disease and parasitism.

Question 27

What factors are positively density dependent?

Answer 27

Cooperative behaviours require minimum population size. Mating pairs require a certain population density. Penguins?

Question 28

What is cobwebbing?

Answer 28

Plot population density next gen against density this gen. Draw a line from the population now until you meet the curve. Then reflext in y=x axis.

Question 29

What happens in scramble competition populations?

Answer 29

If population is very large one generation, it will result in a very small population the next generation.

Boom and bust.

Question 30

What happens as you increase the boom & bust of the population?

Answer 30

Takes longer to correct when it overshoots the equilibrium.

Question 31

What happens when the boom and bust (extent of over compensation) is extremely high in a population?

Answer 31

Chaos.

A trajectory that at first appears random, but within limits. Has extreme sensitivity to initial conditions, meaning that there are limits on what you can predict with the model.

No patterns that repeat themselves. As it doesn’t align to a certain pattern, cant predict very far into the future.

Question 32

What does a birufication diagram look like when degree of overcompensation is on the y axis?

Answer 32

X axis shows the points that the graph settles to

Question 33

What are the points on a birufication diagram called?

Answer 33

Attractors. The equilibrium attracts trajectories to these points, independent of starting point.

Question 34

Example of chaos in nature?

Answer 34

Childhood measles. Prior to 1960 when the vaccine started there was underlying chaos.