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4.1.U1 Species are groups of organisms that can potentially interbreed to produce fertile offspring.
4.1.U1 Species are groups of organisms that can potentially interbreed to produce fertile offspring.
Be able to:
Describe limitations of the biological species concept.
Define species according to the biological species concept.
When two members of the same species mate and produce an offspring it is called interbreeding. Their offsprings it is often fertile.
When two different species breed together it is called cross-breeding. This type of breeding happen once in awhile, but the offspring is not fertile, which does not let this to reproduce, because it is infertile.
Interbreeding: When 2 members of same species mate
Cross-breeding: When 2 members of different species mate happens sometimes but cross-bred offspring is usually infertile so genes of 2 species do not mix
4.1.U2 Members of a species may be reproductively isolated in separate populations.
4.1.U2 Members of a species may be reproductively isolated in separate populations.
Be able to:
Define population.
Outline how reproductive isolation can lead to speciation.
A population is a group of organisms of the same species that are living in the same area at the same time
Members of a species may be reproductively isolated in separate populations
Organisms that live in different regions (i.e. different populations) are reproductively isolated and unlikely to interbreed, however are classified as the same species if interbreeding is functionally possible
4.1.U3 Species have either an autotrophic or heterotrophic method of nutrition (a few species have both methods).
4.1.U3 Species have either an autotrophic or heterotrophic method of nutrition (a few species have both methods).
Be able to:
Define autotroph and heterotroph.
Living organisms obtain chemical energy in one of two ways:
Organisms that make their own carbon compounds from carbon dioxide and other simple substances – autotrophic (self-feeding)
Organisms that obtain their carbon compounds from other organisms – heterotrophic (feeding on others)
Some unicellular organisms use both methods of nutrition
Eg Euglena gracilis – has chloroplasts and carries out photosynthesis when there is sufficient light. Can also feed on detritus or smaller organisms by endocytosis.
Organisms that are not exclusively autotrophic or heterotrophic are mixotrophic
4.1.U4 Consumers are heterotrophs that feed on living organisms by ingestion.
4.1.U4 Consumers are heterotrophs that feed on living organisms by ingestion.
Be able to:
Describe the feeding behaviors of consumers.
List three example consumer organisms.
Heterotrophs obtain organic molecules from other organisms via different feeding mechanisms and different food sources. Consequently, heterotrophs can be differentially classified according to their feeding pattern. They are divided into two groups according to the source of organic molecules that they use and the method of taking them in.
Consumers feed off other organisms (either still alive or have already been dead for a short time)
examples:
A mosquito sucking blood from a larger animal is a consumer on an organism that’s still alive
A lion feeding of a gazelle that it has killed is a consumer
Heterotrophs divided into two groups according to the source of organic molecules that they use and the method of taking them in.
One group of heterotrophs is called consumers:
Consumers feed off other organisms (either still alive or have already been dead for a short time)
Consumers ingest their food – they take in undigested material from other organisms. They digest it and absorb products of digestion.
Consumers are sometimes divided into trophic groups according to what other organisms they consume.
Primary consumers feed on autotrophs
Secondary consumers feed on primary consumers
4.1.U5 Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion.
4.1.U5 Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion.
Be able to:
Describe the feeding behaviors of detritivores.
List two example detritivore organisms.
Organisms discard large quantities of organic matter.
Examples include:
Dead leaves and other parts of plants
Feathers, hair, and dead parts of animal bodies
Feces from animals
This dead organic matter rarely accumulates in ecosystems – instead it is used as a source of nutrition by two groups of heterotroph-detritivores and saprotrophs.
Detritivores ingest dead organic matter then digest it internally and absorb products of digestion
Large multicellular detritivores such as earthworms ingest dead matter into their gut
Unicellular organisms ingest into food vacuoles.organic matter discarded by organisms
Rarely accumulate in ecosystem → used as source of nutrition for detritivores & saprotrophs detritivores
Ingest dead organic matter → digest internally → absorb products of digestion
example ; earthworms (large multicellular): ingest dead matter into gut
4.1.U6 Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion.
4.1.U6 Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion.
Be able to:
Describe the feeding behaviors of saprotrophs.
List two example saprotroph organisms.
Saprotrophs secrete digestive enzymes into dead organic matter and digest it externally – absorb products of digestion. Also known as decomposers – they break down carbon compounds in dead organic matter and release elements such as nitrogen into ecosystem so they can be used again by other organisms secrete digestive enzymes into dead organic matter → digest externally → absorb products of digestion
example; bacteria & fungi
4.1.U7 A community is formed by populations of different species living together and interacting with each other.
4.1.U7 A community is formed by populations of different species living together and interacting with each other.
Be able to:
Define species, population and community.
