Structure and Functioning of a Managed Grassland Ecosystem
Exercise F: Fauna

EQUIPMENT

Field

• tapes and pins for positioning sampling points
• random number table

Earthworms

• spade
• plastic trays
• collecting jars

Surface macrofauna

• pitfall traps (plastic cups)
• water and 1 drop washing-up detergent/cup

Soil fauna

• soil corers (squares of metal)

Laboratory

• balance
• 70% industrial methylated spirit
• soil fauna extractor (This can simply be a rack supporting plastic funnels containing a 2 mm mesh tray to hold the samples, with overhead heat provided by a bench light)

METHOD

Field procedure

Earthworms

• Earthworms can be driven out of the soil using 0.25% formaldehyde solution. However, this is considered hazardous, so digging up and hand sorting soil samples is recommended instead.
• Six samples are taken, three located at random from each side (mown and unmown).
• A turf 10 cm deep and the width of a spade on each side is cut. The width of the spade is measured.
• The sample is broken up on a tray and the worms from each sample are placed in jars for examination in the laboratory.
• The soil is replaced in the hole.
• The worms are released as soon as possible after they have been examined in the laboratory, and covered with soil or litter to protect them from sunlight and birds.

Surface active macrofauna

• Plastic cups are used as pitfall traps. Ten traps are located in each plot (mown and unmown).
• Holes are dug and the cups are sunk in until the rims are flush with the soil surface. One cup is used to fit the hole and, as this often gets cracked or damaged, another is slipped in to contain liquid.
• 2 cm depth of detergent solution is added and the traps are covered with a lid at least 5cm above the cups to protect against rainfall. Lids may be pieces of plywood, stiff plastic or plastic Petri dishes supported by wires.
• A week later the pitfall traps and contents are retrieved. The material inside is preserved in 70% industrial methylated spirit.

Soil fauna

Soil cores are taken. To avoid compacting the soil the best method is to place squares of metal on the ground and cut small blocks of soil with a knife.

Laboratory procedure

Earthworms

• The number of worms from each sample that have dark or pale pigment are recorded separately.
• The worms are weighed and the wet weight of worms of each colour from each site is calculated.

Surface active macrofauna

• The invertebrates from the pitfall traps are identified as far as possible, using basic keys and illustrations (e.g. in the references cited below).
• Data are presented as counts of individuals for each taxon.

Soil fauna

• Invertebrates are extracted from soil core samples taken from layers 0-5 cm and 5-10 cm deep. The simplest method is to break up each core carefully and spread it on a 2 mm mesh sieve sitting on top of a plastic funnel. A light bulb placed above will heat and dry the sample. Animals are collected beneath the funnels in vials of 70% alcohol. For demonstration purposes, animals may be collected alive in layers of moist filter paper.
• Nematodes, enchytraeid worms and other animals living in water-filled pores can be extracted in a similar manner but the neck of the funnel is closed with a piece of rubber tubing and clamp. The funnel is then filled with water until the surface just wets the soil sample in the sieve.
• Both of these methods have poor extraction efficiencies and more accurate enumeration requires better equipment and procedures (details readily available in literature or WWW sites).
• The invertebrates from the core samples are identified as far as possible, using basic keys and illustrations (e.g. in the references cited below).
• The internal diameter of the core is measured and results are expressed as numbers per square metre.

Data handling and statistical techniques

Earthworms

• The earthworm results are presented as
• number of worms m^-2 soil
• mass of earthworms in g m^-2 soil.
• Means ± standard errors of the results from mown and unmown areas are calculated

Surface active macrofauna

• Means ± standard errors of the pitfall trap results from mown and unmown areas are calculated.

Soil fauna

Means per square metre of the numbers of individuals in each taxonomic group for each type of sample are calculated.

Timetable

The pitfall traps must be set out a week before the laboratory practical. The enumeration takes 2-3 hours, depending on sample sizes and numbers of students.

SPECIMEN RESULTS

Invertebrate populations

* Pitfalls are not a suitable method for sampling these groups and the numbers have little ecological significance (but see data below).

Soil fauna (core samples)

DATA INTERPRETATION

Earthworms

• Earthworms of different colours belong to ecological types and have different effects on soil structure.
• The earthworms in the mown plot are mainly in the pale (pink) category. This group of earthworms (e.g. Aporrectodea caliginosa) lives entirely within the soil (euedaphic), rarely coming to the surface, and feeding on soil organic matter. Their burrowing activities increase the porosity of soil and the drainage of water down the soil column (hydraulic conductivity).
• The pigmented earthworms (e.g. Lumbricus rubellus) are more surface active (epigeic) and feed on plant litter, but the short grass and compact soil of the mown plot site provides little habitat space for this group. These epigeic earthworms do not contribute significantly to surface porosity and hence water infiltration.
• In the unmown site the pigmented earthworms include Aporrectodea longa which creates larger, more vertically orientated burrows that increase water infiltration. (Root channels and an open structured soil surface under vegetation cover also contribute to this).

Surface macrofauna

• Higher numbers of woodlice (Isopoda) and millipedes (Diplopoda) in the unmown site reflect the food and habitats provided by the large standing crop of dead grass.
• The spiders (Araneae) show similar numbers in the two sites because there were not divided into the two main families found in the pitfalls. The Lycosidae (wolf spiders) are mainly found in the unmown site and move around seaching for prey. The females also carry a cocoon of eggs to optimise microclimatic conditions for development. The family Linyphiidae comprises most spider species in the UK and the majority are tiny (aeronaught or money spiders). These spiders are more commonly trapped in the mown site because the grass is short.
• Two groups of beetles, the Carabidae and Staphylinidae also show habitat preferences. The Carabidae are active, nocturnal predators that spend the day in the rough grass of the unmown site. At night they emerge to forage over the short grass of the mown site. The Staphylinidae have reduced elyta and so have a more flexible abdomen than the carabids and are adapted to living in grass and more confined spaces. Although they also hunt on the mown site, spatial arrays of pitfalls have shown they do not move so far out into the short turf.

Soil fauna

• The Enchytraeidae are small white (oligochaete) worms that are abundant in moist soils. Their populations are underestimated using dry extractors and they are better extracted using water-filled funnels.
• The Collembola and mites are generally small species (20 - 1000µm) living in soil cavities. The populations are higher in the unmown site but the differences are not so marked because the samples excluded surface litter.

REFERENCES

Bebbington, A., Bebbington, J. & Tilling, S. 2003. The woodland name trail. A key to the invertebrates of soil and leaf litter. 2^nd. Ed. Field Studies Council.

Chinery, M. 1973. A field guide to insects of Britain and Northern Europe. Collins, London.

Tilling, S. M. 1987. A key to the major groups of British terrestrial invertebrates. An AIDGAP key. Field Studies 6, 695-766.

Copyright 2003 British Ecological Society. All Rights Reserved