To bee or not to bee aggressive

A honey bee (Apis mellifera) collecting nectar to bring back to the hive. Photo by Andreas Trepte www.photo-natur.net

The activities are as follows:

Honey bees are highly social creatures that live in large colonies of about 40,000 individuals and one queen. Every member of the hive works together to benefit the colony. Some of the tasks adult bees perform include making honey, nursing young, foraging for food, building honey comb structures, and defending the colony.

From spring through fall, the main task is turning nectar from plants to honey. The honey is stored and eaten over the winter, so it is vital for the colony’s survival. Because honey is an energy-rich food source, hives are targets for break-ins from animals, like bears, skunks, and humans that want to steal the honey. Bees even have to fight off bees from other colonies that try to steal honey. Research shows that colonies adjust their defenses to match threats found in their environment. Hives in high risk areas respond by becoming more aggressive, and hives that do not face a lot of threats are able to lower their aggression. This flexibility makes sure they do not waste energy on unnecessary behaviors.

Clare is a scientist studying the behavior of social animals. There is an interesting pattern seen in other social animals, including humans, that Clare wanted to test in honey bees. In these species, the social environment experienced when an individual is young can have lasting effects on their behavior later in life. This may be because this is the time that the brain is developing. She thought this would likely be the case with honey bees for two reasons. First, bees can use social information to help coordinate group defense. Second, young bees rely completely on adult bees to bring them food and incubate them, so there are a lot of social interactions when they are young. After reading the literature and speaking with other honey bee experts, Clare found out that no one had ever tested this before!

Honey bee larva (top) and an emerging adult (bottom).

Clare chose to look at aggression level as a behavioral trait of individual bees within a colony. She predicted that young honey bees raised in an aggressive colony would be more aggressive as adults, compared to honey bees raised in a less aggressive colony. To test her predictions, Clare used 500 honey bee eggs from 18 different queens. To get these 500 eggs she collected three times in the summer, for two years. Each time she collected, she went to two different locations. Collecting from so many different queens helped Clare make sure her study included eggs with a large genetic diversity.

To test her questions, she used these eggs to set up an experiment. Eggs from each of the 18 queens were split into two groups. Each group was put into one of two types of foster colonies – high aggression and low aggression. Clare determined whether each foster colony was considered high or low aggression using a test. Because half of each queen’s eggs went into a low aggression foster colony, and the other half in a high aggression foster colony, this represents the experimental treatment.

Clare left the foster colonies alone and waited for the bees to develop in the hives. Eggs hatch and turn into larvae. These larvae mature into pupae and then into adults. Just before the young bees emerged from their pupal stage to adulthood, Clare removed them from the foster colonies and brought them into the lab. This way the bees would spend their whole adult life in the lab together, sharing a common environment.

After a week in the lab, Clare tested the aggressiveness of each individual bee. Her test measured aggressive behaviors used by a bee to defend against a rival bee from another colony. Clare observed and counted a range of behaviors including attempts to sting the rival and bites to the rival’s wings and legs. She used these values to calculate an offspring aggression score for each bee.

To select high and low aggression foster colonies to be used in her experiment, Clare first had to identify which colonies were aggressive and which were not. To do this, she put a small amount of a chemical that makes bees aggressive on a piece of paper at the front of the colony entrance. The top two photos show two colony entrances before the chemical. The bottom two photos show the same two colonies 60 seconds after the chemical. The more bees that come out, the more aggressive the colony. You can see from these images that the colony on the right is much more aggressive than the colony on the left. Clare counted the number of bees and used this value to calculate the colony’s aggression score.

Featured scientist: Clare C. Rittschof from the University of Kentucky

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Bon Appétit! Why do male crickets feed females during courtship?

Mating pair of Hawaiian swordtail cricket with macrospermatophore on the male (left). The male and female (right) are marked with paint pens for individual identification.

