3.26.20

Where to find the hungry, hungry herbivores

Carina and some pokeweed plants in Tennessee.

The activities are as follows:

Éste Data Nugget también está disponible en Español:

When travelling to warm, tropical places you are exposed to greater risk of diseases like malaria, yellow fever, or dengue fever. The same pattern of risk is true for other species besides humans. For example, scientists have noticed that crops seem to have more problems with pests if they grow at lower latitudes (closer to the equator). Locations that are at lower latitudes have warm climates. We don’t know exactly why there are more pests in warmer places, but it could be because pests have a hard time surviving very cold winters. 

Carina is interested in figuring out more about this pest-y problem. She first got excited about plants in school, when she learned that they use photosynthesis to make their own food out of light, air, and water. She thought it was fascinating that plants have evolved so many different strategies to survive. Even though they don’t have brains, plants do have adaptations that help them compete for light and mate in many different habitats. Carina continues to learn more every day, and especially enjoys researching how plants defend themselves against herbivores, or animals that eat plants. Herbivores pose a challenge because plants can’t run away or hide! 

Carina studies ways wild plants can defend themselves against herbivores. What she learns in wild plants could give us ideas of how to help crops defend against pests too. Scientists aren’t sure why crops have more pest problems in warmer places, but it would help to understand if wild plants also have the same pattern. 

Pokeweed (Phytolacca americana) is a common wild plant that grows all over the eastern US. Pokeweed has beautiful pink stems and dark purple berries. In fact, the Declaration of Independence was written with ink made from pokeweed berry juice!

So Carina decided to travel all across the eastern United States to measure herbivory on pokeweed, a common wild plant there. Carina drove a lot for this project! In one summer, she visited ten patches of pokeweed spread out between Michigan and Florida. Carina thought that the pokeweed found at lower latitudes (Florida, 27° N) would have higher herbivory than pokeweed at northern latitudes (Michigan, 42° N) because pests may not be able to survive as well in places with harsh winters. 

At each of the ten sites, she marked five very young leaves on 30 to 40 plants. That equals over 1,500 leaves! She then came back six weeks later to measure how much the leaves were eaten as they grew into large, mature leaves. When leaves are young, they are more tender and can be more easily eaten by herbivores (that’s why we eat “baby spinach” salad). To measure herbivory she compared the area that was eaten to the total area of the leaf, and calculated the percent of the leaf area eaten by caterpillars, the main herbivores on pokeweed. She then averaged the percent eaten on leaves for each plant. Some plants died in those 6 weeks, so the sample size at the end of the study ranged from 4 to 37 depending on the site.

Featured scientist: Carina Baskett from Michigan State University

Flesch–Kincaid Reading Grade Level = 9.4

There is one scientific paper associated with the research in this Data Nugget. The citation and link to the paper is below.

Baskett, C.A. and D.W. Schemske (2018) Latitudinal patterns of herbivore pressure in a temperate herb support the biotic interactions hypothesis. Ecology Letters 21(4):578-587.

1.15.20

The end of winter as we’ve known it?

Forrest standing in front of the ice road that forms between Bayfield and LaPointe each winter, preventing ferry traffic but allowing cars to travel between the mainland and island.

The activities are as follows:

As a boy growing up in Bayfield, Wisconsin, Forrest was familiar with the seasonal rhythms of Lake Superior and the nearby Apostle Islands. Forrest watched each year as ice formed in the Bayfield Harbor, stopping the boat traffic each winter. Eventually, as the ice thickened even more, an ice road would open between Bayfield and LaPointe. The small town of LaPointe is located on Madeline Island just over two miles from the shore of Bayfield. When the ice road opens, it frees the island residents from working around the ferry schedule and they can drive on the ice to get to the mainland.

As a senior at Bayfield High School, Forrest became interested in conducting a scientific study related to the ice season on Lake Superior. He knew that Lake Superior plays a vital role in the lives of people who live and work on its shores and therefore all sorts of data are recorded to help understand and take care of it. Based on his own observations and comments of other area residents, Forrest thought that winters were getting shorter. He wanted to know whether the length of the ice season was changing over time. Forrest turned to historical data to answer his question. 

Forrest’s first stop on his quest to find data was the Madeline Island Ferry Line, a company that operates the ferries between Bayfield and LaPointe. Since 1970, the ferry line has kept yearly records of the date on which the last ferry traveled between Bayfield and LaPointe before the water was too frozen for travel. They also recorded the date on which the first ferry traveled the channel when ice melted in the spring. That gave Forrest a start, but he wanted data that would date farther back than 1970. 

