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Learn about host/parasite interactions and dwarf mistletoe (Arceuthobium) through this lesson. 

Get this lesson: You can download the full packet here or read a condensed version of this unit below.

Worksheet: Download just the worksheet or there’s a copy included in the packet.

Overview: 

Host/Parasite interactions: In evolutionary ecology, a parasite is an organism, plant, or fungus that lives in or on another organism, called the host. Without a host, a parasite cannot live, grow, or multiply, so it does not usually kill its host. Both parasite and host evolve together, in a relationship where the parasite benefits from the host, harming it in some way. Some hosts develop ways of getting rid of or protecting themselves from parasites, while others live with the relationship for some time.

Dwarf Mistletoe is a small, leafless parasitic plant which parasitizes native ponderosa and lodgepole pines by slowly robbing them of food and water. They will generally focus their life cycle on one species of pine tree. Dwarf mistletoe has very little chlorophyll so they must put roots into the host tree to extract nutrients. Often at the anchor site this parasitic species will secrete hormones to produce a structure called a “witches broom” which is an overgrowth and will disrupt the branching structure. Dwarf mistletoe can stunt tree growth, reduce seed production and wood quality, and occasionally kill the host tree in times of drought or forest stress.

 

Dwarf mistletoe also has a well studied connection to fire events. As early as the 1970s it was evident that fire suppression was a primary driver of increased dwarf mistletoe abundance in North American forests. A denser forest will aide the reproduction success of this parasite. The resulting witches brooms can act as fire ladders.

Some benefits of this parasite are that squirrels and blue grouse like to eat the mistletoe and infected branches, and witches’ brooms can serve as ideal nesting platforms for birds and small mammals.  

Video resources:

Dwarf mistletoe overview – Visuals and an explanation of what dwarf mistletoe is, plus a comparison between that and the “holiday” version of this plant. 

Dwarf mistletoe music video –  A fun, approachable music video made by students about the seed “explosion” process.

Mistletoe/tree interactions – A concise description with footage of actual infected lodgepole pines discussing the impacts of mistletoe growth. 

Sample Research Project:

Description: students analyze forests near their home for signs of dwarf mistletoe interaction.

Methods:  Students look for signs of parasitism in their local forests within a study area measured with a transect. Students track findings in multiple areas to get an average. If known beetle damage is present, students can also observe localized areas within a single tree using a quadrat.

• Making a transect video
• Creating a quadrat video

Sample Research Questions: 

• Is there more mistletoe on trees at a lower or higher elevation?
• Is mistletoe the same size or different sizes on each tree? How might this correlate?
• Do trees that are closer together have more mistletoe?
• Do larger or smaller trees have more mistletoe?
• Which part of the tree has the most infection?

NGSS Standards:

MS-LS2-2; MS-LS2-3; MS-LS2-4 Ecosystems: Interactions, Energy, and Dynamics

HS-LS2-3; HS-LS2-6; HS-LS2-8 Ecosystems: Interactions, Energy, and Dynamics

SEPs:

• Analyzing and interpreting data
• Constructing Explanations and designing solutions
• Scientific knowledge based on empirical evidence
• Planning and carrying out investigations

CC:

• Stability and change
• Patterns
• Cause and effect

Get The Lesson

Learn about the Mountain Pine Bark Beetle (Dendroctonus ponderosae) through this lesson. 

Get this lesson: You can download the full packet here or read a condensed version of this unit below.

Worksheet: Download just the worksheet or there’s a copy included in the packet.

Overview: 

The Mountain Pine Bark Beetle (Dendroctonus ponderosae) is a species of bark beetle native to forests in North America. It is the size of a grain of rice and has a hard black exoskeleton. This beetle inhabits Ponderosa, Whitebark, and Lodgepole Pines, normally playing an important role in the life of a forest, but unusually hot, dry summers and mild winters in the mountains have led to an unprecedented epidemic of this insect.  Coupled with a century of fire suppression and monoculture replanting, the infestation may have significant effects on the capability of the forests to thrive and  remove greenhouse gases from the atmosphere.

