ecology of phasmids - KLUEDO - Universität Kaiserslautern

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Adult female feeding preference & nymph performance 54 attained in all cases. However, failure to meet the assumption of homogeneity of variances is not fatal to ANOVA. Analysis of Variance still remains robust, even when groups are of different sample sizes (Zar 1999, p. 185 and references therein). Data on leaf toughness, specific leaf weight and total phenol content were log-transformed before statistical analysis. As water content and MAI were expressed on a relative scale data were arcsine transformed. Interspecific variation in leaf characters was then analyzed in ANOVA. 4.3.1 Analysis of preference In relation to P. marginatum preference of M. diocles females for 12 Piper and two Philodendron species was tested. On the base of consumed leaf dry material I calculated a mean acceptability index (MAI) (Richardson & Whittaker 1982) from the ratios of consumed dry weight (dw) of test material to the total of consumed dry weight in each replicate: (Equation 4-1) [consumed dw] test MAI = [consumed dw] + [consumed dw] test reference The MAI allows to group plant species to their ranking as acceptable food source of a distinct phasmid species and ranges from cero to one. MAI-values below 0.5 and down to cero thereby indicate preference for P. marginatum whereas values above 0.5 represent preference towards the test plant species. Consumption ratios from feeding trials were not normally distributed. The distribution of MAI values was two-tailed as 0 and 1 ratios derived frequently resulting from females eating only one food source. Consequently differences in preference among food plant species were tested by nonparametric Kruskal-Wallis ANOVA. Preference is expressed as median MAI. The median of the MAI corresponded significantly with its mean (Product Moment Correlation r = 0.98, df = 12, P < 0.01) and median MAI values were normally distributed. Thus the relationships between each leaf trait and the established preference pattern were analyzed in parametric Product Moment Correlation Analysis. A test series of dual-choice feeding trials was conducted where nymphs were offered leaf discs with artificially increased phenol and tannin contents. Resulting preferences, expressed as MAI, were compared in Mann-Whitney U-tests. The calculation of the MAI is described above. 4.3.2 Analysis of performance Survival of nymphs was analyzed by the Kaplan-Meier estimate (also known as the product-limit estimate). The survival function gives the probability that an individual survives past a given time. Differences in survival times were analyzed by the Mantel-Cox log-rank test (Mantel 1966; Cox 1972). Under the assumption that deaths of nymphs were independent the Mantel-Cox test proved suitable for the dataset as it gives equal weight to all events.
Adult female feeding preference & nymph performance 55 For reasons of sample size resulting from partially high nymph mortality (in D. longispatha and P. grande no nymphs had survived beyond week three) relative growth rates of nymphs were calculated after approximately 14 days. For the same reasons weight measures spread from day eight to day 17 with 73 % of values referring to days 11 to 16. To account for temporal differences growth was calculated on a daily base as growth rate [mg*d -1 ]. Initial weight of nymphs was significantly different among groups (i.e., nymphs fed on different plant species) (ANOVA, F = 31.9, df = 12, P < 0.01). Calculation of relative growth rates (RGR) accounted for initial weight of nymphs and incorporated possible covariate effects: Equation 4-2 final weight - initial weight 1 RGR = × days initial weight The relative growth rate expresses the weight gain relative to the initial weight at the start of an experiment per unit time (relative weight gain per day). Plant species-specific relative growth rates of nymphs were then compared in Analysis of variance (ANOVA). The relationships between each leaf trait and survival and growth of nymphs were analyzed in parametric Product Moment Correlation Analysis. D. longispatha was not included in correlation analysis, because representative measurements of leaf traits could not be taken before the end of the study period. 4.4 Results 4.4.1 Interspecific differences in physical and chemical leaf properties All measured leaf characters showed significant interspecific differences indicating that host plant species of M. diocles varied in nutritional quality. Mean values are listed in Table 4-1 including the short names for plant species that are used in the Figures. M. diocles food plants showed expressed heterogeneity in leaf toughness (Figure 4-2). Relative leaf toughness varied significantly among host plant species with leaves of Philodendron sp. possessing a fivefold higher relative toughness (505.47 ± 41.68) than Piper marginatum (102.40 ± 14.82). Although P. marginatum had lowest leaf toughness there was no significant difference to P. arboreum and P. hispidum. All tested Piper species showed significantly lower relative toughness in leaf tissue than the tested Araceae of the genus Philodendron. However, variation in toughness among Piper congeners was considerably high: P. cordulatum and P. grande (296.37 ± 29.98 and 323.36 ± 31.38) had threefold tougher leaves than P. marginatum. The pattern of interspecific differences in relative leaf toughness seemed to be expressed stronger than patterns assessed from other leaf characters (see below). No more than three plant species had similar toughness values.
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ECOLOGY OF PHASMIDS (PHASMATODEA) I
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ECOLOGY OF PHASMIDS (PHASMATODEA) I
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Acknowledgements I Acknowledgements
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Table of Contents III 3 Life cycle,
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List of Figures V List of Figures F
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List of Abbreviations VII List of A
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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
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
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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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