Populations in ecosystems

Question 1

What is ecology?

Answer 1

The study of inter-relationships between organisms and their environment.
The environment includes non-living (abiotic) factors - rainfall and temperature - and living (biotic) factors - competition and predation.

Question 2

What are ecosystems?

Answer 2

Dynamic systems made up of a community and all the non-living factors of its environment.
They can range in size from very small to very large.

Question 3

What are the major proccesses to consider in an ecosystem?

Answer 3

The flow of energy through the system.
The cycling of elements within the system.

Question 4

What is an example of an ecosystem?

Answer 4

A freshwater pond or lake.
It has its own community of plants to collect the necessary sunlight energy to supply organisms within it.
Nutrients such as phosphate ions are recycled within it.
There is little loss or gain between it and other ecosystems.

Question 5

What is a population?

Answer 5

A group of individuals of one species that occupy the same habitat at the same time and are potentially able to interbreed.
An ecosystem supports a certain size of population of a species called the carrying capacity.

Question 6

How does the size of a population vary?

Answer 6

As a result of the effect of abiotic factors.
Interactions between organisms, e.g. intraspecific and interspecific competition and predation.

Question 7

What is a community?

Answer 7

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

Question 8

What is a habitat?

Answer 8

The place when an organism 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 habitat there are smaller units, with their own microclimate.

Question 10

What is an ecological niche?

Answer 10

This is how an organism fits into the environment.
It includes all the biotic and abiotic conditions to which an organism is adapted in order to survive, reproduce and maintain a viable population. .
No two species occupy the same niche - competitive exclusion principle.

Question 11

What is population size?

Answer 11

The number of individuals in the population.

Question 12

What are abiotic factors?

Answer 12

Non-living that influences population size:
Temperature
Light
pH
Water and humidity

Question 13

How does temperature influence population size - plants and cold blooded animals?

Answer 13

Temperatures below optimum means enzymes work slower and metabolic rate falls.
Populations have a lower carrying capacity.
Temperatures above optimum means enzymes work less efficiently because they are gradually denatured.

Question 14

How does temperature influence population size - warm blooded animals?

Answer 14

Birds and mammals - maintain a constant body temperature.
The further the external temperature gets from the optimum, the more energy the organisms spend in trying to maintain normal temperature, so less energy for individual growth, mature slower and reproductive rate slows.
So the carrying capacity is reduced.

Question 15

How does light influence population size?

Answer 15

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

Question 16

How does pH influence population size?

Answer 16

This affects enzyme action.
Each enzyme has an optimum pH for operating most efficiently.
A population of organisms is larger when the appropriate pH exists.

Question 17

How does water and humidity influence population size?

Answer 17

Where water is scarce, populations are small and consist only of a species that are well adapted to living in dry conditions.
Humidity affects transpiration in plants, and the evaporation of water from animals.
In dry air conditions, the populations of species adapted to tolerate low humidity will be larger than those without.

Question 18

What is intraspecific competition?

Answer 18

When individuals of the same species compete for resources - food, water, breeding.
The greater the availability of resources, the larger the population.

Question 19

What is an example of intraspecific competition?

Answer 19

Oak trees compete for resources.
In a large population of small trees some will grow larger and restrict the availability of light, water and minerals to the rest, which then die.
The population becomes reduced to relatively few large dominant oaks.

Question 20

What is interspecific competition?

Answer 20

When individuals of different species compete for resources.
The population of the advantaged species will increase in size while the other diminishes.
If conditions remain, this leads to the complete removal of a species- exclusion principle.

Question 21

What is the exclusion principle?

Answer 21

Where two species are competing for limited resources, the one that uses them most efficiently will ultimately eliminate the other.

Question 22

How have predators evolved?

Answer 22

Better adapted for capturing their prey:
Faster movement, more effective camouflage, better means of detecting prey.

Question 23

How have prey evolved?

Answer 23

More adept at avoiding predators:
Better camouflage, more protective features such as spines, concealment behaviour.

Question 24

What is predation?

Answer 24

When one organism is consumed by another.

Question 25

What is the effect of predator-prey relationship on population size?

