Doctor of Philosophy
School of Biological Sciences
Hermansen, Tyge Dahl, Reproductive biology and genetic structure in fragmented populations of the temperate mangrove Avicennia marina, Doctor of Philosophy thesis, School of Biological Sciences, University of Wollongong, 2013. https://ro.uow.edu.au/theses/4014
Land clearance and conversion have resulted in habitat loss and anthropogenic fragmentation (including reduction of stand size and increased isolation), which are some of the greatest threats to plant populations today. It is of immense importance that we uncover the mechanisms behind these threats (i.e. impact on pollen and seed vectors and ecological consequences of this, leading to higher levels of inbreeding and reduced production and quality of fruits), because ignoring them would expose many anthropogenically disturbed plant populations to the risk of extinction. I investigated the impacts of stand size on temperate anthropogenically fragmented populations of the mangrove Avicennia marina in three Sydney and Minnamurra estuaries on the coast of New South Wales (NSW) in Australia, near the southern limits of mangroves, where mangrove populations have suffered from anthropogenic fragmentation, dividing them into stands of varying size, from large stands of 10000 trees or more down to single isolated trees. My study investigated the impacts of stand size (in the present study comparisons were done between large stands of 1500-10000 trees, medium stands of 300-500 frees and small stands of up to ca. 100 trees) on pollination biology, mating systems and reproductive output. It also combined highly replicated surveys of pollinator activity and diversity and reproductive success, experimental tests of pollinator activity and the use of neutral DNA markers to estimate the effects of stand size on genetic diversity and mating systems.
Today it is thought that a range of generalized pollinators pollinate mangroves. To test this hypothesis in temperate populations of A. marina flower visiting insects were captured during multiple surveys of flower visitation and it was investigated which species touched the stigma during foraging and which species carried pollen on body parts touching the stigma. Species that did were tested for pollen removal and deposition to establish their identity as pollinators.