Unit 3 in a Nutshell

[K.Smithy]

Hi all - just your friendly neighbourhood biology student passing through

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 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

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 Also, don't be shy to ask/answer any questions

Thread Index - Jump ahead to your relevant topic :)

Biodiversity
Biodiversity Practise Questions
Classification Processes
Functioning Ecosystems
Population Ecology
Changing Ecosystems

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



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" ): "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

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

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

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!

[K.Smithy]

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

[Bri MT]

Thanks for creating this thread! I'm sure it'll be a great help for many students in the future

One thing I do want to note is that the description of niches you have provided only considers fundamental niches which are defined by abiotic conditions. Ecological niches, like fundamental niches are constrained by abiotic conditions but ecological niches also consider interactions between organisms.

I would not describe co-operation as a type of symbiosis and please note that mutualism does not have to involve dependency for survival. Co-operation necessarily involves both organisms benefitting (as in mutualism) however symbiosis exclusively describes scenarios where the organisms are in intimate long-term association whereas co-operation does not necessarily have to be long term. Co-operation is not necessarily long-term. To distinguish between mutualism where there is survival-dependency and not, the terms you are looking for are obligate mutualism (the mutualistic relationship is necessary for survival) and facultative mutualism (the mutualistic relationship is not necessary for survival).

Also, if you were going to distinguish between types of symbiosis on the basis of survival you would also want to distinguish between parasites and parasitoids however I do not believe this is required for the QCE syllabus.

I am not sure why you have included mutualism as a form of predation. Mutualism can involve predation (generally of a 3rd party ) but I certainly wouldn't consider mutualism to be a subset of predation and I have been unable to find any ecological literature that describes mutualism as a type of predation.

I doubt amensalism will be focused on in QCE biology but it also hasn't been ruled out so no harm in including it but I wouldn't focus on it all that much.

In regards to population growth, in the syllabus the phrasing used is "logistic growth S curve" and thus I doubt you are expected to show fluctuation of population size around the carrying capacity.

percentage frequency of a species in a given area is just: (frequency of that species)/(sum frequency of all species) * 100



Overall really fantastic job and thank you again for creating this

[K.Smithy]

One thing I do want to note is that the description of niches you have provided only considers fundamental niches which are defined by abiotic conditions. Ecological niches, like fundamental niches are constrained by abiotic conditions but ecological niches also consider interactions between organisms.

Yeah, that one was my bad... I think got carried away thinking about all the abiotic aspects of ecosystems (in hindsight, I probably shouldn't have wrote the post in the weird order that I did ) - I will correct this error and ensure that I don't omit important information like this in future posts. Thanks for bringing it to my attention

I would not describe co-operation as a type of symbiosis and please note that mutualism does not have to involve dependency for survival. Co-operation necessarily involves both organisms benefitting (as in mutualism) however symbiosis exclusively describes scenarios where the organisms are in intimate long-term association whereas co-operation does not necessarily have to be long term. Co-operation is not necessarily long-term. To distinguish between mutualism where there is survival-dependency and not, the terms you are looking for are obligate mutualism (the mutualistic relationship is necessary for survival) and facultative mutualism (the mutualistic relationship is not necessary for survival).

Oh wow, I haven't even heard of obligate mutualism and facultative mutualism... you really do learn something new every day As for describing cooperation as a type of symbiosis, the five that I mentioned are what my textbook talks about and what my teacher has brought up in class - so that's why I included it. But the syllabus is very vague about a lot of things so I don't even know if we need to know all the different types of symbiosis. I'm interested to know if other QCE bio students have learnt about the different types of symbiosis and whether their textbooks consider cooperation as being a type of symbiosis too. Hopefully next year more QCE students will join the forums and offer some insight.

I'm trying to pinpoint where I may have said or suggested that mutualism involves dependency for survival. Would you be able to point me in the right direction so I can fix that up?

I am not sure why you have included mutualism as a form of predation. Mutualism can involve predation (generally of a 3rd party ) but I certainly wouldn't consider mutualism to be a subset of predation and I have been unable to find any ecological literature that describes mutualism as a type of predation.

Honestly, ngl I was hella confused last night when I read that mutualism was a form of predation. I never would have thought of considering it a type of predation but here are some links to resources that explain it:
https://biologydictionary.net/predation/
https://en.wikibooks.org/wiki/Ecology/Predation_and_Herbivory

I highly doubt, however, that QCAA will expect us to look at parasitism and mutualism as forms of predation and instead will focus on the whole predator eats prey idea. Would you suggest that I remove mutualism as a form of predation in my initial post?
 

