Category: Data Nugget | Page 11

3.25.16

Keeping up with the sea level

A view of salt marsh hay (Spartina patens) growing in a marsh

The activities are as follows:

Salt marshes are ecosystems that occur along much of the coast of New England in the United States. Salt marshes are very important – they serve as habitat for many species, are a safer breeding location for many fish, absorb nutrients from fertilizer and sewage coming from land and prevent them from entering the ocean, and protect the coast from erosion during storms.

Unfortunately, rising sea levels are threatening these important ecosystems. Sea level is the elevation of the ocean water surface compared to the elevation of the soil surface. Two processes are causing sea levels to rise. First, as our world gets warmer, ocean waters are getting warmer too. When water warms, it also expands. This expansion causes ocean water to take up more space and it will continue to creep higher and higher onto the surrounding coastal land. Second, freshwater frozen in ice on land, such as glaciers in Antarctica, is now melting and running into the oceans. Along the New England coast, sea levels have risen by 0.26 cm a year for the last 80 years, and by 0.4 cm a year for the last 20 years. Because marshes are such important habitats, scientists want to know whether they can keep up with sea level rise.

Researcher Sam Bond taking Sediment Elevation Table (SET) measurements in the marsh

When exploring the marsh, Anne, a scientist at the Plum Island Ecosystems Long Term Ecological Research site, noticed that the salt marsh appeared to be changing over time. One species of plant, salt marsh cordgrass (Spartina alterniflora), appeared to be increasing in some areas. At the same time, some areas with another species of plant, salt marsh hay (Spartina patens), appeared to be dying back. Each of these species of plants is growing in the soil on the marsh floor and needs to keep its leaves above the surface of the water. As sea levels rise, the elevation of the marsh soil must rise as well so the plants have ground high enough to keep them above sea level. Basically, it is like a race between the marsh floor and sea level to see who can stay on top!

Anne and her colleges measured how fast marsh soil elevation was changing near both species of plants. They set up monitoring points in the marsh using a device called the Sediment Elevation Table (SET). SET is a pole set deep in the marsh that does not move or change in elevation. On top of this pole there is an arm with measuring rods that record the height of the marsh surface. The SETs were set up in 2 sites where there is salt marsh cordgrass and 2 sites where there is salt marsh hay. Anne has been taking these measurements for more than a decade. If the marsh surface is rising at the same rate as the sea, perhaps these marshes will continue to do well in the future.

Featured scientist: Anne Giblin from the Marine Biological Laboratory and the Plum Island Ecosystems Long-Term Ecological Research site

Flesch–Kincaid Reading Grade Level = 9.1

Additional resources related to this Data Nugget:

New research on salt marshes in Massachusetts finds they may actually thrive despite higher water levels. How is this possible? The answer has to do with sediment. Share this article with students after they complete the Data Nuggets activity, discussing research led by Brian Yellen.

3.18.16

Does sea level rise harm Saltmarsh Sparrows?

Painting of the saltmarsh sparrow

The activities are as follows:

For the last 100 years, sea levels around the globe have increased dramatically. The cause of sea level rise has been investigated and debated. Data from around the world supports the hypothesis that increasing sea levels are a result of climate change caused by the burning of fossil fuels. As we warm the Earth, the oceans get warmer and polar ice caps melt. The dramatic increase in sea level that results could seriously threaten ecosystems and the land that humans have developed along the coast.

Salt marshes are plains of grass that grow along the east coast of the United States and many coasts worldwide. Salt marshes grow right at sea level and are therefore very sensitive to sea level rise. In Boston Harbor, Massachusetts, the NOAA (National Oceanic and Atmospheric Administration) Tide Gauge has measured a 21mm rise in sea level over the last 8 years. That means every year sea level has gone up an average of 2.6mm since 2008 – more than two and a half times faster than before we started burning fossil fuels! Because sea level is going up at such a fast rate, Robert, a scientist in Boston, became concerned for the local salt marsh habitats near his home. Robert was curious about what will happen to species that depend on Boston’s Plum Island Sound salt marshes when sea levels continue to rise.

