Populations

Question 1

Name the two major processes to consider within an ecosystem

Answer 1

• the flow of energy through the system

- the cycle of elements within the system

Question 2

Provide an example of an ecosystem and describe the interactions within it

Answer 2

A fresh water pond or lake.
It has its own community if plants to collect the necessary sunlight energy to supply organisms with it.
Nutrients such as Nitrates and Phosphates are recycled within the pond/lake.

Question 3

Define a population

Answer 3

A population is a group of interbreeding organisms of one species in a habitat

Question 4

Define a community

Answer 4

A community is all the populations of different organisms living and interacting at the same place at the same time.

Question 5

Define a habitat

Answer 5

A habitat is the place where a community of organisms lives.

Question 6

Define a microhabitat

Answer 6

Groups of smaller habitats forming the makeup of a habitat

Question 7

Define an ecological niche

Answer 7

A niche describes how an organism fits into the environment (i.e. It’s role)

A niche refers to where an organism lives and what it does there. It includes all the biotic and abiotic conditions required for an organism to survive, reproduce and maintain a viable population

Question 8

Name and explain the three factors to consider when using a quadrat

Answer 8

1) The size of the quadrat to use (this depends upon the size and distribution of the plants or animals being counted in that area)
2) The number of sample quadrats to record within the study area (the larger the number of sample quadrats the more reliable the results)
3) The position of each quadrat within the study area (statistically significant results require random sampling to be used)

Question 9

Describe the importance of using random sampling

Answer 9

It is important that sampling is random to avoid any bias in collecting data. Avoiding bias ensures that the data obtained is valid.

Question 10

Describe a method of producing random sampling

Answer 10

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

Question 11

Describe a method for systematic sampling along a transect to measure the abundance and distribution of a species

Answer 11

Place a tape measure or string along the study area, and record the number and type of different species within a quadrat places at regular intervals along the transect

Question 12

Give two methods for measuring abundance and give pros and cons for each method

Answer 12

Frequency (the likelihood of a particular species occurring in a quadrat)
-Pro : useful when a species is hard to count (e.g. grass)
-Con : doesn’t provide information on density or detail distribution
Percentage cover (an estimate of how much of a quadrat a plant species covers)
-Pro : useful where individual plants are hard to count
-Con : less useful where organisms occur in overlapping layers

Question 13

Explain why it is necessary to ensure the sample size is large

Answer 13

Because the larger the number of samples, the more representative of the community as a whole will be the results

Question 14

Name and describe a method for recording the abundance of animals

Answer 14

Mark-release-recapture
A known number of animals are caught, marked and released back into the community. Another random sample of a given number is recorded and the number or marked animals is recorded.
Population size = (No. in 1st × No. in 2nd) ÷ No. of marked in 2nd

Question 15

Give examples of some ethical considerations that should be regarded when carrying out fieldwork

Answer 15

• Organisms should be studied in situ. The frequency of moving an organism should be minimal
• Any organism removed should be returned ASAP (inc. dead)
• A sufficient time should be left before site is used for studies again
• Disturbance and damage to the habitat should be avoided. Damaged can adversely affect habitats

Question 16

Suggest a reason why even dead organisms should be returned to the habitat from which they came

Answer 16

They can be eaten by other organisms and so provide energy and nutrients to the ecosystem

Question 17

Suggest why it is beneficial to a habitat that further investigations are not carried out too soon after an initial study

Answer 17

It allows the habitat to recover from any disturbances/removal of organisms.
The results of a further study carried out out too soon after may result in data that is not typical of the habitat under ‘normal’ conditions

Question 18

In a study of a seashore, students turn over large stones to record the numbers of different organisms on their underside. Suggest reasons why it is important that these stones are replaced the same way up as they were originally

Answer 18

The organisms live under the stone so they remain moist when not covered by the tide. If the stone is left upside down the organism may be come desiccated and die.

