Disruption to Ecosystems Student Learning Guide

1. Introduction

Congratulations! You’ve reached the last module of this course. Since biology is the study of life, it’s fitting that we end by looking at the impact that our species is having upon the living world.

2. Welcome to the Anthropocene Age and the Sixth Extinction

Some of the animals our ancestors hunted to extinction, about 10,000 years ago. By Mauricio Antón via Wikipedia. Click to enlarge.

For as long as we’ve been a species, we humans have caused significant changes to the environment. Even before agriculture, when we lived as nomadic hunter-gatherers, we never lived in peaceful harmony with the environment. As humans spread from Africa to populate the rest of the world, waves of extinctions of megafauna (large animals including woolly mammoths, mastodons, and giant sloths) quickly followed. When we spread to Europe, most European megafauna became extinct. When we spread to North America, most North American megafauna became extinct. Why? Almost certainly because of overhunting.

As our population and technological prowess have grown, so has our impact. According to many geologists, we’re now living in the Anthropocene Age (the root “anthropo-” refers to humans, as in “anthropology.” The suffix “-cene” denotes a geological age). To say that we’re living in the anthropocene is to say that humans have become the dominant biological force on the planet. Here are some of the effects our species is having on the living (and non-living) world.

  1. The Sixth Extinction: We’ve vastly accelerated the rate of extinction to somewhere between 100 and 1000 times its background rate. This rate of extinction qualifies as a mass extinction event, similar in scale to what happened when an asteroid impact wiped out the dinosaurs 65 million years ago. That was the fifth mass extinction. We’re the cause of the sixth.
  2. Invasive Species: As we’ve spread over the globe we’ve deliberately and inadvertently moved other species around the globe with us. Many of the species that have been introduced into new regions have caused significant changes in their new environments, often outcompeting or directly destroying native species. As we’ll see below, these invasive species have been a major driver of extinction.
  3. Climate Change: Combustion of fossil fuels has changed the composition of our atmosphere. Carbon dioxide, which acts as a heat-trapping greenhouse gas, has increased from about 280 ppm (parts per million) before the Industrial Revolution to over 400 ppm today. This 30% increase has caused an increase in average global temperatures of about 1° C.  This has already led to significant melting of polar and glacial ice and melting of permafrost, both of which could accelerate warming trends. It’s also causing sea levels to rise, changing rainfall patterns, and altering wildlife habitats.
  4. Ocean Acidification: Absorption of carbon dioxide by the oceans has led to ocean acidification, which has affected marine life such as coral (which can’t form their exoskeletons if the pH is too low). As a result, coral reefs are in decline around the world.

3. What The Matrix Gets Right (and Wrong) about Humans and Biodiversity

One of my favorite movies is The Matrix. This science fiction movie is about a band of humans who are trying to free the rest of humanity from enslavement by an artificial intelligence that has all of humanity trapped inside a vast computer simulation. Within that simulation, “intelligent agents” keep humans under control.

Here’s how one of these intelligent agents — Agent Smith (played by Hugo Weaving)— explains himself to Morpheus, one of the leaders of the human resistance movement (played by Laurence Fishburne).

My guess is that their might be copyright issues with this excerpt, and that YouTube won’t allow this video to last for very long, so here’s a transcript of what Agent Smith says to Morpheus. Please email me if the video is missing.

Agent Smith: I’d like to share a revelation that I’ve had during my time here. It came to me when I tried to classify your species. I realized that you’re not actually mammals. Every mammal on this planet instinctively develops a natural equilibrium with the surrounding environment but you humans do not. You move to an area and you multiply and multiply until every natural resource is consumed. The only way you can survive is to spread to another area. There is another organism on this planet that follows the same pattern. Do you know what it is? A virus. Human beings are a disease, a cancer of this planet. You are a plague, and we are the cure.

Agent Smith gets a few things right: For tens of thousands of years, our pattern as a species was to move to an area and consumed the resources there, and then move on. That’s what nomadic hunter gatherers do. This worked fairly well when all of Earth’s human population numbered no more than 10,00,000 or so (the estimated number before the dawn of agriculture, about 10,000 years ago). We might have hunted the woolly mammoth and the giant sloth to extinction, but the Earth’s basic systems were relatively unharmed.

But it’s not true that “Every mammal on this planet instinctively develops a natural equilibrium with the surrounding environment.” Every mammal exploits its environment as effectively as it can. If an equilibrium is reached, it’s because of regulation from below (a lack of resources such as food) or from predators, parasites, or competitors that keep population in check.

We humans have been doing what every animal does. We’ve tried to exploit our environment as effectively as we can, and to reproduce as much as is natural for our species. The problem is that we’re so smart that we figured out (for the most part) how to expand our food supply, to destroy or marginalize our potential predators, to outcompete our competitors, and cure ourselves (mostly) of parasites. With the advent of agriculture and then industrialization, this has allowed our population to expand into the billions, and allowed us to modify the environment to meet our ends. That, however, has been disastrous for most of the other species we share the planet with. Hence, the Sixth Extinction of the Anthropocene.

Let’s see what we’ve done.

4. Destruction of Habitat

All of the following activities have taken natural habitats that other species live in, and converted them into the artificial, non-natural habitats where humans live, play, and work.

  1. Development of housing and urban areas, commercial and industrial areas, developed recreation areas (golf courses, skiing areas, etc. )
  2. Agriculture and aquaculture.
  3. Energy production and mining.
  4. Fishing methods such as bottom trawling for shellfish or dredging. These types of fishing drag nets along the ocean floor, damaging or destroying whatever they encounter.
  5. Forestry methods such as clear cutting.
  6. Natural system modification that changes habitats. This includes
    1. Fire suppression and/or Increasing fire frequency
    2. Damming rivers

Once converted into artificial habitats, the species that used to inhabit that area have to flee or perish.

If an animal or plant is endangered or threatened, habitat loss or degradation is the most likely cause. 80% of all threatened birds are experiencing habitat loss or degradation. The same is true for 83% of all threatened mammals, and 91% of all threatened plants.

Note that none of these activities are bad in and of themselves. People need houses, food, materials, energy, and so on. It’s the extent to which we’ve utilized the surface of our planet to do the following.