 

Female beetles initiate attacks. As they chew into the inner bark and phloem, pheromones are released, attracting male and female beetles to the same tree. They chew through the bark until they reach the phloem, a cushy resinous layer between the outer bark and the sapwood that carries sugars through the tree. There, they lay their eggs in tunnels, and eventually a new generation of beetles hatches, grows up, and flies away. But before they do, the mature beetles also spread a special fungus in the center of the trunk. The fungi leave blue-gray streaks in the trees they kill. A healthy tree can usually beat back invading beetles by deploying chemical defenses and flooding them out with sticky resin. But just as dehydration makes humans weaker, heat and drought impede a tree’s ability to fight back—less water means less resin.

Video resources:

Tiny Beetle Outbreak – University of Montana Professor Diana Six summarizing beetle problem and how to approach it.
What is The Mountain Pine Beetle? – A basic overview of the beetle infestation.

Sample Research Project:

Description: students analyze forests near their home for signs of bark beetle infestation 

Methods: Students look for signs of beetles Using this guide and measuring a study area with a transect. Students track findings in multiple areas to get an average. If known beetle damage is present, students can also observe smaller areas of dead or dying trees using a quadrat.

• Making a transect video
• Creating a quadrat video

Sample Research Questions: 

• Are there more signs of beetle destruction in a certain area?
• What signs of beetle destruction are most common?
• Do trees that are closer together have more beetle destruction?
• Do larger or smaller trees have more beetle destruction?

NGSS Standards:

MS-LS2-1; MS-LS2-2; MS-LS2-4 Ecosystems: Interactions, Energy, and Dynamics

HS-LS2-1; HS-LS2-2; HS-LS2-6; HS-LS2-8 Ecosystems: Interactions, Energy, and Dynamics

SEPs:

• Analyzing and interpreting data
• Constructing Explanations and designing solutions
• Scientific knowledge based on empirical evidence
• Planning and carrying out investigations

CC:

• Stability and change
• Patterns
• Cause and effect

Get The Lesson

Learn about the ecosystems of the Sierra Nevada through this lesson.

Get this lesson: You can download the full packet here or read a condensed version of this unit below.

Worksheet: Download just the worksheet or there’s a copy included in the packet.

Overview: 

An ecosystem is a biological community of interacting organisms and their physical environment.  Scientists have classified 8 major ecosystems on Earth called Biomes, which encompass smaller ecosystems. The Sierra Nevada mountains are within the temperate coniferous forest biome.

The Sierra Nevada also includes different vegetation zones, from montane forests to subalpine and alpine zones all determined by elevation. Ecosystems are dynamic and continually changing through time.

 

The Sierra Nevada ecoregion harbors one of the most diverse temperate conifer forests on Earth displaying an extraordinary range of habitat types and supporting many unusual species. Fifty percent of California’s estimated 7,000 species of vascular plants occur in the Sierra Nevada, with 400 Sierra endemics and 200 rare species.  

Ecosystems are dependent on a balance of producers and consumers. The producers are at the base of the energy cycle using photosynthesis and chemosynthesis to make their own food, omnivores and carnivores follow. Decomposers finish the cycle. At each level only 10% of energy is passed on, the other 90% is lost as heat.   

Video resources:

The Cost of Ecosystem Change: The Sierra Nevada Bighorn Sheep – A talk with field biologists studying declining Bighorn Sheep populations

High Elevation Forest Monitoring in the Sierra Nevada – A discussion on forest health and efforts to preserve it by the National Park Service

Sample Research Project:

Project: Sierra Nevada food web activity

Methods: Examine the interactions between animal and plant species in the Sierra Nevada by charting their interactions with one another and labeling them producer, consumer, scavenger, or decomposer.

Sample research questions: 

• What happens to the population of one species as another declines?
• Can consumers live without decomposers?
• What happens to the population of scavengers as consumers decline?

NGSS Standards:

MS-LS2-3; MS-LS2-4 Ecosystems: Interactions, Energy, and Dynamics

HS-LS2-6; HSLS2-7; HS-LS2-8 Ecosystems: Interactions, Energy, and Dynamics

SEPs: Analyzing and interpreting data
Constructing Explanations and designing solutions
Planning and carrying out investigations
Obtaining, evaluating, and communicating information
Systems and system models

CC: Cause and effect
Stability and change
Patterns