Give an example of a community of organisms.
Sometimes interaction between two species is of benefit to one species and harms the other (eg parasite and host). Sometimes interaction benefits both species (eg hummingbird and flower – hummingbird feeds on nectar and pollinates it)
A group of populations living together and interacting with each other – community
4.1.U8 A community forms an ecosystem by its interactions with the abiotic environment.
4.1.U8 A community forms an ecosystem by its interactions with the abiotic environment.
Be able to:
Define abiotic and ecosystem
A community is composed of all organisms living in an area. Community of organisms in an area and their nonliving environment. A ecosystem is a highly complex interacting system that has both abiotic and biotic factors. The organisms depend on the non-living surroundings of air, water, soil, rock. –> abiotic environment.
Many interactions take place between organisms and the abiotic environment.
Rocky intertidal zone: All in the same ecosystem but have multiple habitats because of the amount of water available – how much time they spend under water
Depends a lot on the abiotic factors
Temperature also affects the different habitats
Rainforest: Each layer is a different habitat as there are different species living in each layer.
Light intensity affects each habitat – there will be different species of autotrophs and will therefore provide different food for different consumers.
4.1.U9 Autotrophs obtain inorganic nutrients from the abiotic environment.
4.1.U9 Autotrophs obtain inorganic nutrients from the abiotic environment.
Be able to:
Define nutrient.
List the common nutrients needed by organisms.
Outline how nutrients enter living systems.
Autotrophs synthesise organic molecules from simple inorganic substances
Living organisms need a supply of chemical elements from the abiotic environment in their ecosystem:
Carbon, hydrogen, oxygen (to make carbohydrates, lipids, other carbon compounds)
Nitrogen and phosphorus needed to make compounds comes from the soil (for plants taking up nutrients from the ground)
15 other elements are needed too
Heterotrophs obtain these as part of the carbon compounds in their food.
Obtain inorganic nutrients from abiotic environment (sodium, potassium, calcium)
4.1.U10 The supply of inorganic nutrients is maintained by nutrient cycling.
4.1.U10 The supply of inorganic nutrients is maintained by nutrient cycling.
Be able to:
State that chemical elements can be recycled but energy can not.
Outline the generalised flow of nutrients between the abiotic and biotic components of an ecosystem
Nutrients refer to the material required by an organism, and include elements such as carbon, nitrogen and phosphorus. The supply of inorganic nutrients on Earth is finite – new elements cannot simply be created and so are in limited supply
Chemical elements can be endlessly recycled
Organisms absorb the elements they require from abiotic environment, use them, then return them to the environment with atoms unchanged
Passed from organism to organism before it is released back into abiotic environment
Nutrient = an element that an organism needs (in this context)
4.1.U11 Ecosystems have the potential to be sustainable over long periods of time.
4.1.U11 Ecosystems have the potential to be sustainable over long periods of time.
Be able to:
Define sustainability.
Give an example of an unsustainable practice.
Outline three requirements of a sustainable ecosystem.
Ecosystems describe the interaction between biotic components (i.e. communities) and abiotic components (i.e. habitat). They are largely self-contained and have the capacity to be self-sustaining over long periods of time
There are three main components required for sustainability in an ecosystem:
Energy availability – light from the sun provides the initial energy source for almost all communities
Nutrient availability – saprotrophic decomposers ensure the constant recycling of inorganic nutrients within an environment
Recycling of wastes – certain bacteria can detoxify harmful waste byproducts (e.g. denitrifying bacteria such as Nitrosomonas) Sustainable: it can continue indefinitely
4.1.S1 Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode of nutrition.
4.1.S1 Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode of nutrition.
Be able to:
Use a dichotomous key to identify the mode of nutrition of an organism.
Species can be classified according to their mode of nutrition
Autotrophs produce their own organic molecules using either light energy or energy derived from the oxidation of chemicals
Heterotrophs obtain organic molecules from other organisms via one of three methods:
Consumers ingest organic molecules from living or recently killed organisms
Detritivores ingest organic molecules found in the non-living remnants of organisms (e.g. detritus, humus)
Saprotrophs release digestive enzymes and then absorb the external products of digestion (decomposers)
4.1.S2 Setting up sealed mesocosms to try to establish sustainability. (Practical 5)
4.1.S2 Setting up sealed mesocosms to try to establish sustainability. (Practical 5)
Be able to:
Outline why sampling must be random.
Explain methods of random sampling, including the use of a quadrat.
State the null and alternative hypothesis of the chi-square test of association.
Use a contingency table to complete a chi-square test of association.
4.1.S3 Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
4.1.S3 Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
Be able to:
Calculate a chi-square statistic based on observed and expected values.
State the null and alternative hypothesis of statistical tests.
