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View metadata, citation and similar papers at core.ac.uk brought to you by CORE Submitted to Phil. Trans. R. Soc. B - Issue provided by University of Liverpool Repository The underestimated biodiversity of tropical grassy biomes Journal: Philosophical Transactions B For ReviewManuscript ID RSTB-2015-0319.R2 Only Article Type: Research Date Submitted by the Author: n/a Complete List of Authors: Murphy, Brett; Charles Darwin University, School of Environment Andersen, Alan; CSIRO, Ecosystem Sciences Parr, Catherine; University of Liverpool, 4School of Environmental Sciences Issue Code: Click <a href=http://rstb.royalsocietypublishing.org/site/misc/issue- GRASS codes.xhtml target=_new>here</a> to find the code for your issue.: Ecology < BIOLOGY, Environmental Science < Subject: BIOLOGY biodiversity conservation, diversity, species Keywords: richness, tropical forest, tropical savanna, rain forest http://mc.manuscriptcentral.com/issue-ptrsb Page 1 of 31 Submitted to Phil. Trans. R. Soc. B - Issue 1 2 3 1 The underestimated biodiversity of tropical grassy biomes 4 5 2 6 7 3 *Brett P. Murphy 8 4 9 10 5 Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, 11 12 6 NT 0909, Australia 13 7 14 15 8 16 17 9 Alan N. Andersen 18 10 For Review Only 19 20 11 CSIRO Land & Water, Tropical Ecosystems Research Centre, Winnellie, NT 0822, Australia 21 22 12 23 13 Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, 24 25 14 NT 0909, Australia 26 27 15 28 16 29 30 17 Catherine L. Parr 31 32 18 33 19 School of Environmental Sciences, University of Liverpool, Liverpool, L69 3GP, United 34 35 20 Kingdom 36 37 21 38 22 School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Wits 39 40 23 2050, South Africa 41 42 24 43 25 *Corresponding author: [email protected] 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 1 http://mc.manuscriptcentral.com/issue-ptrsb Submitted to Phil. Trans. R. Soc. B - Issue Page 2 of 31 1 2 3 26 Abstract 4 5 27 6 7 28 For decades there has been enormous scientific interest in tropical savannas and grasslands, 8 29 fuelled by the recognition that they are a dynamic and potentially unstable biome, requiring 9 10 30 periodic disturbance for their maintenance. However, that scientific interest has not translated 11 12 31 into widespread appreciation of, and concern about threats to, their biodiversity. In terms of 13 32 biodiversity, grassy biomes are considered poor cousins of the other dominant biome of the 14 15 33 tropics – forests. Simple notions of grassy biomes being species-poor cannot be supported; 16 17 34 for some key taxa, such as vascular plants, this may be valid, but for others it is not. Here we 18 35 use an analysis ofFor existing toReview demonstrate that hig h-rainfallOnly tropical grassy biomes have 19 20 36 vertebrate species richness comparable to that of forests, despite having lower plant 21 22 37 diversity. The Neotropics stand out in terms of both overall vertebrate species richness and 23 38 number of range-restricted species in tropical grassy biomes. Given high rates of land cover 24 25 39 conversion in Neotropical grassy biomes, they should be a high priority for conservation and 26 27 40 greater inclusion in protected areas. Fire needs to be actively maintained in these systems, 28 41 and in many cases re-introduced after decades of inappropriate fire exclusion. The relative 29 30 42 intactness of tropical grassy biomes in Africa and Australia make them the least vulnerable to 31 32 43 biodiversity loss in the immediate future. We argue that, like forests, tropical grassy biomes 33 44 should be recognised as a critical – but increasingly threatened – store of global biodiversity. 34 35 45 36 37 46 38 47 Key words: 39 40 48 biodiversity conservation, diversity, species richness, tropical forest, tropical savanna, rain 41 42 49 forest 43 50 44 45 51 46 47 52 1. Introduction 48 49 53 50 54 The Earth’s tropical landscapes are dominated by two strongly contrasting biomes – savannas 51 52 55 and grasslands on the one hand and closed-canopy forests on the other (figure 1a). Together 53 54 56 they support much of the Earth’s biodiversity, and both have been subject to similar high 55 57 rates of land cover conversion in recent decades. Somewhat paradoxically, however, 56 57 58 savannas and grasslands – henceforth, tropical grassy biomes (TGBs) – have remained 58 59 60 2 http://mc.manuscriptcentral.com/issue-ptrsb Page 3 of 31 Submitted to Phil. Trans. R. Soc. B - Issue 1 2 3 59 conspicuously absent from the global discourse on land clearing and biodiversity loss. Only 4 5 60 very recently is society beginning to appreciate the biodiversity values of TGBs, and the 6 61 extent to which they