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66 The abundance of soil fauna, i.e. numbers of individuals per sample, was compared between S. inaequidens and S. jacobaea by an ANOVA for effects of species, zone and their interaction. For the main taxa, the numbers of individuals were compared between the two plant species by Mann-Whitney U tests. A principal components analysis (PCA) was used to extract the axes summarising the community structure of soil samples. These analyses were performed with STATISTICA 7 (Statsoft 2006). In addition, Shannon-Wiener’s index (H’) was calculated for soil arthropod communities associated to S. inaequidens and S. jacobaea. A t-test was applied on these data to test for a difference between the two Senecio species. Results The overall abundance of soil fauna was significantly lower (F= 7.46, p= 0.014) under S. inaequidens in comparison with S. jacobaea, with respectively 76 ± 62 (or 15,300 individuals m -2 ) and 186 ± 153 individuals per sample (or 37,000 individuals m -2 ). This difference was essentially due to the Collembola Arthropleona (Table 1), which were very abundant in S. jacobaea samples (19,000 individuals m -2 ), while they were six fold less abundant in S. inaequidens samples (3,500 individuals m -2 ). Gamasid mites were twice more abundant in S. jacobaea samples compared to S. inaequidens, but this difference was only marginally significant. None of the other taxa differed significantly in their abundance under the two plant species. Notably, no significant difference was detected in the number of homopteran and heteropteran herbivores (Table 1). The effect of the zone was marginally significant on the abundance of soil fauna, with a tendency of higher densities in the mixed zone (Figure 1). No significant interaction zone*species was detected. Taxonomic richness was similar between S. inaequidens and S. jacobaea (Table 1). However, the Shannon diversity index was lower for S. jacobaea (H=1.54 and evenness = 0.52) than for S. inaequidens (H= 1.96 and evenness = 0.71) and this difference was highly significant (T-test: t=-10.19, p
Table 1. Abundance of soil fauna expressed as the total number of individuals (N) for each identified taxon in soil samples collected under S. inaequidens and S. jacobaea (12 samples per species) and percentage of the total number of individuals (%). Feeding groups: herbivore (H), microbivore-mycophagous (M), predator (P), honeydew (*), saprophagous (S), undetermined or diverse (?). Numbers in brackets are the minima and maxima per sample. Mann-Whitney U tests for difference between the two plant species (for taxa present in more than half the samples): * and + indicate respectively significant (p
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Science Facing Aliens Proceedings o
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Segers, H & E. Branquart (Eds). Sci
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Welcome to the World? Non-native br
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these geese species exchange betwee
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References Anselin A., Geers V. & K
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8 variables, hydro-morphological ch
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10 References Bollache, L., Devin,
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12 Figure 1 - USDA hardiness zones
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Page 55: References Berger, L., 1988. On the
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Page 60 and 61: 54 Ring-necked parakeets in Belgium
Page 62 and 63: 56 Our models predict a mean number
Page 64 and 65: 58 Strubbe D. & Matthysen E., 2009c
Page 66 and 67: 60 Study area & data collection Lie
Page 68 and 69: 62 cm) and age of the tree and comp
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