Mowing for monarchs, Part II

In Part I you explored data that showed monarchs prefer to lay their eggs on young milkweeds that have been mowed, compared to older milkweed plants. But, is milkweed age the only factor that was changed when Britney and Gabe mowed patches of milkweeds? You will now examine whether mowing also affected the presence of monarch predators.

A scientist measuring a milkweed plant.
A scientist, Lizz D’Auria, counting the number of monarch predators on milkweed plants in the experiment.

The activities are as follows:

The bright orange color of monarch butterflies signals to their enemies that they are poisonous. This is a warning that they do not make a tasty meal. Predators, like birds and spiders, that try to eat monarch butterflies usually become sick. Many people think that monarch butterflies have no enemies because they are poisonous. But, in fact they do have a lot of predators, especially when they are young.

Monarchs become poisonous from the food they eat. Adult monarchs lay their eggs on milkweed plants, which have poisonous sap. When the eggs hatch, the caterpillars chomp on the leaves. Young caterpillars are less poisonous because they haven’t eaten much milkweed yet. And monarch eggs are not poisonous at all to predators.

Britney and Gabe met with their friends, Doug and Nate, who are scientists. Doug and Nate thought that Britney and Gabe’s experiment might have changed more than just the age of the milkweed plants in the patches they mowed. By mowing their field sites they were also cutting down the plants in the rest of the community. These plants provide habitat for predators, so mowing all of the plants would affect the predators as well. These ideas led to another potential explanation for the results Britney and Gabe saw in their data. Because all plants were cut in the mowed patches, there was nowhere for monarch predators to hang out. Britney and Gabe came up with an alternative hypothesis that perhaps monarch butterflies were choosing to lay their eggs on young milkweed plants because there were fewer predators nearby. To test this new idea, Britney and Gabe went back to their experimental site and started collecting data on the presence of predators in addition to egg number. Remember that in each location, they had a control patch, which was left alone, and a treatment patch that they mowed. The control patches had older milkweed plants and a full set of plants in the community. The mowed patches had young milkweed plants with short, chopped plants nearby. For the whole summer, they went out weekly to all of the patches. They counted the number of predators found on the milkweed plants so they could compare the mowed and unmowed patches.

Predators of monarch butterflies.
There are many different species that eat monarch butterfly eggs and young caterpillars. These are just a few of the species that Gabe and Britney observed during their experiment.

Featured scientists: Doug Landis and Nate Haan from Michigan State University and Britney Christensen and Gabe Knowles from Kellogg Biological Station LTER.

Flesch–Kincaid Reading Grade Level = 8.2

Additional resources related to this Data Nugget:

Ant wars!

Three pavement ants touch antennae to determine if they are nestmates. Photo courtesy Michael Greene.

The activities are as follows:

The ants crawling into and out of cracks along sidewalks are called pavement ants. They live in groups called colonies, which are made up of a few queens and many worker ants. A colony lives together inside a nest, a physical structure. Worker ants use their antennae to touch the bodies of other ants. Certain chemicals tell them if the ant is from their colony or a different colony. Nestmates are ants from the same colony, and non-nestmates are ants from other colonies. 

Neighboring colonies often compete for food, leading to tension. If an ant finds a non-nestmate, it organizes a large war against the nearby colony. This results in huge sidewalk battles that can include thousands of ants fighting for up to 12 hours! These ant wars often involve worker ants grabbing body parts of non-nestmate ants. 

Andrew, Jazmine, John, Mike, and Ken all work together to study the social and chemical cues that drive behaviors in animals. They were curious to learn more about the triggers that lead to colony wars. Worker ants don’t have a leader, so the scientists wanted to know how large wars are organized. The team started by reading lots of research articles and learned that there are several factors that may affect an ant’s decision to fight. These include the odor of other ants they meet, the size of the ant’s colony, and the season. The team also knew from their own experiments that if an ant meets a fellow nestmate before meeting a non-nestmate, it was more likely to fight.

A colony war involving thousands of pavement ants. Photo courtesy Michael Greene.

