© 2008 Society of Systematic Biologists
Ghosts of Gondwana: The History of Life in New Zealand.—George Gibbs. 2006, reprinted 2007. Craig Potton Publishing, Nelson, New Zealand. 232 pp. ISBN 978-1-877333-48-4 (ISBN-10 1-877333-48-4). NZ$49.99 (hardcover)
School of Botany and Zoology, The Australian National University Canberra, ACT 0200, Australia; Email: Mike.Crisp{at}anu.edu.au
Ghosts of Gondwana: The History of Life in New Zealand.—George Gibbs. 2006, reprinted 2007. Craig Potton Publishing, Nelson, New Zealand. 232 pp. ISBN 978-1-877333-48-4 (ISBN-10 1-877333-48-4). NZ$49.99 (hardcover)
Gary Nelson (1975) notably wrote: "With regard to general problems of biogeography, the biota of New Zealand has been, perhaps, the most important of any in the world ... explain New Zealand and the world falls into place around it." This long-standing fascination with New Zealand for historical biogeographers—from Darwin and Hooker, through Darlington to Nelson, Heads, McGlone, Pole, and Trewick—reflects its dual roles as a microcontinent and as an oceanic island. Does ancient Gondwanan vicariance (Nelson, 1975; Heads, 2006) or more recent trans-oceanic dispersal (Pole, 1994; McGlone, 2005; Trewick et al., 2007) explain the assembly of the New Zealand biota?
In this new book, Gibbs acknowledges a role for both, giving examples of taxa that appear to have descended in situ from Gondwanan ancestors (e.g., acanthisittid wrens), and of dated transoceanic divergences that are much too young to be vicariant (e.g., many plants such as the hebes/Veronica). The catchy title of the book refers to the surviving Gondwanan lineages but is a misnomer—a ghost is the faint trace of something that did not survive.
Ghosts of Gondwana attempts to synthesize what is important about the biota of New Zealand and to put it into a global context. However, there is a tension between the author's enthusiasm for unique weird wonders and his desire to explore links with the rest of the world. Repeatedly, he emphasizes that each group of organisms has its own history and warns against generalization. Yet, he presents (Chapter 20) the geographically congruent phylogenies of four genera of mayflies and scorpionflies to illustrate the shared pattern predicted by a hypothesis of Gondwanan vicariance. Without a hypothesis-testing approach, biogeography is merely a series of improbable stories (Ball, 1976; Nelson, 1978; Penny and Phillips, 2004), and much of this book consists of such stories.
According to the publisher's blurb, and as suggested by the title, Ghosts of Gondwana is intended to be a popular book, and this is reflected in a superficial treatment of some complex questions. The book is a compilation of recent studies on diverse taxa rather than a critical evaluation of their conclusions. Nevertheless, the author cites many primary references and attempts to explain in layman's terms the concepts and methods behind the research. The book is written in an engaging, accessible style, is well illustrated with color photographs and diagrams, and includes numerous boxes relating interesting stories about organisms. There is a tendency to hyperbole, such as frequent and usually incorrect use of "ancient" to describe a group of organisms (see below).
The book commences with a chapter designed to capture the reader's imagination by focusing on the weird wonders of New Zealand, and thus on the consequences of its long history as an oceanic island. Examples are given of the unbalanced and highly endemic biota, e.g., radiations of carnivorous land snails and flightless birds along with a lack of terrestrial vertebrate and butterfly groups that are present in Australia. In a similar vein, Chapter 2 highlights unusual adaptations apparently resulting from imbalance in the island biota, in this case a historical absence of terrestrial mammalian predators and competitors. We are told about the mostly terrestrial nectar-eating bat Mystacina and about the kakapo, a large, cryptic, nocturnal, flightless, lekking, slow-breeding parrot that is now disappearing under pressure from introduced rats. Such inferred shifts into apparently vacant niches are referred to as "the New Zealand syndrome," although the underlying nature of this syndrome is never made clear. Later in the book (p. 169), the term refers to a high frequency of small, white, generalist-pollinated flowers in New Zealand plants. Perhaps this syndrome reflects no more than a tendency for improbable events to occur on islands.
The central core of the book is Section III, describing the biogeographic history of New Zealand and highlighting seven main factors influencing the assembly of the extant biota. These factors are lack of mammals, Gondwanan founders (oxymoron?), Oligocene inundation of the land, trans-oceanic immigration, Mio-Pliocene mountain building, Pleistocene glaciation, and the human invasions.
