Drifting can be an effective way for aquatic organisms to disperse and colonise new areas. Increasing connectivity between European large rivers facilitates invasion by drifting aquatic macroinvertebrates. The present...Drifting can be an effective way for aquatic organisms to disperse and colonise new areas. Increasing connectivity between European large rivers facilitates invasion by drifting aquatic macroinvertebrates. The present study shows that high abundances of invasive species drift in the headstream of the river Rhine. Dikerogammarus villosus and Chelicorophium cur- vispinum represented up to 90% of the total of drifting macroinvertebrates. Drift activity shows seasonal and diel patterns. Most species started drifting in spring and were most abundant in the water column during the summer period. Drift activity was very low during the winter period. Diel patterns were apparent; most species, including D. villosus, drifted during the night. Drifting macroinvertebrates colonised stony substrate directly from the water column. D. villosus generally colonised the substrate at night, while higher numbers of C. curvispinum colonised the substrate during the day. It is very likely that drifting functions as a disper- sal mechanism for crustacean invaders. Once waterways are connected, these species are no longer necessarily dependent on dispersal vectors other than drift for extending their distribution range展开更多
There are gaps in our understanding of plant responses under different insect phytophagy modes and their subsequent effects on the insect herbivores＇ performance at late season. Here we compared different types of in...There are gaps in our understanding of plant responses under different insect phytophagy modes and their subsequent effects on the insect herbivores＇ performance at late season. Here we compared different types of insect feeding by an aphid, Lipaphis erysimi, and a lepidopteran, Plutella xylostella, and how this affected defensive metabolites in leaves of 2 Brassica species when plants gain maturity. Thiocyanate concentrations after P xylostella and L. erysimi feeding activities were the same. Total phenolics was higher after the phloem feeder feeding than the folivore activity. The plants compensatory responses （i.e., tolerance） to L. erysimi feeding was significantly higher than the responses to P xylostella. This study showed that L. erysirni had higher carbon than P xylostella whereas nitrogen in P xylostella was 1.42 times that in L. erysimi. Population size of the phloem feeder was not affected by plant species or insect coexistence. However, there was no correlation between plant defensive metabolites and both insects＇ population size and biomass. This suggests that plant root biomass and tolerance index after different insect herbivory modes are not necessarily unidirectional. Importantly, the interaction between the folivore and the phloem feeder insects is asymmetric and the phloem feeder might be a trickier problem for plants than the folivore. Moreover, as both plants＇ common and special defenses decreased under interspecific interference, we suggest that specialist insect herbivores can be more challenged in ecosystems in which plants are not involved in interspecific interference.展开更多
文摘Drifting can be an effective way for aquatic organisms to disperse and colonise new areas. Increasing connectivity between European large rivers facilitates invasion by drifting aquatic macroinvertebrates. The present study shows that high abundances of invasive species drift in the headstream of the river Rhine. Dikerogammarus villosus and Chelicorophium cur- vispinum represented up to 90% of the total of drifting macroinvertebrates. Drift activity shows seasonal and diel patterns. Most species started drifting in spring and were most abundant in the water column during the summer period. Drift activity was very low during the winter period. Diel patterns were apparent; most species, including D. villosus, drifted during the night. Drifting macroinvertebrates colonised stony substrate directly from the water column. D. villosus generally colonised the substrate at night, while higher numbers of C. curvispinum colonised the substrate during the day. It is very likely that drifting functions as a disper- sal mechanism for crustacean invaders. Once waterways are connected, these species are no longer necessarily dependent on dispersal vectors other than drift for extending their distribution range
文摘There are gaps in our understanding of plant responses under different insect phytophagy modes and their subsequent effects on the insect herbivores＇ performance at late season. Here we compared different types of insect feeding by an aphid, Lipaphis erysimi, and a lepidopteran, Plutella xylostella, and how this affected defensive metabolites in leaves of 2 Brassica species when plants gain maturity. Thiocyanate concentrations after P xylostella and L. erysimi feeding activities were the same. Total phenolics was higher after the phloem feeder feeding than the folivore activity. The plants compensatory responses （i.e., tolerance） to L. erysimi feeding was significantly higher than the responses to P xylostella. This study showed that L. erysirni had higher carbon than P xylostella whereas nitrogen in P xylostella was 1.42 times that in L. erysimi. Population size of the phloem feeder was not affected by plant species or insect coexistence. However, there was no correlation between plant defensive metabolites and both insects＇ population size and biomass. This suggests that plant root biomass and tolerance index after different insect herbivory modes are not necessarily unidirectional. Importantly, the interaction between the folivore and the phloem feeder insects is asymmetric and the phloem feeder might be a trickier problem for plants than the folivore. Moreover, as both plants＇ common and special defenses decreased under interspecific interference, we suggest that specialist insect herbivores can be more challenged in ecosystems in which plants are not involved in interspecific interference.
