Populations

Question 1

Define abiotic

Answer 1

Non-living factors such as temperature, rainfall, pH and light intensity in an environment that influences the size of a population.

Question 2

Define adaptation.

Answer 2

An organism adapts to their environment by adjusting their behaviour, physiology and structure of itself to become better suited to survive and successfully pass their genes onto the next generation.

Question 3

Define biotic.

Answer 3

Living factors eg competition and predation in an environment that influence the size of a population.

Question 4

Define community.

Answer 4

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

Question 5

What is the ‘competitive exclusive principle’?

Answer 5

Interspecific competition leads to populations of two species competing for resources. One species usually has a competitive advantage over the other. Thus, the population of this species will gradually increase in size whilst the other diminishes.

Question 6

Define population.

Answer 6

A group of individuals of one species that occupy the same place at the same time (with the potential to interbreed).

Question 7

The size of a population can vary as a result of:

Answer 7

• the effect of abiotic factors.

- interactions between organisms (eg intra and inter specific competition and prediction).

Question 8

Define habitat.

Answer 8

The place where an organisms normally lives and is characterised by physical conditions and the other types of organisms present.

Question 9

What is a microhabitat?

Answer 9

Within each habitats are smaller units, each with their own microclimate.

Question 10

Define niche.

Answer 10

Where an organism lives and what it does there. It includes all the abiotic and biotic conditions to which an organism is adapted.

Question 11

Define competitive exclusion principle.

Answer 11

No two species occupy exactly the same niche. For example due to different tolerance of environmental factors eg pollution.

Question 12

What is the carrying capacity determined (limited) by?

Answer 12

Factors such as:

• availability of food
• light
• water
• oxygen
• shelter
• accumulation of toxic waste
• predators
• disease

Question 13

What abiotic factors influence the size of a population?

Answer 13

• temperature
• light
• pH
• water and humidity

Question 14

Outline how pH is an abiotic factor that can influence the size of a population.

Answer 14

pH affects the action of enzymes. Each enzyme has an optimum pH at which it operates most effectively.

A population is larger where appropriate pH exists. And smaller, of non-existent populations where the pH differs from the optimum.

Question 15

Outline how water and humidity, as an abiotic factor, influences the size of a population.

Answer 15

Where water is scarce, populations are small and only consist of populations adapted to dry conditions.

Humidity affects transpiration rates in plants and the evaporation of water from the bodies of animals. So, again, in dry air conditions, the populations adapted to tolerate low humidity will be larger than those with no such adaptions.

Question 16

Define ecosystem.

Answer 16

A dynamic system made up of a community and all non-living factors of its environment. They can range in size from very small to very large. Eg: freshwater pond, lake, a woodland.

Question 17

Define environment.

Answer 17

The external surroundings including all the biotic and abiotic factors that surround and affect the survival and development of organisms of a population.

Question 18

Define habitat.

Answer 18

The place where an organism normally lives and is characterised by physical conditions (abiotic factors) and with other types of organisms present. Within an ecosystem, there are many habitats.

Question 19

Define interspecific competition.

Answer 19

Competition between organisms of different species. Eg for resources such as food, water, light.

Question 20

Define intraspecific competition.

Answer 20

Competition between organisms of the same species. Eg for food, water, breeding sites.

Question 21

How can intraspecific competition lead to smaller populations?

Answer 21

The availability of resources (eg food) can affect the degree of competition between organisms - resulting in a smaller population.

Question 22

Define prediation.

Answer 22

A relationship between two organisms of different species in which one organism is a predator that captures and feeds in the organism that serves as prey. This affects population size.

Question 23

What is the difference between a habitat and a niche?

Answer 23

Habitat = where a species lives. Niche = what it does in that habitat.

Question 24

What are 3 ways that organisms can adapt?

Answer 24

Physiological (inside their body), behavioural and anatomical (structural features of their body).

Question 25

What is population size?

Answer 25

The total number of organisms of one species in a habitat.

Question 26

Define carrying capacity.

Answer 26

The maximum stable population size of a species that an ecosystem can support. The carrying capacity carries as a result of abiotic and biotic factors.

Question 27

Outline how inter specific competition can be a problem (re food).

Answer 27

If two species share the same food source, there will be less available to both of them. This means both populations will be limited by a lower amount of food. They'll have less energy for growth and reproduction, so the population size will be lower for both species.

Question 28

What happens in inter specific competition if one species is better adapted?

Answer 28

The less well adapted species is likely to be outcompeted (eg the grey squirrel outcompetes the red squirrel).

Question 29

In intra specific competition, how can population fluctuate?

Answer 29

The population of a species increases when resources are plentiful. However, as the population increases, there'll be more organisms competing for the same amount of space and food. Eventually, resources eg food become limiting (there isn't enough) so population begins to decline. A smaller population then means there's less competition for resources eg space and food, which is better for growth and reproduction - so the population starts to grow again.

Question 30

How can predation cause the population to fluctuate?