I doubt amensalism will be focused on in QCE biology but it also hasn't been ruled out so no harm in including it but I wouldn't focus on it all that much.

Me too, but my teachers reckons that we might get a multiple choice question on the types of symbiosis. Something like "Which of the following is not a type of symbiosis" or something like that.

In regards to population growth, in the syllabus the phrasing used is "logistic growth S curve" and thus I doubt you are expected to show fluctuation of population size around the carrying capacity.

I originally wasn't going to include the sigmoidal/logistic curve in my post (mainly because we haven't covered K- and r-selection in class yet so we haven't looked at them), but I thought "why not?". Anywho, the textbook had a whole big scary section on the fluctuation of population size so I thought I would include it just to be safe (knowing my luck, if I don't include it and I don't study it, it's going to be on the exam )

percentage frequency of a species in a given area is just: (frequency of that species)/(sum frequency of all species) * 100

Awesome, thank you!

Overall really fantastic job and thank you again for creating this

Thank you for all the awesome feedback and for taking the time to read through it! You are a legend

[Bri MT]

Yeah, that one was my bad... I think got carried away thinking about all the abiotic aspects of ecosystems (in hindsight, I probably shouldn't have wrote the post in the weird order that I did ) - I will correct this error and ensure that I don't omit important information like this in future posts. Thanks for bringing it to my attention

No worries! Don't beat yourself up about leaving it out - there's so much you did remember to include and AN is a safe place to make and learn from errors like that

Oh wow, I haven't even heard of obligate mutualism and facultative mutualism... you really do learn something new every day As for describing cooperation as a type of symbiosis, the five that I mentioned are what my textbook talks about and what my teacher has brought up in class - so that's why I included it. But the syllabus is very vague about a lot of things so I don't even know if we need to know all the different types of symbiosis. I'm interested to know if other QCE bio students have learnt about the different types of symbiosis and whether their textbooks consider cooperation as being a type of symbiosis too. Hopefully next year more QCE students will join the forums and offer some insight.

I'm trying to pinpoint where I may have said or suggested that mutualism involves dependency for survival. Would you be able to point me in the right direction so I can fix that up?

The only reason I brought up facultative and obligate mutualism is because of this:

Symbiosis: There are 5 types of symbiosis:
1) Mutualism: both species benefit from the interaction (e.g. the relationship between an oxpecker (a kind of bird) and a rhino is mutualistic. The oxpecker eats ticks and parasites that live on a rhino's skin. The rhino free of pests and the oxpecker gets food).
2) Cooperation: 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)

To me, this read as though you were implying that the distinction between cooperation and mutualism is that in cooperation the presence of one is not essential for the survival of the other.

Honestly, ngl I was hella confused last night when I read that mutualism was a form of predation. I never would have thought of considering it a type of predation but here are some links to resources that explain it:
https://biologydictionary.net/predation/
https://en.wikibooks.org/wiki/Ecology/Predation_and_Herbivory

I highly doubt, however, that QCAA will expect us to look at parasitism and mutualism as forms of predation and instead will focus on the whole predator eats prey idea. Would you suggest that I remove mutualism as a form of predation in my initial post?

Those came up when I ran a search to see why they were being grouped as a type of predation but they don't provide links to scientific literature or other reputable authority so I remain unconvinced. I would write something along the lines of "mutualism can involve transfer of energy from one organism to another and therefore, in those cases, may be considered a form of predation under this definition".

Me too, but my teachers reckons that we might get a multiple choice question on the types of symbiosis. Something like "Which of the following is not a type of symbiosis" or something like that.

Better to be safe than sorry (especially since it actually is a type of symbiotic interaction ) 

I originally wasn't going to include the sigmoidal/logistic curve in my post (mainly because we haven't covered K- and r-selection in class yet so we haven't looked at them), but I thought "why not?". Anywho, the textbook had a whole big scary section on the fluctuation of population size so I thought I would include it just to be safe (knowing my luck, if I don't include it and I don't study it, it's going to be on the exam )

K and r selection are life history strategies and you definitely don't need to know them to understand logistic population growth

Textbooks always include more than you need to know so - even though I agree that it's better safe than sorry - it's good to look at some of this stuff as extra/extension/insurance rather than needed info

Awesome, thank you!

