4.1 Species, Communities and Ecosystems Flashcards
Species
A group of organisms that can potentially interbreed to produce fertile offspring
Each species is a recognisable type of organisms with characters that distinguish it from even the most closely related species because of the reproductive separation between species
Method to ensure species produce with other members of their species
Courtship ritual - show females that they are fit and that they are the same species
Interbreeding
When two members of the same species mate and produce fertile offspring
Cross-breeding
When two members of a different species breed together
Occasionally occurs
Cross-breeding between species are almost always infertile. This prevents genes of two species from becoming mixed.
Population
A group of organisms of the same species who live in the area at the same time
Populations in different areas
Members of the same species may be reproductively isolated in separate populations.
If two populations live in the same area, they are unlikely to interbreed with each other but this does not mean they are a different species because they potentially could interbreed.
Populations in different areas with different characters
If two populations of a species never interbreed they may gradually develop differences in their characters but they are still considered to be the same species until they can not interbreed and produce fertile offspring.
In practice, it is very difficult to decide whether two populations have reached this point as biologists sometimes disagree whether populations are the same of different species.
Method of nutrition
All organisms need a supply of nutrients (e.g. glucose, amino acids) as it is needed for growth and reproduction
Species have either an autotrophic or heterotrophic method of nutrition and only a few species have both methods
Autotrophic
Self feeding
Some organisms make their own carbon compounds from carbon dioxide and other simple substances
Heterotrophic
Feeding on others
Some organisms obtain their compounds from other organisms
Mixotrophic
Some organisms use both methods of nutrition
e. g. unicellular organisms (Euglena gracilis)
- has chloroplasts that carries out photosynthesis when there is sufficient light
- can also feed on detritus or smaller organisms by endocytosis
Consumers
Consumers are heterotrophs that feed on living organisms by ingestion
Relationship between heterotrophs and consumers
Heterotrophs are divided into groups by ecologists according to the source of organic molecules they use and the method of taking them in (one group of heterotrophs = consumers)
Consumers feed off other organisms
Consumers feed off other organisms that are either still alive or have been dead for a relatively short time
e.g. mosquito - still alive
sucks blood from larger organisms
e.g. lion - recently dead
kills a gazelle and feeds off it
Consumers ingest their food
Consumers take undigested material from other organisms and digest it and absorb the products of digestion
unicellular organisms - e.g. paramecium
take in food by endocytosis and digest it inside vacuoles
multicellular organisms - e.g. lion
take food into digestive system by swallowing it
Consumers and trophic groups
Consumers are sometimes divided up into trophic groups according to organisms they consume
Primary consumers feed on autotrophs, secondary consumers feed on primary consumers, etc.
In practice - most consumers do not fit neatly into any one of these groups because their diet includes material from a variety of trophic groups
Detritivores
Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion
Organic matter discarded by organisms
Organisms discard large quantities of organic matter
- e.g. dead leaves + other parts of plants - feathers and other dead parts of animal bodies - feces from animals
Dead organic matter rarely accumulates in ecosystems
- instead used as a source of nutrition by 2 groups of heterotrophs: detritivores and saprotrophs
Ways detritivores digest dead organic matter
- Detritivores ingest dead organic matter and digest it internally and absorb the products of digestion
- Unicellular organisms - ingest it into food vacuoles
- e.g. the larvae of dung beetles feed by ingestion of fees (rolled into a ball by their parents)
- Multicellular organisms - ingest dead matter into their gut
- e.g. earthworms
Saprotrophs
Saprotrophs are heterotrophs that obtain organic nutrients from dead organic matter by external digestion.
Saprotrophs = Decomposers
Saprotrophs secrete digestive enzymes into the dead organic matter and digest it externally then absorb the products of digestion
Many types of bacteria and fungi are saprotrophic
Also known as decomposers bc they break down carbon compounds in dead organic matter & release elements such as nitrogen into the ecosystem so they can be used again by other organisms
Modes of nutrition - Either ingests organic matter by endocytosis (no cell walls) or by taking it into its gut
Either consumer or detritivore
Modes of nutrition - Cell walls present. No ingestion of organic matter. No gut.
Either producer or saprotroph
Modes of nutrition - Feeds on living or recently killed organisms
Consumer
Modes of nutrition - Feeds on dead organic matter
Detritivore
Modes of nutrition - Secretes enzymes into its environment to digest dead organic matter
Saprotrophs
Modes of nutrition - Enzymes not secreted. Only requires simple ions and compounds such as CO2.
Autotrophs
Modes of nutrition - Cell walls present. No ingestion of organic matter. No gut.
Saprotrophs or autotrophs
Communities
A community is formed by populations of different species living together and interacting with each other.
