Posts Tagged ‘inbreeding depression’

Trophic Downgrading or Where Have All the Predators Gone?

Jul 17th, 12 / 0 Comments

THE TROPHIC DOWNGRADING OF PLANET EARTH

(Or, where have all the predators gone?)

  J.A. Estes, et al. (2011) The Trophic Downgrading of Planet Earth (2011) Science, 15 July, 333(6040) 301-306.

Summary and Comments by Ken Fischman, Ph.D.

This is a paper that is worth your diving into because the information it contains is important to the health of our planet. I will help you get through it by summarizing and commenting on it. You can either read the summary or skip directly to my comments on it at the end of this post. What is it about? It deals with the recent and rapid disappearance of top predators, such as wolves, lions, & sharks, mostly brought about by the actions of that top predator of all – mankind, and the surprisingly profound effects their loss is having on ecosystems worldwide.  It was the feature article in the July, 2011 issue of Science, one of the most prestigious scientific journals in the world. Among its 23 authors are: John Terborgh, Joel Berger, Michael Soule, and William Ripple. The former three are considered to be among the founders of the field of Conservation Biology, and Ripple is our foremost researcher into the effects of top predators on the ecosystems of North America. Simply put, a trophic cascade (TC) is the effect that the absence or abundance of a top or apex predator has on succeeding levels of the rest of the ecosystem. The authors have gathered a vast array of evidence showing that these losses lead to ever-increasing and widespread effects on other living creatures, on ecosystems, and on the Earth itself. Terborgh pioneered this type of study by showing the profound effects of the presence or absence of predators on the fauna and flora of isolated islands in the Barro Colorado, a recently flooded region near the Panama Canal. Soule, in a classic paper, neatly demonstrated how the presence or absence of coyotes effected the bird and cat populations within the urban canyons of San Diego. Ripple has shown the profound influence that the reintroduction of wolves in Yellowstoneand loss of mountain lions in Zion National Park  have had on the animals and plants in those areas. In this paper, these scientists turn their attention to the effects of predators on ecosystems worldwide and warn us of the present and impending dangers that our  steady & seemingly inexorable extermination of predators is having on the Earth