All of this information helped the team realize that interactions with nestmates were an important part of the decisions that start ant wars with non-nestmakes. To build on this, they wanted to know whether the decision to fight was affected by ant density, which is the number of ants within an area. They thought that at higher densities the ants would be more likely to interact, leading to more fights with non-nestmates. If more wars are observed at higher ant densities, increased interactions with nestmates might be part of the story.

To answer their question, the team collected ants from different colonies in Denver, Colorado for two separate experiments. They brought them back to the lab to set up trials in a plastic tank arena.

Experiment 1: For the first set of behavioral trials, the researchers varied the number of ants in the tank, ranging from 2 to 20 ants. The size of the tank remained constant, and there were always equal numbers of nestmates and non-nestmates. This means the ratio of nestmates to non-nestmates was always 1:1, but the density varied by how many ants were included in the experiment. They performed 18 trials for each density treatment in their experiment.

At the start of every trial, ants from each colony were in separate areas so that they could interact with nestmates first. Earlier work had shown that when ants in each area interact, they touch antennae to another ant’s body. These interactions create a brain state that makes an ant more likely to fight an ant from another colony. Then the scientists removed a barrier revealing the ants from the other colony. They watched the ants for 3 minutes. During that time they recorded the number of ants that were fighting. This way they could compare how likely the ants were to fight at different densities. They predicted there would would be more fighting at higher ant densities.

Experiment 2: The scientists also wanted to measure the effect of density on the interaction rates between just nestmates. This experiment allowed the scientists to understand how the rate of interactions affected levels of neurochemicals in brains, creating the brain state that increased the likelihood that an ant would be aggressive. For these trials, they placed different densities of nestmate ants in a tank. They randomly picked an ant during each trial and counted the number of times it contacted a nestmate ant. Different groups of ants were used in each trial and each experiment. They observed the number of interactions at different densities and expected nestmate ants to have more interactions at higher densities.

Featured scientists: Andrew Bubak, Jazmine Yaeger, John Swallow, and Michael J. Greene from the University of Colorado-Denver; Kenneth Renner from the University of South Dakota. Written by: Gabrielle Welsh

Flesch–Kincaid Reading Grade Level = 9.0

Additional teacher resources related to this Data Nugget:

A news article about the research:

David vs. Goliath

Stalk-eyed flies have their eyes at the end of long stalks on the sides of their head. These stalks are used by males when fighting for resources.

The activities are as follows:

Animals in nature often compete for limited resources, like food, territory, and mates. To compete for these resources, they use aggressive behaviors to battle with others of the same species. Aggressive behaviors are meant to overpower and defeat an opponent. The outcome of a battle depends on many different factors. In insects, one important factor is body size. Larger individuals are usually more aggressive and often win more battles. Chemicals in the brain can also influence who wins a fight. One chemical, called serotonin, can cause insects to have more aggressive behaviors. It is found in the brains of all animals, including humans.

Andrew had always been curious about what makes an animal decide to use aggressive behaviors in battle, or when to end one. He worked with researchers Nathan, Michael, Ken, and John to study the role that chemicals in the brain have on behaviors. The team was interested in how brain chemicals, like serotonin, affect aggression. They have been studying an insect species called stalk-eyed flies. These flies have eyes on the ends of long eyestalks that protrude from their heads. Male stalk-eyed flies use these eyestalks when battling each other. In a previous experiment, they found that serotonin can cause these flies to have more aggressive behaviors. They also knew that flies with shorter eyestalks usually lose fights to larger flies. 

This made them curious about whether extra serotonin could make flies with shorter eyestalks act more aggressive and help them win fights against flies with longer eyestalks. The team of researchers discussed what they knew from past research and predicted that if they gave serotonin to short eyestalk flies, it might help them win fights against long eyestalk flies. They thought this made sense because they already knew that serotonin make flies more aggressive, and more aggressive behaviors could help the shorter flies win more fights. 

The fighting arena where stalk-eyed flies battle. The camera is set up to help the scientists observe both the high intensity behaviors and retreats.

