Print PageTropical plant diversity is extraordinarily high both at local and regional scales. Increasing evidence has demonstrated the critical role of natural enemies in maintaining local diversity via negative density-dependence, but we know very little about how natural enemies influence beta-diversity across habitats and/or regions. One way natural enemies could influence plant beta-diversity is by driving allocation tradeoffs that promote habitat specialization across resource gradients. We therefore predict that increasing resource availability should be accompanied by increasing herbivory rates and decreasing plant allocation to defense; and second, that relative abundances within plant lineages will reflect patterns of habitat specialization and allocation tradeoffs. A phylogenetic context is vital not only to compare homologous plant traits (including defense strategies) across habitat types, but also to be able to connect evolutionary tradeoffs to patterns of species diversification in each phylogenetic lineage. We test these predictions for forest trees in white-sand, clay terra firme and seasonally-flooded forests in Peru and French Guiana that well represent the range of soil fertility, forest structure, and floristic compositions found throughout the Amazon region. We established 74 0.5-ha plots in these habitats across ca. 50,000 km2 in each region, in which we characterized soil properties, forest structure, and floristic composition. We sampled all tree taxa and additionally focused on six focal lineages: Swartzia and Inga (Fabaceae), Protieae (Burseracaeae), Bombacoideae (Malvaceae), Micropholis (Sapotaceae), and Eschweilera+Lecythis (Lecythidaceae).To examine herbivory rates, we marked newly expanding leaves of saplings of the three most locally-abundant species in addition to representatives from the six focal lineages within 12 representative plots, and we tracked their fates bi-weekly for 32 weeks. We also measured total leaf production during this time and calculated relative herbivory impact by dividing herbivory rate by leaf production rate.
Results/Conclusions
Herbivory rates averaged 1.7% per week and did not vary across habitats and regions, but in French Guiana leaf production rate was significantly higher in terra firme and flooded forests than white-sand. Species with high rates of leaf production exhibited significantly higher relative abundances in terra firme and flooded forests with the reverse pattern true in white-sand forests Overall, focal species within lineages present contrasting patterns with regard to their herbivory rates and leaf production rate within habitats. These results highlight why a lineage-based approach is necessary when attempting to connect hypotheses regarding evolutionary trade-offs to community assembly patterns.
