How Many Bears Can Live in this Forest?

Understanding the Factors Affecting An Ecosystem

Carrying capacity may be defined as the ability of a given unit of habitat to supply food, water, shelter, and necessary space to a given species. It is the largest population the unit can support on a year-round basis, or during the most critical season. Carrying capacity varies throughout the year---and from year to year---depending on conditions within the habitat such as rainfall, competition from domestic animals, and the impact of human activity.

An area of bear habitat can support only a specific number of bears, just as a one gallon bucket can hold only one gallon of water. All habitats, for whatever species, vary seasonally and/or yearly in their carrying capacity. Habitats can therefore only support the numbers that can be carried at the lowest ebb of the season or year. Those surplus animals, born during richer season, must be lost to some "limiting factor" before or during the harsher season. This activity deals with the black bear (commonly found throughout Pennsylvania and New Jersey), and their habitats.

Procedures:

1) Write your name on a piece of tape and attach it to a tray/piece of paper. This will represent your "den site" and should be left on the ground (perhaps anchored with a rock) at the starting line on the perimeter of the field area.

2) You, along with your classmates, will line up on the starting line, leaving your "den" between your feet on the ground. You are all now black bears. All bears are not exactly alike, just like you and the person next to you, are not exactly alike. The following are some of the specialized bears among you.

(A)Among you is a young male bear that has not yet found his own territory. Last week he met up with a larger male bear in the big bear's territory, and before he could get away, his leg was severely injured (this student must hunt hopping on one leg).

(B)Another bear is a young female who investigated a porcupine too closely and was blinded by the quills (this student must hunt with a blindfold).

(C)There is a mother bear with one to two small cubs. She must gather twice as much food as the other

bears just to keep her and the cubs alive. The cubs cannot hunt by themselves (this student will have 1 to 2 other students taped to his/her legs to simulate a mother with 2 cubs).

(D)The small cubs cannot hunt on their own (these students, while taped to the legs of another, are not

allowed to gather food AT ALL!)

(E)There is a female bear in "heat." All the male bears are after her. Every time a male meets up with her, she must stop her hunting and gathering activities to mate (this student must spend at least 15 seconds with each male bear if they catch her, before continuing to hunt & gather food).

3) The wooden blocks scattered in front of you represent various kinds of bear food; since bears are omnivores, they like a wide assortment of foods, so make sure to collect a wide variety of squares!

4) You are to walk into the "forest." Bears do not run down their food; they gather it. When you find a colored square, you should pick it up (one at a time) and return it to your "den" before picking up another colored square. (Bears would not actually return to their den to eat; they would eat food as they find it.) Pushing and shoving--any competitive activity--is acceptable as long as it is under control. Snatching food right out from under the blind bear or the crippled bear is natural--but stealing from each other's den is not. Remember that if bears fight (which they seldom do) they often become injured and unable to gather sufficient food; then they starve.

5) When all the colored squares have been gathered, the food gathering and hunting is over. Pick up your den and return to class.

Analysis:

1) Each color and number represents a different food source. The key is as follows:

Orange--nuts (acorns, pecans, walnuts, hickory nuts)

N-10 = 10 poundsN-20 = 20 pounds

Blue--berries (blackberries, elderberries, raspberries)

B-10 = 10 poundsB-20 = 20 pounds

Yellow--insects (grub worms, larvae, ants, termites)

I-12 = 12 poundsI-6 = 6 pounds

Red--meat (mice, other rodents, peccaries, beaver, muskrats, young deer)

M-8 = 8 poundsM-4 = 4 pounds

Green--plants (leaves, grasses, herbs)

P-20 = 20 poundsP-10 = 10 pounds

2) Add up the total number of pounds of food you gathered and categorize it as nuts, berries, insects, meat, or plants. Use the table below for assistance:

Food Source / Nuts / Berries / Insects / Meat / Plants / Total lbs

3) Record the amounts that each student obtained, especially the "special" bears. Please use a separate sheet of paper to record the results for the whole class.

Bear (Role & Initials) / Nuts / Berries / Insects / Meat / Plants / Total lbs
Blind
Crippled
Mother
2 Cubs
“In Heat”
Average
Average
Average
Average

Analysis/Conclusions: Please use a separate sheet of paper!

1) A study in Arizona determined that a mature black bear could typically eat about 8 pounds of food per day in a ten-day period (that is a total of 80 pounds)! However, the study illustrated that the breakdown was as follows:

Nuts=20 pounds=25%

Berries=20 pounds=25%

Insects=12 pounds=15%

Meat=8 pounds=10%

Plants=20 pounds=25%

On the basis of the above figures, did you, as a black bear, consume enough food, in the right categories, to survive? Why or why not?

2) Is there enough food for every bear to survive? To determine this, first total the pounds of food obtained. Divide the number of bears into the total pounds available to find out how much is available for each bear. Each bear needs 80 pounds of food to survive. Is there enough food (energy) for all the bears to survive? If not, how many bears can live in this area? Diagram the energy flow in this ecosystem.