The team designed a lab study to look into this question about the importance of eyestalk length and serotonin for battles in stalk-eyed flies. First, the researchers raised male stalk-eyed flies in the lab. They made sure the flies were around the same age and were raised in a similar lab environment from the time they were born. Then, they measured the eyestalk length for each fly and divided them into two groups. One group had flies with longer eyestalks (Goliaths) and one group had flies with shorter eyestalks (Davids). They took the group of Davids with shorter eyestalks and fed half of them food with a dose of serotonin. This became the treatment group. They fed the other half of the Davids group food, but without serotonin. This was the control group. The treatment group and control group each had 20 flies.

To prepare the flies for battle, all flies were all starved for 12 hours before the competition to increase their motivation to fight over food. The researchers paired each David with a Goliath in a fighting arena. They observed the flies and recorded aggressive behaviors shown by each opponent. The researchers labeled any behavior where the fighting flies touch each other as a “high intensity behavior”. They labeled any behavior where the flies backed away as a “retreat”. Flies that retreated less than their opponent were declared the winners.

Featured scientists: Andrew Bubak, Nathan Rieger, and John Swallow from the University of Colorado, Denver; Michael Watt and Kenneth Renner from the University of South Dakota. Written by: Gabrielle Welsh.

Flesch–Kincaid Reading Grade Level = 9.3

Mowing for monarchs, Part I

A monarch caterpillar on a milkweed leaf.
A monarch caterpillar on a milkweed leaf.

With their orange wings outlined with black lines and white dots, monarch butterflies are one of the most recognizable insects in North America. They are known for their seasonal migration when millions of monarch butterflies migrate from the United States and Canada south to Mexico in the fall. Then, in the spring the monarch butterflies migrate back north. Monarch butterflies are pollinators, which means they get their food from the pollen and nectar of flowering plants that they visit. The milkweed plant is one of the most important flowering plants that monarch butterflies depend on.

During the spring and summer months female butterflies will lay their eggs on milkweed plants. Milkweed plays an important role in the monarch butterfly’s life cycle. It is the only plant that monarchs will lay their eggs on. Caterpillars hatch from the butterfly eggs and eat the leaves of the milkweed plant. The milkweed is the only food that monarch caterpillars will eat until they become butterflies.

A problem facing many pollinators, including monarch butterflies, is that their numbers have been going down for several years. Scientists are concerned that we will lose pollinators to extinction if we don’t find solutions to this problem. Doug and Nate are scientists at Michigan State University trying to figure out ways to increase the number of monarch butterflies. They think that they found something that might work. Doug and Nate have learned that if you cut old milkweed plants at certain times of the year, then younger milkweed plants will quickly grow in their place. These new milkweed plants are softer and more tender than the old plants. It appears that monarch butterflies prefer to lay their eggs on the younger plants. It also seems that the monarch caterpillars prefer to eat the younger plants.

Britney and Gabe are two elementary teachers interested in monarch butterfly conservation. They learned about Doug and Nate’s research and wanted to participate in their experiment. The team of four met and designed an experiment that Britney and Gabe could do in open meadows throughout their community.

Britney and Gabe chose ten locations for their experiment. In each location they set aside a milkweed patch that was left alone, which they called the control.  At the same location they set aside another milkweed patch where they mowed the milkweed plants down. After a while, milkweed plants would grow back in the mowed patches. This means they had control patches with old milkweed plants, and treatment patches with young milkweed plants. Gabe and Britney made weekly observations of all the milkweed patches at each location. They recorded the number of monarch eggs in each of the patches. By the end of the summer, they had made 1,693 observations!

Featured scientists: Doug Landis and Nate Haan from Michigan State University and Britney Christensen and Gabe Knowles from Kellogg Biological Station LTER.

Flesch–Kincaid Reading Grade Level = 8.2

Additional resources related to this Data Nugget:

Round goby, skinny goby

An invasive round goby from the Kalamazoo River, Michigan.
An invasive round goby from the Kalamazoo River, Michigan.

The activities are as follows:

Animals often have adaptations, or traits that help them live in certain environments. For fish, that can mean having a body shape that allows them to feed on available prey, better hide from predators, or swim more effortlessly. When these traits vary within the same species from one location to another, they are called local adaptations. Such adaptations were once thought to only evolve slowly over hundreds or thousands of generations. However, new evidence shows that evolution can result in meaningful adaptations much more quickly than originally thought, sometimes in just a few generations!

