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Topic 4.1 EcologyIB DP – CORE
Understandings: Species are groups of organisms that can potentially interbreed
to produce fertile offspring.
Members of a species may be reproductively isolated in separate populations.
A community is formed by populations of different species living together and interacting with each other
A community forms an ecosystem by its interactions with the abiotic environment
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Species have either an autotrophic or heterotrophic method of nutrition (a few species have both methods)
Autotrophs obtain inorganic nutrients from the abiotic environment
Consumers are heterotrophs that feed on living organisms by ingestion
Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion
Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion
The supply of inorganic nutrients is maintained by nutrient cycling
Ecosystems have the potential to be sustainable over long periods of time
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Species and Population
A species is a group of organisms that can potentially interbreed to produce fertile, viable offspring.
Members of a single species are unable to produce fertile, viable offspring with members from a different species.
When two different species do produce offspring by cross-breeding, these hybrids are reproductively sterile (e.g. liger, mule)
A population is a group of organisms of the same species that are living in the same area at the same time
Organisms that live in different regions (i.e. different populations) are reproductively isolated and unlikely to interbreed, however are classified as the same species if interbreeding is functionally possible
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Community, Habitat, Ecosystem, Ecology
Community:A group of populations living together and interacting with each other within a given area
Habitat:The environment in which a species normally lives, or the location of a living organism
Ecosystem:A community and its abiotic environment (i.e. habitat)
Ecology:The study of the relationship between living organisms, or between living organisms and their environment
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Environment
It has 4 main components
Hydrosphere (water)
Atmosphere (gases)
Lithosphere (rocks)
Biosphere (all living beings) The first 3 are abiotic components while the 4th is the Biotic
component
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Assessment Statement
Distinguish between autotroph and heterotroph.
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Autotrophs & heterotrophs
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Living organisms obtain chemical energy in one of two ways:
Autotrophs•Synthesises its own organic molecules from simple inorganic substances (e.g. CO2, nitrates)•Energy for this process is derived from sunlight (photosynthesis) or via the oxidation of inorganic molecules (chemosynthesis)•Because autotrophs synthesise their own organic molecules they are commonly referred to as producers
Heterotrophs•Obtains organic molecules from other organisms (either living / recently killed or their non-living remains and detritus)•Because heterotrophs cannot produce their own organic molecules and obtain it from other sources, they are called consumers
Mixotrophs•Certain unicellular organisms may on occasion use both forms of nutrition, depending on resource availability•Euglena gracilis possess chlorophyll for photosynthesis (autotrophic) but may also feed on detritus (heterotrophic) 01/22/18
Heterotrophs
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Consumers ingest organic molecules from living or recently killed organisms
Detritivores ingest organic molecules found in the non-living remnants of organisms (e.g. detritus, humus)
Saprotrophs release digestive enzymes and then absorb the external products of digestion (decomposers)
Detrivores & saprotrophs• Detrivores are the organism that consumes dead organic
matter.
• Ex.: earthworm, woodlice.
• Saprotrophs are the organisms that live on, or in, dead organic matter. (digesting the food by secreting enzymes)
• Ex. Bacteria, Fungus.
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Autotrophs
Most autotrophs derive the energy for this process from sunlight (via photosynthesis)
Some may derive the needed energy from the oxidation of inorganic chemicals (chemosynthesis)
Autotrophs obtain the simple inorganic substances required for this process from the abiotic environment
These nutrients – including carbon, nitrogen, hydrogen, oxygen and phosphorus – are obtained from the air, water and soil.
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Vocabulary Practice
Autotroph:
Heterotroph:
Consumer:
Detritivore:
Saprotroph:
Species.
Habitat.
Population.
Community
Ecosystem:
Ecology:
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Assessment Statement State that saprotrophic bacteria and fungi (decomposers)
recycle nutrients.
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01/22/18By Mariam Ohanyan Date: 1.22.2018
15 Nutrient Cycling
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•Autotrophs obtain inorganic nutrients from the air, water and soil and convert them into organic compounds
•Heterotrophs ingest these organic compounds and use them for growth and respiration, releasing inorganic byproducts
•When organisms die, saprotrophs decompose the remains and free inorganic materials into the soil
•The return of inorganic nutrients to the soil ensures the continual supply of raw materials for the autotrophs
Assessment Statement
Explain that energy can enter and leave an ecosystem, but that nutrients must be recycled.
Energy enters as light and usually leaves as heat.
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18Energy cycling
Nutrient Cycle
Nutrient Cycle vs. Food ChainNutrient Cycle vs. Food Chain
Food Chain
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The Carbon Nutrient Cycle
CO2 in Atmosphere
Photosynthesis
feeding
feeding
Respiration
Deposition
Carbonate Rocks
Deposition
Decomposition
Fossil fuel
Volcanic activity
Uplift
Erosion
Respiration
Human activity
CO2 in Ocean
Photosynthesis
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Positive and negative association
If two species are typically found within the same habitat, they show a positive association
Species that show a positive association include those that exhibit predator-prey or symbiotic relationships
If two species tend not to occur within the same habitat, they show a negative association
Species will typically show a negative association if there is competition for the same resources
One species may utilise the resources more efficiently, precluding survival of the other species (competitive exclusion)
Both species may alter their use of the environment to avoid direct competition (resource partitioning)
If two species do not interact, there will be no association between them and their distribution will be independent of one another
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IB Assessment Statement
Distinguish between organic and inorganic nutrients.