Summary of the Paper

 The loss of apex predators all over the world is having a pervasive influence on nature. There are cascading effects of the disappearance of predators. These “top-down forcings” (causes of variability) are having unanticipated effects, such as increase in disease, wildfires, losses in carbon sequestration, appearance of invasive species, and disruption of biogeochemical cycles. In its 4.5 billion years of existence, our planet has undergone several mass extinctions, with huge loss of biodiversity, followed by novel changes. We are now in the early to middle stages of a sixth mass extinction. Man has mostly caused these recent extinctions. Many of them are started by the removal of apex predators. These extinctions may be mankind’s most pervasive effect on the natural world. Extinction obviously means a permanent loss of these animals, which in turn often has a ripple effect, causing many other changes throughout the ecosystem. These widespread changes are what are referred to by scientists as “trophic cascades” (TCs). Some of the ultimate outcomes of TCs are: fires, disease, climate change, habitat loss, and pollution. Theory behind concept of TCs: (1)  An ecosystem is shaped by its top consumers (usually apex predators). (2)  Alternative stable states. TCs push a system, and it reaches tipping points. These are thresholds or breakpoints, and when they are reached, significant phase shifts occur. (3)  Connectivity – this is built around connection webs and through the mechanics of predation, competition and mutualism (organisms that have a supportive effect on each other), biologically, and through physicochemical processes. Cryptic nature of TCs: Species interactions are usually invisible under stable conditions. They may require years to become evident due to the long generation times of some species.  The effects usually do not become evident until after the loss. The scales of TC s can be much more vast than most feasible scientific studies can handle. Most field biology studies concentrate on small, discrete areas, and on non-motile species, with short generation times, making them easy to  manipulate. This results in an incomplete and distorted picture of apex predator influence. Hence, the authors have written what is called a mega study, which brings together the results of many other similar studies, using similar protocols & subjects. This enables them to combine the studies & to note general principles and draw important conclusions with more certainty. Widespread Occurrence of TCs: TCs have been documented throughout the world. When apex predators are reduced or removed, and sufficient time and space are accounted for, their influence becomes obvious. “Natural experiments” showing these effects are pervasive: e.g. loss of: killer whales, lions, wolves, cougars, sharks, sea otters.           These interactions are often complex. e.g. apex predators have little influence on megaherbivores:  Elephants, hippos, rhinoceroses, etc. in Africa are basically invulnerable to predation. Mostly, therefore effects are seen in the increase in smaller herbivores: e.g. Thompson’s gazelle, impala. Influence of apex predators on autotrophs (An organism capable of synthesizing its own food from inorganic substances, using light or chemical energy. Most plants are autotrophs): (a)  Increase of autotrophs – by suppression of herbivory (any animal that feeds mostly on plants), e. g. the loss of sea otters, which prey on shellfish,  have diminished the health of kelp forests. The extirpation of wolves from forests has resulted in a corresponding increase of ungulates adversely effecting other animals and plants in various ecosystems. e.g. the removal of wolves from what has become Rocky Mountain NP in Colorado has resulted in the overgrowth of elk, which in turn have devastated much of the plant life. (b) Decrease of autotrophs – e. g. large mouth bass by feeding on smaller fish, which feed on 200 kinds of plankton (microscopic aquatic plants & animals)  have decreased their numbers to such an extent in many mid western US lakes, that this has resulted in a loss of oxygen, leading to the demise of other life forms in these lakes. Herbivory and Wildlife: Increase in herbivory (mostly domestic animals that eat plants) has resulted in a change from grass lands to scrub lands, & the burning up to 500 million hectares (ha) in the global landscape and has released over 4,000 metric tons (Tg) of CO2 into the atmosphere. Diseases: e.g. Rinderpest (an infectious viral disease) in East Africa decimated ungulates. (animals like wildebeests & buffalos that chew their cud). This led to an increase in plant biomass, which in turn led to wildfires. Vaccination and control eliminated Rinderpest and this led to the recovery of the wildebeests and buffalos. Because of this, shrub lands became grass lands, which reduced the frequency and intensity of wild fires. e.g. Impacts of predatory fish on mosquito larvae: effects the incidence of Malaria. Physical & Chemical Influences: There is a linkage between apex predators & atmospheric CO2. e.g.  presence or absence of predatory fish in lakes can effect the production & uptake of CO2. e.g. whaling transferred 105 million tons of carbon from whales to the atmosphere. e.g. Extinction of Pleistocene herbivores reduced atmospheric methane & contributed to a drop of 9° C. temperature drop in the Younger-Dryas period, some 12,900 years ago. Soils: e.g. Herbivores profoundly influence soils. e.g. introduction of rats & arctic foxes in high latitude (mostly arctic) islands reduces soil nitrogen by disturbing nesting birds. Water: e.g. collapse of large demersal (bottom feeders) fish in the Baltic Sea led to a 20% decrease of silica in pelagic diatoms (one-celled organisms that make up the majority of plants found in the open sea). e.g. Yellowstone wolves protect riparian vegetation from over-browsing herbivores. This leads to more shade & cooling of streams, which in turn decreases streambed erosion & increases cover for fish & other aquatic organisms & leads to an increase in songbirds.. Invasive Species: Lack of top-down predators allows invasive species to spread. e.g. spread of the brown tree snake, originally from the Solomon Islands, on Guam, which has exterminated most of its birds, was due to lack of other predators, which could have held the snake population in check. e.g. reduced fish predation in the Mississippi River led to the invasion of zebra mussels. Biodiversity (Abundance of & diversification in living creatures): Biodiversity(BD) is now largely confined to protected areas (e.g. national parks, designated wildernesses). Loss of BD has been mostly caused by over-exploitation (hunting, fishing, increase of areas reserved to domestic & other ungulates, etc.) has led to habitat loss & fragmentation of ecosystems. e.g. over browsing by an increasing population of elk in Rocky Mountain NP is due to lack of natural predators,(i.e. wolves). The same situation occurred in: the Kaibab Plateau, adjacent to the Grand Canyon in Arizona, which was overrun with deer. Minnesota has a serious problem with areas overrun by more than 1 million deer. Princeton NJ had to employ sharpshooters to kill deer, which were overrunning suburban gardens. Deer (ironically) starved on Deer Island in San Francisco Bay due to their burgeoning population, which was unchecked by predators.  Mesopredators (coyotes) in San Diego canyons strikingly changed populations of songbirds and cats. e.g. Sea Stars in intertidal areas interact with mussels, wiping out many species. e.g. loss of small vertebrates after the extirpation of wolves, cougars & bears in temperate & boreal North American forests changed the ecology of these forests. Effects of Tree Longevity: e.g. wolves & other megapredators were almost entirely eliminated in the US by the 20th century. At that time there began to be recruitment failure & reduced tree growth rate in many places (most obvious in national parks). e.g. wolves were eliminated 100 yrs. ago on Anticosti Island in mouth of the St Lawrence River. This led to a decrease in the number of saplings & an increase in graminoids (grasses), e.g. wolves were extirpated from the Scottish island of Rum 250 -500 years ago, resulting in total loss of its forest. It is now treeless. Conclusion: “Best management solution is likely restoration of effective predator regimes.” [English translation: Bring back the predators] Paradigm Shift in Ecology: There is clearly a top-down forcing in ecosystem dynamics.  [We argue that ] “burden of proof be shifted to show for any ecosystem, that consumers do (or did) not exert strong cascading effects.” Conclusions: Unanticipated changes in the distribution & abundance of key species, as well as pandemics, population collapses, eruptions of unwanted species, major shifts in ecosystem states, are caused by altered top down forcing , brought about by loss of native apex consumers. Repeated failures to anticipate & moderate such events arise through  fundamental misunderstandings of their causes. Resource managers usually base their actions on the expectation that physical causes are the ultimate drivers of ecological change. “Top-down forcing must be included if there is to be any real hope of understanding & managing the workings of nature.”

