1. SPECIES, COMMUNITIES & ECOSYSTEMS
The continued survival of living organisms including humans depends on sustainable communities.
Topic 4.1
IB Biology
Miss Werba

2. SPECIES, COMMUNITIES & ECOSYSTEMS
TOPIC 4 – ECOLOGY
4.1
SPECIES, COMMUNITIES & ECOSYSTEMS
4.2
ENERGY FLOW
4.3
CARBON CYCLING
4.4
CLIMATE CHANGE

3. THINGS TO COVER U.1 U.2 U.3 U.4 U.5 U.6 U.7 U.8 Statement Guidance
Species are groups of organisms that can potentially interbreed to produce fertile offspring.
U.2
Members of a species may be reproductively isolated in separate populations.
U.3
Species have either an autotrophic or heterotrophic method of nutrition (a few species have both methods).
U.4
Consumers are heterotrophs that feed on living organisms by ingestion.
U.5
Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion.
U.6
Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion.
U.7
A community is formed by populations of different species living together and interacting with each other.
U.8
A community forms an ecosystem by its interactions with the abiotic environment.

4. THINGS TO COVER U.9 U.10 U.11 S.1 S.2 Statement Guidance
Autotrophs obtain inorganic nutrients from the abiotic environment.
U.10
The supply of inorganic nutrients is maintained by nutrient cycling.
U.11
Ecosystems have the potential to be sustainable over long periods of time.
S.1
Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode of nutrition.
S.2
Setting up sealed mesocosms to try to establish sustainability. (Practical 5)
Mesocosms can be set up in open tanks, but sealed glass vessels are preferable because entry and exit of matter can be prevented but light can enter and heat can leave. Aquatic systems are likely to be more successful than terrestrial ones.

5. THINGS TO COVER S.3 S.4 Statement Guidance NOS 3.1
Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
To obtain data for the chi-squared test, an ecosystem should be chosen in which one or more factors affecting the distribution of the chosen species varies. Sampling should be based on random numbers. In each quadrat the presence or absence of the chosen species should be recorded.
S.4
Recognizing and interpreting statistical significance.
NOS
3.1
Looking for patterns, trends and discrepancies —plants and algae are mostly autotrophic but some are not.

6. ECOLOGICAL DEFINITIONS
U.1
Ecology:
The study of the relationships between living organisms and between organisms and the environment
Species:
A group of organisms that can potentially interbreed to produce fertile offspring.

7. ECOLOGICAL DEFINITIONS
U.2
Habitat:
The environment in which a species normally lives or the location of a living organism
Population:
A group of organisms of the same species who live in the same area at the same time
Members of a species may be reproductively isolated in separate populations.

8. ECOLOGICAL DEFINITIONS
U.7
U.8
Community:
A group of populations of different species living together and interacting with each other.
Ecosystem:
A community (biotic) interacting with its abiotic environment
Temp
Light
Water
Humidity pH
Nutrients
Wind
Tides
Turbidity

9. ?

10. CLASSIFYING ORGANISMS
U.3
S.1
Species can be classified according to their method of nutrition:
Autotrophs
Heterotrophs
However, a few species have both methods (NOS 3.1).

11. CLASSIFYING ORGANISMS
U.3
S.1
Autotroph:
An organism that synthesises its organic molecules from inorganic substances
Photosynthesis
Heterotroph:
An organism that obtains its organic molecules from other organisms
Digestion

12. Looking for patterns, trends and discrepancies.
AUTOTROPH EXCEPTIONS
NOS 3.1
Looking for patterns, trends and discrepancies.
Plants and algae are mostly autotrophic but some are not.

13. AUTOTROPH EXCEPTIONS Sundews Sacoglossan sea slugs
NOS 3.1
Sundews
are carnivorous plants
autotrophic but they "hunt" for insects to get additional nutrients, eg. nitrogen 
Sacoglossan sea slugs
are heterotrophic
perform kleptoplasty to capture intact, functional chloroplasts from algal food sources and retain them within specialised cells in their digestive system 

14. CLASSIFYING ORGANISMS
Producers:
Do not consume!
Mostly autotrophs
Covert light energy into chemical energy
Produce their own organic matter

15. CLASSIFYING ORGANISMS
U.4
S.1
Consumers:
that feed on living organisms by ingestion
ingests other organic matter that is living or recently killed
Classified by what they eat:
can be herbivores, omnivores or carnivores
Also classified according to their level in the food chain:
can be primary, secondary or tertiary consumers

16. 5.5.2
DIET
MISS J WERBA - TERM 16

17. 5.5.2
DIET
MISS J WERBA - TERM 17

18. 5.5.2
MISS J WERBA - TERM 18

19. CLASSIFYING ORGANISMS
U.5
U.6
S.1
Decomposers:
organisms that decompose organic material
eg. bacteria and fungi
Detritivores
heterotrophs that obtain organic nutrients from detritus by internal digestion
Saprotrophs
heterotrophs that obtain organic nutrients from dead organisms by external digestion

20. SOURCE OF NUTRIENTS
U.9
U.10
Autotrophs obtain inorganic nutrients from the abiotic environment.
The supply of inorganic nutrients is maintained by nutrient cycling.
Decomposers (saprotrophic bacteria and fungi) recycle nutrients by returning them to the soil for plants to use.