Thank you for all the awesome feedback and for taking the time to read through it! You are a legend

No worries at all! I love ecology and I love helping (especially teaching) others so it's a win-win   

[rcour16]

Hi would you be able to do this with the rest of the topics in units 3 and 4 as well. That would be great. Cheers

[K.Smithy]

Hi would you be able to do this with the rest of the topics in units 3 and 4 as well. That would be great. Cheers

Hi! I'm hoping to finish up the notes for Unit 3 within the next few weeks, and will start a Unit 4 thread ASAP

[Bri MT]

Hi! I'm hoping to finish up the notes for Unit 3 within the next few weeks, and will start a Unit 4 thread ASAP

You're a legend. I'm happy to take a look over at any additions if you'd like

[K.Smithy]

You're a legend. I'm happy to take a look over at any additions if you'd like

Would be awesome, if you have time of course

[K.Smithy]

Topic 1:  Part 2

Describing Biodiversity

Classification Process

- interpret cladograms to infer the evolutionary relatedness between groups of organisms

A phylogeny is a species' evolutionary history - thus, phylogenetic classification systems show the evolutionary history of species. Notably, it indicates the points at which different groups separate from a recent common ancestor. Cladistics is a form of phylogenetic analysis that groups taxa based on shared or derived characteristics (note: while Linnaean classification acknowledges evolutionary history, it focuses on homologous structures).
Cladistics has three basic assumptions:
- groups of organisms are related due to descent from a common ancestor
- there are bifurcating patterns (there is the potential for new types of organisms to arise if a population were to divide into two groups... this assumption does not take into consideration the possibility of interbreeding)
- changes in characteristics will occur in lineages over a specific length of time.

- analyse data from molecular sequences to infer species evolutionary relatedness

An organism's karyotype describes the arrangement of DNA into chromosomes present in the cell. Differences in chromosomes between species can be determined by the:
- position of the centromere
- banding on chromosomes
Stains can be used to observe banding on chromosomes. Patterns made are unique to certain chromosomes. Thus, the patterns can be analyse to compare species. The differences between karyotypes of species can be caused by chromosomal mutations. If organisms share similar proteins, similar nucleic acids will be produced - thus, there may be a common origin.

- recognise the need for multiple definitions of species

The concept of a species is the basic unit of biological classification. Generally, a species is defined as a group of organisms whose members are able to interbreed (in their natural environments) to produce viable and fertile offspring. Implying that organisms from different species cannot produce viable and fertile offspring (they are reproductively isolated).
This definition of a species, however, presents problems when classifying organisms who reproduce asexually, those that are not currently alive (e.g. trying to classify species of dinosaurs based on fossil records), and organisms (namely, some social insects) that have different castes of males, fertile females and infertile females.
Other examples of definitions of species include:
- the morphological species concept
- genotypic species concept
- ecological species concept
- evolutionary and phylogenetic species concept

- identify one example of an interspecific hybrid that does not produce fertile offspring (e.g. mule, Equus mulus)

- Mules and Hinneys --> cross between horse and donkey
- Zonkeys and Donkras --> cross between zebra and donkey
- Ligers and Tigions --> cross between lion and tiger

- understand that ecosystems are composed of varied habitats (microhabitat to ecoregion)

An ecosystem is a biological community of interacting organisms and their physical environment.
Scientists have classified terrestrial environments by dividing them into biomes (a large area defined by its climate and dominant plant species). Biomes are classified by community units (notably, vegetation types) that are found in specific climate regions. Some biomes display vertical stratification (the arrangement of vegetation into layers, providing a variety of niches).
Microhabitats describe small habitats that may be different from the large habitat surrounding it. Sub-communities can form within the microhabitats.
Another way to classify the terrestrial biosphere is through ecozones (large areas in which organisms evolve in relative isolation over long periods of time).  Ecozones are characterised by the evolutionary history of the organisms contained within them. Ecozones may contain multiple biomes. Each ecozone is geographically isolated. Ecozones can be further divided into ecoregions

- interpret data to classify and name an ecosystem

Holdridge Life Zone System
A system that classifies areas of land, encompassing the climate and ecological types. This system takes into account:
- annual precipitation
- mean annual bio-temperature
- potential evapotranspiration
- humidity levels
- latitudinal regions
- altitudinal belts
This system makes the assumption that soil and vegetation communities can be mapped if climactic factors are known. This system struggles to classify subpolar and polar regions (both of which have low temperatures and little available water --> meaning they have low potential evapotranspiration).

Specht's Classification System
Another method of classifying ecosystems is by analysing the structural features of the plants in the area. This system uses foliage cover of the tallest plants and the heights of the plants.

Australian National Aquatic Ecosystem (ANAE) Classification Framework
This is a semi-hierarchical system designed to classify different aquatic ecosystems. It is based on their region, landscape, climate, hydrology and topography. It provides context for the classification of water-based systems. It is intended to be flexible, while identifying and describing aquatic ecosystems in Australia.

