Tree Frog Biodiversity

A Stony Brook University team has determined that the more millions of years a creature has lived in a place, the more species of it are there. The time factor statistically outweighs all other ecological parameters. As a consequence, Dr. John Wiens warns that “The loss of species richness during our lifetimes may actually take tens of millions of [years] to recover from.”

Seeking to explain the biodiversity of rainforest tree frogs, the group compared the number of non-interbreeding frog species—both living and extinct—to ecological parameters and frog body size. The yardstick for comparison was the molecular clock of frogs.

The first frog genome was sequenced about a year ago,1 but mitochondrial genomes have been known for several years. Frog Phylogenetic Trees and Molecular Clocks Are Based on Those Mitochondrial Genomes,” 2 Molecular clocks are built on the assumption that creatures evolved from common ancestors according to the timescale inferred from the dating of fossils—information based on additional assumptions. Then, the differences between mitochondrial genomes of the species are compared to the fossil ages to calculate mutation rates. Those mutation rates are used to determine how long ago species diverged from the evolutionary tree. The reasoning is circular because the timescale used to determine how long a molecular tick takes is already assumed from the fossil record.

The Stony Brook team measured the geographical distribution of 362 types of tree frogs against molecular clock data derived from “up to 11 genes each” and “10 fossil calibration points.”3 From these statistics they determined that “the most diverse sites were established over 60 million years ago and more recently colonised areas had fewer unique species.”

Then they compared the number of unique frogs in each area to ecological parameters. The degree of speciation correlated better with molecular clock data than with ecological data. This result should come as no surprise since the molecular clock data is derived from the patterns of speciation, and both are based on the same evolutionary timescale.

Basically, this study assumes that evolution happened, assumes it took a long time to happen, assumes that lots of diversity should evolve given long enough, and based on the original assumptions comes up with numbers which correlate the time required to achieve the diversity with the diversity that is seen. Then, bursting forth from this circular reasoning comes the conclusion that what took millions of years to evolve will take millions of years to evolve again if we don’t take care of the rainforests. Never mind that no new kinds of animals evolved anyway because the frogs were still frogs.

The biodiversity of tree frogs should remind us of the possibilities for variation within the created kinds. We can count it a bit of God’s grace that we in this sin-cursed world are probably privileged to see more variations in beautiful tree frogs than Adam did, but that level of speciation only took a few thousand years. And while we ponder how to be good stewards of the rainforests and everything else in the world God has given us, we should keep in mind that human habitat invasion isn’t always the enemy: another recent study has suggested that tree frog species get wiped out more readily as a result of a fungus that thrives far better in pristine forests than in areas disturbed by human civilization.4 Sometimes it seems like you just can’t win!