Cornus stolonifera is a ornamental trce species which was introdced to China in 1982. During the period of ten-year cxperiment a complete and systematic study on its botanical features, biological charcteristics, grow...Cornus stolonifera is a ornamental trce species which was introdced to China in 1982. During the period of ten-year cxperiment a complete and systematic study on its botanical features, biological charcteristics, growth rhythm and propagation tcchniques was carried out on basis of the comparison withthe native species Corms alba. The research results showed thatCornus stolonifera has many advantages over Cornus alba in those such as fast growing, cold endurance, drought resistance, easy propagation.disease and pest-resistance, beautiful tree form,bright colour branches, long florcscence, persistant fruits and intcgrate visual cffects. Practice has proved that it is reslly a fine species for tree-planting. Not only does it have the function of water conservation, but also its branches can be uscd as a fine wcaving matcrial. Up to the present,about ten thousand plant stocks have bcen planted by more than 30 units in l l cities of 6 provinces and it has been well recicved by people.展开更多
Context dependence arises when ecological relationships vary with the conditions under which they are observed. Context dependence of interactions involving parasites is poorly known, even if it is key to understandin...Context dependence arises when ecological relationships vary with the conditions under which they are observed. Context dependence of interactions involving parasites is poorly known, even if it is key to understanding host–parasite relationships and food web dynamics. This paper investigates to which extent predation pressure on an avian ectoparasite (Carnus hemapterus) is context-dependent. Based on a predator-exclusion experiment, predation pressure on C. hemapterus pupae in the host's nest for 3 years, and its variation between habitat types are quantified. Variation in precipitation and normalized difference vegetation index (NDVI) is also explored as a likely cause of context dependency. We hypothesize that predation pressure should fluctuate with such surrogates of food availability, so that inter-annual and intra-annual differences may emerge. The number of nests with significant reduction of pupae varied widely among years ranging from 24% to 75%. However, average pupae reduction in nests where a significant reduction occurred did not vary between years. No differences in predation rates between habitat types were detected. Precipitation and NDVI varied widely between years and NDVI was consistently lower around nests on cliffs than around nests on trees and farmhouses. Parallels were found between variation in predation pressure and precipitation/NDVI at a wide scale (highest predation the driest year, and much lower the 2 rainier ones), but not at the nest scale. This paper shows clear context-dependent insect predation pressure on an ectoparasite under natural conditions, and that such interaction changes in signs rather than magnitude between years. The causes for these variations require longer-term studies and/or well-designed, large-scale experiments.展开更多
文摘Cornus stolonifera is a ornamental trce species which was introdced to China in 1982. During the period of ten-year cxperiment a complete and systematic study on its botanical features, biological charcteristics, growth rhythm and propagation tcchniques was carried out on basis of the comparison withthe native species Corms alba. The research results showed thatCornus stolonifera has many advantages over Cornus alba in those such as fast growing, cold endurance, drought resistance, easy propagation.disease and pest-resistance, beautiful tree form,bright colour branches, long florcscence, persistant fruits and intcgrate visual cffects. Practice has proved that it is reslly a fine species for tree-planting. Not only does it have the function of water conservation, but also its branches can be uscd as a fine wcaving matcrial. Up to the present,about ten thousand plant stocks have bcen planted by more than 30 units in l l cities of 6 provinces and it has been well recicved by people.
文摘Context dependence arises when ecological relationships vary with the conditions under which they are observed. Context dependence of interactions involving parasites is poorly known, even if it is key to understanding host–parasite relationships and food web dynamics. This paper investigates to which extent predation pressure on an avian ectoparasite (Carnus hemapterus) is context-dependent. Based on a predator-exclusion experiment, predation pressure on C. hemapterus pupae in the host's nest for 3 years, and its variation between habitat types are quantified. Variation in precipitation and normalized difference vegetation index (NDVI) is also explored as a likely cause of context dependency. We hypothesize that predation pressure should fluctuate with such surrogates of food availability, so that inter-annual and intra-annual differences may emerge. The number of nests with significant reduction of pupae varied widely among years ranging from 24% to 75%. However, average pupae reduction in nests where a significant reduction occurred did not vary between years. No differences in predation rates between habitat types were detected. Precipitation and NDVI varied widely between years and NDVI was consistently lower around nests on cliffs than around nests on trees and farmhouses. Parallels were found between variation in predation pressure and precipitation/NDVI at a wide scale (highest predation the driest year, and much lower the 2 rainier ones), but not at the nest scale. This paper shows clear context-dependent insect predation pressure on an ectoparasite under natural conditions, and that such interaction changes in signs rather than magnitude between years. The causes for these variations require longer-term studies and/or well-designed, large-scale experiments.