Robert preparing his team for a morning of salt marsh bird surveys.

Robert decided to look at species that are very sensitive to changes in the salt marsh. When these sensitive species are present, they indicate the marsh is healthy. When these species are no longer found in the salt marsh, there might be something wrong. The Saltmarsh Sparrow is one of the few bird species that builds its nests in the salt marsh, and is totally dependent on this habitat. Saltmarsh Sparrows rely completely on salt marshes for feeding and nesting, and therefore their numbers are expected to decline as sea levels rise and they lose nesting sites. Robert heard that scientists studying Connecticut marshes reported the nests of these sparrows have been flooded in recent years. He wanted to know if the sparrows in Massachusetts were also losing their nests because of high sea levels.

For the past two decades Robert has kept track of salt marsh breeding birds at Plum Island Sound. In his surveys since 2006, Robert counted the number of Saltmarsh Sparrows in a given area. He did these surveys in June when birds are most likely to be breeding. He used the “point count” method – standing at a center point he measured out a 100 meter circle around him. Then, for 10 minutes, he counted how many and what kinds of birds he saw or heard within and just outside the circle. Each year he set up six count circles and performed counts three times in June each year at each circle. Robert also used sea level data from Boston Harbor that he can relate to the data from his bird surveys. He predicted that sea levels would be rising in Plum Island Sound and Saltmarsh Sparrow populations would be falling over time.

Featured scientist: Robert Buchsbaum from Mass Audubon. Written by: Wendy Castagna, Daniel Gesin, Mike McCarthy, and Laura Johnson

Flesch–Kincaid Reading Grade Level = 9.5

Additional teacher resources related to this Data Nugget include:

A PDF of the 2014 overview report on the Saltmarsh Habitat and Avian Research Program (SHARP) for the east coast marshes from Maine down to Maryland, which includes Massachusetts. The report may be helpful for students as they come up with other research questions.
A blog by SHARP, covering a wide diversity of salt marsh research!
Data from the Plum Island Sound LTER project.
Data from NOAA tide gauges in Boston Harbor. This dataset expands on that found in Table 1. Students can explore long-term data for Boston Harbor, or can explore other areas for independent research.
For more Boston Harbor tide information, or to look up tides in their area, students can also explore Tideschart.

3.11.16

CSI: Crime Solving Insects

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

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

The activities are as follows:

Most people think that maggots are gross, but they are important decomposers in many ecosystems. Without maggots and other decomposers, we would all trip over the bodies of dead organisms every time we went outside! Not only do maggots break down dead animal bodies in nature, but they also decompose human bodies!

Forensic entomology is a science that uses these amazing insects to help the criminal justice system. Maggots are the larvae of blow flies. 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 lay their eggs, or oviposit, 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 Parker, two forensic entomologists, were in the field one 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 can affect a blow fly’s decision to oviposit because wasps attack adult blow flies and also eat their eggs. Kristi and Parker knew that blow flies have an incredible sense of smell and sight. They wondered if blow flies are able to use their senses to detect if a wasp is near a body and then choose to avoid the area or delay laying their eggs. The scientists predicted that blow flies should delay their oviposition when wasps were present near a body. If wasps indeed 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

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. Kristi and Parker 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 Parker Stoller from Valparaiso University

Flesch–Kincaid Reading Grade Level = 7.6

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1.12.16

What do trees know about rain?

A cypress pine, or Callitris columellaris. This species is able to survive in Australia’s dry climates.

The activities are as follows:

Did you know that Australia is the driest inhabited continent in the world? Because it is so dry, we need to be able to predict how often and how much rain will fall. Predictions about future droughts help farmers care for their crops, cities plan their water use, and scientists better understand how ecosystems will change. The typical climate of arid northwest Australia consists of long drought periods with a few very wet years sprinkled in. Scientists predict that climate change will cause these cycles to become more extreme – droughts will become longer and periods of rain will become wetter. When variability is the norm, how can scientists tell if the climate is changing and droughts and rain events today are more intense than what we’ve seen in the past?

