Ecological factors influencing the survival of the Brenton Blue butterfly Orachrysops niobe (Trimen) (Lepidoptera: Lycaenidae)
The Brenton Blue butterfly, Orachrysops niobe (Trimen) is currently only known to be extant at one locality in the southern Cape (the Brenton Blue Butterfly Reserve = BBBR), and currently globally Red Listed as "Critically Endangered". This research investigates the life history and ecological interactions of o. niobe and recommends management techniques for the BBBR. Adult nectar sources and female oviposition behaviour are described. The first two larval instars feed on the leaflets of the host plant Indigofera erecta Thunb., and the 3rd and 4th instar larvae feed on this plant's woody rootstock, attended by ants Camponotus baynei Arnold. Cannibalism takes place in the early larval stages. Adults emerge from late October - early December, from late January to early March, and occasionally there is a third brood in April. Morphological and behavioural features of the larvae are described, and larval growth patterns are compared to other polyommatines. The nature of the myrmecophilous behaviour is assessed and the phylogenetic relationships between Orachrysops, Euchrysops, Lepidochrysops, and other polyommatine genera are discussed. Ant assemblages at the BBBR are described from pitfall trap sampling and field observations of interactions between O. niobe larvae and ants. The ant assemblages at the BBBR, Nature's Valley Fynbos Reserve (NVFR) and Uitzicht 216/ 40 are compared. The potential impact of the Argentine ant at the BBBR is discussed. Adult and egg counts are used to study the population dynamics of O. niobe, leading to an estimate of the adult butterfly population and its fluctuations. A population dynamics model is constructed, and several factors impacting fecundity and mortality are assessed. Population studies on other polyommatines are compared and discussed. The morphology, reproductive biology and autoecology of the papilionoid legume I. erecta are described. An explanation is offered why the larvae of O. niobe are monophagous on this plant. Microhabitat variations cause changes in its vegetative morphology and this further explains the restricted range of O. niobe. The population dynamics of I. erecta is investigated and the effects of biotic and abiotic factors (including fire) assessed. Braun Blanquet methodology is used to sample and classify the vegetation communities at the BBBR. Ordination techniques are used to confirm the classification and to diagnose for environmental gradients. Hypotheses are generated about the ecological processes functioning at the site, and the environmental niche occupied by I. erecta. Correlations between the occurrence xxii of vegetation types and other plant species and I. erecta are sought and a strong association with Pterocelastrus tricuspidatus is demonstrated. Three study sites are described and the ecological history of the region is reconstructed. Ecosystems are no longer fully functional because natural fire regimes and megaherbivores are absent. It is suggested that O. niobe currently inhabits an interglacial refugium under stress from the current global warming trend. The remaining suitable habitat is threatened by coastal property development and environmental degradation. An increased population of o. niobe at the BBBR, and establishment of new populations is essential to avoid extinction. Management techniques are evaluated and a management strategy for the BBBR is proposed.
- ETD@PUK