There is a lot of negative talk these days about human planted non-native species. Burmese pythons that were once household pets are wiping out the small animal population in parts of Florida in part because they have no predators to control their population. The tamarisk bush is decimating the native cottonwood and willow populations of the Southwest U.S. by adding alkalinity to the soils. In the Northeast and other parts of the U.S., purple loosestrife, a pretty flower that holds together river banks, is taking the place of cattails – a popular bird food and habitat. The list goes on and on.
With all these stories of humans inadvertently wreaking havoc on the natural environment, how about a story of hope? Once in a while, a non-native species can actually have a positive effect on the environment. Read on for a success story right here in Southwest Colorado.
Lodgepole pines are native in Colorado and are mostly found on the Front Range in areas such as Rocky Mountain National Park and Summit County. (Lodgepoles are a type of pine widely decimated by pine beetles.) However, lodgepole pines are not native to Southwest Colorado. There is a large area of these pines between Coal Bank and Molas passes along US highway 550and the story about how they got there is interesting.
Back in 1879, there was a major forest fire in that area. It was named the Lime Creek burn because of its vicinity to Lime Creek. It was assumed that the area would regenerate naturally as do many forests after a fire. It did not. To this day, burned out stumps from this fire can be seen along the Colorado Trail heading west from Little Molas Lake. Some stand like sentinels in the high open meadows along the trail.
In the early 1900’s there was some concern about the lack of regrowth. Many trees were replanted including lodgepole pines. Some thought that the non-native pines would give way to native subalpine fur and Engelmann spruce, but that never happened. The pines thrived and multiplied.
Fortunately, lodgepole pines do not have some of the mechanisms to take over other plants the way tamarisk or purple loosestrife do. In fact these lodgepole pines have helped an animal on the U.S. Fish and Wildlife Service’s threatened species list – the Canada lynx.
Canada Lynx are wild cats that thrive in the snow. Their range covers much of Alaska and Canada as well as parts of the Northern U.S. Lynx can often be confused with bobcats although there are subtle differences. Lynx are usually larger than bobcats and are not as spotted. Their tails generally have a solid black tip and their ear tufts can be as large as the ears themselves. Lynx have large feet that act as snowshoes and are specially adapted to keep them somewhat on top of the snow. The favorite food of the lynx is the snowshoe hare although it will also eat carrion, ground-dwelling birds such as grouse and ptarmigan, and small mammals like mice and voles. A lynx can spot a mouse 250 feet away!
The lynx, much like other beautifully furred mammals of Colorado, were hunted nearly to extinction in the state. It is thought that the lynx may have disappeared from Colorado around 1973 mostly due to being trapped for their fur as well as habitat destruction. However, in 1999 a reintroduction program started to get a population going in the San Juan Mountains. By 2005, 200 lynx had been released, and kittens were even being born! It is only through reintroduction, careful monitoring and a chance lodgepole pine replanting that lynx are beginning to thrive again in Southwest Colorado.
Snowshoe Hares – the Links to Survival
At this point you may be wondering what the connection is between lynx and lodgepole pines. The links (no pun intended) are snowshoe hares.
Snowshoe hares are a major food source for the lynx. Lynx will eat other small mammals, but the hares are preferred. Interestingly, lynx populations are so dependent on snowshoe hares that when the hare population decreases, so does the lynx’s. This cycle occurs about every 10 years. The evidence is astounding for this relationship.
Snowshoe hares love to feed on lodgepole pine needles in the winter. They prefer this food source over other available conifers. There are a number of statements to support the snowshoe hare’s love of lodgepole pines as a food source in a report published by the US Forest Service. (Click here: http://www.fs.fed.us/database/feis/animals/mammal/leam/all.html ) Mainly,” Winter snowshoe hare pellet counts were highest in 20-year-old lodgepole pine stands, lower in older lodgepole stands, and lowest in spruce-dominated stands” and “In British Columbia overstocked juvenile lodgepole pine (Pinus contorta) stands formed optimal snowshoe hare habitat”.
