frogs, bison, overkill, and extinction

I left home and drove through the Flint Hills of Kansas on my way to the airport to catch my flight to Panama City. It was a frigid morning, and the tallgrass prairie was starkly beautiful. The sun was rising and the light gave a slight orange/pink hue the wind-burnished patches of snow clinging to the northern slopes of the rolling hills. The old big bluestem grass stalks were buffeted by the winds. This was the kind of morning that made me glad not to be living as the indigenous people did during this inhospitable time of year. This was the type of morning where the Native Americans, and later the European settlers that invaded the area, would have stayed inside till the sun took the bite off the bitter windy cold. The icy landscape was stark contrast to the tropical mountain rainforest that I was headed to.

As I drove through these prairie hills, my mind started worrying on the idea of extinction, ecological loss, and the modern world. Only a fiftieth of tallgrass prairie remains in the North America, much of it in the Flint Hills of Kansas and Oklahoma. As I drove to the east, and out of the Flint Hills, the land was taken over by croplands. In a few minutes I was witnessing the transition that altered the vast North American prairies when Europeans broke the sod in the 1800’s. Much of the Midwest’s productive cropland was once a sea of grass.
The Flint Hills only retain grassland by lucky accident. The shallow rocky soils make them better for raising cattle than cropland. The ranchers burn yearly to keep the trees at bay and the cattle simulate the herds of grazing bison that historically roamed the prairie. Where fire has been suppressed, the trees invade. Prairie is becoming more imperiled in the Flint Hills because of the human influence changing the natural fire frequency that occurred. This effect is particularly pronounced in areas with higher population densities where people have built their houses out in the country… an effect that we will see has parallels in Panama.

Bison (popularly referred to as buffalo) are a “keystone” species that shaped prairie ecology, and their loss from the prairies could be considered analogous to the loss of the frogs in the jungle streams. The researchers I work with in Kansas have found that bison are key in maintaining the very high diversity of plants found in tallgrass prairies. There are literally hundreds of species of plants in a healthy prairie. The bison stimulate this productivity by grazing the main grasses that would outcompete the forbs (leafy plants). They also leave fertilizer packets (dung and urine) that stimulate plants that require higher nitrogen conditions. Bison disturb areas with their hoof-prints, their wallows where they take dust baths, and the trails they cut through areas as the herd moves across the landscape. The tadpoles, in the streams, do analogous things. They graze selectively, they disturb some areas more than others, and they excrete and enrich areas with their fecal pellets.

As impressive as the accounts were of massive bison herds on the prairies, there were once much more impressive herds of large mammals that roamed the prairies. Humans were responsible for even move extensive alteration of the natural ecosystems of North America. Before the end of the last ice-age approximately 10,000 years ago, the plains and forests of North America once were home to an astounding diversity of large animals. When tribes of hunter-gatherers that ultimately became the Indians of North America crossed the land bridge and spread across North America, they found a land of plenty.
The diversity of North America rivaled that of the plains of Africa. Camels, horses, huge bison, ground sloths, saber-tooth cats, giant beavers, giant armadillos, mammoths and mastodons were here. These large animals had no evolutionary experience with humans, and within a few human generations they were hunted to extinction.

Similar extinctions of large animals occurred in Central and South America as people swept in from Siberia, through North America and to the south. The America’s are not unique. In Australia, New Zealand, Madagascar and many other smaller islands the archeological and fossil record is unequivocal. When humans arrive, the large animals disappear. Marsupials disappeared from Australia, giant flightless birds were slaughtered in New Zealand, giant birds and lemurs were hunted to extinction in Madagascar. People are consistent in their heavy-handed environmental presence. We are the most successful species because we shape each environment we enter to meet our own needs.

The ecological effects of the extinction of the large herbivorous mammals and their predators are not well understood, but they were probably significant. Some species of plants remain that have large fruits with seeds that are only dispersed successfully over any distance when they pass thought the guts of large animals. The animals ingest the large fruits and carry the seeds within them substantially away before depositing the seeds with a packet of fertilizer. But, animals large enough to pull down tree limbs and graze the crowns of trees no longer range across the landscape.

One difference between historic extinctions and the ongoing disappearance of the frogs of high-elevation Central American habitats is that we can study the ecosystem effects of the removal of an entire taxonomic group in Panama. Perhaps these studies will help us understand the unintended ways that humanity is influencing global ecology and aid in mitigating or minimizing future impacts. At least it could help document some of the negative consequences that could come about from extinctions or extirpations of species.

