Mycogeography

Introduction
The influences governing the distribution of species
The tools of mycogeographical research
Relationships between Australian and non-Australian fungi
Cosmopolitan and Pantropical species
Species with an Australasian - South American distribution
Species found in Australasia - Africa - South America
Species of Australasia-Asia-Africa
Species in the Australian neighbourhood
Endemic fungi
Introduced by humans
Exported by humans
Puzzling distributions
Mycogeography within Australia

Introduction

Biogeography is the study of both the current distribution of living organisms and the reasons for those distributions. Mycogeography is the biogeography of fungi. Current plant and animal distributions around the world are the result of the interplay of numerous geological, biological and commercial influences. In this regard, fungi are no different to plants or animals, and are subject to the same influences. However, when compared to our knowledge of (and the reasons behind) the current world distribution of plant and animal species, similar knowledge about fungi is rather poor.

Before you undertake any detailed mycogeographical analysis, you need to have comprehensive and accurate lists of species for the different areas of the world, in order to be able to produce accurate distribution maps. Such lists (or maps) are a fundamental requirement. Yet, many areas of the world are still virtually unexplored from a fungal point of view and, not surprisingly, discoveries in such areas may dramatically alter thoughts about origin, evolution and migration of fungal species. The tropics produce numerous new species each year and the odd surprising find. For example, in 2001 a team of mycologists reported the discovery of a very unusual ascomycete in the west of Guyana. At first, the team had thought their new genus Pseodotulostoma to be a basidiomycete in the puffball group.

Australia has also produced a number of interesting finds. For example, we have numerous truffle-like species, unlike any in the northern hemisphere, and these discoveries have shown Australia to be a significant centre of evolution of these fungi. These are dealt with in the TRUFFLE SECTION.

Armillaria luteobubalina

Even when areas have been mycologically explored to any degree, there is still the question of the accuracy of the names applied. While there is still much to be learnt about Australian fungi, they have been studied for over two hundred years with many species recorded. Numerous Australian specimens were given European species names during the 1800s and early 1900s. Such identifications were based largely on macroscopic similarities. Microscopic re-examination of numerous old collections has shown that many of those European species do not in fact occur in Australia and that the old collections are in fact new species. Conversely, new species have been described from Australian specimens, where more detailed microscopic examination has in fact shown such species to be the same as previously known overseas species. So, you need to be careful when using old literature to make conclusions about the relationships between Australian and world fungi.

For a long time the European name Armillaria mellea was applied to what is now known to be an Australian endemic species - Armillaria luteobubalina. Similarly the name Pisolithus tinctorius was once applied to many Pisolthus collections around the world. It is now clear that many of the collections given this name are in fact various other species of Pisolithus.

The influences governing the distribution of species

Different fungi have different habitat and substrate (or host) requirements and so factors such as soil type, rainfall pattern, temperature ranges and plant community composition will influence the fungi to be found in a given area. These factors are acting now to define different fungal habitats, but there are also many factors which have acted in the past to help produce current distributions.

No continent is truly disconnected from the rest of the world - though in some cases the physical connections may have been cut many millions of years ago, during the breakups of super-continents such as Gondwana or Pangaea. But even now, connections remain in the form of related plant or animal species. Think of the broad coniferous zone of North America and northern Eurasia. Similarly, there are strong Gondwanan vegetation links between the southern hemisphere land masses. As Gondwana is particularly relevant to Australia, there will be more about Gondwana below.

There have been numerous ice ages during the earth's existence and such episodes have major effects on the distributions of living organisms. During an ice age, as ice caps spread out from the poles, the vegetation either retreats before the advancing ice or becomes extinct. As the climate becomes colder, cold climate plants can occupy a relatively large proportion of the available ice-free land, while plants of warmer areas will find themselves much more restricted. With the end of the ice age, there is a dramatic increase in the area suitable for warm weather plants and these can now expand their territory, and displace the cold climate species. Of course, the latter species have the newly uncovered sub-polar areas available for re-colonization. But the cold climate plants need not disappear from all of their ice age range. Some may remain in the alpine areas that are found in many, otherwise temperate parts of the world. So you can find isolated "islands" of cold climate plants, surrounded by warmer climate species.

