Biodiversity of spiders (Araneae) at Makalali Private Game Reserve
4.4 DISCUSSION
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explore this further.
4.4.2 Higher taxon method as surrogates for species diversity
The only properties required of higher taxa for estimating wholescale biodiversity are that their richness distribution can be predicted by the distribution of species richness and that the information to map their distribution is more readily acquired than for species (Williams &
Gaston 1994).
Williams& Gaston 1994; Oliver& Beattie 1996 and Balmford et al. 1996b have shown a significant positive correlation between higher taxa and species richness. It could be inferred from these results that by surveying only a higher level more time is saved (Balmford et al. I996a). Other scientists (Oliver& Beattie 1993; Skerl & Gillispie 1999) have shown that the method is cost effective and that it is possible to try and avoid misidentifications by doing a genus- or family-level analysis (Norris 1999). The results from this study confirm the
work of others and a significant positive correlation between the species and families as well as the species and genera was found. From these results we may be tempted to infer that surveys at the level of genus or family are reliable as a surrogate measures for species richness.
This is unfortunately not the case. The answers obtained from different identification levels of identification give very different results. The data obtained from biodiversity surveys needs to be applied to real situations. An area may show a strong family: species correlation yet significant changes or impacts on biodiversity may only be detected at lower levels (genera or species). The example used here shows that significant differences between sampling periods are only detected at the level of species and genus but not at the level of family.Thus from a biological perspective we would need to use at least the level of genus and not family. These results are supported by Prance (1994) who recommends that if higher- taxon surveys are to be used, then genus- and not family-level identification be used.
For some groups, e.g. plants it may be possible to use higher taxon level
identifications and the method works very well but for spiders specialist taxonomic expertise are required for identification even to the level of genus. The genera and species descriptions for many of the 5 500 spiders in southern Africa is simply not readily available. Therefore, for spiders, species level identifications may as well be done as the time and effort required for identification to the level of genus would be similar to that required for species
identifications.
Gaston & Blackburn (1995) point out that the strength of the correlation between numbers of species and higher taxa is likely to decline rapidly towards progressively higher taxonomic levels (e.g. from genera to tribes to families;Williams& Gaston 1994). The strength of the correlation coefficients was greater for number of genera (R2==0.736) than for
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numbers of families (R2
=
0.505). In addition, the more species a given higher taxon represents the poorer an indicator of species richness that higher taxon becomes (Gaston&Blackburn 1995). A consequence of this is that there is a trade off between time saved by higher taxon surveys and the quality of information obtained from those surveys (Balmford et al. 1996a).
Despite a positive correlation between higher-taxa and species richness,Balmford et al. (I996a) have shown that the precision with which absolute species richness in reserves could be predicted from higher-taxon richness was surprisingly low, particularly for rich sites where surveying higher taxa rather than species would save the most time. Furthermore, the
.work of Van Jaarsveld et al. (1998) does not support the use of surrogate measures for the
selection of reserves. Their results suggest the use of higher taxa as surrogates for species cornplementarityhold little promise at a scale relevant for practical conservation planning (Van Jaarsveld et al. 1998).
Therefore, although the number of higher-taxa present in an area may be easily and rapidly assessed (Williamset al. 1994; Harper& Hawksworth 1994), the results do not convey information about the total number of species which these higher taxa represent (Bulmford et al. 1996a). On this basis Prance (1994) argues that when assessing biodiversity for conservation planning we need to focus our attention on species.
Not knowing the names of the species in a community severely limits the ability to compare different systems and to understand the biology and ecology of such organisms by .comparing them to their better-known relatives (D.S. National Report, 1995). Species data is
essential for the understanding of the ecosystem and to allow for adequate management (Goldstein 1999). Many conservationists seek Sh0l1 cuts to the interpretation of data believed .to represent key aspects of the ecosystem. Some shortcuts have sacrificed their scientific
underpinnings, to the extent that basic scientific considerations are bypassed (Goldstein 1999).Selecting conservation areas from genus- or family-level data cannot result in efficient species level conservation (Van Jaarsveld et al. 1998). While useful,the methods may
downplaythe role of the species and population specific requirements (Goldstein 1999).
4.4.3 Morphospecies identifiedbynon-specialists as surrogates for species diversity
In this study measures of species richness were influenced by the level of experience of individuals conducting the sorting of material. Inexperienced undergraduate students
overestimated species richness significantly when compared to more experienced participants.
Initially students were very cautious and whenever in doubt chose to separate species.
Other arthropods were also included in the samples (e.g.ticks, mites and some insects). When sorting was done in the laboratory as opposed to the field students noticed that some species
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that were initially thought to be different were actually the same (personal observation).
Despite noticing their mistake there was still a tendency for students to keep samples separate if there was any doubt, resulting in an overestimation of species richness. Oliver& Beattie (1996) have shown that morphospecies generally provide overestimation and genus and family richness tend to underestimate actual species richness when richness is high and overestimate when richness is low (Gaston& Blackburn 1995).