How much of the Earth’s surface have humans developed? In a 2012 report by the Geological Society of America, Roger Hooke and Jose Martin Duque estimated that humans have modified more than 50% of the Earth’s land surface. 

5. Habitat Fragmentation

5a. What is Fragmentation?

[qwiz]

[q]Imagine that you’re a forest manager. One of your goals is maintaining the biodiversity of your forest. But you’re also responsible for harvesting timber. To meet your goals, you can choose to create one large, undisturbed reserve, and harvest the timber outside of it. This is what’s labeled as “contiguous” below.  Or you could create many smaller reserves. This is labeled as”fragmented.” Note that the green area in both panels has the same area.

From Biodiversity Conservation in Canada by Richard Schneider.

Which situation would help you to best meet both goals?

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[f]IOKAiklmIHlvdXIgYW5zd2VyIHdhcyAmIzgyMjA7Y29udGlndW91cyYjODIyMTsgeW91IG1hZGUgdGhlIHJpZ2h0IGNob2ljZS4gUmVhZCBiZWxvdyB0byBsZWFybiB3aHku

[/qwiz]

In addition to destroying habitat, one of the main ways that humans have affected the environment has been to fragment it into discontinuous, unconnected pieces. For any non-flying species, any difficult-to-cross highway will cut their territory into separate fragments. Even flying species like bats and birds might refrain from flying from an enclosed habitat (like a forest) through open territory to get to the next bit of forest.

Fragmentation causes several problems for the species living in these fragments .

5b. Fragmentation results in insufficient area for populations to maintain themselves

Depending on its ecological niche, any population of a species needs a certain amount of area to maintain itself. For top level carnivores, a sustainable amount of area can be difficult to fit within any sized reserve, much less a fragment of a reserve. A pride of lions, for example, needs 20 square kilometers to maintain itself when prey is abundant. If prey is scarce, that same pride might need 400 square km. (source: Britannica).  A wolf pack needs 130 square kilometers to sustain itself when prey is abundant. That number increases to 2600 square kilometers when prey is scarce. (source: US Fish and Wildlife Service).

5c. Fragmentation causes population bottlenecks

To avoid a population bottleneck that leads to loss of genetic diversity, populations need to 1) maintain themselves above a certain minimum level, and 2) exchange genes with neighboring populations. To stick with the example of lions, an area with only one or two prides is prone to a population bottleneck where random genetic drift will cause each small population to lose genetic diversity. To prevent that, each pride needs its territory to adjoin with an adjacent pride’s territory. This allows for genes to flow between prides, and keeps each pride from suffering from inbreeding. In an isolated fragment, that’s exactly what happens: populations experience a bottleneck that leads to inbreeding and  loss of genetic diversity through genetic drift.

5d. The Edge Effect

The boundary of any natural area has an edge, and the environment at the edge is often quite different from the environment in the interior. As you can see at left, fragmented areas have much more edge habitat. This habitat experiences much more disturbance, which creates stress for the organisms living at the edge.

One of the largest studies of the edge effect is the Biological Dynamics of Forest Fragments Project. This project, set in Brazil’s Amazon rainforest, involves dozens of study fragments of different sizes, along with undisturbed areas of equal size deep within undisturbed tracts of forest. These fragments and the control areas have been studied for over 40 years.

Here’s an example of what researchers found. (source: Brazil’s Fragmented Forests).

The open flank of a newly created clearing leaves the remaining forest more vulnerable to wind and weather. Wind shear and turbulence forces on the forest edge lead to a higher tree mortality. Desiccation caused by the inferior water retention capacity of the clearing adds to the damage…Research has shown that the drier air above a clearing can then suck the moisture out of the adjoining forest and cause desiccation penetrating hundreds of metres deep into the forest. Recent satellite measurements of moisture in the canopy even indicate that the effects can still be felt 2.7 kilometres away from the nearest forest edge.

5e. Fragmentation and the Extinction Vortex

When a population is stuck in a fragment of insufficient size, it can get sucked down into a death spiral called the extinction vortex. A whirlpool above a drain is an example of a vortex. In the same way that a vortex pulls water down a drain, an extinction vortex pulls a population toward extinction. The extinction vortex works like this:

  1. Ecological disturbances make it difficult for a species to successfully exploit its niche. As a result, there’s a decrease in the population size. Fragmentation increases the chance that the population will be isolated
  2. This lowered size leads to genetic drift, which decreases genetic variability.
  3. Decreased variability makes the population less fertile and less able to adapt to change.
  4. Additional disturbances lead to further population decline.

Because the system is a positive feedback loop, species that enter the vortex often quickly decline toward extinction.

6. Threats to Biodiversity (part 1): Checking Understanding

[qwiz qrecord_id=”sciencemusicvideosMeister1961-threats to biodiversity 1″]

[h]Threats to Biodiversity, quiz 1

[i]

[q]Because of humanity’s ongoing impact upon the Earth’s systems, the current age has come to be known as the [hangman]

[c]YW50aHJvcG9jZW5l

[q]Loss of biodiversity caused by human activities is giving rise the Earth’s sixth [hangman] [hangman].

[c]bWFzcw==

[c]ZXh0aW5jdGlvbg==

[q]A major driver of extinction has been the many fast-growing species that humans have introduced throughout the world. When these introduced species spread and outcompete native species, they become known as [hangman] species.

[c]aW52YXNpdmU=

[q]Combustion of fossil fuels has changed the amount of [hangman] [hangman] in the atmosphere. Because this gas is a greenhouse gas, it’s causing [hangman] change. This is disrupting the [hangman] of many plants and animals.

[c]Y2FyYm9u

[c]ZGlveGlkZQ==

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[q]When carbon dioxide is absorbed by the oceans, it creates carbonic acid. This is causing ocean [hangman]. One immediate effect has been the decline of one of the oceans most biologically diverse habits: [hangman] reefs

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[q]Development of cities, farms, recreation areas have all resulted in the destruction of wildlife [hangman].

[c]aGFiaXRhdA==

[q labels = “top”]If an animal or plant is ______________ or threatened, ____________ loss or ______________ is the most likely cause. Note that the problem isn’t development in and of itself. The problem is the _____________ to which development has modified the surface of the Earth: up to 50% of the Earth’s surface has been in someway ___________ by human activity.

[l]degradation

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]endangered

[fx] No. Please try again.

[f*] Correct!

