«Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften (Dr. rer. nat.) dem Fachbereich Biologie der Phlilipps-Universität Marburg ...»
Phylogenetic community structure of ants in
secondary tropical forests in Brazil.
zur Erlangung des Doktorgrades der Naturwissenschaften
(Dr. rer. nat.)
dem Fachbereich Biologie
der Phlilipps-Universität Marburg
Rossa Ng’endo Nyoike
aus Embu, Kenya
Vom Fachbereich Biologie der Philipps-Universität Marburg als Dissertation angenommen am 14. 07. 2011.
Erstgutachter: Prof. Dr. Roland Brandl
Zweitgutachter: Prof. Dr. Lothar A. Beck Tag der Disputation: 14. 07. 2011.
For my daughter Eleanor Wangeci Nyoike Erklärung Ich versichere, daß ich meine Dissertation „Phylogenetic community structure of ants in secondary tropical forests in Brazil.” selbständig und ohne unerlaubte Hilfe angefertigt habe und mich keiner als der von mir ausdrücklich bezeichneten Quellen und Hilfen bedient habe. Diese Dissertation wurde in der jetzigen oder einer ähnlichen Form noch bei keiner anderen Hochschule eingereicht und hat noch keinen sonstigen Prüfungszwecken gedient.
Rossa Ng’endo Nyoike Marburg.
To be willing is to be able.
TABLE OF CONTENTS1 GENERAL INTRODUCTION
1.1 TROPICAL FORESTS BIODIVERSITY AND COMMUNITY ORGANIZATION
1.2 BIODIVERSITY OF A HYPERDIVERSE ANT GENUS IN SECONDARY TROPICAL FORESTS............ 5
1.3 PHYLOGENETIC COMPOSITION AND STRUCTURE OF ANT COMMUNITIES IN SECONDARYTROPICAL FORESTS
1.4 THE STUDY AREA
1.5 MAIN OBJECTIVES
1.6 RESULTS AND DISCUSSION
1.7 CONCLUSIONS AND RECOMMENDATIONS
2 DNA BARCODES FOR SPECIES IDENTIFICATION IN THE HYPERDIVERSE ANTGENUS PHEIDOLE (FORMICIDAE: MYRMICINAE)
2.3 MATERIALS AND METHODS
3 PHYLOGENETIC COMPOSITION AND COMMUNITY STRUCTURE OF ANTGENUS PHEIDOLE ALONG FOREST SUCCESSION GRADIENT
3.3 MATERIALS AND METHODS
4 DETERMINANTS OF PHYLOGENETIC COMMUNITY STRUCTURE OF ANT
GENERA ALONG SUCCESSION GRADIENT IN SECONDARY TROPICAL FORESTS. 714.1 ABSTRACT
4.3 MATERIALS AND METHODS
1 General Introduction
1.1 Tropical forests biodiversity and community organization Tropical forests are one of the most diverse habitats on Earth (Whitmore, 1998), hosting at least two-thirds of the Earth’s terrestrial biodiversity (Gardner et al., 2009). However, the future of tropical forest species has been more uncertain since only few areas of the tropics have escaped some form of human impact (Kareiva et al., 2007). The combined influence of persistently high rates of deforestation and forest degradation, over harvesting, invasive species and global environmental change threatens to make tropical forests the epicentre of current and future mass species extinctions (Bradshaw et al., 2009), if current rates of deforestation continue (Pimm et al., 1995; Dirzo & Raven, 2003).
Deforestation of tropical forests is rarely total or permanent. Small patches of original habitat remain and succession leads to secondary forests. Succession involves a gradual replacement of species that differ in traits (which allow for quick colonization or competitive ability) and that differ in the degree they tolerate, facilitate or inhibit certain environmental conditions and other species (Rossi et al., 2009). Therefore, it is an important process in determining how, and how fast, ecological communities return back to their original state, especially in terms of biodiversity composition in recovering ecosystems such as secondary forests.