Luckily, Forrest’s father, Neil, was an interpretive ranger for the Apostle Islands National Lakeshore. Neil showed Forrest local newspaper archives that were stored in the basement of their headquarters building. News about shipping and fishing have been important to the people in the community throughout history, so it was common to find articles referencing the first and last boat of each year. Looking back through newspaper records, Forrest and Neil were able to collect data for almost every year dating back to 1857!

Armed with these data, Forrest began his analyses. He chose to define the length of the ice season as the time between the last boat each winter and the first boat each spring. This also represents the time during which there was no boat navigation due to ice cover. Forrest’s next step was to choose how to quantify the dates. He decided to use Julian dates, which start with January 1 as Day 1 and continue to count up by 1 for each day. This means that January 31 would be Day 31, February 1 would be Day 32, and March 1 would be Day 61. After assigning Julian dates to each historical data point, Forrest subtracted the day of the last boat from the day of the first boat to find the number of days without boat traffic each year. This number serves as a consistent way to estimate the length of the ice season each year. Winter begins in one calendar year but ends in the next, so Forrest identified the year based on the calendar year that the winter began.

Featured scientist: Forrest Howk, Bayfield High School. Written by: Richard Erickson, Bayfield High School and Hannah Erickson, Boston Public Schools

Flesch–Kincaid Reading Grade Level = 10.1

Additional teacher resources related to this Data Nugget include:

  • If you would like your students to interact with the raw data, we have attached the original data here.
  • Forrest’s study was published in the Journal of Great Lakes Research.
  • Scientists at the Large Lakes Observatory in Duluth, MN have conducted studies related to Lake Superior’s water temperatures. This website includes real-time data collection from buoys in Lake Superior that would likely yield usable data for student investigations.
  • Dr. John Magnuson of the University of Wisconsin has conducted studies of ice cover for lakes at latitudes across the globe. He wrote an article about projected changes in ice cover due to climate change at various latitudes around the world. In addition, his website has links to publications and further information.


12.20.19

Fishy origins

Fred Bogue holding a striped bass.

The activities are as follows:

Striped bass, or stripers, make up one of the most important fisheries for seafood and sport fishing on the East Coast of the United States. Carleigh and Chelsea, biology teachers in New Jersey, were at the beach one day when they saw a couple of stripers in the Barnegat Bay Inlet. Both teachers have always been interested in research and even met while participating in a summer research program as undergraduate students. Since then, both have gone on to complete more research projects in biology and education. Their curiosity about striper populations led them to work together yet again! 

They headed to Monmouth University in New Jersey, where they began working with two scientists, Megan and John. They learned that locations where fish reproduce are called spawning grounds. Young stripers spend 2-3 years developing in the spawning ground before moving downstream. When stripers become adults, they return to the same location to breed. 

There are four main spawning grounds for stripers on the East coast: the Hudson River, the Chesapeake Bay, Delaware River, and the Albermarle Sound. Stripers from these areas are considered to be different stocks. Stripers are migratory fish, and generally move north in the spring and south in the fall. Because they all migrate to New Jersey, fish from different stocks combine, which results in a mixed stock. When there is a population that has a mixed stock, we don’t know which spawning ground the fish originally came from. Conservation and management of New Jersey’s striper fishery requires knowing where the fish come from. Understanding which spawning grounds stripers are using helps managers make sure we are not overfishing or damaging these important environments. So, Carleigh and Chelsea joined a project that is working to find out how we can identify where mixed stock stripers come from. 

For their study, the scientists caught stripers in three different locations off the New Jersey coast in 2017. The fish were sampled by clipping off a small portion of the right pelvic fin. The scientists then extracted the DNA from each sample in the lab. They used polymerase chain reaction (PCR) to then copy regions of the DNA, called microsatellites. Microsatellites are small, repeating sections of DNA that can be variable enough to distinguish even close relatives. These data were then used to compare DNA samples from the unknown mixed stocks to the known spawning ground stocks. The scientists also recorded whether each fish was young or mature. The scientists then used the age data to tell whether the spawning grounds might be changing over time. 

Featured scientists: Carleigh Engstrom, Chelsea Barreto, Megan Phifer-Rixey, and John Tiedemann from Monmouth University 

Flesch–Kincaid Reading Grade Level = 9.2

12.11.19

A window into a tree’s world

Neil taking a tree core from a pine tree.

