The Incredible Shrinking Megafauna
By Ken Fischman, Ph.D.
Part 1 – Of Wolves and Elk
Doug Smith, who is in charge of the Wolf Recovery Team in Yellowstone National Park (YS) said, during a December 17, 2009 interview by The Billings Gazette, that he had recently been seeing something that he never before witnessed. Several times he had watched a bull elk successfully fight off a pack of wolves. Smith said that the bulls had become so large and had such massive racks, that they were now a match for the wolves. What has happened to the Yellowstone elk to bring this about, and why?
As background to this question, you should know that a fascinating, natural experiment has been taking place in YS ever since wolves were reintroduced there in 1996. By “natural experiment,” I mean one that was unplanned and unforeseen. The last naturally occurring wolf in Yellowstone was killed in 1927. Lacking natural enemies with the wolves gone, and with hunting also prohibited in national parks, the elk proliferated over the years. By 1996 the YS elk population had burgeoned to from 15,000 – 18,000. They overran the area, overbrowsing and damaging the ecosystem in many ways. Then came the wolves, 45 of them. In the 17 years since then, the wolf and elk numbers have changed drastically. The wolves increased, up to around 160 individuals, and thereafter they have fluctuated periodically between that and to less than 70 animals, while the elk have decreased to between 5 – 7,000 animals. You can say that the elk and wolves are participating in a mutual dance of death. The wolves reduce the number of elk by preying on them until the elk become scarce enough so that the wolves find it hard to continue to maintain their own numbers. That situation, together with other stresses, such as hard winters and disease, reduce the number of wolves. Up come the numbers of elk until the wolves, with prey easier to obtain, become healthier, less stressed, and begin to increase their population again. This dynamic fluctuation of the wolf and elk populations has occurred several times during the relatively short span that these animals have been interacting in Yellowstone.
Other dramatic changes have taken place in the Park during this period. William Ripple and his colleagues have documented several changes in YS riparian habitat. It is rapidly being restored, with cottonwoods, willows, and aspen again growing along the hitherto eroded stream banks, which have regained stability. This has resulted in clearing the water of turbidity and debris. Expanded tree coverage along creeks and rivers has also lowered water temperatures, bringing back cold water fish, such as trout, along with song birds, and many amphibians.. The presence of more carrion, a byproduct of wolf predation, has proven beneficial to a whole string of scavengers, like vultures, crows, ravens, foxes, and coyotes.
Ripple attributes these changes to the presence of wolves, and indeed he has documented similar changes in Banff National Park in British Columbia, as well as in other locales. But aside from all these changes, the one that strikes me from an evolutionary point of view, is the vision of these elk bulls, with their majestic racks. Why has this happened? From the point of view of genetics, the answer seems simple enough. Wolves prey mostly on the weak, disabled, and sick, as well as on bulls, calves, and does, simply because the former are the easiest to kill. Thus, the wolves are removing genes from the elk population for smaller, less robust bulls. If you think about it, hunters do the opposite. They go after the big bulls with the most imposing racks. Their success therefore removes the very genes they most prize, and results in smaller, weaker elk. Now, you may find it hard to believe that humans can have such drastic effects on the genetics of wild animals. However, I have come across some rather startling evidence that I believe will convince you.
First of all, we can turn to the father of the theory of evolution himself, Charles Darwin. Much of the evidence that Darwin accumulated in the eighteen hundreds for his then revolutionary theory, was obtained through observation of and breeding experiments on domestic animals.
Part 2. The Tuskless Elephants
The breeding of domestic animals was deliberate on our part. What is more surprising is the inadvertent effects that man has had on a wide variety of wild animals. I recently came across an article in Newsweek Magazine, of January 2, 2009 that describes some of these effects. The most startling one was the discovery of the tuskless elephant.
Elephants use their tusks to root around the ground for food, and in fighting between males during their rutting season. We also know that historically, and from the study of fossils, about two percent of elephant bulls have been tuskless. This was obviously caused by recessive mutations, which have put these animals at a disadvantage from their tusky relatives. Their loss of these useful appendages has undoubtedly been the main factor in winnowing out these genes from the population, thus keeping the number of such elephants low – until recently.