 COMMENTS – Ken Fischman, Ph.D.

 I find it helpful in understanding TDG to picture a pyramid, with the predator at the peak or top & prey animals at several successive & increasingly wider levels, (indicating larger populations) underneath. For example, sharks are the top predators in our oceans & they prey on smaller fish such as tuna, which in turn prey on smaller fish like anchovies, etc. until the lowest & most fundamental layer is reached, which consists of microscopic plankton (autotrophs) & is effected in a profound way. Along this line, I recently read a paper published in Nature by Daniel Boyce of Dalhousie University in which the author utilized hundreds of thousands of historical records to show that the clarity of most of our oceans has been greatly increasing in the past few years. This is an indirect but powerful method, showing that plankton populations are decreasing rapidly. Because plankton are the base prey in our oceans, their scarcity would adversely effect all fish populations & since they are the ultimate autotrophs (think of what would happen if their dry land equivalent, grasses, were to decrease considerably) tend to increase CO2. Such a profound worldwide change undoubtedly has more than one cause, but the disruption of world fisheries through the loss of top predators is probably a contributing factor. It is easy to overlook the effects of some predators, either because they are not charismatic megafauna, like “lions & tigers & bears oh my!” or are out of sight much of the time. For instance, who would even thought of sea stars as predators? I know that I had not until recently despite my background in Zoology.  Yet it has been shown that their loss can have profound effects on shellfish.  And those cute little sea otters. Who would have thought that they have an important effect on kelp beds? The film, “Jaws,” which came out in 1975, gave sharks a bad name that they have yet to overcome. That, together with the insatiable appetite of Chinese & other Orientals for shark fin soup (Talk about waste. They cut off the fins & throw the shark carcass away) & the dislike of commercial fishermen for sharks, who they view as competitors, in the same way that many elk hunters view wolves, has led to their wholesale destruction. No thought was given to the sharks’ role as the ultimate apex predator in the sea & the  effect their demise is having on other fish lower in the TC pyramid. It is quite possible, even probable, that the loss of many commercial fish species is linked not only to overfishing but also to the destruction of sharks, which has upset the ecological balance in oceans. In this connection, commercial fishermen may be doubly responsible for the serious depletion of fisheries worldwide, through their overfishing & destruction of apex predators. My own studies on wolves and as an advocate for them has given me a fresh perspective on their importance in maintaining healthy forests. In this respect, the authors’ citing of studies showing that the eradication of wolves changed the flora of Anticosti Island in the St. Lawrence estuary & deforested the Scottish island of Rum, is instructive & worrying. We do not however, need to go to the ends of the earth to find examples of TDG. In my own little part of northern Idaho, we have seen the results of overfishing in Lake Penderay, invasive species like spotted knapweed & the infamous zebra mussels, and loss of biodiversity caused by overpopulation of elk in the Clearwater NF. There are a substantial number of elk hunters in the state of Idaho, whose idea of heaven seems to be forests containing only elk & hunters. One of their leaders recently stated that he would only be satisfied when hunters success rates reached 90% Success rates throughout the Northwest have been historically at around 18 -20% (Spokesman Review 2/22/08). Idaho already contains over 100,000 elk. He apparently wants to turn Idaho into an elk farm, where hunters do not even have to get off their ATVs to kill elk. I doubt that many other Idahoans would agree with that vision. These hunters & the politicians who support them are responsible for the present vendetta against wolves, which in the last year has resulted in the killing of around 429 out of only 760 wolves in this state & the extension of the wolf hunt to year around, a hitherto unheard of strategy for “managing” wildlife. I hope that this publication on the importance of top predators, like wolves, will be brought to the attention of state wildlife organizations like IDF&G and will result in a change of their policy toward a greater respect for these animals. For those of you who are interested in finding out more about this fascinating & important subject of how the loss of top predators is effecting the earth, I recommend the following books: Monster of God – by David Quammen A very readable account of how our fear & killing of predators is changing the          world. Where The Wild Things Were – by William Stolzenberg A journalist writes about the research that been revealing the key role that          predators play in ecosystems. Song of the Dodo – by David Quammen One of our best scientific & nature writers chronicles the researchers & their          studies who have created the new field of Conservation Biology. Of Wolves and Men – by Barry Lopez A brilliant examination of wolf biology & the often-searing history of mankind’s relationship to these fascinating & badly misunderstood animals.

