Ch 15 Research Methods

The results from a number of quadrats can be scaled up to estimate the overall situation for the entire area.

Quadrat size

·       Lichens: 10cm x 10 cm

·       Ground flora: 0.5m x 0.5m

·       Trees in a forest: 100m x 100m

·       Bird survey: 10km x 10km

 Types of quadrat

·       Open frame quadrats: these mark out a study area. Smaller ones may be made of a metal or plastic frame. Larger ones use reference coordinates marked out by measuring tapes or GPS coordinates.

·       Grid quadrats: these are sub-divided into smaller squares, for example 10 x 10, each small square representing 1% of the area.

·       Point quadrat: these are used to collect similar information to other quadrats but they do not use a square area. They can be used where ground flora is too tall for other quadrat types because it would be flattened and provide unrepresentative results: a percentage cover estimate would be inaccurate and shorter plants may be obscured by the flattened foliage of taller plants. A wooden frame supports metal rods, usually 10. each time a rod touches a leaf it counts as 10% cover.

 Limitations

·       Subjective judgement may be involved, for example, estimating percentage cover.

·       The quadrat frame may flatten or move plants.

Pond net

Method:

1.       Pond nets can be swept through the water or aquatic vegetation to capture invertebrates, amphibians and fish.

2.       Using a particular length of sweeps, or no. of sweeps, can be used in an attempt to standardise the method and produce comparative data.

Limitations:

Mobile species may escape.

Kick sampling

Collects invertebrates that live on riverbeds.

Method:

1.       A net is held with its straight edge on the river bed and its face open to the current.

2.       The riverbed in front of the net is disturbed by repeatedly scraping a boot over it. Invertebrates that are dislodged are caught in the net.

3.       Controlling the length and number of kicks can be used to standardise the method.

Limitations:

·       Accurate standardisation is difficult.

·       Buried organisms or those fixed on stones may not be dislodged.

·       Some organisms can swim and avoid the net.

·       The water flow rate is variable and affects the capture rate.

·       Fragile organisms may be destroyed.

Surber samplers

Provide a more standardised technique than kick sampling.

Method:

1.       A fixed area of riverbed is sampled within a box-like frame.

2.       The riverbed is disturbed using a trowel or similar tool and stoned are inspected manually.

3.       Netting at the sides of the net opening reduces the number of organisms that escape.

Limitations:

·       They can only be used where the water flow is fast enough to carry organisms into the net.

·       The sampler's small size can make it difficult to set on rough substrates in deep water resulting in the loss of large organisms.

Plankton net

Catch planktonic organisms floating in water. Some plankton nets can be used to give quantitative estimates of populations.

Method:

1.       A fine mesh is pulled through the water and can be used vertically or horizontally.

2.       The net can be fixed where there is a current or maybe towed through the water.

3.       Different mesh sizes are used for different sizes of organisms. Phytoplankton are smaller than zooplankton so a smaller mesh size is used.

Limitations:

·       Nets with a coarse mesh size do not catch smaller organisms.

·       Nets with a fine mesh may become clogged by phytoplankton, preventing water flowing into the net.

Sweep nets

Method:

1.       Sweep nets are sturdy nets used to sample invertebrates in ground vegetation such as grassland. The net is swept through the vegetation so that organisms that are dislodged are caught.

2.       Standardisation of the method can be attempted using the same number of sweeps of the same length.

Limitations:

·       Mobile species may escape, such as flying insects.

Aerial insect nets

Method:

1.       These are lightweight nets used to capture flying insects such as butterflies.

Limitations:

·       Successful collection depends on the agility of the researcher and the prey.

Method:

• Some species can be monitored by providing suitable habitats that they may colonise.

Limitations:

• Not all species can be monitored as they may not use the media.
• Accurate population estimates are not possible as the proportion that colonise the media is not known.

