❌Genetics, Populations, Evolution and ecosystems - populations in ecosystems

Question 1

What does biotic mean?

Answer 1

The living components of an ecosystem

Question 2

Define habitat

Answer 2

The place an organism usually lives

Question 3

Define biosphere

Answer 3

The regions of earth where life exists

Question 4

Define population

Answer 4

A group of individuals of the same species that are found in the same area at the same time

Question 5

Define niche

Answer 5

The role of an organism in an ecosystem including what it eats, where it lives and its behaviour, including all the biotic and abiotic conditions to which an organism is adapted in order to survive

Question 6

Define abiotic

Answer 6

The non-living components of an ecosystem

Question 7

Define ecosystem

Answer 7

A community and its abiotic environment

Question 8

Define ecology

Answer 8

The study of inter-relationships of organisms and their environment

Question 9

What is competitive exclusion?

Answer 9

Where if two species occupy the same niche, they will compete so that only one will survive and the other dies or moves away and so no two species occupy the same niche

Question 10

Give 4 abiotic factors that influence population size

Answer 10

• water
• temperature
• light
• pH

Question 11

Give 4 biotic factors that influence population size

Answer 11

• disease
• food availability
• predators
• competitors

Question 12

How does temperature influence population size in:
Plants and cold blooded animals?
Warm blooded animals, birds and mammals?

Answer 12

• in plants and cold blooded animals: Temperatures below the optimum for that species reduce rate of enzyme activity hence metabolic rate leading to a reduced carrying capacity. Temperatures above the optimum reduce enzyme activity as they denature reducing the carrying capacity
• in warm blooded animals, birds and mammals: the further the temp is away from their optimum, the more energy used in maintaining body temp so less energy is used for growth reducing the carrying capacity

Question 13

What is carrying capacity?

Answer 13

The maximum possible population size an ecosystem can support

Question 14

How does light influence population size?

Answer 14

Higher light intensity means higher rate of photosynthesis so faster plant growth and more spores produced which leads to higher carrying capacity

Question 15

How does pH influence population size?

Answer 15

As the further away the pH is from the optimum, the lower the rate of enzyme action and so the smaller the population and the carrying capacity

Question 16

How does water and humidity affect population size?

Answer 16

As humidity affects transpiration rate in plants and evaporation of water from animals so less water means population are small and only consist of species adapted to living in dry conditions

Question 17

What does abundance mean?

Answer 17

The number of individuals of a species in a given space/ area

Question 18

Give the three steps in order to describe random sampling

Answer 18

1. Arrange 2 tape measures at right angles to each other in the study area
2. Use a random number generator or table to obtain a series of coordinates
3. Place the quadrant at the intersection of each pair of coordinates and count the number of organisms of interest inside

Question 19

How are belt transects used in systematic sampling?

Answer 19

1. A string/ tape is stretched across the ground in a straight line
2. A frame quadrant is laid down alongside the line and the species within it is recorded
3. It’s then moved its own length along the line and the process is repeated giving a record of the species in a continuous belt

Question 20

What are the two ways quadrants can be used to measure abundance?

Answer 20

% frequency and % cover

Question 21

What is % frequency? Give advantages and disadvantages

Answer 21

It’s the likelihood of a particular species occurring in the quadrat where you position the quadrant and only record the presence/ absence of the species of interest

• adv: it’s quick and it’s useful if the species are hard to count as individuals e.g. moss as it gives their general distribution within the area
• disadv: it doesn’t provide info on the density and detailed distribution of a species

Question 22

What is % cover? What are its advantages and disadvantages?

Answer 22

It’s an estimate of the area within a quadrat that a particular plant species covers.

• adv: useful when the species is particularly abundant/ difficult to count so data can be collected rapidly and individual plants don’t need to be counted
• disadv: it’s harder to count organisms that occur in several overlapping layers

Question 23

How can you increase the reliability of the results when using a quadrat?

Answer 23

By increasing the sample size to more accurately represent the community as a whole

Question 24

What technique is used to measure the abundance of motile species?

Answer 24

The Mark-release-capture method

Question 25

Outline the methodology of the mark release capture method

Answer 25

1. An area is defined and marked off. Then a selection of individuals are captured, counted, marked and then released. The marking must not be easily removable or effect the organisms survival prospects
2. After the organisms have reintegrated in the population, the second capture is made
3. Both marked and unmarked organisms are counted and population size can then be calculated

Question 26

What is the formula for counting population size in mark-release-capture?

