ecology of phasmids - KLUEDO - Universität Kaiserslautern

More documents

Recommendations

Info

Introduction 4 Description of phasmid community parameters (in the field from linetransects) Diversity Top-down control Predation-mediated mortality of nymphs (field experiment) Biotic Distribution Focus on population Estimates potential Abundance parameters of from lab Potential food Realized niche Metriophasma diocles population niche Bottom-up control leaf traits of host-plants and their effects on performance of nymphs and preference of adults (feeding trials in the lab) Figure 1-1: Study design: The outer circles represent the main focuses of Chapters 2 to 5. As a first step, Chapter 2 addresses the structural aspects of the phasmid community on BCI. Distribution and abundance of herbivores may be modulated by resource limitation (e.g., Joern & Gaines 1990), and knowledge about the food niche of herbivores is crucial for an evaluation of resource restrictions. If phasmids behave as specialists, their habitat should generally reflect the habitat of their host plants. In contrast, generalists should be less dependent on host plant distribution. Thus uncovering the diet breadth of herbivores directly relates to understanding habitat choice. In combining information on (1) plant species phasmids were observed on along line-transects with (2) feeding-trials in the lab the realized food niche can be separated from other niche dimensions that are typically incorporated in field studies. The difference between realized and absolute food niche then allows to conclude on other impact factors like climate or natural enemies. The estimation of phasmid densities provides a basis for the following chapters. The realized population densities reflect an organism in the boundaries of its environment (Begon et al. 1996). In Chapter 3, I meet the question what is the inherent potential of the phasmid species Metriophasma diocles to reproduce free from environmental limitations. I modeled the potential population growth of M. diocles on the basis of life cycle parameters like sex ratio, female fecundity and generation time assessed from a laboratory population. The difference between potential and realized
Introduction 5 population densities then reflects the impact of control. Population control factors can act pre- or postnatal. Here, I present a first estimate of egg mortality and failed hatching and show the effect of prenatal mortality on potential population increase of M. diocles. Dietary constraints of M. diocles are the subject of Chapter 4, addressing the bottom-up view of herbivore regulation. Nutritious requirements of phasmids may be age or sex-specific (e.g., Cassidy 1978; Sandlin & Willig 1993), and early life stages of herbivorous insects may suffer high mortality depending on the food source and its species-specific physical and chemical leaf characteristics (Joern & Gaines 1990; Belovsky & Slade 1995). In feeding-trials, I observed performance (sensu growth and survival) of first instar nymphs and preference of adult females on different host plants reflecting M. diocles host range. Performance of nymphs and preference of adults were analyzed with respect to particular defensive leaf traits that potentially reduce digestibility of the foliage or are toxic to the organism. In Chapter 5 I am concerned with the top-down view of M. diocles population regulation. In a predation-exclusion field experiment I assessed the impact of predators on first instar nymphs of M. diocles. A general pattern in insects is high mortality of early life stages with high impact of predation, particularly by parasitoids (Cornell & Hawkins 1995; Cornell et al. 1998). While these patterns arose from studies on holometabolous insects, knowledge on hemimetabolous herbivores mainly originates from studies on temperate grasshoppers (e.g., Joern & Gaines 1990; Belovsky & Slade 1995; Oedekoven & Joern 1998). 1.3 Site characterization and general methods 1.3.1 Study site, vegetation and climate The study took place on Barro Colorado Island (BCI; 9 o 09’N, 79 o 51’W), a field site of the Smithsonian Tropical Research Institute (STRI) in Panamá (Figure 1-2). The island of 1567 ha is located in the lake Gatun. This freshwater lake was dammed up between 1911 and 1914 during construction of the Panama Canal. The island is the centerpiece of the 5600 ha Barro Colorado Nature Monument (BCNM) that was established in 1978 and includes the adjacent mainland peninsulas. In 1923, BCI was declared as biological reserve and in 1946 it became a unit of the Smithsonian Institution. Since then, the island has become one of the most intensively studied areas in the tropics. BCI is completely covered with semi-deciduous tropical moist forest of several successional stages (Foster & Brokaw 1982). The northeastern part of the island consists of 100 to 200 year old secondary forest whereas old forest of 200 to 400 years covers most of the southeast of BCI. A small strip of old forest remained south of the laboratory (surrounding Lutz Creek). The area around the laboratory is cleared and the vegetation is dominated by pioneer plant species such as Cecropia, Ochroma, Trema,
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 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 68 and 69:
Adult female feeding preference & n
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?