[l]extent

[fx] No. Please try again.

[f*] Good!

[l]habitat

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]altered

[fx] No. Please try again.

[f*] Great!

 

[q]Habitat [hangman] occurs when humans divide wildlife habitat into discontinuous, unconnected pieces.

[c]ZnJhZ21lbnRhdGlvbg==

[q]Particularly for [hangman] species like wolves and lions that are at the top of the [hangman] [hangman], the problem with fragmentation is that the remaining area can be insufficient for these animals to find enough prey to sustain themselves

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[c]Zm9vZA==

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[q]Fragmentation also leads the populations trapped within the fragment to experience a population [hangman]. Without [hangman] flow from adjacent populations, each isolated population will experience [hangman] drift, leading to a loss of genetic [hangman].

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[c]Z2VuZQ==

[c]Z2VuZXRpYw==

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[q]Assume that the two images below represent proposed nature reserves. The problem with proposal 2 is the the four combined fragments will have much more [hangman] habitat than proposal 1. This habitat will be unsuitable for species that require the environment that’s only available in the interior. As a result, you can predict that overall [hangman] will be lower in proposal 2. In addition, the populations in each fragment in proposal 2 will be smaller, subjecting them to more genetic [hangman].

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[q labels = “top”]Small populations can also become trapped in a disastrous __________ feedback loop called an ____________  _________. In this situation, small size leads to a lack of _________ diversity, which reduces ________, which lowers the rate of  _____________, which further reduces population size.

[l]extinction

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]fitness

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]genetic

[fx] No. Please try again.

[f*] Excellent!

[l]positive

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]reproduction

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]vortex

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[x]

[/qwiz]

7. Overharvest/Hunting to Extinction

As omnivores, humans have always harvested animals for food (or other animal parts, such as skins, bones, guts, or horns). In terms of biodiversity, this is only a problem when harvest becomes overharvest. As discussed above, humans have an ancient legacy of hunting their prey to extinction. This goes back at least as far as the extinction of animals like woolly mammoths 10,000 years ago.

American Bison, Montana, USA

With modern hunting methods, this process has accelerated. In the 1800s, the American Bison was nearly hunted to extinction. Their numbers were reduced from 60,000,000 just a few hundred animals by 1900. (source: wikipedia). Under subsequent protection, they now number about 500,000.

The Passenger Pigeon

A North American bird called the passenger pigeon was once thought to be the most abundant bird in the world. Witnesses from the 1800s reported how it could take hours for a single flock to pass overhead. Overhunting led this species to become extinct in 1914, when the last surviving Passenger Pigeon died in the Cincinnati Zoo.

Other animals that have become extinct because of overharvest include:

  • The Stellar’s Sea Cow (a northern relative of the manatee, extinct since 1768)
  • The Bubal Hartebeest (an antelope that lived in Northern Africa and the Middle East, extinct since the mid-1900s).
  • The Pyrenean Ibex (a wild goat that lived in the Pyrenees Mountains between Spain and France, extinct since 2000).
  • The Western Black Rhino. This rhinoceros population was hunted to extinction within the last decade. Rhinos are killed for their horns, which are used in traditional Chinese and Vietnamese medicine. There are five existing rhinoceros species, and all are endangered.
Tasmanian Wolf

Animals that have been killed for predator control include:

  • The Grizzly Bear: The last Grizzly in California was killed in 1922. Ironically, California’s official animal is the Grizzly bear.
  • The Gray Wolf: The gray wolf was wiped out in the lower 48 states in 1926. However, wolves were reintroduced into Yellowstone National Park in 1995.
  • The Tasmanian Wolf: The Tasmanian wolf, which lived in New Guinea, Australia, and Tasmania, became extinct in the 1930s.

While there’s a growing movement for sustainable fishing, many fish stocks have been overexploited. According to the Food and Agriculture Organization of the United Nations, “the state of marine fishery resources…has continued to decline.” Whereas the proportion of sustainable fish stocks was 90% in 1974, that number fell to 65.8% in 2017.

8. Introduced/Invasive Species

Introduced species (also known as non-native or exotic species)  are species that were moved intentionally or accidentally from one location to another. In that new area, freed from the controls that kept their population in check, they often grow exponentially. If that’s the case, they become biological invaders: invasive species.

A few characteristics predispose species to becoming invaders. See if you can complete the following table.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-traits of invasive species”]

[h]Traits of invasive species

[q labels = “top”]

  1. ________ growth
  2. Rapid _______________.
  3. High ____________ ability
  4. _____________ plasticity: able to to alter their ________ to suit current _____________.
  5. ____________ of a wide range of environmental conditions.
  6. For animals, an ability to live off of a _______ range of food types (____________, rather than specialist)

[l]conditions

[fx] No. Please try again.

[f*] Correct!

[l]dispersal

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]form

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]generalist

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]Phenotypic

[fx] No. Please try again.

[f*] Great!

[l]Rapid

[fx] No. Please try again.

[f*] Good!

[l]reproduction

[fx] No. Please try again.

[f*] Great!

[l]Tolerance

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]wide

[fx] No. Please try again.

[f*] Correct!

[/qwiz]

Credit: Mark Marek Photography, via Wikipedia

You don’t have to look far to find invasive species. They’re everywhere. If you have a house cat, then you own a particularly destructive invasive species. House cats kill between  1.3–4.0 billion birds and 6.3–22.3 billion mammals annually. These kills are both by pets and feral cats (cats without an owner that live on their own). Source: Nature Communications, The American Bird Conservancy.

Rats are another invasive species. They’re responsible for 40 to 60 percent of all bird and reptile extinctions on islands. (source) The famously extinct Dodo bird of the island of Mauritius, once thought to have been hunted to death by Dutch sailors who first reached the island in the 1600s, was probably done in by rats, which raided Dodo nests and destroyed their eggs.

European Starling

While birds are often the victims of invasive species, certain bird species are also invasive. The European Starling was released into New York’s Central Park by Shakespeare enthusiasts in the 1890s (because starlings are mentioned in Shakespeare’s plays). Now there are 200 million starlings in North America. They compete with native birds for nest sites, and with other insect-eating birds for food.

