Ecosystems and Sampling Techniques

What is a population?

All the individuals of the same species at any one time living in a certain area at a certain time

What is a community?

All of the organisms of all of the species living in an area at one time

What is an ecosystem?

A community and the abiotic factors of it’s environment

What is an abiotic factor?

Non-living factors in an ecosystem

What is a biotic factor?

The living factors in an ecosystem

What is a habitat?

The area in which an organism lives

What is interspecific competition?

Competition between member of different species

What is intraspecific competition?

Competition between members of the same species

What are some example of abiotic factors?

Temperature, pH (of soil/water), conc. of mineral ions, light intensity, salinity, humidity, aspect (gradient of the land)

What are some examples of biotic factors?

Predators, competition and disease

What does carrying capacity mean?

The maximum number of individuals of a population that the ecosystem can support

What are the stages of the growth distribution curve?

• Lag phase

• Rapid/exponential growth phase

• Stationary phase

Describe the growth distribution curve

• Lag phase- the population size increases very slowly at first

• Exponential growth- The population size increases vary rapidly

• Stationary phase- the population has reached it carrying capacity

  • The population size fluctuates due to different abiotic and biotic factors such as predator prey cycles and mating seasons

Explain the lag phase of an population growth curve for asexually in bacteria and sexually reproducing organisms

Asexual

• Little growth- bacteria are transcribing genes and synthesising the appropriate enzymes for new conditions

  • These enzymes may include DNA helicase and DNA polymerase

Sexual

• Individuals rarely meet

• Long gestation periods so few births

Explain the rapid growth phase of a population growth curve in asexually and sexually reproducing organisms

Asexual

• Rapid exponential growth

• No limiting factors as bacteria are at relatively low density

Sexual

• Rapid growth through not exponential

• Few limiting factors and population is low density

Explain the stationary phase of a population growth curve for asexually (bacteria) and sexually reproducing organisms

Asexual

• Slow growth due to accumulation of ethanol

• Lack of glucose

• Limiting factors increase

Sexual

• Slow growth due to intraspecific competition for food, territory, predators

• Also disease can reduce population size

Why do we use logs for counting the number of bacteria cells in a culture for example?

Logs allow us to deal with very small and very large values

What is a niche?

• Where an organism lives and all of the biotic and abiotic factors that influence it

• The niche is the organisms role within the ecosystem

Why do niche’s for difference species exist within ecosystems?

• Different species can occupy the same area as they require different resources meaning they are not competing

• Different species having different niches increases species diversity

• Members of the same species always have the same niche and will be well adapted to that niche

What does a narrow niche mean for a population?

• It only has a narrow range of resources like food sources that it needs to survive

• Therefore it has a lower carrying capacity

• There are fewer numbers of this species and they are less likely to cope with environmental change?

What does a broad niche mean for a population?

• The population has a greater carrying capacity

• This is because it would have a greater range of food sources for example so there is more food available to support the population

What are the names for species with a narrow and broad niche?

• Narrow- specialists

• Broad- generalists

What is the competitive exclusion principle?

• Two species cannot co-exist in the same habitat if they have the same niche

• One species will be more successful than the other until there is only one species left

• We say that the less successful species is driven to exclusion

How does competition differ between an environment with extreme abiotic factors compared to those with moderate abiotic factors?

• In moderate conditions, many different species may survive

  • Therefore there is a lot of competition

• In extreme conditions, only the very best adapted species will survive

  • Therefore there is very little if any competition from other species tic factors dictate who survives

In extreme environments, abiotic factors dictate who survives. In less extreme environments, biotic factors dictate who survives

What is magnesium used for in plants?

To make chlorophyll

How can seasonal changes affect population sizes?

• Abiotic factors vary with seasons, causing a periodic oscillation in the population size

• In summer it tends to be warmer, meaning there is more reproduction and less organisms dying of exposure to the cold, with the opposite being true for winter

What kinds of organisms have a population size which is affected by seasonal changes?

• Species with short life cycles like insects

• Species with long life cycles (longer than a year) do not change with the seasons like this

What do animals compete for?

