Distribution Patterns of Epigaeic Invertebrates in an Afromontane Forest-Grassland Mosaic in Kwazulu-Natal, South Africa

DISTRIBUTION PATTERNS OF EPIGAEIC INVERTEBRATES IN AN AFROMONTANE FOREST-GRASSLAND MOSAIC IN KWAZULU-NATAL, SOUTH AFRICA by Johan Kotze Submitted in partial fulfilment ofthe requirements ofthe degree of Doctor ofPhilosophy in the School ofBotany and Zoology University ofNatal, Pietermaritzburg, South Africa February 2000 Distribution patterns of epigaeic invertebrates in an Afromontane forest-grassland mosaic in KwaZulu-Natal, South Africa by Johan Kotze This thesis is based on the following articles which will be referred to in the text by their Roman numerals: I Kotze, D.J. and Samways, M.J. 1999. Support for the multi-taxa approach in biodiversity assessment, as shown by epigaeic invertebrates in an Afromontane forest archipelago. Journal o/Insect Conservation 3, 125-143. II Kotze, D.l and Samways, MJ. 1999. Invertebrate diversity at forest-grassland ecotones in an Afromontane forest landscape in South Africa. - Submitted III Kotze, D.J. and Samways, M.J. 1999. Inter-seasonal consistency in spatial pattern of invertebrates across a forest patch-grassland matrix ecotone in KwaZulu-Natal, South Africa. - Submitted IV Kotze, D.J. and Samways, M.J. 1999. Invertebrate conservation at the interface between the grassland matrix and natural Afromontane forest fragments. Biodiversity and Conservation 8, 1339-1363. In my PhD thesis I have studied the abundance and species richness of various epigaeic invertebrates (in particular terrestrial amphipods, carabids and ants) in Afromontane forests and grasslands and at the interface between these two systems. The field work for the thesis was done in 1993-1996. PREFACE This study and preparations for this thesis were done while the author was a full-time student in the School of Botany and Zoology, University of Natal, South Africa, from July 1993 to November 1997, with Professor M.J. Samways as supervisor. This thesis, unless specifically referred to in the text, is my own original work, and has not been submitted in any other form to another University. 9 February 2000 School ofBotany and Zoology University ofNatal Pietermaritzburg South Africa 11 General abstract effects quite often occur across anthropogenically-created habitat junctions, but it is not clear whether they do across Considered key landscape elements, ecotones natural ones. play an important role in landscape ecology. In To test this hypothesis, the following heavily fragmented, or heterogeneous secondary hypotheses were evaluated. Firstly, landscapes, ecotones become a major, even often a single invertebrate taxon is used for dominant, feature. Yet, there are relatively few assessmg changing landscape patterns. studies investigating communities of However, recent work has suggested that invertebrates associated with ecotones, patterns and responses vary widely between especially across natural boundaries. taxa, and that management programmes based Furthermore, most analyses of habitat loss do on the knowledge of a single taxon would not not consider the characteristics of the areas necessarily predict or safeguard that of others. surrounding remaining habitat, the matrix. This Therefore, in chapter I, the hypothesis whether thesis attempts to partially fill the gap. a single taxon could be used in biodiversity Afromontane forest-grassland studies, or alternatively, whether it is better to ecotones are characteristically sharp (usually a select an array of taxa, was tested. Several few metres), are mainly fire-maintained, and invertebrate taxa were selected to investigate have been in existence for, perhaps, millions of this. These included terrestrial amphipods, years. Therefore they provide a good spiders, carabids, staphylinids and ants. opportunity to study ecotone, forest patch and Indeed, results showed that species diversities grassland matrix characteristics together, and and assemblage-compositions of epigaeic the associated species assemblages. In short, I spiders, carabids, staphylinids and ants were investigated the diversity and distribution significantly different m different-sized patterns of eplgaelc invertebrates across Afromontane forest patches. Only carabids and ecotones between the natural and isolated staphylinids correlated positively with each patches of Afromontane forests and the other in terms of numbers ofspecies. The other surrounding natural grassland matrix, in the taxa showed only weak positive, or negative, province ofKwaZulu-Natal, South Africa. correlations in their species richness. Results In particular, the following primary supported the multi-taxa approach m hypothesis was evaluated; do edge effects, in conservation studies, even among groups terms of elevated abundance and species sharing a common habitat stratum. richness, and in