Breaking News, genetics, Idaho Fish & Game, wolf facts, wolf hunt

Scientists debate number of wolves needed for species’ survival

Aug 4th, 11 / 0 Comments

 

Scientists debate ‘magic number’ of wolves needed for species' survival

[To my knowledge, this is the first article in the media to address from a scientific point of view the important issue of how many wolves are needed for a viable population. Chaney points out that according to the Conservation Biology 50/500 rule, from 2,000 - 5,000 wolves are needed in the Northern Rockies to insure a population with sufficient genetic diversity.

He also points out that the areas chosen for reintroduction, Idaho, Montana, and Wyoming, are artificial, ignoring the fact that wolves regularly move back and forth between these states and Canada. 

He looks at the much cited 1987 restoration goal of 150 wolves per state, and bluntly labels it as a dishonest political, and not a scientific number. Ed Bangs, the retiring Wolf Coordinator for USFW has admitted as much in a recent interview.

Finally, I would be remiss in not stating that Chaney's enlightening article appears to have come too late to save Northern Rockies wolves. As most readers know, they have been removed from the protection of the ESA. Idaho's and Wyoming's stated plans for them, will basically lead to either their total extermination or to their reduction to a few struggling packs and lone wolf wanderers, that will have little or no effect on the ecosystem and will be seldom even glimpsed in our forests.]

by Ken Fischman

By ROB CHANEY of the Missoulian | Posted: Sunday, May 22, 2011 7:00 am 

Conservation groups and the federal government continue to disagree how many gray wolves are needed in the Northern Rockies to ensure the species’ survival. National Park Service photo

One of the biggest arguments left unresolved by last year's wolf lawsuit was the most obvious: How many wolves are enough?

The U.S. Fish and Wildlife Service took the gray wolf off the endangered species list in 2009, with the caveat that at least 150 wolves and 15 breeding pairs endure in each of the three states in the northern Rocky Mountain population (Montana, Idaho and Wyoming).

Recent surveys found at least 1,700 wolves in that area – more than enough to justify delisting.

But a coalition of environmental groups sued the government, claiming those numbers were wrong. To survive and thrive, they argued, the population needed at least 2,000 and preferably 5,000 wolves.

FWS biologists said they used the best available science to pick their number. Coalition members cited the well-established rules of conservation biology to justify their threshold. While the scientists dueled, U.S. District Judge Donald Molloy decided the case on a technicality and Congress reversed him with a budget rider. Wolves in the Northern Rockies are now delisted, but almost nobody's happy.

*****

Over the past decade, biologists have sought a "magic number" that would simplify endangered species debates. In 2010, an Australian team led by Lochran Traill of the University of Adelaide published a study declaring 5,000 was the population size required to prevent any species' extinction.

"We don't have the time and resources to attend to finding thresholds for all threatened species," Traill told Science Observer Magazine. "(T)hus the need for a generalization that can be implemented across taxa (classes of animals and plants) to prevent extinction."

But another group of U.S. Forest Service researchers along with American and British professors warn that a simple tool may be a flawed tool. While they agree that an easily understood standard helps persuade judges or members of Congress of the need for action, the 5,000 figure doesn't add up. Their paper will be published in the journal Trends in Ecology and Evolution.

"It's natural for any policy maker and practitioner to look for ways of simplifying the overwhelming process of endangered species management," said Greg Hayward of the Forest Service's Alaska Region Office. "If that worked, it would be a delightful world to live in. But if you're really going to do anything positive, in terms of turning around the situation for these species, going for that simple rule of thumb isn't going to help."

Both sides use a lot of math to make their points. Traill and company looked at 1,198 species with a computer model that calculated how many of each would be needed for the plant or animal to survive in the long term. In particular, the study looked at how many are needed to ensure a species doesn't in-breed itself into extinction.

That's key because one requirement to getting off the endangered species list is a population big enough to guarantee genetic diversity. Earthjustice attorney Doug Honnold relied on that in his argument to Molloy, to show why the wolf should remain a listed species.

"If you're talking about genetics, then there are some basic genetic principles that apply across all species," Honnold said. "It's been documented with every species that's been studied."

Honnold referred to what's called the "50-500 rule" which states you need at least 50 breeding-age females of a species for short-term survival or 500 for the long term. In the case of wolves, there's usually only one breeding female in a pack of four to 10 wolves, so the total population number balloons to 2,000-5,000.