Getting the team back to Panama

Now, I was starting to see the direct evidence of the die off as it came through, provided by my colleagues on the ground as the disease wave passed. Scott sent photos of dying frogs around to the group. Alex had videos of dying frogs. The frogs look duller skinned and are lethargic. Their skin is sloughing off of their bodies. The frogs that are not quite dead are not able to right themselves when turned on their backs.

During the die off, the Scott and the other researchers that were there collected as many dead frogs as they could find. He sent a picture of gallon pickle jars full of preserved dead frogs. The frogs in the jars will be identified, but not all species are collected before they decompose.

The species apparently contract the disease when they contact other sick frogs or come in contact with the stream. Some of the species in the trees might avoid contact for some time, but eventually, they will become infected. Thus, the die off is fairly concentrated, but some obscure species might hold on for a few weeks or months after the main epidemic sweeps through the jungle. Some of the species of frogs will probably never be known to science and will be lost in nature before they are described. Watching these videos and seeing these pictures made me even more apprehensive about returning to El Valle.

This group was to be slightly different from the last. Matt, Bob, Alex, Piet, and Cathy all were coming. In addition Karen Lips was going to be able to participate (if her luggage made it this time). Emma Rosi-Marshall from Loyola University is a professor who had been working with Bob on the effects of flooding and other influences of the dams in Grand Canyon. She had also been involved with the nitrogen tracer work our groups were doing in the U.S. She was interested in advanced techniques to separate the nitrogen label from the sediments.
Emma’s recent project with Matt on the effects of genetically engineered corn on stream invertebrates had generated considerable interest in the press. The paper she wrote for the Proceedings of the National Academy of Sciences with her colleagues documented how the toxin engineered in corn to kill the corn borer can enter agricultural streams where it could harm caddis fly larvae. Caddis larvae are important members of the stream community. The agribusiness community was extremely unhappy with her results, and she was attacked for them.

The tactic is familiar. Rachael Carson wrote the famous book, Silent Spring, that brought to light the problems with pesticide use. She was attached personally after critics could not rebut her scientific reporting. Tommy Edmondson, a professor at University of Washington, documented the decline of Lake Washington from sewage pollution generated by cities in the Seattle area. He carefully presented the scientific facts and left the politics out of his public statements. His critics could not assail the science, so resorted to attacks on his character. Emma had experienced a similar backlash.

Emma had strong expertise on stream food webs, and was a welcome addition to the project. Emma is a very boisterous and enthusiastic woman who loves to talk and argue science. She is an original thinker, and driven to do the best research that can be done. She is a tireless worker who is difficult to keep up with. I can see how she complements Bob, because he is the typical absent minded academic, and Emma is organized and gets down to business. Now we had the benefit of this dynamic duo.

Matt’s new graduate student Amanda, was also participating; she and Piet were already down in Panama working and she would stay and do the long term work after the rest of us returned to the US. As I would find out, Amanda was quite the character and had fantastic experience doing field work in streams.

A fantastic array of frogs

What is it about frogs and popular culture? They seem to be a very fashionable small animal. Unlike insects or snakes, almost everybody likes frogs. It could be that there is not a natural aversion toward frogs because they will generally not bother you if you don’t bother them. Human’s evolutionary history does not include natural selection for avoidance of frogs like it does for avoidance of snakes. A frog jumping underfoot seen out of the corner of the eye catches attention. A snake slithering through the grass underfoot caught with the corner of the eye causes me to jump. Some princesses are even willing to kiss frogs (not a snake or a rat, but a frog, yes).

Some species of frogs have extremely potent toxin in their skins (the legendary poison dart frogs), but it is only dangerous if you eat or touch them. So, while we have a long evolutionary history of avoiding more aggressive toxic snakes and spiders, there is no similar danger from frogs through human history. Frogs have big eyes, and seem mostly un-threatening. Better yet, there are fantastically colored and shaped frogs that are fascinating to anybody who appreciates the natural world. Frog enthusiasts may not be as common as bird lovers, but there are plenty of them out there.

This attraction to frogs makes it all the more ironic that they are disappearing from under our very noses. If all the ticks and chiggers were disappearing, I would have difficulty working up as much emotion over it.