terms of abrupt, significant Secondly, organismal diversity usually changes .in environmental conditions, occur increases at disturbed habitat edges. This across near-natural ecotones. These edge phenomenon is commonly referred to as the ll1 biological edge effect. This pattern, however, patterns across an ecotone change from one is not universal and a number of authors have season to the next (chapter ill). For example, it shown evidence contradicting this hypothesis. is expected that certain winter-active species In chapter H amphipods, ground beetles and might disperse from one location along the ants were collected to test the biological edge gradient to another, perhaps to escape effect hypothesis. In addition, a number of predators, or find winter-refugia. This would, abiotic factors were measured across these in turn, change the pattern ofdistribution ofthe forest-grassland boundaries in an attempt to selected taxa across these ecotones. relate the biotic with the abiotic. Little Surprisingly, the general pattern ofdistribution evidence was found to support the classical across these ecotones changed little. However, edge-effect hypothesis (elevated species there were significant differences between richness at the ecotone). In fact, carabid summer, spring, winter and autumn catch, and abundance and species richness was high in species identities changed from one season to forests, decreasing gradually through the the next. For example, carabid abundance and ecotone to a low in grasslands. In contrast, ant species richness was higher in the forest, species richness increased significantly from a compared to in the grassland, while ants were low in forests, increasing gradually through the species richer in the grassland, compared to in ecotone, to a high in grasslands. Certain the forest. These patterns were consistent from species did, however, show a significant one season to the next. Again, as was found in increase in abundance at the ecotone, such as chapter H, T. africana was significantly more Talistroides africana, a terrestrial amphipod, abundant at the ecotone, compared to either and Tetramorium avium, a seed-predatory ant. forest or grassland interiors, in all seasons Afromontane forest-grassland ecotones are throughout the year. To summarise, amphipods natural and are not the result of anthropogenic favoured the ecotone environment, carabids clear-cut fragmentation. They also lacked any the forests and ants the grasslands, throughout great changes ill micro-environmental the year. conditions. I hypothesise that edge effects are Finally, scientists have recently of less importance at more naturally become aware ofthe importance of the matrix maintained habitat boundaries even if these surrounding habitat patches, in the survival and boundaries are sharp. occurrence of organisms in the habitat patch. I Thirdly, climatic variation has a major tested whether the quality of the matrix, as a impact on invertebrate communities. The function of human disturbance, has an Afromontane landscape experiences hot and influence on invertebrate occurrence and wet summers, and cool and dry winters. I distribution patterns across Afromontane hypothesised that invertebrate distribution forest-grassland boundaries. Redgrass IV (Themeda triandra Forssk.) dominated recommendations. Of course, not all taxa can Afromontane grasslands are, and have been be considered, and the selection of appropriate experiencing varying degrees of anthropogenic taxa still poses a problem, but a set oftaxa that disturbance. Consequently, ecotones vary from are considerably different biologically is a being very abrupt (heavy disturbance in the good start. Native Afromontane forest matrix) to gradual (little disturbance in the grassland mosaics are in urgent need of matrix), although still sharp compared to most conservation, as much of this habitat is subject ecotones elsewhere. Level of grassland to heavy anthropogenic disturbance such as disturbance influenced amphipod, carabid and human settlement, forestry, cattle grazmg, ant assemblage-structure across Afromontane agriculture, and frequent, out of season, fires. ecotones (chapter IV). Results support the Unfortunately only 2% of this biome is hypothesis that the dynamics of remnant areas protected in South Africa. Furthermore, matrix are influenced by factors arising in the quality is important because it determines the surrounding landscape. In particular, carabid survival rate of propagules moving between assemblage-composition changed highly remnant patches of habitat, and therefore the significantly from undisturbed to disturbed success rate of such movements. Private land- 7 \ sites (this taxon was mainly captured from owners own most of this grassland area in the ., forests). Furthermore, only a single carabid

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