21. SOURCE OF NUTRIENTS
U.9
U.10 C
H2O N

22. SUSTAINABLE ECOSYSTEMS
Ecosystems have the potential to be sustainable over long periods of time.
Set practical 5 – Setting up sealed mesocosms to try to establish sustainability.
Click to read the related article

23. SUSTAINABLE ECOSYSTEMS
Mesocosms are:
Small scale investigations
Self-sustaining natural systems
Allow a bridge between controlled lab experiments and more variable, uncontrolled field investigations.
Allow more variables to be controlled
Allow sufficient complexity to model the natural environment

24. CHI SQUARE ( )TESTS
S.3
S.4
𝝌 𝟐
An important question to answer in any population size experiment is how can we decide if our data fits any of the known/expected ratios.
A statistical test that can test out ratios is the Chi-Square
Chi-Square Formula:
Degrees of freedom (df) = n-1 where n is the number of groups investigated

25. CHI SQUARE ( )TESTS
S.3
S.4
𝝌 𝟐
Let’s do an example with a dihybrid genetic cross.
The expected ratio for a Mendelian dihybrid cross between heterozygotes is 9:3:3:1
The following data was obtained for 556 seeds:
Observed Values
315 Round, Yellow Seed
108 Round, Green Seed
101 Wrinkled, Yellow Seed
  32 Wrinkled, Green
556 Total Seeds

26. CHI SQUARE ( )TESTS
S.3
S.4
𝝌 𝟐
Let’s do an example with a dihybrid genetic cross.
Firstly, the expected values need to be determined:
Observed Values
Expected Values
315 Round, Yellow Seeds
(9/16) x 556 =
Round, Yellow Seeds
108 Round, Green Seeds
(3/16) x 556 =
Round, Green Seeds
101 Wrinkled, Yellow Seeds
(3/16) x 556 = Wrinkled, Yellow Seeds
  32 Wrinkled, Green Seeds
(1/16) x 556 =   Wrinkled, Green Seeds
556 Total Seeds

27. CHI SQUARE ( )TESTS
S.3
S.4
𝝌 𝟐
Let’s do an example with a dihybrid genetic cross.
Then, apply the formula:
𝜒 2 = 0.47
Then, calculate the degrees of freedom:
df = n – = 4 groups – = 3

28. CHI SQUARE ( )TESTS
S.3
S.4
𝝌 𝟐
Let’s do an example with a dihybrid genetic cross.
Then, we need to use the Chi-Square table at df = 3.
We need to see if the probability of our chi-square value is greater than the value in the table.
By statistical convention, we use the 0.05 probability level as our critical value.

29. CHI SQUARE ( )TESTS
S.3
S.4
𝝌 𝟐
Let’s do an example with a dihybrid genetic cross.
If the calculated chi-square value is less than the value, we accept the hypothesis – ie. That the results match the expected ratios.
If the value is greater than the value in the table, we reject the hypothesis – ie. That the results do not match the expected ratios.
Therefore, because the calculated chi-square value of is less than the critical value of 7.81, then we accept the hypothesis that the data fits a 9:3:3:1 ratio.

30. CHI SQUARE ( )TESTS 𝝌 𝟐 We are going to do this in a “prac” :)
We are going to do a quadrat survey of an “ecosystem” to try to determine the number of organisms in the community.
This will involve counting the number of organisms in randomly selected sample areas and trying to generalise them to the population.

31. CHI SQUARE ( )TESTS
S.3
S.4
𝝌 𝟐
Some of you will be establishing our sampling area.
Some of you will counting and randomly distributing the organisms into our sampling area.
Some of you will be randomly selecting the quadrats and counting the organisms within.
Then we will use the known area to estimate the population sizes.
Then we will use a chi square test to check the accuracy of our estimate!

32. SPECIES, COMMUNITIES & ECOSYSTEMS
Q1.
Zoophobas morio is an insect. Its larvae feed on bat faeces in caves in Guatemala. What type of organism is a Zoophobas morio larva?
Autotroph
Consumer
Detritivore
Saprotroph
J WERBA – IB BIOLOGY 32

33. SPECIES, COMMUNITIES & ECOSYSTEMS
Q2.
Which of the following ecological units includes abiotic factors?
A community
An ecosystem
A population
A trophic level
J WERBA – IB BIOLOGY 33

34. SPECIES, COMMUNITIES & ECOSYSTEMS
Q3.
Define the term random sample.
The masses of two different populations of sparrows (Passer domesticus) are shown in the table below.
Calculate the mean value of the mass of birds for population 1.
With reference to the data shown, explain what is meant by the term standard deviation. No calculation is expected.
Population 1:
 mass of birds / g
Population 2:
 mass of birds / g
24.5
25.0
24.0
24.8
26.9
23.2
23.6
31.0
27.9
28.3
J WERBA – IB BIOLOGY 34

35. SPECIES, COMMUNITIES & ECOSYSTEMS
Q4. In communities, groups of populations live together and interact with each other. Outline the importance of plants to populations of other organisms in a community. 6 marks
J WERBA – IB BIOLOGY 35