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Tropical biodiversity results from age of species argues new theory
University of Chicago Press Journals
November 1, 2006


Why are there more species in the tropics than in the temperate regions of the globe? Many of the world's species live in the tropics (perhaps more than half), but the reason has been debated for more than 100 years.

Many researchers have hypothesized that climatic factors somehow cause species to originate more quickly in tropical regions. In a paper appearing in the November issue of The American Naturalist, John Wiens and a group of researchers from Stony Brook University have shown that, contrary to expectations, species seem to evolve at similar rates in tropical and temperate regions. What causes the difference in species numbers between tropical and temperate regions is not something special about the tropics that leads to more rapid speciation, but rather that the temperate areas were colonized more recently, leaving less time for species to originate and accumulate in these regions.

Monkey frog in Peru. Photo by Rhett A. Butler Does tropical biodiversity increase during global warming?. Forest fragmentation may cause biodiversity loss lasting millions of years according to a new study published in the March 31, 2006 issue of the journal Science. Using cores drilled through 5 kilometers of rock in eastern Colombia and western Venezuela, Carlos Jaramillo of the Smithsonian Tropical Research Institute (STRI) in Panama and a team of researchers derived a fossil pollen record for a 72 million-year period with samples ranging from 10 to 82 million years ago. They then correlated pollen diversity with global temperature estimates for the middle part of that sequence (20-65 million years ago) and found that plant diversity seems to increase when tropical forests cover large areas. Evolution is twice as fast in the tropics. Tropical species evolve twice as fast as temperate species according to research published in Tuesday's Proceedings of the National Academy of Sciences (PNAS). The study, which compared the genetics of 45 common tropical plants with similar species from cooler geographical areas, suggests that evolution takes place at a faster rate in warmer climates either due to higher rates of metabolism, which leads to more genetic mutation, or shorter generations, so genetic changes are rapidly passed on to offspring. Study uncovers how thousands of tree species coexist in rain forest. A group of scientists have a developed a new theory to explain why the biodiversity of tropical rain forests is so high and how species are assembled in an ecological community. According to their research presented in Nature, the answer can be found in "neutral theory" whereby community membership is determined by just five fundamental processes. The scientists say that species will regulate themselves to make room for each other if they follow the "membership rules." The new theory undermines the conventional "niche theory" which has been traditionally used to explain community assemblages. A press release detailing the reseach is found below.

The researchers studied the causes of high tropical species richness in treefrogs in the Americas. Combining analyses of evolutionary trees based on DNA sequences with GIS-based methods for analyzing the effects of climate on species distributions, the researchers found no relationship between how quickly species originate within a group and whether that group is tropical or temperate.

However, they did find a strong relationship between when each region was colonized and the number of species there today. Thus, the high species richness of tropical regions seems to be explained by the ancient origin of many groups in the tropics, more recent colonization of temperate regions, and by the inability of most tropical species to tolerate the variable temperatures of temperate areas.

According to John Wiens, the study has important conservation implications: "If the pattern we see in treefrogs holds true for most other groups, then the tropics may have more ancient lineages and more genetic diversity per species than temperate regions. So there may be far more loss of diversity going on as we lose tropical rainforests than would be suggested by the number of species alone."




This is a modified news release from University of Chicago Press Journals.

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