Method:

• A container is placed in a hole in the ground with its open end making a close fit with the soil and the top being level with the ground surface.
• A cover is supported over the opening to exclude oredators that may eat animals that are caught to prevent flooding by rain.
• The trap is checked after a standard period of time, for example, 24 hours.
• A preservative fluid may be used to kill captured animals for later study.

Limitations:

• Only mobile animals that live on the ground surface are caught.
• More mobile species are more likely to be caught.
• Trapped carnivorous animals may kill other organisms that have been caught.
• If a preservative is used, it may attract or repel certain species.
• Some species avoid traps or can escape.

Method:

• A sheet or tray is placed beneath the vegetation which is beaten several times with a stick. The invertebrates that are dislodged fall onto the sheet and are collected for identification and counting.

Limitations:

• It is difficult to standardise the method between researchers, for example, the vigour of hitting the branches.
• Some species are not dislodged.
• Thicker branches shake less, so organisms are less likely to be dislodged.
• Some species fly away and are not caught.
• Higher branches cannot be reached.

Used to collect night-flying insects that are attracted by bright lights, usually UV lights.

Method:

• Flying insects, expecially moths that are attracted to the light fall into the a container. The container is then checked the following morning.
• The insects that have been caught are identified and counted.

Limitations:

• Moths only fly during their adult phase and activity is affected buy the weather and seasons, so the failure to find a species does not mean it is absent.
• The brightness and light wavelengths emitted by the light can affect their attractiveness to insects, so it may be difficult to compare results produced by different types of trap.

Used to sample mobile invertebrates in leaf litter or the soil.

Method:

• A sample of leaf litter or soil is placed on a mesh beneath a light.
• The light and heat repel some mobile invertebrates which move downwards, pass through the mesh, and fall into a container.
• The Tullgren Funnel is left operating for a standard period of time.
• The invertebrates collected are identified and counted.

Limitations:

• Only species that are repelled by heat or light will be collected. 
• Some organisms may die or stop moving due to heating or desiccation before they are collected.
• Some organisms are too large to pass through the mesh.

Capture airborne insects or invertebrates that were dislodged from vegetation. Some just show the presence of the organisms but some give quantitative data.

Method:

• There are several types of suction sampler which can be used to collect invertebrates from the ground, vegetation or the atmosphere.
• Air suction samplers capture flying insects. If the air flow rate is measured and the cross-sectional area of the collector tube is known then the number of insects per unit volume of air can be estimated.
• Motor-driven suction smaplers can be used to smaple invertebrates on the ground vegetation. The area of ground that is covered by the suction pipe is knwon, so the population density od the invertebrates can be estimated.
• A pooter is a suction sampler used to pick up invertebrates that have been found. It is a handling method, not a population sampling technique.

Limitations:

• Some invertebrates may not be caught by an air sampler. They may sense the air sampler and fly away.
• Some insects may not be dislodged from vegetation by a suction sampler.

Soil flooding

Method:

• Mark out a sample area of a suitable size 0.5m x 0.5m or 1m x 1m
• Remove vegetation that may hide words at the surface
• Add an irritant solution, for example, detergent or mustard in water
• Keep adding until the soil is saturated.
• Saturate the surrounding area(so the worms are less likely to move sideways).
• Add more as the solution infiltrates into the soil.
• Collect worms that come to the surface.
• Continue collecting until no more worms appear/for a suitable time period/standardised time period.
• Count/measure/weigh/identify the collected worms.

Limitations:

• Irritant solution may not percolate through impermeable soils.
• Irritant soulution may not reach deepest worms.
• Worms may move sideways or down.
• Worms may not move.
• Worms may die.
• Worms may move too slowly to be collected during the study period.

Method:

• A pit of a chosen area and depth is dug, for example, 0.5m x 05.m x 0.5m.
• The soil is hand sorted and worms collected.

Limitations:

• Smaller worms may be overlooked.
• Digging may disturb worms that move sideways or down, out of the sample site.