Most species of terrestrial amphipods are local endemics and this is true for the South African fauna (Griffiths 1999). There are only two genera and seven species of terrestrial amphipods in South Africa (Griffiths 1999). Only one species of terrestrial amphipod is known within the study area, Talitriator eastwoodae Methuen, 1913 (Griffiths 1999).
2.3.8 Additional taxa
Additional taxa, including pollinating flies (Order: Diptera), butterflies and moths (Order:
Lepidoptera), plant wandering spiders (Order: Araneae), dragonflies (Order: Odonata, Suborder: Anisoptera) and damselflies (Order: Odonata, Suborder: Zygoptera) were collected during this study and many additional invertebrate groups were collected in pitfall traps. However, these data were incomplete and could not be analyzed (see Section 2.4.4). Therefore, these specimens were merely identified as far as possible and are listed in Appendix 1 and 2.
individuals were sampled except for molluscs, where both live individuals and empty shells were collected. Ground wandering spiders and terrestrial amphipods, which are also ground-dwelling invertebrates, were not sampled in quadrats because they are highly mobile and could not be reliably captured by hand.
Quadrat sites were selected according to a stratified random method. Within each forest, sites were chosen to account for varying elevation, slope, soil type, soil moisture and microhabitat availability based upon a visual assessment. Because steep, slippery slopes and rocky outcrops were common in most forest patches, accessibility was a limiting factor to study site locations.
Each quadrat was two by ten metres and all quadrats were subdivided into five two by two metre plots (Figure 2.2). Each two by two metre plot within each quadrat was sampled separately to allow species accumulation curves to be drawn for each quadrat site (Appendix 3). Five quadrats were completed in each of the 11 forests, for a total of 55 quadrats for the study. Species accumulation curves were also drawn for each forest sampled (see Section 3.2, Appendix 4).
2 m 0 m 2 m 4 m 6 m 8 m 10 m
Figure 2.2: Standard quadrat size and shape for active sampling of ground-dwelling invertebrates.
Once a specific site was chosen within a forest, the quadrat search area was set up according the Gradient Directed Transect, or Gradsect concept. A Gradsect is any transect that is purposely oriented to correspond with the perceived most significant environmental gradient in the sample area (Gillison & Brewer 1985). According to this method, sampling oriented across the greatest environmental gradient should account for the maximum number of species in an area (Wessels et al. 1998). Although this method is usually used for longer-distance transects, it was used in this case with respect to the gradient of microhabitats. The rectangular quadrat was oriented up the slope and situated to
encompass as many different microhabitats as possible. These microhabitats included various sized trees, rocks and logs and different leaf litter depths.
Each quadrat area was marked out and a GPS coordinate was recorded for the location.
The total time spent searching each two by two metre plot was also recorded. Sampling was always conducted between 8:00 and 17:00 when enough light was available to see the forest floor properly.
Target invertebrates were collected using the hand-to-jar technique. All leaf litter was carefully turned over, along with any logs and rocks within each plot. Using a small hand trowel, the loose layer of topsoil was also excavated. Depending upon the degree of soil compactness, the amount of topsoil searched varied in depth from one centimetre in severely compacted soils to as much as 10 centimetres in plots with very loose soil. The depth searched was noted. Invertebrates from each plot within the quadrat were placed in separate jars.
Upon completion of the total two by ten metre quadrat, each jar was emptied and individuals were sorted to morphospecies based solely on external characteristics and without the aid of keys. In most cases all individuals were kept for identification.
However, in cases where more than 100 individuals of the same, distinct species were collected, only about 50 individuals were kept for identification and the remainder were counted and released on site. Releases were performed with caution and all individuals were kept when there was any uncertainty of identity. Specimens returned to the laboratory from each forest were kept separate in glass tubes, preserved in 70% ethanol and were labelled with a unique code.
The number of individuals for each potential species found in each two by two metre plot was counted and entered into a large Microsoft Excel database by group.
2.4.2 Line transect sampling
Web-building spiders were collected by active searching along 100 metre line transects.
Transect locations were selected according to a stratified random method, but were limited to existing foot paths or accessible areas in the forest where walking was possible through
the undergrowth and where the slope was not extreme. Transects were oriented according to the Gradsect method (see Section 2.4.1). Five line transects were completed in each of the 11 forests, for a total of 55 line transects for the study.
While walking slowly along the transect, all web building spiders seen on trees, in branches, among rocks or in herb or grass vegetation within one metre of either side of the transect line were collected. Spiders were collected off webs using small jars and lids and each was labelled with a unique numerical code. After collecting each individual, the jar code and the distance from the starting point ‘0’ was noted in metres. The location of the web, i.e. in a tree, grass or herbs and the canopy cover of the web location was noted.
Upon completion of the 100 metre transect, the total search time was noted. The live spiders in the labelled jars were then returned to the laboratory where they were killed and preserved in glass tubes of 70% ethanol. Each specimen retained its unique code.
Because few spiders can be accurately identified in the field, specimens must be killed and preserved (Marc et al. 1999). However, often many spiders of the same distinct species were present within a single line transect. In these cases, they were all assigned the same code, only two or three individuals were returned to the laboratory and the others were released on site. Releases were only performed when there was no uncertainty in morphospecies identification.