Importance of communities
Important part of ecology - research into relationships between organisms
- Relationships are complex and varied
- Some cases - interaction between 2 species is of benefit to one species and harms the other
- e.g. parasite and host
- Other cases - both species benefit
- e.g. hummingbird feeds on nectar from a flower and helps the plant by pollinating it
- All species are dependent on relationships with other species for their long term survival
- reason why a population of one species can never live in isolation ⇒ groups of populations live together
- Typical communities consist of hundreds or even thousands of species in an area
Chi-squared test
Testing used for finding associations between 2 species/variables
Quadrat & quadrat sampling
Square sample areas usually marked out using a quadrant frame
Quadrat sampling involves repeatedly placing a quadrant frame at random positions in a habitat and recording the number of organisms present each time
Usual procedure for randomly positioning quadrats
- Baseline is marked out along the edge of a habitat using tape
- must extend all the way along the edge of the habitat
- Random # is obtained using either a table or a random # generator on a calc.
- First random # - used to determine a distance along the measuring tape
- all distances along the tape must be equally likely
- Second random # - used to determine a distance out across the habitat at right angles to the tape
- all distances along the tape must be equally likely
- The quadrat is is placed precisely at the distances determined by the two random #s
Quadrat sampling method
- If this procedure is followed correctly w/ a large enough # of replicates, reliable estimates of population sizes are obtained
- Method is only suitable for plants + other organisms that are not motile
- quadrat sampling is not suitable for populations of most animals
Quadrat sampling and chi-squared test
- If the presence or absence of more than one species is recorded in every quadrat using sampling of a habitat, is it possible to test for an association between species
- Populations are often unevenly distributed bc some parts of the habitat are more suitable for a species than others
- If 2 species occur in the same two parts of a habitat, they will tend to be found in the same quadrats
- positive association
- There can be negative associations (tend to be found in separate quadrats) or the distribution of two species can be independent
Hypothesis and chi-squared testing
Ho (null hypothesis): Two species are distributed independently
H1 (alternative hypothesis): Two species are associated
- either positively [tend to occur together] or negatively [tend to occur apart])
- We can test these hypothesis using a statistical procedure called the chi-squared test
- Chi-squared test - only valid if all the expected frequencies are 5 or larger & the sample size was taken at random from the population
Method for chi-squared testing
- Contingency table
- Expected frequencies
- Degrees of freedom
- Critical region for chi-squared from a table of chi-squared values
- Calculate chi-squared using this equation
- Compare the calculated value of chi-squared w/ the critical region
Contingency table
Species A (present), Species A (absent)
Species B (present), Species B (absent)
Row total, column total
Grand total
Expected frequencies
Expected frequencies equation
Expected frequency = (row total * column total)/grand total
Number of degrees of freedom equation
df = (m-1)(n-1)
m & n - number of tows in the contingency table
Critical region
Use the degrees of freedom that you have calculated and a significant level (p) of 0.05 (5%)
The critical region is any value of chi-squared larger than the value in the table
Chi-squared equation
x^2 = sum of ([fo-fe]2)/fe
Comparing the calculated value of chi-squared w/ the critical region
- If the calculated value is in the critical region, there is evidence at the 5% level of an associated between the 2 species
- REJECT THE NULL HYPOTHESIS
- If the calculated value is not in the critical region, there is no evidence at the 5% level of an associated between the 2 species
- ACCEPT THE NULL HYPOTHESIS
“Statistically significant”
- term used by biologist when discussing results of an experiment
- refers to the outcome of a statistical hypothesis test
2 types of hypothesis
- Ho (null hypothesis):
Belief that there is no relationship
e. g. 2 means are equal or no association/correlation between 2 variables
- H1 (alternative hypothesis)
Belief that there is a relationship
e.g. 2 means are different or association between 2 variables
Calculated statistic > critical region
- null hypothesis is considered to be false & ∴ rejected
- though it has not been proved w/ certainty
What does it mean when results are “statistical significant”
- Ho was true
- the probability of getting results as extreme as the observed results would be very small
- Decision has to be made about how small this probability needs to be - known as significance level
- cut off point for the probability of rejecting Ho when in fact it was true
- level of 5% is often chosen (min acceptable sig. level published in research)
- If there is a diff. between the mean results for 2 treatments in an experiment, stat. test will show if sig. at 5% level
- if there is less than 5% probability of such large diff. between the sample means arising by chance (even when pop. means are equal)
- There is statistically significant evidence the populations means differ
Example of association between 2 species
- Example of association between 2 species: chi-squared test
- Shows whether there is a less than 5% probability of diff. between observed + expected results being as large as it is
- w/o species being either (+) or (-) associated
Letters to indicate significance on a bar chart
- When results are displayed on a bar chart, letters are often used to indicate significance
- 2 diff. letters (usually a &b) indicate mean results w/ a stat. sig. diff.