Naturally, as plant territories contract or expand, the same happens with animals. Many animals, from tiny invertebrates to large mammals, have food or shelter preferences that necessitate particular plant communities as habitats. In such cases the animals must migrate as plant communities change, adapt to the new habitats or die. Fungi are subject to the same influences. Mycorrhizal fungi often have strong preferences for plant partners, so if the relevant plant species migrates to a new area the fungal partner will often move as well, though there are well-established cases where mycorrhizal fungi have changed partners. Parasitic fungi are also commonly tied to particular plant or animal hosts, and so are subject to the same territorial changes as their hosts. Even amongst the saprotrophs there may be specific requirements. For example, amongst the polypores of the northern hemisphere there are many which are found only on non-coniferous wood, while a smaller number will grow only on conifers.

Panellus stypticus

During ice ages, the lowering of sea levels creates land-bridges between areas previously separated by seas and this allows the migration of organisms that cannot cross a sea. Moreover, land-bridges allow the passage of numerous individuals (of any given species) over a considerable time, so the colonists of a new area can display considerable genetic diversity. Panellus stypticus has a very widespread distribution and its migrations have been helped by land bridges. There's more about this species in the COSMOPOLITAN SECTION. At other times there may also be random, one-off introductions. For example, a pregnant insect is carried across a normally impassable sea by unusually powerful storm winds. Or a few spores are carried from one continent to another by similar winds. Such events may happen just once, or exceedingly rarely, and such random introductions are called founder events. In such an event the number of migrating individuals is small and so all may die because none can overcome the obstacles to a successful colonisation. If some (or all) survive and have descendants, those descendants will show greatly reduced genetic variety when compared to the population from which the original colonisers came.

A more recent form of inter-continental connection is international trade. Humans have always carried goods between places, and over the past few hundred years the extent of such trade has increased dramatically. As well as intentional cargo, humans have unintentionally carried various plants and animals to remote parts of the globe. Rats are an obvious example. Similarly, there are many examples of fungi which have been carried from one country to another as unintentional extra cargo.

The tools of mycogeographical research

Valid mycogeographical analysis requires a good understanding of past geological, climatological and biological changes. Fossil evidence is extremely useful, but fungi often don't fossilise well. DNA analysis can help overcome the paucity of fossil evidence. Knowledge of trading patterns and human migration can help determine if human introduction is a plausible explanation for the occurrence of a species in two widely separated places.

Of course, you obviously need to know your species well. In addition to knowing their distinguishing macroscopic and microscopic features, this also means knowing their current distribution, their preferred habitats and climatic conditions, and the plants or animals they associate with. Information about known distribution along with associated data about preferred habitats and climatic conditions can be used in ecological analysis and prediction programs to predict other areas in which the species might be found, and where additional fieldwork could be productive. The predicted distribution can also help in deducing possible migration routes.

Different tools give different ways of looking at the same question and a good mycogeographical analysis will bring together the evidence from all viewpoints.

Healthy scepticism is useful, especially when you come across an odd point on a distribution map. In many cases it will be a valid observation, supported by irrefutable evidence, but inevitably mistakes do occur. Specimens may be mis-identified and surprising geographical errors do occur. One paper published in 1932 mistakenly reported that a specimen, actually collected from Bendigo in the Australian state of Victoria, came from Victoria in the Canadian province of British Columbia! Many collections made in the 1800s and early 1900s are accompanied by limited, handwritten notes - at times with poor (or ambiguous) locality data and the handwriting barely legible. Yet old collections (provided they have good, accompanying field notes and the identity of the specimens has been checked) can be very valuable for mycogeographical purposes. For example they may be the only representatives of some species, from an area now dramatically changed by expanding urbanisation or forest clearing.

All mycogeographical statements are simply hypotheses based on existing knowledge and so may change dramatically in the light of new evidence. For example, the wide acceptance of continental drift in the 1960s (though the idea had been around for some decades) saw almost an about-face in some theories of animal and plant origins and migrations.