The number of tuskless elephants has lately climbed to 38% in Gambia, and even more startlingly, to 98% in one South African population. The factor that brought about this change is the poaching of elephants for their tusks. The price on the market for tusked animals has recently risen to $10,000 per animal. That is a lot of money for a poor African, thus making these animals tempting targets. Furthermore, this is not just an African phenomenon. In Asia, female elephants do not have tusks, but the proportion of tuskless male elephants has more than doubled in recent years, rising to greater than 90%. This has happened even on the island of Sri Lanka, where male elephants are used in the work force, and their tusks are valued as tools. As scientist, Mario Festa Bianchet of the University of Sherbrook, who has been documenting this phenomenon, pointed out, “You end up with a bunch of losers to do the breeding.” Both sexes of these elephants are also getting smaller. “These changes make no evolutionary sense,” he said.
Part 3. A Whale of a Tale, or Floundering Around in the Mediterranean
Lest you think that these strange goings-on are confined to pachyderms, there is another, perhaps even weirder story about fish. It seems that fishermen as well as scientists have noticed that several different kinds of commercially valuable kinds of fish, such as flounder and groupers in the Mediterranean Sea, are getting smaller. Once again, the cause is painfully obvious. Fishermen, using more and more trawlers equipped with dragnets that cannot distinguish between species or size, have made it a practice to keep only the larger individuals of fish such as groupers. After sorting the fish on deck, they throw the smaller ones back, perhaps in the mistaken belief that they are being good stewards of the sea in doing so. This practice has resulted in the removal of genes for larger size from these fish populations, producing ever more smaller cod, salmon, flounder, and groupers, at least since the 1980s.
Scientists have been curious to know how far back this trend of the shrinking fish goes. After all, fishermen have been plying the Mediterranean for thousands of years. As Samir Patel reported in the January/February 2013 issue of “Archaeology,” scientists from Stanford and the University of Salento, Italy hit upon an ingenious and novel way to find out. They went to various museums, examined mosaic tiles of fishing scenes from antiquity, and measured the fish depicted there by comparing them with objects in the mosaics whose size was known. Lo and behold, they found out that dusky groupers (Epinephelus marginatus) have been shrinking considerably for thousands of years. Even if the man-swallowing grouper in the mosaic pictured here is more than a slight exaggeration, it is obvious how far back the phenomenon of the shrinking fish goes.
Man’s unknowing tinkering with nature is widespread. Big Horn sheep from Horn Mountain in Alberta, Canada have had a 25% decrease in horn size because trophy hunters only go after the ones with imposing horns. In Australia, red kangaroos have become smaller in size because poachers target the biggest ones for leather.
None of this information will come as a big surprise for readers of this blog. Last year, I posted a summary and analysis of an article appearing in the journal, Science, entitled “Trophic Downgrading of Planet Earth.”Its author, James Estes, along with 22 eminent collaborators, describes how apex predators, such as wolves, sharks, tigers, and lions, are being rapidly eliminated by humans, and that this loss is having profound effects on the Earth’s ecosystems through the phenomenon of trophic cascades, by which an ever widening number of other animals and plants are being negatively effected.
Part 4. How to Make More Coyotes
Doctor Robert L. Crabtree, is Research Associate Professor at the University of Montana. He is one of North America’s foremost researchers into predator/prey relationships, and an expert particularly on the coyote (Canis latrans). He has recently described a similar situation with regard to the coyote populationin the western United States. It seems that the US Wildlife Services (WS), a little known federal agency that kills millions of wild animals every year, mostly at the behest of ranchers and farmers, has unknowingly gone into the coyote growth business. Apparently most of WS ‘s “predator control” programs are indiscriminate, in the sense that the animals killed are probably not the offending ones. (The same is true for wolves. Their haphazard removal by WS and others is grimly reminiscent of the slaughter of Greek villagers in WW II by SS troops, in retaliation for partisan attacks on German soldiers. Most of the villagers killed were not the same people as the partisans, but the act satisfied the blood lust for revenge on all Greeks).
Crabtree reports that coyote populations compensate powerfully for reductions in their populations, and WS ‘s widespread control measures (traps, poison, explosives, shooting from the air, etc.) only increase immigration, reproduction, and survival of remaining coyotes. He makes the following observations:
(1) These control campaigns result in immediate immigration into the control area by lone animals and/or invasion by other neighboring coyote groups.
(2) Litter size increases, probably due to better nutrition, caused by greater availability of prey, which results in higher birth rates and better pup survival.
(3) There is recruitment of adults from outside sources into the pack. This situation results in a doubling or tripling of the number of hungry pups to feed, and recruitment of larger and more available prey (usually sheep) to do so. Therefore, these control measures result in the opposite effect from that wanted, with more attacks on domestic animals (Note: coyotes are responsible for over 60% of livestock killings, while wolves account for less than 0.1% This means that for every sheep killed by wolves, 600 are killed by coyotes. The constant clamor by ranchers to WS and state authorities to kill more wolves is not exactly cost-effective, but what the heck, its not the ranchers, but the tax payers who are paying for this).