European Nature Information System (EUNIS) Habitat Classification
EUNIS is a way of classifying all natural and artificial habitats. It identifies topography of land, characteristics of soil, climate and/or water quality, as well as the appearance of organisms. EUNIS is hierarchical, with Level 1 containing broad, general groups, and lower levels containing small, more specific groups.

- explain how the process of classifying ecosystems is an important step towards effective ecosystem management (consider old-growth forests, productive soils and coral reefs)

Classification allows scientists to communicate with clarity. By classifying ecosystems, there is a general understanding regarding factors such as soil type, climate, topography and vegetation. All of which impact the fauna present in the area. Classification, and ultimately communication, are vital for understanding, managing and protecting ecosystems.
An ecosystem encompasses the biotic and abiotic aspects of environments. Humans have a tendency to prefer ecosystems that are managed over wild ecosystems, as it ensures that the manipulation of components of the ecosystem can be utilised to achieve maximum benefit for ourselves. Ecosystem management promotes or prevents a specific goal - and the path taken to achieve this is dependent upon the classification of the ecosystem.
Productive Soils
- health of soil is linked to growth of plants (which, in turn, affects consumers)
- e.g. continuous growth of monocultures can have detrimental impacts on soil chemistry (including pH, and the presence of nitrogen and other nutrients).
- constant grazing can cause the soil to become compact - further restricting the growth of plants
- tillage can result in water loss or soil erosion
- soil management can improve the quality of soil and can be achieved through: using plants to anchor soil and prevent erosion, rotating monoculture crops with legume-based crops to increase nitrogen levels in the soil (as legumes contain nitrogen-fixing bacteria), and mulching the soil to reduce erosion and water loss

Coral Reefs
- coral reefs protect coastlines from the effects of waves and storms
- they provide essential nutrients, shelter and habitats for marine species
- coral bleaching, as a result of increased water temperatures, illustrates the need to manage these ecosystems
- reefs are formed from colonies of polyps. Each polyp extracts calcium from the water and deposits it as calcium carbonate exoskeleton. These exoskeletons then merge to form an individual, solid structure
- polyps form mutualistic relationships with zooxanthellae who live inside the tissue of coral, providing oxygen to the coral and removing their waste. In return, the coral provides shelter and nutrients
- increased water temperatures cause coral to reject zooxanthellae, causing bleaching
- increase CO₂ in atmosphere increases the amount that is dissolved into the sea water --> causing the formation of carbonic acid, which ends up reacting with the calcium carbonate that constitutes coral, as well as the shells of shellfish

Old Growth Forests
- significant ecosystems with high biodiversity
- many organisms are reliant on these forests - they provide a range of nesting hollows, microclimates and greater structural complexity

- describe the process of stratified sampling in terms of

- purpose (estimating population density, distribution, environmental gradients and profiles, zonation, stratification)

- site selection

- choice of ecological surveying technique (quadrants, transects)

- minimising bias (size and number of samples, random-number generators, counting criteria, calibrating equipment and noting associated precision)

- methods of data presentation and analysis



- recognise that biological classification can be hierarchical and based on different levels of similarity of physical features, methods of reproduction and molecular sequences

Classification describes the process by which things are arranged into groups on the basis of observed similarities. There are many different forms of classification, each of which is tailored for a specific need. Fauna can be grouped according to dietary habits (carnivory, herbivory, and omnivory) or by the manner in which food is obtained (chunk feeders, particle feeders, or fluid feeders). Plants, on the other hand, can be grouped according to the environmental conditions needed for their survival (mesophyte, xerophye, hydrophyte and halophyte).

Physical Features
- uses observable structural features
- these play a role in the Linnaean classification system

Molecular Sequences
- identification of genetic material and sequencing of DNA

Methods of Reproduction
- asexual reproduction vs sexual reproduction
- can also be classified on the basis of population growth (r- and k-selective species)

- describe the classification systems for
- similarity of physical features

Taxonomy is the process by which living things are classified on the basis of physical and biochemical characteristics. Carolus Linnaeus classified plants by comparing reproductive structures and classified animals based on physical features. Each category of the Linnaean system works its way down from a large general group (taxon) to a smaller group with more specific characteristics. The Linnaean system includes: domain, kingdom, phylum, class, order, family, genus and species. The order can be remembered through the mnemonic "Do Keep Ponds Clean Or Frogs Get Sick"

