Unit 3 - Topic 2: Ecosystem Dynamics

Question 1

Sequence and explain the transfer and transformation of solar energy into
biomass as it flows through biotic components of an ecosystem;
- converting light to chemical energy
- producing biomass and interacting components of the carbon cycle

Answer 1

Autotrophic organisms use the process of photosynthesis to capture solar radiation in the form of light energy and use this captured energy to transform, inorganic molecules into organic molecules such as simple sugars, storing energy in the bonds.

Stored chemical energy in the bonds of molecules in autotrophs are consumed and then assimilated by herbivour thus transferring energy from one organism (and trophic level) to the next. Not all this energy is assimilated, some is lost through resparation resulting in carbon dioxide as a biproduct, and some is lost in the death of organisms that are not consumed.

Question 2

Analyse and calculate energy transfer (food chains, webs and pyramids) and transformations within ecosystems, including
­ - loss of energy through radiation, reflection and absorption
­ - efficiencies of energy transfer from one trophic level to another
­ - biomass

Answer 2

• All energy that enters the system is eventually either not absorbed by primary producers or lost via radiation, reflection and absorption.
• The efficiency of transfer of energy that has been absorbed at each trophic level is calculated by
  dividing the amount from the higher trophic level by the amount from the lower trophic level and multiply by one hundred. That is, we divide the smaller number by the bigger one (and multiply by one hundred).
  -

Question 3

Describe the transfer and transformation of matter as it cycles through the water cycle

Answer 3

the cycle of processes by which water circulates between the earth’s oceans, atmosphere, and land, involving precipitation as rain , drainage in streams and rivers, and return to the atmosphere by evaporation and transpiration (from plants).

Question 4

Describe the transfer and transformation of matter as it cycles through the carbon cycle

Answer 4

the series of processes by which carbon compounds are interconverted in the environment, chiefly involving the incorporation of carbon dioxide into living tissue, by photosynthesis in producers and assimilation into consumers; and its return to the atmosphere through respiration, the decay of dead organisms, and the burning of fossil fuels.

Question 5

Describe the transfer and transformation of matter as it cycles through the nitrogen cycle

Answer 5

the series of processes by which nitrogen and its compounds are interconverted in the environment and in living organisms, including nitrogen fixation, denitrification and decomposition.

Question 6

Define ecological niche in terms of habitat, feeding relationships and interactions with other species

Answer 6

describes the functional position and role of an organism in its environment. It considers where the organism lives, what it eats and what wants to it, and also the species’ interactions with other species (predation, competition etc)

Question 7

Understand the competitive exclusion principle

Answer 7

two or more resource-limited species, having identical patterns of resource use, cannot coexist in a stable environment: one species will be better adapted and will out-compete or otherwise eliminate the other(s)

Question 8

Define keystone species and understand the critical role they play in maintaining the structure of a community

Answer 8

defined as a plant or animal that plays a unique and crucial role in the way an ecosystem functions.
Roles may include:
- maintaining biodiversity (through ecological services)
- controls populations (controlling dominant species)
- provides critical resources for a wide range of species
- maintains balance of ecological relationships.

Question 9

Define the term carrying capacity

Answer 9

Maximum population size of a biological species that can be sustained in that specific environment, given the food, habitat, water, and other resources available.

Question 10

Explain why the carrying capacity of a population is determined by limiting
factors (abiotic)

Answer 10

Temperature and Rainfall
Rainfall is needed for plant growth and so to support grazers of that plant material
Low rainfall reduces plant growth, biomass and available water for animals, ultimately reducing population sizes

Question 11

Explain why the carrying capacity of a population is determined by limiting
factors (biotic)

Answer 11

Biotic factors include the amount of food that is available to that species and the number of organisms that also use that food source.
Predator and prey populations frequently show regular population cycles – therefore regulating population numbers to avoid reaching carrying capacity

Question 12

Calculate population growth rate and change

Answer 12

pop growth = births - deaths + immigration - emmigration
pop growth = b - d + i - e

Question 13

Use Lincold Index to estimate population size

Answer 13

N = M x n
m

M = # caught, marked and released initially
n = # caught on second sampling
m = # recaptured that were marked

Question 14

Graphs

Answer 14

J shaped: depicts exponential growth, are likely r strategists, population continues to increase while resources are unlimited.

S shaped: depicts logistic growth, are likely k strategists, population growth increases slowly, then exponentially until it levels due to environmental resistance and a carrying capacity is reached.

Question 15

Discuss the effect of changes within population-limiting factors on the carrying
capacity of the ecosystem.

Answer 15

Carrying capacity of a system will increase or decrease due to changes in any density factors that might limit the productivity of the system. For example

Question 16

Explain the concept of ecological succession (refer to pioneer and climax
communities and seres)

Answer 16

1. during the first stage of succession, pioneer species that are generally able to grow fast, survive harsh environments and environments with poor soils, grow back first .
2. Following this the ecosystem transitions through a a series of sere communities that are dominated by fast growing plants, and increasing ecological complexity and productivity.
3. Eventually, the secondary community (sere) is slowly overtaken and replaced by dominant slow growing climax species and a highly productive climax community is formed.

Question 17

Differentiate between the two main modes of succession: primary and
secondary

Answer 17

Primary Succession:
Begins in a place without any soil
- In the beginning there is only rock, sand, volcanic ash.
- Since there is no soil, there is no community.

Secondary Succession:
It is defined as ‘successive, natural changes in plant communities in an area where a previous community has been removed’.
- Soil is already present.
- There are already some organisms and organic matter present at the site.

Question 18

Identify the features of pioneer species that make them effective colonisers

Answer 18

ability to fixate nitrogen
tolerance to extreme condition
rapid germination of seeds
ability to photosynthesise