Hi all - just your friendly neighbourhood biology student passing through ;D
The QCE forums are a bit quiet, so I thought I would try to liven it up a bit :)
This thread will contain my class notes that I will write up as I am completing unit 3 Biology - so I hope that it is of some use to other QCE (maybe even HSC and VCE?? Who knows...) students out there 8) I will also include any thoughts or questions (and hopefully some answers to those questions) that I have had throughout unit 3. If my notes are any good I might also upload them to the notes section of ATAR notes.
I will also make one of these threads for Psychology and Physics - so feel free to come say hi ;D
This thread will follow a simple structure, and I will try to be as consistent as possible to ensure comprehensibility. I will follow the criteria set out by the syllabus - which can be accessed here. If you haven't checked out the syllabus, I recommend you do so. After all, on the external exam QCAA can't ask any questions relating to content outside of the syllabus. Anywho, please feel free to contribute your own notes and help this thread grow :D Also, don't be shy to ask/answer any questions :)
Thread Index - Jump ahead to your relevant topic :)
So lets kick this thread off, shall we!
Topic 1: Part 1
Describing Biodiversity
Biodiversity
Important Formula
Simpson's Diversity Index
SDI is used to quantify the biodiversity within a habitat - in other words, it tells you the probability that two individuals from a sample will belong to a different species. Results will range between 0 and 1. For example, a SDI of 0.65 tells you that there is a 65% chance that any two individuals that are randomly selected from a sample will belong to different species.
Higher SDI = Higher diversity
(https://i.imgur.com/2D3nEIW.png)
Where:
N = total number of organisms of all species
n = number of organisms in one species
- recognise that biodiversity includes the diversity of species and ecosystems
Biodiversity refers to the variety of species and ecosystems within a given area. Variation is important! A greater variety of species boosts ecosystem productivity. Having a variety of different ecosystems also benefits different species. Every organisms has an ecological niche, this describes the conditions that will either benefit a particular organism or harm it and includes the organisms position within its ecosystem and the interactions it has with other organisms - I have put a graph in this post down below :)
The definition of ecosystem is: a biological community of living organisms that interact with each other and their surroundings.
- determine diversity of species using measures such as species richness, evenness (relative species abundance), percentage cover, percentage frequency and Simpson's Diversity Index
Species richness (S): when looking at an ecosystem, ask yourself: How many different species can I see? This will give you your species richness. Put simply, species richness is the number of different species in an ecosystem - it does not pay any attention whatsoever to evenness, distribution, population size of each species, etc.. It is simply, how many different species there are.
Relative species abundance: aka evenness. It is a measurement that describes how common or rare a species is compared to other species in a particular area.
Percentage cover: this describes how much space a particular species in a sample occupies. It focuses on the geographical distribution of species within an ecosystem.
Percentage frequency: this is a measurement describing how often a species pops up when taking a sample of an ecosystem - it gives us insight into how common particular species are.
Simpson's Diversity Index: this was discussed above, so I won't discuss it in this section.
*note: I will post some example questions and practice questions later on so that we can really tick off the "determine" criteria - also, I don't want to make this post too long, so stay tuned for my next post in this thread :)
- use species diversity indices, species interactions (predation, competition, symbiosis, disease) and abiotic factors (climate, substrate, size/depth or area) to compare ecosystems across spatial and temporal scales
Species Diversity Indices
This relates to the dot point above ^^^
You can use the measure of species diversity (species richness, relative species abundance, percentage frequency, percentage cover, and SDI) in order to compare different ecosystems. E.g. does one species have a higher percentage frequency in one ecosystem than it does in another? Does one ecosystem have an increased species richness than another ecosystem
Species Interactions
Species interactions are very important within ecosystems. The definition of an ecosystem is quite literally: a biological community of organisms interacting with each other and their environment. Species interactions help keep balance and order in the ecosystem.
