Populations and Communities

Question 1

What is a population?

Answer 1

A group of organisms of the same species living in a particular area at the same time

Question 2

What factors influence population growth

Answer 2

Birth Rate and Immigration INCREASE
Death Rate and Emigration DECREASE

Question 3

What are the 4 main stages of population growth?

Answer 3

Lag, Exponential, Stationary and Decline

Question 4

Describe the Lag phase.

Answer 4

Very slow increase in numbers; bacteria may be activating genes and enzymes for nutrient assimilation

Question 5

Describe the Exponential phase.

Answer 5

Exponential growth with no restrictions as resources are plentiful and organisms are reproducing at the maximum rate

Question 6

Describe the Stationary phase.

Answer 6

The birth rate and death rate are in equilibrium. Resources become limiting and toxins start to build up.

Question 7

Describe the Decline phase.

Answer 7

Resources and nutrients run out and toxic waste accumulates, causing death rate to exceed the birth rate. Competition within the population has increased

Question 8

What organism is used to show the decline phase in population growth?

Answer 8

Bacteria grown in a nutrient medium in closed conditions (beaker)

Question 9

How might population grown differ in other species?

Answer 9

Other organisations typically display a sigmoidal (s) shaped growth curve as conditions aren’t closed and the resources are renewable so the curve stops at the stationary phase

Question 10

What is the biotic potential of a population?

Answer 10

The population is reproducing at its maximum rate under optimum environmental conditions, as seen in the exponential phase

Question 11

What is environmental resistance?

Answer 11

The environmental restrictions that prevent a population from achieving its biotic potential and maximum growth

Question 12

List examples of environmental resistance

Answer 12

Lack of nutrients
Accumulation of Waste
Competition
Predation
Climatic factors

Question 13

What are biotic factors

Answer 13

Living Factors. Due to other organisms such as competition and predation.

Question 14

What are abiotic factors?

Answer 14

The non-living physical and chemical factors such as nutrients, oxygen availability, light availability, rainfall and temperature.

Question 15

What is the carrying capacity of a population?

Answer 15

This is the maximum number of a population that the ecosystem can support.

Question 16

What causes a J-shaped growth curve?

Answer 16

There is a period of very rapid growth. Followed by a crash when nutrient supplies are exhausted and predation/grazing increases

Question 17

What is competition?

Answer 17

Different organism are competing for the same resource which is in limited supply

Question 18

What is intraspecific competition?

Answer 18

Competition between members of the same species

Question 19

What is interspecific competition?

Answer 19

Competition between members of different species.

Question 20

What is the competitive exclusion principle?

Answer 20

No 2 species can occupy the same ecological niche. One will always lose (the least well adapted one).

Question 21

Explain the typical predator-prey interactions.

Answer 21

1) As the number of prey increases, there is more food available for predators. So number of predators increase.

2) Prey numbers subsequently decreases, followed by a decrease in predator as there is less food available.
Competition increases between the predator species.

3) As predator numbers decrease, prey numbers increase

4) Predator numbers will always be lower than prey numbers

Question 22

What is the equation for working out population growth?

Answer 22

Population Growth= (Births - Deaths) + (Immigration - Emigration)

P = (B-D) + (I-E)

Question 23

What are “r-strategists”

Answer 23

Opportunistic short-lived species with a fast rate of reproduction who typically display a J-shaped growth curve due to rapid growth.

They tend to be small, not good competitors and display little parental care

Are not specialised but can inhabit unstable habitats (good colonisers)

Question 24

What are “k-strategists”?

Answer 24

Organisms who reproduce slowly, with a longer life-cycle and fewer offspring

Populations tends to remain stable around the carrying capacity (K)

Larger size, good competitors and display parental care

Question 25

Give examples of + / - interactions.

Answer 25

Predator-Prey interactions and Grazing by herbivores

Question 26

What is parasitism?

Answer 26

A + / - interaction in which the parasite lives in or on the host. Benefitting from it and causing it harm over a long period.