*****

The "magic number opponents" respond that genetics isn't everything. In the case of wolves, where might that 2,000-5,000 figure apply? Do we need a minimum viable population in the three states where wolves were reintroduced back in 1995? Or should the figure be spread across the six-state area now delisted by congressional fiat (adding Utah, Washington and Oregon to Montana, Idaho and Wyoming)? Does it count the Canadian wolves that have relations with American packs along the international border?

"Under the Endangered Species Act, we sort of ignore other segments of populations that are outside the United States," said Hayward's colleague, Steven Beissinger of the University of California-Berkeley. "In the case of the paper we did, one thing we found was, the particular technique people used to come up with this minimum number was very context-specific."

In other words, each animal needs its own formula. Passenger pigeons had different lifespans and breeding rates than wolves. They could fly across continents at will, while wolves may be stymied by freeways. Passenger pigeons were, in fact, the most abundant land bird in the continental United States – 3 billion to 5 billion individuals – before the population crashed between 1870 and 1890. [ note: Here I disagree with the reporter. The passenger pigeon population did not crash. It was deliberately exterminated, using the most atrocious means imaginable.]

Science rarely gets to be just science. Lots of scientific reasons justify the wolf's presence on the landscape: It reduces elk populations, which in turn improves the plant communities along streams, which brings back songbirds and beavers.

But reduced elk numbers aggravate a hunting community that's invested millions of dollars to improve elk habitat. Wolves also have proved a poster target for politicians who want to leash the Endangered Species Act.

Natural Resources Defense Council staff scientist Sylvia Fallon said the U.S. Fish and Wildlife Service knew it would face public resistance if it proposed reintroducing lots of wolves, so it picked a deliberately low 150-per-state figure to get the reintroduction in play.

"They (FWS biologists) say they came up with that number in consultation with scientists, but they never said who they were," Fallon said. "It was some guesswork factoring in social and political considerations at the time, what would be acceptable to the states and the public."

FWS attorneys rejected that claim in their court briefs, but they never got to have the argument in Molloy's courtroom. Without ever discussing what an appropriate number should be, the judge only said the federal government illegally used state boundaries to divide a natural population.

*****

Beissinger suggested a better target in the search for the elusive magic number. Instead of a unified field theory of how many of a species is needed to survive, we humans should settle on what risk factor we're willing to work with, he said.

"In my profession, we don't have a single standard that's been set for what degree of risk we're willing to accept for a species to go extinct," he said. "I could make a calculation for a species and say nine times out of 10, it would be viable there, for 50 years. Would that be good enough, or would you want a 95 percent chance, or an 80 percent chance? But it's too naive to use just measures of population size and come up with some rule of thumb whether a population is safe or not."

Reporter Rob Chaney can be reached at 523-5382 or at rchaney@missoulian.com.

Note: some passages were bolded by KF for emphasis

 

genetics, News, Wolves

Wolves Don’t Belong On The Firing Line

Dec 19th, 10 / 0 Comments

Wolves Don’t Belong On The Firing Line

WRITERS ON THE RANGE - September 23, 2009By Ken Fischman

Signs of the times

 The day before the first-ever official wolf hunt started in Idaho on Sept. 1, I stood on the sidewalk outside the county courthouse in Sandpoint, watching cars stream into town. As demonstrators on the sidewalk waved placards protesting the hunt, people in those vehicles reacted, and I focused on their hands, counting waves and thumbs-up as being for the wolves, and middle fingers and thumbs-down as against. The results of my hour-long, admittedly crude poll were 128 for the wolves, 14 against. Surprisingly, truck drivers overwhelmingly sided with the demonstrators and against a hunt.

It occurred to me then that Idaho’s reputation as the most dependably conservative state might be based on a misunderstanding. But then again, where emotions are high, truth flies out the window. When you bring up the subject of wolves at a cafe or gas station in the nearby town of Clark Fork, you’re likely to hear people telling or accepting the most outlandish tales. For instance, many hunters insist that Idaho’s 846 wolves are devastating Idaho’s elk, even though the opposite is true. The Rocky Mountain Elk Foundation, an organization dedicated to hunters, reported in 2009 that although Idaho’s elk population fluctuates, it has risen above 100,000 animals for several years.

Many ranchers in Idaho believe that wolves are decimating livestock. But the Idaho Fish and Game Department found that wolves are responsible for only 1 to 2 percent of sheep depredation. In fact, feral dogs killed four times as many sheep in 2008 as did wolves.

Of all the questions surrounding wolves, the most crucial — and the one that has proved most intractable — is whether the population of wolves in the Northern Rockies has sufficiently recovered to warrant their being taken off the endangered species list. Looking for the right answer is like driving down a winding mountain road in the dark, without headlights.

