Chapter 5: Study of an Ecosystem

A Broad Overview of a Selected Ecosystem

Suitable ecosystems include:

  • hedgerow
  • stream
  • rock pool
  • rocky seashore
  • old wall
  • small woodland
  • small meadow
  • freshwater pond
  • waste land
  • an overgrown garden
  • soil
  • peatland
  • grassland

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Practical Activity: Select and visit one ecosystem, e.g. woodland

Physical properties:

  • Presence of large mature trees with some areas of grassland and the presence of a large rock
  • It is close to a main road
  • Provides a home to main species of animals
  • There is a large gradient in the ecosystem
Map of a woodland with a key

General presence of life:

  • Flora: many trees and shrubs, plants, and grasses
  • Fauna: herbivores, birds and predators

Practical Activity: Observation and Scientific Study of a Selected Ecosystem

Identify any five fauna and any five flora using simple keys:

Flora:

  • Hawthorn
  • Blackthorn
  • Gorse
  • Blackberry bramble
  • Fuschia
  • Holly
  • Rowan (Mountain ash)
  • Ash saplings
  • Hazel
  • Willow

Fauna:

  • Beetles
  • Butterflies
  • Hoverflies
  • Snails
  • Ladybirds
  • Hare
  • Foxes
  • Badgers
  • Hedgehog
  • Mice

Identify a variety of habitats within the selected ecosystem
There are a number of habitats in the selected ecosystem of the woodland:

  • Soil
  • Leaf litter
  • Shrub level
  • Canopy level

Different organisms are found in each of the habitats.

Ecology Apparatus

Identify and use various apparatus required for collection methods in an ecological study

  • Mammal trap
  • Pitfall trap
  • Cryptozoic trap
  • Beating tray
  • Pooter
  • Nets (to include – sweep net, insect net, plankton net or fish net)
  • Direct search
  • Tullgren funnel

Traps:
Mammal trap

  • Bait attracts small mammals into box
  • Once they enter the trap door prevents exit
  • Bedding provides comfort

Pitfall trap

  • Involves simple metal can or plastic cup embedded in the ground and covered to prevent water entering
  • Bait is sometimes used

Cryptozoic trap

  • Shelter trap involving a piece of old wood, a log, or a large stone
  • Small animals like slugs and woodlice hide under a cryptozoic trap during periods of inactivity

Beating tray

  • A large sheet/plastic tray held under a tree or bush
  • The tree or bush is shaken gently
  • Insects fall onto tray and can be identified

Pooter

  • Device ecologists use to pick up small organisms, like insects
  • Suck in the tube with the gauze on the end and place the other tube over the insect to be captured.

Sweep nets, insect nets, plankton nets

  • Have a lightweight aluminium frame
  • The net bags usually have curved tips to help prevent insects escaping
  • Sweep net usually have a 5-sided frame designed to give a better sampling sweep than circular frames
  • Plankton nets are long and very light designed to capture very small aquatic organisms
A sweep net
A plankton net

Tullgren funnel

  • Used for both dry and wet extraction of soil organisms from soil samples
  • A soil sample is placed in the removable upper part of the funnel
  • Heat and light from the lamp creates a temperature gradient of approximately 14°C in the soil sample
  • This stimulates the downward movement of soil arthropods, and similar organisms, through the gauze to a receiver attached to the base of the funnel
A tullgren funnell

Organism Distribution

There are two ways in which organism distribution is determined:

  1. Qualitative survey – record the presence or absence of a species in a habitat.
  2. Quantitative survey – record the number of organisms of a species in a habitat.

Quantitative Surveys

  • Count the number of organisms of a species in a habitat
  • Ecological apparatus used depends on the species; e.g. mammal traps for fast moving animals such as mammals; sweep nets for insects; pitfall traps for beetles; cryptozoic traps for worms and woodlice; quadrats for small plants.

Quantitative survey of plants/flora:

  • Plants and flora can be quantified using either quadrats, belt transects or line transects.

Quadrats:

A basic quadrat
A graduated quadrat
  • Quadrats can be used to quantify plants/flora and slow-moving animals (e.g. shellfish on the rocky seashore).
  • Quadrats can be plastic, wooden or metal square frames of various sizes e.g. 1, 0.5, or 0.25 metres squared.
  • Quadrats can be graduated (sub-divided into smaller squares) or a basic quadrat.
  • Disadvantages of using quadrats is that they cannot be used to quantify trees or large bushes and cannot quantify fast-moving animals.
  • Quadrats are always placed randomly in habitat by throwing a pencil over your shoulder and placing the quadrat where the pencil landed.
  • Two possible types of measurement can be taken with a quadrat:
  1. Percentage frequency
  2. Percentage cover

Percentage frequency:

  • Percentage frequency: chance of finding a named species with any one throw of the quadrat.
  • A basic quadrat is assigned randomly within the habitat (as described previously).
  • The presence or absence of a named species is noted.
  • This is repeated at least 5 times for each species.
  • A table of results is drawn up as shown.
% FREQUENCY TABLE