- methods of reproduction

Sexual Reproduction
- DNA is present in chromosomes in linear pairs (diploid) and arise through sexual reproduction
- one chromosomes of each pair is gain from the male parent (via sperm) and the other is gain from the female parent (via the ovum)
- when the gametes are combined (fertilisation) a zygote is formed
- the zygote develops into an individual through repeated cell division and differentiation

r-Strategists
- some species produce large numbers of offspring with little parental investment
- usually live in unstable environments (i.e. predation may be high)
- organisms are generally small, mature rapidly and are short-lived

K-Strategists
- live in more stable environments
- population density is as high as carrying capacity will allow
- population is affected by density
- long life-expectancy, produce few offspring, and invest extensive parental care
- have ability to compete for limited resources

- molecular sequences (molecular phylogeny - also called cladistics)

- phylogenetic classification that shows evolutionary history
- shows bifurcation points
-  cladistics uses shared or derived characteristics as the only criteria for grouping taxa
- there are three assumptions

Chromosomal and DNA Analysis
- staining to look at banding
- each chromosome will have a specific banding pattern, thus chromosomes can be compared to determine relatedness of organisms

- define the term clade

A clade is a group of organisms that is believed to comprise a common ancestor and all of its evolutionary descendants

- recall that the common assumptions of cladistics include a common ancestry, bifurcation and physical change

1. Any group of organisms are related by descent from a common ancestor
2. There are bifurcating patterns in cladogenesis
3. Changes in characteristics occurs in lineages over time

[K.Smithy]

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

[K.Smithy]

Topic 2: Part 2

Ecosystem Dynamics

Population Ecology
Important Formula

Lincoln Index
N = (M*n)/m

Where:
M = number of individuals caught, marked and released initially
n = number of individuals caught on second sampling
m = number of individuals recaptured that we marked


- define the term carrying capacity

Carrying capacity: total population that is able to be supported by an environment – that is, the number of organisms within a population that can be supported indefinitely on the resources available in the ecosystems

- explain why the carrying capacity of a population is determined by limiting factors (biotic and abiotic)

Density-Independent Factors
Birth rates and death rates may vary regardless of population density. Population density is independent of population size. A small population may be spread over a large area and have a low density. Alternatively, the population may be limited to a small area, causing organisms to crowd together in a high-density environment. Both of these scenarios present their own challenges to the survival of an organism. Factors that affect populations regardless of density are density-independent factors.

Density-Dependent Factors
As a population grows it may deplete its food supply, leading to increased competition for food among members. Factors that affect population growth as density increases are termed density-dependent factors. Limiting factors are factors that restrict the size of a population. Examples include:
-   competition: competitive exclusion principle states that two species cannot simultaneously occupy the same niche in the same place for long. If two species occupy the same niche one is more likely to be competitively superior.
-   predation: the removal of predation pressure allows the populations to return to the norm for environmental conditions. In natural situations predation may alter the age structure of the population because young, diseased or aged members are more easily captured.
-   infection: high-density populations are vulnerable to the spread of infection. Crowded conditions can result in simple infections being easily spread through contact, food supply or water.

If a population does not have any limiting factors, then the population will start to increase. The factors that would normally inhibit population growth will be non-existent, and death rate will be low. The species will realise its full reproductive biotic potential. If this continued indefinitely, the population would rise without limit.
Each environment has a carrying capacity for a population. Environmental resistance is the sum total of all environmental limiting factors – preventing populations from getting too high. There are two possible outcomes for unrestricted growth.
1.   Rapid population growth may continue until they are above carrying capacity, a climatic factor reduces population, or most migrate. This results in a J-shaped curve. These growth patterns are characteristics of opportunistic species.
2.   The increasing density of the population smoothly slows down the rate of growth as environmental resistance increases. The carrying capacity is reached. The result is an S-shaped curve.

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

For a given species in an environmental situation there will be a certain optimum population that the environment can support. This is the equilibrium – the point at which a system can be maintained. If the population rises above this point, competition, predation or disease will result in a decline in population. If it falls below the equilibrium, environmental resistance will temporarily be relieved, and the population will rise. This results in ecological homeostasis – the fluctuation of the population around the equilibrium. Changes in population size results in negative feedback, which keeps the population at the carrying capacity. Occasionally, environmental conditions can change. As a result, the carrying capacity changes to reflect the environmental conditions.

[K.Smithy]

Topic 2: Part 3

Ecosystem Dynamics

Changing Ecosystems

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

Ecological succession describes the gradual evolution of an ecosystem. Many environments start with bare soil before being colonised. Eventually, grasses will come along, which will then be replaced by a succession of larger plants/trees, until a stable climax community is achieved. Each stage is termed a sere.

