Dissertation Research: Herbivory and the Evolution of Habitat Specialization in Amazonian White Sand and Clay Forests

热带森林包括多种多样的生境，这导致了植物的专业化。在秘鲁亚马逊的伊基托斯附近，营养贫乏的白色沙地森林与营养丰富的粘土森林相邻，每一个都有一种独特的栖息地专家树木。为什么会发生栖息地专业化？我们的假设是贫瘠的土壤和草食动物的结合为白色沙地森林中的植物防御创造了强大的选择压力。因此，没有进化出高水平的抗草食动物防御的物种在白色沙地森林中处于不利地位，并被草食动物排除在外。为了测试草食动物是否在白色沙地植物中选择更高的最佳抗草食动物防御，我们比较了来自6个属的33个物种的防御投资，其中包括几对遗传上独立的密切相关的白色沙地和粘土专家。此外，我们还建立了一个相互移植实验，以操纵草食动物的存在，并直接测试在何种程度上草食动物保持两种森林类型之间的物种组成的低重叠。如果食草动物对栖息地特化有显著影响，这将表明食草动物可能影响植物进化的一种新方式：由于非生物因素，通过锐化栖息地边界，从而增加栖息地特化的潜力。

Tropical forests include a diversity of habitats, which has lead to specialization inplants. Near Iquitos, in the Peruvian Amazon, nutrient-poor white sand forests are foundimmediately adjacent to nutrient-rich clay forests, each harboring a unique compositionof habitat specialist trees. Why does habitat specialization occur? Our hypothesis is thatthe combination of impoverished soils and herbivory creates strong selective pressure forplant defenses in white sand forest. Species that have not evolved high levels ofantiherbivore defense are therefore at a disadvantage in white sand forests and excludedby herbivores.To test whether herbivores select for higher optimal antiherbivore defense inwhite sand plants, we are comparing defense investment in 33 species from 6 genera thatinclude several phylogenetically independent pairs of closely-related white sand and clayspecialists. In addition, we have established a reciprocal transplant experiment tomanipulate the presence of herbivores and directly test to what degree herbivoresmaintain the low overlap in species composition between the two forest types. Ifherbivory has a significant effect on habitat specialization, it will suggest a new way thatherbivores may influence plant evolution: by sharpening habitat boundaries due to abioticfactors and thereby increasing the potential for habitat specialization.