Are macroevolutionary patterns of tropical forests correlated to climatic perturbations? How did different scales of space and time affect those patterns and their underlying processes? I have been studying the patterns of plant diversity in equatorial latitudes during the Paleocene-Eocene warming and Oligocene cooling climates. The Paleogene offers a unique opportunity to study the coordination of tropical rain forests and climate change. I have studied the response of tropical forests in northern South America (mainly Colombia and Venezuela) to global warming at two different scales of time and warming intensity. The first warming event that I studied occurred 55.5 million years ago. This event was intense, very short (~125,000 years), and was produced by the release of methane stored in ocean floor. It constitutes one of the best examples in the fossil record that is similar in magnitude and duration to the pace of anthropogenic emissions of greenhouse gases. This warming event seemed to have had a negative consequence on tropical vegetation, with a decrease in diversity and a significant floral turnover. The second warming event was the Eocene thermal maximum (51-53 my), which was more intense than the first one and occurred over a much longer time scale (~ 2 my). The pollen and spore record indicates a significant increase in plant diversity as a result of the increase in speciation rate rather than a decrease in the rate of extinction. The contrasting results from both events suggest that warming rates have variables effects on tropical vegetation. Currently, I am expanding this study to similar strata in Nigeria and Venezuela, in order to evaluate how widespread those changes were.
I have also studied the effect of global cooling on primary producers on land (plants) and in the ocean (dinoflagellates). In a number of papers (see vitae) addressing the cooling at the Eocene-Oligocene boundary in subtropical and tropical latitudes, my co-investigators and I have shown that the effects of long-term global cooling resulted in a slow and gradual change in floral composition, without any marked difference, or a change in plant or dinoflagellate diversity in subtropical latitudes. On the contrary, there is marked rate of extinction in tropical latitudes.
What is the climate of the tropics during major global warmings? One of the major issues in modern paleoclimatic studies is the behavior of the tropics during a global warming because the tropics exert a major control on global climate. Paleoclimatic data from the tropics are very rare especially during times of past global warmings. Current General Circulation Models (GCM) predict warming in all latitudes, including the tropics, involving high concentrations of CO2. We are using the Paleocene as a study case for a major global warming. In collaboration with Scott Wing from Smithsonian Institution, we have estimate Mean Annual Temperature and Mean Annual Precipitation during the Late Paleocene for a site in the tropics of South America (Cerrejon, northern Colombia) using Leaf Margin and Leaf Area Analyses, methods that use the morphology of plant megafossils (leaves) to estimate climatic parameters. Our results suggest a cool (23 Celsius) and very wet (more than 4 meters a year) tropical climate, results extremely exciting for understanding ancient global warming and opposite to current models involving greenhouse gases. We just finish analyzing these data and expect to submit a paper to Science before the end of the year-
What are the patterns of plant diversification in the Neotropics throughout the last 70 million years. The tropic of South America holds one the highest plant diversities in the world. Several mechanisms have been proposed to explain this large diversity, such as an equable tropical climate with low rates of extinction and steady rates or origination. In contrast, the patterns of diversification of Neotropical floras through geological time have been little studied. These patterns could be used to test the mechanisms proposed. I have been studying the pollen and spore diversity record of Colombia and Western Venezuela from the upper Maastrichtian to the Middle Miocene. Data from thirty-nine sections, including outcrops, cores, and ditch-cuttings, and more than 6000 samples and 1.200.000 individual record of pollen & spores have been analyzed. The record shows a moderately diverse flora dominated by angiosperms, ferns and gymnosperms during the Maastrichtian, followed by a diversity crisis at the Cretaceous-Tertiary boundary. Tropical floras suffer a major change from non-angiosperm dominated floras to angiosperm-dominated floras. Paleocene floras have a low diversity and are dominated by angiosperms. Diversity significantly increases at the early to middle Eocene, reaching levels similar to modern Neotropical lowland humid forests. This increase could be related to the Eocene thermal maximum. The extinction rate increases by the end of the Eocene. During the Oligocene and early Miocene there is a period of low background origination and extinction never again reaching the levels seen in the Eocene. The overall pattern shows that plant diversity in the Neotropics is subject to historical accidents through geological time that have produced discrete pulses of origination and extinction rather than a constant high rate of origination or low rate of extinction.
I am also been actively collaborating with plant systematists like Charles Davies, U. Michigan, to use fossils in a phylogenetic context to help molecular studies to understand the history of major clades. In a paper in press in American Naturalist we show how the Malphigiales clade rapidly radiated during the Mid-Cretaceous and probably used a similar habitat to modern Malphigiales.