I asked Scott Connelly to send me pictures of frogs from the El Valle forests, and those that were dying from the disease in Panama. I had not seen many of these frogs when I was in Panama before because some are quite rare or active in other seasons. Still, I was curious about what was being lost. Scott is also deeply affected by the extinctions. He takes any chance he can to give public lectures using his extensive collection of photographs. He is surprised by how few people know about these frog extinctions, including other biologists. My experience parallels his on this score.

What Scott finds most amazing about these frogs is the astonishing diversity of form and function. For example reproductive strategies vary widely among species. Some frogs simply lay their eggs and leave, others care for the young. Male poison dart frogs of some species keep the eggs they fertilize on leaves wet by bringing water from nearby pools or tree holes. When the eggs hatch these males then transport the tadpoles on their backs to a suitable small pool and release them there to mature. Some frog species live in trees, others only on the ground. They all have different diets or other variations in their way of life.

Bufo coniferous is the green climbing toad found in El Valle. The adult looks like a typical warty (but attractive) greenish toad, but as a juvenile, it has brilliant red dots on its “warts”. Another member of the same genus, Bufo haematiticus is the blackbelly toad. This toad is light tan or grey on top and dark brown on bottom, with an attractive mottling of dark and light brown on the inside of its legs. It is thought to be abundant and not in much threat of extinction, but the chytrid was recently found to infect this species in high altitude areas.

Then there is Cochranella euknemos, the San Jose chochran frog. It is a pleasing, small, light green frog with all black eyes and a body covered with tiny neon yellow dots. This frog lives near streams in the vegetation and its populations are declining according to the Global Amphibian Assessment.

And there are more- Eleutherodactylus musous is a small, green, splotched frog that has protrusions of green and brown all over its body, and looks more like a clump of moss than a frog. Up to now this adaptation has aided the species survival because the camouflage helps it escape predation. This adaptation will do it no good against the chytrid. This frog only lives in the mountains of Panama and will probably go extinct from the disease. One cousin of this frog, Eleutherodactylus bufoniformis, the rusty robber frog, is an inch long round bodied animal that lies very flat to the ground. It has a splotchy skin that makes it look like a rock in the bottom of the stream or in the forest where it sits completely camouflaged.

There are even more colorful frogs. Rana warszewitchii, the brilliant forest frog, lives close to streams in forested areas and its tadpoles develop in the streams. It has a short trilled soft call. This forest frog is slender and brown with bright green splotches on its back, a yellow stripe in its groin and two bright yellow spots on the backs of its upper hind legs. One side of the bottom of each back leg is brown with black spots and the other side is pinkish red. It truly is a brilliant forest frog.

The coronated tree frog, Anotheca spinosa has striking strips of silver and pearl on its sides. It looks like a cross between a grey zebra and a triceratops dinosaur. It is three or four inches long, with bone spines on its neck; supposedly these spines are used to fight other male frogs to defend breeding holes high in the trees. After breeding, the female continues to return to the hole and lay additional eggs. The earlier batch of larvae consumes the eggs that the female lays. Presumably the purpose of the later eggs is to feed the earlier tadpoles.

Hemiphractus fasciatus is a 3 inch, buff, tan-colored, horned tree frog, with a flat five-pointed head. It has irregular splotchy bumps over its body. This frog looks more like a leaf than an animal. Initially scientists could not keep it alive in culture until they figured out it only eats other frogs. The habit of eating other frogs explains why it is only found in areas with high densities of other frogs. This frog does not need standing water to breed, although it is found in extremely humid forests, because the eggs are carried on the back of the female.

The jungle around Rio Maria is also the habitat of Dendrobates auratus, the green and black poison dart frog. These frogs have active males that sing a trilling note while perched on twigs or rocks above the ground. If multiple females are attracted they wrestle each other to mate with the male.

This is a personal favorite because we have some as family pets in aquaria at home and at work. We purchased frogs that were bred by a co-worker in the US, but unwittingly contributed to pet frog collection just by buying them. It is possible that much of the spread of the chytrid disease is caused by the pet trade in frogs. Furthermore, some species of frogs have been collected toward extinction for the pet and zoo trade. While this may be a way to preserve species, rarely are adequate records kept of collection location and breeding lines, so the genetics of the frogs is not preserved.

Dendrobates minutus, is the blue-bellied poison frog. This tiny frog is one of the few poison dart frogs that is not collected for the pet trade. It is a beautiful frog with alternating yellow and black stripes along its entire body. It has bright blue spots on its lower belly.

The above are only a few of the more than hundred species of frogs that could be found at El Valle. The main remaining species of frogs from this area now are in quarantined aquaria or have populations that also occur in lower, warmer elevation areas where the disease apparently is not fatal.