Answer 30

As the prey population increases, there's more food for the predators, so the predator population grows. As the predator population increases, more prey is eaten so the prey population begins to fall. This means that there's less food for the predators, so their population decreases and so on.

Question 31

What is mark-release-recapture?

Answer 31

M-R-R is a method used to measure the abundance of more motile species.

Question 32

What's the equation for mark release recapture?

Answer 32

Total population size = no caught in 1st sample x no caught in 2nd sample / no marked in second sample

Question 33

Outline the mark-release-recapture technique.

Answer 33

1. Capture a sample of species using an appropriate technique. 2. Mark them in a harmless way (eg spot of paint). 3. Release them back into their habitat. 4. Wait a week, then take a second sample from the same population. 5. Count how many of the second sample are marked. Then use the equation to estimate the total population size.

Question 34

There are sources of error in the mark-release-recapture technique. What are the assumptions the experimenter makes?

Answer 34

- the mark is not lost or rubbed off - few births and deaths in the time period - the population has a definite boundary - the marked population have sufficient time to redistribute themselves evenly - the proportion of marked to unmarked animals is the same in the 2nd sample as in the population as a whole

Question 35

What are ethnical assumptions with the mark-release-recapture technique?

Answer 35

- the marking is non-toxic - the mark does not make the animal more conspicuous to predators - the capture and marking method is not harmful / overly stressful to the animal

Question 36

What's the problem with the mark-release-recapture method if the 2nd sample is left too long a time before being repeated?

Answer 36

The animals may migrate away.

Question 37

What's the problem with the mark-release-recapture method if the 2nd sample is too soon after the 1st sampling?

Answer 37

The animals haven't had time to redistribute themselves

Question 38

Why use quadrats when you could just count the number of individuals in a species?

Answer 38

Because that would be too time consuming

Question 39

How to do a random quadrat?

Answer 39

1. Set out two measuring tapes at right angles with each other. 2. Choose pairs of random numbers using a random number generator. 3. These random numbers will give you the coordinates of the point where you should place your quadrat.

Question 40

What does a quadrat actually measure?

Answer 40

Studying the distribution of non-motile plants or animals in a fairly uniform area. You can measure either the frequency or percentage cover of a sample of organisms.

Question 41

What is a transect?

Answer 41

A line through a study area along which samples are taken.

Question 42

Why would you use a transect?

Answer 42

Usually where one or more abiotic factors in the environment gradually vary. Or if there appears to be a change in communities from one place to another.

Question 43

How do you use a line transect?

Answer 43

You place it so it follows the environmental gradient (eg from sunlight into shades or up a seashore).

Question 44

How do you do a belt transect?

Answer 44

Quadrats are used continuously along a transect to sample in more detail.

Question 45

In quadrats, what is percentage cover?

Answer 45

% cover measures the proportion of the ground in a quadrat occupied by a particular species.

Question 46

In quadrats, what is frequency?

Answer 46

The likelihood of a particular species occurring in a quadrat. Eg if a species occurs 15 out of 30 quadrats - then the frequency of its occurrence is 50%.

Question 47

Define succession.

Answer 47

The process by which an ecosystem changes over time (eg sand dunes), creating a new community. The biotic conditions (eg plants and animal communities) change S the abiotic conditions (eg water availability) change. There are 2 types of succession: - primary succession - secondary succession

Question 48

Define primary succession.

Answer 48

A slow process where the land is completely exposed, bare or newly formed. Eg a lava flow or the edge of a retreating glacier.

Question 49

Define secondary succession.

Answer 49

A rapid process where land has been cleared of all the plants, but some soil is already present. Eg in a ploughed field or bush fire.

Question 50

Outline how succession works.

Answer 50

1. At first, the abiotic conditions are hostile. Only pioneer species grow as they are adapted to cope with the conditions. Eg marram grass. 2. The pioneer species change the abiotic conditions - they die and decompose the humus. This forms a basic soil. 3. This makes conditions less hostile, meaning new organisms with different adaptations can move in and grow. These then die and are decomposed, adding more organic material, making the soil deeper and richer in minerals. This means larger plants eg shrubs can grow deeper into the soil. 4. Some new species may change the environment so it becomes less suitable for the previous species. Making the conditions less suitable for marram grass. 5. In secondary succession, at each stage, different plants and animals that are better adapted for the improved conditions move in, out compete the plants already there, and become the dominant species in the ecosystem. 6. Biodiversity increases and new species grow alongside existing species. 7. Then reaches climax community - the ecosystem supports the largest and most complex community of plants it can.

Question 51

Define climax community.

Answer 51

Climax communities are in a stable equilibrium with the prevailing climate. This community is determined by the limiting abiotic factors. Eg trees may not develop of very high mountains because it's too cold or windy, however may be in a climax community elsewhere.

Question 52

Define plagioclimax.

Answer 52

When succession is stopped artificially due to human activities that stop them from developing. Eg a regularly mown lawn won't develop shrubs or trees even if the climate of the ecosystem could support them.