So, back in the aftermath of the Lime Creek Burn, who would have ever suspected this result? Lynx were not even endangered at the time of the replanting. Also, it was expected that the lodgepole pines would be taken over by the other trees. It was really just a happy accident. In winter 2012, retired National Park Service employee Steve Chaney, photographed two lynx from the window of his car on Molas Pass in the San Juan National Forest. So, be on the lookout for these fine and resilient felines the next time you are driving, hiking, or otherwise recreating in the Coal Bank and Molas Pass area. If nothing else, you may see a snowshoe hare!
Field and Classroom Activities
Field Trip: Visit the Lime Creek Burn Area:
Get the kids outside to see the lodgepole pines in the Lime Creek Burn Area.
– The Coal Creek Trail ascends through the lodgepole pines. Although it is a generally steep trail, the lower portion is not too bad.
– An informational sign about the fire is located along the east side of the highway.
– Be on the lookout for lynx and snowshoe hare!
Outdoor Activity: Oh Deer!
Taken From: http://www.projectwild.org/documents/ohdeer.pdf)
Grade Level: 5–8
Subject Areas: Science, Environmental Education, Mathematics, Expressive Arts
Duration: one 30- to 45-minute session
Group Size: 15 and larger recommended
Setting: indoors or outdoors; large area for running needed
Key Terms: habitat, limiting factors, predator, prey, population, balance of nature, ecosystem
Objectives: Students will (1) identify and describe food, water, and shelter as three essential components of habitat; (2) describe factors that influence carrying capacity; (3) define “limiting factors” and give examples; and (4) recognize that some fluctuations in wildlife populations are natural as ecological systems undergo constant change.
Method: Students portray deer and habitat components in a physical activity.
Materials: An area—either indoors or outdoors—large enough for students to run (e.g., playing field), chalkboard or flip chart, writing materials
Carrying capacity refers to the dynamic balance between the availability of habitat components and the number of animals the habitat can support. A variety of factors related to carrying capacity affect the ability of wildlife species to successfully reproduce and to maintain their populations over time. The most fundamental of life’s necessities for any animal are food, water, shelter, and space in a suitable arrangement. Without these essential components, animals cannot survive.
However, some naturally caused and culturally induced limiting factors serve to prevent wildlife populations from reproducing in numbers greater than their habitat can support. Disease, predator and prey relationships, varying impacts of weather conditions from season to season
(e.g., early freezing, heavy snows, flooding, drought), accidents, environmental pollution, and habitat destruction and degradation are among these factors. An excess of such limiting factors leads to threatening, endangering, and eliminating whole species of animals.
This activity illustrates that:
• good habitat is the key to wildlife survival,
- a population will continue to increase in size until some limiting factors are imposed,
- limiting factors contribute to fluctuations in wildlife populations, and
- nature is never in “balance,” but is constantly is changing. Wildlife populations are not static. They continuously fluctuate in response to a variety of stimulating and limiting factors. We tend to speak of limiting factors as applying to a single species, although one factor may affect many species. Carrying capacity limitations can result in competition among domestic animals, wildlife, and humans. Natural limiting factors, or those modeled after factors in natural systems, tend to maintain populations of species at levels within predictable ranges. This kind of “balance in nature” is not static but is more like a teeter-totter than a balance. Some species fluctuate or cycle annually. Quail, for example, may start with a population of 100 pairs in early spring, grow to a population of 1,200 birds by late spring, and decline
slowly to a winter population of 100 pairs again. This cycle appears to be almost totally controlled by the habitat components of food, water, shelter, and space, which are also limiting factors. Habitat components are the most fundamental and the most critical of limiting factors in most natural settings. This activity is a simple but powerful way for students to grasp some basic concepts: first, that everything in natural systems is interrelated; second, that populations of organisms are continuously affected by elements of their environment; and third that populations of animals are continually changing in a process of maintaining dynamic equilibrium in natural systems.