Answer 25

Predators eat their prey, which reduces population of the prey.
With fewer prey available, the predators are in greater competition with each other for the remaining prey.
The predator population is reduced as some are unable to obtain enough prey to survive.
With fewer predators left, fewer prey are eaten and so more survive and reproduce.
With more prey now available, the predator population increases.

Question 26

What is abundance?

Answer 26

The number of individuals of a species in a given space.
It is impossible to identify every organism, so representative samples are taken.

Question 27

What is a point quadrat?

Answer 27

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 that the pin touches is then recorded.

Question 28

What is a frame quadrat?

Answer 28

A square frame divided by string or wire into equally sized subdivisions.
The quadrat is placed in different locations within the area being studied.
The abundance is then recorded.

Question 29

What are the factors considered when using a quadrat?

Answer 29

Size of quadrat
Number of quadrats
Position of quadrat - random sampling used

Question 30

How does size of quadrat vary?

Answer 30

Larger species require larger quadrats.
Where a population of species is not evenly distributed throughout the area, a large number of small quadrats will give a more representative result than a small number of large ones.

Question 31

How does the number of quadrats vary?

Answer 31

The larger the number of quadrats the more reliable the results.
The greater the number of different species in the area, the greater the number of quadrats required to produce reliable results.

Question 32

What is the method of random sampling?

Answer 32

Lay out two long tape measures at right angles, along two sides of the study area.
Obtain a series of coordinates using a random number generator.
Place a quadrat at the intersection of each pair and record the species within it.

Question 33

What is systematic sampling?

Answer 33

Used when it is more informative to measure the abundance and distribution of a species systematically not randomly.
Particularly when some form of gradual change in the communities of animals and plants takes place.

Question 34

What is an example of needing systematic sampling?

Answer 34

The distribution of organisms along a line of succession - sand dunes by the edge of the sea and inland up into woodland.
The stages of succession are especially well shown using belt transects.

Question 35

What is the method of systematic sampling?

Answer 35

A belt transect is made by stretching a tape across the ground in a straight line, parallel to the line of succession.
A frame quadrat is laid down alongside and the species within it recorded.
It is then moved its own length along the line and the process repeated.

Question 36

What is frequency?

Answer 36

The likelihood of a particular species occurring in a quadrat.
Useful when a species is hard to count.
It does not provide information on the density and detailed distribution of a species.

Question 37

What is percentage cover?

Answer 37

An estimate of the area within a quadrat that a particular plant species covers.
Useful when a species is particularly abundant or difficult to count.
Data is collected rapidly, but less useful when organisms overlap in layers.

Question 38

How do you obtain reliable results in sampling?

Answer 38

Use a large sample size, many quadrats, and the mean of all the samples.

Question 39

What is mark-release-recapture?

Answer 39

Used for motile animals (move away on approach). They are often hidden and difficult to find.

Question 40

What is the method of mark release recapture?

Answer 40

A known number of animals are caught, marked, and released back to the community.
Some time later, a given number of individuals are collected randomly and the number of marked individuals is recorded.

Question 41

What is the equation for mark recapture?

Answer 41

Estimated population size = total number of individuals in first sample x total number in second sample / number of marked individuals recaptured.

Question 42

What does mark recapture rely on?

Answer 42

The proportion of marked:unmarked in the second sample is the same as the whole population.
The marked individuals distribute themselves evenly and have time to do so.
The population has a boundary so no emmigration or immigration.
There are few deaths and births.
The method is not toxic or make the individual more conspicuous.
The mark is not lost or rubbed off.

Question 43

How does succession change the environment?

Answer 43

The new species at each stage make it less suitable for existing species, so they out-compete the existing one and take over the area.
Make it more suitable for other species with different adaptations and the species may be out-competed by the better adapted new species.

Question 44

What is succession?

Answer 44

Ecosystems are dynamic - they change from day to day as the populations fluctuate.
Succession describes these changes, over time, in the species that occupy a particular area.

Question 45

How does barren land arise?

Answer 45

A glacier retreating and depositing rock, sand being piled into dunes by wind or sea, volcanoes erupting and depositing lava, lakes created by land subsiding, silt and mud being deposited at river estuaries.

Question 46

What are pioneer species?

Answer 46

A species that can colonise the new land, often lichen and moss, of bare rock or ground.

Question 47

How are the pioneer species suited for colonisation?

