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The Distribution of Galls of Neuroterus (Hym: Cynipidae) on oak

R. R. Askew
Journal of Animal Ecology
Vol. 31, No. 3 (Oct., 1962), pp. 439-455
DOI: 10.2307/2045
Stable URL: http://www.jstor.org/stable/2045
Page Count: 17
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The Distribution of Galls of Neuroterus (Hym: Cynipidae) on oak
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Abstract

1. Spangle galls of Neuroterus numismalis (Fourc.), N. quercusbaccarum f. lenticularis (Oliv.), N. albipes f. laeviusculus Schenck and N. tricolor f. fumipennis Htg. often occur together in high densities suggesting the possibility of interspecific competition for leaf space. 2. More trees than would be expected if the species were distributed independently bore galls of all four species or of none, and discounting the rarer fumipennis a positive correlation between the distributions of any two of the remaining three species was found. 3. Any one tree usually supported a similar gall population in 1958 and 1959. 4. Galls of numismalis, and to a lesser extent lenticularis, were most abundant on the trees whose leaves opened later; those of laeviusculus were distributed independently of the date of leaf opening. 5. The date of leaf opening could account for the positive association between numismalis and lenticularis galls, but the positive associations between numismalis and laeviusculus and between laeviusculus and lenticularis were probably the result of another tree factor. 6. This tendency for all species to occur on the same trees increases the possibility of interspecific competition. 7. Galls of numismalis were most abundant towards the top and periphery of a tree, laeviusculus towards the base and near to the trunk, and lenticularis was concentrated in an intermediate position. 8. Galls of fumipennis were almost entirely confined to lammas leaves, on which they were the only gall occurring. 9. Galls of numismalis were concentrated towards the apex of a leaf, laeviusculus galls towards the base, and lenticularis galls towards the central region. 10. This zonation of galls of numismalis, lenticularis and laeviusculus on a tree and on a leaf, and the occurrence of fumipennis galls on lammas leaves, must reduce any tendency towards interspecific competition for space. 11. There was a slight tendency for galls of the sexual generations, N. numismalis f. vesicator (Schlecht.), N. quercusbaccarum (L.), N. albipes (Schenck) and N. tricolor (Htg.), to occur together on the same trees, and also on the leaves formed from the same bud. 12. Similar populations of galls of the sexual generations were borne in 1958 and 1959 on any particular tree. 13. Galls of numismalis and quercusbaccarum occurred in larger numbers on those trees whose leaves opened first. The distribution of galls of albipes, and possibly tricolor, was independent of the date of leaf opening. 14. The distributions of galls of numismalis and its alternate generation vesicator were negatively correlated, as were the distributions of lenticularis and quercusbaccarum. The distributions of galls of laeviusculus and albipes were slightly positively correlated. 15. The negative association between numismalis and vesicator, and between lenticularis and quercusbaccarum, was probably a result of the preference of the agamic generations for trees whose leaves opened late, and of the sexual generations for trees whose leaves opened early. 16. This negative association was less pronounced than expected; this, together with the positive association between laeviusculus and albipes, perhaps indicates another tree factor which renders a tree either more or less suitable for supporting galls of all species. 17. Critical dates in the life cycles of the species are discussed. 18. The distribution and numbers of Neuroterus galls on mature oak trees differs from that on young trees, and the differences could in part be due to the earlier date of leaf opening of the mature trees. No spatial zonation of spangle galls was apparent on the mature trees.

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