Comparative population structure and reproductive biology of the critically endangered shrub Grevillea althoferorum and two closely related more common congeners

Abstract

Grevillea althoferorum is a critically endangered, sprouting shrub known from two disjunct populations within the South-West Botanical Province of Western Australia. This study compares the conservation biology of G. althoferorum and two closely related but more common congeners, the non-sprouter G. rudis and the sprouter G. synapheae subsp. pachyphylla in order to determine whether there are differences in reproductive and ecological attributes that might explain why G. althoferorum is rare. In contrast to the more common species, neither population of G. althoferorum exhibited evidence of seedling recruitment. However, the northern population was confirmed to be clonal and was actively recruiting from root suckers. Both populations of G. althoferorum were found to have reduced amounts of viable pollen on stigmas in comparison with the other species. The fruit set at the southern population of G. althoferorum was considerably lower than that found for the common species, with only 0.15% of flowers setting fruit and no fruit was produced in the northern population. In addition no evidence of a soil seed bank was found for either population of G. althoferorum, but G. rudis and G. synapheae subsp. pachyphylla both had soil stored seed which germinated following treatment with aqueous smoke solution. Sexual recruitment at both populations of G. althoferorum was absent, and reproduction appears to be predominantly clonal in the northern population. Management strategies for G. althoferorum should therefore focus on the protection of adult plants from accidental destruction.