topic 4.1 species, communities and ecosystems

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

By Mariam Ohanyan Date: 1.22.2018

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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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01/22/18By Mariam Ohanyan Date: 1.22.2018

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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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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


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

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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topic 4.1 species, communities and ecosystems

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