To make rainfall predictions for the future, scientists need data on past rainfall. However, humans have only recorded rainfall in Australia for the past 100 years. Because climate changes slowly and goes through long-term cycles, scientists need very long term datasets of rainfall.

Scientist Alison coring a cypress pine

The answer to this challenge comes from trees! Using dendrochronology, the study of tree rings, scientists get a window back in time. Many tree species add a ring to their trunks every year. The width of this ring varies from year to year depending on how much water is available. If it rains a lot in a year, the tree grows relatively fast and ends up with a wide tree ring. If there isn’t much rain in a year, the tree doesn’t grow much and the ring is narrow. We can compare the width of rings from recent years to the known rain data humans have collected. Then, assuming the same forces that determine tree ring width are operating today as in the past, we can go back and interpret how much rain fell in years where we have no recorded rainfall data. This indirect information from tree rings is known as a proxy, and helps us infer data about past climates.

For this study, the scientists used cypress-pine, or Callitris columellaris. This species is able to survive in Australia’s dry climates and is long lived enough to provide data far back in time. Fortunately, scientists don’t have to cut down the trees to see their rings. Instead, they use a corer – a hollow metal drill with the diameter of a straw. They drill it through the tree all the way to its core, and extract a sample of the tissue that shows all the tree rings. The scientists took 40 cores from 27 different cypress-pine trees. The oldest trees in the sample were more than 200 years old. Next, they developed a chronology where they lined up ring widths from one tree with all the other trees, wide with wide and narrow with narrow. This chronology gives them many replicate samples, and data going back all the way to the 19th century! Next, they used a dataset of rainfall from rain gauges that have been set out in Australia since 1910. They then take this precipitation data and overlay it with the tree ring widths since 1910. For tree rings before 1910, they then project back in time using a rainfall formula.

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

Featured scientist: Alison O’Donnell from University of Western Australia

Flesch–Kincaid Reading Grade Level = 8.0

This Data Nugget was adapted from a primary literature activity developed by Science Journal For Kids. For a more detailed version of this lesson plan, including a supplemental reading, videos, and extension activities, visit their website and register for free!

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

O’Donnell, A.J., E.R. Cook, J.G. Palmer, C.S.M. Turney, G.F.M. Page, and P.F. Grierson (2015). Tree Rings Show Recent High Summer-Autumn Precipitation in Northwest Australia Is Unprecedented within the Last Two Centuries. PLoS ONE 10(6) e0128533.
The same paper, written at a middle/high school reading level by Science Journal for Kids, can be found here.

Growth rings from a Callitirs tree.

12.21.15

The Flight of the Stalk-Eyed Fly

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.

Moment 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.

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!

11.3.15

Lizards, iguanas, and snakes! Oh my!

The Common Side-blotched Lizard

The activities are as follows:

Throughout history people have settled mainly along rivers and streams. Easy access to water provides resources to support many people living in one area. In the United States today, people have settled along 70% of rivers.

Today, rivers are very different from what they were like before people settled near them. The land surrounding these rivers, called riparian habitats, has been transformed into land for farming, businesses, or housing for people. This urbanization has caused the loss of green spaces that provide valuable services, such as water filtration, species diversity, and a connection to nature for people living in cities. Today, people are trying to restore green spaces along the river to bring back these services. Restoration of disturbed riparian habitats will hopefully bring back native species and all the other benefits these habitats provide.

Scientist Mélanie searching for reptiles in the Central Arizona-Phoenix LTER.

Scientists Heather and Mélanie are researchers with the Central Arizona-Phoenix Long-Term Ecological Research (CAP LTER) project. They want to know how restoration will affect animals living near rivers. They are particularly interested in reptiles, such as lizards. Reptiles play important roles in riparian habitats. Reptiles help energy flow and nutrient cycling. This means that if reptiles live in restored riparian habitats, they could increase the long-term health of those habitats. Reptiles can also offer clues about the condition of an ecosystem. Areas where reptiles are found are usually in better condition than areas where reptiles do not live.