The biogeographic history is presented as a narrative in eight chapters, focused around interesting case studies. Recently discovered lake deposits in the south island have revealed the middle Miocene to have been a warm "Australian" period of floristic dominance by eucalypts, acacias, araucarias and casuarinas—now all extinct in New Zealand. The author considers this shift away from an Australian character in the biota over the last 10 Myr to be one of the most important features of New Zealand's present-day biota. Section IV, titled "Made in New Zealand: Special Evolutionary Opportunities," presents a miscellany of case studies on radiations (cicadas, frogs, and geckos). Here, also, are included ecological controversies: did browsing by moas drive the evolution of the divaricating growth habit in shrubs (better candidates for ghosts, perhaps?); the small white-flower syndrome; and distributional disjunctions within New Zealand, such as the "beech gap" in the middle of the south island.
All of the studies in Sections III and IV are taken from the primary literature, requiring an understanding of underlying concepts in phylogenetics and biogeography. So, Gibbs provides some theoretical background early in the book (Section II), but these treatments are brief and I wonder how helpful they would be to a lay reader. Moreover, this attempt is undermined by the author's misreading of trees. Often, he refers to extant taxa as "basal," "ancestral," "ancient," or "primitive," reflecting a common error in which a species-poor lineage is assumed to be ancestral relative to its species-rich sister group (Krell and Cranston, 2004; Baum, 2005; Crisp and Cook, 2005). Examples occur on p. 72 (Dracophyllum), p. 75 (monotremes), p. 95 (moths), p. 103 (kauri), p. 120 (rata), p. 128 (lowland relatives of alpine taxa), p. 130 (cicadas), and p. 191 (crayfish).
To elaborate on one of these examples, to help make the point clear, a phylogeny of black cicadas on p. 131 shows a clade of three lowland species sister to a large clade of mostly alpine species. The caption and text state that the tree implies that the lowland habitat is "ancestral," whereas in fact the ancestral habitat is ambiguous when optimized at the base of the tree. It seems that the state in the species-poor sister group has been incorrectly assumed to be ancestral. Independent evidence, i.e., that the alpine zone is much younger than the lowland habitat, suggests that the latter may indeed be ancestral, but this was not determined from the tree. Similarly, on p. 151 a New Caledonian origin for a more species-rich New Zealand clade of cicadas was inferred, but from the tree presented the area of origin is ambiguous and is more likely to be either Australia or New Zealand than New Caledonia.
From the title and the above quotation from Nelson (1975), which is also cited in the Introduction to the book, it is clear that the central theme of the book is how many of today's biota are in situ Gondwanan survivors (the so-called Moa's Ark hypothesis) versus how many immigrated following the Oligocene drowning. Gibbs clearly recognizes that, in the absence of a comprehensive fossil record for most taxa, answers to these questions hinge on the times of divergence between extant lineages in New Zealand and their sisters overseas. Divergences older than 60 Ma could have been the result of Gondwanan vicariance, whereas younger divergences are best explained by trans-oceanic dispersal, especially if they are post-Oligocene (
30 Ma), when the west wind drift system was established and dry land became continuously available to the present.
In Chapter 11, Gibbs reports an increasing number of studies on plant groups that find divergence times (not "times of arrival," as stated) consistent with immigration. So he concludes (Chapter 22), in agreement with Sanmartín and Ronquist (2004), that most plant taxa are immigrants—even classic Gondwanan groups such as Nothofagus (Knapp, 2005; Cook and Crisp, 2005a). A nice animal example is that of the flightless rails (pp. 115–116; Trewick, 1997), which appear to have established multiple species in New Zealand from independent arrivals by flighted ancestors. In cases of repeated establishments resulting from unidirectional dispersal from the same source, standard methods of ancestral-area inference can be misleading (p. 71; Cook and Crisp, 2005b), and evidence independent of phylogenies is needed to improve biogeographic reconstructions. Such evidence is provided by the rails, which can repeatedly lose but are unlikely to regain flight (Slikas et al., 2002), indicating that multiple dispersals occurred into, rather than out of, New Zealand.
As potential examples of vicariant Gondwanan survivors, Gibbs cites the kauri (Agathis australis), wrens (Acanthisittidae), tuatara (Sphenodon guntheri), and the endemic frog family Leiopelmatidae (Chapters 9 and 16). The case for Agathis is good because it has an antediluvian fossil record in New Zealand, and A. australis has been estimated by molecular dating to have diverged from the rest of the genus elsewhere 60 to 80 Ma (Knapp et al., 2007). However, the animal examples are all problematic.