Mating pair of Hawaiian swordtail cricket with macrospermatophore on the male (left). The male and female (right) are marked with paint pens for individual identification.

The activities are as follows:

In many species of insects and spiders, males provide females with gifts of food during courtship and mating. This is called nuptial feeding. These offerings are eaten by the female and can take many forms, including prey items the male captured, substances produced by the male, or parts from the male’s body. In extreme cases the female eats the male’s entire body after mating! Clearly these gifts can cost the male a lot, including time and energy, and sometimes even their lives.

So why do males give these gifts? There are two main hypotheses explaining why nuptial feeding has evolved in so many different species. First, giving a gift may attract a female and improve a male’s chance of getting to mate with her, or of fathering her young. This is known as the mating effort hypothesis. Second, giving a gift may provide the female with the energy and nutrients she needs to produce young. The gift helps the female have more, or healthier, offspring. This is known as the paternal investment hypothesis. These two hypotheses are not mutually exclusive – meaning, for any given species, both mechanisms could be operating, or just one, or neither.

Biz is a scientist who studies nuptial gifts, and he chose to work with the Hawaiian swordtail cricket, Laupala cerasina. He chose this species because it uses a particularly interesting example of nuptial feeding. In most other cricket species, the male provides the female with a single package of sperm, called a spermatophore. After sperm transfer, the female removes the spermatophore from her genitalia and eats it. However, in the Hawaiian swordtail cricket, males produce not just one but a whole bunch of spermatophores over the course of a single mating. Most of these are smaller, and contain no sperm – these are called “micros”. Only the last and largest spermatophore to be transferred, called the “macro” actually contains sperm. The number of micros that a male gives changes from mating to mating.

From some of his previous research, and from reading papers written by other scientists, Biz learned that micros increase the chance that a male’s sperm will fertilize some of the female’s eggs. Also, the more micros the male gives, the more of the female’s offspring he will father. This research supports the mating effort hypothesis for the Hawaiian swordtail cricket. Knowing this, Biz wanted to test the paternal investment hypothesis as well. He wanted to know whether the “micro” nuptial gifts help females lay more eggs and/or help more of those eggs hatch into offspring.

Biz used two experiments to test the paternal investment hypothesis. In the first experiment, 20 females and 20 males were kept in a large cage outside in the Hawaiian rainforest. The crickets were allowed to mate as many times as they wanted for six weeks. In the second experiment, 4 females and 4 males were kept in cages inside in a lab. Females were allowed to mate with up to 3 different males, and were then moved to a new cage to prevent them from mating with the same male more than once. In both experiments Biz observed all matings. He recorded the number of microspermatophores transferred during each mating and the number of eggs laid. If females that received a greater number of total micros over the course of all matings produced more eggs, or if their eggs had a higher rate of hatching, then the paternal investment hypothesis would be supported.

Featured scientist: Biz Turnell from Cornell University & Dresden University of Technology

Flesch–Kincaid Reading Grade Level = 8.9

Additional teacher resources related to this Data Nugget include:

How do brain chemicals influence who wins a fight?

fighting-fly-360wThe activities are as follows:

In nature, animals compete for resources. These resources include space, food, and mates. Animals use aggression as a way to capture or defend these resources, which can improve their chances of survival and mating. Aggression is a forceful behavior meant to overpower opponents that are competing for the same resource. The outcome (victory or defeat) depends on several factors. In insects, the bigger individuals often win. However, if two opponents are the same size, other factors can influence outcomes. For example, an individual with more experience may defeat an individual with less experience. Also individuals that are fighting to gain something necessary for their survival have a strong drive, or motivation, to defeat other individuals.

Researchers Andrew, Ken, and John study how the brain works to regulate behavior when motivation is present. They wanted to know if specific chemicals in the brain influenced the outcome of a physically aggressive competition. Andrew, Ken, and John read a lot papers written by other scientists, and learned that there was a chemical that played an important role in regulating aggressive behavior. This chemical compound, called serotonin is found in the brains of all animals, including humans. Even a small amount of this chemical can make a big impact on aggressive behavior, and perhaps the outcome of competition.