The activities are as follows:

According to National Aeronautics and Space Administration (NASA) and the National Oceanic Atmospheric Administration (NOAA), the years 2015-2018 were the warmest recorded on Earth in modern times! And it is only expected to get warmer. Temperatures in the Northeastern U.S. are projected to increase 3.6°F by 2035. Every year the weather is a bit different, and some years there are more extremes with very hot or cold temperatures. Climate gives us a long-term perspective and is the average weather, including temperature and precipitation, over at least 30 years. 

Over thousands of years, tree species living in each part of the world have adapted to their local climate. Trees play an important role in climate change by helping cool the planet – through photosynthesis, they absorb carbon dioxide from the atmosphere and evaporate water into the air. 

Scientists are very interested in learning how trees respond to rapidly warming temperatures. Luckily, trees offer us a window into their lives through their growth rings. Growth rings are found within the trunk, beneath the bark. Each year of growth has two parts that can be seen: a light ring of large cells with thin walls, which grows in the spring; and a dark layer of smaller cells with thick walls that forms later in the summer and fall. Ring thickness is used to study how much the tree has grown over the years. Dendrochronology is the use of these rings to study trees and their environments.

Different tree species have different ranges of temperatures and rainfall in which they grow best. When there are big changes in the environment, tree growth slows down or speeds up in response. Scientists can use these clues in tree’s rings to decipher what climate was like in the past. There is slight variation in how each individual tree responds to temperature and rainfall. Because of this, scientists need to measure growth rings of multiple individuals to observe year-to-year changes in past climate.

Jessie taking a tree core in the winter.

Jessie and Neil are two scientists who use tree rings for climate research. Jessie entered the field of science because she was passionate about climate change. As a research assistant, Neil saw that warming temperatures in Mongolia accelerated growth in very old Siberian pine trees. When he later studied to become a scientist, he wanted to know if trees in the eastern U.S. responded to changes in climate in the same way as the old pine trees in Mongolia. As a result, there were two purposes for Jessie’s and Neil’s work. They wanted to determine if there was a species that could be used to figure out what the climate looked like in the past, and understand how it has changed over time.

Jessie and Neil decided to focus on one particular species of tree – the Atlantic white cedar. Atlantic white cedar grow in swamps and wetlands along the Atlantic and Gulf coasts from southern Maine to northern Florida. Atlantic white cedar trees are useful in dendrochronology studies because they can live for up to 500 years and are naturally resistant to decay, so their well-preserved rings provide a long historical record. Past studies of this species led them to predict that in years when the temperature is warmer, Atlantic white cedar rings will be wider. If this pattern holds, the thickness of Atlantic white cedar rings can be used to look backwards into the past climate of the area. 

To test this prediction, Jessie and Neil needed to look at tree rings from many Atlantic white cedar trees. Jessie used an increment borer, a specialized tool that drills into the center of the tree. This drill removes a wood core with a diameter about equal to that of a straw. She sampled 112 different trees from 8 sites, and counted the rings to find the age of each tree. She then crossdated the wood core samples. Crossdating is the process of comparing the ring patterns from many trees in the same area to see if they tell the same story. Jessie used a microscope linked to a computer to measure the thickness of both the early and late growth to the nearest micrometer (1 micrometer = 0.001 millimeter) for all rings in all 112 trees. From those data she then calculated the average growth of Atlantic white cedar for each year to create an Atlantic white cedargrowth index for the Northeastern U.S. She combined her tree ring data with temperature data from the past 100 years.

Featured scientists: Jessie K Pearl, University of Arizona and Neil Pederson, Harvard University. Written by Elicia Andrews.

Flesch–Kincaid Reading Grade Level = 9.9

Suggestions for inquiry surrounding this Data Nugget:

These videos, demonstrating the science of dendrochronology, could be a great way to spark class discussions:

11.4.19

Streams as sensors: Arctic watersheds as indicators of change

Jay taking field notes next to a rocky Tundra stream.

The activities are as follows:

The Arctic, Earth’s region above 66° 33’N latitude, is home to a unique biome, known as tundra. A defining trait of tundra ecosystems is the frozen land. Permafrost is the underground layer of organic matter, soil, rock, and ice that has been frozen for at least 2 full years. Plant material decays slowly in the Arctic because of the cold temperatures. Building up over thousands of years, the plants become frozen into the permafrost. Permafrost represents a very large “sink” of dead plant material, nutrients, and soil that is locked away in a deep freeze. 