Lessons from extinctions

Frog extinctions from the chytrid fungus are particularly troublesome because there is literally nothing that be done to stop them. Helplessness is a bad feeling, particularly for a scientist. Generally, a scientist thinks that we can control much of our world through knowledge. Species out of the wild can be propagated. If there is no way for them to survive in the wild, then they are doomed to be caged creatures. Somehow, animals in zoos do not seem the same to me.

I have mixed feelings about captive animals. A recent visit I made to an aquarium with extensive coral reef fish exhibits illustrates the paradox. I was thinking how much more I enjoyed seeing fish in the wild by scuba diving or snorkeling. Then it occurred to me that the resources used for me to travel to a coral reef were tremendous, and that the environmental damage would be immense if each of the visitors to the aquarium traveled to see all these fishes in their native habitat. The educational value of having these fish available for public viewing is high. Still, an animal or plant that only exists in zoos or botanical gardens seems more like a collector’s item than anything relevant to the natural world. For many of the frog species that are threatened by the chytrid disease, life in captivity is the only way the species will avoid complete extinction.

The El Valle Amphibian Rescue Center is attempting to save 1000 animals from 40 species. They are concentrating on 15 priority species now, and building capacity to save more. The center started in the same hotel (Campsetre) where we stayed. Heidi and Edguardo felt they had to do something, and rented rooms to set up aquaria in them. They collected frogs from areas where the disease had not invaded. They experimented with ways to kept the caged frogs from getting the disease, including washing with Clorox solutions, and heavy use of disinfectants of any materials that entered the area from outsize.

Since then, the El Nispero Zoo at El Valle de Antón and a number of US zoos (notably the Houston zoo and the Atlanta zoo) and conservation agencies have supported building a center to house the animals. The Houston Zoo manages contributions to frog conservation efforts.

In captivity, each frog must be kept quarantined from any materials that might bring the disease into their cages and as far as is known can never be released into the wild. To make the job even more difficult, it is not possible to maintain just a few frogs of each species because a minimum amount of genetic diversity is necessary to save a species. So, many individuals of each species must be housed. Furthermore, little is known about the mating and food requirements for many of the species, so research into these details is required.

Edgardo and Heidi were the first local collaborators (they became closer collaborators when they got married) on the conservation project, and now several zoos have pitched in to consult and provide financial support. Many hours of work a day at the Rescue Center are required to keep the frogs healthy including collecting the insects that each species needs to survive. Before the Rescue Center gained the ability to culture them in the lab, these insects had to be collected from the wild.

The golden frogs like termites, and many of the other frogs like cicadas, crickets, or other insects. The very small frogs need fruit flies or other tiny insects. A huge amount of work goes into cleaning cages, treating sick frogs, quarantining frogs that have been collected, keeping track of where each frog came from and recording breeding activity. This last is important to avoid inbreeding on one hand and to avoid breeding what might be distinct sub-species from different areas on the other.

Videos were coming out on the frog extinctions and the rescue center. I saw interviews of Edgardo, and pictures of the facilities and Heidi and Edgardo collecting insects to feed the frogs. Soon I would be able to visit and see for myself.

What are the lessons from the Panamanian frog extinctions? One is that diseases can wipe out species before people can find a cure. We are part of the natural world and are not exempt from the generalization. A disease could arise that kills much or all of humanity. With rapid air travel, pandemic’s are more likely. With more contact with wild animals, the probability increases that an animal disease will jump to humans. When people live in close contact with livestock (particularly pigs and waterfowl) development of diseases is particularly likely. It is not impossible that one of these diseases will be lethal enough to sweep through humanity causing mass mortality. If it can happen to frogs, it might happen to us.

Another lesson from the frog extinctions is that we need to preserve the species we can because we will lose many anyway from the unintended consequences of human activity. As already stated, humans are causing massive extinctions. If some of those can be avoided, the unintended extinctions we cause will have less of an overall impact on the planet’s diversity.

A third lesson is that we should not introduce species to other habitats (such as the African Clawed Frog) because there is always the potential for unintended harm. Species introductions have caused damage to numerous species and are in important factor in endangerment of many species. The chitryd and the frogs may be the most extreme example of a single introduction leading to extinction of 10’s to 100’s of species, but the lesson is an important one. These lessons still seem to me to be small comfort in the face of the loss of hundreds of frog species from our planet.