Heather and Mélanie wanted to look at how disturbances in riparian habitats affected reptiles. They wanted to know if reptile abundance (number of individuals) and diversity (number of species) would be different in areas that were more developed. Some reptile species may be sensitive to urbanization, but if these habitats are restored their diversity and abundance might increase or return to pre-urbanization levels. The scientists collected data along the Salt River in Arizona. They had three sites: 1) a non-urban site, 2) an urban disturbed site, and 3) an urban rehabilitated site. They counted reptiles that they saw during a survey. At each site, they searched 21 plots that were 10 meters wide and 20 meters long. The sites were located along 7 transects, or paths measured out to collect data. Transects were laid out along the riparian habitat of the stream and there were 3 plots per transect. Each plot was surveyed 5 times. They searched for animals on the ground, under rocks, and in trees and shrubs.

Featured scientists: Heather Bateman and Mélanie Banville from Arizona State University. Written by Monica Elser from Arizona State University.

Flesch–Kincaid Reading Grade Level = 9.8

Check out this video of Heather and her lab out in the field collecting lizards:

Virtual field trip to the Salt River biodiversity project:

Additional resources related to this Data Nugget:

For more background on the importance of biodiversity, students can eat this article in The Guardian – What is biodiversity and why does it matter to us?

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10.21.15

Is your salt marsh in the zone?

Scientist James collecting plants in a Massachusetts marsh, part of the Plum Island Ecosystems Long Term Ecological Research site

The activities are as follows:

Tides are the rise and fall of ocean water levels, and happen every day like clockwork. Gravity from the moon and sun drive the tides. There is a high tide and a low tide, and the average height of the tide is called the mean sea level. The mean sea level changes seasonally due to the warming and cooling of the ocean throughout the year. It also changes annually due to a long-term trend of ocean warming and the melting of glaciers. Scientific evidence shows that climate change is causing the sea level to rise faster now than it has in the past. As the climate continues to warm, it is predicted that the sea level will continue to rise.

Salt marshes are wetlands with plains of grass that grow along much of the ocean’s coast worldwide. These marshes are important habitats for many plants and animals, and protect our shores from erosion during storms. They grow between mean sea level and the level of high tide. Marshes flood during high tide and are exposed to the air during low tide. The health of a salt marsh is determined by where it sits relative to the tide (the “zone”). A healthy marsh is flooded only part of the time. Too much flooding and too little flooding are unhealthy. Because they are so important, scientists want to know if salt marshes will keep up with sea level rise caused by climate change.

A picture of James’ “marsh organ” which holds plants at different elevations relative to mean sea level. He gave it that name because it resembles organ pipes!

In the 1980s, scientist James began measuring the growth of marsh grasses. He was surprised to find that there was a long-term trend of increasing grass growth over the years. James wanted to know if grasses could continue to keep up with rising sea levels. If he could experimentally manipulate the height of the grasses, relative to mean sea level, he might be able to figure out how grasses will do when sea levels are higher. To test this, James invented a way to experimentally grow a marsh at different elevations relative to mean sea level. He built a device he called the “marsh organ”. This device is made of tubes that stand at different elevations and are filled with marsh mud and planted with marsh grasses. He measured the growth of the grass in each of the pipes. If grasses will continue to grow taller in the future with higher water levels, then plants growing in pipes at lower elevations should grow more than plants growing in pipes with higher elevations.

Featured scientist: James Morris from the University of South Carolina

Additional teacher resource related to this Data Nugget: Jim has created an interactive salt marsh model called the “marsh equilibrium model”. This online tool allows you to plug in different marsh levels to explore potential impacts to the salt marsh. To explore this tool click here.

To read more about Jim’s research on “tipping points” beyond which sediment accumulation fails to keep up with rising sea level and the marshes drown, click here.

