Populations in Ecosystems

Question 1

Define Environment:

Answer 1

all the living and nonliving components of a particular area

Question 2

Define Biosphere:

Answer 2

The global ecosystem composed of biota and the abiotic factors.

Question 3

Define Biotic:

Answer 3

living

Question 4

Define Abiotic:

Answer 4

nonliving

Question 5

What is meant by an ecosystem?

Answer 5

A community of interacting organisms and their physical environment.

A community and the abiotic components.

Question 6

Define Population:

Answer 6

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

Question 7

Define Community:

Answer 7

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

Question 8

Define Habitat:

Answer 8

The place where and organism lives within an ecosystem.

Question 9

Explain what an abiotic factor is
and give some examples. Explain
how each would influence
population size.

Answer 9

A nonliving factor which affects the distribution of an organism

The more extreme the abiotic factors the fewer number of species that can tolerate them and the smaller the resultant population size.

Question 10

What is meant by an ecological niche?

Answer 10

Where an organism lives and its role within an ecosystem, including what it feeds on and how it interacts with other organisms and the environment.

Occupying niches reduce interspecific competition.

habitat
*food sources
use of abiotic resources – light, CO2, oxygen
* The way in which it is influenced by abiotic factors – the maximum and minimum temperatures in which it can survive, for example
* The way in which it interacts with other individuals of the same species and with individuals of other species

Question 11

Can you explain the stages of a population growth curve?

Answer 11

Lag phase: Small numbers introduced to new habitat, time to secually mature, reproduce, reach reproductive age, Birth rate is greater than death rate slightly.

Exponential phase: rapidly increasing numbers in the population, no limiting factors, little competition, birth rate greater than death rate.

Stationary Phase: Carrying capacity reaches, relatively constant population, slight fluctuations due to competition, birth rate is greater than death rate.

Decline phase: resources depleted, nutrients run out and death rate us greater than birth rate.

Question 12

What is meant by
intraspecific competition?

Answer 12

Intraspecific competition: competition for resources between members of the same species, this is most intense as members have the same niche competing for exactly the same resources. This has a stabilising effect on a population.

Causes population to fluctuate around the carrying capacity.

Question 13

What is meant by
interspecific competition?

Answer 13

Competition for resources between members of different species usually having evolved slightly different ecological niches.

Question 14

What factors do different species compete for?

Answer 14

Temperature: enzyme action, dehydration, energy required for thermoregulation.

Light intensity: photosynthesis for survival, more plants means more food for animal populations, affects flowering in plants and reproductive cycles in animals, depth of aquatic plants.

Water availability and humidity: water is useful, used for thermoregulation and transpiration, less humid causes more water loss.

pH: can affect extracellular enzymes and surface proteins, may affect availability of mineral salts in soil and can affect plant growth.

Question 15

How does interspecific competition influence
population size?

Answer 15

Resources have to be shared between species so less available to either. So less energy for growth and reduced populations for both.

Question 16

What is predation?

Answer 16

one animal species (the predator) feeding on another animal species (the prey). It normally involves the predator capturing and killing the prey.

Question 17

How does the predator-prey
relationship affect the population
size of the predator and prey?

Answer 17

As prey increase, intraspecific comp is reduced so predators increase.

More feeding, so prey decrease, intraspecific comp increases so predators decrease and prey begins to recover and the cycle repeats.

Natural Disease or climatic factors may also periodically crash the population and provide selection pressures for evolution.

Question 18

How do you calculate population growth?

Answer 18

Population growth = (births + immigration) – (deaths and emigration)

Question 18

Can you explain how a transect is used to
obtain quantitative data about changes in
communities along a line.

Question 18

What factors need to be considered when
using a quadrat?

Question 18

Describe how the abundance of different species is measured:

Answer 18

Abundance= population size of each species

Estimates are made using a quadrat measuring count, percentage cover or frequency of quadrats that contain species X.

Question 18

How is the mark-release-recapture method used to measure the abundance of motile species?
What assumptions does this technique rely on?

Answer 18

Method
1 Capture a sample of animals using one of the trapping techniques described above. The larger the sample the better the estimate works.

2 Count all the animals in this sample (N1) and mark (using one of methods below) then so that they can be recognised later.

3 Release all the animals where they were caught and give them time to mix with the rest of the population (typically one day).

4 Capture a second sample of animals using the same trapping technique.

5 Count the animals in the second sample (N2), and the number of marked (i.e. recaptured) animals in the second sample (Nm).