The researchers decided to do an experiment to test what happens with increasing serotonin levels in the brain. They used stalk-eyed flies in their experiment. Stalk-eyed flies have eyes on the ends of stalks that stick out from the sides of their heads. They thought that brain serotonin levels in stalk-eyed flies would influence their aggressive behaviors in battle and therefore impact the outcome of competition. If their hypothesis is true, they predicted that increasing the brain serotonin in a stalk-eyed fly would make it more likely to use aggressive behaviors, and flies that used more aggressive behaviors would be more likely to win. Battling flies use high-intensity aggressive attacks like jumping on or striking an opponent. They also use less aggressive behaviors like flexing their front legs or rearing up on their hind legs.

Two stalk-eyed flies rearing/extending forearms in battle. Photo credit: Sam Cotton.

Two stalk-eyed flies rearing/extending forearms in battle. Photo credit: Sam Cotton.

To test their hypothesis, the researchers set up a fair test. A fair test is a way to control an experiment by only changing one piece of the experiment at a time. By changing only one variable, scientists can determine if that change caused the differences they see. Since larger flies tend to win fights, the flies were all matched up with another fly that was the same size. This acted as an experimental control for size, and made it possible to look at only the impact of serotonin levels on aggression. The scientists also controlled for the age of the flies and made sure they had a similar environment since the time they were born. The experiment had 20 trials with a different pair of flies in each. In each trial, one fly received corn mixed with a dose of serotonin, while another fly received plain corn as a control. That way, both flies received corn to eat, but only one received serotonin.

The two flies were then placed in a fighting arena and starved for 12 hours to increase their motivation to fight over food. Next, food was placed in the center of the arena, but only enough for one fly! The researchers observed the flies, recording various behaviors of each opponent. They recorded three types of behaviors. High intensity behaviors were when the fighting flies touched one another. Low-intensity behaviors were when the flies did not come in contact with each other, for example jump attacks, swipes, and lunges. The last behavior type was retreating from the fight. Flies that retreated fewer times than their opponent were declared the winners. After the battles, the researchers killed the flies and collected their brains. They then measured the concentration of serotonin in each fly’s brain.

Featured scientists: Andrew Bubak and John Swallow from the University of Colorado at Denver, and Kenneth Renner from the University of South Dakota

Flesch–Kincaid Reading Grade Level = 9.2

There is a scientific paper associated with the data in this Data Nugget. The citation and PDF for the paper is below.

Bubak, A.N., K.J. Renner, and J.G. Swallow. 2014. Heightened serotonin influences contest outcome and enhances expression of high-intensity aggressive behaviors. Behavioral Brain Research 259: 137-142.

An article written about the research in this Data Nugget: John Swallow: Co-authors study on insect aggression and neurochemistry

Videos of a experimental trial – two stalk eyed flies battling in the fighting arena. The video was filmed during the experiment by the researchers listed in this Data Nugget!

Video showing how the long eyestalks of males form!

Beetle battles

Erin has always loved beetles! Here she is with a dung beetle in Tanzania, during a graduate school class trip.

Erin has always loved beetles! Here she is with a dung beetle in Tanzania, during a graduate school class trip.

The activities are as follows:

Male animals spend a lot of time and energy trying to attract females. In some species, males directly fight with other males to become socially dominant. They also fight to take over and control important territories. This process is known as male-male competition. The large antlers of male elk are an example of a trait that has been favored by male-male competition. In other species, males try to court females directly. This process is known as female choice. The flashy tails of male peacocks are a good example of a trait that has been favored by female choice. Lastly, in some species, both male-male competition AND female choice determine which males get to mate. In order to be successful, males have to be good at both fighting other males and making themselves attractive to females. Erin is a biologist interested in these different types of mating systems. She wondered if she could discover a single trait that was favored by both male-male competition and female choice.