Finally, in collaboration with Scott Wing, we have been studying the diversity of the Paleocene Cerrejon flora, a unique site from northern Colombia that we found over a year ago. The site has very good preservation of plant megafossils and pollen & spores. We just finish the first ever census of plant megafossils in the Neotropics and surprisingly found that plant diversity was similar, if not lower, than counterpart floras in temperate latitudes. Regional pollen record shows a similar pattern. Result is even more interesting because we estimate a mean annual temperature of 23 degrees and 4 meters of mean annual rainfall, a wet tropical climate, but with a low-diverse rainforest. Results suggest that high diversity we see in the modern tropics may be the result of major historical accidents (e.g. Eocene Thermal Maximum).
Quantitative biostratigraphy for Colombia, improving palynological resolution for oil exploration. Oil exploration in Colombia has traditionally taken place in areas with relatively few structural complexities. However, in the last decade, exploration has moved to regions characterized by complex structural deformation, poor seismic resolution, and many stratigraphic problems, such as in the Llanos Foothills. In this region, the major reservoirs occur in mostly continental Paleogene sequences, where palynomorphs are usually the only fossil group found. Thus, palynology has become an important tool in controlling the stratigraphic position of a well during drilling, in testing diverse seismic and structural interpretations, and correlating reservoirs. My team at ICP has been developing a biostratigraphic framework for Colombia, making use of several quantitative techniques as graphic correlation and constrained optimization. We also constructed a large tropical fossil pollen and spores slide collection with more than 600 specimens spanning from the Aptian to the Pliocene as well as an electronic morphological relational database of fossil pollen, spores and dinoflagellates for the tropics with over 2000 entries. We have developed a palynological zonation for the Tertiary and Cretaceous of Colombia. We have successfully used this zonation during several exploratory wild-cat wells in Colombia, including the Gibraltar well, the major hydrocarbon field found by Ecopetrol (the Colombian Oil Company) in the last 25 years.
Future research plans
What kinds of historical conditions create biodiversity hotspots? What kinds of rules govern biodiversity? Do they apply at diverse time-space scales? One of the world's biodiversity hotspots is located in the semiclosed forearc basin of Chocó, a tropical rain forest area located in western Colombia. Chocó constitutes an excellent area to address these questions. It is characterized by highly diverse plants and animals, with an extensive and unexplored sedimentary record that encompasses the whole evolution of the basin, from the Oligocene deep sea of a trench environment to the present-day, fully terrestrial basin. Its fossil record, mainly pollen, spores, and dinoflagellates, can offer a unique window to understand how its extraordinary biodiversity was produced.
How do tropical floras respond to the Cretaceous-Tertiary bolide impact? Data we have collected in the past year suggest that the change of the tropical flora at the K/T was larger that currently believed. In fact, it seems that a major change in composition and ecological structure of the flora occurred, and that angiosperms found the opportunity to become the dominant clade in the tropics. This seems similar to the rise of the mammals. Two new fossil megaflora sites that we have found in the Maastrichtian and the Paleocene could help to understand this change.
Are Cretaceous- Tertiary tropical forests more or less diverse than modern tropical forests? Has a vegetation diversity latitudinal gradient been present since the origin of the angiosperms? We have found several new tropical plant megafossil sites: an Albian deposit in eastern Colombia, a Maastrichtian site in central Colombia, a Paleocene site in western Venezuela, and an Oligocene site in eastern Colombia. These new sites combined with the Cerrejon flora, and the expanding pollen & spore record database we have been collecting from the tropics will produce a plant diversity record for the Neotropics since the origin of the angiosperms. We could use this pattern to explore new questions in relation to the history of tropical rainforest. How, When, and Where are high diversity rainforests created?
Modeling tropical plant diversification throughout macroevolutionary times. I would like to incorporate the diversity pattern of fossil pollen-spore we have found for the Neotropics into current ecological models that have tried to explain tropical diversity. I would like to produce a hypothesis that can conjugate what we know about modern floras and a diversity that greatly fluctuates in evolutionary times and it is dominated by historical accidents.
To produce a high resolution Cretaceous to Tertiary biostratigraphy for northern South America. I expect to expand the scope of the palynological zonation to Panama, Ecuador, western Venezuela, and northern Peru and Bolivia. Palynology can become a more precise tool for dating terrestrial and marginal marine sediments in the tropics, and could be very useful for many types of research because they are often the only fossil group available.