In March of 1999 I considered myself a non-specialistas I had little previous
experience in sorting and identifying spiders. There is clearly a large difference in the degree of overestimation made between the March and November samples.Norris (1999)
acknowledges that mistakes are common when non-specialists identify specimens and the misidentifications are due to a lack of experience. In November far fewer mistakes were made indicating an improvement in the identification process. This was only after I had completed a week-long spider identification course with Dr A.S. Dippenaar-Schoeman and sorted many spiders.
The improvement may also be a result of having a reference collection, identifiedto the level of species, from the March sampling period with which I could compare the November specimens. The reference collection proved very valuable for this study. The amount of time required from experts was considerably less for the November and December samples. Attempts were made to identify spiders to level of species by comparing new specimens to the reference collection. The identifications were then verified by an expert.
Oliver& Beattie (1993) indicate that estimates will improve as biodiversity technicians gain experience with the taxa they are sorting.
The students, however, did not show an improvement with time when sorting in the field and consistently overestimated species. This highlights the fact that non-specialists can not be expected to do good quality work without first having some training in the groups that they are dealing with. In addition, the students made more overestimations for the sweep samples than for the active search samples. This could be attributed to that fact that twice as many spiders were captured by the sweeps than the active searching and as the volume of spiders increased so too did the level of overestimation. This highlights the care needed when selecting biodiversity technicians so that they have the appropriate level of qualification for the job.Some level of training is essential before non-specialists can be used beneficially to facilitate the process. The students used in this study represent an extreme case and are not equivalent to biodiversity technicians and it is not recommended that people at this level be used as biodiversity technicians.
These results were contrary to some other studies. Oliver & Beattie (1996) and Oilver
& Beattie (1993) showed that morphospecies estimates made by biodiversity technicians may be sufficiently close to formal taxonomic estimates of species richness to be useful for the
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rapid assessmentof biodiversity.This contradiction may be because for their study, only mature spider specimens were used which could account for the high degree of agreement between non-specialist and specialist estimates.They acknowledge that including other life stages(e.g. juveniles) in rapid biodiversity assessment may lead to large errors (Oliver&
Beattie 1993).The data also suggests that the use of morphospecies require a minimum of unambiguous morphological features that arelatively untrained individual can easily and quickly utilise.
While the morphospecies method is appealing and there are studies supporting its use, some authors are not convinced about the general applicabilityof the data.Goldstein(1996) expresses concern about the morphospecies approach of Oliver& Beattie (1993) ancl the usefulness of the data forsetting conservation priorities and establishing protocols for biological monitoring. Traditionally, the role of the non-specialists (parataxonomists or bioclivers itytechnicians) has been to help with the preliminarysorting of samples prior to their exam ination by specialists. This cuts down on the amount of time required by the specialist in routine general sorting, allowing more time for accurate determinations (Goldstein 1996). However, in some parts of the world, non-specialists are being used to collect and act as a substitute for, rather than a supplement to, the examination of organisms by specialists(Goldstein 1996). Any faulty estimation of the numbers and identities of species mayhavefar reaching consequences and impede,rather than enhance, understanding,so that great careis needed to ensure the quality of the results produced (New 1995). The assumption that non-special istpersonnel can replacespecialist taxonomic expertise at a fraction of the cost is patently false. Biodiversity technicians ,however, can play a majorrole in extending the eff iciency of the limited number of taxonomists by effective sorting and preparation of speci me ns from bulk samples,and thus rendering specialists' time more effective (New 1995).
Oliver and Beattie (1993) use the approach that species richness should be the primarycriterion on which both the prioritisation of natural areas for conservation and monitoring of naturalcommunities should be based (Goldstein 1996).However, those areas that are species-rich often do not support many species that are actually of conservation concern .Hence, surrogate measures of species richness will likely overlook areassupporting rare.endemic or threatened organisms (Goldstein 1996).
McGeoch (1998) cautions that the use of morphospecies should be undertaken with greatcare asproblems may arise when different study sites are to be compared.The morphospecies may not be assigned consistently during different surveys. This ultimately necessitatesspecies-level taxonomy or a standardised method of classifying species.
McGeoch (1998) also indicates that the quality of the data on which bioindicatorpredictions and conservation are made is fundamental to their accuracy.Slotow& Hamer (2000)also discourage the use of morphospecies,especially for conservation planning.
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Melbourne (1997) feels that rapid assessment of species assemblages may not be possible because,as illustrated by Hinkley& New (1997), new species are discovered with each new sampling period and 75% of the species present were only obtained after 3 to 5 sampling periods.This pattern was certainly reflected in this study.With each new sampling trip new species were added to the species checklist. This is not very encouraging if very rapid assessments want to be carried out since continued sampling or long-term studies would be necessary to sampling all species in the environment. Therefore, despite the widespread interests in promoting rapid biodiversity assessments,there are clear indications that this may not always be berieficial (Melbourne 1997).