There are two publications related to the data included in this activity:

Morris, J.T., Sundberg, K., and Hopkinson, C.S. 2013. Salt marsh primary production and its responses to relative sea level and nutrients in estuaries at Plum Island, Massachusetts, and North Inlet, South Carolina, USA. Oceanography 26:78-84.
Morris, J.T., P.V. Sundareshwar, C.T. Nietch, B. Kjerfve, D.R. Cahoon. 2002. Responses of coastal wetlands to rising sea level. Ecology 83:2869-2877.

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10.20.15

Invasion meltdown

A flower of the invasive plant, Centaurea stoebe (spotted knapweed).

The activities are as follows:

Humans are changing the earth in many ways. First, by burning fossil fuels and adding greenhouse gasses to the atmosphere we are causing climate change, or the warming of the planet. Scientists have documented rising temperatures across the globe and predict an increase of 3° C in Michigan within the next 100 years. Second, we are also changing the earth by movingspecies across the globe, introducing them into new habitats. Some of these introduced species spread quickly and become invasive. Invasive species harm native species and cost us money. There is also potential that these two changes could affect one another; warmer temperatures from climate change may make invasions by plants and animals even worse.

All living organisms have a range of temperatures they are able to survive in, and temperatures where they perform their best. For example, arctic penguins do best in the cold, while tropical parrots prefer warmer temperatures. The same is true for plants. Depending on the temperature preferences of a plant species, warming temperatures may either help or harm that species.

Katie, Mark, and Jen are scientists concerned that invasive species may do better in the warmer temperatures caused by climate change. There are several reasons they expect that invasive species may benefit from climate change. First, because invasive species have already survived transport from one habitat to another, they may be species that are better able to handle change, like temperature increases. Second, the new habitat of an invasive species may have temperatures that allow it to survive, but are too low for the invasive species to do their absolute best. This could happen if the invasive species was transported from somewhere warm to somewhere cold. Climate change could increase temperatures enough to put the new habitat in the species’range of preferred temperatures, making it ideal for the invasive species to grow and survive.

A view of the plants growing in a heated ring.
Notice the purple flowers of Centaurea stoebe.

To determine if climate change will benefit invasive species, Katie, Mark, and Jen focused on one of the worst invasive plants in Michigan, spotted knapweed. They looked at spotted knapweed plants growing in a field experiment with eight rings. Half of the rings were left with normal, ambient air temperatures. The other half of the rings were heated using ceramic heaters attached to the side of the rings. These heaters raised air temperatures by 3° C to mimic future climate change. At the end of the summer, Mark and Katie collected all of the spotted knapweed from the rings. They recorded both the (1) abundance, or number of spotted knapweed plants within a square meter, and (2) the biomass (dry weight of living material) of spotted knapweed. These two variables taken together are a good measure of performance, or how well spotted knapweed is doing in both treatments.

Featured scientists: Katie McKinley, Mark Hammond, and Jen Lau from Michigan State University

Flesch–Kincaid Reading Grade Level = 10.0

10.19.15

Green crabs: invaders in the Great Marsh

Scientist Alyssa holding a non-native green crab, introduced from Europe to the American Atlantic Coast. This crab causes many problems in its new range, including the loss of native eelgrass.

The activities are as follows:

Marshes, areas along the coast that flood with each tide, are incredibly important habitats. They act as homes to large number of species, protect the coast from erosion during storms, and act as a filter for nutrients and pollution. Many species are unique to these habitats and provide crucial support to the marsh. For example, native eelgrass, a type of plant, minimizes erosion by holding sediments in place with their roots.

In an effort to help protect and restore marshes, we must understand current-day issues that are affecting their health. The introduction of non-native species, species that are not originally from this ecosystem, into a marsh may disrupt the marsh ecosystem and threaten the survival of native species. One species that has recently caused a lot of trouble is the European green crab. This crab species was accidentally carried to the Atlantic coast back in the early 1800s from Europe. Since then, they have become extremely invasive and their numbers have exploded! Compared to native crabs, the green crab digs a lot when it searches for food and shelter. This digging uproots eelgrass and causes its population numbers to fall. In many spots where green crabs have been introduced, marshes are now bare and no more grass can grow.

