Abstract:
The inclusion of spiders in conservation planning initiatives is confounded by several factors. Surrogates
could facilitate their incorporation. In this paper we investigate the performance of a number of surrogate
measures, such as higher taxa (genus, family), cross-taxon surrogates that are subsets of the spider
assemblages (certain spider families) or non-overlapping groups (woody vegetation and birds), and the
use of morphospecies. Birds and woody vegetation were included because they often form the focus of
conservation planning initiatives. We assessed the surrogate measures based on their predictive power
for species richness and extent to which conservation planning that maximizes representation of the surrogate
is effective in representing spider diversity. A measure for the latter is the Species Accumulation
Index (SAI). Generic richness as a higher taxon surrogate and the combined richness of the families Thomisidae
and Salticidae were the best estimators of total species richness. Based on the surrogacy efficiency
criterion, genera and the family Salticidae had species accumulation indices (SAIs) that were significantly
larger than 95% confidence intervals of a random curve, while woody vegetation and birds turned out to
be poor surrogates for spider diversity. The use of morphospecies as estimators is cautiously supported
(adjusted R2 = 0.85, for species richness, SAI = 0.73). The surrogates identified here provide a viable alternative
to whole assemblage analysis but should be used with caution. The use of genera is confounded by
unstable taxonomy and the difficulty of identifying specimens up to genus level. Geographic location and
varying sampling effort between surveys did not have an effect on the surrogate performance of the two
spider families, viz. Salticidae and Thomisidae. The former family has seen a flood of recent systematic
work, whereas the latter’s taxonomy is fairly well developed. These two families comprise ca. 20% of spider
species observed in the Savanna Biome of South Africa and could provide a viable handle on spider
diversity in this region.