The House Sparrow, one of the most commonly seen birds in North America, is another invasive bird species. These birds were introduced into Brooklyn, New York, in 1851. Additional introductions occurred in San Francisco and Salt Lake City in the 1870s. Since 1900, they’ve been established in all of the lower 48 states.

Worldwide amphibian declines caused by Bd. Source: Science Magazine.

As we saw above, amphibians are the vertebrate clade that’s experiencing the highest rate of extinction, with over 40% of the world’s 8000 species listed as threatened or endangered. Why? The main cause is an invasive fungal pathogen called Batrachochytrium dendrobatidis (Bd). According to Australia’s department of Sustainability,

The fungus invades the surface layers of the frog’s skin, causing damage to the outer keratin layer. Amphibian skin is unique because it is physiologically active, allowing the skin to tightly regulate respiration, water, and electrolytes. It is not yet known exactly how the fungus kills amphibians but it is thought that it may cause mortality through disrupting the normal function of the skin resulting in electrolyte depletion and osmotic imbalance.

Bd has caused declines in 500 amphibian species worldwide, and driven dozens to extinction. The map above shows the extent of amphibian decline worldwide.

Kudzu overgrowing an area near Atlanta, Georgia

Plants can be invasive, too. As they spread, they can overrun entire ecosystems, outcompeting native plants and disrupting food webs, causing biodiversity losses. The image at left shows one invasive plant called kudzu. Kudzu, which originated in Asia, was promoted as an ornamental plant and later grown for forage (food for animals) in the southeast. Millions of acres were deliberately planted to reduce soil erosion in deforested areas. But with an ability to grow up to a foot each day, kudzu has overgrown entire forests.

Invasive species can cause huge agricultural losses. 

  • The Asian Citrus Psyllid is a gnat-sized insect. It carries a bacterium that causes citrus greening, a disease that kills citrus trees.
  • The European Gypsy Moth is originally from France. It was introduced into the United States in the 1890s. Its caterpillars devour budding leaves, which can weaken and kill a variety of trees such as oaks, maples, apples, aspens, willow, birch, and pine. Its relative, the Asian Gypsy moth, has recently been detected in Washington State, Oregon, Oklahoma and South Carolina. With a wider host range than its European cousin, it’s feared that the Asian Gypsy moth could cause significant damage throughout the United States and Canada.
  • Cryphonectria parasitica is a parasitic fungus that attacks chestnut trees, causing a disease called chestnut blight. Introduced into the United states in the 1900s, it killed an estimated 4 billion chestnut trees. These trees were habitat for many native species of birds, insects, etc, so that loss of chestnuts had cascading ecological effects.

8a. Interactive Species Case Study: The Japanese Barberry

Japanese Barberry

Let’s look in a bit more detail at how an invasive plant species, the Japanese Barberry, can have effects that cascade throughout an ecosystem.

The Japanese Barberry, shrub with green leaves and bright red fruit, was introduced to North America as an ornamental plant in 1975. It soon began to spread, growing in dense, prickly thickets.

Unlike other shrubs, the barberry is avoided by deer, enabling it to grow without any top-down control.

In a recent study, Japanese barberry was found to reduce the number of arthropod herbivores (such as insect larvae or caterpillars) and predators (such as spiders). Species richness was “significantly lower in the leaf-litter around the Japanese barberry and on the … plants themselves.” Compared to otherwise similar landscapes that had not been invaded, the barberry-infested community structure is much less complex, a process known as “trophic downgrading.”

Use the interactive diagram below and the questions that follow it to demonstrate your understanding of the Japanese Barberry’s effect upon biodiversity. The term detritivore refers to an an organism that eats detritus — leaves and other organic material that falls to the ground.

[qwiz style=”width: 700px !important; min-height: 700px !important;” qrecord_id=”sciencemusicvideosMeister1961-Invasive species case study”]

[h] Interactive Case Study: The Japanese Barberry

[q labels = “top”]In the diagram below, label the lines and the trophic levels.

 

[l]detritivore

[f*] Excellent!

[fx] No, that’s not correct. Please try again.

[l]direct effects

[f*] Correct!

[fx] No. Please try again.

[l]indirect effects

[f*] Great!

[fx] No, that’s not correct. Please try again.

[l]herbivore

[f*] Correct!

[fx] No. Please try again.

[l]leaf litter

[f*] Correct!

[fx] No. Please try again.

[l]leaves

[f*] Correct!

[fx] No, that’s not correct. Please try again.

[l]predator

[f*] Great!

[fx] No, that’s not correct. Please try again.

[q]Let’s summarize. The lines at 1, 2, 4, and 5 are showing the [hangman] effects of the Japanese Barberry. These include [hangman] the biomass and richness of the [hangman] in niche A. The effect is the same upon the detritivores in niche B. That creates an [hangman] effect upon the [hangman] in niche C. Together, these effects add up to an overall decrease in [hangman].

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[c]ZGVjcmVhc2luZw==

[c]aGVyYml2b3Jlcw==

[c]aW5kaXJlY3Q=

[c]cHJlZGF0b3Jz

[c]YmlvZGl2ZXJzaXR5

[q]Here’s a graph of arthropod abundance upon Japanese Barberry and native shrubs. Abundance, ecologically speaking, is the number of individuals/species. Based on what you’ve read above, which letter represents the Japanese Barberry?

[textentry single_char=”true”]

[c]IE E=

[f]IENvcnJlY3QuIEFidW5kYW5jZSBpcyBzaWduaWZpY2FudGx5IGxvd2VyIGluIEEsIGFuZCB0aGF0JiM4MjE3O3Mgd2hhdCB3ZSYjODIxNztkIGV4cGVjdCBmcm9tIHRoZSBkaXZlcnNpdHkgaW1wYWN0cyBjYXVzZWQgYnkgYW4gaW52YXNpdmUgc3BlY2llcyBsaWtlIHRoZSBKYXBhbmVzZSBCYXJiZXJyeS4=

[c]IEVudGVyIHdvcmQ=

[c]ICo=

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[q multiple_choice=”true”]In the graph below the difference between data point “A” and “B” is significant