Invasive species are those that have been moved by humans to areas where they do not usually exist and cause disruptions to native ecosystems. Because they have been moved to new places where they did not evolve, invasive species often have traits that aren’t matched to their new habitats. When mismatches occur, species may be able to adapt in just a few generations in their new locations.

Several invasive species have been problematic in the Great Lakes of North America. The round goby is a small invasive fish species that arrived in the Great Lakes around 1990. It is a bottom-dwelling species that is able to quickly reproduce and crowd out native fish species. Both avid anglers, Jared and Bailey observed the increasing numbers of round gobies during their time spent outdoors. They noticed that sometimes round gobies would even outnumber all other native fish in an area.

Originally appearing just in the Great Lakes themselves, the species is increasingly being found in rivers throughout the region. Jared and Bailey were surprised this species did so well in both river and large lake habitats since they are very different environments for fish to live. For example, water is constantly flowing downstream in rivers, whereas lakes can be still or have waves near the shore. Also, these two habitats have different predator and prey species living in them and differ in water chemistry characteristics. With the spread of more and more round gobies into rivers, Jared and Bailey set out to learn how this species is successful in both habitats. They thought that round gobies found in rivers would have adaptations to help navigate fast flowing waters. Fish with narrower body shapes can move more easily in flowing waters, giving narrow-bodied individuals an advantage over those with bulkier bodies. Over time, those individuals with such an advantage would be more likely to survive and reproduce in the rivers, eventually shifting the entire river-dwelling population to a narrow body shape. They predicted that round gobies from rivers would have shorter body depths and narrower caudal peduncles, which is the area between the fish’s body and tail. To test their idea, Jared and Bailey captured and measured hundreds of round gobies from both Great Lakes and inland river habitats.

Michigan State University researcher Bailey Lorencen fishing for gobies in a Michigan river.
Michigan State University researcher Bailey Lorencen fishing for gobies in a Michigan river.

Featured scientists: Jared Homola (he/him) and Bailey Lorencen (she/her) from Michigan State University

Flesch–Kincaid Reading Grade Level = 11.2

Trees and bushes, home sweet home for warblers

Matt, Sarah, and Hankyu – a team of scientists at Andrews Forest, measuring bird populations.

The activities are as follows:

The birds at a beach are very different from those in the forest. This is because each bird species has their own set of needs that allows them to thrive where they live. Habitats must have the right collection of food to eat, places to shelter and raise young, safety from predators, and the right environmental conditions like temperature and moisture. 

The vast coniferous forests of the Pacific Northwest provide rich and diverse habitat types for birds. These forests are also a large source of timber, meaning they are economically valuable for people. Disturbances from logging and natural events result in a forest that has many different habitat types for birds to choose from. In general, areas of forest that have been harvested more recently will have more understory, such as shrubs and short trees. Old-growth forests usually have higher plant diversity and larger trees. They are also more likely to have downed trees or standing dead trees, which are important for some bird species. Other disturbances like wildfire, wind, large snow events, and forest disease also have large impacts on bird habitat.

At the Andrews Forest Long-Term Ecological Research site in the Cascade Mountains of Oregon, scientists have spent decades studying how the plants, animals, land use, and climate are all connected. In the past, Andrews Forest had experiments manipulating timber harvesting and forest re-growth. This land use history has large impacts on the habitats found in an area. Many teams of scientists work in this forest, each with their own area of research. Piece by piece, like assembling a puzzle, they combine their data to try to understand the whole ecosystem. 

Collecting data on a warbler.

Matt, Sarah, and Hankyu have been collecting long-term data on the number, type, and location of birds in Andrews Forest since 2009. Early each morning, starting in May and continuing until late June, teams of trained scientists hike along transects that go through different forest types. Transects are parallel lines along which data are collected. At specific points along the transect, the team would stop and listen for bird songs and calls for 10 minutes. There are 184 survey locations, and they are visited multiple times each year.

