ecology of phasmids - KLUEDO - Universität Kaiserslautern

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Community structure & host range 30 decreasing availability of patches with suitable hosts is inherent (particularly in high diverse tropical rainforests). This may explain why both sexes of M. diocles dispose of cost intensive wings. Higher mobility as compared to wingless phasmids may allow them to search for scattered resources more efficiently. But finding suitable resource patches also represents a critical challenge for nonvolant phasmids like the generalistic O. martini and B. ploiaria. In B. ploiaria only the male is winged and able to fly short distances (personal observation) while in O. martini both sexes are wingless. Their restricted host range consisting of characteristic gap plant species involves the risk of depleting host plants when a light gap closes. Then the detection of a new gap becomes crucial; the more as nonvolant phasmids were shown to move at low velocities (a maximum of 6 m per day; Willig et al. 1986). I suggest that gap phasmid species may escape from being doomed because their diet contains liana species. I argue that the wingless habitus of the Otocrania species does not contradict its specialization, because Otocrania specialized on Sapindaceae, a plant family that contains many lianas such as Paullinia spp. and Serjania spp. (Croat 1978). Lianas may contribute up to 14 % of above ground biomass in tropical forests (Gerwing & Farias 2000). They are characteristic components of early successional habitats such as gaps, but they are also present all over the canopy (Putz 1984, DeWalt et.al. 2000; Schnitzer & Bongers 2002). Thus, phasmids that include lianas into their diet may find sufficient food in upper canopy. The generalistic O. martini and B. ploiaria that were abundant in forest edges may on their search for new light gaps be able to traverse the forest canopy and rely on lianas. In contrast, the forest canopy may represent the preferred habitat of the specialist Otocrania sp. and thereby explain its low abundance in my study. 2.4.4 Conclusions Broadening the meaning of specialization, I presented evidence that phasmids are specialized to habitat specific food resources and that their distribution was clearly connected to the distribution of their host plants (as reflected by their successional status). The higher density and species richness of phasmid species in forest edges as compared to the understory may reflect their evolution with less defended fast growing pioneer plants of high nutritious quality (Coley 1983; Coley et al. 1985). The refusal of foliage of persistent late successional tree species gives support to this view. Other than by resources, the distribution of an herbivore can be influenced by its natural enemies. Contagiousness could then be due to differential predation, i.e. an herbivore species suffers less predation related mortality on a particular host plant species (Sandoval 1994; Price et al. 1980; Bernays & Graham 1988). Such mechanisms could have led to narrow host range including unrelated plant species of M. diocles. Low abundances of M. diocles in the understory then would result from high predation pressure rather than from nutritious limitations through the host plants.
Life history & potential population growth 31 3 Life cycle, potential population growth, and egg hatching failure of Metriophasma diocles 3.1 Introduction Great variation in patterns of population densities clearly exists in herbivorous insects, but generally most insect species in the tropics occur in low numbers (e.g., Elton 1973; Basset et al. 1992; Basset 1997, 1999; Novotny & Basset 2000). Such low population densities reflect the biotic potential of a species in the limiting boundaries of habitat capacity, intraspecific competition and regulating mechanisms within trophic cascades. A whole wealth of factors acts on individuals in a population thereby affecting net recruitment (i.e., births minus deaths). These factors either do not respond to population density or are density-dependent and can be roughly categorized as: (1) intraspecific density-dependent factors, (2) environmental density-dependent factors, and (3) density-independent factors. The upper limit of population size is defined by intraspecific competition. Intraspecific competition as density-dependent regulation factor increases with population size. Higher competition leads to increasing death and decreasing birth rates resulting in a population decline (and vice versa). At a certain density, birth and death rate are equal and there is no net change in population size. This density is known as carrying capacity (K). The carrying capacity represents the population size the resources of the environment can just maintain without a tendency to either increase or decrease (Begon et al. 1996). However, natural populations lack simple carrying capacities. Alongside with intraspecific competition, populations are regulated by multiple factors reducing the population size below the carrying capacity. Most factors in the biotic setting of a species respond to population size. Density of prey translates into predator densities (Volterra 1926; Lotka 1925), and diseases spread faster in higher populated areas (e.g., Stevenson 1959). Increasing population density also involves decreasing food availability and higher levels of interspecific competition (reviewed in Schoener 1983). Other biotic factors like intrinsic food quality or breeding sites on the other hand do not relate to population density, but their limited nutritious value or availability may act as regulators (Andrewartha & Birch 1954, 1984). Likewise, abiotic factors such as climate and natural disasters are density independent and can cause drastic impact on populations (e.g., Willig & Camilo 1991). Releasing a population from regulating constraints can uncover the impact of the above described control factors. When there are no limits on its growth, the population of a species will increase infinitely according to its biotic potential, i.e. the inherent power of an organism to reproduce and survive (Chapman 1931). The intrinsic rate of natural increase (r) will then be at its maximum. That means each individual of the population will contribute to population growth with peak reproduction (Begon et al. 1996). In natural populations, most individuals are not capable of peak productivity
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 16 and 17: Introduction 2 Regardless whether s
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 92 and 93: Predation mediated mortality & migr
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Predation mediated mortality & migr
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Concluding remarks 91 6 Concluding
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Abstract 93 7 Abstract Herbivory is
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Literature cited 96 Basset, Y. 1997
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Literature cited 98 Brown, B. J., M
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Literature cited 100 Croat, T. B. 1
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Literature cited 102 Hagerman, A. E
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Literature cited 104 Kearsley, M. J
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Literature cited 106 McNeill, S., T
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Literature cited 108 Reich, P. B.,
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Literature cited 110 Strong, D. R.,
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Appendix 113 9 Appendix Please cont
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Appendix 1: Phasmid species previou
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Tabellarischer Lebenslauf Angaben z
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Berger J., Schaefer, M., 1997. Wild
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