Plant Dispersal N.E.W.S from New Zealand

514 Review TRENDS in Ecology & Evolution Vol.17 No.11 November 2002 Plant dispersal N.E.W.S from New Zealand Richard C. Winkworth, Steven J. Wagstaff, David Glenny and Peter J. Lockhart Although New Zealand separated from Gondwana during the late Cretaceous explain the extant New Zealand flora, there has been (80 million years ago) it shares strong floristic affinities with other Southern little direct evidence for dispersal. Until recently, Hemisphere landmasses. For 150 years, biogeographers have debated whether the strongest support came from fossil pollen. these similarities reflect the ancient Gondwanan connection or subsequent Comparisons of the palynological records for Southern dispersal events. Molecular phylogenies are providing new insights into the Hemisphere landmasses show temporal differences in history of Southern Hemisphere plant groups. These studies show that many the first appearance of shared taxa, a pattern that plant lineages are recent arrivals in New Zealand, diversifying rapidly and then could indicate dispersal [2,5,7,11]. Such inferences are travelling to other Southern Hemisphere landmasses. suggestive of general patterns; however, the limited taxonomic resolution of the fossil record has prevented Published online: 19 August 2002 the reconstruction of dispersal histories within specific groups. Even with evidence from comparative Almost certainly New Zealand’s first flora would have morphology and contemporary distribution patterns, migrated from Gondwana as the ancestral landmass it is difficult to infer unambiguously dispersal within was uplifted along the eastern edge of the lineages. For example, in the Australasian apioid supercontinent (Box 1). Although the origins of the Umbelliferae, alternative interpretations of earliest colonists seem straightforward, contrasting morphological data support opposing hypotheses for hypotheses about the significance of geological and the origins of contemporary taxa [15,16]. climatic change in the New Zealand environment have Molecular phylogenetic studies both provide an polarized opinions about the relationships of this independent test of previous hypotheses and highlight first flora and the contemporary assemblage. One novel insights into the origins and evolution of hypothesis is that the modern flora represents a New Zealand plants. Here, we review recent studies Gondwanan relict that is relatively unaltered by that, with a few exceptions, have focused on large, dramatic changes in geology and climate (Box 1). morphologically and ecologically diverse plant groups Perhaps more importantly, this hypothesis also of the New Zealand mountains. Often the phylogenetic suggests that the geological isolation of New Zealand analyses are consistent with the rapid diversification acted as a barrier to biotic exchange. That is, lineages of the lineage in New Zealand following the onset of in the contemporary flora must have been present late Tertiary mountain building (5–2 mya) and when New Zealand separated from Gondwana (Box 1) Quaternary climate change [2 mya–14 000 years because, following separation, the distance from ago (ya)]. Perhaps more interesting, however, are the Richard C. Winkworth* potential source areas rules out dispersal. insights these studies provide into the relationships Dept of Ecology and Panbiogeographers have been strong advocates of this between the New Zealand taxa and their Southern Evolutionary Biology, view, explaining the entire New Zealand biota in Hemisphere relatives. Molecular phylogenies clearly Yale University, terms of Gondwanan break up and rafting of the indicate that the patterns of transoceanic dispersal in PO Box 208105, New Haven, fragments to their present-day positions [1]. Long- the southern Pacific are more complex than have CT 06520-8105, USA. term geological isolation will certainly have influenced previously been envisaged. The results highlight both *e-mail: the composition of the New Zealand flora; however, the dynamic nature of plant evolution and the Richard.Winkworth @yale.edu it has been questioned whether the barrier has been importance of Southern Hemisphere models for impermeable. Indeed, many workers [2–13] have explaining biodiversity. Steven J. Wagstaff David Glenny argued that the fossil record [5,7,11] and the diverse Manaaki Whenua geographical affinities of the modern assemblage Dispersal patterns in the southwestern Pacific Landcare Research, [4,12,13] provide evidence for the role of dispersal in A controversial aspect of dispersal hypotheses is the PO Box 69, Lincoln 8152, establishing the contemporary New Zealand flora. significance of west-wind drift, a meteorological New Zealand. To explain the observed similarities been Southern phenomenon that, at high southern latitudes, causes