Yellowstone Food Web 426x52

Food Web, Rev 7, Jan 2014

Environmental Stewardship

FDSCI 203

Yellowstone Ecosystem Food Web In this activity we will examine the interconnectedness of various organisms in the greater Yellowstone ecosystem and the number of individuals required to a top predator. A variety of organisms in the ecosystem are listed below and their feeding preferences indicated. This obviously is not a complete list of species that occur in the Yellowstone ecosystem. Producers: algae, grass, sunflower, huckleberry, bitterbrush, whitebark pine C o ns um e r s organism)

Feeding Preferences (% of the consumer’s diet coming from this

stonefly

algae (100%)

cutthroat trout

stoneflies (100%)

grasshopper (10%)

grass plants (80%), sunflower plants (10%), bitterbrush plants

miller moth

grass plants (90%), sunflower plants (10%)

mouse

sunflower seeds (30%), grass seeds (30%), huckleberries (10%), miller moths (10%), bitterbush seeds (10%), grasshoppers (10%)

sparrow

grass seeds (30%), sunflower seeds (30%), grasshoppers (20%), miller moths (20%)

Nutcracker crow whitebark pine seeds (70%), sunflower seeds (20%), huckleberries (10%) squirrel

whitebark pine seeds (60%), sunflower seeds (10%), huckleberries (10%), grass seeds (10%), grasshoppers (10%)

rabbit

grass plants (100%)

deer

bitterbrush (40%), huckleberry bushes (30%), grass plants

(30%) elk

grass plants (80%), bitterbrush (10%), huckleberry bushes

(10%) sparrow hawk

sparrows (40%), grasshoppers (30%), mice (20%),

nutcrackers (10%) bobcat (10%)

rabbits (50%), squirrels (20%), mice (20%), deer 1

Food Web, Rev 7, Jan 2014

wolf

elk (75%), deer (15%), rabbits (10%)

grizzly bear

whitebark pine seeds (60%), miller moths (20%), cutthroat trout (10%), elk (10%)

2

PART 1 ― YELLOWSTONE FOOD WEB. Using the information on the previous page, diagram this food web by drawing arrows to indicate which organisms are consumed by other organisms in the ecosystem. Arrows point towards the consumer. (Some have already been done for you to illustrate how to do this.)

wolf

grizzly bear

sparrow hawkbobcat

deer elk squirrel rabbit nutcracker crow sparrow

mouse

miller moth

cutthroat trout

grasshopper

stonefly CONSUMERS PRODUCERS

white pine seeds

algae

huckleberry plants or fruit

grass plants or seeds

bitterbrush plants or seeds

sunflower plants or seeds

How long is the longest food chain in this food web? (i.e., the one with the most “links”) Example: The algae–stonefly–trout food chain involves 3 trophic levels (i.e., it has 3 “links”).

The longest food chain is the grizzly bear. Part 2 ― Caloric Values and Energy Requirements for Individual Organisms Using the following caloric values and requirements, calculate the TOTAL number of both producers and consumers needed to one grizzly bear for one year (all trophic levels). Producers algae grass plant/seed sunflower plant/seed huckleberry bush/fruit bitterbrush plant/seed whitebark pine seed stonefly (1 g) grasshopper (5 g) miller moth (1 g) mouse (25 g)

Caloric Value (cal) 0.05 cal

—

100 cal/1 cal

100 seeds/plant

200 cal/0.5 cal

2000 seeds/plant

200 cal/5 cal 250 cal/0.5 cal

200 berries/bush

1 cal

500 seeds/bush

Caloric value 5 cal 20 cal 0.5 cal 30

sparrow (25 g)

30

nutcracker crow (130 g) squirrel (500 g)

10 0 80 0 160 0 24,00 0 60,00

rabbit (1500 g) deer (100 kg) elk (250 kg) Carnivores (weight) required cutthroat trout (0.5 kg)

Annual Seed Production

Caloric value (cal)

sparrow hawk (100 g)

1500 cal —

bobcat (15 kg)

—

wolf (45 kg)

—

300 seeds/tree 300 0 750 0 500 0 10,00 0 50,00 0 90,00 0 40,00 0 120,00 0 1,500,000 4,000,000 Calories/year 18,00 0 75,00 0 300,00 0 800,00 0

grizzly bear (300 kg)

—

3,000,000

Calculating Numbers. In this exercise, you will need to calculate the number of organisms needed to a top predator in an ecosystem. This can be done using the information on the preceding page, and the first page. The following example will demonstrate how this is to be done. Look at the previous page to find caloric values (e.g., one elk equals 200,000 calories; one deer yields 100,000 calories; and one rabbit has 2000 calories). In this first table, you will calculate the numbers of organisms directly consumed by the predator. In this example it is useful to that wolves form packs, which hunt and feed together. Pack size varies but can range from 5―20 individuals. Although the numbers of prey per individual wolf may seem small, if you multiply that number by how many wolves are in the pack, you get a much bigger number (e.g., if a pack has 10 , then the pack may be killing as many as 100 elk and 40 deer per year). Top predator:

wolf

Caloric requirement for one year: 800,000 (or 800 K) calories AMOUNT OF BIOMASS DIRECTLY REQUIRED

