Populations In Ecosystems

Question 1

What Is Ecology?

Answer 1

Study of inter-relationships between organisms and their environment,

The environment includes both non-living and living factors, such as rainfall and predators.

Question 2

Biotic?

Answer 2

Living factors.

Question 3

Abiotic?

Answer 3

Non-living factors.

Question 4

What Are Ecosystems?

Answer 4

Dynamic systems made up of a community and all the abiotic factors of its environment,

Within an ecosystem, there are two major processes to consider.

Question 5

Two Major Processes In An Ecosystem?

Answer 5

• The flow of energy through the system,

- The cycling of the elements within the system.

Question 6

What Is A Population?

Answer 6

A group of organisms of the same species that occupy the same habitat at the same time and are potentially able to interbreed.

Question 7

Why Might A Population Size Vary?

Answer 7

• The effect of abiotic factors,

- Interactions between organisms,e.g. intraspecific and interspecific competition and predators.

Question 8

What Is A Community?

Answer 8

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

Question 9

What Is A Habitat?

Answer 9

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

Question 10

What Is A Microhabitat?

Answer 10

Within each habitat, there are smaller units, each with their own micro-climate called microhabitats.

Question 11

What Is A Ecological Niche?

Answer 11

A niche is how an organism fits into the environment. This refers to where the organism lives and what it does there,

It includes all the biotic and abiotic conditions to which an organism is adapted to survive, reproduce and maintain a viable population.

Question 12

Competitive Exclusion Principle?

Answer 12

No two species occupies the exact same niche.

Question 13

Biome?

Answer 13

A specific environment that’s home to living

things suited for that place and climate.

Question 14

Biodiversity?

Answer 14

The number and variety of living organisms in the living world.

Question 15

Abiotic Factors Sub-Groups?

Answer 15

Abiotic factors are divided further into three categories:

• Climate factors,
• Edaphic factors,
• Topographic factors.

Question 16

Climate Abiotic Factors?

Answer 16

Involves factors relating to climate,

E.g. humidity and sunlight.

Question 17

Edaphic Abiotic Factors?

Answer 17

Involves factors relating to soil and geography of the land,

E.g. soil conditions.

Question 18

Topographic Abiotic Factors?

Answer 18

Involves factors relating to physical features of the land,

E.g. height, direction of slope and steepness of slope.

Question 19

Population Size?

Answer 19

Number of individuals in a population.

Question 20

Logarithmic Scale?

Answer 20

A way of making the number in your results smaller (for example, the number of a certain species in a community) so the results are easier to plot.

Question 21

Intraspecific Competition

Answer 21

Occurs when individuals of the same species compete with each other for resources,

The availability of resources determines the size of the population,

i.e. the larger the availability, the large the
population,

E.g. oak trees – in a large population of
smaller oak trees some will grow bigger, they will
restrict the availability of resources and the
others will die which in turn reduces the
population.

Question 22

Interspecific Competition?

Answer 22

Occurs when individuals of the different species
compete with each other for resources,

Usually one species will have a competitive
advantage over the other causing one population
to increase and the other to decrease,

This could lead to the removal of one species (if
condition remain the same) – known as the
competitive exclusion principle,

i.e. no 2 species can occupy the same niche
indefinitely,

E.g. grey and red squirrel.

Question 23

Plotting A Growth Curve?

Answer 23

Plot a graph of numbers in a population against time,

May not be possible if the growth is rapid - e.g. microorganisms,

We use a logarithmic scale when the curve runs off the graph. E.g. bacteria grow so quickly so the curve runs off the graph and we use a logarithmic scale to make these numbers smaller so they’re easier to plot and clearer.

Question 24

Carrying Capacity?

Answer 24

Each population has a certain size that can be sustained over a long period of time and is determined by the limiting factors (abiotic factors).

Question 25

Limiting Factors?

Answer 25

Also known as abiotic factors:
Temperature,
Light,
pH,
Water and humidity.

Question 26

Temperature As A Limiting Factor?

Answer 26

Each species has an optimum tempreture that they will best survive,

The further from this optimum they go, the less likely the species is able to survive, therefore, the population will get smaller.

Question 27

Optimum Temperature In Plants + Cold-Blooded Animals?

Answer 27

As temperature falls below the optimum, the enzymes work slower and the metabolic rate is reduced. Populations therefore have a smaller carrying capacity,

If temperatures go above the optimum, the enzymes work less efficiently because they undergo denaturation. Again, this reduces the carrying capacity.

Question 28

Optimum Temperature In Warm-Blooded Animals?