- Tell students they will be participating in an activity that emphasizes the most essential things animals need in order to survive. Review the essential components of habitat with the students: food, water, shelter, and space in a suitable arrangement. This activity emphasizes three of those habitat components—food, water, and shelter—but the students should not forget the importance of the animals having sufficient space in which to live, and that all the components must be in a suitable arrangement for wildlife populations to reach their maximum size.
- Ask the students to count off in fours. Have all the ones go to one area; all twos, threes, and fours go together to another area. Mark two parallel lines on the ground or floor 10 to 20 yards apart. Have the ones line up behind one line; the rest of the students line up behind the other line, facing the ones.
- The ones become “deer.” All deer need good habitat to survive. Again ask the students what the essential components of habitat are
(food, water, shelter and space in a suitable arrangement). For this activity, assume that the deer have enough space in which to live.
The deer (the ones) need to find food, water, and shelter to survive. When a deer is looking for food, it should clamp its “hooves” over its
stomach. When it is looking for water, it puts its “hooves” over its mouth. When it is looking for shelter, it holds its “hooves” together over its head. A deer can choose to look for any one of its needs during each around or segment of the activity;
the deer cannot, however, change what it is looking for (e.g., when it sees what is available during that round). It can change what it is looking for in the next round,
if it survives.
- The twos, threes, and fours are food, water, and shelter—components of habitat.
Each student is allowed to choose at the beginning of each round which component he or she will be during that round. The students depict which component they are in the same way the deer show what they are looking for (i.e., hands on stomach for food, and so on).
- The activity starts with all players lined up behind their respective lines (deer on one side, habitat components on the other side)—and with their backs facing the students along the other line.
6. Begin the first round by asking all of the students to make their signs—each deer
deciding what it is looking for, each habitat component deciding what it is. Give the students a few moments to put their hands in place—over stomachs, over mouths, or over their heads. (The two lines of students normally will display a lot of variety—with some students portraying water, some food, and some shelter. As the activity proceeds, sometimes the students confer with each other and all make the same sign. That’s okay.
- When the students are ready, say, “Oh Deer!” Each deer and each habitat component turn to face the opposite group, continuing to hold their signs clearly.
- When deer see the habitat component they need, they should run to it. Each deer must hold the sign of what it is looking for until getting to the habitat component student with the same sign. Each deer that reaches its necessary habitat component takes the “food,” “water,” or “shelter” back to the deer
side of the line. “Capturing” a component represents the deer successfully meeting
its needs and successfully reproducing as a result. Any deer that fails to find its food, water, or shelter dies and becomes part of the habitat. That is, any deer that died will be a habitat component in the next round and so is available as food, water, or shelter to the deer that are still alive. NOTE: When more than one deer reaches a habitat component, the student who arrives there first survives. Habitat components stay in place until a deer chooses them. If no deer needs a particular habitat component during a round, the habitat component just stays where it is in the habitat. The habitat component can, however, change which component it is from round to round.
- Record the number of deer at the beginning of the activity and at the end of each round. Continue the activity for approximately 15 rounds. 10. At the end of the 15 rounds, bring the students together to discuss the activity.
Encourage them to talk about what they experienced and saw. For example, they saw a small herd of deer (7 students in a class size of 28) begin by finding more than enough of its habitat needs. However, because the population of deer expanded over two to three rounds of the activity until it exceeded the carrying capacity of the habitat, there was not sufficient food, water, and shelter for all
members of the herd. At that point, deer starved or died of thirst or lack of shelter,
and they returned as part of the habitat. Such things happen in nature also. NOTE: In real life, large mammal populations might also experience higher infant mortality and lower reproductive rates.