At each sampling point, Matt, Sarah, and Hankyu carefully recorded a count for each bird species that they hear within 100 meters. They then averaged these data for each location along the transect to get an average number for the year. The scientists were also interested in the habitats along the transect, which includes the amount of understory plants and tall trees, two forest characteristics that are very important to birds. They measured the percent cover of understory vegetation, which shows how many bushes and small plants were around. They also measured the size of trees in the area, called basal area. 

Using these data, the research team is looking for patterns that will help them identify which habitat conditions are best for different bird species. With a better understanding of where bird species are successful, they can predict how changes in the forest could affect the number and types of birds living in Andrews Forest and nearby.  

Wilson’s Warblers and Hermit Warblers are two of the many songbirds that these scientists have recorded at Andrews Forests. Wilson’s Warblers are small songbirds that make their nests in the understory of the forests. Therefore, the team predicted that they would see more of Wilson’s Warblers in forest areas with more understory than in forest areas with less understory. Hermit Warblers, on the other hand, build nests in dense foliage of tall coniferous trees and search for spiders and insects in those coniferous trees. The team predicted that the Hermit Warblers would be observed more often in forest plots where there are larger trees.  

Featured scientists: Hankyu Kim, Matt Betts, and Sarah Frey from Oregon State University. Written with Eric Beck from Realms Middle School and Kari O’Connell from Oregon State University.

Flesch–Kincaid Reading Grade Level = 10.5

Additional teacher resource related to this Data Nugget:

Spiders under the influence

Field picture of an urban web. Dark paper is used to make the web more visible for data collection

The activities are as follows:

People use pharmaceutical drugs, personal care products, and other chemicals on a daily basis. For example, we take medicine when we are sick to feel better, and use perfumes and cologne to make ourselves smell good. After we use these chemicals, where do they go? Often, they get washed down our drains and end up in local waterways. Even our trash can contain these harmful chemicals. For example, when coffee grounds are thrown into the trash, caffeine gets washed into our waterways.

Animals in waterways, like insects, live with these chemicals every day. Many insects are born and grow in the water, absorbing the drugs over their lifetime. As predators eat the insects, the chemicals are passed on, working their way through the food web. For example, spiders living along riverbanks feed off aquatic insects and absorb the drugs from their prey.

Just as chemicals change human behavior, they change spider behavior as well! Effects of drugs on spiders have been studied since the 1940s. Dr. Peter Witt first discovered that chemicals change spider web construction. Peter gave caffeine, and a few other drugs, to spiders to see if they would build their webs during the day instead of at night, which is when they usually work. After giving his test spiders some of the drugs, the spiders still created their webs at night. However, he noticed something unexpected – the web structure of spiders on drugs was completely different from normal webs. The webs were different sizes and had more spacing between each thread. Normal webs help spiders to easily catch prey. Irregularly shaped webs were not good at catching prey because insects could fly right through the large spaces. After his study, Peter knew that drugs were bad for spiders.

Chris (they/them), a current resident of Baltimore and a spider enthusiast, lives in a watershed that is affected by chemical pollution. They wanted to build on Peter’s research by looking at spider webs in the wild instead of in the lab. Chris knew that many types of spiders live near streams and are exposed to toxins through the prey they eat. Chris wanted to compare the effects of the chemicals on spiders in rural and urban environments. By comparing spider webs in these two habitats, they could see how changed the webs are and infer how many chemicals are in the waterways.

Chris worked with Aaron, a local high school teacher, to do this research. They collected images of spiderwebs in areas around Baltimore. They chose two sites: Baisman Run, a rural site far from the city, and Gwynns Run, an urban site close to the city. Chris traveled to the sites and took pictures of eight spiderwebs at each location. Chris and Aaron expected that urban streams would have higher concentrations of chemicals than rural areas because more people live in cities.

When they got back to the lab, Aaron took the pictures and used a computer program to count the number of cells and calculate the total area of each web. These data offer a glimpse into whether spiders near Baltimore are exposed to harmful pharmaceutical chemicals and personal care products. If spiders are exposed to these chemicals, the webs will have fewer, but larger cells than a normal web. The cells will also have irregular shapes.

