Populations and ecosystems

Question 1

Define a Population

Answer 1

A group of interbreeding organisms of one species in a habitat.

Question 2

Define a Community

Answer 2

All the populations of different organisms living and interacting in a particular place at the same time.

Question 3

Define a Habitat

Answer 3

The place where a community of organisms live.

Question 4

Define a Niche

Answer 4

A niche describes how an organism fits into the environment.

Question 5

Define Abundance

Answer 5

Number of organisms in a given space.

Question 6

What are the three factors to consider when using quadrats?

Answer 6

1. The size of the quadrat
2. The number of sample quadrats to record within the study area
3. The position of each quadrat within the study area

Question 7

What is a good method of random sampling?

Answer 7

1. Lay out two long tape measures at right angles along two sides of the study area
2. Obtain a series of coordinates by using random numbers taken from a table or generated by a computer
3. Place a quadrat at the intersection of each pair of coordinates and record the species with it

Question 8

When is it better to use systematic sampling along transects?

Answer 8

Where some form of transition in the communities of plants and animals takes place.

Question 9

What is the difference between a line transect an a belt transect?

Answer 9

A line transect comprises a string or tape stretched across the ground in a straight line. A belt transect is a strip, usually a metre wide, marked by putting a second line parallel to the first.

Question 10

What is the frequency of abundance?

Answer 10

The likelihood of a particular species occurring in a quadrat.

Question 11

What is the percentage cover of abundance?

Answer 11

An estimate of the area within a quadrat that a particular plant species covers.

Question 12

Estimated population size =

Answer 12

(Total number of individuals in first sample x total number of individuals in second sample)/ number of marked individuals recaptured

Question 13

What are the 5 assumptions mark, release recapture relies on?

Answer 13

1. The proportion of marked to unmarked in second sample is the same as the proportion of marked to unmarked individuals in the population as a whole
2. Marked individuals released distribute themselves evenly amongst the remainder of the population and have sufficient time to do so
3. No deaths, births, immigration, emigration
4. Method of marking is not toxic nor does it make the individual more conspicuous to predators
5. Mark or label is not rubbed off during investigation

Question 14

Why is there an initial period of slow growth in a population growth curve?

Answer 14

The initially small number of individuals reproduce to slowly build up their population size.

Question 15

Why is there a period of rapid growth in a population growth curve?

Answer 15

The ever-increasing number of individuals continue to reproduce.

Question 16

Why is there a period when the population growth declines until it remains stable in a population growth curve?

Answer 16

The decline may be due to food supply shortage, increased predation or competition.

Question 17

What are the abiotic conditions that influence the size of a population?

Answer 17

Temperature, light, pH, water and humidity

Question 18

What is intraspecific competition?

Answer 18

Individuals of the same species compete with one another for resources such as food, water, breeding sites, etc.

Question 19

What is interspecific competition?

Answer 19

Individuals of different species compete for resources

Question 20

What is the competitive exclusion principle?

Answer 20

Where 2 species occupy the same niche, one will normally have a competitive advantage over the other. If conditions remain the same, this will lead to complete removal of one species.

Question 21

What kind of fluctuations are seen in predator-prey relationships?

Answer 21

Cyclic

Question 22

How are periodic population crashes important in evolution?

Answer 22

They create a selection pressure whereby only those individuals who are able to escape predators, or withstand disease or an adverse climate, will survive to reproduce.

Question 23

Two major events that led to exponential growth in human population

Answer 23

1. Development of agriculture

2. Development of manufacturing and trade which led to industrial revolution

Question 24

Population growth =

Answer 24

(Births + Immigration) - ( deaths + emigration)

Question 25

Percentage population growth =

Answer 25

(Population change during period / population at start of period) x 100

Question 26

Birth rates are affected by :

Answer 26

1. economic conditions
2. cultural and religious backgrounds
3. social pressures and conditions
4. birth control
5. political factors

Question 27

Birth rate =

Answer 27

(Number of births per year / total population in the same year) x 1000

Question 28

Death rates are affected by :

Answer 28

1. age profile
2. life expectancy at birth
3. food supply
4. safe drinking water and effective sanitation
5. medical care
6. war
7. natural disasters

Question 29

Death rate =

Answer 29

( Number of deaths per year/ total population in same year) x 1000

Question 30

Define Demographic Transition

Answer 30

A change from where life expectancy is short and birth rates are high to where life expectancy is long and birth rates are low

Question 31

What is the average life expectancy in a survival curve?

Answer 31

The age at which 50% of the individuals in a particular population are still alive.