11.Using a flip chart pad or chalkboard, post the data recorded during the activity. The number of deer at the beginning of the activity and at the end of each round represents the number of deer in a series of years. That is, the beginning of the activity is year one; each round is an additional year. Deer can be posted by fives for convenience. For example, the students will see this visual reminder of what they experienced during the activity: the deer population fluctuated over a period
of years. This process is natural as long as the factors that limit the population do not become excessive to the point where the animals cannot successfully reproduce. The wildlife populations will tend to peak, decline, and rebuild; peak, decline, and rebuild—as long as there is good habitat and sufficient numbers of animals to reproduce successfully, although do not encourage it. For example, all the students in habitat might decide to be shelter. That could represent a drought year with no available food or water.) NOTE: Switching symbols in the middle of
a round can be avoided by having stacks of three different tokens—or pieces of colored paper—to represent food, water, and shelter at both the habitat and deer ends of the field. At the start of each round, players choose one of the symbols before turning around to face the other group.
12.What is realistic and unrealistic about this simulation? (Deer that do not survive
Do become recycled as nutrients but it is not instantaneous. Deer need all habitat components to survive. Poor habitat usually results in a weakened individual that succumbs to disease, not instant death.)
- In discussion, ask the students to summarize some of the things they learned from this activity. What do animals need to survive? How do these components influence carrying capacity? What are some “limiting factors” that affect the survival of animals? How do factors that limit carrying capacity affect the health, numbers, and distribution of animals? How do these factors affect competition within a species? Why is good habitat important for animals? Are wildlife populations static
, or do they tend to fluctuate as part of an overall “balance” of nature? Is nature ever really in “balance” or are ecological systems involved in a process of constant change?
Indoor Activity: Predator-Prey Models: Canadian Lynx and Snowshoe Hares
(Taken from https://www.math.duke.edu//education/ccp/materials/diffeq/predprey/pred1.html)
In the study of the dynamics of a single population, we typically take into consideration such factors as the “natural” growth rate and the “carrying capacity” of the environment. Mathematical ecology requires the study of populations that interact, thereby affecting each other’s growth rates. In this module we study a very special case of such an interaction, in which there are exactly two species, one of which — the predators — eats the other — the prey. Such pairs exist throughout nature:
- lions and gazelles,
- birds and insects,
- pandas and eucalyptus trees,
- Venus fly traps and flies.
To keep our model simple, we will make some assumptions that would be unrealistic in most of these predator-prey situations. Specifically, we will assume that
- the predator species is totally dependent on a single prey species as its only food supply,
- the prey species has an unlimited food supply, and
- there is no threat to the prey other than the specific predator.
Very few such “pure” predator-prey interactions have been observed in nature, but there is a classical set of data on a pair of interacting populations that come close: the Canadian lynx and snowshoe hare pelt-trading records of the Hudson Bay Company over almost a century. The following figure (adapted from Odum, Fundamentals of Ecology, Saunders, 1953) shows a plot of that data.
To a first approximation, there was apparently nothing keeping the hare population in check other than predation by lynx, and the lynx depended entirely on hares for food. To be sure, trapping for pelts removed large numbers of both species from the populations — otherwise we would have no data — but these numbers were quite small in comparison to the total populations, so trapping was not a significant factor in determining the size of either population. On the other hand, it is reasonable to assume that the success of trapping each species was roughly proportional to the numbers of that species in the wild at any given time. Thus, the Hudson Bay data give us a reasonable picture of predator-prey interaction over an extended period of time. The dominant feature of this picture is the oscillating behavior of both populations.
- On average, what was the period of oscillation of the lynx population?
- On average, what was the period of oscillation of the hare population?
- On average, do the peaks of the predator population match or slightly precede or slightly lag those of the prey population? If they don’t match, by how much do they differ? (Measure the difference, if any, as a fraction of the average period.)
To be candid, things are never as simple in nature as we would like to assume in our models. In areas of Canada where lynx died out completely, there is evidence that the snowshoe hare population continued to oscillate — which suggests that lynx were not the only effective predator for hares. However, we will ignore that in our subsequent development.