Though the Alaskan Arctic may seem far away from where you live, tundra permafrost is important for the entire globe. During the past few thousand years, Earth’s climate has naturally changed a little over time, but because humans are adding greenhouse gases to the atmosphere, the average global temperature may increase by as much as 2 to 4oC over the next century. As a result of global climate change, permafrost has become less stable. By causing warmer and wetter conditions in the Arctic, thawing permafrost soils release ancient material that was previously frozen and locked away. Two important materials are dissolved nitrogen (N), which is a nutrient critical for plant growth, and carbon (C), which is stored in plant matter during photosynthesis. These released materials can be used again by plants, but some is carried away as melted water flows from the land into rivers and streams. You can imagine N and C in permafrost like a bank account where the landscape is the savings account. The land slowly deposits or withdraws N and C from the savings account, while the water receives any excess N and C that the land does not save.

Arial downloads data from a water quality monitoring station at the Kuparuk River. The station is connected a sensor that stays in the river and takes a reading for both carbon and nitrogen concentrations every 15 minutes.

The water that melts as permafrost thaws flows into a stream, ultimately ending up in an ocean. Watersheds are the network of streams and rivers that flow to a single point as they empty out into the ocean. The water at the end of the watershed therefore reflects all the changes that happened across a large area. Scientists use Arctic watersheds as large “sensors” to understand how and when landscapes may be releasing material from thawing permafrost. 

Because the Alaskan Arctic is a vast, sparsely populated area, scientists often rely on established field stations to conduct experiments, collect observational data, and develop new understanding of Arctic ecosystems. One of these field sites is Toolik Field Station. Scientists working at Toolik have been monitoring terrestrial and aquatic Arctic ecosystems since the late 1970s. 

Arial and Jay are aquatic scientists who work at Toolik. They are interested in how Arctic watersheds respond to climate change. Together, Arial and Jay act like ecosystem accountants: they use the chemistry within the water to monitor changes in ecosystem budgets of C and N. Arial and Jay used both historic data and water quality sensors deployed in 2017 and 2018 to monitor the N and C budget in the Kuparuk River. They use this data to calculate how much N and C the river is spending. They measure this as the total export in units of mass per year. This mass per year is determined by multiplying concentration (mass/volume) by flow (volume/day) and adding these values across the whole season (mass/year). These budgets at the watershed outlet help reveal signals of how this tundra landscape may be changing. In this way, they can assess if the landscape savings account for N and C is being depleted due to climate change. 

Featured scientists: Arial Shogren and Jay Zarnetske from Michigan State University

Flesch–Kincaid Reading Grade Level = 10.8

11.4.19

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

10.29.19

The carbon stored in mangrove soils

Tall mangroves growing close to the coast.

The activities are as follows:

In the tropics and subtropics, mangroves dominate the coast. There are many different species of mangroves, but they are all share a unique characteristic compared to other trees – they can tolerate having their roots submerged in salt water.

Mangroves are globally important for many reasons. They form dense forested wetlands that protect the coast from erosion and provide critical habitat for many animals. Mangrove forests also help in the fight against climate change. Carbon dioxide is a greenhouse gas that is a main driver of climate change. During photosynthesis, carbon dioxide is absorbed from the atmosphere by the plants in a mangrove forest. When plants die in mangrove forests, decomposition is very slow. The soils are saturated with saltwater and have very little oxygen, which decomposers need to break down plants. Because of this, carbon is stored in the soils for a long time, keeping it out of the atmosphere.

Sean is a scientist studying coastal mangroves in the Florida Everglades. Doing research in the Everglades was a dream opportunity for Sean. He had long been fascinated by the unique plant and animal life in the largest subtropical wetland ecosystem in North America. Mangroves are especially exciting to Sean because they combine marine biology and trees, two of his favorite things! Sean had previously studied freshwater forested wetlands in Virginia, but had always wanted to spend time studying the salty mangrove forests that exist in the Everglades. 

Sean Charles taking soil samples amongst inland short mangroves.

Sean arrived in the Everglades with the goal to learn more about the factors important for mangrove forests’ ability to hold carbon in their soils. Upon his arrival, he noticed a very interesting pattern – the trees were much taller along the coast compared to inland. This is because mangroves that grow close to the coast have access to important nutrients found in ocean waters, like phosphorus. These nutrients allow the trees to grow large and fast. However, living closer to the coast also puts trees at a higher risk of damage from storms, and can lead to soils and dead plants being swept out to sea. 

Sean thought that the combination of these two conditions would influence how much carbon is stored in mangrove soils along the coast and inland. Larger trees are generally more productive than smaller ones, meaning they might contribute more plant material to soils. This led Sean to two possible predictions. The first was that there might be more carbon in soils along the coast because taller mangroves would add more carbon to the soil compared to shorter inland mangroves. However, Sean thought he might also find the opposite pattern because the mangroves along the coast have more disturbance from storms that could release carbon from the soils. 