[c]YmVjYXVzZSBpdCYjODIxNztzIGEgcmVhbGx5IGJpZyBkaWZmZXJlbmNl

[f]Tm8uIEl0JiM4MjE3O3Mgbm90IHRoZSBzaXplIG9mIHRoZSBkaWZmZXJlbmNlIGJldHdlZW4gdHdvIHNldHMgb2YgZGF0YSB0aGF0IGRldGVybWluZXMgd2hldGhlciB0aGUgZGlmZmVyZW5jZSBpcyBzdGF0aXN0aWNhbGx5IHNpZ25pZmljYW50IG9yIG5vdC4=

[c]YmVjYXVzZSB0aGUgbWVhbiB2YWx1ZSBhdCAmIzgyMjA7QSYjODIyMTsgaXMgbW9yZSB0aGFuIDAuNSB1bml0cyBsb3dlciB0aGFuIHRoZSB2YWx1ZSBhdCAmIzgyMjA7Qi4mIzgyMjE7

[f]Tm8uIEl0JiM4MjE3O3Mgbm90IHRoZSBzaXplIG9mIHRoZSBkaWZmZXJlbmNlIGJldHdlZW4gdHdvIHNldHMgb2YgZGF0YSB0aGF0IGRldGVybWluZXMgd2hldGhlciB0aGUgZGlmZmVyZW5jZSBpcyBzdGF0aXN0aWNhbGx5IHNpZ25pZmljYW50IG9yIG5vdC4gSGVyZSYjODIxNztzIGEgaGludDogTG9vayBhdCBob3cgdGhlIGF1dGhvcnMgYXJlIGdyYXBoaW5nIHRoZSBkYXRhLiBMb29rIGF0IHRoZSBlcnJvciBiYXJzLg==

[c]YmVjYXVzZSB0aGVyZSYjODIxNztzIG5vIG92ZXJsYXAgYmV0d2VlbiB0aGUgZXJyb3IgYmFycyBhdCAmIzgyMjA7QSYjODIyMTsgYW5kIC YjODIyMDtCLCYjODIyMTsgaW5kaWNhdGluZyB0aGF0IHRoZSBkaWZmZXJlbmNlIHdhcyBzdGF0aXN0aWNhbGx5IHNpZ25pZmljYW50Lg==

[f]VGhhdCYjODIxNztzIGV4YWN0bHkgcmlnaHQuIFdoZW4gdGhlcmUmIzgyMTc7cyBubyBvdmVybGFwIGJldHdlZW4gdGhlIGVycm9yIGJhcnMsIGl0IG1lYW5zIHRoYXQgdGhlIGRpZmZlcmVuY2Ugd2FzIHN0YXRpc3RpY2FsbHkgc2lnbmlmaWNhbnQu

[q]A correct interpretation of the graph below is that as the density of Japanese barberry [hangman], arthropod abundance [hangman]. And, based on the error bars in the graph, we know that the difference is statistically [hangman] because there’s no [hangman].

[c]aW5jcmVhc2Vz

[c]ZGVjcmVhc2U=

[c]c2lnbmlmaWNhbnQ=

[c]b3ZlcmxhcA==

[/qwiz]

9. There are many other threats to biodiversity

There are entire courses devoted to learning about threats to biodiversity. The ones listed above are most relevant to an AP Biology course. But there are others, including pollution and climate change. One effect of pollutants in the environment is biological magnification, which you can learn about by following the preceding link to our module on Trophic Levels and Ecological pyramids. If you’re interested in learning more about climate change, you can go to this page for a series of music videos and a tutorial about the Greenhouse effect and Global warming.

10. Threats to Biodiversity Part 2: Checking Understanding

[qwiz qrecord_id=”sciencemusicvideosMeister1961-threats to biodiversity 2″]

[h]Threats to biodiversity, part 2

[i]

[q]The American Bison and the passenger pigeon are examples of species that have suffered from [hangman].

[c]b3Zlcmh1bnRpbmc=

[q]California Grizzly bears, the Gray Wolf, and the Tasmanian wolf were hunted to extinction or to the brink of extinction in the name of [hangman] control.

[c]cHJlZGF0b3I=

[q]When an introduced species starts to grow exponentially in its new environment, it can become what’s called an [hangman] species. Such species often have very high rates of [hangman].

[c]aW52YXNpdmU=

[c]cmVwcm9kdWN0aW9u

[q]One of the most destructive invasive species in North America is the [hangman], which is commonly owned as a pet. These animals are responsible for the death of over a [hangman] birds every year.

[c]aG91c2VjYXQ=

[c]YmlsbGlvbg==

[q]Most invasive species can make a living from many food sources, rather than one. In other words, they tend to be [hangman], rather than the more specialized native species that they often outcompete.

[c]Z2VuZXJhbGlzdHM=

[q labels = “top”]The diagram below shows the effect of the fox, which is an invasive species in Australia, upon the quoll, a marsupial that’s native to Australia. Based on the diagram, the quoll is a __________ consumer. Therefore it’s in _____________ with the fox for resources. The fox has a ________ impact on the grasshopper and the dragonfly. It’s effect upon the quoll is ________. Because the fox and the quoll share a large part of their ecological _________, the principle of competitive __________ suggests that only one of them will survive. Because it can take a _________ variety of prey, the winner of this competition will probably be the fox. Again we see how the effect on an invasive species is to reduce ____________.

[l]biodiversity

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]competition

[fx] No. Please try again.

[f*] Correct!

[l]direct

[fx] No. Please try again.

[f*] Correct!

[l]exclusion

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]indirect

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]niche

[fx] No. Please try again.

[f*] Correct!

[l]tertiary

[fx] No. Please try again.

[f*] Excellent!

[l]wider

[fx] No, that’s not correct. Please try again.

[f*] Great!