The divergence between the wrens and their sister group (all other passerines) was either assumed to be vicariant, and therefore no test of that hypothesis, or dated assuming a strict molecular clock, which is dubious for estimating such a deep divergence.
The tuatara diverged from its sister group, which comprises all other reptiles, 
230 Ma (Hay et al., 2003). There are no fossils attributable to the sphenodont lineage between 115 Ma and the Miocene (p. 156; Hay et al., 2003). The Miocene fossil, from Otago, New Zealand, is the oldest fossil from the Australasian region. In other words, the sphenodont line has left so few traces over the last 115 Myr that its more recent biogeography is entirely a matter of speculation. It might have survived in situ for 230 Myr, or it might have arrived from elsewhere (where?) at any time before 20 Ma, and subsequently become extinct in the source area. Moreover, there is no fossil evidence that it was in New Zealand before the Oligocene drowning.
Leiopelmatid frogs have essentially no fossil record (except in the Holocene), and they diverged from their American sister group > 180 Ma (Roelants and Bossuyt, 2005). The latter authors envisage no simple explanation for the presence of this group in New Zealand. It needs to be emphasized that a hypothesized geological (vicariance) event should not be linked to a much older divergence event. A minimum requirement for inferring causal links between independent events is that they should, within error estimates, coincide (Penny and Phillips, 2004).
Finally (Chapter 20), Gibbs proposes that the best candidates for his "ghosts" (in situ Gondwanan survivors) are freshwater invertebrates, though his evidence is indirect. He argues that organisms such as mayflies, caddisflies, stoneflies, freshwater shellfish, freshwater crayfish, and their commensals, are totally dependent on cool, flowing, clear, freshwater streams, whereas seawater is "poison" to them—unlike galaxid fish, some of which have a marine larval stage. In his view, long-distance dispersal and establishment of such animals across wide oceanic gaps would be near impossible—though perhaps not, considering observations of a frequent rain of Australian insects on New Zealand (Fox, 1978; Withers, 2001)—and considering that the adults of these aquatic insects can fly. The cool stream habitat has probably been continuously available in New Zealand since before the breakup of eastern Gondwana, notwithstanding the unknown extent of the Oligocene inundation.
The only phylogenetic evidence presented by Gibbs for freshwater invertebrates is from Edmunds (1981). Undated cladograms show congruent (New Zealand, (South America, Australia)) relationships across three genera of mayflies and one of scorpionflies, as expected from the breakup sequence of eastern Gondwana. Therefore, Gibbs calls for molecular dating studies of freshwater invertebrates to test his prediction that these groups should show old divergences reflecting the Gondwana breakup; i.e., 60 to 80 Ma for New Zealand versus Australia plus South America and 30 Ma for Australia versus South America. A study on freshwater crayfish published after the book (Apte et al., 2007) dates the divergence between Paranephrops (New Zealand) and Parastacoides (its Australian sister) at around 50 Ma, which could be too young for vicariance, though the error was not estimated. Interestingly, the divergence time suggests that the Paranephrops lineage could have survived the Oligocene drowning of New Zealand.
To return to the quote from Nelson at the beginning, does an understanding of New Zealand explain the biogeography of the rest of the world? Insofar as recent evidence tends to favour colonization of New Zealand by trans-oceanic dispersal after it rifted away from Gondwana—at least in most of the plant groups examined—this is consistent with findings for the southern hemisphere as a whole (Sanmartín and Ronquist, 2004) and also for that other iconic microcontinental island, Madagascar (Yoder and Nowak, 2006). Gibbs concludes that animals show a pattern more consistent with Gondwanan vicariance, but there is increasing evidence supporting trans-oceanic dispersal of animals into New Zealand as well (Trewick et al., 2007).
Ghosts of Gondwana will inform and entertain readers who have a general background in natural history and biogeography and who wish to learn more about New Zealand, its fascinating organisms, and the controversies surrounding their history. I found it to be easy, enjoyable reading, and many of the examples were interesting and novel, at least with respect to the animals (I am a botanist). The book provides a valuable complement to those that already exist for other biogeographically notable regions, such as Madagascar (Goodman and Benstead, 2003) and the Cape Region of South Africa (Cowling and Richardson, 1995).
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Thanks to Lyn Cook and Kevin Omland for comments on the manuscript.
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