When the federal government brought wolves back to the West in the mid-’90s, spending some $21 million in the effort, the U.S. Fish and Wildlife Service said that the wolf population would be considered recovered when Idaho, Montana and Wyoming each had 100 wolves. I would have loved to have been a fly on the wall when they came up with that goal.

Common sense tells us that a few hundred wolves in each state can’t be defended as a biologically viable population, yet legislators and wildlife professionals keep trotting out these figures as though they were holy writ to justify their insistence that wolves must be hunted. The latest federal report says that there are 846 wolves in Idaho, 497 in Montana, and 302 in Wyoming. The best minds in conservation biology — the science that deals with the preservation of species — are in agreement that the full recovery of these three distinct populations requires not hundreds, but thousands of animals. 

That means that a hunt at this time is premature. Compare Idaho to Minnesota, where there are 3,000 wolves, almost four times the number in Idaho. The Minnesota wildlife agency will not even consider holding a hunt for five years after wolves are delisted there.
    
Let’s put the issue in perspective. There are four times as many human beings in the tiny town of Bonners Ferry, up the road from Sandpoint, than there are wolves in all of Idaho. If hunters kill as many wolves as they plan to in this hunt, it will leave small, disconnected populations of wolves genetically isolated from each other and in danger of becoming inbred.

A few months ago, a study by Rolf Peterson of the Michigan Technological Institute, revealed what can happen when wolf populations drop too low. Peterson looked at genetically isolated wolves on Isle Royale National Park, an island in Lake Superior off the coast of Minnesota. All the wolves there have deformities of their backbones, making it difficult and painful for them to run. This is due to inbreeding.
    
As for what happens now that hunting wolves has begun, the political battle continues. Federal Judge Donald Molloy recently rejected a request from 13 environmental groups that he block wolf hunts in Idaho and Montana. Molloy said that the plan to kill 20 percent of the wolves does not put them in danger of extermination. He warned, however, that the federal government probably violated the Endangered Species Act by leaving Wyoming out of its plan, distinguishing a natural population of wolves “based on a political line, not the best available science.”  By definition, the judge added, that seems “arbitrary and capricious.”

Ken Fischman is a contributor to Writers on the Range, a service of High Country News (hcn.org). He is a retired geneticist and member of the Northern Idaho Wolf Alliance. He lives in Sandpoint, Idaho.

Idaho Fish & Game, projects, wolf hunt, Wolves

Biogeographic And Genetic Factors In Northern Rockies Wolf Populations

Dec 19th, 10 / 0 Comments

 

       Biogeographic and Genetic Factors in Northern Rockies Wolf Populations

Ken Fischman, Ph.D.(Genetics)   April 9, 2008

 

         As we all know, Fish & Wildlife (USFW) has proposed delisting the wolf populations of Idaho, Montana, and Wyoming. They have recently estimated total wolf populations in these three states to be 1,242, with 92 breeding pairs.  Wolf population in Idaho is currently estimated at 672 ( Nadeau et al., 2007), with 42 breeding pairs (Bangs, Personal Communication, 3/8/07).

         Idaho Fish & Game proposes maintaining a minimum of 100 wolves in their state, with a minimum of 15 breeding pairs (IDFG, 10/07). 

         This paper examines these two population targets, some recent thinking about the genetics and biology of wild animal species, and finally the possible biogeographic and genetic consequences of the minimum number of wolves projected by the Idaho authorities.

          First, let’s look at the effects of population size on the viability of a species. The Hardy-Weinberg Principle states that allele frequencies (that is different forms of a gene) will not vary over time in a population. However, this principle only holds for a population sufficiently large to overcome the tendency for Genetic Drift to change gene frequencies. 

         Genetic Drift refers to the tendency for genes to become more common or more rare in successive generations.  It has no preferred direction, and it tends to sweep genetic variants out of the population with time.  It thus opposes Mutation, which introduces novel variants into the population, thus increasing species resiliency.  i.e. the ability to resist demographic shocks and adapt to changed conditions.

         Small populations often show a Founder Effect, in which one or more gene variants increasingly predominate as inbreeding increases. Inbreeding Depression, results from an increase in homozygosity. That is the state in which there are two identical copies of genes.  Homozygosity increases the possibility of recessive alleles expressing themselves. Some of these will turn out to be valuable, but most will be deleterious, thus weakening the genetic fitness of the population.

         Wolf packs, due to their size, and if they are effectively isolated from other wolf populations, also may show a Founder Effect, thus adversely effecting the long-term survival of the population. The increase in homozygosity would in turn be responsible for high frequencies inherited diseases.  This is something that wolf biologists should be on the watch for.