• Food

• Mates

• Habitat/territory

• Water

What do plants compete for?

• Light

• Mineral ions

• Water

Explain the predator-prey cycle

• There are a low number of predators so not many prey are eaten

• The prey are more likely to survive and reproduce so their numbers increase

• This increase in prey numbers means that there is more food for the predators to eat so the ecosystem can support more predators (i.e. their carrying capacity increases)

• The predator population increases, meaning that they eat more prey causing prey numbers to decrease

• This causes a food shortage for a large predator population- intraspecific competition means that predators are now competing with each other for food meaning the less successful predators will die of starvation, causing predator numbers to decrease

• Less prey are eaten, so the prey numbers increase and the cycle begins again

Why is the number of predators normally lower than the number of prey?

• The population of the number of predator depends on the number of prey

• The population of the prey depends on another food sources, prey often reproduce often, if the predator eats they prey too much, it causes a decrease in the predator population

Why is there a lag time between prey and predator population peaks in a predator-prey cycle?

• Time taken for the prey numbers to increase again

• Time to find partners, breed and also gestation periods

Why do predator-prey cycles often not lead to the extinction of a prey within an natural area?

• In nature, habitats provide a safe place for the reproduction of prey

• There is predation of the primary predators so less of they prey would be eaten

• Disease can reduce prey numbers

• Smaller populations are more difficult to hunt

What is a quadrat and when is it used?

• Normally a square frame allowing organisms within the square to be counter

• It used to calculate the abundance of organisms and make comparisons between other organisms

• They are difficult to use for tall vegetation or uneven ground

• Can vary in size and doesn’t have to be a square

How would you estimate the number of dandelions in a field?

• Grid the area of the field and split the squares/spaces into coordinates

• Use a random number generator to produce two numbers to use as your coordinates

• Place the quadrat at the coordinate and count the number of dandelions within the quadrat

  • Alternatively if the number of dandelions is hard to count because there’s too many, you can calculate % cover

• Repeat many times/gain a large sample

• Calculate the mean number of dandelions per m²

• Assuming that your quadrat is 1m² - Area of field/area of quadrat x mean number of dandelions gives you the total number on the field

Why do we want large and random samples?

• Large- to be representative

• Random- to avoid bias

What are the two ways to place a quadrat down to avoid bias?

• Systematic sampling - placing a quadrat down every 3rd square for example

• Random sampling - using a random umber generator to produce coordinates

What is a point quadrat and how is it used?

• Its a frame shaped like a T

• Any species touching the pins stuck in the ground is only counted once

• This allows us to also count overlapping vegetation and elevated vegetation

What is a transect and why are they useful?

• A line through a habitat along which the species can be sampled

• These are useful because it allows us to also study how the change in an abiotic factor affects the distribution of an immobile organism

What are the two types of transect?

• Line transect- a tape measure is placed along the transect and the species that touch the line are counted

• Belt transect- quadrates are placed at regular intervals along a transect to work out the species frequency/percentage cover along the transect

What is the difference between a continuous and interrupted belt transect and what are the strengths and weaknesses?

• A continuous belt transect is where you place a quadrat down, then flip it over to record the space next to it

  • A strength of this is that you don’t miss any species (along the transect)

  • A weakness is that it can be very time consuming

• A interrupted belt transect is where you place the quadrates at regular intervals

  • A strength is that it is less time consuming

  • A weakness is that you may miss some species along the transect between intervals

Method for systematic sampling with a belt transect

• Lay out a tape measure along the area of land to sample

• Place the start of the transect at random

  • You need to be clear where you’re placing the tape measure/quadrat and how- for example if you’re measuring plant distribution away from a roadside, place the tape measure perpendicular to the road side

• Place quadrats at regular intervals and place a quadrat down, counting the number of organisms or percentage cover

• Repeat with many transects across the area of land

What does an organism being sessile mean?

It remains stationary

How can we measure organism abundance for organisms that are mobile?