To test these competing hypothesis, the team of scientists set out into the Everglades in the Biscayne National Park in Homestead, Florida. Their mission was to collect surface soils and measure mangrove tree height. To collect soils, they used soil cores, which are modified cylinders that can be hammered into the soil and then removed with the soil stuck in the tube. Tree height was measured using a clinometer, which is a tool that uses geometry to estimate tree height. They took these measurements along three transects. The first transect was along the coast where trees had an average height of 20 meters. The second transect between the coast and inland wetlands where trees were 10 meters tall, on average. The final transect was inland, with average tree height of only 1 meter tall.  With this experimental design Sean could compare transects at three distances from the coast to look for trends. 

Once Sean was back in the lab, he quantified how much carbon was in the soil samples from each transect by heating the soil in a furnace at 500 degrees Celsius. Heating soils to this temperature causes all organic matter, which has carbon, to combust. Sean measured the weight of the samples before and after the combustion. The difference in weight can be used to calculate how much organic material combusted during the process, which can be used as an estimate of the carbon that was stored in the soil. 

Featured scientist: Sean Charles from Florida International University

Flesch–Kincaid Reading Grade Level = 9.6

Additional teacher resources related to this Data Nugget:

9.29.19

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:

9.29.19

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 preference for 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.


9.16.19

Testing the tolerance of invasive plants

Casey out in the field.

The activities are as follows:

Casey is a biologist who grew up with dogs as pets. His dogs were all the same species and had some things in common – they all had a tail, ears, and fur. But, each dog also had its own unique appearance – tail length, ear shape, and fur color. These things are called traits. Casey became interested in how slight differences in traits make individuals unique. 

As Casey observed in dogs, not all individuals in the same species are exactly alike. This is also true in plants. When we look closely at individual plants of the same species, we often see that each is slightly different from the next. Some grow faster. Some have more leaves than others. Some are better at defending themselves against herbivores that might eat them. 

People move species around the globe, and some of these species cause problems where they are introduced. These trouble-making species are called invasive species. Casey wanted to apply what he knew about trait differences to the environment around him, so he chose to study invasive plants and their traits. He wants to know what it is about invasive species that make them able to invade. Casey thought that maybe certain traits cause invasive species to be more troublesome than others. The individual plants that have invaded other parts of the world might have different traits that made them successful in that environment. Plants in their new invasive range might be slightly different than plants in the native range where they came from.  

Along with other members of his lab, Casey is studying an invasive plant species called burr clover. The lab collected seeds of burr clover from all different parts of the world. Some of the seeds came from the native range around the Mediterranean Sea (e.g. Italy, France, and Morocco) and some came from areas where they are invasive (e.g. Japan, Brazil, and the United States). The plants from the invasive range have already proven that they can invade new areas. Studying traits in native and invasive ranges would allow Casey to learn more about how those individuals invaded in the first place. Because Casey thought trait differences might have caused certain individuals of burr clover to become invasive, he predicted that individuals from the invasive range would have different traits than those from the native range. 

Casey’s field site where he studies Burr Clover

The lab decided to look at one trait in particular – how much an individual plant was affected by herbivores, which is called tolerance. The most tolerant individuals can still grow and produce fruits, even when herbivores eat a lot of their tissue. Casey thought that individuals from the invasive range would be more tolerant than individuals from the native range. One reason the invading individuals may have been successful is that they were more tolerant of herbivores in their new environment.The fruits contain seeds that make new plants, so plants that make more fruits can invade more easily. If individuals from the invasive range can make more fruits, even when herbivores are around, then they may reproduce and spread more quickly. 

So, Casey and his lab collected seeds from 22 individual plants from the native range and 22 individual plants from the invasive range. Each plant produces many seeds, so they collected several seeds from each individual. They created 24 2×2-meter plots in a field in California. Into each plot they planted 2-4 seeds from each individual plant and the seeds were planted in a random order in each plot. In all, there were 3,349 plants! In half of the plots, they removed any insects that might eat the plants. To do this they randomly chose half of the plots and sprayed them with insecticide, which kills insects. They sprayed the other half of the plots with water as a control. They wanted to know how many fruits were made by plants under good conditions so they could compare to plants that are being eaten by herbivores. After the plants grew all spring, they measured how many small, spiky fruits each plant produced. They compared how many fruits each plant produced in the plots with insects and the plots without insects. 

Featured scientist: Casey terHorst from California State University, Northridge

Flesch–Kincaid Reading Grade Level = 8.3

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