Percentage cover:

  • Percentage cover: area of the ground covered by the aerial parts of the plant.
  • A graduated quadrat is assigned randomly within the habitat (as described previously).
  • If the graduated quadrat has 25 squares, each individual square represents 4% of the entire quadrat.
  • The area of each square each species covers is estimated. In this way, it is subjective (depends on the individual’s opinion) and can be very inaccurate method.
  • The totals from each square is totalled to come up with a percentage cover value for each species.
% COVER TABLE

Transects:

  • There are two types: belt transects and line transects.
  • Transects are useful for studying numbers of plants/flora that vary due to the topography of the land.
  • They are also used very often to quantify flora/slow moving animals on the rocky seashore.

Belt transects:

  • Set up using two long ropes marked off at regular intervals (e.g. 1m/ 2m/ 5m etc) or one long rope and a graduated quadrat.
  • If using the two ropes the number of each species is counted at each interval and recorded.
  • If using the rope and the quadrat, the number of organisms of each species is counted in the usual way (see “quadrats” above).
Belt transect using a rope and a graduated quadrat

Line transects:

  • Consists of a long piece of rope/string marked off at regular intervals (e.g. 1m)
  • Very useful for quantifying species along a gradient in a habitat.
  • Line transects are carried out by recording the presence or absence of a particular species at the regular intervals along the rope.
  • This is repeated at different locations.
  • Line transects have the advantage that they can include and quantify large trees (unlike quadrat studies).
A line transect

Quantitative survey of animals/fauna:

  • Slow-moving animals such as barnacles/limpets can be quantified using quadrats in the same way plants are quantified.
  • Most animals are fast-moving and need to be quantified using the capture-recapture technique.

Capture-recapture technique:

  • In the capture-recapture technique, animals are caught using one of the methods listed earlier – e.g. mammal traps.
  • For Leaving Certificate Biology it is best to use the recapture technique on easily caught animals such as snails.
  • Snails live in long grass, bushes/shrubs and in trees.
  • Search for snails in the habitat and mark each one with a small inconspicuous mark on the side of their shell (e.g. using Tippex)
  • Record the total number found and marked.
  • It is important that the mark does not harm the snail or make the snail more visible to predators.
  • Place the snails back in the same position.
  • Approximately one week later, return to the same habitat and search for the snails again, taking note of the total number found and the total number of these snails that had the mark.
  • Use the formula below to estimate the number of snails in the habitat:

Sources of error in studying an ecosystem:

  • Miscalculation – e.g. when estimating percentage frequency
  • Misidentification – e.g. species not identified correctly
  • Sample size too small

Study the effects of abiotic factors on the suitability of an organism to its habitat
You must study at least 3 abiotic factors:

An abiotic factor is a non-living, environmental condition that affects living organisms in a habitat.

Example of abiotic factors:

  • Soil/water pH level
  • Soil/water/air temperature
  • Light intensity
  • Water current speed/direction
  • Wind speed/direction
  • Soil/water/air oxygen levels
  • Soil/water mineral content
  • Percentage humus content
  • Water salinity
  • Degree of exposure
  • Aspect
  • Slope

Examples of instruments used to measure abiotic factors:

  • pH levels are measured using a pH meter
  • Air temperature is measured using a thermometer
  • Light intensity is measured using a light meter
  • Water current speed/direction is measured using a water flow meter
  • Wind speed/direction is measured using an anemometer
  • Aspect is measured using a compass
  • Slope is measured using a tape measure and a spirit level

Then describe how each of the three factors you chose affects living organisms in your choice of habitat; e.g. Ferns only grow under the shade of large trees; moss requires a large moisture content to live/survive; broad-leaved trees cannot survive at high altitude or on ground with a very steep slope.

Identifying Organism Adaptations

  • Adaptations are necessary for an organism to survive new conditions
  • Adaptations may be structural, competitive, or behavioural
  • Describe ONE adaptation of an organism you studied in your habitat
  • Snail has a protective shell
  • Ladybird has a red covering to warn birds that it is poisonous to eat
  • Blackthorn has thorns to protect its fruits
  • Bladder wrack seaweed has vesicles full of air so that the fronds of the seaweed float in the water increasing levels of photosynthesis.

Identifying Organisms’ Role in Energy Transfer

  • Identify where each organism in your habitat is positioned in the food chain/food web
  • From the data collected on your field trip construct a food chain, food web, and pyramid of numbers
A woodland food web
A rocky seashore food chain
A rocky seashore pyramid of numbers
A rocky seashore food web

Analysis

  • Learn to analyse, assess, and discuss your results and conclusions
  • Is there any relationship between the results and conclusions of your study and local ecological issues
  • Prepare a portfolio/report/project (no less than 1,000 words, no more than 2,500 words)