Lessons of the Lost
Amphibians are all but gone, bequeathing us lessons that must not be squandered
Death in the Family
The scope and scale of these declines is truly difficult to grasp. Up until about the late 1980s there were at least 97 species of harlequin frog (Atelopus) in the Neotropics (several of them now known only because of the forensic taxonomy skills of my colleague Luis Coloma in Ecuador); only about 10 species can now be located. Perhaps 38 species of northern rain frogs (Craugastor rugulosus group) were distributed along montane streams in Central America; only four or five are still extant. I personally found the last known individual of one of these species in southern Mexico in 2000. The concept of “endangered species” does not apply here. We are witnessing the nearly complete elimination of entire clades of species. This is another lesson learned, as we were all trained that such things are only to be observed in the fossil record. This precedent from the amphibians forces us to address the serious implications for possible disease-driven losses among other major clades. Consider for a moment the potential consequences of clade-level extinctions among monocot plants (corn, rice, wheat), pollinating insects, salmonids or scombrid fishes (mackerel, tuna), mammals or birds.
Amphibians are the typically uncredited vertebrate basis of almost all ecosystems on the planet, by virtue of the astounding biomass and population densities they can achieve despite their typically small body size. However, they are secretive and often nocturnal, so their reign is a well-kept secret, even among most ecologists. In light of this, a couple of qualifications about extinction are required. First, extinction is difficult to demonstrate unequivocally (as it is based on negative evidence), so organizations such as the International Union for the Conservation of Nature (IUCN) justifiably are quite conservative in their assignment of the term, and we sometimes get it wrong. Second, extinction is simply defined by zero living representatives, but we are in need of a conceptually clear categorization of “functionally extinct” to account for the many hundreds of species of amphibians that swirl in the so-called extinction vortex, no longer able to provide the important goods and services they once contributed to ecosystems. They are only nearly extinct, which may make us feel better (or worse), but they don’t really exist in a functional sense. The typical biomass of amphibians and the sheer magnitude of their declines and extinctions requires me to make bold statements, such as “There no longer exists a natural upland ecosystem in Mesoamerica” despite many fully protected reserves. I published that statement recently in Herpetological Review, and I note that no one has argued with it. In fact, my colleague Larry David Wilson extended the concept to suggest that virtually all publications of field-based research should bear a label: “Warning: this study was conducted in a disturbed ecosystem.” The point is that the baseline of amphibian diversity and populations has shifted dramatically in many areas and no one—not even amphibian biologists—is adequately addressing that reality.
Amphibian declines must affect any ecological studies at famously “pristine” sites like La Selva Biological Station in Costa Rica, and they also affect evolutionary studies, taxonomic reviews and biotic inventories. In the latter case, we will never know the true biodiversity of some areas that are yet unsurveyed, and thus we will never be able to fully understand the interdependencies of those ecosystems in their fully evolved complexity. With my colleague Martin Bustamante, I recently learned this lesson the hard way in southern Ecuador, when cumulative months of field work revealed only a handful of amphibian species (several of them new to science) in a “pristine” upland cloudforest reserve that should have harbored dozens of amphibian species. Local ranchers described in wonderful detail a species of harlequin frog they had not seen in years. Quite possibly it represented a species unknown to science, but we will never know because Martin and I arrived after the massacre, too late even to accomplish a decent forensic taxonomic survey of the region. My graduate-school experience in Guatemala in 1989 taught me not to assume that we had simply failed to find the regional amphibians.