RESULTS

A total of 4832 individuals from 268 species, 147 genera and 37 families were sampled in Makalali Private Game Reserve during the study period using the four different sampling techniques. Although the sampling effort was considerable not all species have been sampled

There was a marked difference in the number of individuals and species caught by each sampling method: sweep netting (2 150 individuals and 120 species), beating (885 individuals and 125 species), active searching (l 450 individuals and 188 species) and pitfall traps (174 individuals and 56 species) (Figure 2.2). The greatest number of individuals (2 150) were sampled using the sweep net but it is interesting to note that this method does not

Whitmore -Spi~lerBiodiversity 25

sample the highest number of species. The highest numbers of species were sampled by active searching (188), followed by the beating (125). The pitfalls produced the fewest individuals and species.

There was a highly significant difference in the number of individuals sampled by different techniques, with sweeping and active searching sampling the most and pitfalls sampling the least (ANOVA: F3, I46

=

78.151,P<0.0001). There was also a highly significant difference in the number of species captured using different techniques, with sweeping and beating sampling the most and pitfalls the least (ANOVA: F3, 146

=

63.346,P<0.0001; Figure 2.2).

Very few families were captured by all four techniques. There was a highly

significant difference in the number offamilies sampled among the different techniques, with active searching sampling the greatest variety of different families (32), followed by pitfalls (19), beating (18) and sweeping (16), (ANOV^A: F3, 146

=

53.770,P<0.0001; Figure 2.3).

Again, although sweeping yields the highest number of individuals, the number of families represented is lowest. Further, although pitfall traps had the lowest numbers of species and individuals they yield a relatively large proportion of the total families sampled (52%).

However, there are no families sampled by pitfalls that were not sampled by at least one other method (Figure 2.4).

Beating yields the greatest number of unique species for any particular method (16%) while sweeping yields a very low percentage (6.25%) that are unique to this technique (Figure 2.4).

2.4.1 Sampling for all species and all microhabitats

In most sampling periods the species accumulation curves indicate that a saturation level has been reached (Appendix 2.1). The same patterns are seen when sampling methods are considered separately (Appendix 2.2). However, there is some indication that the full compliment of species have not yet been found (new species are still being added) this is because there are new habitats, e.g. riverine, that would contribute towards increasing the species list. Likewise by adding a new method, e.g.fogging, the species list would increase.

2.4.2 Cost effectiveness and efficiency EfFectiveness

Juveniles comprised 85% of all spiders sampled and the remaining 25% were made up of adult males and 01'females (Table 2.1). Adults are important taxonomic ally, as the

characteristics of mature specimens are often required for species level identifications. The pitfalls sampled the highest number of adults (28.5%),making them the most effecti ve

Whitmore - SpiderBiodiverslty 26

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Figure 2.2: The effect of sampling technique on the number of individuals (D) and species (0) sampled at Makalali Private Game Reserve. The mean and 95% confidence limits are presented.

Whitmore - Spider Biodiversity 27

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Figure 2.3: The effect of different sampling techniques on the number of families.The mean and 95% confidence intervals are presented. N= number of different families sampled with each technique.

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Whitmore -SpiderBiodlversity 28

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Figure 2.4: The effectof sampling technique on the percentage of shared and unique spider families obtained from Makalali Private Game Reserve.

Whitmore - SpiderBiodiversity 29

method,followed by active searching (13.12%),beating(10.15%)and sweeping (7.21%).

Effici ency

Sweeping requires more time investment thanalternativetechniques that samples spiders alone, e.g.activesearching or beating.Approximately 20 minutes were needed to complete the sweeping from each sitethus requiring a totalof 13.33person hours for the entire study (excludingthe timerequired to sort).

It tookapprox imatel y 1Yzhours to beat eight trees in asite, totalling 60person hours required to complete40 sites (excluding the time required for sortingandidentifying

specimens).Considerablyless effort is required for sorting of beating samples than sweeping as there areno other invertebratesorplantmaterial thatfirst need to be separated

ouLApproximately80 person hours were requiredto actively samplethe 40 sitesin this study (excludingsettingup quadratsand sorting of specimens) and approximately21 hours were required for inserting and collecting of the pitfalls at each sampling period.The total number of person hours required for pitfalls for this study was 64 hours (excluding time required for sorting). Again, the sorting of the contents from thepitfallsrequire moreeffort thanfor a technique that samples spiders alone, e.g.beating or active searching.

The number of person hoursrequired to sample 40 sites is summarised in Table 2.1.

The efficiency of the differentmethods (expressed as the numberof species captured per hour) was thencalculated by dividing the number of species sampled by each method by the number of person hours required to complete the 40 sites.Sweeping was themost efficient method followed by active searching, beating and pitfalls.

Table 2.1: Totalnumberofhours requiredto sample 40 sites using thedifferentsampling techniques and the efficiency of each method.

