Section 7 - Genetics, populations, evolution and ecosystems: 19. Populations in ecosystems

Question 1

What is ecology

Answer 1

The study of the inter-relationships between organisms and their environment, including biotic (living) and abiotic (non-living) factors

Question 2

What is an ecosystem

Answer 2

Dynamic system made up of a community and the abiotic factors of it’s environment
- Elements and nutrients are cycled and reused
- Energy flows through the system (food chains)

Question 3

What is a population

Answer 3

A group of individuals of one species that live in the same habitat at the same time

Question 4

What is a community

Answer 4

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

Question 5

What is a Habitat

Answer 5

The place where an organism lives
- Characterised by the physical conditions and types of organisms present
- Made up of smaller units called ‘microhabitats’

Question 6

What is an Ecological Niche

Answer 6

How an organism fits into it’s environment, referring to where it lives, and what it does
- Links to how the organism is is adapted to survive within an area
- No two species can occupy the same exact niche (competitive exclusion principle)

Question 7

What is the ‘Carrying capacity’ of an ecosystem

Answer 7

The maximum population size of a species that an ecosystem can support
- Affected by abiotic factors, and interactions between organisms

Question 8

What are examples of Abiotic factors that can effect population size

Answer 8

• Temperature
• Light
• pH
• Water levels
• Humidity
• etc.

Question 9

How can temperature effect population size

Answer 9

Each species has an optimum temperature for it to survive, and deviation away from this will reduce the population size

Question 10

How can light levels effect population size

Answer 10

Light is the ultimate energy source for most ecosystems
∴ Increased Light energy increases the rate of photosynthesis, leading to an increase in Plant/animal population size

Question 11

How can pH (eg. soil pH) effect population size

Answer 11

pH effects enzyme action, as each enzyme has an optimum working pH
- ∴ Altering the pH will cause the enzymes to be denatured, reducing metabolic activity
- This can lead to a reduction in population size (eg. bacterial population)

Question 12

How can water levels effect population size

Answer 12

Different species are adapted to live in conditions with varying water levels, so if the water level varies from the optimum, the population size will be reduced

Question 13

How can humidity effect population size

Answer 13

Varying the humidity will vary the population size
- Effects transpiration rate in plants, effecting the rate of photosynthesis
- Effects the rate of evaporation of water (eg. from the body of animals as sweat)

Question 14

What is Intraspecific Competition

Answer 14

When individuals of the same species compete for resources
- ∴ Availability of resources will effect the population size
- Results in natural selection as individuals with favourable traits are advantageous, so more likely to survive and breed

Question 15

What is Interspecific Competition

Answer 15

When individuals of different species compete for resources
- Species with advantageous characteristics will grow in population size, as other species population is gradually reduced
- If conditions remain the same, one population will be completely wiped out (Competitive exclusion principle)

Question 16

What is the ‘Competitive exclusion principle’

Answer 16

Principle stating that two species which compete for the same limited resource cannot coexist with constant population sizes
- ∴ No two species can occupy the exact same niche
- ∴ Intraspecific competition under constant conditions will eventually lead to one species being wiped out

Question 17

What is predation and the ‘Predator-prey’ relationship

Answer 17

When one organism is consumed by another, as part of an interspecific relationship that occurs as species evolve alongside each other, with the predator adapted to hunt and the prey adapted to evade

Question 18

What are the 4 stages of the ‘Predator-Prey cycle’

Answer 18

1) Predators eat prey, reducing the prey population size
2) Fewer available prey results in competition among predators, reducing their population size
3) Fewer predators allows for an increase in the number of prey, as more survive and reproduce
4) More available prey reduces the competition among the predators, allowing more to survive and breed, so predator population increases

• They cycle then repeats, with the peak population sizes varying based on selection pressures
• Variations in the two populations are less dependant on each other if the predator has multiple prey

Question 19

What is ‘Abundance’

Answer 19

The number of individuals of a particular species in a given space
- Can’t be fully counted (time-consuming, destructive, etc.)
- ∴ Samples are used to represent the whole population

Question 20

What are the two types of Quadrats that can be used when investigating populations

Answer 20

• Point quadrat
  
  • Horizontal bar supported by two legs
  • A vertical pin is placed in holes set at intervals along the horizontal bar
  • Each species the pin touches is recorded
• Frame quadrat
  
  • Square frame with equally sized subdivisions
  • Placed at different locations, with abundance measured for each, so average for the whole area can be determined

Question 21

How can random sampling be used to investigate a population

Answer 21

• Lay 2 perpendicular tape measures as axis along the edges of the area being studied
• Obtain coordinates with a random number generator
• Place the quadrat at these coordinates and count the species within it
• Repeat for at least ten locations
• Calculate the abundance for the whole area based on the mean per quadrat

Question 22

How can systematic sampling be used to investigate a population

Answer 22

• Place a tape measure along the ground in a straight line (belt transect)
• Frame quadrat is placed at set intervals along the transect, and the species within it recorded
• Method used when there is some form of gradual change within a community
  
  • eg. Distribution of organisms along a line of succession (from the sea, through the dunes, into woodlands)
  • eg. Through changing abiotic factors (light intensity, water level, etc.)