          What counts in small populations is not their census size, but the Effective Population size or number of breeding individuals in the population. The literature on wolves indicates that most packs have only two Effective Breeders.  However, the latest data on Yellowstone packs show multiple breeders within some packs (Smith, 2006).  I am curious as to whether this is also true for other northern Rockies wolf populations.  On the other hand, can this situation be attributed to something unique about Yellowstone wolves, such as access to large prey populations or lack of stress?  An answer to this question would be important for calculating viable population numbers.

         Let’s examine some of the other possible consequences of small population size.  Small populations in particular are prone to large fluctuations in size. Therefore, it is important to consider this in some detail.  Why does this occur?

           Inbreeding is one source of changes in population size.  The smaller the population, the more likely it is that related individuals will breed with each other, and their offspring will have a far higher number of homozygous genes.

         That is hard to detect, but its consequences, although sometimes subtle, can be severe.  Michael Soule showed that inbreeding of Poland Swine lead to deleterious effects in as soon as the second generation.  The inbreeding resulted in decrease in piglets/litter, decreased survival of newborns, and skewed sex ratios.  As we shall see, this last may be of particular importance for wolves.

         As I previously stated, inbreeding leads to lack of genetic diversity, which in turn may result in inability to adapt and evolve under changing conditions.

         There are also Demographic effects.  One such effect would be fluctuations in the size of small populations. Another is possibility of imbalance of sexes, and increasing chances of a same sex generation. For example, 3 offspring’s chance of being the same sex is 0.25 or 1/4.  If a population remains at a low level for several generations, then a same sex generation becomes almost inevitable.

         Here is an example of a problem resulting from such a situation. One of the last populations of Kakapo, an extremely rare, flightless parrot, was found on an island off the coast of New Zealand.  There were 18 of them. Unfortunately, they were all male.

         A small population is also susceptible to  Environmental effects, such as forest fires, disease, climate change, etc

         Anthropogenic effects loom large for small populations.  These are events such as: accidents, hunting, killing of so-called problem Wolves, and illegal takings. This last is of particular importance in Idaho.  Since wolf reintroduction, 59 cases of illegal hunting/killing have been documented by ID F&G.  Due to its furtive nature, this is probably only a portion of such deaths. 

         Also, last year, 45 Wolves were deliberately killed by ID F&G, USFW, and ranchers. These deaths add up to more than 6% of the Idaho Wolf population.

         All of these effects contribute to population decrease, both directly and indirectly by damaging the social structure of a pack.  Most anthropogenic effects are indiscriminate acts with unforeseen consequences.  For instance one of the pack members killed might be the Alpha female.

         There are of course important Genetic consequences, resulting from the decreases in population size brought about by these demographic, environmental, and anthropogenic effects. As previously stated, inbreeding and small population size will increase the degree of Homozygosity. Recessive genes only express themselves when there is a double dose of them. And, because most harmful genes are recessive, this will result in a larger number of unfit animals and a greater number of deaths.

         Homozygosity also results in an increase of Monomorphisms and an associated  decrease of Polymorphisms, which are multiple functional alleles in a population. This can be damaging, especially if genes effecting the Immune system are involved.  The situation can also lead to a continuous and therefore increasing fixation of deleterious genes. We give this the fanciful name of “Muller’s Ratchet,” which is the continual loss of individuals with the smallest number of deleterious genes because there are so few such individuals.  Due to the elimination of these individuals, generation by generation, the population’s genetic load of damaging genes increases, thus decreasing its adaptive fitness, and leading to its eventual extinction.

         As the expression of recessive alleles become more common due to increase in homozygosity, a species becomes less fit because they are less diverse and therefore more subject to mass die-offs due to disease, etc.  Heterozygosity, in contrast, is increased by outbreeding, leading to improved adaptive fitness of the animals.                

          I would like to put the 673 wolves in Idaho in demographic and geographical perspective.  The size of Idaho is 82,751 square miles. That works out as one wolf for every 123 square miles.  The Human population is more than 1,240,000, which means one wolf for every 1,842 people.

         The chief prey of Idaho wolves are Elk. Their 2006 numbers were estimated  by IDFG as 102,706. The Wolf population of Idaho is actually very small in comparison.  There are 153 Elk for every wolf. 

         Geneticists and Biogeographers find it useful to employ the term Minimum Viable Population or MVP.  This is defined as the smallest population size likely to persist indefinitely in a particular area.

         Here is a little history lesson.  Main and Yadov(1971) examined marsupial populations on several Australian offshore islands and came to the conclusion that a minimum of 200 – 300 animals was necessary to maintain those populations.  However, they also concluded that MVP differs from one species to another, and according to conditions.

