Populations In Ecosystems

Question 1

Define abiotic factors?

Answer 1

Non living factors such as light intensity.

Question 2

Define biotic factors?

Answer 2

Factors relating to living organisms such as predation.

Question 3

Define biosphere?

Answer 3

The part of the earth and its atmosphere inhabited by living organisms, consists of many ecosystems.

Question 4

Define carrying capacity?

Answer 4

The maximum population size of a species that the environment can support given the food, habitat, water and other necessities are available in the environment.

Question 5

Define community?

Answer 5

All the organisms of different species present in a habitat.

Question 6

Define ecology?

Answer 6

The study of the relationship between plants and animals and their interactions with their chemical and physical surrounding.

Question 7

Define ecological niche?

Answer 7

The role of an organism in its ecosystem/habitat.

Question 8

Define ecosystem?

Answer 8

A natural unit of biotic and abiotic parts that interact to produce a stable system.

Question 9

Define habitat?

Answer 9

The place where an organism lives.

Question 10

Define population?

Answer 10

A group of individuals of one species found in the same habitat.

Question 11

Define population density?

Answer 11

The number of individuals per unit of area/volume.

Question 12

Define population growth?

Answer 12

All living organisms reproduce and so populations tend to increase in number.

Question 13

What are Environment Resistance or Limiting factors?

Answer 13

There are many factors limiting the size of populations, both biotic and abiotic. Changes in these factors will influence the rate of growth and final size of the population. For example; grazing, predators, shelter, food and mate availability (biotic) and light intensity, wind velocity, humidity, soil pH and temperature (abiotic).

Question 14

What are the factors that limit population size called?

Answer 14

Environmental Resistance or Limiting factors.

Question 15

Why are logarithmic graphs useful?

Answer 15

A logarithmic graph creates much smaller values allowing you to plot a straight line so it’s usable.

Question 16

What do animals compete for?

Answer 16

Food sources, water sources, shelter sources, light availability and mates.

Question 17

What are the 2 types of competition?

Answer 17

Intraspecific competition and interspecific competition.

Question 18

Intraspecific competition?

Answer 18

This is competition between individuals of the same species. The more competitions there are the greater the effect of intraspecific competition.

Question 19

Interspecific competition?

Answer 19

This is competition between individuals of different species.

Question 20

Competitive exclusion?

Answer 20

If 2 species are competing for the same limited resources, the one that is able to use the resources more effectively will survive and will eliminate the other.

Question 21

Random Sampling?

Answer 21

Using a frame or point quadrat

Question 22

Systematic sampling?

Answer 22

Using a belt transect, samples are taken at regular intervals within a set sampling area. It is sometimes more informative to measure the abundance and distribution of a species in a systematic matter, this is particularly important where some form of gradual change takes place in the communities of plants and animals e.g. The distribution of organisms along a line of succession such as through sand dunes, by the edge of the sea and inland. The stages of succession are shown especially well using a transect.

Question 23

Point quadrat?

Answer 23

It consists of a horizontal bar supported by two legs. At set intervals along the horizontal bar are ten holes through each of which a long pin may be dropped. Each species which is touched by a pin is recorded.

Question 24

Frame quadrat?

Answer 24

Which is a square frame divided by string or wire into equally sized subdivisions. It is often designed so that it can be folded to make it more compact for storage and transport. The quadrat is placed in different locations within the area, the abundance of each species is then recorded.

Question 25

What are the three factors to consider when using quadrats?

Answer 25

• size
• number of sample quadrats
• the position of the quadrat

Question 26

Why should the size of the quadrat be considered?

Answer 26

This will depend on the size of the plants or animals being counted and how they are distributed within the area. Larger species require larger quadrats. Where a population of species are not evenly distributed throughout the area a large number of small quadrats will give more representative results.

Question 27

Why should the number of sample quadrats be considered?

Answer 27

The larger the number of sample quadrats the more reliable the results will be. As recording of species within a quadrat is a time consuming task, a balance needs to be struck between the reliability of the results and the time available. The greater the number of different species present in the area being studied, the greater the number of quadrats required to produce reliable results for a valid conclusion.

Question 28

Why should the position of the quadrat be considered?

Answer 28

To produce statistically significant results a technique known as random sampling must be used.

Question 29

Why is random sampling used?

Answer 29

To avoid bias and ensure that the data obtained is reliable.

Question 30

How to sample randomly?

Answer 30

Lay out two long tape measures at right angles along two sides of the study area.

Obtain a series of coordinates by using random numbers generated by a computer or taken from a table.

Place the quadrat at the intersection of the coordinates and record the species within it.

Question 31

How to do systematic sampling?