Answer 28

(Such as birds and mammals) can maintain a relativity constant body temperature regardless of the external temperature,

However, the further the external temp moves from the optimum, the more energy the organism will loose in trying to maintain their internal temp,

This leaves less energy for individual growth and so they mature more slowly and their reproductive rate slows,

Therefore, the carrying capacity is reduced again.

Question 29

Light As A Limiting Factor?

Answer 29

Source of energy for most ecosystems,

The rate of photosynthesis increases as light intensity increases,

The greater the rate of photosynthesis, the faster plants grow and the more spores or seeds they produce. Therefore, their carrying capacity is greater,

The carrying capacity that feeds on these plants is also potentially greater.

Question 30

PH As A Limiting Factor?

Answer 30

This affects the actions of enzymes,

An enzyme will work most efficiently at an optimum pH. The carrying capacity and population of an organism is larger when the optimum pH exists and is smaller (or non-existent) when the pH is different from optimum.

Question 31

Water And Humidity As A Limiting Factor?

Answer 31

Where water is scarce, populations are small and consist only of species that are well adapted to living in dry conditions,

Humidity affects the transpiration rates in plants and the evaporation of water from the bodies of animals,

Again, in dry air conditions, the populations of species adapted to tolerate low humidity will be larger than those with no adaptions.

Question 32

What Is Predation?

Answer 32

Predation occurs when one organism is consumed by another,

The prey is usually exterminated by the predators in a lab because there is less area, less shelter and the prey provided is limited to the lab. In nature, this is usually not true because the variety of habitat is more,

The population of prey may fall to a low level but it is unlikely that it will become extinct,

It is difficult to obtain data on population size for prey and predators because organisms cannot possibly be counted in the wild. They can only be estimated.

Question 33

Effect Of Predator-Prey Relationships On Population Size?

Answer 33

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

Question 34

Selection Pressure?

Answer 34

individuals who are able to escape predators (or withstand disease/adverse climate) are more likely to survive and reproduce,

The population therefore evolves to be better adapted to the prevailing conditions.

Question 35

Abundance?

Answer 35

Abundance is the number of individuals of a species in a given space.

It is almost impossible to count this number - would damage the habitat and be time-consuming. For this reason, small samples of a habitat are counted and as long as these readings are accurate, the conclusions from the findings will be reliable.

Question 36

Quadrat Types?

Answer 36

There are two types:

• A point quadrat,
• A frame quadrat.

Question 37

Point Quadrat?

Answer 37

Consists of a horizontal bar supported by two legs. At set intervals along the bar are 10 holes. A long pin may be dropped at each hole. Each species that the pin touched will then be recorded.

Question 38

Frame Quadrat?

Answer 38

Which is a square frame divided by wring or wire. It is often designed so that it can be folded to make it more compact for storage and transport. The quadrat is placed in different locations within an area being studied. The abundance of each species within the quadrat is then recorded.

Question 39

Factors To Consider When Using Quadrats?

Answer 39

Three Factors To Consider:

• Size of the quadrat to use,
• Number of sample quadrats to record within the study area,
• The position of each quadrat within the study area.

Question 40

Why Consider Size Of Quadrat?

Answer 40

The size of the quadrat you should use depends on the size of the plants or animals being counted and how the distribution of the species within the area.

Where a population of species is not distributed throughout the area, a large number of small quadrats will give more representative results than a small number of large ones.

Question 41

Why Consider The Number Of Sample Quadrats To Record Within The Study?

Answer 41

The larger the number of quadrats. the more reliable the results.

As the recording of species within a quadrat is a time-consuming task, a balance needs to be struck between the reliability of the results and the time available.

The greater the number of different species present, the greater the number of quadrats required to produce reliable results for a valid conclusion.

Question 42

Why Consider Of Each Quadrat Within The Study Area?

Answer 42

We do this to produce statistically significant results, a technique called random sampling must be used. This is so the results are not biased.

Question 43

Random Sampling?

Answer 43

To avoid any bias in collecting data. Avoiding bias ensures that the data obtained are reliable.

When comparing species in one place to species in another place (a.g. effects of grazing animals on plants growing in a field), we choose two places as close together as possible. This minimises other affects we are not measuring such as soil, climatic and other abiotic factors.

Take samples at may random sites by placing the quadrat on the floor and recording the names and numbers of every species found within the quadrat.

To get a truly random sample (which isn’t throwing the quadrat over your shoulder without looking - one way):

• Lay out two tape measures at right angles, along two sides of the study area,
• Obtain a series of random numbers taken from a table or generated from a computer,
• Place the quadrat at the intersection of each pair of coordinates and record the species within it.