Two dung beetle males fighting for ownership of the artificial tunnel. Why is the photo pink? Because beetles mate and fight in dark, underground tunnels, Erin carried out all of her experiments in a dark room under dim red-filtered light. Beetles can’t see the color red, so working under red-filtered light didn’t affect the beetles’ behavior, and allowed Erin to see what the beetles were doing.

Two dung beetle males fighting for ownership of the artificial tunnel. Why is the photo pink? Because beetles mate and fight in dark, underground tunnels, Erin carried out all of her experiments in a dark room under dim red-filtered light. Beetles can’t see the color red, so working under red-filtered light didn’t affect the beetles’ behavior, and allowed Erin to see what the beetles were doing.

In horned dung beetles, male-male competition and female choice are both important in determining which males get to mate. Females dig tunnels underneath fresh piles of dung where they mate and lay their eggs. Beetles only mate inside these underground tunnels, so males fight with other males to become the owner of a tunnel. Males that control the tunnels have a better chance to mate with the female that dug it. However, there is often more than one male inside a breeding tunnel. Small males will sneak inside a main tunnel by digging a connecting side tunnel. Additionally, the constant fights between large males means that the ownership of tunnels is constantly changing. As a result, females meet many different males inside their tunnels. It is up to them to choose the male they find the most attractive, and with whom they’ll mate. In this species of dung beetle, males try to persuade females to mate by quickly tapping on the females’ back with their forelegs and antennae. Previous research has found that females are more likely to mate with males that perform this courtship tapping at a fast rate. Because both fighting and courtship tapping take a lot of strength, Erin wondered if the trait of strength was what she was looking for. Would stronger male dung beetles be favored by both male-male competition and female choice?

To keep beetles alive in the lab, Erin set up a bucket with sand, and placed one pile of dung in the center. Female beetles dug tunnels below the dung.

To keep beetles alive in the lab, Erin set up a bucket with sand, and placed one pile of dung in the center. Female beetles dug tunnels below the dung.

To test her hypothesis, Erin conducted a series of experiments to measure the mating success, fighting success, and strength of male dung beetles. First, Erin measured the mating success of male beetles by placing one male and one female in an artificial tunnel (a piece of clear plastic tubing). She watched the pair for one hour, and measured how quickly the males courted, and whether or not the pair mated. Second, Erin measured the fighting success of males by staging fights between two males over ownership of an artificial tunnel. Beetle battles consist of a head-to-head pushing match that results in one male getting pushed out of the tunnel, and the other male remaining inside. To analyze the outcome of these fights, Erin randomly selected one male in each pair as the focal male, and scored the interaction as a “win” if the focal male remained inside the tunnel, and as a “loss” if the focal male got pushed out of the tunnel. In some cases, there was not a clear winner and loser because either both males left the tunnel, or both males remained inside. These interactions were scored as a “tie”. Finally, Erin determined each beetles’ strength. She measured strength as the amount of force it took to pull a male out of an artificial tunnel. To do this, she super-glued a piece of string to the back of the beetle, had it crawl into an artificial tunnel, attached the string to a spring scale, and then pulled on the scale until the beetle was pulled out of the tunnel.

Featured scientist: Erin McCullough from the University of Western Australia

Flesch–Kincaid Reading Grade Level = 8.8

There is one scientific paper associated with the data in this Data Nugget. The citation and PDF of the paper is below:

McCullough, E.L. and L.W. Simmons (2016) Selection on male physical performance during male–male competition and female choice. Behavioral Ecology


erinAbout Erin: I am fascinated by morphological diversity, and my research aims to understand the selective pressures that drive (and constrain) the evolution of animal form. Competition for mates is a particularly strong evolutionary force, and my research focuses on how sexual selection has contributed to the elaborate and diverse morphologies found throughout the animal kingdom. Using horned beetles as a model system, I am interested in how male-male competition has driven the evolution of diverse weapon morphologies, and how sexual selection has shaped the evolution of physical performance capabilities. I am first and foremost a behavioral ecologist, but my research integrates many disciplines, including functional morphology, physiology, biomechanics, ecology, and evolution.