Question 53

How do conservation and succession link?

Answer 53

Conservation caincolve preventing succession in order to preserve and ecosystem at its current stage of succession. This could be done by: - allowing animals to graze on the land - managed fires

Question 54

Outline temperature, as an abiotic factor, that can influence the size of a population.

Answer 54

Each species has a different optimum temperature at which it is best suited to survive. The further away from this optimum, the fewer individuals in a population are able to survive - and the smaller is the population that can be supported. In plants and cold blooded animals, as temperatures fall below the optimum, the enzymes work more slowly and so their metabolic rate is reduced. Therefore the populations have a smaller carrying capacity. When temperatures are above optimum, the enzymes work less efficiently because they gradually undergo denaturation - so carrying capacity is also reduced.

Question 55

Temperature is an abiotic factor that influences the size of a population. However, even though warm blooded animals can maintain a relatively constant body temperature, despite the external temperature, how is the carrying capacity still affected?

Answer 55

The further the temperature of the external environment it gets from the optimum, the more energy these organisms expend in trying to maintain their normal body temperature. This leaves less energy for individual growth and so they mature more slowly and their reproductive rates slows. The carrying capacity is therefore reduced.

Question 56

How can light, as an abiotic factor, influence the size of a population?

Answer 56

The rate of photosynthesis increases as light intensity increases. The greater the rate of photosynthesis the faster plants grow and more seeds they produce. Their carrying capacity is therefore greater. In turn, the carrying capacity of animals that feed on plants is potentially larger.

Question 57

Although prediation may lead the prey population to decrease in size, why doesn't the population (usually) go extinct?

Answer 57

Because the fewer prey there are, the harder it is to catch them.

Question 58

What's the relationship between predators and their prey on population size?

Answer 58

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

Question 59

Define selection pressure.

Answer 59

Those individuals who're able to escape predators, or withstand disease, or an adverse climate are more likely to survive and reproduce. The population therefore evolves to be better adapted to the prevailing conditions.

Question 60

What is a point quadrat?

Answer 60

A horizontal bar which is supported by two legs. At set intervals along the horizontal bar are 10 holes, through each of which a long pin is dropped. Each species that the pin touches is recorded.

Question 61

What is a frame quadrat?

Answer 61

A square frame divided by wire into equally sized subdivisions.

Question 62

What are the 3 factors to consider when using quadrats?

Answer 62

- the size of quadrat to use - the number of sample quadrats to record in the sample area - the position of each quadrat within the study area

Question 63

Why do you need to consider the size of the quadrat to use?

Answer 63

The size of quadrat will depend on the size of plants or animals being counted and how they're distributed within the area. Where a population isn't evenly distributed, a large number of small quadrats will give more representative results than a small numbe roof large ones.

Question 64

Why do you need to consider the number of sample quadrats within the study area?

Answer 64

The larger the number of sample quadrats, the more reliable the results will be. However, this is time consuming so there needs to be a balance.

Question 65

Why do you need to consider the position of each quadrat within the study area?

Answer 65

To produce statistically significant results, random sampling must be used.

Question 66

Why would you use random sampling?

Answer 66

To avoid any bias in the data collection. Avoiding bias ensures the revisits are reliable.

Question 67

Advantage and disadvantage of % cover when using quadrats?

Answer 67

+ data can be collected rapidly + individual plants don't need to be counted - not useful where plants occur in several overlapping areas (like plants)

Question 68

In succession, give examples of adaptions that pioneer species have to suit them to colonisation.

Answer 68

- asexual reproduction (so a single organism can rapidly multiply to build up a population). - tolerance of extreme conditions. - the ability to fix nitrogen from the atmosphere (because, even if there is soil, it has no or few nutrients). - the ability to photosynthesis (as light is available but food isn't. They're therefore not dependent on animal species). - the production of vast quantities of wind dispersed seeds, so they can easily reach isolated situations eg islands).

Question 69

As a result of succession, what features emerge?

Answer 69

- the non-living (abiotic) environment becomes less hostile. - a greater number and variety of habitats and niches. - increased biodiversity. - more complex food webs. - increased biomass (esp mid-succession).

Question 70

Define conservation.

Answer 70

The management of the Earth's natural resources by humans in a way that maximises use of them can be made in the future. To involves active intervention by humans to maintain ecosystems and biodiversity.

Question 71

What are the main reasons for conservation.

Answer 71

Personal Ethical Economic Cultural and aesthetic

Question 72

Outline 'personal' as a reason for conservation.

Answer 72

To maintain our planet and therefore support our life system.

Question 73

Outline 'ethical' as a reason for conservation.

Answer 73

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

Question 74

Outline 'economic' as a reason for conservation.

Answer 74

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

Question 75

Outline 'cultural and aesthetic' as a reason for conservation.

Answer 75

Habitats and organisms enrich our lives. Their variety adds interest to everyday life and inspires writers, singers, artists who all entertain us.