Featured scientists: Chris Hawn from University of Maryland Baltimore County and Aaron Curry from Baltimore Ecosystem Study LTER

Flesch–Kincaid Reading Grade Level = 7.8

Additional teacher resources related to this Data Nugget include:

  • You can watch Aaron describe his Research Experience for Teachers project here.

Crunchy or squishy? How El Niño events change zooplankton

Laura identifies and counts zooplankton from a net tow using a microscope. Laura conducted these identifications while on a research ship at sea. 

The activities are as follows:

El Niño events happen every 5 to 10 years and take place in the Pacific Ocean. El Niño occurs when the winds that blow west over the equator temporarily weaken, and even switch direction. This allows warm surface waters that typically pile up on the western side of the Pacific Ocean to flow to the east. In South America, El Niño brings heavy rains and floods because the warm water moves toward that continent. On the other hand, the warm water moves away from the continent of Australia, causing drought. In the U.S., warm waters travel up to California during El Niño years, causing the ocean to be much warmer than usual. El Niño’s effects are so strong that it even changes the marine animals that live off the California coast in those years! 

Laura’s first experience with El Niño came when she was growing up in California. A strong El Niño event hit in 1997-98, and many cities in California flooded because of heavy rainstorms. The event even made the national news on TV! Laura’s second El Niño experience came in 2015, the year she started training to become a scientist. These events had such a big impact on her that she decided to study how zooplankton in the ocean are affected by El Niño. Zooplankton are tiny drifting ocean animals (“zoo” = animal + “plankton” = drifter) that eat phytoplankton (“plant drifters”). Zooplankton are important for the ocean’s food web because they are food for fish, whales, and seabirds. 

Doliolids are a type of gelatinous zooplankton, meaning they have soft, watery bodies and not a lot of nutrition for other animals to eat. They can form large groups in the ocean called ‘blooms’.

Zooplankton come in many shapes, sizes, and species. The two main groups are crustaceans and gelatinous animals. Crustaceans look like small shrimp and crabs, with hard, crunchy shells and segmented legs like insects. In contrast, gelatinous animals are watery and squishy, like jellyfish. Laura wanted to know how El Niño events might affect which group of zooplankton are found off the coast of California. 

Warm ocean waters during El Niño events have lower nutrient levels, so fewer phytoplankton grow leading to less food available for zooplankton. Gelatinous animals can survive in areas of the ocean where there is less food available. They are also able to live in warmer water than crustaceans. For these two reasons, Laura though that gelatinous animals may be able to live in the warmer water off California during El Niño events. Laura predicted that during the El Niño events of 1992-93, 1997-98, and 2015-16, the balance would shift in favor of gelatinous animals over crustaceans

To test her idea, Laura used a long-term dataset that documents zooplankton collected offshore of southern California since 1951. Every spring, a ship goes out on the ocean and tows plankton nets for 30 minutes at 40 different locations. The ship brings back jars full of zooplankton. Scientists look at samples from those jars and identify the species and measure the lengths of each individual zooplankton in the sample. They then add up all the lengths of individual plankton to get the total biomass of each group. Biomass is similar to weight and shows us how big each animal is and how much space their group takes up. Scientists also measure water temperature and how much phytoplankton is found. The amount of phytoplankton is measured by detecting chlorophyll in the water. Chlorophyll from phytoplankton is a measure of how much food is available to zooplankton.

A euphausiid, or “krill”, is a type of crustacean zooplankton, meaning that it is related to shrimp and crabs. It has a hard, segmented shell (exoskeleton). It is the main food source for blue whales and other whales and birds.

Featured scientist: Laura Lilly from Scripps Institution of Oceanography, UC San Diego

Flesch–Kincaid Reading Grade Level = 10.0

Candid camera: Capturing the secret lives of carnivores

Erik demonstrating how to place a camera trap on a tree on Stockton Island.

