HABITAT CONDITIONS, POPULATION GENETICS AND NICHE PARTITIONING OF THE NAMIBIAN RESURRECTION PLANT

Abstract: Chamaegigas intrepidus is a tiny poikilohydrous member of the Linderniaceae which grows endemically in ephemeral rock pools on granite outcrops in Central Namibia. Habitat conditions are characterised by (1) frequent and fast desiccation and rehydration during the rainy summer season, (2) complete dehydration during the dry winter season of up to 11 months, (3) high solar irradiation (especially in the ultraviolet range) and high temperatures during the dry season, (4) extreme nutrient deficiencies, especially nitrogen, and (5) diurnal oscillations of pH in the pool water up to 6 units. The plants are adapted to this complex of multiple interacting stress factors via a range of anatomical, biochemical and physiological mechanisms. Furthermore, Chamaegigas populations on single inselbergs are genetically isolated, whereas gene flow between sub-populations from different pools on one inselberg is rather high. This pattern of gene flow is in accordance with the predominantly outcrossing breeding behaviour and seed dispersal mode of Ch. intrepidus. Within the pools, there is a clear niche partitioning between Ch. intrepidus and the less desiccation-tolerant species Limosella grandiflora (Scrophulariaceae) with respect to depth (i.e. maximum water level) of the pools. In conclusion, the patchy spatial distribution of suitable habitats within a rather impermeable landscape matrix causes a highly structured genetic diversity. Chamaegigas intrepidus survives at its most stressful habitats with dramatic fluctuations of environmental conditions only by immediate responses to de- and rehydration and availability o