CSI: Crime Solving Insects

Scientist Paula catching blow flies in the field using an insect net.

Scientist Paula catching blow flies in the field using an insect net.

The activities are as follows:

Most people think that maggots (larvae of blow flies) are gross, but they are important decomposers in many ecosystems. Without maggots, we would all trip over dead bodies every time we went outside! Not only do maggots break down dead animal bodies in nature, but they decompose human bodies as well!

Forensic entomology uses these amazing insects to help the criminal justice system. Remember the next time you swat away a fly, these little insects help police solve crimes! Adult blow flies are usually the first to arrive at a crime scene with a dead body. The blow flies oviposit, or lay their eggs, shortly after their arrival. These eggs hatch and become maggots that feed on the body. Scientists can use the age of the maggot to help estimate how long someone has been dead. The longer a body has been dead, the longer ago the eggs hatched and the older the maggot larvae will be.

Kristi and Paula, two forensic entomologists, were in the field on day, documenting the timing of blow fly oviposition. They noticed something unexpected! There were wasps stuck in the traps they were using to catch blow flies. The scientists wondered if these wasps would affect a blow fly’s decision to oviposit. Wasps will attack adult blow flies and will also eat their eggs. Blow flies have an incredible sense of smell and sight. Blow flies may be able to use their senses to detect if a wasp is near a body. If a wasp is detected, blow flies could choose to avoid the area or delay laying their eggs. The scientists predicted that blow flies would delay their oviposition when wasps were present near a body. If wasps cause blow flies to delay oviposition, this could change how scientist’s use maggot age to determine how long ago a body died.

Control bait cup with a large number of blow flies on the chicken liver

Control bait cup with a large number of blow flies on the chicken liver

To test their hypothesis, the scientists did 10 trials in the field. They used bait cups that contained chicken liver to simulate a dead human body. A total of 9 bait cups were used in each of the 10 trials, for a total of 90 cups. Of the 9 cups used in each trial, three contained only chicken liver, to represent a body with no wasps present. These cups were used as controls. Three cups contained chicken liver and a wasp pinned to the side of the bait cup so that there was a visual cue of the wasp. The final three cups had a crushed wasp sprinkled over chicken liver to see if blow flies could use a smell cue to tell that a wasp was present without seeing them. Researchers checked the cups every half hour for the presence of blow fly eggs. If they saw any eggs, they recorded the time of oviposition in hours after sunrise. They then brought the maggots to the lab and raised them to the third larval stage and identified them to species.

Featured scientists: Kristi Bugajski and Paula Stoller from Valparaiso University

Flesch–Kincaid Reading Grade Level = 7.6

The Flight of the Stalk-Eyed Fly

Variation between stalk-eyed fly species in eyestalk length.

Variation between stalk-eyed fly species in eyestalk length.

The activities are as follows:

Stalk-eyed flies are insects with eyes located on the ends of long projections on the sides of their head, called eyestalks. Male stalk-eyed flies have longer eyestalks than females, and this plays an important role in the flies’ mating patterns. Female stalk-eyed flies prefer to mate with males with longer eyestalks. In this way, the eyestalks are much like the bright and colorful peacock’s tail. This kind of sexual selection can lead to the evolution of longer and longer eyestalks over generations. But do these long eyestalks come at a cost? For example, longer eyestalks could make it more difficult to turn quickly when flying. As with all flies, stalk-eyed flies do not fly in a straight line all the time, and often zigzag in air. If long eyestalks make quick turns more difficult, we might expect there to be a trade-off between attracting mates and flight.