The activities are as follows:

Carnivores, animals that eat meat, captivate people’s interest for many reasons – they are charismatic, stealthy, and can be dangerous. Not only are they fascinating, they’re also ecologically important. Carnivores help keep prey populations in balance. They often target old, sick, or weak individuals. This results in more resources for healthier prey. Carnivores also impact prey’s behavior and population sizes, which can have further effects down the food web. For example, if there are too many herbivores, such as deer, the plants in an ecosystem may be eaten to a point where they can’t survive. In this way, carnivores help the plant community by either reducing the number of herbivores in an ecosystem, or changing how or where prey forage for food. 

Despite their importance and our interest in carnivores, they are very hard to monitor. Not only do they have naturally low population sizes because they are at the top of the food chain, they also have a natural ability to hide and blend into their environment. Erik is a wildlife biologist who is interested in taking on this challenge. He wants to learn more about carnivores and what factors affect where they live. Learning more about where carnivores are found can help scientists with conservation efforts.

Erik lives on the southern shore of Lake Superior, the largest lake (by area) in the world. This area is home to the Apostle Islands National Lakeshore – including 21 islands and a 12-mile stretch of the mainland in northern Wisconsin. The Apostle Islands vary in many ways – size, distance from the mainland, highest elevation, historical and current human use, plant communities, and even small differences in climate. The islands are so remote that scientists really didn’t know which carnivores lived on the islands. There is evidence from historical reports that red fox and coyotes lived on some of the islands. More recently, black bears have been observed by visitors as they are hiking or camping. Erik wanted to know which species of carnivores are on each island. As he began to explore methods to document wildlife on the islands, Erik and his collaborators were shocked to discover that American martens, Wisconsin’s only state endangered species, live on some of the islands.

Erik thought a promising step in learning more about what drives carnivores to live on different islands in the archipelago would be to apply what has been learned from islands in the ocean. He referred to a fundamental theory in ecology called the theory of island biogeography. This theory predicts that island size and its distance to the mainland affects the biodiversity, or number of species, found on that island. Specifically, larger islands will have higher carnivore biodiversity because there are more resources and space to support more species than smaller areas. In contrast, islands farther away from the mainland will have lower carnivore biodiversity because more isolated islands are harder for wildlife to reach. 

Erik wanted to test whether the theory of island biogeography also applied to the Apostle Islands. Just like the classic research on island biogeography, some islands are closer to the mainland and they range in size. To inventory where each carnivore is found, Erik and his collaborators and students set up 164 wildlife cameras on 19 of the islands. They made their way out to the remote islands by boat and then bushwhacked their way to the sites, which are not along trails. Often this means they have to push through thick brush and climb over fallen trees, but it’s important to put the cameras in all habitat types, not just those that are enjoyable to walk through. When the research team arrived at a site, they mounted a camera on a tree at waist height. Whenever an animal came into the frame of a camera, a photo was taken and stored on a memory card. The cameras were left on the islands year-round from 2014-2019. Every 6 months Erik and his collaborators would traverse through the thick woods to swap out memory cards and batteries. During this time, they noticed that four of the cameras had not worked properly, so they used the pictures from 160 of the cameras. 

Back at the college, the research team spent countless hours identifying which animals triggered the cameras. The cameras had taken over 200,000 photos over three years including 7,000 wildlife visits. Of these visits, 1,970 were from carnivores! They found 10 different kinds of carnivores, including: American marten, black bear, bobcat, coyote, fisher, gray fox, gray wolf, raccoon, red fox and weasels. After the pictures were processed, Erik used this information to map out which islands the animals were found. For this study, he used species richness, or the number of different species observed on each island, to answer his question. 

Map of the Apostle Islands with the richness, or number of different carnivore species, detected on each island.

Featured scientists: Erik Olson from Northland College, Tim Van Deelen, and Julie Van Stappen from the National Park Service. Support for this lesson was provided by the National Park Service with funding from the Great Lakes Restoration Initiative.

Flesch–Kincaid Reading Grade Level = 11.2

Additional teacher resources related to this Data Nugget:

The study and results described in this Data Nugget have been published:

  • Allen, M.L., Farmer, M.J., Clare, J.J., Olson, E.R., Van Stappen, J., Van Deelen, T.R. 2018. Is there anybody out there? Occupancy of the carnivore guild in a temperate archipelago. Community Ecology 19(3): 272-280.