(N1total x N2total)/ Nmarked

Assumptions:
The population size does not change
Birth=death
No em/immigration
Marking does not affect survival
The mark does not come off
Sufficient time should be left after the released, so marked individuals to fully disperse
Large population

Question 19

Explain what is meant by the term random
sampling, and how you would ensure that a
sample is truly random:

Answer 19

Two measuring tapes are arranged at right angles to each other to form the axes of a grid of coordinates.

Random coordinates are generated using a random number table or calculator. A quadrat is placed at the intersection of these coordinates.

Abundance can then be estimated using quadrat by one of the following methods:

a) Repeat the measurement many times and calculate a running mean, stop when the running mean shows little change.

b) A statistical test should then be used to check the results (such as a t test if comparing two means - different areas)

Question 20

Describe changes that occur in the variety of species that occupy an area over time:

Answer 20

Succession

environment changes: less suitable for existing species so pop decreases

more suitable for other species so outcompete old dominant species

Question 21

What is meant by the term climax community?

Answer 21

The climax community contains the best adapted species to the environment (they are the final community, there will be no more succession after them)

Question 21

What is meant by the term succession?

Answer 21

The change in a community over time due to changing environmental (abiotic) and biotic factors conditions.

Primary succession: when succession begins on an area that has not been inhabited previously (a slow process)

Question 22

What is meant by conservation?

Answer 22

the concept of preservation/maintenance of biodiversity, through sustainable management of resources to maintain forests and the habitats/niches and food they supply that ultimately maintains biodiversity.

Question 23

Describe the difference between primary and
secondary succession:

Answer 23

Secondary succession occurs on previously inhabited areas by which the ecosystem returns to its climax community through recolonisation. This is much faster as soil already exists and seeds remain alive, the climax community reached may be different to the original.

Secondary succession starts from small plants not pioneer species (soil and nutrients already present) and secondary succession is faster (soil, nutrients and seeds already present)

Question 24

Explain how managing succession can help to conserve habitats:

Answer 24

active intervention to manage succession and maintain a wide range of plagioclimaxes (false climax communities)

Thinning of woodland to ensure light reaches the ground encouraging shrubs and wildflowers to grow.

Hedgerows maintained in farmland, providing ecological corridors for animals to move between areas, nesting sites, food sources, habitats.

Grazing by animals, maintains grassland but prevents growth of tress and shrubs

Periodic burning to remove saplings and allow fire resistant heather to thrive

Cutting back reeds that dominate and dry out fenland, pump water into the fenland to keep it waterlogged

Question 25

What is meant by the term Carrying Capacity?

Answer 25

The maximum population size that can be sustainably maintained over a period of time in a particular habitat.

No population will grow indefinitely as the availability of resources and competition for these will limit growth.

Question 26

What is competitive exclusion?

Answer 26

When species which occupy a similar niche are brought in close contact one will usually out-compete the other, this will be the best adapted.

Thus two species cannot occupy the same niche indefinitely, when resources are limited due to interspecific competition.

Question 27

Seral stages to succession:

Answer 27

Pioneer plant species settle, and are adapted to hostile conditions.

Over time, land erodes, soil forms, pioneers die and decompose adding humus and nutrients to the soil making the environment less hostile.

Small plants with shallow roots can grow and out-compete the pioneer species.

Overtime, more soil forms as small plants die and larger plants with deeper roots outcompete etc.

Over time, the climax community is reached.

Colonisation of area by pioneer species;
These organisms changes the environment;
This enables new species to colonise;
Repetition of this process results in the environment becoming less hostile,
Biodiversity increases, providing food, habitat, nesting sites and niches,
Eventually a climax community is reached

Question 28

What is the role of pioneer species?

Answer 28

Their organic material will be decomposed after they die forming basic soil
They will make the abiotic conditions less hostile so new organisms can survive there

Question 29

Properties of succession

Answer 29

species diversity increases (peaks just before climax – species in climax will out compete others)
habitat diversity increases
environment becomes less hostile
food chains become more complex & biomass increases

Question 30

Suggest conservation methods and reasons for protecting endemic species.

Answer 30

1. Protection of habitat;
2. Legal measures, e.g. quotas, hunting bans;
3. Capture/culling of non-native species;
4. Captive breeding;
5. Surrogacy / artificial insemination / genetic manipulation techniques;
6. Ethical / aesthetic reasons for conservation / tourism;
7. Possible undiscovered benefits, e.g. crop plants, drug sources;
8. Maintaining genetic diversity for future breeding programmes;
9. Avoid damage to food webs / control local pests;

Question 31

How can conservation be used to prevent succession?

Answer 31

used to prevent formation of woody forests – either on hill sides (for tourism) and farms (space for crops)

involves: deforestation, burning trees, grazing, using pesticides