Investigating Populations & Succession

Question 1

Definition of species

Answer 1

A group of similar organisms with similar features which are capable of reproducing to produce fertile offspring

Question 2

Definition of population

Answer 2

Alll the individuals of a given species living together in the same area
at the same time

Question 3

Definition of carrying capacity

Answer 3

The maximum, equilibrium number of organisms of a
particular species that can be supported indefinitely in each stable environment
Birth rates and
death rates are in equilibrium

Question 4

The limiting factors of the carrying capacity include abiotic factors:

Answer 4

Temperature & pH
Light
Water and Humidity

Question 5

The limiting factors of the carrying capacity include biotic factors:

Answer 5

Interspecific competition (between different species)

Intraspecific competition (within the same species)

Predation

Question 6

Factors that species compete for:
- Food
- Water
- Mates
- Shelter
- Minerals
- Light

Question 7

Definition of community

Answer 7

All the individuals of all the species living together in the same area
at the same time

Question 8

Definition of habitat

Answer 8

Place where an organism lives within an ecosystem

Question 9

Definition of niche

Answer 9

A niche describes where an organism lives and what it does (its role). This includes what it feeds on and how it interacts with other organisms and the environment

Question 10

Predation is when one species (the prey) is caught and eaten by another species (the predator).

Question 11

Predator-prey relationships:
1. When the prey is eaten by the predator the population of the prey falls.
2. This results in the predator population growing, however means that more prey is consumed.
3. Therefore the population of prey reduces and there is increased competition for the the prey
between the predators.
4. The lack of food for the predators means that the population falls meaning that less prey is
eaten.
5. This allows the population of the prey to recover and therefore the cycle occurs over in a
oscillating manner.

Question 12

The size of a population can be estimated by:

Answer 12

Randomly placing quadrats, or quadrats along a belt transect, for slow-moving or non-motile organisms. Can count the number of individuals of each species in the quadrat or percentage cover.

The mark-release-recapture method for moving organisms. It assumes there is no deaths, births, migration, marking has no effect and enough time for the animals to mix.

Question 13

The abundance of different species can be measured in 3 main ways these are:

1. Percentage cover - suitable for plants or algae whose individuals numbers are difficult to count.
2. Frequency - expressed as a decimal or percentage, and is the number of times an organism appears in the sampling area.
3. Density - Actual count of ALL individuals present (in a given area or area of quadrat)

Question 14

When to use percentage cover:

· Too many individuals to count.
· Organism is too small.
· Hard to identify.
· Overlap with other species.

Question 15

Random quadrating is done to:

a) Find out what species are present and their relative abundance in / on / at a specified AREA.

b) Compare the species abundance in two different AREAS.

c) Compare the species abundance at one site (one AREA) at different seasons / years.

Question 16

Random Quadrating: Method

1. Use a grid / split area into squares/sections.
2. Method of obtaining random coordinates / numbers, e.g. calculator/computer/random numbers table/random number generator;
3. Count number/frequency of plants in a quadrat
4. Large sample and calculate mean/average number (per quadrat/section)

Question 17

% Cover = (Total area covered by species ÷ Total area of all quadrats) x 100

Question 18

How many quadrats should you use in the sample?

1. Calculate running mean
2. Stop sampling when there is little change/levels out (if plotted as a graph)
3. Enough to carry out a statistical test
4. A large number to make sure mean is reliable (20 or more)
5. Need to make sure work can be carried out in the time available

Question 19

Systematic Sampling: Changes across an area

1. Transect- Recording what species are touching the line at each sampling point.
2. Belt transect - Placing two parallel lines across, a metre apart and recording what species are found between the two lines.
3. Interrupted belt transects - using one line and placing a quadrat down at equally spaced sampling points and recording abundance of species within the quadrat.

The position of the transect across the area should be random and enough transects should be performed to ensure data collected is reliable.

Question 20

Describe how you would investigate the distribution of marram grass from one side of the dune to the other

Answer 20

1. Transect/lay line/tape measure (from one side of the dune to the other)
2. Place quadrats at regular intervals along the line
3. Count plants/percentage cover/abundance scale (in quadrats)
   OR
   Count plants and record where they touch line/transect;

Question 21

Mark–release-recapture: Mobile/moving organisms

Method

1. Animals of a particular species are ETHICALLY collected (usually by a netting or trap technique) and counted.
2. The animals are then marked in some way that does not affect ability to feed or increase chance of predation (paint dots, UV dye tagged, etc.)
3. The animals are then released and left to redistribute into their population.
4. After a reasonable time (hours, days or weeks depending on organism) a second capture is carried out and the total number caught is recorded, as well as how many of those released and recaptured which were previously marked
5. No in Population = (No in Sample 1 x No in Sample 2) ÷ No marked in Sample 2

Question 22

Important considerations:

a) The population size does not change between the two capture times. There should be very few or no increase in birth rate or death rate, emigration or immigration (migration).

b) The marking should not make the marked animals more susceptible to predators or harm the animals. The formula is based on the ratio of marked to unmarked individuals remaining the same.

c) The marking should not rub off or be lost.

d) Sufficient time should be left for the released, marked individuals to fully disperse equally through the rest of the population (however, it should not be that long that births or deaths occur).

Question 23

Abiotic factors affecting distribution of species: Temperature

Answer 23

Extreme temperatures affect enzymes in the organism and therefore its overall metabolism (chemical reactions).

If the temperature is too cold, the enzymes will not have enough kinetic energy to catalyse reactions quickly enough. The organism’s overall activity will drop and may not be sufficient for survival. E.g. Photosynthesis and aerobic respiration.