are under threat [1, 2]. The historical underappreciation of the 7 8 62 conservation value of TGBs has stemmed from a widespread and persistent misconception 9 10 63 that they are anthropogenically ‘derived’, representing forests degraded by human activities 11 64 [3]. Clearly some TGBs have been derived from forest [4]. However, there is also a 12 13 65 widespread and entrenched misunderstanding of the status of ancient TGBs that dominate the 14 15 66 tropics wherever disturbance or aridity severely limit woody cover [5, 6]. Ancient TGBs have 16 67 long evolutionary histories, as demonstrated by their high species diversity, endemism and 17 18 68 functionally distinctFor biotas [7],Review including floras withOnly many adaptations to frequent 19 20 69 disturbance by fire and grazing [8]. TGBs are only just beginning to be recognised as globally 21 70 important reservoirs of biodiversity. 22 23 71 24 25 72 Tropical forests are renowned for their remarkable diversity of trees, yet diversity of other 26 73 plant life forms can be very high in savannas. For example, 230 (mostly herbaceous) vascular 27 28 74 plant species have been recorded in a single 0.1 ha plot in the Brazilian Cerrado [9]. 29 30 75 Moreover, diversity is much more conspicuous in TGBs than in tropical forests. The great 31 76 diversity of grass-layer plants is there for all to see (even if only at certain times, such as 32 33 77 following fire), rather than towering 30 m or more overhead. In forests, the vast majority of 34 35 78 invertebrate species are either secreted in the litter layer or out of sight in the canopy, 36 79 whereas the savanna invertebrate fauna is concentrated in the grass-layer or on open ground 37 38 80 [10, 11]. Most of the tropics’ mammalian megafauna occurs in open savanna rather than 39 40 81 forest. Large vertebrates are highly visible in savannas, but in forest are typically hidden by 41 82 dense foliage and low light. The tropical savanna biome has particular significance for our 42 43 83 own species because it was the cradle of hominid evolution [1]. 44 45 84 46 85 While we emphasise the need for conservation of TGBs in general, there are clear ecological 47 48 86 and evolutionary differences among regions dominated by grassy biomes [12-14]. Just as 49 50 87 major differences among tropical forest regions have been recognised [15, 16], there is a need 51 88 to consider how savanna regions differ too. There are some obvious differences in biotic 52 53 89 composition due to biogeographic history. For example, the dominant trees of Australian 54 55 90 savannas, eucalypts, do not occur on other continents. Fungus-growing termites (family 56 91 Macrotermitinae) are restricted to the Old World [15], and fungus-growing ants (tribe Attini) 57 58 92 occur only in the Neotropics. Australian and Neotropical savannas support contrasting ant 59 60 3 http://mc.manuscriptcentral.com/issue-ptrsb Submitted to Phil. Trans. R. Soc. B - Issue Page 4 of 31 1 2 3 93 faunas that are dominated by arid-adapted and forest-adapted elements respectively, 4 5 94 reflecting their contrasting biogeographic histories [16]. Such compositional differences can 6 95 have important functional implications. For example, eucalypts have been suggested to be 7 8 96 unique among savanna trees in their ability to escape the recruitment bottleneck imposed by 9 10 97 high fire frequency [17, 18]. Ants are major herbivores in Neotropical savannas, as they 11 98 collect substrate for their fungal gardens [19]. Neotropical savannas have an extremely 12 13 99 diverse fauna of tree-nesting ants, a habit which is very uncommon in savannas elsewhere 14 15 100 [16]. Intra-biome comparisons not only provide important insights into the ecology of these 16 101 systems, but also help identify regionally distinct conservation priorities [15]. Given the 17 18 102 divergent biogeographicFor histories Review of TGBs globally [20, Only 21], combined with differing threats, 19 20 103 it is likely that conservation needs and priorities will vary. 21 104 22 23 105 Despite the growing appreciation of TGBs and the threats they face, there remains a poor 24 25 106 understanding of their biodiversity values at a global scale. Here we seek to redress this by 26 107 analysing global patterns of species richness of vertebrates and vascular plants. We build on 27 28 108 recent regional-scale research to evaluate the biodiversity consequences of land cover 29 30 109 conversion in TGBs [22]. Specifically, we examine how species richness of TGBs compare 31 110 with that of tropical forests in each of the tropical biogeographic realms. We also compare the 32 33 111 extent to which TGBs and forests are formally protected, and how this varies regionally.