|dc.description.abstract||Aim: Climate-modelling exercises have demonstrated that the Cape Floristic Region is highly sensitive to climate change and will apparently lose much of its
northern limits over the next few decades. Because there is little monitoring of diversity in this area, ant assemblage structure was investigated within the main
vegetation types in the Greater Cederberg Biodiversity Corridor. In particular, we sought to determine how ant assemblage structure differs between the main
vegetation types, how restricted ants – and in particular the major
myrmecochores – are to the major vegetation types, and which environmental variables might underlie differences in the ant assemblages and in the specificity
of species to particular areas.
Location: Northern Cape Floristic Region, Western Cape, South Africa.
Methods: Sampling was undertaken during October 2002 and March 2003
across an altitudinal gradient ranging from sea level (Lambert’s Bay) to c. 2000 m
a.s.l. (Sneeukop, Cederberg) and down again to 500 m a.s.l. (Wupperthal) in the
Western Cape, South Africa. Pitfall traps were used to sample ants at 17 altitudinal bands, stretching over three vegetation types (Strandveld, Mountain
Fynbos and Succulent Karoo). Biotic and abiotic environmental variables were collected at each sampling site. Generalized linear models were used to determine
the relationships between species richness, density, abundance and the abundance
of the major myrmecochores, and the environmental variables. Redundancy analysis was used to determine the relationship between ant assemblage structure
and the environmental variables. The Indicator Value Method was used to identify characteristic ant species for each vegetation type and altitudinal site.
Results: Temperature explained significant proportions of the variation in
species density and abundance, and, together with area and several vegetation
variables, contributed significantly to the separation of the assemblages in the
major vegetation types and biomes. Four major myrmecochores were identified
[Anoplolepis sp. (cf. custodiens), Anoplolepis sp. (cf. steinergroeveri), Camponotus
niveosetosus, Tetramorium quadrispinosum]. The abundances of the two
Anoplolepis species were related to vegetation variables, while the abundance of
the other two species showed opposite relationships with temperature variables.
Fourteen ant species were characteristic of certain vegetation types and altitudes.
Several of these species contributed to the differences between the assemblages.
Main conclusions: There are likely to be substantial and complex changes to ant assemblages as climates change in the northern Cape Floristic Region.
Moreover, the importance of ants for ecosystem functioning suggests that these
responses are not only likely to be a response solely to vegetation changes, but
might also precipitate vegetation changes. The changes that are predicted to take
place in the next 50 years in the Cape Floristic Region could be substantially
exacerbated by such synergistic effects, which have major implications for long-term conservation plans. Ongoing monitoring of this transect will reveal the
nature and pace of the change as it unfolds.||en_ZA