Ecological communities refer to assemblages of species that occur together in time and space, and whose composition and aspect is determined by the properties of the environment and by the relations of the organisms to each other (modified from Begon et al., 2006), while an assemblage refers to a taxonomic subset of a community (Fauth et al., 1996).
With the continued increase in secondary forests throughout the tropics, conservation has a key role to play in safeguarding the future of tropical forests
Introductionbiodiversity (Gardner et al., 2010; Bihn et al., 2008, 2010). However, a major challenge to conservation is due to the large number of undescribed species in the tropics, especially the invertebrates (Gentry, 1992; Hodkinson & Casson, 2008), with conservation prioritization having largely focused on vertebrates. Therefore, species identification of such large numbers of undescribed taxa forms the first step towards achieving conservation agenda.
Human-induced environmental change in forest ecosystems has also been linked to significant changes in the species composition of communities, with implications for the persistence of ecological communities and ecological processes of even the most remote and pristine areas of tropical forest (Lewis et al., 2009).
Community composition is influenced by a range of ecological factors (dispersal ability and habitat selection of a species, interspecific interactions), evolutionary processes and historical events (Morin, 1999). Since differences in ecological characteristics of species lead to differences in their functionality and their role in ecosystem processes (Darwin & Wallace, 1858; Loreau et al., 2001), there have been questions on which factors structure local communities; and how regional species pools contribute to local communities continue to be among the central topics in ecology (Diamond, 1975). Starting from the early studies of Hutchinson (1959) and MacArthur (1958; MacArthur, 1972), research efforts in community ecology have attempted to reveal the mechanisms that allow the coexistence of species in local habitats and ecosystems (Brown 1995).
A range of mechanisms has been suggested in order to understand the underlying reasons for the co-occurrence of closely related, ecologically similar species (e.g., Chesson, 2000; Hubbell, 2001; McPeek, 2000). Furthermore, community studies have also focused on how factors such as spatial or taxonomic scales, null models and metrics among others, may influence the observed community patterns (Webb et al., 2002; Cavender-Bares et al. 2006). Moreover, recent research studies have emphasized the adoption of biodiversity indices that take into account phylogenetic information of species, when assessing dynamics in species composition and community patterns (Webb et al., 2002; Chave et al., 2007). This is expected to allow for better interpretation of e.g. effects of anthropogenic impacts on phylogenetic composition/structure of ecological communities as opposed to the case with classical indices (see Warwick & Clarke, 1995, 1998; Anu & Sabu, 2006).
IntroductionTo establish the absolute effect of succession on communities in secondary tropical forests, we need to know species diversity in order to examine phylogenetic composition and how communities are organized along the succession gradients. In this study, I first assessed the diversity of a hyperdiverse ant genus Pheidole (Hymenoptera: Formicidae) in Rio Cachoeira Nature Reserve found in the tropical secondary forests of Brazil. Next, I examined the phylogenetic composition/ relatedness and structure of ant communities in this genus, and the processes structuring these communities. I also looked at how succession influences phylogenetic composition of species and community patterns. Lastly, I examined the phylogenetic structure of ant genera occurring in the tropical secondary forests and related this to the patterns observed when using species in the genus Pheidole alone.
1.2 Biodiversity of a hyperdiverse ant genus in secondary tropical forests
Globally, loss of tropical forest habitats has been identified as a major threat to biodiversity (Jenkins, 1992; Whitmore & Sayer, 1992; Pimm & Raven, 2000). This is likely so because most biodiversity is extraordinarily concentrated in tropical forests and habitat loss is widely anticipated to lead to a mass extinction of species if current rates of deforestation continue (Pimm et al., 1995; Dirzo & Raven, 2003). The biodiversity value of secondary forests in the tropics is an area of much uncertainty because most species of small-bodied taxa, which account for the vast majority of species in these forests, are under-described (Bihn et al., 2008). In addition, secondary forests are increasing in extent and importance as forest habitats throughout the tropics, and with the increased land-use dynamics; they are highly vulnerable to human degradation (Chazdon et al., 2009).This raises concerns over the threats to biodiversity and the desire to accurately describe and monitor as many species as possible before they disappear (Wiens, 2007).
