Tropical forests are extremely diverse. One can find more than 1000 species of trees within a few square miles in many areas. For comparison, the entire U.S. contains about 600 species. It is also common to find many closely-related species in close proximity, despite predictions that close relatives should share similar traits and therefore competitively exclude one another. One phenomenon that may explain this pattern is that species composition can change dramatically with habitat. This idea will be tested by studying five common and diverse tree lineages that occur in three distinct forest types, surveying all of their species across large areas of Peru and French Guiana. Floras of both countries are highly diverse yet share very few species; this allows a powerful, replicated test of habitat specialization. DNA will be used to construct phylogenies of these five lineages to test if close relatives are generally found in different environments. Finally, a reciprocal transplant experiment will help determine whether closely related tree species share traits that confer flood tolerance, nutrient use efficiency, and defenses against natural enemies, and how these traits benefit survival in each habitat.
This project will determine the relationship between environmental heterogeneity, habitat specialization and species coexistence. The results will have importance to policy makers interested in conserving the forests with the highest biodiversity on Earth. The project will provide research opportunities for students within U.S. institutions and will also foster international exchange among the three countries by including Guianan and Peruvian students.
Tropical forests are extremely diverse and one can find more than 1000 species of trees within a few square miles in many; for comparison, the entire U.S. contains about 600 species. It is also common to find many closely-related species in close proximity, despite predictions that close relatives should share similar traits and, therefore, compete for the same resources. One phenomenon that may explain this pattern is that species composition can change dramatically with habitat. This idea was be tested by studying five common and diverse tree lineages that occur in three distinct forest types (white sand WS, terra firme TF, and flooded forests FF) and by surveying all of their species across large areas of Peru and French Guiana. Both countries are highly diverse yet share very few species; this allows a powerful, replicated test of habitat specialization. We found more than 300 species of trees from our five lineages in all three of the habitat types. A great majority of the species were found only in one of the three habitat types, confirming our hypothesis that habitat specialization is an important contributor to regional tree diversity in the Amazon basin. DNA was sequenced to both confirm our identifications as well as to construct phylogenies of these five lineages to test if close relatives are generally found in different environments. Different lineages exhibited radically different patterns. For example, in Protium (Burseraceae) white-sand specialists are generally not closely-related to one another, but in Pachira (Malvaceae) the two white-sand specialists in our forests are sister species. Finally, a reciprocal transplant experiment was used to determine whether closely related trees share traits that confer flood tolerance, nutrient use efficiency, and defenses against natural enemies, and how these traits benefit survival in each habitat. We found that habitat specialist species exhibited different traits corresponding to their home habitats, including large differences in specific leaf area, wood density and root morphology. Although species did not change their morphology or physiology when transplanted into a different habitat, most species were able to survive in all three habitats when transplanted; however, a combination of biotic (natural enemies and competition) and abiotic (soil nutrients, flooding regime) factors work in concert to produce the patterns of habitat specialization found in Amazonian forests. The results will have enormous importance to policy makers interested in conserving the forests with the highest biodiversity on Earth. Global climate change may change both flooding frequency and the abundance of insect herbivores in Amazonian forests of different habitat types, and knowing the mechanisms underlying species composition and habitat specialization will allow us to predict the future composition of these forests. Funds from this grant have provided research opportunities for U.S. undergraduate and graduate students as well as included French Guianan and Peruvian students and thus has fostered international exchange among the three countries.