Predation: when thinking of predation, it is common to just go: predator eats prey. However, if we look at predation ecologically, predation can be defined as being any interaction between two organisms that results in the transfer of energy. There are four commonly recognised types of predation: 1) carnivory, 2) herbivory, 3) parasitism and 4) mutualism (3 and 4 will be explored when looking at symbiosis).
*note: in some cases, mutualism may not be considered a form of predation (there is a lack of scientific literature supporting mutualism as being predation). However, in some cases, mutualism may involve the transfer of energy from one organism to another and thus, under the definition stated above, some mutualistic interactions may be considered a form of predation.
Carnivory = the consumption of meat (a predator kills prey)
Herbivory = the consumption of autotrophs
*note: the syllabus does not state how in depth it wants us to explore predation. So I am unsure as to whether or not we need to know the 4 commonly recognised types of predation or just the whole predator eats prey thing. My textbook (Biology for Queensland: An Australian Perspective - the Oxford textbook) defines predator as: "an organism that captures, kills and feeds on another animal." So I am assuming that their definition of predation is the simple: predator eats prey (which is essentially an interaction between two organisms that results in the transfer of energy)
When comparing predation across ecosystems it may be beneficial to examine the species diversity in particular areas and the abundance of prey.
Competition: competition is a biological interaction that can be intraspecific (between organisms of the same species) or interspecific (between organisms of different species). It is defined as the struggle between organisms for a specific resource(s). Resources are aspect or components of the environment that are necessary for survival or reproduction - e.g. food, water, shelter, light, space... Organisms may also compete for a mate.
As with predation, to compare competition across different ecosystems or areas within an ecosystem, it may be beneficial to pay attention to species abundance, species distribution, species diversity... Competition will increase if resources are limited.
Symbiosis: There are 5 types of symbiosis:
1) Obligate mutualism: both species benefit from necessary interaction - this interaction is vital for their survival (e.g. the relationship between ants and the acacia plant - the plant provides food and shelter for the ants, and the ants defend the plant from herbivores)
2) Facultative mutualism: each species benefits from the interaction, but the presence of one is not essential to the survival of the other (e.g. the relationship between sea anemones and hermit crabs. Sea anemones provide the crab defence against predators - if attacked, the crab can retreat into its shell while the anemone stings the attacker. By living on the crab's shell, it allows the anemone to disperse offspring more efficiently (because the crab is moving) and they can share food. When the crab changes shells it just puts the anemone on it's new shell. If you are interested, you can watch a video of this shell-changing process here - it starts at 46 seconds)
3) Commensalism: a biotic interaction in which one organism is benefitted while the other is not affected (e.g. epiphytic ferns and orchids on rainforest trees). *note: examples of commensalism may be difficult to come across due to the fact that it is unlikely that an interaction has no affect at all on one party
4) Amensalism: one species inhibits another - one is negatively affected, while the other isn't affected at all (e.g. antibiosis. An example of antibiosis can be observed with the black walnut - it secretes juglone, which is a substance that can destroy herbaceous plants within its root zone... Definition of antibiosis (according to the dictionary that pops up when I google "antibiosis definition" ;D): "an antagonistic association between two organisms (especially microorganisms), in which one is adversely affected.")
5) Parasitism: a biotic relationship in which one organism (the parasite) is benefitted at the expense of another (the host). Parasites can live on or in the host, reducing the host's fitness but increasing its own (e.g. human parasites include roundworms. They can infest the human digestive tract and use the human body to stay alive and reproduce. Symptoms of roundworm infection can include: high temperatures, mild stomach pain, nausea and vomiting and diarrhoea)
*note: my textbook had the first two as mutualism and cooperation, but after discussing this with Bri we believe that there may have been an error in the textbook. There doesn't exist any scientific literature (from what I can find) that considers cooperation a form of symbiosis. Additionally, the definition for mutualism provided by the textbook perfectly describes obligate mutualism and the definition provided for cooperation perfectly describes facultative mutualism.
When comparing ecosystems, you can look at how the frequency of the various types of symbiosis differs. E.g. does one ecosystem contain more organisms that exhibit mutualistic interactions than another ecosystem?