A biodiversity survey using an invertebrate group would be of much relevance in regenerating forests owing to the major roles they play in ecosystems. For instance, ants (Hymenoptera: Formicidae) are a dominant invertebrate group in tropical forests, and their strong interactions with other organisms make them important ―keystone species in tropical forests (Bihn et al., 2008). Furthermore, ants structure their environment through their roles as seed dispersers (Beattie, 1985; Levey & Byrne, 1993), predators (Andersen, 1992; Kaspari, 1996; Philpott & Armbrecht,
2006) and ecosystem engineers (Lobry de Bruyn & Conacher, 1990; Folgarait, 1998).
Their abundance, as well as diversity, should trigger ecosystem functions (Walker, 1995). Given their importance, they are an obvious choice for a biodiversity study.
Ant systematics has a long history, summarized in Brown (1955) and Bolton (2003), yet our understanding of the species-level diversity of these organisms is far from complete and especially for hyperdiverse taxa such as the genus Pheidole. This genus ranges worldwide, and is particularly abundant in the tropics and subtropics.
According to Wilson (1976) it is one of the three most prevalent world ant genera in terms of its geographic range, species diversity and local abundance. Identification of
Introductionspecies rich taxa such as Pheidole can be challenging because; sometimes comprehensive identification (keys) literature is usually not available or is inadequate for most groups of arthropods (Brehm et al., 2008), dwindling finances and taxonomy experts and methodological issues among others (Knowlton, 1993;
Jarman & Elliot, 2000; Rubinoff, 2006; Rubinoff et al., 2006; Pires & Marinoni, 2010).
Nevertheless, species identification still continues either using traditional based methods especially morphological characters (Wiens & Penkrot, 2002; Ward, 2007), molecular characters (Blaxter, 2004; Floyd et al., 2002; Hebert et al., 2003a,b; Tautz et al., 2003) or a combination of multiple methods (Mengual et al., 2006, Smith et al., 2008).
In order to accelerate the analysis of biodiversity (Brooks et al., 2004; Smith et al., 2005) and thus increase the number of biodiversity inventories, DNA sequence data is successfully being used to test morphology-based taxonomies (Wiens & Penkrot, 2002; Smith et al., 2005; Smith et al., 2008). Congruence in biodiversity estimates when using any two or more methods in species identification is an indicator of methodological effectiveness, while inconsistency would mean the need for a further detailed examination of species in question. Furthermore, a combination of methods is likely to offer reliable biodiversity estimates and such information is of much value for conservation planning.
1.3 Phylogenetic composition and structure of ant communities in secondary tropical forests Habitat alterations and its effects to biodiversity is currently a main challenge for community ecologists and conservation biologists. Habitat disturbance leads to biodiversity losses, thus affecting species composition in communities (Fahrig, 2003) and also changes the balance of forces acting on local communities (Dinnage, 2009).
However, most studies of phylogenetic community structure especially in species rich tropical ecosystems have largely focused on plant communities (Chazdon et al., 2003;
Kembel & Hubbell, 2006; Letcher, 2010), and such high attention is yet to be given to invertebrates such as ants, despite their abundance, species richness (Floren & Linsenmair, 2000) and ecological dominance (Fittkau & Klinge, 1973; Rockwood & Glander, 1979; Floren et al., 2002; Rico-Gray & Oliveira, 2007) in these ecosystems.
IntroductionFurthermore, the search for patterns in the species composition, phylogenetic structure, and for the processes that cause these patterns, has seldom employed information about the phylogenetic relationships of species within those communities. Instead, in most studies, species are usually treated as equivalent units, with independent functional traits (Diamond & Case, 1986; Roughgarden, 1989;
Webb & Peart, 1999; Weiher & Keddy, 1999; but see Cotgreave & Harvey, 1991).