3) What happened to the "specialty bears?"

(A)Did the blind and crippled bears obtain enough food to survive? Explain.

(B)What about the mother bear? Did she get one and a half to two times the amount of food needed to survive? What will happen to her cub(s) if she didn't get enough food to survive and feed them? Will she feed her cub(s) first, or herself? Why? What would happen to her if she fed the cub(s) first? What if she ate first before the cub(s)? If the cub(s) die, can she have more cubs in the future, and perhaps richer, years?

(C) What about the female bear in estrus/heat? Did she gather enough food to survive? Why or why not?

4) This area of black bear habitat can only support a certain number of bears. This number is called the "carrying capacity." Describe some of the ABIOTIC and BIOTIC factors that determine the carrying capacity for a species of animal. Which has the stronger impact on the other, the abiotic factors or the biotic factors? Explain your reasoning. Also, explain why carrying capacity is important for wildlife and for people.

5) Another factor that controls a population is the relationship between predator and prey species. There is a hundred years, or more, of records of the activities of the Hudson Bay Trappers. In those records are some interesting data. These data refer to pelts shipped from America to Europe, particularly the pelts of snowshoe hares and lynx.

Researchers have found that snowshoe hare populations seem to peak about every seven to nine years and then crash, repeating the process over each comparable time period. So, a snowshoe hare population graph would look like this:

It has also been discovered that lynx populations do the same thing--except that they do it one year behind the hare populations. The combined graph would look like this:

Are the predators controlling the prey, or is the prey controlling the predators?

6) Some recent research has added a new dimension to the story of the snowshoe hare and the lynx. It has been found that the major food of the hare is a small willow. As hare populations grow, the use of the willow plants grows too, but when the willow plant has been "hedged" or eaten back so far, the plant generates a toxin, which precludes use by the hare. That is when the hare population crashes, followed by the crash of the lynx population about a year later. Then the willow, relieved of pressure, begins to grow again. The hare population begins to grow in response, and last of all, within a year or so, the lynx population follows. The cycle has begun again--over and over--every seven to nine years.

Based on this information, discuss the "balance of nature." Is it ever in "balance?" What term should be used instead?

7) More frequently, bears are coming into contact with humans (i.e., national parks, suburbs). Either they run away on their own or are trapped and tranquilized (many end up dying in transport). A black bear was videotaped entering a liquor store (2009) and consuming large quantities of beer before it was tranquilized and relocated (no death or internal injuries). What relationship do you think we as humans currently have, and should have with other creatures in our ecosystem? Do you think the humans see themselves as a part of the food web, or apart from it? Why? Please explain yourself fully.

8) Read the following case study about the reintroduction of bears to federal parks developed by Grace A. Wang (1999-2000), from Huxley College of the Environment (Bellingham, Washington).

(A) Should bears be reintroduced to federal parks, just like the wolf was reintroduced to Yellowstone?

Why or why not (use facts from the case study to develop a stronger answer)

(B) What are the factors involved in the reintroduction of any species (economic, environmental, etc.)?

(C) How would reintroduction affect the different communities commonly found throughout the Bitterroot

Mountains? Which alternative should be chosen?

BACKGROUND

Few species have captured the imagination of the American public like the grizzly bear (Ursus arctos horribilis). It is one of the largest North American land mammals, with male grizzly bears often reaching 7 feet tall, weighing 300-600 pounds, and female grizzly bears 200-400 pounds. They are an omnivorous species, with a diet that includes elk carcasses, sometimes sheep, berries, and whitebark pine seeds, among other items.

Although grizzly bears historically ranged throughout most of the western United States, habitat loss and excessive human-caused mortality have drastically reduced numbers of this species. It is estimated that prior to European settlement there were ~50,000 grizzly bears; it is estimated that only 800-1,000 grizzly bears exist on approximately 2 percent of their historic range in the lower 48 states now. Biologically, grizzly bears have the second slowest reproductive rate of all North American mammals, making it difficult for them to rebound from threats to their survival. Females reach maturity at 4-9 years, and generally give birth to two cubs every three years.

THE ENDANGERED SPECIES ACT

Congress enacted the Endangered Species Act of 1973. The ESA declared national policy "that all Federal departments and agencies shall seek to conserve endangered species and threatened species and shall utilize their authorities in furtherance of the purposes of this [Act]." The ESA defines an endangered species as "any species which is in danger of extinction throughout all or a significant portion of its range." A threatened species is defined as "any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range." Four key sections of the ESA provide its basic structure:

  • A formal listing process used to identify threatened and endangered species, protect critical habitats, and the drafting of recovery plans.
  • Federal agency consultation with the appropriate Secretary (Interior or Commerce) before taking any action that might affect a listed species.
  • Prohibition of the "taking" of listed species and damage to their habitats. The term "take" means to "harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct."
  • Penalties for violations of the ESA.