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Organic and inorganic compounds
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Essential Elements of Life
• About 25 of the 92 elements are essential to life
• Carbon, hydrogen, oxygen, and nitrogen make up 99% of living matter
• Most of the remaining 1% consists of calcium, phosphorus, potassium, iron and sulfur
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Sustainability of Ecosystem
Something is Sustainable - if something that can continue indefinitely
There are three requirements for sustainability
1. Nutrient availability
2. Detoxification of waste products
3. energy availability
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Mesocosms – Lab/ practical 5
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Mesocosms are enclosed environments that allow a small part of a natural environment to be observed under controlled conditions
A terrarium is a small transparent container (e.g. glass or plastic) in which selected plants (or animals) are kept and observed
Making a Self-Sustaining Terrarium
A terrarium can be created using a glass or plastic bottle with a lid, according to the following steps:
Building a verdant foundation
Add a bottom layer of pebbles, gravel or sand – this layer exists for drainage (smaller vessels require thinner rock layers)
Add a second thin layer of activated charcoal – this will prevent mold and help to aerate the soil
Spread a thin cover of sphagnum moss (or use an organic coffee filter) to create a barrier between the lower layers and soil
The final layer is the pre-moistened growing medium (i.e. potting mix)
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Selecting the right plants
Ideally, choose plants that are both slow growing and thrive in a bit of humidity (e.g. most ferns, club moss, etc.)
Inspect the plant thoroughly for any signs of disease or insects before introducing to the terrarium
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Terrariums
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Maintaining appropriate conditions
Ensure the terrarium is placed in a location that provides a continuous source of light
Locate the terrarium in a place that does not experience fluctuating temperature conditions (i.e. avoid direct sunlight)
Do not initially over-water the plants – once the right humidity is established, a terrarium can go months without watering
Occasional pruning may be required – however, as level of soil nutrients decrease, plant growth should slow down
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Quadrat Sampling A quadrat is a rectangular frame of known dimensions
that can be used to establish population densities Quadrats are placed inside a defined area in either a random arrangement or according to a design (e.g. belted transect)
The number of individuals of a given species is either counted or estimated via percentage coverage
The sampling process is repeated many times in order to gain a representative data set
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Chi-Square Test
A chi-squared test can be applied to data generated from quadrat sampling to determine if there is a statistically significant association between the distribution of two species
A chi-squared test can be completed by following five simple steps:
Identify hypotheses (null versus alternative)
Construct a table of frequencies (observed versus expected)
Apply the chi-squared formula
Determine the degree of freedom (df)
Identify the p value (should be <0.05)
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Example of Chi-Squared Test Application
The presence or absence of two species of scallop was recorded in fifty quadrats (1m2) on a rocky sea shore. The following distribution pattern was observed:•6 quadrats = both species ; •15 quadrats = king scallop only ;•20 quadrats = queen scallop only ; •9 quadrats = neither species
Step 1: Identify hypotheses
A chi-squared test seeks to distinguish between two distinct possibilities and hence requires two contrasting hypotheses:
Null hypothesis (H0): There is no significant difference between the distribution of two species (i.e. distribution is random)
Alternative hypothesis (H1): There is a significant difference between the distribution of species (i.e. species are associated)
Step 2: Construct a table of frequencies
A table must be constructed that identifies expected distribution frequencies for each species (for comparison against observed)
Expected frequencies are calculated according to the following formula:
Expected frequency = (Row total × Column total) ÷ Grand total
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Expected frequencies are calculated according to the following formula: Expected frequency = (Row total × Column total) ÷ Grand total
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36The formula used to calculate a statistical value for the chi-squared test is as follows
These calculations can be broken down for each part of the distribution pattern to make the final summation easier
Where: ∑ = Sum ; O = Observed frequency ; E = Expected frequency
These calculations can be broken down for each part of the distribution pattern to make the final summation easier
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Based on these results the statistical value calculated by the chi-squared test is as follows:
�2 = (2.20 + 2.38 + 1.59 + 1.73) = 7.90
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Step 4: Determine the degree of freedom (df)
In order to determine if the chi-squared value is statistically significant a degree of freedom must first be identified
The degree of freedom is a mathematical restriction that designates what range of values fall within each significance level
Step 5: Identify the p value
The final step is to apply the value generated to a chi-squared distribution table to determine if results are statistically significant
A value is considered significant if there is less than a 5% probability (p < 0.05) the results are attributable to chance
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The degree of freedom is calculated from the table of frequencies according to the following formula:df = (m – 1) (n – 1) Where: m = number of rows ; n = number of columnsWhen the distribution patterns for two species are being compared, the degree of freedom should always be 1
When df = 1, a value of greater than 3.841 is required for results to be considered statistically significant (p < 0.05)
A value of 7.90 lies above a p value of 0.01, meaning there is less than a 1% probability results are caused by chance
Hence, the difference between observed and expected frequencies are statistically significant.
As the results are statistically significant, the null hypothesis is rejected and the alternate hypothesis accepted:
Alternate hypothesis (H1): There is a significant difference between observed and expected frequencies
Because the two species do not tend to be present in the same area, we can infer there is a negative association between them
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Practice Question Two species of fir tree are found along the coast of Southern
California. These two tree species are the Grand Fir (Abies grandis) and the Noble Fir (Abies procera). Their distribution patterns were establsihed via 150 quadrat samples, yielding the following results: 25 = both present ; 30 = Noble Fir only ; 45 = Grand Fir only ; 50 neither present Activity: Use the chi-squared test to determine if these two plant species show association.
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