Primary Succession
The development and change in plant communities over time, leading from bare ground to climax community. Colonisation is initiated by the dispersal of spores or seeds of hardy autotrophs (pioneer species). These autotrophs must withstand conditions such as:
-   High light intensity
-   Low water holding capacity of soil

Secondary Succession
The ‘second time’ an area is being colonised. Secondary succession may occur when the dominant species of a plant community is removed, and the area is left to natural interactions. Secondary succession is faster than primary succession as there is already existing soil and plants and animals are present in the area already.

- differentiate between two main modes of succession: primary and secondary

Primary succession is the development and change in plant communities over time, leading from bare ground to climax community. Colonisation is initiated by the dispersal of spores or seeds of autotrophs. These autotrophs need to have one or more of the following features:
-   Tolerant to extreme conditions
-   Able to photosynthesise
-   Rapid spore or seed germination
-   Use wind pollination and/or seed/spore dispersal
-   Ability to fix nitrogen from the air
-   Opportunists (r-strategists)

Lichens (mutualistic relationship between fungi and algae) are often pioneer species. A product of their metabolism is an acid that causes rock erosion. Temperature differences cause the expansion and contraction of rocks – this results in cracks and fragmentation. As lichens die, decomposing bacteria break down small amounts of organic matter, leading to the formation of soil. This gradual build-up of soil makes these places unsuitable for rock-dwelling lichens, but suitable for the colonisation of mosses. Further soil enrichment is provided by the decomposition of mosses. Over time, more complex plant life will be able to grow. Each successive change is characterised by vegetation types that are better able to compete for resources than their predecessors.
Changes in vegetation result in changes in animal life. Over time, the bare rock becomes covered in deep soil – this enables the ecosystem to support growing biodiversity and increases total biomass.
Each stage of succession changes the abiotic and biotic conditions of the environment, paving the way for another species to colonise the area. Eventually, a relatively stable, complex community will be reached (this community has reached an ecological equilibrium).
Primary succession starts with bare rock and is the first attempt to colonise an area. Secondary succession is the second time the area is colonised. When the dominant species is removed and the area is left to natural interactions, secondary succession will occur.

A disclimax community is the final community formed after succession and is the result of degrading environmental factors. These factors cause a disruption in the water cycle and the area becomes more arid.

- identify the features of pioneer species (ability to fixate nitrogen, tolerance to extreme conditions, rapid germination of seeds, ability to photosynthesise) that make them effective colonisers

Pioneer species are autotrophs who are tolerant of extreme conditions, can photosynthesise, have rapid spore or seed germination, use wind pollination and/or dispersal of spores or seeds, ability to fix nitrogen from the air, and are r-strategists.

- analyse data from the fossil record to observe past ecosystems and changes in biotic and abiotic components

Since ecosystems are dynamic entities, it is reasonable to assume that there have been dramatic changes in them over Earth’s long history. Earth has experienced periods of cooling and warming. Additionally, it has be subjected to large meteor damage and volcanic activity – ultimately resulting in mass extinctions. The length and severity of climate change events can be determined by the levels of carbon dioxide in the polar ice caps. Atmospheric carbon dioxide is trapped in snow. Each season a layer of ice is formed from the snowfall. By taking core samples of ice, scientists can determine:
-   The age of each layer
-   The depth of each layer (thus the duration of the cold period)
-   Carbon dioxide present in each layer (higher temperatures result in more carbon dioxide in the atmosphere)
Similar techniques can be used to examine deep-sea sediments. Two different forms of oxygen isotopes exist: 16O and 18O. 18O has two more neutrons than 16O and so is slightly heavier. The analysis of the ratio between the two isotopes in deep-sea sediments gives an indication of climate variations. Higher 18O levels can be associated with cooler temperatures – this is because 16O is lighter and evaporates more easily, particularly during cold climactic phases.
These changes in climate can affect different species of organisms that are able to grow and reproduce. The fossilised remains of organisms that were present during that period can provide more evidence regarding the components of ecosystems. This is due to the fact that all organisms depend on each other (whether that be directly or indirectly). Thus, the presence of particular fossils provides good evidence of the presence of other organisms.
Unfortunately, fossil records are incomplete since fossil formation requires particular conditions which may not be uniform in any environment. Fossils are most commonly in areas where their remains are protected from consumption or decomposition.
Pollen grains and spores are resistant to decay and are produced in large quantities. Pollen walls are composed of a strong, stable chemical. Since they are dispersed easily, they may be distributed widely from their source. Pollen can accumulate on undisturbed surfaces and can be found in sediments (in peat bogs, lake beds, alluvial deposits, ocean floors) and in ice cores. The amount of pollen, however, may not be indicative of relative abundance since species may produce differing amounts of pollen, or pollen may have different dispersion rates. Pollen grains, do however, have their own unique sizes and shapes. Thus, allowing scientists to determine from core samples the exact species present.
Fossilised plant remains can indicate the degradation of forests due to cataclysmic events (i.e. climate change). Fossils also indicate mass movements of tectonic plates.