Poronia erici

The ascomycete Poronia erici grows on herbivore dung. To the naked eye it looks very much like Poronia punctata, a species that was commonly recorded in Europe in the 19th century. For a long time the name Poronia punctata was regularly given to Australian collections of Poronia, but microscopic examination of Australian collections has shown differences and led to the realisation that Poronia erici is a common species in Australia. Poronia erici has also been found in Europe and for a while it seemed that the species had travelled from Australia to Europe, since all the known European collections dated from the 1920s, whereas earlier collections were known from Australia. Recently some earlier, 19th century Poronia erici collections from Europe have been found. So the Australia-to-Europe hypothesis is now less certain, a good illustration of the change in mycogeographical hypotheses as knowledge increases.

Relationships between Australian and non-Australian fungi

The relationships between Australian fungi and those of the rest of the world are quite varied. We have endemic species, cosmopolitan species, Gondwanan species and some with puzzling distributions.

Australia's long isolation from the rest of the world has led to the evolution of numerous animals and plants that are unique to this continent, and everyone is aware of at least some of these. It should therefore be no surprise to learn that during these millions of years of isolation, numerous endemic fungal species evolved.

Before that isolation Australia was part of the ancient super-continent Gondwana [www.scotese.com/late1.htm], shown here 150 million years ago, which broke up to produce Australia, Africa, Antarctica, India and South America. Various facts about Gondwana and continental drift are given in this link: [www.earth.monash.edu.au/dinodream/faq/faqgond.htm].

Today, in those modern continents, there is still living evidence of the earlier Gondwanan connection. For example, the plant family Proteaceae is Gondwanan and is widespread in southern Africa, Australasia and South America. You would of course not expect uniform vegetation across a land mass the size of Gondwana. Even across a smaller continent like Australia you find considerable differences between the plants of west and east Australia. Moreover, the break-up of Gondwana was not a single event, with some areas breaking off millions of years before others. Thus, for various reasons, there are Gondwanan plants with a much more restricted distribution. An example of this is Nothofagus, a genus of tree found in Argentina, Chile and parts of Australasia. But there is no evidence of Nothofagus ever having been in those parts of Gondwana that are now India and Africa. Understanding the history of Nothofagus is important for the proper understanding of the southern hemisphere distribution of some major fungal families.

Not surprisingly, there are also fungi which show varying types of Gondwanan distribution. In some cases a Gondwanan origin is quite clear, while in others the Gondwanan origin may become harder to discern. For example, as India and Australasia have moved northward following the breakup of Gondwana they have moved closer to, or collided with, what are now parts of non-Gondwanan Asia. India is now joined with Eurasia while Australasia is quite close to south-east Asia - and has at times been connected via temporary land-bridges. Such connections allow the spread of Gondwanan species into wider territories. Conversely, in such circumstances, non-Gondwanan species can move into what were once parts of Gondwana.

Before Gondwana, there was the even larger continent of Pangaea, which included modern Eurasia and North America as well. While some cosmopolitan fungal genera or species may have their origins in Pangaea, long distance spore dispersal in later times is also possible. There is strong evidence suggesting that spores of a wheat rust (a microfungus) were carried from Africa to Australia by high altitude winds in 1968-69. The distance involved is at least 12,000 kilometres. While transport over such distances can happen, it is likely to be rare because spores face many hazards and obstacles. At high altitudes spores have to survive freezing temperatures and exposure to greater levels of UV radiation. Many are also likely to be washed out of the sky by rain before travelling those thousands of kilometres. However, laboratory tests have shown that spores of various micro and macro fungi are capable of surviving high altitude environments and are of small enough size to, theoretically, be capable of being carried high and far. After a successful long-distance trip, the surviving spores will still face obstacles to a successful colonisation in the area they've landed.

Within Australasia the wind patterns easily allow particle flow across the 2,000 kilometres from Australia to New Zealand. There is striking visual evidence of this after severe dust storms in Australia, when Australian soil ends up on the Alps of the south island, at times in enough quantity to colour the snow red.

Now we will look at the distribution patterns of various fungi that are found in Australia (and often elsewhere as well). The aim is to illustrate the various distribution patterns, using a few specific examples, rather than through an exhaustive list in each category.

Mycogeography cont...