Non-native green crabs caught in trap that has been underwater for 25 hours

The Great Marsh is one of the coastal habitats affected by invasive green crabs. Located on the North Shore of Massachusetts, the Great Marsh is known for being the longest continuous stretch of salt marsh in all of New England. Alyssa is a restoration ecologist who is very concerned with the conservation of the Great Marsh and other important coastal ecosystems. She and other scientists are trying to maintain native species while also reducing the effects of non-native species.

A major goal for Alyssa is to restore populations of a native eelgrass. Eelgrass does more than just prevent erosion. It also improves water quality, provides food and habitat for native animal species, and acts as an indicator of marsh health. If green crabs are responsible for the loss of eelgrass from the marsh, then restorations where eelgrass is planted back into the marsh should be more successful where green crab numbers are low. Alyssa has been measuring green crab populations in different areas by laying out green crab traps for 24 hours. Alyssa has set these traps around Essex Bay, an area within the Great Marsh. She recorded the total number of green crabs caught at each location (as well as their body size and sex).

Native eelgrass growing in Essex Bay, an area within the Great Marsh

Featured scientist: Alyssa Novak, Center for Coastal Studies/Boston University. Written by: Hanna Morgensen

Flesch–Kincaid Reading Grade Level = 8.8

10.7.15

How to Escape a Predator

A stalk-eyed fly and spider interacting in the arena.

The activities are as follows:

Stalk-eyed flies are insects that have their eyes on the ends of eyestalks, or long projections from the sides of their head. Eyestalks are a sexual signal that males use to attract females. The longer the eyestalks, the more attractive a male is to females and the more mates he gets. For these flies, sexual selection leads to an elaborate trait, just like a peacock’s tail. Males with longer eyestalks have more babies and pass their traits on. Over generations, sexual selection leads to longer and longer eyestalks in males.

However, these eyestalks may come with a cost. Males with longer eyestalks may not be able to move easily and quickly. If they can’t move as fast, males with long eyestalks are potentially worse at escaping predators. Natural selection may select against long eyestalks if males with more elaborate traits are killed and eaten more often by predators. If predators eat males with longer eyestalks before the flies reproduce, they will not get to pass on their traits, regardless of how attractive they are to females.

Variation between stalk-eyed fly species in eyestalk length.

In addition to eyestalk length, other traits could affect survival in male stalk-eyed flies. Perhaps the fly’s behavior is more important than its eyestalk length when faced with a predator. When biologists Amy and John first started researching how eyestalk length affected survival, they noticed something intriguing! The flies showed many different behaviors when face to face with a spider predator. Some examples of behaviors included grooming, walking or flying towards the predator, quickly walking or flying away from the predator, displaying forelegs, and bobbing their abdomens. When prey use these antipredator behaviors, predators must put in more work to catch prey, and they will sometimes give up. Therefore, antipredator behaviors may influence the predator’s choice of prey, and certain behaviors that make prey harder to catch could lead to increased survival.

To test whether differences in eye stalk length and/or antipredator behavior were important for survival, male stalk-eyed flies were put in cages with predators. Amy and John filmed the fly behaviors and analyzed the footage. They calculated the frequency and proportion of time that flies were displaying antipredator behaviors. If males with longer eyestalks have lower survival than males with shorter eyestalks, it suggests that longer eyestalks make it harder to avoid predators. However, if eyestalk length has no effect on survival, it suggests that male flies with long eyestalks are able to compensate for their lack of speed through behavior.

Featured scientists: Amy Worthington and John Swallow from Washington State University and University of Colorado, Denver. Written by: Brooke Ravanelli from Denver Public Schools and John Swallow.

Flesch–Kincaid Reading Grade Level = 10.7

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

Worthington, A.M. and J.G. Swallow (2010) Gender differences in survival and antipredatory behavior in stalk-eyed flies. Behavioral Ecology 21 (4):759-766.

Video showing how the long eyestalks of males form!

Videos of a stalk eyed fly and spider predator together in cages. First video shows male fly displaying, grooming, and approaching spider.