2 Populations In Ecosystems

Question 1

Define community

Answer 1

Populations of different species in a habitat

Question 2

Define ecosystem

Answer 2

A community, plus all the abiotic conditions in the area in which it lives. Ecosystems can be small or large.

Question 3

Define niche.

Answer 3

Describe how an organism fits into the environment. A niche refers to where an organism lives and what it does there. Includes all the biotic and abiotic conditions to which an organism is adapted to in order to survive, reproduce and maintain a viable population. No 2 species occupy the same niche.

Question 4

Why does every species occupy a different niche?

Answer 4

• the niche a species occupies within its habitat includes:
  
  • it’s biotic interactions eg. The organism it eats, those it’s eaten by
• it’s abiotic interactions eg. The oxygen organism breathes in and CO2 breathes out.

Question 5

Explain how the size of a population can be estimated using the mark-release-recapture method.

Answer 5

• capture sample of species using an appropriate technique
• mark them in a harmless way eg. By putting spot of pain on them
• release them back to habitat
• wait a week, then take a second sample from same population
• count how many of second sample are marked
• use equation to estimate total population size.

Question 6

What is the equation for the mark-release-recapture method?

Answer 6

Total population size= (number caught in 1st sample x number caught in 2nd sample) / number marked in 2nd sample.

Question 7

What are the assumptions when using the mark-release-recapture method?

Answer 7

• marked sample had enough time + opportunity to mix back in with the population
• marking hasn’t affected the individuals’ chances of survival (eg by making them more visible to predators) and the marking itself is still visible
• there are no changes in population size due to births, deaths and migration during the period of study.

Question 8

How does temperature ( abiotic factor) affect population size?

Answer 8

• each species has different optimum temp at which it’s best able to survive.
• further away from this, fewer individuals in pop able to survive, and smaller is pop that can be supported.
• in plants + cold-blooded animals, as temp fall below optimum, enzymes work more slowly + so metabolic rate is reduced. Pops therefore have smaller carrying capacity. At temp above optimum, enzymes work less efficiently because they gradually undergo denaturation.
• in warm-blooded animals, further temp of external environment is from optimum, more energy organisms expend trying to maintain normal body temp. Leaves less energy for individual growth + so they mature more slowly + their reproductive rate slows. Carrying capacity of pop reduced.

Question 9

How does light (abiotic factor) affect population size?

Answer 9

• light is basic necessity in life
• rate of photosynthesis increases as light intensity increases
• greater the rate of photosynthesis, faster plants grow + more spores or seeds they produce
• carrying capacity therefore potentially greater. In turn, carrying capacity of animals that feed on plants is potentially larger.

Question 10

How does pH (abiotic factor) affect population size?

Answer 10

• affects action of enzymes
• enzyme has optimum pH at which it operates most effectively
• population of organisms larger where appropriate pH exists + smaller, or non-existent, where pH different from optimum.

Question 11

How does water and humidity (abiotic facto) affect population size?

Answer 11

• where water scarce, populations small + consist only of species that are well adapted to living in dry conditions
• humidity affects transpiration rates in plants + evaporation of water from bodies of animals
• in dry air conditions, populations of species adapted to tolerate low humidity will be larger than those with no such adaptations

Question 12

Describe intraspecific competition.

Answer 12

Occurs when individuals of same species compete with one another for resources. It’s availability of such resources that determines size of population. Greater availability, larger pop. Lower availability, smaller pop.

Question 13

Give an example of intraspecific competition.

Answer 13

Limpets competing for algae, which is their main food. More algae available, larger limpet population becomes.

Question 14

Describe interspecific competition.

Answer 14

Occurs when individuals of different species compete for resources. When pops of 2 species in competition 1 will normally have competitive advantage. Pop of this species gradually increase in size while population of other will diminish. If conditions remain same, this will lead to complete removal of 1 species. This is known as competitive exclusion principle.

Question 15

Explain how interspecific competition influences population size.

Answer 15

Link to birth + death rate of individuals in pop. Increase in food supply doesn’t necessarily mean there’ll be more individuals. Could just result in bigger individuals. Decrease in food supply could lead to individuals dying of starvation + directly reduce size of pop. Increase in food supply means more individuals likely to survive + so there’s increased probability that they,, produce offspring and pop will increase.

Question 16

Explain what is meant by predation.

Answer 16

Occurs when one organism is consumed by another. When pop of a predator and a pop of its prey brought together in a lab, prey usually exterminated by predator. Because range + variety of habitat provided normally limited to confines of lab. In nature, area over which pop can travel is greater and variety of environment more diverse. Prey can escape because fewer there are the harder they are to find and catch. Therefore, although prey pop falls to low level, it rarely becomes extinct.

Question 17

Describe the effects of predator-prey relationships on population size.

Answer 17

• predators eat their prey, reducing pop of prey
• fewer prey available, predators in greater competition with each other for prey left
• predator pop reduced as some individuals unable to obtain enough prey for their survival or to reproduce
• fewer predators eating prey, so more prey survive and reproduce
• prey pop therefore increases
• More prey available as food, predator pop in turn increases

Question 18

Why should the size of the quadrat be considered when using quadrats?