Screen Shot 2015-12-21 at 2.45.44 PMMoment of inertia (I) is defined as an object’s tendency to resist rotation – in other words how difficult it is to make something turn. An object is more difficult to turn (has a higher moment of inertia) when it is more massive, and when it is further from its axis of rotation. Imagine trying to swing around quickly holding a gallon of water – this is difficult because the water has a lot of mass. Now imagine trying to swing around holding a baseball bat with a jug of water attached to the end. This will be even more difficult, because the mass is further away from the axis of rotation (your body). Now lets bring that back to the stalk-eyed fly. The baseball bat now represents the eyestalk of the fly, while the gallon of water represents the eye at the end of the stalk. We can express the relationship between the mass of the object (m = mass of the eye), its distance from the axis of rotation (R = length of eyestalk), and the moment of inertia (I) using the following equation: I = mR2.

Because moment of inertia goes up with the square of the distance from the axis, we might expect that as the length of the flies’ eyestalks goes up, the harder and harder it will be for the fly to maneuver during flight. If this is the case, we would predict that male stalk-eyed flies would make slower turns compared to similar sized female flies with shorter eyestalks.

Differences in male and female eyestalk length.

Differences in male and female eyestalk length.

To address this idea, scientists measured the effect of eyestalk length on the moment of inertia of the body needs. In addition, they measured differences in turning performance during flight. Scientists Gal and John tracked free flight trajectories of female and male stalk-eyed flies in a large flight chamber. Because female and male stalk-eyed flies have large differences in eyestalk length, their flight performance can be compared to determine the effects of eyestalk length on flight. However, other traits may differ between males and females, so body size and wing length measurements were also taken. If increased moment of inertia does limit turning performance as expected, the male flies that have significantly longer eyestalks should demonstrate slower and less tight turns, indicating a decrease in free flight performance. If there is no difference in turning performance between males and females with significantly different eyestalk lengths, then males must have a way to compensate for the higher moment of inertia.

Featured scientists: Gal Ribak from Tel-Aviv University, Israel and John Swallow from University of Colorado, Denver. Written by: Brooke Ravanelli from Denver Public School, Zoё Buck Bracey from BSCS, and John Swallow.

Flesch–Kincaid Reading Grade Level = 9.0

Once your students have completed this Data Nugget, there is an extension lab activity where students can conduct their own experiment testing moment of inertia. Students simulate the flying experience of stalk-eyed flies and go through an obstacle course carrying their eyestalks with them as they maneuver through the cones to the finish line. To access this lab, click here!

Video showing how the long eyestalks of males form!

Shooting the poop

The activities are as follows:butterfly

Imagine walking through a forest in the middle of summer. You can hear birds chirping, a slight breeze rustling the leaves, and a faint pinging noise like rain. However, what you hear is not rain – it is the sound of millions of forest insects pooping!

If we look closer to see who is making all this frass (insect poop) you’ll notice there are tons of caterpillars amongst the leaves. You might see caterpillars eating plants and hiding from predators. Some caterpillars might camouflage themselves, while others build shelters from leaves to avoid being seen. Others are brightly colored to warn predators that they have chemicals that make them taste awful.

The silver-spotted skipper is a caterpillar that lives in the forest. They have a variety of defense strategies against enemies, including building leaf shelters for protection. For these insects, the sight and smell of poop might alert predators that there is a tasty meal nearby. Usually caterpillars keep moving and leave their frass behind, but this species builds shelters and isn’t able to keep moving because they need their shelters for protection.

Martha is a behavioral biologist who studies these insects. While raising silver-spotted skipper caterpillars in the lab, Martha noticed that they were making a pinging noise in their containers. Upon further observation, she discovered that they “shoot their poop”, sometimes launching their frass over 1.5m! Martha wanted to figure out why these caterpillars might have this very strange behavior. Perhaps launching their frass is a way to avoid being found by predators.