Citizen science site where students can view and identify animals found in pictures from cameras placed around Wisconsin.

There have been several news articles about this research:

Picky eaters: Dissecting poo to examine moose diets

Moose chomping on a forest plant

When you eat at a restaurant, do you always order your favorite meal? Or do you like to look at the menu and try something new? Humans have so many meal options that it can be hard to decide what to eat, but we also have preferences for certain food over others. Animals have fewer decisions to make. They have to choose from food options available in their environment. Do animals search for specific food types or eat any food they find?

Scientists who study the ecology of the remote Isle Royale National Park are interested in knowing more about how moose decide which plants to eat. Isle Royale is a large (44 miles long and 8 miles wide) island found within Lake Superior. On the island, wolves are the main predators of moose. The wolf and moose populations have been studied there for over 60 years, making it the longest continuous study of predator-prey dynamics.

In recent years, the wolf population struggled to rebound because there were very few adults reproducing. Without their natural predators, the moose population has increased dramatically, in 2000 there were approximately 500 moose, but since that time the population has grown to over 2,000 moose! Moose are browsers, meaning they eat leaves and needles, fruits, or twigs that are found on woody plants. Having too many moose on the island would take a toll on the island’s plant community. Bite by bite, moose may be chomping away at the forest and changing the Isle Royale ecosystem as we know it.

To try to fix this problem, the National Park Service is working to restore the wolf population by relocating adults from other Lake Superior packs to the island. However, this will take several years and in the meantime moose will continue to have an effect on the plant community. Scientists Sarah, John, and their colleagues realize how important it is to monitor which plants the moose are eating. The scientist team wanted to know whether moose simply eat the plants that they come across, or if they show preference for certain plants. 

Surveying woody plants in Isle Royale National Park

One thing that could affect moose food preference is the nutrition level of the different plants. In the winter, deciduous plants lose their leaves, unlike conifers that are green all year round. In the winter, moose end up eating the edges of twigs from deciduous plants, but can still eat needles of conifers. Needles are easier for moose to digest and have more nutrients than twigs so the scientists thought moose would seek out coniferous plants, like balsam fir and cedar, even if they were less common in the environment.

Starting in 2004, the scientist team selected 14 sites across the island and started collecting moose poop, also called fecal pellets, at the end of winter. Back in the lab, the fecal pellets were examined closely under a microscope to determine what the moose were eating. Many plants have identifiable differences in cellular structures, so the scientists were able to look at the magnified fragments and record how much balsam fir, cedar, and deciduous plants the moose had been eating. 

To understand preference, the scientists also needed to know which plants were in the area that the moose were living. They did plant surveys at the beginning and end of the study to estimate the percent of different woody plants that are in the forest. Because woody plants are long-living, the forest didn’t change too much from year to year. 

Once they had the forest plant surveys and the moose diets analyzed from the fecal pellets, they were able to analyze whether moose selectively eat. If a moose was randomly eating the plant types that it came across, it would have similar amounts of plants in its diet than what is found in the forest. If a moose shows preferencefor a plant type, it would have a higher percent of that food in their diet than what is found in the forest. Moose could also be avoiding certain food types, which would be when they have a lower percent of a plant type in its diet than in the environment.

Featured scientist: Sarah Hoy, John Vucetich and John Henderson from Michigan Technological University.Support for this lesson was provided by the National Park Service with funding from the Great Lakes Restoration Initiative.

Flesch–Kincaid Reading Grade Level = 10.1

Additional teacher resources related to this Data Nugget:

The study and results described in this Data Nugget have been published. If students are curious to know more about the study design and how sites were selected, there is an approachable methods section available in the article:

  • Hoy, S.R., Vucetich, J.A., Liu, R., DeAngelis, D.L., Peterson, R.O., Vucetich, L.M., & Henderson, J.J. 2019. Negative frequency-dependent foraging behavior in a generalist herbivore (Alces alces) and its stabilizing influence on food-web dynamics. Journal of Animal Ecology.

There have been several news stories about this research:

Website with more information on the Isle Royale Wolf-Moose Study, including additional datasets to examine with students.