If the temperature is too high, the enzymes may start to denature and the overall activity will decrease, again reducing ability to survive.

In particularly hot environments, the organism may also experience problems with excess water loss and dehydration

The more extreme the temperature, the fewer the species that can survive. For those species that do survive, the more extreme the temperature the population size is smaller. (Lower carrying capacity)

Temperature can be measured using thermometer or data logger with temperature probe

Question 24

Abiotic factors affecting distribution of species:
Light Intensity

Answer 24

Light is required for photosynthesis, therefore higher light intensity, the greater the rate of photosynthesis. As plants photosynthesise more, the more energy that they will have for seed / spore production and the population will increase faster.

Question 25

Abiotic factors affecting distribution of species:
Water & Humidity

Answer 25

All organisms need water. It acts as a solvent in cells and is involved in many reactions directly. It acts as a hydrostatic skeleton in many species of animals and plants.

Different species vary in their ability to tolerate low water availability.

Organisms tend to lose water to the environment by evaporation although this can be used for various useful processes, such as thermoregulation (due to sweating) or movement of mineral salts and water through the xylem.

The lower the humidity of the environment, the more this water loss will occur. Again, different species have different tolerances to this water loss. Humidity is measured using a whirling hygrometer or data logger with humidity probe.

Question 26

Abiotic factors affecting distribution of species:
pH

Answer 26

The pH of the environment can affect extracellular enzymes and surface proteins. The more extreme the pH, the more an organism will be affected and the lower the population size and range of species present. pH may also affect the availability of mineral salts in the soil and therefore can affect growth of plants.

Question 27

Biotic factors affecting distribution of species:
Competition

Answer 27

Any individual requires a range of resources from its environment e.g. mineral salts, light, space, a mate and so on.

If several individuals share the same habitat they will compete for these resources. The more individuals present, the greater the competition for the resources will become. Competition also increases when resources are limited (in short supply).

Competition may be intra-specific so between members of the same species.

Or may be inter-specific so between members of different species.

As members of the same species have exactly the resource requirements. Intra-specific competition tends to be fiercer than inter-specific competition.

Question 28

If two species initially occupy the same niche, one species tends to out-compete the other. Eventually, the niche will be occupied by only the one species (this is known as the competitive niche exclusion principle)

Question 29

Biotic factors affecting distribution of species:
Predation

Answer 29

Predators have evolved mechanisms to improve the capturing ability (high speed, venomous secretions etc). Prey has also evolved defence mechanisms (e.g. camouflage, protective spines, etc).

The populations of predator and prey are linked. As the prey population increases, there is more food for the predators and intra-specific competition is reduced. The population of the predator increases.

More and more of the prey are consumed, so the prey population falls. Intra-specific competition now increases in the predator population as there is less food available. The predator population starts to reduce again. The prey population starts to recover and the cycle repeats.

Question 30

Succession is a series of changes within a community
During succession the species within the community are gradually replaced by other species
As succession proceeds there is a change from a less diverse, hostile environment with a simple food web to a more diverse, less hostile environment with a complex food web.

Question 31

At the start of a succession the initial environment is hostile, few organisms are adapted to the abiotic conditions and survive in this environment. However, over time these organisms change the environment making the abiotic conditions less harsh. This allows other organisms to become established, and outcompete the original pioneers. If left undisturbed for long enough, this replacement of species continues as the abiotic environment become less and less harsh, until eventually a climax community is reached.

Question 32

Pioneer species - the organisms that first colonise an area

Question 33

Sere - A sere is a complete succession from pioneer community to climax community, and a seral stage is a particular stage in this succession with its own distinctive community of organisms.

Question 34

Climax community -
The final stage in succession. A climax community is stable and changes very little. The type of community formed depends to a large extent on the ABIOTIC factors

Question 35

Hostility - Abiotic factors are unfavourable, few species adapted to survive in these conditions

Question 36

In hostile environments the diversity is low and abiotic factors dominate the distribution of species

In less hostile environments the diversity is high and biotic factors dominate the distribution an abundance of organisms

Question 37

Abiotic environment -
Non-living parts of environment
Eg: temperature, or soil mineral ion concentration, salt conc, amount of humus or water retention

Question 38

Diversity - the relationship between the number of individual organisms and the number of species within a community. A diverse community will have a wider range of species and a greater number of individuals of each species present than a less diverse community

Question 39

High diversity - is associated with a stable ecosystem and a complex food web. If the population of one species in the ecosystem drops then others will be able to increase in numbers and fill the niche so that the community is not affected that much by the change.

Question 40

Low diversity - is associated with an unstable ecosystem and a less complex food web. If one species dies out then the whole ecosystem may be disrupted e.g. marram grass on sand dunes - any factor that causes the death of marram grass will disrupt the whole sand dune community.

Question 41

Succession occurs in natural ecosystems. Describe and explain how succession occurs
(5m)

Answer 41

1. (Colonisation by) pioneer species
2. Pioneers/species/organisms change the environment/habitat/conditions/factors
3. (Environment becomes) less hostile for other/new species
4. Change in diversity/biodiversity;
5. Stability (population numbers & Biodiversity) increases / less hostile environment;
6. Climax community is formed

Question 42

Secondary succession occurs in a previously colonised area in which an existing community has been cleared. This type of succession can occur after events such as forest fires. As a soil layer is already present, succession begins at a later stage.

Question 43

Conservation is the human management of the Earth’s resources and typically involves the managing of succession. For example the controlled burning of land is done in order to stop the formation of a climax community