[q multiple_choice=”true”]When introduced into a new area, the most likely thing that an invasive species will do is

[c]aW50ZXJicmVlZCB3aXRoIGNsb3NlbHkgcmVsYXRlZCBuYXRpdmUgc3BlY2llcw==

[f]Tm8uIEl0JiM4MjE3O3MgdW5saWtlbHkgdGhhdCB0aGUgaW52YWRlciB3b3VsZCBiZSBjbG9zZWx5IHJlbGF0ZWQgZW5vdWdoIHRvIGEgbmF0aXZlIHRvIGludGVyYnJlZWQu

[c]aW50ZWdyYXRlIHRoZW1zZWx2ZXMgaW50byBleGlzdGluZyBmb29kIHdlYnMsIGtlZXBpbmcgdGhvc2UgZm9vZCB3ZWJzIGludGFjdC4=

[f]Tm8uIFJlbWVtYmVyIHRoYXQgaW52YXNpdmUgc3BlY2llcyBnZW5lcmFsbHkgY2F1c2UgYmlvZGl2ZXJzaXR5IGxvc3Nlcy4gV2hpY2ggb2YgdGhlIGNob2ljZXMgd291bGQgaW5kaWNhdGUgdGhhdD8=

[c]Z3JvdyBleHBvbmVudGlhbGx5IGFuZCBv dXRjb21wZXRlIG5hdGl2ZSBzcGVjaWVz

[f]TmljZSBqb2IuIEludmFzaXZlIHNwZWNpZXMgdGVuZCB0byBncm93IGV4cG9uZW50aWFsbHkgYW5kIG91dGNvbXBldGUgbmF0aXZlIHNwZWNpZXMu

[c]ZGV2ZWxvcCBzeW1iaW90aWMgcmVsYXRpb25zaGlwcyB3aXRoIHNwZWNpZXMgdGhhdCBoYXZlIGNvbXBsZW1lbnRhcnkgYWRhcHRhdGlvbi4=

[f]Tm8uIFJlbWVtYmVyIHRoYXQgaW52YXNpdmUgc3BlY2llcyBnZW5lcmFsbHkgY2F1c2UgYmlvZGl2ZXJzaXR5IGxvc3Nlcy4gV2hpY2ggb2YgdGhlIGNob2ljZXMgd291bGQgaW5kaWNhdGUgdGhhdD8=

[q]Invasive species like the Japanese Barberry are said to cause trophic “downgrading.” This is another way of saying the the communities that are invaded become [hangman] complex.

[c]bGVzcw==

[q]By reducing the populations of their competitors and prey, invasive species can force native species to enter an extinction [hangman] that can be hard to escape from.

[c]dm9ydGV4

[/qwiz]

11. What can be done?

Stemming the tide of the sixth extinction will require changes in the way we humans interact with one another and with the natural world. Some of these changes include

  • Controlling human population growth. The Earth is finite. To large degree, more people on the planet means more resources (especially land) that get allocated to meeting human needs. The more land that gets devoted to human needs, the less undeveloped habitat there is for wildlife.A hopeful trend already underway is that the growth rate for the human population is dropping. This process is called the demographic transition. We covered it in this tutorial about population growth.Elevating the economic and educational status of women —a good thing in and of itself— is the most effective way to limit human population growth. Why? Because women with more economic and educational opportunities tend to have smaller families, simply because they have their first child later in life. So promoting women’s equality worldwide helps humanity, and promotes diversity.
  • Shifting from fossil fuels to renewable energy in order to reduce climate change. Anthropocentric climate change is creating habitat disturbances at a rate that wildlife can’t adapt to. If we want to maintain habitat, especially in tropical areas that are the highest in biodiversity, we need to slow the rate of human-caused climate change (or stop it altogether). To do that, we need to stop releasing carbon dioxide and other greenhouse gases into the atmosphere.  And to do that, we need to shift from fossil fuel combustion in cars, factories, and powerplants to non-carbon based energy sources like wind and solar.

These changes are outside the scope of an AP or freshman Biology course. But we can take some actions to rescue and preserve species that are in (or on the verge of entering) the extinction vortex. So to start, let’s review how the extinction vortex works.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-extinction vortex review”]

[h]Reviewing the Extinction Vortex

[q labels = “top”]

 

[l]smaller population

[fx] No. Please try again.

[f*] Great!

[l]less fertility, more mortality

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]genetic drift

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]loss of genetic diversity

[fx] No. Please try again.

[f*] Excellent!

[/qwiz]

11a. Protecting endangered species

Species are disappearing at such an high rate that many are being lost before we can take any action. However, legislation like the US’s Endangered Species act, passed in 1973, has made it a legal obligation to “protect and recover imperiled species and the ecosystems upon which they depend” (US Fish and Wildlife Service). Because of laws like the Endangered Species Act, many species are recovering from direct or indirect threats. This includes the California condor, the Black Footed Ferret, the Florida Manatee, the American Alligator, and many others (see this article in the Washington Post).

11b. Renewing Genetic Variation in Declining Populations

In some cases, it’s possible to introduce genetic diversity into a declining population. This was what was done to prevent the Illinois population of the Greater Prairie Chicken from becoming extinct.

Greater Prairie Chickens are known for their incredible mating displays. Here’s how this is described in All About Birds from Cornell University.

Few performances in the bird world are more memorable than the dawn display of Greater Prairie-Chickens at their booming ground, or lek—the traditional spot where males dance, call, and try to impress females with their vigor. When displaying, the males erect ear-like plumes on the head and blow up bright orange air sacs on the neck, transforming themselves from brownish chicken-like birds into brightly colored performers, all the while drumming with their feet and producing whooping and cackling calls.

Here’s a short video of a these birds in action.

Based on historical records, Greater Prairie chickens in Illinois had experienced a steep decline in numbers and distribution, as shown below.

Based on everything you’ve learned above, you could expect that  by 1994, the two isolated Illinois populations were experiencing genetic drift and reduced fertility.

 

You can see this in the graph below. The triangles show the number of males observed at the breeding areas. The circles represent the percentage of eggs hatched, and the numbers below the error bars represent the number of nests.

By the late 1980s, the number of males on the breeding grounds had declined to perilously low levels. The total number of birds in Illinois was less than 50. Following the prediction that low population leads to lowered fertility, the percentage of eggs hatching was also dropping. During several years during the 1980s, success rates fell below 80%, and there was a steep decline in successful egg hatching in 1990.

To reverse the slide toward extinction, researchers brought in 271 Greater Prairie chickens from large populations in Minnesota, Kansas, and Nebraska. While some transplanted birds didn’t survive beyond their first year, others did, and integrated into the breeding population.

The results can be seen in the years following 1992, with the percentage of eggs hatching rising to 94%. This was accompanied by an increase in the number of males displaying on breeding grounds.

Obviously, this kind of intervention only worked because there were other populations whose genetic variability could be used to replenish the gene pool of the Illinois population. For isolated populations in steep decline, that might not be possible.