Answer 18

Size will depend on size of plants or animals being counted + how they’re distributed within the area. Larger species require larger quadrats. Where pop of species not evenly distributed throughout area, large number of small quadrats will give more representative results.

Question 19

Why should the number of sample quadrats to record within the study area be considered when using quadrats?

Answer 19

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

Question 20

Why should the position of each quadrat within the study area be considered when using quadrats?

Answer 20

To produce statistically significant results random sampling must be used.

Question 21

Describe how a transects is used to obtain quantitative data about changes in communities along a line.

Answer 21

Lines called transects used to help find out how plants are distributed across an area. In belt transects, quadrats placed next to each other along the transect to work out species frequency and % cover along transect. To cover larger distances, quadrats can be placed at intervals along the line. This known as interrupted belt transect.

Question 22

Define abundance.

Answer 22

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

Question 23

How does frequency measure the abundance for species that don’t move around?

Answer 23

Frequency is the likelihood of a particular species occurring in a quadrat. This method useful where species is hard to count. Gives a quick idea of the species present and their general distribution within an area. However, doesn’t provide information on density + detailed distribution of a species.

Question 24

How does percentage cover measure the abundance for species that don’t move around?

Answer 24

Percentage cover is an estimate of area within a quadrat that a particular plant species covers. Useful where species is particularly abundant or is difficult to count. Data can be collected rapidly + individual plants don’t need to be counted. However, less useful where organisms occur in several overlapping layers.

Question 25

Define succession.

Answer 25

Succession takes place in a series of stages. At each stage new species colonise the area and these may change the environment. Species may alter the environment in a way that makes it:

• less suitable for existing species, new species out compete existing ones
• more suitable for other species with different adaptations, this species may be our competed by better adapted new species

Question 26

What features suit the pioneer species to colonisation?

Answer 26

• asexual reproduction so that a single organism can rapidly multiply to build up pop
• production of vast quantities of wind-dispersed seeds or spores, so they can easily reach isolated situations
• rapid germination of seeds on arrival as they don’t require a period of dormancy
• ability to photosynthesis, not dependent on animal species
• ability to fix nitrogen from atmosphere, even if there’s soil, it has few or no nutrients.
• tolerance to extreme conditions.

Question 27

Describe sages of primary succession.

Answer 27

Starts when species colonise a new land surface. Seeds + spores blown in by wind + begin to grow. This first species called pioneer species.

• abiotic conditions hostile. Pioneer species grow because they’re specially adapted
• pioneer species change abiotic conditions, they die + microorganisms decompose dead humus. This forms basic soil
• makes conditions less hostile, basic soil helps retain water means new organisms with different adaptations can move in and grow. These then die and are decomposed, adding more organic material, making soil richer deeper in minerals.

Question 28

Describe secondary succession.

Answer 28

Happens in same way as primary succession, but because there’s already soil layer succession starts at a later stage, pioneer species in secondary succession are larger plants.

Question 29

Describe a climax community.

Answer 29

The ecosystem is supporting the largest and most complex community of plants and animals it can. It won’t change much more, it’s in a steady state.

Question 30

What common features emerge during any succession?

Answer 30

• abiotic environment becomes less hostile
• greater number and variety of habitats and niches in turn produce:
  - increased biodiversity
  - more complex food webs
  - increased biomass

Question 31

What is meant by conservation?

Answer 31

The management of the earths natural resources by humans in such a way that maximum use of them can be made in the future. This involves active intervention by humans to maintain ecosystems and biodiversity.

Question 32

What are the personal reasons for conservation?

Answer 32

To maintain our planet and therefore our life support system.

Question 33

What are the ethical reasons for conservation?

Answer 33

Other species have occupied the earth far longer than we have and should be allowed to coexist with us. Respect for living things is preferable to disregard for them.

Question 34

What are the economic reasons for conservation?

Answer 34

Living organisms contain a gigantic pool of genes with capacity to make millions of substances, many of which may prove valuable in the future. Long-term productivity is greater if ecosystems are maintained in their natural balanced state.

Question 35

What are the cultural and aesthetic reasons for conservation?

Answer 35

Habitats and organisms enrich our lives. Their variety adds interest to everyday life and inspires writers, poets and others who entertain and fulfill us.

Question 36

Explain how managing succession can help to conserve habitats. Eg moorland ecosystem

Answer 36

• allow animals to graze on land, animals eat growing points of shrubs and trees, which stops them from establishing themselves and helps keep vegetation low
• managed fires are lit. After fires, secondary succession will occur- species that grow back first are species that are being conserved. Larger species take longer to grow back and will be removed again next time moor is burnt.

Question 37

Why do we need to prevent succession for conservation in moorland ecosystem?

Answer 37

Large areas of Moreland provide habitats for many species of plant and animals. If moorland left to natural processes, succession would lead to climax community if spruce forest. This would mean loss of moorland habitat and thus loss of some plants and animals living there. Preventing succession keeps moorland ecosystem intact.