The written data were then entered into a Microsoft Excel database. Species accumulation graphs were drawn for transects searched in each forest (see Section 3.2, Appendix 5).
2.4.3 Pitfall trap sampling
Plastic and glass test tubes, all 30 millimetres in diameter and 100 millimetres in length, were used as pitfall traps. Each was half filled with a solution of three parts 70% ethanol and one part glycerol. The ethanol killed and preserved any invertebrate that fell into the trap and the glycerol prevented ethanol evaporation.
To set the traps, holes were dug into the soil with a hand trowel and each trap was placed so that the top lip was flush with the surrounding soil level. Each set of pitfall traps
consisted of five individual traps placed at two metre intervals in a linear pattern. Five sets of five traps were set in each of the 11 forests. A total of 55 trap sets (275 individual traps) were used during this study. Because road and forest accessibility was dependent upon the weather, all traps could not be collected at the exact same interval. However, all traps were collected after five to seven days.
After five to seven days, the contents of each trap set were combined and treated as one sample unit. Individual traps in the same set were combined because they were not independent from one another due to the short distance between traps (two metres).
Specimens were then sorted, identified as far as possible (see Section 2.4.6) and placed in glass tubes with 70% ethanol. The number of individuals in each taxon was counted for each set of pitfall traps. All animals found in the traps were retained, identified as far as possible and ultimately were lodged in museum collections for further study. All of these data, including target and non-target groups, were entered into a Microsoft Excel database.
Species accumulation graphs for ground wandering spiders collected in pitfall traps were drawn (see Section 3.2, Appendix 6).
2.4.4 Other sampling techniques
Attempts were made to use other sampling techniques during this study to collect additional proposed invertebrate focal groups. Vegetation was swept to sample plant wandering spiders, leaf litter and soil was collected to extract micromolluscs and pollinating flies, butterflies, moths, dragonflies and damselflies were collected during the line transects. In addition, any focal invertebrates seen in the forest outside of study sites were collected as ‘random samples.’ However, the number and diversity of individuals collected using these methods were insufficient, could not be quantified or could not be consistently identified to species level. Further, effective sampling of flying insects is weather dependent and many of these taxa are seasonal, with adults only flying for short periods. Therefore, comparisons between sites sampled at different times would be unreliable and these data were not included in the analysis of this study. However, all specimens collected were identified as far as possible and are included in the taxon list (Appendix 1) and the collection locations list (Appendix 2).
2.4.5 Specimen identification
Each target invertebrate was identified using methods unique to each group.
Millipedes: Specimens with dissected out gonopods were sent to Dr. Michelle Hamer, University of Natal, Pietermaritzburg, for identification. Distribution information was obtained from Hamer (1998).
Centipedes: Scolopendromorphs, scutigeromorphs and some lithobiomorphs were sent to Dr. Michelle Hamer, University of Natal, Pietermaritzburg, for identification. The remaining lithobiomorphs were sent to Dr. Gregory Edgecombe, Australian Museum, Sydney. No specialist was available to identify the Geophilomorphs further. Distribution information was obtained from various published works including Lawrence (1955a; 1984).
Scorpions: Only one scorpion was collected in the duration of this study. The scorpion was identified to family using Lawrence (1955b).
Web building and ground wandering spiders: Using a Wild M50 stereo microscope, J. Horn identified most spiders to family using Dippenaar-Schoeman & Jocque (1997). All spiders were then sent to Dr. Ansie Dippenaar-Schoeman, Agricultural Research Council - Plant Protection Research Institute, Pretoria, for species identification and distribution information.
Terrestrial molluscs: All molluscs were identified by Dr. Dai Herbert, Natal Museum, Pietermaritzburg. Distributions of the collected molluscs were determined using the Natal Museum Mollusc Database and various published species accounts.
Earthworms: Earthworms were identified by Dr. Danuta Plisko, Natal Museum, Pietermaritzburg. The distribution of each species was determined using a variety of publications including Plisko (1997) and Pickford (1937) and from the Natal Museum Earthworm Database.
Terrestrial amphipods: There was only one species of amphipod present within the study area, Talitriator eastwoodae Metheun, 1913. This was confirmed using Griffiths’ (1999) description of the species.
Non-target groups collected in pitfall traps: The many non-target invertebrates collected in pitfall traps were identified by J. Horn to the most specific level
possible. Insects were sorted to family or subfamily using Scholtz and Holm (1985). Non-target arachnids were sorted to order.
Other non-target invertebrates: Fly families Bombyliidae, Acroceridae, Asilidae and Syrphidae were sent to Dr. David Barraclough, Natal Museum, Pietermaritzburg, for further identification. Dr. Werner Barkemeyer, Naturwissenschaftliches Museum, Flensburg, Germany, also assisted in the syrphid identification. Ants were identified by Dr. Hamish Robertson, South African Museum, Cape Town. Butterflies and moths were identified by J. Horn using Pringle et al. (1994) and Pinhey (1962; 1975).
All specimens were lodged in appropriate museums for further future verification and study.
CHAPTER 3
INVERTEBRATE SPECIES DIVERSITY OF LIMPOPO PROVINCE FORESTS