Falko T. Buschke

Functional Feeding Groups as a Taxonomic Surrogate for a Grassland Arthropod Assemblage

ABSTRACT Considering the precarious conservation status of the grassland biome in South Africa, effective assessment and monitoring is imperative. The potential use of terrestrial arthropods in ecological assessment has received much attention, but little headway has been made in formulating standardised bioassessment protocols. A suggested reason for this lack of progress is the high diversity of terrestrial arthropods and the high taxonomic expertise required. Sampling was carried out across 12 months in the Bloemfontein Dry Grassland vegetation type and the potential of using functional feeding groups (FFG) as taxonomic surrogates for family level arthropods was investigated. An F-test associated with an analysis of covariance (ANCOVA) found a significant correlation between FFG and families for measures of richness, Shannon and Simpson diversity. Accumulation curves indicated that a higher proportion of FFG than families could be assessed with the same sampling intensity. Both families and FFG best fitted the stochastic normal and geometric series relative abundance distribution models, implying that there is no distinction between the taxonomic units with regard to abundance distributions. The reality remains that information does become lost when using surrogacy, so there will continue to be a need for specialist ecological proficiency for the highest risk assessments. It was concluded that for rapid monitoring and snap-shot assessments, FFG could be used as a valuable and reliable taxonomic surrogate.

Invertebrates or Iron: Does Large-Scale Opencast Mining Impact Invertebrate Diversity In Ephemeral Wetlands?

Disturbance has been offered as an explanatory mechanism in structuring the variation of species across a landscape. In this study, we investigated the effect of the impact by Kolomela Iron Mine on the variation of species occurring in temporary pans. Using a novel null model approach to partitioning two sets of data (from before and after the establishment of the mine) into independent alpha (&agr;) and beta (&bgr;) components, we determined that the mining practices have had little to no impact on the invertebrate diversity. This suggests that these communities were more resilient than previously assumed. The results were, however, confounded by the fact that the resting eggs of pan inhabitants could remain dormant in the sediment for decades; suggesting that observed diversity patterns were possibly remnants of unknown past events. To ensure that the effects of present-day impacts are assessed, continuous monitoring is recommended. Similarly, the preservation of conservation areas and a landscape wide management system were proposed to ensure that large-scale ecological process are not jeopardized by the gradual fragmentation of the pan metacommunity.

The conservation status of African vertebrates is unrelated to environmental and spatial patterns in their geographic ranges

Statistical predictions of the impact of climate change on biodiversity assume that the environmental and spatial characteristics of contemporary species’ distributions reflect the conditions needed for their continued and prolonged existence. Here we explore this assumption by testing whether a species’ threatened status is associated with the amount of variation in its distribution range attributable to environmental and spatial patterns. Using a variation partitioning approach, we decomposed variation in the distribution ranges of 4423 vertebrate species in sub-Saharan Africa into components attributable exclusively to environmental variables (E|S), exclusively to spatial variables (S|E) or to the collinearity between environmental and spatial variables (E∩S). We found that species’ threatened status was unrelated to E|S, S|E or E∩S variation components, but that unexplained variation was higher for species threatened with extinction. This suggests that spatio-environmental patterns in species’ ranges likely underestimate the overall extinction threat caused by climate change. We also found clear geographic patterns in the strength of E|S, S|E or E∩S that differed amongst biogeographical regions, but no component was over- or underrepresented in the present-day protected area network. While there may be benefits to tailoring protected area expansion to differences between biogeographical regions, this should aim to incorporate species-specific information wherever possible.

Intra-annual variation of arthropod-plant interactions and arthropod trophic structure in an endangered grassland in the Free State province, South Africa

Arthropods are valuable biological indicators owing to strong relationships with primary producers. The supposition that arthropod-plant interactions are constant over seasons was tested using Mantel tests on correlations between these groups. A total of 78 plant species and 108 arthropod families were sampled monthly from the endangered Bloemfontein Dry Grassland at the Free State National Botanical Gardens between April 2009 and March 2010. Interaction strengths between plants and arthropods varied within a calendar year; being strongest in winter months (July and August), initiation of the growth season (November) and peak growth season (February and March). It was hypothesised that variation was caused by changing primary productivity. The trophic composition of the arthropod community supported this hypothesis as the ratio between primary consumers (herbivores) and secondary consumers (predators and parasitoids) showed patterns that coincided with periods of strong arthropod-plant interactions. Patterns were explained by multiple theories linking plant and arthropod diversity. It was concluded that arthropod assemblages are closely linked to primary producers, the abiotic environment and top-down trophic forces at different times of the year. Future arthropod-based studies should be performed with clear objectives and seasonal benchmark conditions to overcome these variations.