Peter J. Lockhart Hemisphere floras, authors have proposed hypotheses cyclonic weather systems to move progressively The Allan Wilson Centre for Molecular Ecology and ranging from migration across early Tertiary eastward. These circumpolar westerly winds and Evolution, Institute of [65–37 million years ago (mya)] land bridges to long- ocean currents were established during the Miocene Molecular BioSciences, distance dispersal over vast oceans during the late (23–5 mya) as South America and Australia Massey University, Tertiary (15–2 mya) and more recently [2–11,14] (Fig. 1). separated from Antarctica [17]. This eastward flow Private Bag 11222, Palmerston North, Although distributional and fossil data [4,5,7,11–13] intensified throughout the late Tertiary but was New Zealand. hint that Gondwanan ancestry cannot be used to fully probably strongest during the Pleistocene glacial http://tree.trends.com 0169-5347/02/$ – see front matter © 2002 Elsevier Science Ltd. All rights reserved. PII: S0169-5347(02)02590-9 Review TRENDS in Ecology & Evolution Vol.17 No.11 November 2002 515 Box 1. A brief history of New Zealand Geology climatic fluctuations – alternating between cold, dry glacial Originally uplifted along the eastern edge of Gondwana maxima and warm, moist interstadials and interglacials [f,g]. 150–140 million years ago (mya) (Fig. I), tectonic spreading The final glacial retreat began 14 000 ya and was followed by began to isolate New Zealand ~115 mya. A seaway a warm, moist thermal optimum before cooler, drier separated the two landmasses by 85 mya, although contemporary conditions were established 7000 ya [f]. tectonic movement continued into the Paleocene (65–58 mya) [a]. Throughout the Cretaceous (144–65 mya) Vegetation and early Tertiary (65–37 mya) steady erosion reduced both As elsewhere, nonflowering plants dominated Cretaceous the extent and topology of New Zealand, so that during the assemblages in New Zealand. Although these lineages Oligocene (37–23 mya) only a scattered archipelago of continued to predominate in early Tertiary floras, low-lying islands remained. However, activation of the angiosperms also featured prominently [e]. The first contemporary Pacific–Australian plate boundary (25 mya) angiosperm-dominated assemblages appear during the resulted in the emergence of a narrow, elongate landmass Eocene. Similar to earlier palynofloras, these were uniform during the Miocene (23–5 mya) [a,b]. Tectonic activity in composition; however, from the Oligocene onward, the intensified throughout the Pliocene (5–2 mya), culminating progressive development of environmental gradients in the rapid uplift of the axial mountain ranges [c]; marine resulted in regional differentiation [e,f]. Late Tertiary and transgressions and volcanism also shaped Pliocene Quaternary glaciation dramatically affected both the New Zealand. Late Tertiary and Quaternary glaciation composition and distribution of the New Zealand vegetation. (2.5 mya–14 000 ya) affected the geological setting of During glacial maxima, forests were confined mostly to the New Zealand. Many modern landforms result directly from far north, with extensive grass and shrubland assemblages glacial activity or modification of glacial constructions [d]. dominating the south. During interstadials and interglacials, forest assemblages spread rapidly from the refugia, often re-establishing even in the southernmost areas [f,g]. Following the final glacial retreat (14 000 ya), the thermal optimum supported the rapid, widespread establishment of Arabia forests. More recent climate change also affected the composition and distribution of the vegetation [g]. Africa Madagascar References a Stevens, G.R. (1985) Lands in Collision: Discovering New India New Guinea Zealand’s Past Geography, Science Information Publishing South America Australia Centre, DSIR b Pillans, B. et al. (1992) The age and development of the Antarctica New Zealand landscape. In Landforms of New Zealand (Soons, J.M. and Selby, M.J., eds), pp. 31–62, Longman Paul c Cooper, A. and Cooper, R.A. (1995) The Oligocene bottleneck New Zealand and the New Zealand biota: genetic record of a past Fig. I TRENDS in Ecology & Evolution environmental crisis. Proc. R. Soc. Lond. Ser. B 261, 293–302 d Batt, G.E. et al. (2000) Thermochronological analysis of the dynamics of the southern alps, New Zealand. Bull. Geol. Soc. Climate Am. 112, 250–266 Cool temperate climates dominated much of the prehistory of e Mildenhall, D.C. (1980) New Zealand late Cretaceous and New Zealand [e]. However, extended periods of warming are Cenozoic plant biogeography: a contribution. Palaeogeogr. correlated with both the Eocene (58–37 mya) and Miocene. Palaeoclimatol. Palaeoecol. 31, 197–233 Cool temperature conditions again dominated

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