*note: the syllabus does not state how in depth we need to explore symbiosis - you may not need to know all of these types of symbiosis
Disease: a disease is defined as being an abnormal condition that negatively impacts the structure or function of an organism (or part of an organism), that isn't resultant of external injury. Populations of organisms with higher densities may allow for the easy transmission of disease - thus, potentially resulting in a reduction in population size.
Comparing the rates of disease in different ecosystem can be used to draw conclusions about population density.
Spatial and Temporal Scales
Spatial relates to space
Temporal relates to time
In regard to the spatial aspects of an ecosystem, you can look at and compare:
- substrate: the surface organisms live (you can use it to look at sources of nutrients in the environment and to infer what types of organisms would live there - furthermore, you can look at how a change in/to a substrate over time would affect the species living in that ecosystem)
- size of area: the larger the ecosystem, the more room there is for organisms (allowing for larger population sizes). A larger ecosystem may also mean that there is less competition for land/territory.
- topography: topographic features can affect illumination, temperature, moisture, etc. - how does topography affect populations within different ecosystems?
- shelter: the availability of shelter is crucial for many different types of organisms - how does the availability/unavailability of shelter affect the populations within different ecosystems?
Soil
- pH: can influence the distribution of plants in soil - compare between ecosystems.
- mineral salts and trace elements: the chemical composition of the soil also affects the distribution of plants - compare between ecosystems.
- water retention: differing types of soils retain water to differing extents, this affect the types of plants within certain areas - compare between ecosystems.
In regard to the temporal aspects of an ecosystem, you can look at and compare:
Climate
How has the climate changed over the past however many years? Has this change in climate affected diversity/abundance/distribution/etc.?Furthermore, you could look at how temperature and weather changes cyclically throughout the year (or you could look at anthropogenic climate change and how that is rapidly changing certain aspects of the climate and how that is affecting populations of organisms within particular ecosystems).
- seasons: summer, autumn, winter, spring, rain season - how do different seasons affect populations in different ecosystems?
- water: an organisms ability to conserve water determines how well it can tolerate dry conditions - how available is this resource in different ecosystems?
- radiant energy: light is essential for life - how available is this resource in different ecosystems?
- humidity: affects water evaporation - high humidity can affect an organisms ability to cool itself, low humidity can affect an organisms ability to withstand drought. How does humidity affect populations of organisms differently in different ecosystems?
- wind and air current: strong wind currents can affect plants with a weak root system. Wind and air currents do, however, provide a means of dispersing insects, spores and seeds. Additionally, they are important for flight and gliding modes of locomotion. How do differing air and wind currents affect the distribution/abundance/diversity of species within ecosystems?
You can link these abiotic environmental factors (the spatial and temporal stuff) to ecological niches and use this in you comparison between ecosystems.
ecological niche
(https://i.imgur.com/4fXpJFI.jpg)
Image credits: BioNinja
- explain how environmental factors limit the distribution and abundance of species in an ecosystem
There are many limiting factors that may affect the distribution and abundance of species within an ecosystem. These include:
Density-independent factors: an abiotic factor (independent of population density) that affects the population size. Examples include environmental disasters and pollution
Density-dependent factors: any factor that influences population regulation and has a greater impact on populations as their density increases. Examples include competition, predation and infection.
Definition of limiting factors: conditions that limit the growth, abundance or distribution of a population of organisms
Each population within an environment will be affected by the carrying capacity of the environment. The carrying capacity describes the size of a population that is able to be supported by an environment. Environmental resistance (the sum of all environmental limiting factors) ensures that a population will not become too large. It can be observed that if a population rises above the point of equilibrium (the point at which the population size can be supported) limiting factors will cause the population size to decrease. If it falls below the point of equilibrium the population will rise again. This repeats and the population size will fluctuate around the point of equilibrium. This is an example of ecological homeostasis.
population fluctuation around carrying capacity
(https://i.imgur.com/ogiNsBz.jpg)
Image credits: BioNinja
*note: the syllabus does not state that we need to talk about the fluctuation of population size around the carrying capacity. So instead, you may just want to focus on a normal logistic growth (S) curve (aka a sigmoidal curve) when looking at K-selection. This looks almost identical to the graph above, it just doesn't include any fluctuation.
normal sigmoidal curve
(https://i.imgur.com/fGssbMk.png)
Image credits: Study.com
Definition of ecological homeostasis, as provided by my textbook: "maintenance of a population size commensurate with environmental limiting factors, mediated by feedback systems."
