ecology of phasmids - KLUEDO - Universität Kaiserslautern

More documents

Recommendations

Info

Introduction 2 Regardless whether strong impact from higher or lower trophic levels limits herbivore populations, current theories assume that this selection pressure has led to narrow niches (Pianka 1966; MacArthur & Wilson 1967). Since food is one of the most important dimensions of the niche (Krebs 1989), niche breadth is generally expressed in terms of feeding specialization of herbivores (Bernays & Chapman 1994). This debate is of broad interest because estimates of global biodiversity are largely based on the degree of specialization of tropical insects. Just recently global biodiversity estimates were corrected from formerly stated 31 million (Erwin 1982) to about 4 to 10 million species (Ødegard 2000; Novotny et al. 2002a) because increasing research effort indicates that specialization is less pronounced than formerly supposed (Basset 1996, 1999; Basset et al. 1992, 1996; Barone 1998; Novotny et al. 2002a). Generally, these studies state that most tropical insect herbivores are rare (Basset 1996, 1999; Basset et al. 1992, 1996; Barone 1998; Novotny et al. 2002b), but they represent the plants view of herbivore specialization, i.e. the herbivore communities of one or several plant species are sampled, and thus may cover only a fraction of density and distribution patterns of insect herbivores. There is an enormous lack of research which addresses the densities of insect communities, let alone the densities and distribution of single insect herbivore species in tropical forests. The scarce information on this topic derives from studies using trap techniques (Wolda 1978, 1980, 1983, 1992; Smythe 1982), or describing the overall arthropod community (Janzen & Schoener 1968; Elton 1973). Beyond doubt, these studies contributed important baseline data for the development of general ideas, but they either incorporate species particularly prone to a certain trapping device, or all insect feeding guilds. Surprisingly few studies have reported the most basic demographic parameters for tropical insect herbivores, distribution and population density (Smiley 1978; Willig et al. 1986, 1993; Willig & Camilo 1991). 1.2 Current knowledge about tropical phasmid ecology Although phasmids are common herbivores in many tropical ecosystems, little is known about the biology of these hemimetabolous insects (Bedford 1978; Van den Bussche et al. 1989; Willig et al. 1986, 1993). The order Phasmatodea (walkingsticks and leaf insects) is one out of nine orders of phytophagous insects and contains approximately 3000 described species that occur worldwide with a concentration in tropical regions (Whiting et al. 2003). Generally, phasmids are considered as herbivore generalists although empirical studies on diet breadth of natural populations are missing (Bedford 1978; Willig et al. 1986, 1993; Sandlin & Willig 1993). The significance of phasmids as herbivores has attracted some interest as they can reach plague numbers and may cause severe damage to forests (temperate forests: Graham 1937; Australian Eucalypt forests: Campbell 1960, 1961, 1974; Campbell & Hadlington 1967) or to agricultural plantations (Pacific coconut plantations: Paine 1968; Swaine 1969). Such herbivores exerting strong pressure may be key
Introduction 3 agents in maintaining forest dynamics and ecosystem stability (Lowman 1984; Brokaw 1985; Schowalter et al. 1985; Brown et al. 1987). Their relevance as herbivores in tropical forests was confirmed in studies on the abundant endemic Puerto Rican species Lamponius portoricensis REHN. Population density of this polyphagous species seems to temporally vary to an enormous extent (Willig et al. 1986, 1993; Willig & Camilo 1991). Yet, besides drastic reductions in population densities following natural disturbance of high intensity (Willig & Camilo 1991) the causal factors of these fluctuations largely remain unknown. Host plant densities partly explained distribution patterns and patch densities of L. portoricensis (Willig et al. 1993), and individuals displayed differential preference among hosts depending on age, sex and prior experience (Sandlin & Willig 1993). This preference may be the result of specific nutritional constraints but could also reflect selection by predation pressure: Sandoval (1994) showed that color morphs of an endemic Californian species suffered differential predation on varying host plants thereby propagating specialization and speciation. A variety of behavioral and morphological adaptations underline the importance of predation-related selection on phasmid evolution. Most phasmids species exhibit a repertory of predation-avoidance behaviors (Robinson 1968a, 1968b, 1969; Bedford 1978). They live cryptic, resembling sticks and leaves, and the majority of species is active at nights (Bedford 1978). Most phasmid species dispose of glands (Bedford 1978) whose secretions were shown to deter predators (Eisner 1965; Eisner et al. 1997). Many phasmid eggs attract ants with a protein rich cap (Capitulum) and may thereby be protected from parasitoid wasps (Compton & Ware 1991; Hughes & Westoby 1992; Windsor et al. 1996). Information on phasmid species of Panamá is restricted to the early taxonomic work of Hebard (1923, 1929, 1933) and the studies about the defensive behavior of several phasmids by Robinson (1968a, 1968b, 1969). Panamanian phasmids have been observed feeding on plant species of the family Araceae (Robinson 1969). And phasmids are reported to feed on Piper spp. (Piperaceae) in Costa Rica (Marquis 1991) and Puerto Rico (Willig et al. 1986, 1993; Sandlin & Willig 1993). 1.2.1 Design and aims of the study In this dissertation, I take an approach to contribute to the understanding of the ecological processes affecting distribution and density of tropical insect herbivores. Starting from descriptive information on the phasmid community on Barro Colorado Island (BCI) (Chapter 2), the study then focuses on population parameters of the phasmid Metriophasma diocles WESTWOOD (Chapter 2&3) and on experiments on potential control factors related to the bottom-up (Chapter 4) and top-down (Chapter 5) views of population regulation (Figure 1-1).
Page 1 and 2: ECOLOGY OF PHASMIDS (PHASMATODEA) I
Page 5 and 6: ECOLOGY OF PHASMIDS (PHASMATODEA) I
Page 7 and 8: Acknowledgements I Acknowledgements
Page 9 and 10: Table of Contents III 3 Life cycle,
Page 11 and 12: List of Figures V List of Figures F
Page 13: List of Abbreviations VII List of A
Page 18 and 19: Introduction 4 Description of phasm
Page 20 and 21: Introduction 6 Solanum and Piper (T
Page 22 and 23: Introduction 8 1.3.4 Data analysis
Page 24 and 25: Community structure & host range 10
Page 46 and 47: Life history & potential population
Page 58 and 59: Adult female feeding preference & n
Page 66 and 67:
Adult female feeding preference & n
Page 68 and 69:
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
Page 84 and 85:
Page 86 and 87:
Page 88 and 89:
Page 90 and 91:
Page 92 and 93:
Predation mediated mortality & migr
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
Page 105 and 106:
Concluding remarks 91 6 Concluding
Page 107:
Abstract 93 7 Abstract Herbivory is
Page 110 and 111:
Literature cited 96 Basset, Y. 1997
Page 112 and 113:
Literature cited 98 Brown, B. J., M
Page 114 and 115:
Literature cited 100 Croat, T. B. 1
Page 116 and 117:
Literature cited 102 Hagerman, A. E
Page 118 and 119:
Literature cited 104 Kearsley, M. J
Page 120 and 121:
Literature cited 106 McNeill, S., T
Page 122 and 123:
Literature cited 108 Reich, P. B.,
Page 124 and 125:
Literature cited 110 Strong, D. R.,
Page 127:
Appendix 113 9 Appendix Please cont
Page 130 and 131:
Appendix 1: Phasmid species previou
Page 133 and 134:
Tabellarischer Lebenslauf Angaben z
Page 135:
Berger J., Schaefer, M., 1997. Wild
show all

ecology of phasmids - KLUEDO - Universität Kaiserslautern

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?