11c. Proper nature reserve design is key

A nature reserve is an area that’s managed to preserve its plants, animals, and physical features. Let’s start by applying some of the principles we’ve covered in this tutorial to the design of nature reserves.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-nature reserve design”]

[h] Nature reserve design

[q labels = “top”]The images below show different reserve designs. Label them as “better” or “worse.”

 

[l]better

[f*] Good!

[fx] No, that’s not correct. Please try again.

[l]worse

[f*] Correct!

[fx] No. Please try again.

[q labels =”top”]Now try again with these reserve designs.

 

[l]better

[f*] Excellent!

[fx] No. Please try again.

[l]worse

[f*] Correct!

[fx] No. Please try again.

[q] Let’s analyze these reserves in a bit more detail. All the the reserves in column B are better at preserving biodiversity because they allow for a [hangman] population size (begins with “l”). This reduces genetic [hangman]. Clustering several reserves near to one another allows for [hangman] flow between adjacent populations.

[c]IGxhcmdlcg==

[f]IEdvb2Qh

[c]IGRyaWZ0

[f]IENvcnJlY3Qh

[c]IGdlbmU=

[f]IEdvb2Qh

[q] The corridor in the top left of the diagram below is an even more direct method of allowing for gene [hangman] between adjacent populations. Having diverse ecosystems allows for more complex animal habitat needs. For example, amphibians need both freshwater habitat, and terrestrial habitat. The advantage of the round reserve over the thin reserve is that the round reserve has less [hangman]. In other words, the thin habitat might have no viable interior [hangman].

[c]IGZsb3c=

[f]IEdyZWF0IQ==

[c]IGVkZ2U=

[f]IEdvb2Qh

[c]IGhhYml0YXQ=

[f]IEV4Y2VsbGVudCE=

[/qwiz]

11c. Protect Biodiversity Hotspots

We’ve seen that in some cases, direct interventions can prevent species from becoming extinct. We’ve also looked at how nature reserves can be designed to

  • minimize fragmentation,
  • minimize the edge effect,
  • be large enough to support the wildlife living inside of them
  • maximize healthy population size and gene flow between adjacent wildlife populations.

Another move can be to protect biodiversity hotspots. 

Biodiversity Hotspots. Key to the 35 areas is available on Wikipedia.

Biodiversity hotspots are high biodiversity areas that are under threat. They

  1. Have at least 1500 endemic plant species. Endemic species are those found in one location, and nowhere else. A high diversity of endemic plants is often an indicator of high diversity of all types of wildlife.
  2. Have less than 30% of their original vegetation (because of habitat destruction or degradation).

Around our planet, 36 areas have been identified as hotspots. These areas cover only 2.4% of the Earth’s surface, but they support more than half of the world’s plant species. The hottest hot spots — with a total area of only 1.5% of the Earth’s surface — are home to about a third of the Earth’s birds, amphibians, mammals, and plants.

12. Disruptions to Ecosystems, Cumulative Quiz

[qwiz qrecord_id=”sciencemusicvideosMeister1961-ecosystem disruption cumulative quiz”]

[h] Disruptions to Ecosystems

[i] Biohaiku

The Sixth Extinction.

Anthropocene Legacy

That will long endure

[q] The name of the age in which humans have become the dominant biological force is the [hangman].

[c]IEFudGhyb3BvY2VuZQ==

[f]IEdyZWF0IQ==

[q] A key process that’s driving the biodiversity losses of the Sixth Extinction is human destruction of wildlife [hangman].

[c]IGhhYml0YXQ=

[f]IEV4Y2VsbGVudCE=

[q] Sometimes habitat isn’t completely lost. But its quality can be  [hangman] (begins with “d”) to the point where wildlife can no longer live in it.

[c]IGRlZ3JhZGVk

[f]IEV4Y2VsbGVudCE=

[q multiple_choice=”true”] It’s been estimated the humans have modified ______ percent of the Earth’s land surface.

[c]IDEw

[f]IE5vLiBNb3JlIHRoYW4gMTAlLg==

[c]IDMw

[f]IE5vLiBNb3JlIHRoYW4gMjAl

[c]ID Uw

[f]IEV4YWN0bHkuIEh1bWFucyBoYXZlIG1vZGlmaWVkIGFib3V0IDUwJSBvZiB0aGUgRWFydGgmIzgyMTc7cyBsYW5kIHN1cmZhY2Uu

[c]IDkw

[f]IE5vLiBJdCYjODIxNztzIGxlc3MgdGhhbiA5MCUu

[q] A problem connected with construction of highways and other obstacles to wildlife is habitat [hangman].

[c]IGZyYWdtZW50YXRpb24=

[f]IEdyZWF0IQ==

[q] The problem with small or fragmented areas is that the wildlife populations trapped within them often suffer from the type of genetic [hangman] known as a population [hangman]. As they lose genetic [hangman], they often become less fertile, with causes further decreases in the [hangman] of the population.

[c]IGRyaWZ0

[f]IEdvb2Qh

[c]IGJvdHRsZW5lY2s=

[f]IEV4Y2VsbGVudCE=

[c]IGRpdmVyc2l0eQ==

[f]IENvcnJlY3Qh

[c]IHNpemU=

[f]IEdyZWF0IQ==

[q] Another problem with fragmented habitats is that they contain too much [hangman] habitat, indicated by “B,” and too little [hangman] habitat, indicated by “A.” This creates stressful conditions for the plants and animals that require the conditions found in habitat [hangman].

[c]IGVkZ2U=

[f]IEV4Y2VsbGVudCE=

[c]IGludGVyaW9y

[f]IEdyZWF0IQ==

[c]IEE=

[f]IEV4Y2VsbGVudCE=

[q] The positive feedback loop shown is known as the [hangman] [hangman]

[c]IGV4dGluY3Rpb24=

[f]IEV4Y2VsbGVudCE=

[c]IHZvcnRleA==

[f]IENvcnJlY3Qh

[q] Species like the Passenger Pigeon, the Gray Wolf, the Wooly Mammoth, and many others have all become extinct or nearly extinct because of [hangman].

[c]IG92ZXJodW50aW5n

[f]IEdvb2Qh

[q] Fast growing, fast reproducing species introduced from other habitats that outcompete native species are called [hangman] species.