To evaluate whether the smell of frass helps predators find and locate silver-spotted skippers, Martha conducted an experiment with a wasp predator that eats these caterpillars. She allowed two silver-spotted skippers to build shelters on a leaf and then carefully removed the caterpillars. She then inserted 6 frass pellets into one of the shelters, and 6 beads designed to look like frass but with no smell (control treatment) into the other shelter. She placed the leaf with the two shelters in a cage containing an actively foraging wasp colony (n = 10 wasps). She recorded how many times the wasps visited each shelter (control beads or frass) and how much time the wasps spent exploring each shelter. She expected wasps would spend more time exploring the shelters with the frass than they would the control shelters.

Featured scientist: Martha Weiss from Georgetown University. Written by Kylee Grenis.

Flesch–Kincaid Reading Grade Level = 9.6

Additional teacher resources related to this Data Nugget include:

YouTube videos of the silver-spotted skipper (Epargyreus clarus) “shooting its poop” (aka. ballistic defecation). These videos would be great to show in class after students have read the Research Background section to help engage them with the system.

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Float down the Kalamazoo River

Morrow Lake, a reservoir created along the Kalamazoo River. The water is held in a reservoir by a dam. When water flows into the reservoir it slows, potentially letting some of the total suspended solids settle to the bottom of the river.

Morrow Lake, a reservoir created along the Kalamazoo River. The water is held in a reservoir by a dam. When water flows into the reservoir it slows, potentially letting some of the total suspended solids settle to the bottom of the river.

The activities are as follows:

Ever since she was a kid, rivers have fascinated Leila. One of her hobbies is to kayak and canoe down the Kalamazoo River in Michigan, near where she lives. For her work, she researches all the living things in the river and how humans affect them. She is especially interested in changes in the river food web, caused by humans building dams along the river, and an oil spill in 2010.

Leila knows there is a lot more in river water than what meets the eye! As the river flows, it picks up bits of dead plants, single-celled algae, and other living and nonliving particles from the bottom of the river. The mix of all these particles is called total suspended solids (TSS) because these particles are suspended in the river water as it flows. The food web in the Kalamazoo River depends on the particles that are floating in the water. Invertebrates eat decomposing leaves and algae, and fish eat the invertebrates.

Leila showing off some of the cool invertebrates that can be found in the Kalamazoo River.

Leila showing off some of the cool invertebrates that can be found in the Kalamazoo River.

As you float down the river, particles settle to the river bottom and new ones are picked up. The amount of suspended solids in a river is influenced by how fast the water in the river is flowing. The faster the water flows, the more particles are picked up and carried down the river. The slower the water flows, the more particles will settle to the bottom. Discharge is a measure of how fast water is flowing. You can think about discharge as the number of cubes (one foot on each side) filled with water that pass by a point every second. During certain times of the year, water flows faster and there is more discharge. In spring, when the snow starts melting, a lot of water drains from the land into the river. There also tends to be a lot more rain in the fall. Things humans build on the river can also affect discharge. For example, we build dams to generate hydroelectric power by capturing the energy from flowing water. Dams slow the flow of river water, and therefore they may cause some of the suspended solids to settle out of the water and onto the bottom of the river.

Leila wanted to test how a dam that was built on the Kalamazoo River influenced total suspended solids. If the dam is reducing the amount of total suspended solids, it could have negative effects on the food chain. She was also curious to see if the dam has different effects depending on the time of year. On eight different days from May to October in 2009, Leila measured total suspended solids at two locations along river. She collected water samples upstream of the dam, before the water enters the reservoir, and samples downstream after the water has been in the reservoir and passed over the dam. She also measured discharge downstream of the dam.

KalamazooRiver

Featured scientist: Leila Desotelle from Michigan State University

Flesch–Kincaid Reading Grade Level = 8.7

Do invasive species escape their enemies?

One of the invasive plants found in the experiment, Dianthus armeria

One of the invasive plants found in the experiment, Dianthus armeria

The activities are as follows:

Invasive species, like zebra mussels and garlic mustard, are species that have been introduced by humans to a new area. Where they invade they cause harm. For example, invasive species outcompete native species and reduce diversity, damage habitats, and interfere with human interests. Damage from invasive species costs the United States over $100 billion per year.