Question 19

Name and describe the 3 phases of a population growth curve

Answer 19

1) Slow growth - the initially small number of individuals reproduce slowly to slowly build up their numbers
2) Rapid growth - the number of individuals continue to reproduce. The population size doubles during each interval time
3) Stable state - no growth except small fluctuations due to changes in biotic and abiotic factors

Question 20

Give examples of Abiotic factors and how they affect a population size

Answer 20

1) Temperature - enzyme denaturation slows metabolic activity meaning more energy is needed for homeostasis than growth
2) Light - increases the rate of photosynthesis
3) pH - affects enzymatic action.
4) Water and humidity - where water is scarce, populations are small and consist only of species adapted for dry conditions

Question 21

Explain the difference between Intraspecific and Interspecific competition

Answer 21

Intraspecific - competition between individuals of the same species
(Availability determines population size)

Interspecific - competition between individuals of different species
(Where populations of two species occupy the same niche, one will normally have a competitive advantage and grow in size.

Question 22

Define an ecosystem

Answer 22

An ecosystem is made up of all the interacting biotic and abiotic features in a specific area.

Question 23

State the equation that should be used to determine estimated population size from mark-release-recapture data

Answer 23

Estimated Population Size = (No. of individuals in first sample X No. of individuals in second sample) / number of marked recaptured individuals

Question 24

Describe some assumptions made about data for Mark-release-recapture techniques

Answer 24

• marked individuals distribute themselves evenly amongst the remaining population (and have sufficient time to do so)
• population has a finite boundary (no migration in or out)
• there are very few deaths or “births” within the population
• the method of marking isn’t toxic and doesn’t make the individual more liable to predation
• the mark or label is not rubbed of during investigation

Question 25

Name and describe the 2 types of limiting factors for the size of a population

Answer 25

• Abiotic Factors - the non-living parts of the environments

- Biotic Factors - the activities of living organisms within the environment (including competition and predation)

Question 26

Describe 3 stages for the curve of a population’s growth over time

Answer 26

1) period of slow growth as initially small number of individuals reproduce
2) period of rapid, exponential growth as increasing number of individuals continue to reproduce
3) population growth declines until population size is stable/fluctuating, due to variations in limiting factors

Question 27

Name and explain 4 abiotic factors

Answer 27

1) temperature - species have different optimum temperature, above causes denaturation of enzymes, below causes decreased metabolic activity
2) light - a source of energy for ecosystems and a necessity of life
3) pH - effects enzymatic action
4) water & humidity - when water is scarce, populations remain small and only individuals well adapted to living in dry conditions survive

Question 28

Define predation

Answer 28

Where one organism is consumed by another

Question 29

Describe the effect of a predator-prey relationship on population sizes

Answer 29

• predators eat prey and reduce prey population
• with fewer prey, predators are in greater competition with each other and thus predator population decreases
• with fewer predators, less prey are eaten and prey population increases
• with more prey now available, predator population increases again

Question 30

Explain why a theoretical single predator-prey relationship may be different to that in an ecosystem

Answer 30

Predators may eat a range of prey, so fluctuations in population sizes are often less severe

Question 31

Explain why periodical population crashes are beneficial for a species’ evolution

Answer 31

They create selection pressure whereby only the individuals that can avoid/withstand the cause for the population decrease can survive and reproduce

Question 32

State the difference between immigration and emigration

Answer 32

• immigration - individuals join a population

- emigration - individuals leave a population

Question 33

State the equation for population growth

Answer 33

Population growth = (births + immigration) - (deaths + emigration)

Question 34

State the equation for percentage population growth rate

Answer 34

Percentage population growth rate = (Population change / population at start of period) X 100

Question 35

State and explain some factors affecting birth rates

Answer 35

• Economic Conditions - countries with low per capita incomes tend to have higher birth rates
• Cultural and religious background - some countries encourage large families. Some religions oppose birth control
• Social pressure - large families improve social standing in some countries
• Birth control - the extent to which contraception and abortions are used
• Political Factors - governments influence birth rate through education and taxation policies

Question 36

State the equation for birth rate of a population

Answer 36

Birth rate = (births per year / total population in that year) X 100

Question 37

State and explain some factors affecting the death rate of a population

Answer 37

• Age Profile - higher proportions of elderly means a greater death rate
• Life expectancy at birth - economically developed country residents live longer than less economically developed countries
• Food supply - an adequate and balanced diet reduced death rate
• safe drinking water + sanitation - reduces risk of water-borne disease
• medical care - access to healthcare and education reduces death rate
• natural disasters - more prone regions to drought, famine or disease have higher death rates
• war - deaths during war produce an immediate drop in population

Question 38

State the equation for the death rate of a population

Answer 38

Death rate = (deaths per year / total population in that year) X 100