Answer 31

A belt transect can be made by stretching a string or tape across the ground in a straight line. A frame quadrat is the laid down alongside the line and the species within it recorded. It is then moved its own length along the line and the process is repeated. This gives a record of species in a continuous belt.

Question 32

Define abundance?

Answer 32

The number of individuals of a species within a given area.

Question 33

Define frequency?

Answer 33

The likelihood of a particular species occurring in a quadrat. This method is useful where a species such as grass is hard to count. It gives a quick idea of the species present and their general distribution within an area. However, it does not provide information on the density and detail of the distribution.

Question 34

Define percentage cover?

Answer 34

An estimate of the area within a quadrat that a particular plant species covers. It is useful where a species is particularly abundant or difficult to count. It means data can be collected rapidly and individual plants do not need to be counts. It is less useful where organisms occur in several overlapping layers.

Question 35

How to obtain reliable results?

Answer 35

It is necessary to ensure that the sample size is large, that is, many quadrants are used and the mean of all the samples obtained. The larger the number of samples the more representative of the community as a whole the results will be.

Question 36

Why do we use mark release recapture?

Answer 36

As animals are generally mobile so estimating abundance by percentage cover is not useful.

Question 37

Ho to do mark release recapture?

Answer 37

1. Catch a first sample of animals and record their number.
2. Mark all the animals in the first sample with a non toxic mark that allows them to return as a normal active member of the population.
3. Leave suitable time for full mixing within the population.
4. Collect a second sample.
5. Count the number of marked and unmarked individuals in the second sample.
6. Use a formula to calculate the number I’m the population.

Question 38

Mark release recapture formula?

Answer 38

Number in population = total number in first sample X total number in the second sample / number marked and recaptured.

Question 39

What does mark release recapture rely on?

Answer 39

• that the marks are non toxic
• that animals integrate fully after release
• no births or deaths occur or there’s a balance
• no immigration or emigration
• that the marks do not run off

Question 40

What may occur due to the mark put on those captured in the first sample?

Answer 40

The marks out on the individuals make the, more easily seen by predators therefore some may be killed, those who are marked are more likely to get killed than those who are not marked. It would make the population seem larger as less marked animals would be recaptured.

Question 41

What would an increased birth rate cause?

Answer 41

Between release of the marked individuals and the second collection an increased birth rate results in an increase in population, it would increase the final estimate of the population as there would be less marked individuals collected.

Question 42

What would happen to the final estimate if a disease entered the population?

Answer 42

Between release of the marked individuals and the second collection, a disease kills a large number of the population, the final estimate of a population would stay the same as both marked and unmarked animals would die. The proportion of marked : unmarked should stay the same.

Question 43

Define tropic cascade?

Answer 43

An ecological process which starts at the top of the food chain and so effects the rest of the tropic levels.

Question 44

Define primary succession?

Answer 44

Starts in new habitats with no soil and no previous community. They are in extreme environmental conditions e.g. new volcanoes

Question 45

Define secondary succession?

Answer 45

Starts on bare soil where there had previously been a community where seed and roots already exist. They can be extreme environmental conditions e.g. Forest fires and quarries

Question 46

Factors which reduce the rate of succession?

Answer 46

• human intervention
• environmental intervention
• primary consumers (herbivores)
• anthropogenic factors (human activity)

Question 47

The stages of succession?

Answer 47

The pioneer community, lichens and mosses colonise as they can grow in hostile environments with little or no soil, they are exposed to extreme temperatures, pHs, lack of water wind and soil. Pioneer species die and decompose resulting in organic material and nitrates which form soil, this makes the environment less hostile. Plants with small roots are able to grow in shallow soil and outcompete lichens and mosses. As these plants die they release more organic matter into the soil which continues to develop and is able to hold more water and minerals, making the environment less hostile. These changes in the soil structure enable trees and shrubs to grow outcompeting the other plants. Changes in the plant community leads to a change in the animal community, this cumulates in a climax community.

Question 48

Define conservation?

Answer 48

The management of the earths natural resources so that the maximum use of them can be made in the future.

Question 49

What is the main threat to biodiversity?

Answer 49

Human activity is the main threat to biodiversity, many species are now classified as endangered and may be on the brink of extinction e.g. Dodo. Over 800 species are now extinct, ecosystems are being destroyed and this is a huge threat to biodiversity.

Question 50

Key reasons for conservation of ecosystems and biodiversity?

Answer 50

• economic, species need to be used as food sources, medicine sources, products and tourism.
• aesthetic and cultural, enjoyment of the countryside, parks, natural beauty and enrichment of lives.
• ecological and personal, species are independent, the loss of one has consequences for many other. Loss of trees can lead to soil erosion, flooding and desertification.
• ethical, all species have a right to exist, we should respect wildlife. It is our duty to prevent extinction.