Answer 26

Estimated pop. size = (total number in first sample x total number is 2nd sample ) / number of marked individuals recaptured

Question 27

Give 6 assumptions the mark-release-capture method relies on

Answer 27

• the proportion of marked:unmarked in the 2nd sample is the same as the marked:unmarked in the whole population
• the marked individuals released from sample 1 distribute themselves evenly amongst the population and have enough time to do so
• there is no immigration or emigration out of the population
• there are few deaths and births in the population
• the method of marking is not toxic or make the individual more liable to predation
• the mark/ label isn’t lost or rubbed off during the investigation

Question 28

What is intraspecific competition?

Answer 28

When individuals of the same species compete with each other for food/ resources/ breeding sites etc. hence their availability determine the pop. size meaning the individuals that are best adapted survive in intraspecific competition

Question 29

What is interspecific competition?

Answer 29

Where individuals of different species compete for resources like light, food and water and so one species may have a competitive advantage over another causing its population to increase and lead to the diminish of the other species

Question 30

What is predation?

Answer 30

When one organism is consumed by another. In a diverse environment, there are many potential refuges for prey and so can sometimes escape predation because the fewer they are, the harder they are to catch by the predator hence the prey rarely becomes extinct

Question 31

Explain in steps how predator-prey relationship affects the population size of predator and prey

Answer 31

1. The predators eat their prey, thereby reducing the population of prey
2. With fewer prey available, the predators are in greater competition with each other for the prey that are left
3. The predator population is reduced as some of the individuals are unable to obtain enough prey for their survival or to reproduce
4. The fewer predators left, fewer prey are eaten and so more survive and are able to reproduce
5. The prey population therefor increases
6. With more prey now available as food, the predator population in turn increases

Question 32

What is ecological succession?

Answer 32

The process of change in the species structure of an ecological community over time

Question 33

What are the 3 features of a climax community?

Answer 33

• The community will consist of the same species over long periods of time
• abiotic factors are mostly the same over long periods of time
• population numbers are stable over long periods of time

Question 34

What are the two types of succession?

Answer 34

• Primary succession = bare rocks/ barren land cause species colonisation
• secondary succession = when land that previously sustained life becomes altered or disturbed meaning spores and seeds are often already in the soil

Question 35

What are the 4 features that may suit a pioneer species to colonisation?

Answer 35

• they can asexually reproduce
• produce large quantities of wind dispersed seeds/ spores to easily spread
• they’re able to photosynthesise as light is usually available while food isn’t
• they are tolerant to extreme conditions

Question 36

Why are lichens usually the first pioneer species to colonise?

Answer 36

• can survive considerable drying out
• overtime, they slowly eat away at rock to produce sand/ soil
• when they die, they decompose to release nutrients into the soil

Question 37

Give the 7 stages of succession

Answer 37

1. Colonisation by a pioneer species
2. These change the abiotic environment making it less hostile e.g soil
3. This makes it more suitable for the next species survival and less suitable for the current species causing it to be outcompeted by the new species
4. Biodiversity and species richness increases
5. There is a greater variety and, number of habitats and niches increases creating more complex food webs
6. Causing an increase in biomass
7. Process continues until the climax community is reached which is stable

Question 38

What is conservation?

Answer 38

The method of maintaining ecosystems and the living organisms that occupy them by human intervention

Question 39

What are the four main reasons for conservation?

Answer 39

• personal reasons = to maintain our planet and hence, life support systems
• ethical = respect for living organisms/ coexistence
• economic = organisms genes allow for the manufacture of substances hence long term productivity is greater if ecosystems are sustained
• cultural and aesthetic

Question 40

How does managing succession conserve habitats?

Answer 40

Because it prevents a climax community and so a greater variety of habitats and so species are conserved

Question 41

What are the factors that need to be considered when using a quadrat?

Answer 41

• size of the quadrat; larger species need larger quadrants. If the species in unevenly distributed, a large # of small quadrants will give more representative data than fewer large quadrants
• # of sample quadrants to record. A larger sample size will give more reliable results
• the position of each quadrat within the study area as random sampling avoids bias