EDIT: Thank you Bri for the awesome feedback and for helping this thread to be as beneficial and accurate as possible! :)
Practice Questions
Below is a random sample of birds you found at a local park:
Species | Number |
Crow | 10 |
Magpie | 5 |
Pigeon | 2 |
Unknown | 1 |
1. Calculate Simpson's Diversity Index
answer
SDI = 1- (10(10-1)+5(5-1)+2(2-1)+1(1-1) / 18(18-1))
SDI = 1 - ((10*9)+(5*4)+(2*1) / (18*17))
SDI = 1 - ((90 + 20 + 2) / 306)
SDI = 1 - (112 / 306)
SDI = 1 - 0.37 (2 d.p)
SDI = 0.63 (2 d.p)
2. Identify species richness
answer
What species are there? Crow, magpie, pigeon and unknown. So species richness = 4
3. Calculate the relative species abundance for crows
answer
10/18 = 0.56 (2 d.p)
_______________________
Percentage cover
I don't have any practice questions for this one, but here is a video explaining how it works.
https://www.youtube.com/watch?v=cS4qwSK-Mqw
If anyone has any practice questions please feel free to share them :)
Percentage frequency
I also don't have any practice questions for this one... However, how you calculate it is:
percentage frequency of a species in a given area is just: (frequency of that species)/(sum frequency of all species) * 100
Topic 2: Part 1
Ecosystem Dynamics
Functioning Ecosystems
- sequence and explain the transfer and transformation of solar energy into biomass as it flows through biotic components of an ecosystem, including
- converting light into chemical energy
Solar energy is what sustains majority of the living systems on Earth. However, only ~1% of this solar energy is actually absorbed and utilised by the plants within an ecosystem. Photosynthesis is the process by which solar energy is transformed into chemical energy.
carbon dioxide + water --> glucose + oxygen
CO2 + H2O + energy (sunlight) --> C6H12O6 + 6O2
Producers are responsible for converting simple inorganic chemicals into complex organic molecules.
- producing biomass and interacting with components of the carbon cycle
Biomass means the mass of all organic matter in an area. The measure of the amount of energy fixed within chemical compounds at each trophic level is known as the productivity. In producers it can also indicate the amount that biomass increases over a period of time. The amount of biomass within an ecosystem is the product of photosynthesis.
- analyse and calculate energy transfer (food chains, webs and pyramids) and transformations within ecosystems, including
- loss of energy through radiation, reflection and absorption
After photosynthesis, chemical energy is transferred between molecules in the biosphere before radiating into space in the form of heat energy. As stated earlier, only a small proportion of solar energy is actually utilised by producers. Most solar energy gets reflected back into space or is absorbed by the Earth – only to be radiated back into the atmosphere at night.
Ecosystems conform to the law of conservation of matter and energy (matter and energy cannot be created or destroyed, but they can be changed into other forms).
- efficiencies of energy transfer from one trophic level to another
Net primary production describes the total amount of energy available to a herbivore when they eat a producer (after subtracting the energy required to digest the producer).
Trophic levels describe the relative positions of producers and consumers in a food chain. Each organism in the series gains energy from the preceding organism. The energy stored in the cells and tissues of the organisms is passed along.
However, only 5-20% of the total energy contained at each level is transferred to the next. Thus, there rarely exists more than six links in any food chain.
- biomass
Pyramids of biomass and energy are examples of ecological pyramids. Productivity is measured by the amount of energy that is fixed in chemical compounds or by the increase in biomass.