- predict the impact of human activity on the reduction of biodiversity and the magnitude, duration and speed of ecosystem change

Humans as Consumers
- humans are dependent upon the same sorts of resources as other consumers (water, food, shelter…)
- humans were originally hunter-gatherers, but since they were nomadic and their populations were small, they had little impact on the environment
- humans impacted the environment through the utilisation of fire – fire was used for cooking and flushing out prey… They may also be used to deliberately to maintain open grasslands (these supported herds of grazing animals)
- the hunting mode was succeeded, in many parts of the world, by the domestication of animals
- forests were cleared to increase the land available for pastures for flocs (in some areas this even led to overgrazing – ultimately decreasing soil fertility and increasing erosion)

Effects of Land Clearing
- huge tracts of land can be cleared quickly using modern machinery
- land clearing has catastrophic effects on biodiversity
- the reduction in tree species, results in a reduction in the availability of food and nesting sites
- animals that are unable to relocate will perish

Habitat Fragmentation
- due to the contours of the land, some areas are more suitable for development
- patches of clearing can occur in habitat fragmentation, resulting in some areas being more inaccessible to organisms or causing them to be less fertile
- habitat fragmentation describes the diversion of a habitat into smaller, isolated portions as a result of human activities in the intervening spaces
- habitat fragmentation alters the distribution and abundance of species
- the shape and size of the remaining fragments of vegetation are important when it comes to determining what species can survive in the area
- it is important that appropriate ‘corridors’ are left, to allow for the movement of native fauna and maintain biodiversity

Land Degradation
- clearing land can bring about changes to ecosystems
- reduced vegetation = less organic matter being returned to the soil --> causing nutrient depletion
- the rain causes soil compaction --> reducing ability to absorb water --> this increases surface run-off, resulting in erosion
- water- or wind-eroded topsoil can contaminate marine ecosystems
- lack of vegetation can result in less water being absorbed by plant roots
- this will cause an increase in the height of the water table and can increase the concentration of salt at the water surface and further degrade the soil

Land Pollution
- occurs through land clearing from the extraction of raw materials, the disposal of wastes and from agriculture
- a great bulk of waste is placed on unused land. This results in air pollution and water pollution
- as landfill begins to compact and decompose, methane gas is generated
- this gas contributes to enhanced global warming

Effects of Fertilisers
- fertilisers can be used to overcome the deficiencies of nitrates, phosphates and trace elements necessary for plant and/or animal growth in soil
- fertilisers can be washed by rain into dams, lakes and streams, increasing the concentration of ions in the water
- eutrophication is a natural process in which nutrients, such as nitrates and phosphates, build up in water
- these nutrients are taken up by plants and passed through the community – excessive use of fertilisers can cause rapid population growth in water-based producers
- photosynthesis produces oxygen for cellular respiration to occur at night. At night, there is no sunlight, thus no oxygen production
- thus, water can become deficient of oxygen --> contributing to an increased population of decomposers, this creates further biological oxygen demand (BOD – measure of the quantity of oxygen used by organisms in the oxidation of organic matter in aquatic environments; BOD> = >oxygen available)
- the natural balance in the freshwater ecosystems becomes disrupted and may result in the ‘death’ of that body

Building Damns
- damming of rivers has been used to control flooding
- this causes long-term environmental effects, including erosion, decreased biodiversity, changes in water temperature, and increased soil salinity.

Introduced Species and Pests
- European colonists brought with them a variety of plants and animals
- these species are called exotics, many of these species have major impacts on the terrain (e.g. the environment can become unsuitable for other organisms)
- exotic species may directly impact endemic species through predation and/or competition for resources
- pests (organisms that cause direct or indirect harm to humans or their resources) may be animals or plants
- many pests compete for water, light and mineral nutrients with natural communities… some release powerful chemicals from their roots, which can inhibit plant growth

Pesticide Control
- pesticides can cause widespread pollution
- they seep into rivers and kill organisms, as well as contaminating groundwater, drinking water and food
- many pesticides mimic the female hormone oestrogen resulting in the feminisation of various species of amphibians, birds and mammals (resulting in lower reproduction rates and the possible extinction of species)
- several indices are used to measure the effects of pesticides: biodegradability, biological magnification, half-life and persistence.

