7.4 Populations in Ecosystems

Question 1

What is an ecosystem?

Answer 1

A community and the non-living components of the environment put together

Question 2

What happens within a habitat?

Answer 2

A species occupies a niche

Controlled by biotic and abiotic factors

Question 3

What affects the size of a population?

Answer 3

Initially no limiting factors
Then
Biotic and abiotic factors

Question 4

What are some abiotic factors?

Answer 4

Temperature
Light
pH
Water and humidity

Question 5

What does humidity affect?

Answer 5

Transportation in plants - needs high transpiration

Question 6

What an ecosystem supports is called?

Answer 6

The carrying capacity

Question 7

What factors affect intraspecific competition?

Answer 7

Food
Water
Mates
Shelter 
Minerals
Light

Question 8

What is intraspecific competition? Example?

Answer 8

Competition within a species

Male robins stealing food from other males territories when food is short in winter

Question 9

What is interspecific competition? Example?

Answer 9

Competition between different species

Red and grey squirrels have the same niche

Question 10

What is predetation?

Answer 10

When one species is caught and eaten by another species

Question 11

What occurs in a predator-prey relationship?

Answer 11

Prey is eaten by a predator - population of the prey falls as the predator population increases

= increases competition between predators for prey
Lack of food for predators means their population falls so less prey eaten

Population of prey recovers - cycle occurs in an oscillating manner

Question 12

How can the size of population be estimated for slow moving organisms? Method and measurement?

Answer 12

Methods
Randomly placed quadrats
Quadrats along a transect

Measurements
Percentage cover
Frequency

Question 13

How can the size of population be estimated for fast moving organisms? Method?

Answer 13

Mark-release-recapture

Known number of species is captured and marked - so their chance of survival doesn’t change
They are released where they were caught
After a length of time another known number of organisms are captured - the number of these marked are recorded

Question 14

How is population estimated from mark-release-recapture?

Answer 14

Estimated population =

Total in the first sample 
x 
Total number in the second sample 
—————————————————
Number of marked individuals

Question 15

What does mark-release-recapture rely on?

Answer 15

The proportion of marked to unmarked is the same
The marked individuals have time to distribute evenly
Definite boundary - no immigration/emigration
Few/no births or deaths
Marking isn’t toxic and doesn’t reduce survival chance
Marks don’t rub off during the investigation

Question 16

What is succession?

Answer 16

The change of one community of organisms into the other

Question 17

What is primary succession?

Answer 17

When an area previously devoid of life is colonised by communities of organisms

Eg the eruption of a volcano

Question 18

What is the stages of succession?

Answer 18

Pioneer species
Early coloniser
Late coloniser
Climax community

Question 19

Describe succession?

Answer 19

Pioneer species (eg lichen) survive in harsh conditions
They decompose forming humus (leading to the formation of soil)
The soil becomes rich in minerals for more complex organisms
Each stage of succession tend to out compete the previous one

Question 20

What is secondary succession?

Answer 20

When a previously colonised area has been cleared (eg forest fire) is recolonised
As a soil layer is already present, succession begins at a later stage

Question 21

What is conservation? Example?

Answer 21

The human management of the earth’s resources - typically the managing of succession

Eg the controlled burning of land to stop the formation of a climax community