• Mark-release-recapture

• This method traps to organism (normally in a pitfall trap for small insects)

Method for mark-release-recapture

• Place a trap (trap type depends on the organism) and leave for a long, fixed period of time

• Return to the trap and count the number of organisms

• Mark the sample in a non-harmful, discrete way (the markings may affect the organism’s ability to survive/likely to be rubbed off)

• Release the organisms back into their habitat

• Wait for a long, fixed amount of time and place another trap and capture a second sample

• Count the number of organisms in total, then count the number marked

• Use the formula Total no. in sample 1 x Total no. in sample 2 / No. marked in sample 2

What are the assumptions made when using the mark-release-recapture method?

• The sample has had the time and opportunity to reintegrate back into the population

• Assumes there are no births or deaths

• Assumes there is no immigration or emigration in or out of the population

What is succession?

How an ecosystem changes over a long period of time

Why is bare rock such a hostile environment?

• No soil

• Extremes of temperature

• Lack of water leads to dehydration/desiccation (drying out)

• Extremes of pH

In general the abiotic factors are very unfavourable

What are features of a pioneer species that suit them to colonisation?

• Tolerance to extreme conditions

• Rapid germination of seeds

• Production of large quantities of wind-dispersed seeds or spores

• The ability to photosynthesis

What are the features of a climax community?

• High species diversity

• More niches

• More habitats

• Larger range of food sources

• Abiotic factors are constant

• Population sizes are stable (at carrying capacity)

• Climax community is stable- complex food webs

What are some adaptations of xerophytes that makes them pioneer species?

• Thickened cuticle- reduces the evaporation of water- decreased diffusion pathway

• Rolled leave, stomata sunk in pits, hairs on leaves- Traps water vapour around stomata which reduces the diffusion gradient meaning less diffusion of water out of the plant

• Fewer stomata- less places where transpiration can take place

• Spines instead of leaves/smaller leaves- Reduced surface area for the evaporation of water/transpiration

What happens during succession?

• The pioneer species colonises the hostile environment

• They produce soil and when they die they produce humus (decaying material)

• As they die they will also release phosphates and nitrates into the soil

• This makes the environment less hostile so new species can colonise the area

• The new species are more successful competitors than the pioneer species so they outcompete it

• Biodiversity increases until a climax community is reaches

• This process can take thousands of years to reach a climax community

What is secondary succession?

• Starts with soil unlike primary succession

• Often happens following natural disasters like fires or after grazing, ploughing etc.

• Soil have already been developed s there is no need for a pioneer species

• Seeds are often present and can germinate immediately to give a mixed climax community of trees, grasses, etc.

• It can take just decades for a climax community to be reached

What are the differences between primary and secondary succession?

Primary

• Starts with bare land

• No soil

• Slower

• Harsher abiotic factors

• Requires a pioneer species to make the abiotic conditions less harsh and produce soil

Secondary

• Event destroys an area such as a fire

• Soil is still present

• Faster

• Does not need a pioneer species as soil is already present

What is deflective succession?

• Humans taking action to prevent succession taking place

• Done by using animals to graze and burning

• Sometimes done to conserve land or to keep around important species that may be useful for producing medicines

What is conservation?

The protection and management of species and habitats (ecosystems) in a sustainable way

What does sustainable mean?

Enough resources are taken to meet the needs of the people today without reducing the ability of the people in the future to meet their own needs

What are the main reasons for conservation?

• Ethical- other species have occupied the Earth far longer than we have and should be allowed to co-exist with us. We should respect living things.

• Economical- Living organisms contain a gigantic pool of genes with the capacity to make millions of substances (crucially, medicines)

• Cultural and aesthetic- habitats and organisms enrich our lives (ecotourism)

What are some conservation methods?

• Management of succession- burning land, animal grazing

• Seed banks- keeping seeds stored in a library

• Captive breeding- keeping animals in an enclosed space to breed

• Fishing quotas- limiting fishing at certain times, limiting fishing of certain species

• Protected areas- high species diversity

What are the drawbacks of some conservation methods?

• Seed banks- seeds lose their viability after a while

• Captive breeding- it may be hard to get the animals to breed

• Fishing quotas- limits the income of fishermen

• Protected areas- often funded by tourists

When managing succession, what is the artificial climax community called?

Plagioclimax