Answer 47

Asexual reproduction so a single organism can rapidly multiply to build up a population.
Production of vast quantities of wide-dispersed seeds or spores, to reach isolated areas.
Rapid germination of seeds on arrival as they don’t need a period of dormancy.
The ability to photosynthesise, as light is available but food not.
The ability to fix nitrogen from the atmosphere as any soil has few nutrients.
Tolerance to extreme conditions.

Question 48

What are lichens?

Answer 48

One of the few kinds of organism capable of surviving on such an inhospitable area like a bare rock is lichen.
They are therefore pioneer species, and can also survive considerable drying out.

Question 49

What is the first stage of succession?

Answer 49

Weathering of the base rock by lichens produces sand or soil.
As the lichens die and decompose they release sufficient nutrients to support a community of small plants, so lichens change the abiotic environment for the organisms that follow.

Question 50

What is the second stage of succession - moss?

Answer 50

Mosses are the next, followed by ferns.
With the continuing erosion of the rock and the increasing amount of organic matter available from the death of the plants, a thicker layer of soil is built up.
The organic material holds water, making it easier for other plants to grow.
The species make the abiotic environment less hostile and more suitable for the following organisms, grasses, shrubs and trees.

Question 51

What is the next stage of succession - ultimate community?

Answer 51

The species provide more sources of food, leading to more food chains that develop into complex food webs and lead to more stable communities.
The deciduous oak woodland is likely the ultimate community.

Question 52

What is the climax community?

Answer 52

This stable state comprises a balanced equilibrium of species with few new species replacing the already established ones.
Many species flourish and there is much biodiversity.
This climax community remains stable over a long period of time, and contains animals and plants.

Question 53

How does succession occur for animals?

Answer 53

The successional changes have been largely determined by the food types and habitats available.
Dead lichens provide food for animals such as detritus-feeding mites.
Mosses and grasses provide food and habitat for insects, millipedes and worms.
Secondary consumers centipedes feed on these.
Flowering plants support communities for butterflies and moths, reptiles, mammals and birds.

Question 54

What common features occur during succession?

Answer 54

The abiotic environment becomes less hostile (soil, more nutrients, plants for shelter), leads to
A greater number and variety of habitats and niches, produces
Increased biodiversity, bringing
More complex food webs, leading to increased biomass, especially in mid-succession.

Question 55

How does biodiversity change in succession?

Answer 55

Increased biodiversity is especially evident in the early stages, reaching a peak in mid-succession, but decreasing as the climax community is reached.
The decrease is due to dominant species out-competing pioneer and other species, leading to their elimination from the community.

Question 56

What is secondary succession?

Answer 56

Succession when the land that has already sustained life is suddenly altered, e.g. land clearance for agriculture or forest fire.
The process to return to its climax community is much more rapid than primary succession.
Because soil already exists with alive spores and seeds, and there is an influx of animals and plants through dispersal and migration.

Question 57

What is conservation?

Answer 57

The management of the earth’s natural resources by humans so that maximum use of them can be made in future.
This involves active intervention to maintain ecosystems and biodiversity.

Question 58

What are the reasons for conservation?

Answer 58

Personal - to maintain our life support system.
Ethical - other species have occupied the earth far longer than us and should be allowed coexistence.
Economic - living organisms contain a large gene pool with the capacity to make millions of valuable substances for the future.
Cultural and aesthetic - the variety of habitats adds interests to life and inspires writers, artists, poets and composers who entertain us.

Question 59

What is conservation by managing succession?

Answer 59

Many of the species that existed in earlier stages are not part of the climax community.
Because habitats have been out-competed or taken over for human activites.
To conserve these habitats and so species is by managing succession that prevents a change to the next stage.

Question 60

What is burning to manage succession for conservation?

Answer 60

The burning of heather and grazing by sheep has prevented the moorland on many higher ground from reaching its climax community.
The burning and grazing destroy the young tree saplings and so prevent the natural succession into deciduous woodland.

Question 61

What is clearing to manage succession for conservation?

Answer 61

Most of the oak woodland was cleared to allow grazing and cultivation.
The many heaths and grasslands are as a result.
Chalk downland was cleared of forest and now sheep and rabbits eat any new saplings to prevent them developing into grown trees.