Grizzly bears were listed as a threatened species in the lower 48 states in 1975. At that time, the Bitterroot Ecosystem (BE) was listed as one of three areas where grizzly bears were known or thought to exist and where recovery should be emphasized. Earlier in the 20th century, grizzly bears were widespread inhabitants of the Bitterroot Mountains in central Idaho and western Montana, although the last verified death of a grizzly bear in the BE occurred in 1932 and the last tracks were observed in 1946. No verified tracks or sightings have been documented in more than 50 years, and the best scientific evidence available indicates that there are no grizzly bears in the BE at this time.

Figure 1. Map of Grizzly Bear Ecosystems in the northern Rocky Mountains.

Redrawn by Jim Stamos (UB Dept. of Biological Sciences) from Chapter 2, figure 2-3 of the Grizzly Bear Recovery in the Bitterroot Ecosystem: Draft Environmental Impact Statement. Missoula, Montana: U.S.F.W.S., July 1997.

/ Grizzly Bear ecosystems / / Bitterroot Ecosystem

THE RECOVERY PLAN

In 1982, a federal grizzly bear recovery plan by the U.S. Fish & Wildlife Service (FWS) called for the evaluation of the BE as a potential recovery area. Ensuing studies indicated sufficient habitat existed in the BE to support 200-400 grizzly bears. In 1991, the Interagency Grizzly Bear Committee endorsed the BE as a recovery area and authorized the FWS to pursue grizzly bear recovery. The ultimate long-term goal of the plan is removal of the grizzly bear from threatened status in the lower 48 states.

THE DRAFT ENVIRONMENTAL IMPACT STATEMENT

The FWS released a Draft Environmental Impact Statement (DEIS) in 1997, describing four alternatives that represent different approaches to grizzly bear recovery and management in the Bitterroot Ecosystem of central Idaho and western Montana:

Alternative 1. Reintroduction of a Nonessential Experimental Population Alternative

Section 10(j) of the Endangered Species Act provides the authority to designate certain populations of listed species as nonessential "experimental populations" to promote species conservation. This designation is more flexible than "endangered" and allows private landowners some flexibility in dealing with reintroduced arenas. The goal of this alternative is to accomplish grizzly bear recovery by reintroducing grizzly bears designated as a nonessential experimental population to the Bitterroot Ecosystem. Central to this is creation of a Citizen Management Committee (CMC) to conduct grizzly bear management within the framework of local concerns. The CMC would be given the task of managing this grizzly bear population.

Alternative 2. The No Action Alternative - Natural Recovery

The goal of this alternative is to allow grizzly bears to expand from their current range in north Idaho and northwestern Montana southward into central Idaho and western Montana, and to re-colonize the BE. Ultimately, the goal is natural recovery of grizzly bears in the BE.

Alternative 3. The No Grizzly Bear Alternative

The purpose of this alternative is to prevent grizzly bears from naturally re-establishing in the BE. Congress would need to pass legislation to remove grizzly bears in central Idaho and portions of western Montana from the list of threatened species. The FWS would stop all funding and management activity toward bear research, education, and management in central Idaho. The states of Idaho and Montana would remove grizzly bears from the protection of state law within the BE.

Alternative 4. Reintroduction of a Threatened Population with Full Protection of the ESA

The goal of this alternative is to achieve recovery through reintroduction and extensive habitat protection and enhancement to promote natural recovery. The grizzly bear would have full status as a threatened species under the provisions of the ESA.

These four alternatives represent different approaches to grizzly bear recovery and management. They were developed for evaluation in the DEIS because they encompass public concerns raised during scoping and to reflect a full range of alternatives. Two alternatives (Alternatives 2 and 3) do not necessarily meet the purpose of and need for action, but were included in the DEIS to be responsive to public comments, to provide a full range of alternatives for consideration, and to meet the requirements of NEPA. All four alternatives reflect public comments and suggestions identified through issue and alternative scoping.

Figure 2. Grizzly Bear Recovery Alternatives in the Bitterroot Ecosystem.

Redrawn by Jim Stamos (UB Dept. of Biological Sciences) from Chapter 2, figure 2-2 of the Grizzly Bear Recovery in the Bitterroot Ecosystem: Draft Environmental Impact Statement. Missoula, Montana: U.S.F.W.S., July 1997.

STAKEHOLDERS / PUBLIC CONCERNS

*Governor Phil Batt of Idaho and Senator Conrad Burns of Montana argue that grizzly reintroduction will lock up the region's timber reserves while jeopardizing the safety of constituents in the area: "Reintroduction will pose a significant public safety risk for Idaho's citizens, and many tourists who visit our wilderness areas."

*Ravalli County Commissioner (Montana) Jerry Allen tells the federal government: "We don't want the bears. I'm worried about the livestock and about the safety of my neighbors."