Herbivore defenses of tropical tree species increase across a rainfall gradient
2 Écosystèmes montagnards, Irstea
3 University of Würzburg
O 2.3 in Research in its Prime: First Results of Ongoing Research
10.10.2013, 09:45-10:00, H6, GEO
In tropical forests, species distribution patterns vary across rainfall gradients. Herbivores are thought to play an important structuring role in this system. Under more humid conditions that favor high insect abundance, plant species that have evolved efficient defenses should have an advantage against species with low defenses. We hypothesized that defenses of woody species increase with their association to wet forests, reflecting the role of herbivores in driving species distributions patterns.
As a measure of defense, we assessed a preference index for 74 woody species growing along a rainfall gradient at the Isthmus of Panama through dual choice tests with caterpillars of the generalist Spodoptera frugiperda. We related this index to the distribution of the species across rainfall and nutrient gradients and mechanical defensive plant traits.
As hypothesized, effectiveness of defenses significantly increased with plant association to wet forests and increased with shade tolerance, reflecting the necessity to protect valuable photosynthetic tissue in dark environments. Defenses were not related to associations to soil nutrients nor deciduousness. The preference was not affected by the mechanical defenses assessed, suggesting that chemical defenses play a more important role in this system.
Our results indicate that herbivores and plant defenses against them are an important driver in shaping plant distribution and diversity patterns along tropical rainfall gradients.
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