53 Population Ecology

Question 1

What are the fundamental properties of a population?

Answer 1

Its total number of individuals, its ‘density’ and its ‘dispersion’.

Question 2

In terms of ecology, what does the ‘dispersion’ of a population mean?

Answer 2

The pattern of the distribution of its individuals.

Question 3

What are the basic patterns of ‘dispersion’ in a population?

Answer 3

‘Random’, ‘clumped’ and ‘uniform’

Question 4

What is a ‘random’ distribution of organisms in a population and what is an example?

Answer 4

The organisms are randomly distributed so that there is no pattern

For example flowers in a field gorily randomly based on where the seeds land

Question 5

What is a ‘uniform’ distribution of organisms in a population and what is an example?

Answer 5

All the individuals exhibit near uniform spacing.

For example nesting penguins on the beach maximise the distance between each other due to aggressive interactions between neighbours

Question 6

What is a ‘clumped’ distribution of organisms in a population and what is an example?

Answer 6

Many animals, such as these sea stars, group together where food is abundant.

Question 7

How can the number of individuals in a population be estimated?

Answer 7

With the ‘mark and recapture method’

Question 8

How does the ‘mark and recapture method’ work?

Answer 8

A certain number of organisms are caught and marked. Later a second sample is taken and the number of organisms with and without marks recorded.

To calculate the population size the number of animals in the first sample is multiplied by the number of animals in the second sample divided by the number of those which were marked.

Question 9

What can lead to the population size changing?

Answer 9

Births and immigration add individuals to
a population.

Deaths and emigration remove individuals from a population.

More broadly an increase in nutrients (if limiting factor) or a decrease in predation can increase the population size.

Question 10

What does ‘immigration’ refer to?

Answer 10

The movement of organisms into a population.

Question 11

What does emigration refer to?

Answer 11

The movement of organisms out of a population.

Question 12

What is the typical cause of a uniform distribution of individuals?

Answer 12

’Territoriality’ - the defense of a bounded physical space against encroachment by other individuals

Question 13

What is the most common distribution pattern of individuals?

Answer 13

Clumped. Uniform and Clumped are quite random.

Question 14

Why are random distributions rare even in plants?

Answer 14

Plant seeds might be randomly dispersed. But this in nutrient poor soils might die so clumping does occur around rich soils.

Question 15

What is ‘demography’?

Answer 15

The study of the vital statistics of populations and how they change over time.

Question 16

What is the study of the vital statistics of populations and how they change called?

Answer 16

Demography.

Question 17

What is a ‘life table’?

Answer 17

A table which records the death rate of individuals at certain age bands

Question 18

What is the best way to construct a ‘life table’?

Answer 18

By following a ‘cohort’ (a group of individuals of the same age)

Question 19

What is a ‘cohort’?

Answer 19

A group of individuals of the same age which can thus be followed to see how the survivorship rate changes with age.

Question 20

How can the affect of survival rate against age be plotted?

Answer 20

On a survivorship curve

Question 21

What is a ’survivorship curve’?

Answer 21

A graph which plots the number of survivors against ‘percentage of maximum life span’

Question 22

What features of the ’survivorship curves’ allow vastly different organisms to be compared?

Answer 22

The number of survivors is a log scale and the x-axis uses ‘percentage of maximum lifespans’ so that species with widely varying life spans can be presented together on the same graph.

Question 23

What are the most important features analysed in demographics?

Answer 23

’Survivorship curves’ and ‘Reproductive rate’

Question 24

What are the basic survivorship curves?

Answer 24

Type ‘I’, type ‘II’ and type ‘III’

Question 25

What is a type ‘III’ survivorship curve and what animals is it typical of?

Answer 25

One in which the population rapidly drops then flattens out.

This is typical of a species which releases a huge number of eggs, like fish, of which only a select few survive.

Question 26

What is a type ‘II’ survivorship curve and what animals is it typical of?

Answer 26

The survivorship rate remains relatively constant through the organisms life.

This is typical of organisms like many mammals which provide some parental care and are at a equal chance of being killed by predators throughout their maximum lifespan.

Question 27

What is a type ‘I’ survivorship curve and what animals is it typical of?

Answer 27

On in which the survivorship rate is initially very high before steeply dropping as it approaches the maximum lifespan

This is typical of animals like humans which provide a high level of infant care and which are unlikely to be preyed on and instead typically die of old age.

Question 28

What are the basic factors which indicate the change in population size?

Answer 28

‘Survivorship rates’ and ‘reproductive rates’

Question 29

What type of survivorship curve are humans?

Answer 29

Type I

Question 30

What type of survivorship curve are fish?

Answer 30

Type III

Question 31

What type of survivorship curve are rats?

Answer 31

Type II

Question 32

What is an alternative form to the classical survivorship curve and what causes it?

Answer 32

Some invertebrates, such as crabs, may show a “stair-stepped” curve, with brief periods of increased mortality during molts, followed by periods of lower mortality when their protective exoskeleton is hard.

Question 33

What is a ‘reproductive table’?

Answer 33

A table which depicts reproductive rate by age

Question 34

What is a table which depicts reproductive rate by age called?

Answer 34

A ‘reproductive table’

Question 35

What does a ‘fertility table’ refer to?

Answer 35

A ‘reproductive table’

Question 36

What does a ‘fertility table’ typically track an why?

Answer 36

Only the fertility of females as they are the only ones which yield new offspring.

Therefore it measures the average number of female offspring per female. If this ratio is one then the population will remain constant assuming all survive to adults and 50% of offspring are female.

Question 37

Based on a reproductive table what reproductive patterns can be seen?

Answer 37

The species may exhibit ’semelparity’ or ‘iteroparity’

Question 38

What is ’semelparity’?

Answer 38

Each individual produces many offspring at a time, exactly once.

Question 39

What is ‘iteroparity’?

Answer 39

The individual continues to release offspring throughout its lifetime

Question 40

What are examples of species which use semelparity?

Answer 40

Many species of flower, fungi and trees.

Also salmon and eels.

Question 41

What are the basic models of population growth?

Answer 41

The ‘logistic growth model’ and the ‘exponential growth model’

Question 42

What is the ‘logistic growth model’ and what does it suggest about the population?

Answer 42

In ‘logistic growth model’ the population increases exponentially then begins to level off.

This indicates that the population has reached its maximum size i.e. due to limited resources.

Question 43

What is the ‘exponential growth model’ and what does it suggest about the population?

Answer 43

In the exponential growth model the population continues to increase exponentially.

This suggests that the ovulation is not contained by limited resources.