Effects of Fragmentation and Degradation of Kenyan Rainforests
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Effects of fragmentation and degradation of an afrotropical rain forest on the diversity structure of leaf beetle communities (Coleoptera, Chrysomelidae) Dissertation zur Erlangung des Doktorgrades (Dr. rer. nat.) der Mathematisch-Naturwissenschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn vorgelegt von Wolfram M. Freund aus Buenos Aires / Argentinien Bonn 2004 Angefertigt mit Genehmigung der Mathematisch-Naturwissenschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn 1. Referent: Prof. Dr. Johann Wolfgang Wägele 2. Referent: Prof. Dr. Wolfgang Böhme Tag der Promotion: 18.02.2005 Diese Dissertation ist auf dem Hochschulschriftenserver der ULB Bonn http://hss.ulb.uni-bonn.de/diss_online elektronisch publiziert. Erscheinungsjahr: 2005 Für meinen geliebten Vater, Hans Christian Freund (*1933 − †1990) Chochote chaweza kutukea – Anything can happen anytime Kenianisches Sprichwort 1 Index Index Index ...............................................................................................................................1 1. Introduction................................................................................................................3 1.1. Evolution of African forests ...................................................................................3 1.2. How many species are there?...............................................................................5 1.3. Stochasticity versus deterministic equilibrium models...........................................7 1.4. Objectives .............................................................................................................8 2. Material and methods..............................................................................................11 2.1. Study time and area............................................................................................11 2.2. Canopy dwelling arthropods collected by insecticidal tree fogging .....................16 2.2.1. Sampling procedure .....................................................................................17 2.2.2. Trees investigated ........................................................................................18 2.2.3. Efficiency of the fogging technique...............................................................20 2.3. Evaluation of fogging experiments ......................................................................21 2.3.1. Sample sorting..............................................................................................21 2.3.2. Beetle morpho-types and beetle species......................................................21 2.3.3. Allocation to feeding guilds...........................................................................23 2.4. Diversity measures..............................................................................................23 2.4.1. Alpha-diversity..............................................................................................24 2.4.2. Beta-diversity................................................................................................28 2.5. Statistical approach and multivariate analysis.....................................................29 2.5.1. Statistics .......................................................................................................29 2.5.2. Multivariate analysis .....................................................................................29 3. Results......................................................................................................................31 3.1. Distribution patterns of arthropods ......................................................................32 3.1.1. Rainy season X. 2001 ..................................................................................32 3.1.2. Rainy season X. 2002 ..................................................................................35 3.1.3. Dry season I. 2002 .......................................................................................38 3.1.4. Dry season I. 2003 .......................................................................................40 3.2. Distribution patterns and diversity of beetles.......................................................43 3.2.1. Diversity at different forest sites....................................................................44 3.2.2. Diversity at different seasons .......................................................................45 3.2.3. Feeding guilds ..............................................................................................46 3.2.3.1. Predacious beetles ................................................................................47 2 Index 3.2.3.2. Mycetophagous beetles ........................................................................ 53 3.2.3.3. Chrysomelidae ...................................................................................... 59 3.2.3.4. Weevils (Curculionidae and Apionidae) ................................................ 65 4. Discussion............................................................................................................... 72 4.1. Distribution patterns and seasonality of non-beetle arthropods.......................... 72 4.2. Distribution patterns and seasonality of beetles ................................................. 78 4.3. Critical considerations on the methodology........................................................ 82 4.4. Herbivory, host plant specificity and global diversity .......................................... 83 4.5. Does fragmentation of forests influence beetle communities? ........................... 89 5. Summary ................................................................................................................100 6. References .............................................................................................................105 Appendix ....................................................................................................................128 Introduction 3 1. Introduction Tropical rain forests, which cover only six to seven per cent of the earth’s landmass, deserve our particular attention and protection, since they probably contain 50 % of the global biodiversity (Myers 1979, Wilson 1988, Linsenmair 1990, Bierregaard et al. 2001). The loss of these ‘biodiversity hotspots’ (Myers 1988, Barthlott et al. 1999, Myers et al. 2000) would mean extinction of a tremendous number of species, although they can receive protection with a comparative low expenditure of money and staff. Despite strong efforts of scientists and politicians, many of these regions are highly endangered. With losses of more than five million hectares per year, accounting for 56 % of the global reduction in forest cover (FAO 2003), African forests are among the most threatened ecosystems worldwide (Achard et al. 2002, Groombridge & Jenkins 2002). East African forests are particularly diverse and endangered but are still little-known ecosystems. Distributed over a highly variable landscape dominated by savannas and thorn bushes, these forests are outstandingly species rich as well as centres of endemism (Fjeldsa & Lovett 1997). They play an important role as cultural heritages and are a traditionally and intensively used resource for the local populations (UNEP 2002). With an increase of the human population in East Africa throughout the last decades, the pressure on biodiversity largely increased and the use of the forest ecosystems is far from being sustainable. Generally, there is no doubt on a local and governmental level that at least core areas of tropical forests need to be maintained and conserved for future generations. 1.1. Evolution of African forests It has been suggested that African forests once contained a more diverse fauna and flora, but suffered from extinction processes at times of severe climate changes, especially during dry phases of the Quaternary (Stein & Sarnthein 1984). The forest cover in tropical Africa was strongly affected by climate changes during the Holocene and was at its minimum during the cooler and more arid periods of the ice ages (Hamilton 1992). At this time they were confined to a number of relatively small refugia, isolated from each other, at orographically favoured places, e.g. the mountains of Kenya (Hamilton 1992). Rain forest occurred only at specific altitudes in these mountains, because both open country and high mountain regions became too dry and cold, respectively. During warmer and wetter conditions lowland forest cover could spread from those refugia. The maximum postglacial spread of forests in tropical Africa was attained some thousand years after 10000 BP (before present). Comparisons of pollen from deep-sea cores (e.g. van Campo et al. 1982) and meteorological models of 4 Introduction climatic change (Rossignol-Strick 1983) revealed that most, though not all, ice ages resulted in dry periods in tropical Africa, characterised by forest reduction (for climatic change see also Thompson et al. 2002). The severity of the arid periods increased during the Quaternary (Stein & Sarnthein 1984) and a period of generally drier climatic conditions started about 4000 years ago (Hamilton 1992, Thompson et al. 2002). During interglacial periods wetter conditions returned, correlated with forest expansion. The alternate advances and retreats throughout the last millennia led to a natural fragmentation of the forests. This state of natural forest reduction