Method Sweeping Beating Active searching Pitfalls

EFFECTIVENESS

.Number of individuals 2150 885 1450 174

Number of adults 155(7%) 90( 10%) 191(13%) 51(28%)

Numberof juveniles 1989(93%) 797(90%) 1265(87%) 128(72%)

Numberof species 120 125 188 56

Number of unique species! 6% 17% 16% 0%

Numberof families 16 18 32 19

EFFICIENCY

Time(h) 13.33 60 80 64

Speciesper hour 9.00 2.08 2.35 0.88

'T he unique species are a percentage of thetotal spiders captured by a particularmethod.

Whitmore-SpiderBiodiversity 30

In orderto decide which method was best,the sampling requirements, repeatability and standardisation, number of habitats sampled,efficiency and effectivenessand biases, needed to beexamined more carefully. To determine which methods were most efficient and cost effective it was necessary to rank the various components.The data presented in Table2.2 are based on subjective estimates for the different methods and are rated for their efficiency and effectiveness.The efficiency assessed the species sampled per hour, expertise required, which refers to the levelof difficultyofexecuting the task, therepeatability , which refers to the ease at which other researches can follow the same protocols and the cost of the equipmentneeded to undertake thetask.

Ranking the components from Table 2.1assessed the effectiveness of the techniques.

A valueof I represents the best or most and a value of 4 represents the least or worst. The lowest overall scorerepresentsthe bestmethod.Based these results active searching was the best methods for samplingspiders followed by beating and sweeping and lastly pitfalls. A combination of sweeping, active and beating was the best.

Table 2.2 :Rank values for the efficiency andeffectiveness of different sampling techniques (where I =the highest or most efficient and 4= the lowest or least efficient).

Method Sweeping Beating Active Pitfalls

EFFECTIVENESS

Number of individuals I 3 2 4

Number of species 3 2 I 4

Numberof unique species 3 I 2 4

Num ber of families 4 3 I 2

Total adults 4 3 2 I

Totaljuveniles I 2 3 4

EFFICIENCY

Speciesper hour I 3 2 4

Repeatability' 2 3 4 I

E . ¹

xpertise" 2 3 4 I

Cost of equipment 2 3 I 4

Easeofsorting^J 4 I 2 3

Total 27 27 24 32

IRepeatability

=

the ease atwhichother researches can follow the same protocols

1Expertise

=

the level of difficulty of executing the task

JE r '

- ~ase0 -sorting

=

timeinvestmentrequired for sortingthesamples 2.4.3 Composition of species sampled with the different methods

There wasa clear difference between the spider assemblages sampledandthe technique used (Figure 2.5) .Additionally,the samplingtechniques tend to be biased towards certain spider assemblages.

Whitmore- Spider Biodiversity 31

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Figure2.5: The influence of differentsampling techniques on the spiderfunctional group compositionat MakalaliPrivate Game Reserve. N= total number of species sampledwith a particulartechnique.

Whitmore - Spider Biodiversity 32

Sweeping, which targeted spiders in the field layer, collected a high proportion of plant and web-dwelling individuals but very few ground-dwelling individuals. Beating, which targeted the tree layer, also sampled a high proportion of plant and web-dwellers but very few ground-dwellers (Figure 2.5). The following families were abundant in the field and tree layers: orb-web weavers (Araneidae), jumping spiders (Salticidae), crab spiders (Thomisidae), lynx spiders (Oxyopidae) and sac spiders (Miturgidae).

Active searching, targeting the ground, field and tree layer, sampled individuals from all three functional groups in almost equal proportions (Figure 2.5). This method sampled a species of barychelid, a family not previously thought to occur in South Africa (Appendix 3.3).

The pitfall traps sampled mainly ground-dwellers and also a small proportion of plant-dwellers (Figure 2.5). Ground-dwelling individuals that were abundant included flat- bellied ground spiders (Gnaphosidae), the wolf spiders (Lycosidae) and baboon spiders (Theraphosidae).

The community composition of spiders changed significantly with time. There was a significant interaction between different spider functional group and sampling period (El.I₁₉

=

5.791, P<0.000l)with plant-dwellers and web builders showing similar responses over time while the ground wanderers decrease considerably in the December sampling period. The drop off of ground wanderers in the December period could be a consequence of the flooding of many pitfalls and hence the lower trap catches (Figure 2.6).

A short description of the general biology and appearance of the families sampled in Makalali Private Game Reserve is presented in Appendix 3.2 and also on the CD-ROM enclosed.

Whitmore- Spider Biodiversity 33

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Figure 2.6: The effect of sampling period on the spiderguilds (where0 =ground wanderers, 0 = plant wanderers and b.

=

web builders). The mean and 95% confidence limits are presented. Nis the number of sites withinthe sampling period. Note the low numberof ground wanderers

captured in December probably reflects floodingof pitfalls rather than reduced presence within the community.

Whitmore - Spider Biodiversity 34

Dalam dokumen Biodiversity of spiders (Araneae) in a savanna ecosystem and the processes that influence their distribution. (Halaman 32-42)

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