          Conservation Geneticists usually consider that a population of less than 500 individuals is endangered, Keep in mind however, that what is important to species preservation is not total population, but the number of Effective Breeders, and many Conservation geneticists recommend a minimum of 50  breeder pairs.

          If we assume an average of ten wolves/pack, with one breeding pair, this would extrapolate to a population of 500 wolves.

         It is of course self-evident that larger populations are usually safer for the viability of a species or sub-population of a species. The key question remains as to what is the minimum number of individuals that would put a population at risk of extinction. 

         All of the factors I have previously mentioned are involved in such a determination, but perhaps another factor is more important in this situation. That is whether or not there is such a thing as a megapopulation of wolves in the northern Rockies.

         USFW speaks of a northern Rocky wolf megapopulation, connected by wolves dispersing from packs.  The megapopulation they describe extends from Canada, western Wyoming and Montana to central Idaho, and from there to northern Utah, a distance of approximately 800 miles.

         Such a connection is particularly problematical between central Idaho and Northern Utah, yet the US FW has conflated what appear to be two distinct areas. I do not know of any data that supports this idea. Lets examine the evidence for the existence of such corridors:

         Since wolf reintroduction, and through the winter of 2006, eight wolves traversed between northwest Montana and central Idaho. Of those, only three have successfully bred. Attempts made by wolves to move between the central Idaho and Yellowstone populations have fared even worse. Only one wolf completed the journey in eleven years since reintroduction (Robinson, 2006)

         These numbers of dispersing wolves are so small that they are likely to have little or no effect on gene flow between these populations.  Additionally, the fact that in such a long time, span, only three of the nine dispersing wolves bred, makes it likely that a larger number of wolves would be necessary if their movement between these regions could be successfully translated into significant gene pool effects.

         To settle the question as to whether these so-called corridors have a real effect, it would be best to do comparative genetics studies between populations rather than to continue to track lone wolves.        

         Much has been made of the rapid increase in wolf numbers since the initiation of wolf recovery in the 1990s. This increase has been cited by the USFW as a sufficient reason to remove them from the Endangered Species list.

         Is this population increase truly remarkable, or is it due to the rapid filling of an ecological niche for a keystone predator that had been nearly empty for well over a century?  Only time will tell, but I suspect that as these niches fill, rates of increase in wolf population will slow down. This is especially liable to occur because many of the conditions that led to wolf extinction in the lower 48 in the first place, are recurring. Hunting, culling of so-called problem wolves, and illegal takings may result in destruction of the intricate social fabric of wolf packs, putting them at an even greater risk of a second extinction.  Just the other day, someone in eastern Idaho shot two wolves because they “were near his ranch.”  (KPBX radio, 4/3/08).

         It is a frequent mistake to assume that current trends will persist indefinitely into the future.  To assume that wolf populations will continue to increase at present rates is as biologically naive as were the assumptions of homeowners and Wall Street investors who have lately discovered that ever-increasing housing values are an illusion.  No one escapes the laws of Nature indefinitely.

                  So we turn to the key question of what is the Minimum Viable Population for Canis lupis?  It is important to realize that MVP has two corollaries, having to do with population size and time: (1) The smaller the population, the more likely it will go extinct within a certain time period.  (2) The longer the time period, the more likely extinction is for a population of any size.

         Mark Shaffer, in his studies of Grizzly populations in national parks, suggested that a 95% chance of persistence for 100 years would be a reasonable goal.

         Conservation Geneticists have recently set more stringent parameters of a 99% chance of persistence for 1,000 years.

         In reality, viability is too complex an issue to be reduced to a single number.  A population of some specified size might be viable under one set of circumstances, but not under another set, or viable for one species, but not for another.

         Soule and Gilpin (1987) came to the conclusion that theoretical numbers cannot be relied on, only real data, analyzed in complex ways and checked against real-life situations can be relied upon.  They called this method Population Viability Analysis (PVA).

         So, how large a population is sufficient to insure viability?  Soule stated that arguing from theory, several lines of analysis produce estimates of several thousand or larger. He said “ I am assuming a 95% expectation of persistence, without loss of fitness, for several centuries.  My guess is that it would be in the low thousands.  …estimates below this range should be an automatic signal for scrutiny.” (Soule. 1987)

         However he leaves us with the following warning:  “…anyone who applies the few thousand estimate to a given species, citing this author as an authority, deserves all the contempt that will be heaped on him or her.”

Considering all the evidence accumulated, it is clear that the wolf management plans of the federal and state agencies are not based on sound scientific and genetic data or theory.  If they are carried out as presently planned, they will undoubtedly lead to genetic impoverishment and possibly to a second extinction of wolves in the Rocky Mountain region.

statistics, wolf hunt, Wolves