Plants are attacked by a multitude of（大批的，众多的） insects and mammals. As defense against these herbivores（食草动物） they developed complex defense mechanisms over the course of evolution: spines, thorns, leaf hairs and a number of toxic chemical substances. For decades it has been controversially discussed whether the production of defense traits incurs（招致，引发） costs to the plants. Now, using a new method the ecologists and plant biologists of the University of Zürich together with their American colleagues demonstrate these costs accurately in a Proceedings of the Royal Society article. For their study, the researchers planted different «knockout»-mutants of the same genotype of the model plant Arabidopsis thaliana. They then harvested a subset of these plants in evenly distributed intervals to measure the biomass growth over the whole plant life. «Mutants with suppressed defense mechanisms showed an increased growth rate» Tobias Züst explains the result of his study. But the faster growth comes at an added cost: aphids（蚜虫类） reproduce faster on these plants than on slow growing plants with intact defense mechanisms. This is a result of the fact that fast growing plants provide more resources to the herbivore than slow growing plants in the same amount of time.

The study shows that natural resistance is often not compatible with fast growth. This finding is of great importance for agricultural crops: These crops have been selected for high yield and as a consequence have very low natural resistance to herbivores, consequentially（必然地） requiring high input of insecticides.