(4) Coyotes (and also wolves), learn what constitutes appropriate prey when they are taught as pups by adult pack members. The removal of these adults by control actions makes the pups’ education more problematical.
(5) Reduction in coyote population by control methods results in more females becoming breeders. This increases the number of pups in the ensuing generation.
(6) Removal of coyotes from a pack results in a reduction of the average age of pack members, so that more of them are reproductively active.
(7) Reduction in pack size also induces more young adults not to disperse, but to remain and become permanent pack members. Either that, or they secure breeding positions in the exploited area.
It is clear from these examples how humans can inadvertently and mistakenly have profound effects on the genetics and behavior of wild animal populations, and that much of the time these effects are either unintended or even contrary to the hoped-for results.
Part 5. Of Wolves and Men
This returns us to the wolves. In 1996, wolves were reintroduced in the West. It was hoped at that time, that wolves would resume their natural role in our forests as top predators, bringing more balance into western ecosystems. At their peak, in 2011, the three states of Idaho, Montana, and Wyoming had a combined wolf population of 1,804 animals. Adding in the Great Lakes states’ wolf population, there are about 4,800 wolves in this country. At first glance this might sound like a lot of animals, but compared with other predators in the US, such as black bears (630-725,000) and mountain lions (24-36,000) , prey such as elk (1 million) and white tailed deer (30 million), as well as domestic livestock (169 million), it is a proverbial drop in the bucket.
Wolves were removed from the Endangered Species list in 2011. Since that time each of the three western states have instituted wolf hunting seasons unlike those for most other wild creatures except those considered varmints, such as coyotes and prairie dogs. For instance, Idaho’s season is yearlong, thus overlapping the wolves’ breeding and denning seasons. Methods of killing wolves have been expanded to trapping, use of snowmobiles, electronic wolf calls, along with WS ‘s shooting them from airplanes. How has Idaho’s wolf management plan fared so far?
I was struck by a recent report from Idaho Fish & Game (IF&G) on wolves in Idaho. IDF&G stated that the wolf population there at the end of 2012 was 683 wolves, a decrease of 11% from 2011. Extrapolating from the numbers in the report, only one pack in two has a breeding pair. (I must add the caveat that wild animal populations are notoriously hard to count and IDF&G terms these numbers minimum ones). These figures are in contrast to most wolf populations that I know of, including those in Canada’s Algonquin Park and in YS, in which each pack usually has at least one breeding pair.
Furthermore, 70 wolves were killed by hunters in Idaho’s Panhandle. One of the main reasons given by IDF&G for institution of a wolf hunting season was to decrease livestock depredation by wolves. Yet, there has never been a case of livestock depredation by wolves in northern Idaho. I do not know for certain what has led to these skewed numbers, but the year-long hunting season, together with a limit of six wolves per hunter (which is to be raised this year to ten per hunter) with no upper limit on the number of wolves to be killed, may have damaged both the physical and social structure of these wolf packs.
Wolves are an extremely social species, and the complexity of their interactions is rivaled only by that of ourselves and ants. Within most packs there is a network of adults, sub adults, breeders, hunters, pups, and their caretakers (usually the sub adults). Intricate vocalizations, smells, and body language help them to communicate and coordinate with each other. Teaching and learning appropriate wolf behavior is an important pack function. For example, it is the sub adults who usually teach the pups what is appropriate prey. Therefore the wolves grow up being attracted to elk or deer as the case may be, and not to cattle, sheep, or human beings.
I, along with many wolf biologists, believe that an intact and healthy wolf pack is one of the most important keys to low livestock depredation. One way to test a hypothesis, such as the importance of an intact wolf pack to their appropriate choice of prey, is to examine the effects of damaging that structure. There is an unplanned, inadvertent experiment going on in these three states now with increased hunting and “control” actions considerably lowering the numbers within, ages, and mix of wolves in these packs. In the next few years, we should be able to see the results of this “unnatural” experiment. What sort of effect will these haphazardly reduced wolf populations have on livestock numbers and comparisons of wolf numbers to depredations? Will the reduction in wolf numbers lead to inbreeding and development of birth defects as it has in Isle Royale NP and Scandinavia? This is one experiment that I wish was not taking place.