Over the last half century, complementary theories and hypotheses have been developed to try to explain the extraordinary variation in plant defensive strategies against herbivores, in which, syndromes of plant defences are driven by the influence of community responses, inherited functional traits, abiotic conditions, and the geographical and historical contingencies affecting the community. Therefore, a better understanding of which factors affect plant defences requires the use of holistic approaches. Specifically, we use elevation gradients as natural experiments to test classic hypotheses of plant defence theories across and within species. Recent work is showing two contrasting results.
Results/Conclusions
First, in accordance with the growth-defense trade-off hypothesis, we observed that high elevation plants grow smaller and are more defended than their low elevation congeneric. In opposition, we also observed that at high elevation plants that are less eaten by herbivores, are less defended, and that colder temperature inhibits secondary metabolites induction. To conciliate these two contrasted results we suggest that rare high elevation plants rely on higher toxicity to survive. Whereas high elevation dominant plants rely primarily on tolerance and less on defensive chemistry to cope against herbivores. We thus argue that only a holistic approach such as this one will enable us to fully grasp the factors shaping the incredible diversity of secondary metabolites in plants