KINGSLEY DIXON—LIVING IN A BIODIVERSITY HOTSPOT

SERVENTY MEMORIAL LECTURE 2017

The Serventy Memorial Lecture is held every year by the WA Naturalists’ Club in honour of the outstanding contribution made by the Serventy family to Natural History in Australia and to our Club. The aim of the Serventy Memorial fund is to encourage young people to study natural history by awarding prizes to tertiary students in that field. Before the talk, our president, Mandy Bamford, reminded us about the work of the various members of the Serventy family, starting with the foundation of the Club by Dom Serventy in 1924.

This year’s lecture was delivered in brilliant style by Professor Kingsley Dixon. Kingsley established the Plant Sciences Group at Kings Park Botanic Gardens and directed that excellent research body for 32 years. Last year he was named WA Scientist of the Year in recognition of his work in conservation science, plant science and restoration ecology.

Kingsley showed us some rock samples that he held in his hands. What did these rocks have to do with biodiversity? One was a piece of zircon, aged at an amazing 4.6 billion years old. This rock, close to being part to the original crust of the earth, was still sitting on the landscape after all that time. Another was a piece of banded ironstone, formed by the cyanobacteria that gave us our blue skies and our oxygenated atmosphere. There are also hundred-million-year-old pieces of fossil stromatolite lying on the surface. These ancient rocks, still unchanged after all this time, are evidence of the extreme antiquity of this part of the world, which has escaped major geological change that characterizes much of the rest of the world.  Moreover, Australia has remained isolated from other continents ever since it separated from the rest of Gondwana and slowly transitioned from a tropical to a mostly arid climate.

As a result of this long-term stability and isolation, our continent has aggregated many plant species over a very long time and has derived a unique and extraordinary flora, each species fine-tuned to its specific environment.  This is evident more than anywhere else, in the south west. And yet, says Kingsley, we don’t see our plants as special and we struggle with the idea that we live in one of the world’s 34 biodiversity hotspots.

An illustration of the antiquity of our plants comes from pollen analysis of cores from holes drilled 2 km deep into an 83-million-year-old filled crater at Yalallie. This shows species and families coming in and out over time. Some of those ancient species represented by the fossil pollen can be found today as living plants. Examples are species of Isopogon and Stackhousia.  Another is Ecdeiocolea, which is the ancestor of all the cereals.

Kingsley illustrated the extraordinary plant diversity of the South West with a story of how he and an incredulous European visitor stood at one place near Mt Lesueur and counted 80 plant species without moving from the spot.  In the South West there is a very high turnover of species as one moves across the landscape:  there is typically a 60 per cent turnover over 1 to 1.5 km.

One of our unique plants is Kingia, the extraordinary grass-tree with the knobbly flowering spikes and strange anatomy. There is only one species of Kingia, and its family (Dasypogonaceae) is endemic to the south west. Even its order is endemic. It appeared 120 million years ago, just 15 million years after the earliest evidence of the first flowering plant.

Pollination mechanisms have run riot in our south west, with a high proportion of bird and mammal pollination, and a host of sexual deception mechanisms. European Bee Orchids practice sexual deception, as do some South African daisies, but in our south west the orchids get up to many such tricks. Research in Kings Park bushland has revealed that male fungus gnats are sexually attracted to the Greenhood Orchid Pterostylis sanguinea by a pheromone. The gnat’s tiny body, weighing 0.0001g, triggers the lip of the orchid where it is trapped for a while as it inadvertently transfers pollen.

Black Kangaroo Paw (Macropidia fuliginosa) at Mt Lesueur NP (T Marwood)

Several other genera of our orchids also practice sexual deception.  Kingsley showed us footage of a male wasp vigorously trying to mate with a Hammer Orchid. This ensures pollination by the wasp, which flies away to another Hammer Orchid carrying a bundle of pollen.  Moreover, the flightless female of that wasp species lays its eggs only in the larva of a particular species of scarab beetle. So the orchid is entirely dependent for its survival on the wasp and the beetle. That means that if the orchid is growing in a piece of remnant bush that is not large enough to support a sustainable population of the wasp or the beetle, then it will not reproduce and will become locally extinct, thus threatening the survival of the species.

Other unique features of the hammer orchids are that their roots require a particular species of fungus to supply soil nutrients and also to trigger germination.  Even more remarkable, the Underground Orchid (Rhizanthella gardneri) has neither roots nor leaves. It feeds parasitically from the Broom Honeymyrtle (Melaleuca uncinata), to which it is connected by fungal hyphae. The honeymyrtle does not benefit from the association. This unique orchid is the only plant that can be pollinated by termites.

Poor Charles Darwin!  He arrived at Albany in summer. He was probably seasick and homesick, but he described the surrounding land as a “hostile environment” and had nothing positive to say about it. Little did he know that if he had done some exploration, he may have seen a remarkable display of biodiversity. Not only would he have seen many summer wildflowers, but also Honey-possums, flowers being pollinated by birds, the world’s biggest mistletoe (Nuytsia floribunda), and a special interest of Darwin’s— carnivorous plants. Many and varied species of Sundew (Drosera spp) would have been growing there, as well as the remarkable Albany Pitcher Plant at Lake Seppings.

But there is a dark side to all this wonder. For a region to qualify as a biodiversity hotspot, there have to be significant threats to its high level of diversity. Kingsley said that at least 2000 species in the south west have no habitat or insufficient habitat to support viable populations, and that many of these habitats are subject to threats such as dieback. Fragmentation of habitats lowers the genetic diversity of organisms in those diminished areas, and lowers their chances of survival. Cleared or damaged landscape does not readily restore itself here, in contrast with Europe where species migrate readily and re-colonisation occurs quickly.

Kingsley grew up exploring the bush “in the wilds of Morley”—which was Banksia woodland at the time—and he reminded us that we are privileged to have this bushland in the city. Recent news is that the Banksia woodland of the Swan Coastal Plain, now highly fragmented, has been declared a Threatened Ecological Community (the same status as Carnaby’s Cockatoo), which means that it is now an offence to clear Banksia woodland. This has implications for new housing developments.

Banksia woodland (T Marwood)

Kingsley showed us aerial footage of the scar left after clearing bush in the Beeliar Wetlands for the now abandoned Roe 8 project.  He said that with funding, the bush can be restored and that this can be seen as a wake-up call, reminding us of how precious and ancient our natural environment is here in the south west corner of Australia.

Summing up, Kingsley quoted Sir David Attenborough, speaking when he was filming in the south west:  “There are so many extraordinary stories to tell from this bushland.” He also alluded to a quote from Charles Darwin’s conclusion of The Origin of Species: “There is grandeur in this view of life . . . endless forms most beautiful and most wonderful have been, and are being, evolved.”

Mike Gregson