Determine if the null hypothesis is supported or rejected given a critical value and a calculated statistic.
State the minimum acceptable significance level (p value) in published research.
Explain the meaning of a “statistically significant” result, including the probability of chance having a role in the result
Chi-Square (X2) Test for Independence
Chi-square Test for Independence is a statistical test commonly used to determine if there is a significant association between two variables. For example, a biologist might want to determine if two species of organisms associate (are found together) in a community.
Does Species A associate with Species B?
Species A
Species B
Null Hypothesis:
"There is not a significant association between variables, the variables are independent of each other; any association between variables is likely due to chance and sampling error."
For example:
There is no significant association between Species A and Species B; the species are independent of each other. The location of Species A has no effect on the location of Species B.
Alternative Hypothesis:
"There is a significant (positive or negative) association between variables; the association between variables is likely not due to chance or sampling error."
For example:
There is a significant association between Species A and Species B; the species are dependent. Either Species A significantly associates with Species B or Species A does not significantly associate with Species B.
How to Calculate a Chi-Square Test of Independence
How to Calculate a Chi-Square Test of Independence
The first step is to collect raw data for the occurrence of each variable. This is often done via random sampling using a quadrat. In our example, there are five quadrants. Determine:
The number of quadrats with both species present
The number of quadrats with Species A but not Species B
The number of quadrats with Species B but not Species A
The number of quadrats with neither species
2. Create a "contingency table" to display your results. In the Chi-Square test, these are your OBSERVED values.
3. Next you need to determine what would be EXPECTED assuming the species are randomly distributed with respect to each other. Expected frequencies = (row total X column total) / grand total
4. Now that you have OBSERVED and EXPECTED values, apply the Chi-Square formula in each part of the contingency table by determining (O-E)2 / E for each box.
5. The final calculated chi-square value is determined by summing the values: X2 = 0.0 + 0.1 = 0.1 + 0.2 = 0.4
The calculated X2 value is then compared to the “critical value X2” found in an X2 distribution table. The X2 distribution table represents a theoretical curve of expected results. The expected results are based on DEGREES OF FREEDOM.
Degrees of Freedom = (number of rows - 1) X (number of columns - 1)
In our example, DF = (2-1) X (2-1) = 1 X 1 = 1
*the row and column for the total in the contingency table are not included
The X2 distribution table is organised by the Level of Significance- we use 0.05. The level of significance is the maximum tolerable probability of accepting a false null hypothesis.
If the calculated value is lower than the critical value in the table at the 0.05 level of significance, accept the null hypothesis and conclude that there is NO significant association between the variables.
If the calculated value is higher than the critical value in the table at the 0.05 level of significance, reject the null hypothesis and conclude that there IS a significant association between the variables.
For example, with a DF=1, a value greater than 3.841 is required to be considered statistically significant (at p = 0.05). Since the X2 we calculated (0.4) is less than 3.841, there is NOT a significant association between Species A and Species B. The location of Species A has no significant effect on the location of Species B, any association between species is likely due to chance and sampling error.
The presence of two species within a given environment will be dependent upon potential interactions between them. If two species are typically found within the same habitat, they show a positive association
Species that show a positive association include those that exhibit predator-prey or symbiotic relationships
If two species tend not to occur within the same habitat, they show a negative association
Species will typically show a negative association if there is competition for the same resources
One species may utilise the resources more efficiently, precluding survival of the other species (competitive exclusion)
Both species may alter their use of the environment to avoid direct competition (resource partitioning)
If two species do not interact, there will be no association between them and their distribution will be independent of one another
Quadrat Sampling
The presence of two species within a given environment can be determined using quadrat sampling
A quadrat is a square frame of known dimensions that can be used to establish population densities
Quadrats are placed inside a defined area in either a random arrangement or according to a design (e.g. belted transect)
The number of individuals of a given species is either counted or estimated via percentage coverage
The sampling process is repeated many times in order to gain a representative data set
Quadrat sampling is not an effective method for counting motile organisms – it is used for counting plants and sessile animals
In each quadrat, the presence or absence of each species is identified
This allows for the number of quadrats where both species were present to be compared against the total number of quadrats
Chi-Squared Tests
A chi-squared test can be applied to data generated from quadrat sampling to determine if there is a statistically significant association between the distribution of two species
A chi-squared test can be completed by following five simple steps:
Identify hypotheses (null versus alternative)
Construct a table of frequencies (observed versus expected)
Apply the chi-squared formula
Determine the degree of freedom (df)
Identify the p value (should be <0.05)
4.1.4S Recognizing and interpreting statistical significance.
4.1.4S Recognizing and interpreting statistical significance.
Be able to:
Define mesocosm.
List three example mesocosms.
Outline requirements of setting up a mesocosm.
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