"Salamanders are interesting, and don't let anyone tell you otherwise." - Bill Bryson, A Walk in the Woods.
Why salamanders?
We get asked this question a lot?
To be fair, we are interested in all kinds of organisms. We work on frogs and turtles, have dabbled in lizards and snakes, butterflies and birds; but salamanders remain the core foci of much of our research.
So why salamanders?
The best answer is, why not? The honest answer is, well ... I never planned to work on salamanders. I just wandered into their world and the questions never stopped coming.
The seasoned answer, after 20+ years is far better.
As of 2019, there were 8044 known and recognized amphibian species around the world, only 731 of which are salamanders. So salamanders represent only 9% of known amphibian species worldwide. However, 57% of the amphibian species in North America are salamanders, and in parts of Appalachia, more than 70% of the amphibian species are salamanders. There are 10 families of salamander globally, 9 of which occur in North American, and 5 of which are endemic to North America. In this regard, salamanders are a distinguishing feature of North American ecosystems.
The diversity of salamanders around the world and in North America is nothing short of awe inspring. Whit Gibbons coined the term "hidden biodiversity" [at least I think he did]. Many speices are too small or secretive to be noticed by most people or appreciated for their abundance and diversity. Salamanders are a perfect example of hidden biodiversity. They are nocturnal, and most active on cool, wet nights when few people would venture into the forest. They go largely unseen except when turning stones around a stream or digging in a garden. But salamanders are spectacularly abundant and exhibit wonderful morphological and ecological diversity. Salamanders have also developed unimaginable adaptations, from tongues that project twice the length of their body, to the absence of lungs while living on land. They fill niches that few other vertebrates in the world can fill.
The family Plethodontidae accounts for 67% of all known salamander species, and nearly all of them occur in the New World. The hotspots of diversity for these salamanders are in Central America, where there is the greatest number of species, and the Appalachian Mountains, particularly the southern Appalachian highlands of north Georgia, western North Carolina, eastern Tennessee and southern Virginia, where there is the highest density of species in any particular location. Many of these species are fully terrestrial, laying their eggs on land, never breeding in water, and they provide parental care for their eggs and recently hatched young. They have complex social lives, and powerful senses of smell that they use to recognize kin, mates, rivals, and enemies. Because plethodontids are lungless and ecotherms, they are the most metabolically efficient vertebrates known. An adult salamander can convert 50%-60% of the energy it consumes to tissue, and larvae and junveniles can convert 80%-90% of what they eat to tissue. This is nearly five to ten times the efficiency of many other animals. As a result, salamanders can exploit tiny prey such as mites, springtails, small ants, and beetles that are not sufficiently profitable for animals that have higher calorie demands. Low energy demands also allowed the evolution of extreme minitiarization in species such as the recently discovered patch-nosed salamander.
In 1975, Thomas Burton and Gene Likens provided the first estimates of abundance and biomass of salamanders in the Hubbard Brook Experimental Forest in New Hampshire. They estimated that a single species, the eastern red-backed salamander (Plethodon cinereus), achieved densities of ~ 3,000 individuals per hectare. At this density, red-backed salamanders were more abundant and had a higher biomass than the birds or small mammals in the same forest. With more rigorous methods for estimating salamander abundance, we now know those early estimates were likely low by as much as an order of magnitude. A recent study in the Daniel Boone National Forest estimated there were nearly 10,000 salamanders per hectare for a total of nearly 2 billion salamanders in a 2,800 square kilometer area. We and others have measured densities of 20,000 per hectare in wetter regions of southern Appalachia and 50,000 per hectare in central New York. Within small streams, larval salamanders can occur at densities of 20-70 larvae per meter. Because of their exceptional abundance and biomass, salamanders influence the abundance of other biota such as forest and stream insects, and they influence key ecosystem processes including decomposition, energy flow and nutrient cycling.
So why salamanders? Because, they kick biomass.
Salamanders have also taught us a great deal about evolution and developmental biology. Salamanders have shown us the complex ways in which climate interacts with topography through the processes of migration and isolation to generate diversity. Salamanders have challenged foundational biological concepts such the species concept. They have shown us how altering the timing of development can create diverse and remarkably divergent organisms, giving us an insight into the mechanisms by which evolution can generate dramatic new forms from older ones. Salamanders have challenged the notion of evolutionary progress, by reinvading the water and reaquiring free-swimming larval phases from an ancestor that had successfully been liberated from reproduction in water. And salamanders have invigorated the concept of the superorganism with the discovery of rich microflora that provide antibiotic resistance to protect their delicate skin. And don't get me started on polyploidy, hybridogenesis, and kleptogenesis. It bends the mind.
Salamanders are a remarkable and important part of our natural heritage, and they face a range of contemporary threats. Many tropical salamanders are rare or critically endangered do to deforestation and climate change. A large percentage of salamander diversity occurs within Central American cloud forests and species depend on the wet climate and the epiphytes it supports. Climate warming is causing the lifting of cloud forest and driving the decline of epiphtye communities. Pathogens moved in the bait trade have caused die offs among North American tiger salamanders, and a fungus spread through the exotic pet trade has been linked to mass die offs in European salamander populations and fears of transmission to the New World. In North America, invasive species, logging, mountaintop removal mining, and increasing development of montane forests are all linked to declines in salamander abundance, particualrly in the Appalachian Mountains. Southern Appalachia is experiencing increasing pressure from the rapidly growing urban environments of Atlanta, Charlotte, Asheville, and Knoxville, driving rapid conversion of high elevation forest into cottage homes and golf courses. And ancient and iconic species such as the Eastern Hellbender are declining rapidly from river degradation.
© John Maerz, 2019,