Question 44

Systematic Sampling Along A Belt Transect?

Answer 44

Sometimes more informative to measure abundance and distribution of a species in a systematic way rather than a random manner. This is particularly important when measuring gradual change in communities of plants and animals.

E.g. measuring abundance along a transit from the edge of the sea on sand and to the top of the dunes.

The stages of succession are especially shown using transects. A belt transect can be made by stretching a string or tape along the ground in a straight line. A frame quadrat is then laid down alongside the line an the species within the quadrat are recorded. It is then moved its own length down the line and the process repeated. This gives the record of a species in a continuous belt.

Question 45

Measuring Abundance?

Answer 45

Random sampling with quadrats and counting along transects are used to obtain measures of abundance. Abundance is the number of individuals of a species within the given area. For species that dont move around, it can be measured in several ways, depending on the size of the species being counted and the habitat.
Examples: frequency, percentage cover.

To obtain reliable results, it is necessary to ensure that the sample size is large, that is, many quadrats are used and the mean of all the sample is obtained. The larger the number of samples, the most representative of the community as a whole will be the results.

Question 46

Frequency When Measuring Abundance?

Answer 46

Which is the likelihood of a particular species occurring in a quadrat. If, for example, a species occurs in 15 out of 30 quadrats, the frequency of its occurrence is 50%. This method is useful where a species, such as grass, is hard to count. It gives a quick idea of the species present and their general distribution within an area. However, it does not provide information on the density and detailed distribution of a species.

Question 47

Percentage Cover When Measuring Abundance?

Answer 47

Percentage cover is an estimate of the area within a quadrat that a particular plant species covers. It is useful where a species is particularly abundant or is difficult to count. The advantages in these situations are that data can be collected rapidly and individual plants do not need to be counted. It is less useful where organisms occur in several overlapping layers (more probably plants).

Question 48

Mark-Release-Recapture Techniques?

Answer 48

Methods of measuring abundance such as percentage cover work well with plant species and non-motile or very slow moving animals that remain in one place. Motile animals move away when approached, they are often hidden and are therefore difficult to find and identify. To estimate abundance of most animals requires an altogether different technique.

Mark-release-Recapture Method:
A known number of animals are caught, marked in some way, and then released back into the community Some time later, a given number of individuals is collected randomly and the number of marked individuals is recorded. The size of the population is then calculated as follows:

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

Question 49

Mark-Release-Recapture Techniques Relies On A Number Of Assumptions?

Answer 49

Mark-Release-Recapture techniques relies on a number of assumptions:

• The proportion of marked to unmarked individuals in the second sample is the same as the proportion of marked to unmarked individuals in the population as a whole.
• The marked individuals released from the first sample distribute themselves evenly amongst the remainder of the population and have sufficient time to do so.
• The population has a definite boundary so that there is no immigration into or emigration out of the population.
• There are few, if any, deaths and births within the population.
• The method of marking is not toxic to the individual nor does it make the individual more conspicuous and therefore more liable to predation.
• The mark or label is not lost or rubbed off during the investigation.

Question 50

What Is Succession?

Answer 50

Is the term used to describe these changes, over time,, in the species that occupy a particular area.

An example of succession is when bare rock or other barren land is first colonised. Barren land may rise as a result of: a glacier retreating and depositing rock, sand being pilled into dunes by wind or sea, volcanoes erupting lava, lakes or ponds being created by land subsiding, and silt and mud being deposited at river estuaries.

Question 51

Succession Affecting Other Species?

Answer 51

Succession takes place in a series of stages at each stage, a new species colonise the area and this may change the environment. These species may alter the environment in a way that makes it:

• less suitable for existing species, as a result the new species may outcompete the existing one and so take over a given area.
• more suitable for other species with different adaptations, as a result this species may be out-competed by the better adapted new species.

Question 52

First Stage Of Primary Succession?

Answer 52

The first stage of this type of succession is the colonisation of an in hospitable environment by organisms called pioneer species. Pioneer species make up a pioneer community and often have features that suit them to colonisation. These may include:

• Asexual reproduction so that a single organism can rapidly multiply to build up a population.
• The production of a vast quantities of wind dispersed seeds of pause so they can easily reach isolated situations such as volcanic islands.
• Rapid germination of seeds on arrival as they do not require a period of dormancy.
• The ability to photosynthesise as light is normally available but other food is not. They are they therefore not dependent on animal species. - The ability to fix nitrogen from the atmosphere because even if there was a soil it has fewer no nutrients.
• Tolerance to extreme conditions.

An example of a pioneer species is lichens.