- 2 of the same letters (e.g. a & a) indicate any diff. is not stat. sig.
Ecosystems
A community forms an ecosystem by its interactions with the abiotic environment.
- There are not only complex interactions within communities
- but also many interactions between organisms and the abiotic env.
- The community of organisms in an area and their abiotic environment can be considered as a single system
- Ecologists study both components of ecosystems and interactions between them
Community and their ecosystems
- Community - composed of all organisms living in an area
- These organisms could not live in isolation - they depend on their abiotic environment (non-living surroundings)
- e.g. air, water, soil, rock
Abiotic enviroment influence organisms
- Some cases - abiotic env. exerts a powerful influence over the organisms
- e.g. wave action on rocky shore creates a very specialised habitat
- only organisms adapted to it can survive on cliffs
- rock type determines whether there are ledges on which birds can nest
Organism influence abiotic environment
- Also many cases - where living organisms influence the abiotic env.
- e.g. sand dunes - develop along coats where sand is blow up the shore
- specialised plants grow in the loose wind-blown sand
- roots of these plants stabilise the sand
- their leaves break the wind + encourage more sand to be deposited
Autotrophs + heterotrophs obtaining nutrients
Autotrophs and heterotrophs obtain inorganic nutrients from the abiotic environment.
- Autotrophs - obtain all elements needed as inorganic nutrient from the abiotic env.
- including carbon + nitrogen
- Heterotrophs - obtain these 2 elements + several others as part of the carbon compounds in their food
- also obtain other elements as inorganic nutrients from the abiotic environment (e.g. sodium, potassium, calcium)
Living organisms and chemical elements
- Living organisms need a supply of chemical elements
- Carbon, hydrogen + oxygen - needed to make carbohydrates, lipids + other carbon compounds which life is based
- Nitrogen + phosphorus - also needed to make many of these compounds
- Approx. 15 other elements are needed by living organisms
- some are used in minute traces only but are still essential
Nutrient cycling
The supply of inorganic nutrients is maintained by nutrient cycling.
- There are limited supplies of chemical elements on Earth
- Organisms have been using the supplies for 3 billions years but have not run out
- bc chemical elements can be endlessly cycled
- Organisms absorb elements they require as inorganic nutrients from abiotic env., use them & return them to the env. w/ atoms unchanged
- Recycling of chemical elements is rarely as simple as transferring to and from the biotic env. and living organism
- Element is often passed organism to organism before it is released back into the abiotic env.
- Details vary from element to element
- e.g. carbon cycle is diff. from nitrogen cycle
- “Nutrient cycles”
- Nutrient - ambiguous term
- element that an organism needs
Sustainability of ecosystems
Ecosystems have the potential to be sustainable over long periods of time.
- Sustainability (concept) - risen to prominence recently
- bc it is clear that some current human uses of resources are unsustainable
- Sustainable - can continue indefinitely
- e.g. unsustainable activity - human use of fossil fuels
- not currently being renewed
- supplies are finite
- ∴ can not carry on indefinitely
- Natural ecosystems - sustainable
- teach us how to live sustainably so our children/grandchildren can live w/ the same resources
3 requirements for sustainability
- Nutrient availability
- Detoxification of waste products
- Energy availability
Nutrients and energy in relation to sustainability of an ecosystem
- Nutrients can be recycled indefinitely
- if done, there should not be a lack of chemical elements on which life is based
- Waste products of one species are usually exploited as a resource by another species
- e.g. ammonium - released by decomposers
- absorbed + used for energy by Nitrosomonas bacteria is soil
- ammonium is potentially toxic but bc of the action of these bacteria, it does not accumulate
- Energy can not be recycled
- Sustainability depends on continued energy supply to ecosystem
- most energy is supplied to ecosystems as high from the sun
- Importance of light supply is shown by the eruption of Mt. Tambora (1815)
- dust in the atmosphere reduced intensity of sun-light for some months
- cause crop failures globally & deaths due to starvation
- only a temporary phenomenon - energy supplies to ecosystems in the form of light will continue for billions of years
Mesocosms and sustainability
Setting up sealed mesocosms to try to establish sustainability.
Mesocosms
- Mesocosms - small experimental areas that are set up as ecological experiments
- Fenced-off enclosures in gassed or forests could be used as terrestrial mesocosms
- Tanks set up in the laboratory can be used as aquatic mesocosms
Use of mesocosms
- Ecological experiments can be done to replicate mesocosms
- to find out the effect of varying one or more conditions
e. g. thanks set up w/ and w/o fish to investigate the effects of fish on aquatic ecosystems
- to find out the effect of varying one or more conditions
- Another possible use of mesocosms - test what types of ecosystems are sustainable
- involves sealing up a community of organisms together with air and soil or water inside a container
