keystone in biodiversity : indirect interactions

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(1) Two-factor ANOVAs detected significant herbivore effects and host-herbivore interactions in the three performance characters. In developmental time, a significant host effect was detected. These results indicate geographical difference not only in genetic architecture of P.versicolora but also in quality of S.integra.(2) The experiments demonstrated clearly density-dependent reduction in fitness through exploitative competition, leaf abscission, and egg dropping. However, the decreased fitness in high density was caused by natural enemy attacking. Common clutch size in the field shows the highest fitness, and increased density by aggregated oviposition would not decrease fitness. Hence, the oviposition strategy of the leaf miner would be almost adaptive.(3) Sawfly density and survival rate were negatively correlated with plant population age. Density of leaf-rolling moth and parasitoids increased with population age, but not for weevils. Parasitism was high in young population, whi … More le weevil-caused mortality was high in old population.(4) The number of new buds was greater and the length of new growing shoots was longer on damaged shoots than on non-damaged shoots. These results show that the compensatory shoot growth was caused by the death of the apical regions of the shoots due to spittlebug oviposition.(5) Both of patterns and proportions of leaf volatiles were species specific, although there were a wide variety in amount of each substance among clones. Difference in total amount of main volatiles between species was apparent : S.eriocarpa leaf included twenty times as much as in S.integra leaf.(6) Adult beetles on S.sachalinensis leaves preferred the agar disk treated with S.sachalinensis leaf extract to that treated with S.integra leaf extract. On the other hand, willow beetles fed on S.integra accepted both agar disks treated respectively with S.sachalinensis and S.integra. In both choice tests, the feeding ratio was quite similar to each other. There are at least two chemical species in S.integra (Atsubetsu-type and Shinkawa-type). Willow beetle could renew the generation on Shinkawa-type S.integra, but adult females could not oviposit when they were fed on Atsubetsu-type S.integra. Less