Question 53

Lichens?

Answer 53

One of the few kinds of organism capable of surviving on such an in hospitable area is lichens. Lichens are therefore pioneer species. Lichens can survive considerable drying out and live on bare rock.

In time, weathering of the base rock by the action of the lichens produces sand or soil. As the lichens die and decompose, they realise sufficient nutrients to support a community of small plants. In this way, the lichens change the abiotic environment by creating soil and nutrients for their organisms that follow. Mosses are typically the next stage in succession followed by ferns.

Question 54

Second Stage Of Primary Succession?

Answer 54

Usually misses and followed by ferns.

There is continuing erosion of rock and increasing amount of organic matter available from the death of plants and lichens. A thicker layer of soil is built up. The organic material holds water making it easier for other plants to grow. Again, the species changes the abiotic environment, making it less hostile and some more sustainable for the organisms that follow (for example, small flowering plants such as grasses and internal shrubs and trees). These species provide more sources of food, leading to more food chains that develop into complex food webs and lead to more stable communities.

Question 55

The UK’s Succession?

Answer 55

In the UK the ultimate community is most likely to be deciduous oak woodland.

This stable state comprises a balanced equilibrium of species with few, if any, new species replacing those that have been established. In this state, many species flourish and there is much biodiversity. This is called the climax community which remains more or less stable over a long period of time. This community consists of animals as well as pants.

Question 56

What Is A Climax Community?

Answer 56

A climax community is a community with a balanced equilibrium of species.

This means there are few, if any, species replacing those that have become established.

Many species flourish and there is a wide biodiversity.

A climax community can become less or more stable over time.

Abiotic factors such as climate determine the dominant species in a climax community.

Question 57

Common Factors That Emerge During Succession?

Answer 57

During any succession, there are a number of common factors that emerge:

• The nonliving abiotic environment becomes less hostile. For example, soil forms which helps retain water, nutrients are more plentiful. This provides plants which are shelter from the wind. This leads to:
• A greater number and variety of habitats and niches. This leads to:
• Increased biodiversity. This leads to:
• More complex food webs. This leads to:
• Increased biomass especially during mid season.

Question 58

What Is Secondary Succession?

Answer 58

Another type of succession occurs when land that has already sustained life is suddenly altered.

This may be the result of land clearance for agriculture or a forest fire.

The process by which the ecosystem returns to its community is the same as described above, except that it normally occurs more rapidly. This is because soil already exists and which spores and seeds often remain alive in the soil, and there is an influx of animals and plants through dispersal and migration from the surrounding area. This type of succession is called secondary succession.

Question 59

Percentage Population Growth Rate (In A Given Period)?

Answer 59

Population change during period / population at the start of the period x100.

Question 60

Steps Of Natural Selection?

Answer 60

1. There is a genetic variation in the population. This is usually due to a mutation.
2. The individuals who are best suited to the selection conditions are more likely to survive (better at hiding from predators, camouflaging, resistant to disease) and so they breed.
3. The individuals less suited to selection conditions will die and not breed.
4. Favourable ALLELE is passed onto next generation.
5. The allele increases in frequency in the population.

Question 61

What Is Evolution?

Answer 61

Gradual process where living organisms are believed to have developed from earlier forms during history of the earth.

Question 62

Intraspecific Or Interspecific Competition?

Answer 62

Intraspecific - competition between individuals inside of the same species.

Interspecific - competition between individuals of different species.

Question 63

What Is Conservation?

Answer 63

Conservation is the managements of the earths natural resources by humans so that resources can be used in the future.

This involves active intervention by humans to maintain ecosystems dm biodiversity.

It is a dynamic process that needs management.

The main reasons for conservation are:

• personal,
• ethical,
• economic,
• cultural and aesthetic.

Question 64

Personal Conservation?

Answer 64

To maintain our planet and therefore our life support system.

Question 65

Ethical Conservation?

Answer 65

Other species have occupied the Earth for longer than humans. We should allow them to coexist with us.

Respect for living things.

Question 66

Economic Conservation?

Answer 66

Living organisms contain a gigantic pool of genes with the capacity to make millions of substances, many of which might prove to be valuable in the future (medicines, etc).

Long-term productivity is greater if ecosystems are maintained in their natural balanced state.

Question 67

Cultural And Aesthetic Conservation?

Answer 67

Habitats and organisms enrich our lives.

Their variety adds interest to everyday life and inspires people (writers, artists, entertainers).

We should conserve habitats for aesthetic reasons.

Some animals and habitats are also scared to certain cultures. And should be preserved for religious/cultural reasons.