[c]IGludmFzaXZl

[f]IEdvb2Qh

[q] The purpose of the wildlife overpass shown below is to allow for [hangman] [hangman] between populations that live on opposite sides of the highway.

[c]IGdlbmU=

[f]IEdvb2Qh

[c]IGZsb3c=

[f]IEdvb2Qh

[q] What saved the Illinois population of Greater Prairie Chicken from the extinction vortex was the introduction of new genetic [hangman] (hint: begins with “d”) into the population by bringing in new individuals from other states.

[c]IGRpdmVyc2l0eQ==

[f]IEdvb2Qh

[q multiple_choice=”true”] The combination of factors that constitutes the most common causes of extinction are

[c]IGVtZXJnaW5nIHZpcnVzZXMsIGJhY3RlcmlhbCBpbmZlY3Rpb25z

[f]IE5vLi5Ob25lIG9mIHRoZXNlIGlzIGF0IHRoZSB0b3Agb2YgdGhlIGxpc3Qu

[c]IGxvc3Mgb2YgaGFiaXRhdCwgYW5kIG92ZXJodW50aW5nIGJ5IGh1bWFucw==

[f]IE5vLiBZb3UmIzgyMTc7cmUgcmlnaHQgYWJvdXQgbG9zcyBvZiBoYWJpdGF0LCBidXQgbm90IGFib3V0IG92ZXJodW50aW5nLg==

[c]IGhhYml0YXQgbG9zcyBhbmQg aW52YXNpdmUgc3BlY2llcw==

[f]Q29ycmVjdDogdGhlc2UgYXJlIHRoZSB0d28gYmlnZ2VzdCB0aHJlYXRzIHRvIGJpb2RpdmVyc2l0eS4=

[q multiple_choice=”true”]Compared to the background rate of extinction, the current rate of extinction is

[c]QWJvdXQgdGhlIHNhbWU=

[f]Tm8uIEV4dGluY3Rpb24gcmF0ZXMgdG9kYXkgYXJlIHdheSBhYm92ZSB0aGUgYmFja2dyb3VuZCByYXRlIG9mIGV4dGluY3Rpb24u

[c]MjAwJSBoaWdoZXI=

[f]Tm8uIEV4dGluY3Rpb24gcmF0ZXMgdG9kYXkgYXJlIG1vcmUgdGhhbiAyMDAlIGFib3ZlIHRoZSBiYWNrZ3JvdW5kIHJhdGUgb2YgZXh0aW5jdGlvbi4=

[c]MTAwIHRvIDEwMDAg dGltZXMgaGlnaGVy

[f]VGhhdCYjODIxNztzIHJpZ2h0LiBFeHRpbmN0aW9uIHJhdGVzIHRvZGF5IGFyZSAxMDAgdG8gMTAwMCB0aW1lcyBoaWdoZXIu

[c]b25lIG1pbGxpb24gdGltZXMgaGlnaGVy

[f]Tm8mIzgyMzA7VGhhdCYjODIxNztzIHRvbyBoaWdoLg==

[q multiple_choice=”true”]Of the following, which two are most closely associated with the international pet trade.

[c]Y2xpbWF0ZSBjaGFuZ2UgYW5kIGhhYml0YXQgZGVzdHJ1Y3Rpb24u

[f]Tm8uIFdoaWxlIHRoZSBpbnRlcm5hdGlvbmFsIHBldCB0cmFkZSBjYW4gYmUgYSB0aHJlYXQgdG8gd2lsZGxpZmUgZGl2ZXJzaXR5LCBpdCYjODIxNztzIG5vdCBhIGNhdXNlIG9mIGNsaW1hdGUgY2hhbmdlIG9yIGhhYml0YXQgZGVzdHJ1Y3Rpb24u

[c]aGFiaXRhdCBsb3NzIGFuZCBvdmVyaGFydmVzdA==

[f]Tm8sIGJ1dCB5b3Ugd2VyZSByaWdodCBhYm91dCBvdmVyaGFydmVzdC4=

[c]b3ZlcmhhcnZlc3QgYW5kIGludHJvZHVj dGlvbiBvZiBpbnZhc2l2ZSBzcGVjaWVz

[f]RXhhY3RseS4gVGhlIGludGVybmF0aW9uYWwgcGV0IHRyYWRlIGNhbiByZXN1bHQgaW4gb3ZlcmhhcnZlc3QsIGFuZCBpZiB0aGUgaW1wb3J0ZWQgc3BlY2llcyBhcmUgcmVsZWFzZWQsIHRoZXkgY2FuIGJlY29tZSBpbnZhc2l2ZSBzcGVjaWVzLg==

[q multiple_choice=”true”]To qualify as a biodiversity hotspot, an area must

[c]aGF2ZSBtYW55IHNwZWNpZXMgdGhhdCBhcmUgdW5pcXVlIHRvIHRoYXQgYXJlYQ==

[f]Tm90IHF1aXRlLiBUaGF0JiM4MjE3O3MgY29ycmVjdCwgYnV0IHRoZXJlJiM4MjE3O3MgbW9yZS4=

[c]YmUgdW5kZXIgdGhyZWF0

[f]Tm90IHF1aXRlLiBUaGF0JiM4MjE3O3MgY29ycmVjdCwgYnV0IHRoZXJlJiM4MjE3O3MgbW9yZS4=

[c]Ym90aCBvZiB0 aGUgYWJvdmUu

[f]Q29ycmVjdC4gQmlvZGl2ZXJzaXR5IGhvdHNwb3RzIGhhdmUgaGlnaCBudW1iZXJzIG9mIGVuZGVtaWMgc3BlY2llcywgYW5kIHRoZXkmIzgyMTc7cmUgdW5kZXIgdGhyZWF0Lg==

[/qwiz]

13. Next steps

This is the last tutorial in Mr. W’s AP Biology Curriculum. Use the menus above to choose another topic, or to review for the AP Bio exam.

14. Suggested Reading

  1. The Insect Apocalypse is Here, New York Times, Brooke Jarvis, November 27, 2018.
  2. The Sixth Extinction, The New Yorker. This is the article that Elizabeth Kolbert wrote in 2009. In 2014 she expanded her research to write a book, The Sixth Extinction, which I highly recommend.
  3. The Song of The Dodo, David Quammen. This is a fantastic book about both biogeography (and the origins of biodiversity) and the effects of fragmentation.