- construct and analyse simple energy-flow diagrams illustrating the movement of energy through ecosystems, including the productivity (gross and net) of the various trophic levels
- More energy is stored at lower levels
- Food chains generally have fewer members in each successive trophic level
- Energy is released to the environment at every level
- Energy released is eventually re-radiated into the atmosphere as heat
- describe the transfer and transformation of matter as it cycles through ecosystems (water, carbon and nitrogen)
Water cycle:
Solar energy --> water evaporates from oceans and from freshwater environments, soil and organisms (e.g. transpiration from plant leaves) --> water vapour is carried by air currents into atmosphere --> cool air causes the vapour to condense and form clouds of liquid water droplets or ice --> when volume of water in clouds reaches a critical level it falls as precipitation --> most falls into the ocean, that which falls on land is pulled by gravity to the sea (e.g. surface run-off/streams/rivers/lakes) --> some soaks into the soil, percolating down until it reaches a zone of saturation --> ground water also move towards the ocean.
Most water taken up by plants from the soil returns to the atmosphere during transpiration.
Carbon cycle:
Carbon and oxygen cycles are interwoven. Photosynthesis involves atmospheric carbon dioxide which is converted into complex organic molecules – this process releases oxygen. During cellular respiration, the complex organic molecules are broken down to release carbon dioxide and water back into the atmosphere. A large amount of carbon resides within food chains and is also contained within dead organisms and excretory waste. Detrital organisms and decomposers are involved in releasing the carbon within dead organisms and waste back into the environment.
Additionally, over geological time, carbon is locked within a reservoir pool in the form of coal and oil, and in the wood of trees. As human exploit resources, carbon is returned to the cycling pool.
Nitrogen cycle:
Atmospheric nitrogen can’t be used directly by plants. As it is an essential component of amino acids, nitrogen limits the supply of food available in the food chain more than other plant nutrients. Nitrogen fixation is needed in order plants to utilise the nitrogen. Nitrogen fixation involves the conversion of atmospheric nitrogen into soluble nitrate and is carried out by chemosynthetic microorganisms. The nitrates are used by plants to form proteins.
Nitrifying bacteria are able to obtain energy by converting ammonia to nitrite. Other nitrifying bacteria convert nitrites to nitrates. Both of which can be absorbed and used by plants in the production of amino acids and proteins. These products then become available to other organisms within a food chain. Additionally, the production of nitrites and nitrates releases energy – which is ultimately used by bacteria to synthesise organic compounds.
The bacteria the removes nitrite from the soil are called denitrifying bacteria and tend to live in oxygen-depleted environments. Oxygen is liberated by reducing nitrate to nitrite, ammonia or nitrogen. Liberated oxygen can then be utilised in aerobic respiration, and the released energy can then be used in the synthesis of organic compounds. The nitrogen cycle is characterised by the conversion of gaseous nitrogen into nitrites and nitrates.
- define ecological niche in terms of feeding habitat, feeding relationships and interactions with other species
Niche: the role and position a species has in its environment; including its interactions with the biotic and abiotic factors within its environment. Additionally, it includes the species’ requirements – the physical conditions and resources it needs.
- understand the competitive exclusion principle
Two species cannot simultaneously occupy the same niche in the same place for very long. The niche of a species is an expression of its total environment and way of life. If two species occupy the same niche in the same habitat one is more likely to be competitively superior. Thus, the inferior competitor is eliminated. The species might move to separate habitat patches (spatial separation) of the same environment or may be more prevalent at varying times (temporal separation). These variations would allow both species to survive as they have different niches.
- define keystone species and understand the critical role they play in maintaining the structure of a community
A keystone species describes a species that has a disproportionately large effect on its environment relative to its abundance. The impacts a keystone species may have on a habitat include maintaining local biodiversity within a community (this can be achieved by controlling populations or providing critical resources).
Indications of a keystone species include:
- Ability to eat a variety of organisms
- Influence over other organisms is out of proportion to its biomass or abundance
- There are negative effects if the species is removed from an ecosystem