Air Pollution
- various types of air pollution
- primary pollutant: a substance that has a direct adverse effect. Present in its original form and has a direct effect on the atmosphere (e.g. smoke, dust and oxides of sulphur and nitrogen)
- secondary pollutant: a pollutant that is formed as a result of interactions between waste and the environment (e.g. acid rain and smog).

Photochemical Smog and Temperature Inversions
- photochemical smog is a secondary pollutant that is produced as a result of the chemical reaction between nitrogen oxides and hydrocarbons in the presence of sunlight
- its formation depends on the concentration of primary pollutants in the atmosphere and weather conditions (forming when air is calm and at suitable level of UV light and when there is temperature inversion).
- temperature inversion is characterised by the trapping of a cool layer of air in the atmosphere under a warm layer. This prevents the dispersal of heat and other pollutants
- when a temperature inversion occurs, pollution particles remain trapped in the layers of air closest to the ground

Urban Microclimates
- a microclimate is a climate of a very small or restricted area, especially when this differs from the climate of the surrounding area
- microclimates may vary as a result of the built environment
- concrete city surfaces absorb more heat, thus making the city and urban areas warmer
- in central city areas, tall builds are usually separated by narrow roads – creating wind tunnels which further spread heat
- these microclimates can cause plants to bud and bloom earlier, and also attract some birds to the warmer areas

Natural, Agricultural and Urban Ecosystems
- humans manipulate the environment by growing harvests, rearing animals, manufacturing clothes, constructing houses and other structures, lighting fires and producing energy that can be utilised
- these activities release polluting chemicals which may affect water, soil and climate
- additionally, they add pressure on the environment and ultimately decrease biodiversity (potentially resulting in disclimax succession)
- thus, the biosphere has to support three ecosystems – natural, agricultural and urban
- ecosystems require the cycling of matter and energy to be sustains

[s110820]

Hey everyone!

I just wanted to add to K.Smithy's amazing thread! I have a few analogies that really helped me learn the content  used for Unit 3 and 4, in the weeks leading up to my external exam:

For the different types of evolution, I would recommend using the analogy of a flowing river. For divergent evolution, the river flows in different directions. However, for convergent evolution, the river may flow in different directions at first but may connect to each other during successive generations. Hence, when thinking of divergent = think DIFFERENT vs thinking of convergent = think CONNECT.

Also, for the "Bottleneck Effect" I would recommend using the analogy of baking a cake. When you put flour in a sifter (change in population due to immigration, emmigration, death or other factors), you get less flour than what you started (original population) with. Hence, you can make the cake but it may not taste the same (genetic variation/diversity) due to how the amount of flour (population) was used in the recipe.

Hopefully, that helps

If anyone can help me improve my second analogy (the one about baking) - I would really appreciate it as while it worked for me, it may not make sense to everyone.

Anyway, have a great week and kind regards,

Darcy Dillon

[K.Smithy]

Hey everyone!

I just wanted to add to K.Smithy's amazing thread! I have a few analogies that really helped me learn the content  used for Unit 3 and 4, in the weeks leading up to my external exam:

For the different types of evolution, I would recommend using the analogy of a flowing river. For divergent evolution, the river flows in different directions. However, for convergent evolution, the river may flow in different directions at first but may connect to each other during successive generations. Hence, when thinking of divergent = think DIFFERENT vs thinking of convergent = think CONNECT.

Also, for the "Bottleneck Effect" I would recommend using the analogy of baking a cake. When you put flour in a sifter (change in population due to immigration, emmigration, death or other factors), you get less flour than what you started (original population) with. Hence, you can make the cake but it may not taste the same (genetic variation/diversity) due to how the amount of flour (population) was used in the recipe.

Hopefully, that helps

If anyone can help me improve my second analogy (the one about baking) - I would really appreciate it as while it worked for me, it may not make sense to everyone.

Anyway, have a great week and kind regards,

Darcy Dillon

Love these analogies! Thanks for the contribution
You're memorisation techniques are definitely much more creative than mine! My friend had quite a funny one (well, we thought so anyway) of remembering allopatric speciation. We picture Patrick Star standing really far away, while we call out "Hallo Patrick!". It just reminds us that there is geographic isolation. Idk, it is kind of stupid, but we remember it