Prey Species % of wolf’s # cal needed from diet prey Elk 75% (or 0.75) 800 K × 0.75 = 600,000 cal Deer 15% (or 0.15) 800 K × 0.15 = 120,000 cal Rabbits 10% (or 0.10) 800 K × 0.10 = 80,000 cal

# prey individuals needed 600,000 ÷ 60,000 = 10 Elk 120,000 ÷ 24,000 = 5 Deer 80,000 ÷ 1600 = 50 Rabbits

In addition to the animals directly consumed by the predator, we have to consider the organisms that the prey animals. These species the predator indirectly. The same calculations need to be done for all the prey species the wolves consume. This example demonstrates how to do this for just one of those prey species: deer. AMOUNT OF BIOMASS INDIRECTLY REQUIRED

Biomass need to ALL five deer Calories required/deer/year: 1,500,000 (or 1.5 M) Prey % of deer’s #cal #prey/de total #prey Species diet needed/deer er needed Bitterbrush 40% (or 0.4) 1.5 M × 0.4 = 2400 2400 × 5 = 12,000 Huckleberry Grass

600,000 30% (or 0.3) 1.5 M × 0.3 = 450,000 30% (or 0.3) 1.5 M × 0.3 = 450,000

plants 2250 plants 4500 plants

plants 2250 × 5 = 11,250 plants 4500 × 5 = 22,500 plants

To get the value in the 4th column, divide the number in the 3rd column by the caloric value of that species (e.g., one deer will eat 450,000 cal of grass in one year, since each grass plant contains 100 cal, the deer will require 4500

grass plants to survive). Since one wolf will consume 5 deer, multiply 4500 grass plants by 5 to get the value in the last column (22,500). Add up the numbers in the last column and you will see that it takes 45,750 plants to the five deer needed 1 wolf for one year. Doing the same calculations for elk and rabbits will yield the total number of organisms required to feed a single wolf indirectly through all of its prey species, at all trophic levels (again, for one year).

Name: Bailee Seegmiller

YELLOWSTONE FOOD WEB WORK SHEET Top predator: grizzly bear by this predator/year:

Prey Species White pine (seeds) Miller moths

Calories needed 3,000,000

AMOUNT OF BIOMASS DIRECTLY REQUIRED # cal needed % of bear’s # prey individuals from diet needed 60 1,800,000 1,800,000 pre 20

600,000

1,200,000

Elk

10

300,000

5

Trout

10

300,000

200

AMOUNT OF BIOMASS INDIRECTLY REQUIRED Biomass needed to 1,200,000 miller moths Calories required/moth/year: 5,000 Prey Species % of moth’s #cal #prey/mot total #prey 4,500 54,000,000 diet 90 needed/moth h 45 needed Grass plants Sunflower plants

10

Biomass need to 5 4,000,000 Prey Species % of elk’s diet 80 Grass plants

500

elk

2.5

3,000,000

Calories required/elk/year:

#cal 3,200,000 needed/elk

#prey/elk total #prey 32,000 160,000 needed

Bitterbrush

10

400,000

1,600

8,000

Huckleberry

10

400,000

2,000

10,000

Biomass needed to 200 trout Calories required/trout/year: 18,000 Prey Species % of trout’s #cal #prey/tro total #prey 100 18,000 720,000 diet needed/trout ut 3,600 needed Stonefly Biomass needed to 720,000 required/fy/year: 3,000

stonefies

Calories

Prey Species Algae

% of stonefy’s diet 100

#cal 3,000 needed/fy

#prey/fy 240

total #prey 43,200,000,000 needed

YELLOWSTONE FOOD WEB WORK SHEET Using the numbers calculated on the preceeding page, total the number of organisms at each trophic level needed to one grizzly bear in Yellowstone for one year. Producers 43,258,980,000

Herbivores 1,920,005

Carnivores 200

Part 3 – Looking at the Sustainability of Grizzly Bears in Yellowstone The Yellowstone grizzly bear population crashed in the 1970s, when the park’s open garbage dumps were closed, forcing the bears to revert to a more natural diet. At its lowest, the population was estimated at about 200 bears. Since that time the grizzly population has grown steadily to about 600 bears. Indications are that the current population may be at the carrying capacity of the park. If the carrying capacity for grizzlies is 600 individuals, calculate the total number of organisms at each trophic level needed to the current grizzly population. Producers 25,955,390,000,000

Herbivores 1,152,003,000

Carnivores 120,000

Although the grizzly bear population in Yellowstone seems to be stable, there is much concern for its future. Three of the four primary food sources for grizzlies are seriously threatened: miller moths (from pesticide use & habitat loss), cutthroat trout (from introduced disease and non-native trout species), and whitebark pine (from white pine blister rust, an introduced disease). If these food sources were to disappear, grizzly bears would have to rely more heavily on the park’s elk herd, which is estimated to be about 6,000, although this number flucuates. If grizzlies fed only on elk, how many elk would be needed to feed all 600 bears in Yellowstone for one year? Would the bear population then be sustainable?

There would need to be 50 elk for one bear to eat in a year. All 600 bears would need 30,000 elk in one year. There would not be enough elk to sustain the population.