Scientists want to know, what makes an invasive species become such a problem once it is introduced? Is there something that is different for an invasive species compared to native species that have not been moved to a new area? Many things change for an invasive species when it is introduced somewhere new. For example, a plant that is moved across oceans may not bring enemies (like disease, predators, and herbivores) along for the ride. Now that the plant is in a new area with no enemies, it may do very well and become invasive.

laulab

Scientists at Michigan State University wanted to test whether invasive species are successful because they have escaped their enemies. They predicted invasive species would get less damage from enemies, compared to native species that still live near to their enemies. If native plants have tons of insects that can eat them, while an invasive plant has few or none, this would support enemy escape explaining invasiveness. However, if researchers find that native and invasive species have the same levels of herbivory, this would no support enemy escape. To test this hypothesis, a lab collected data on invasive and native plant species in Kalamazoo County. They measured how many insects were found on each species of plant, and the percent of leaves that had been damaged by insect herbivores. The data they collected is found below and can be used to test whether invasive plants are successful because they get less damage from insects compared to native plants.

Featured scientist: Elizabeth Schultheis from Michigan State University

Flesch–Kincaid Reading Grade Level = 11.3

  • For a lesson plan on the Enemy Release Hypothesis, click here.
  • For a great scientific paper discussing the Enemy Release Hypothesis, click here.
  • The Denver Museum of Nature and Science has a short video giving background on invasive species, here

Do insects prefer local or foreign foods?

One of the invasive plants found in the experiment, Centaurea stoebe.

One of the invasive plants found in the experiment, Centaurea stoebe.

The activities are as follows:

Insects that feed on plants, called herbivores, can have big effects on how plants grow. Herbivory can change the size and shape of plants, the number of flowers and seeds, and even which plant species can survive in a habitat. A plant with leaves eaten by herbivores will likely do worse than a plant that is not eaten.

Native plants are those that naturally occur in an area without human interference. When a plant is moved by humans to a new area and grows outside of its natural range, it is called exotic. Sometimes exotic plants become invasive, meaning they grow large and fast, take over habitats, and push out native species. What determines if an exotic species will become invasive? Scientists are very interested in this question. Understanding what makes a species become invasive could help control invasions already underway and prevent new ones in the future.

Because herbivory affects how big and fast a plant can grow, herbivores may determine if an exotic plant is successful in its new habitat and becomes invasive. Elizabeth, a plant biologist, is fascinated by invasive species and wanted to know why they are able to grow bigger and faster than native and exotic species. She thought that invasive species might get less damage from herbivores, which would allow them to grow more and could explain how they become invasive.

To test this hypothesis, Elizabeth planted 25 native, 25 exotic, and 11 invasive species in a field in Michigan. This field was already full of many plants and had many insect herbivores. The experimental plants grew from 2011 to 2013. Each year, Elizabeth measured herbivory on 10 individuals of each of the 61 species, for a total of 610 plants. To measure herbivory, she looked at the leaves on each plant and determined how much of each leaf was eaten by herbivores. She then compared the area that was eaten to the total area of the leaf and calculated the proportion leaf area eaten by herbivores. Elizabeth predicted that invasive species would have a lower proportion of leaf area eaten compared to native and noninvasive exotic plants.

ERHpics

Featured scientist: Elizabeth Schultheis from Michigan State University

Flesch–Kincaid Reading Grade Level = 10.9

There is one scientific paper associated with the data in this Data Nugget. The citation and PDF of the paper is below, as well as a link to access the full dataset from the study:

For two lesson plans covering the Enemy Release Hypothesis, click here and here. For another great paper discussing the Enemy Release Hypothesis, click here.

Aerial view of the experiments discussed in this activity:

ERH Field site 2

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