Question 23

How do you measure the abundance of a Sessile species (organisms don’t move)

Answer 23

Samples are made using quadrats, and Abundance can be measured in several ways
- Counting the organisms
- Counting the organisms in a quadrat (sample)
- Using this to estimate the total number in the area
- Frequency
- Likelihood of a particular species occurring in a quadrat
- Useful method for species that are difficult to count (eg. grass)
- Does not provide details on species distribution in the area
- Percentage cover
- Estimate of the % area within a quadrat that a plant covers
- Allows species to be compared
- Not as useful for plants that grow in overlapping layers

Question 24

How do you measure the abundance of a Motile species (organisms can move)

Answer 24

Mark-Release-Recapture
- A known number of organisms are caught, marked and released
- Some time later, a given number of individuals are capture
- The number that were already marked in the second group is counted
- The whole population size can then be estimated, based on the assumption that the proportion marked within the second sample is the same as the proportion of marked individual within the total population

Question 25

What is the equation used to determine the size of a population from the ‘Mark-Release-Recapture’ method

Answer 25

Population size = (No. in first sample x No. in second sample) / (No. of marked individuals recaptured)

Based on the assumption that the proportion marked within the second sample is the same as the proportion of marked individual within the total population

Question 26

What assumptions are made for the ‘Mark-Release-Recapture’ method of determining population size

Answer 26

• Proportion of marked to unmarked in the second sample is the same as the proportion of marked to unmarked in the whole population
• The marked individuals distribute themselves evenly among the population after the first sample (given time to do this)
• The population has a definite boundary with no individuals moving in/out between the two samples
• Few/No deaths or births
• The method of marking is not harmful (eg. increases chance of predation)
• The mark is not lost/rubbed off during the investigation

Question 27

What is Succession

Answer 27

The series of progressive changes in the composition of an ecosystem over time
- Abiotic environment becomes less hostile
- Increases number/variety of habitats and niches
- Increases biodiversity
- More complex food webs form
- Increases biomass

Question 28

What is a Pioneer species

Answer 28

The first species to inhabit and colonise a barren ecosystem, beginning the process of primary succession
eg. Lichen

Question 29

What are some common features of pioneer species

Answer 29

• Reproduce Asexually for rapid multiplication
• Produce many widely-dispersing seeds/pores
• Rapid germination
• Can photosynthesis (self-sufficient)
• Can fix nitrogen from the atmosphere
• Tolerant to extreme conditions

Question 30

What Primary Succession

Answer 30

The colonisation of an inhospitable environment (eg. bare rock) that has never supported an ecosystem before
- Slow process
- Results in climax community

Question 31

What is the process of Primary Succession

Answer 31

• Pioneer species will cause changes to the environment, such as the erosion of rock to produce sand/soil, and provide nutrients when the organisms decompose
• This makes the environment more hospitable so new, less hardy, species can begin appear
• In these conditions, the new species now out-compete the pioneer species.
• These species then causes further environmental change to make it less hostile, so more new species can survive
• This cycle repeats as the environmental conditions are improved further, until a climax community is reached and the environment becomes stable

eg. Barren land → Lichen (pioneer species) → moss → Grass → shrubs → woodland (climax community)

Question 32

What is a Climax community

Answer 32

Environment that emerges from succession as the community has become increasing hospitable and stable
- Remains fairly stable over long periods (no new species arise due to better conditions, out competing others)
- Contains complex food webs and Niches that have developed throughout succession

Question 33

What is Secondary Succession

Answer 33

The recolonisation of an ecosystem that has been altered to become less hospitable (eg. Wildfire)
- Faster than primary succession
- Final climax community may be different if the events that impacted the area altered the conditions

Question 34

What is conservation

Answer 34

The management of the Earth’s natural resources by humans, to maximise sustainability for future use
(Active intervention to maintain ecosystem’s and biodiversity)

Question 35

What are the main reasons that conservation is important

Answer 35

• Personal
  
  • Support the future of humanity, as we rely on natural systems
• Ethical
  
  • Moral obligations (respect for living things)
  • Understanding that other species have been around longer than us, so we should be able to coexist with them
• Economic
  
  • Long-term productivity is greater if natural systems are sustained
  • eg. living organisms with the ability (ie. genes) to aid future production
• Cultural/Aesthetic
  
  • The natural world enriches our lives, so should be protected

Question 36

How is conservation achieved through managing succession

Answer 36

• Through natural succession, some species would disappear as they are outcompeted
• ∴ Land can be prevented from reaching a climax community to preserve certain species (eg. burning heathland, grazing livestock, etc.)
• This maintains ecosystems that would otherwise disappear and aids the survival so species that rely on them
• If the factor preventing succession is ever stopped, a climax community will be reached (secondary succession)