Earth at the Crossroads: Understanding the Ecology of a Changing Planet

Course No. 1720
Professor Eric G. Strauss, Ph.D.
Loyola Marymount University
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Course No. 1720
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Course Overview

Every plant, microorganism, and animal on Earth exists within an ecosystem: a complex network of interdependent relationships in which each individual strand is important and contributes to the success of the whole. Ecosystems, in turn, interact with one another to form the biosphere: the zone of life on our planet.

But these systems, so important to the world around us, are far from stable. Instead, ecosystems are constantly changed by the pressures of biological, geological, and physical forces. In addition, the rapid growth of human populations and their attendant technologies has created unprecedented forces of ecological change. Only when you look beyond the individual level and observe how populations of different species interact with themselves, with other species, and with their physical environment, as well as how they respond and adapt to change, can you fully understand how life truly works.

Now, with Earth at the Crossroads: Understanding the Ecology of a Changing Planet, you can explore the rich interconnections that make up the great and fascinating web of life on Earth. In this compelling 36-lecture course, behavioral ecologist Eric G. Strauss of Boston College provides you with a comprehensive overview that is a hallmark of the study of ecology. With Professor Strauss as your guide, you'll investigate the remarkably complex workings of Earth's biosphere and learn about the myriad forces that shape the world's habitats, from the movement of water and nutrients within an ecosystem to the reproductive strategies employed by plants and animals around the world.

As you delve into the biosphere's intricate network of relationships, you develop a deeper appreciation of the rich complexity of the life around you. You'll also strengthen your understanding of some of the most important debates in current affairs, including questions of climate change, protection of endangered species, and alternative energy sources. Earth at the Crossroads exposes you to the science behind these debates, allowing you to develop your own opinions and back them up with the latest scientific evidence.

Examine Ecology's Most Intriguing Questions

The key to understanding and bringing to life these relationships lies in the field of ecology. A science that has come into its own during the modern era, ecology helps humans comprehend—and put into a more coherent perspective—the "big picture" of life on Earth.

In Earth at the Crossroads, you examine the same intriguing questions that ecologists themselves contemplate as they study life from this unique perspective:

  • What forces shape the living systems around us?
  • How do relationships like predation and competition affect communities of organisms?
  • What happens when a new organism is introduced into an environment?
  • How does climate change affect plants and animals in a single ecosystem—or even the world at large?

And perhaps the most crucial question of all:

  • What role do you as a member of Earth's living community play, and how can you use your understanding of these complex patterns to ensure that you and your fellow organisms survive and thrive?

The field of ecology is an applied science whose impact can be felt in a range of areas. The knowledge gained from the study of Earth's living systems has allowed us to

  • conserve endangered habitats,
  • more wisely manage our natural resources,
  • produce higher and healthier yields of agriculture,
  • better prepare for public health concerns, and
  • understand how highly artificial environments such as major cities follow the same rules as more "natural" environments.

Understand the Complexity of Life on Earth

Earth at the Crossroads opens with an introduction in which you explore the development of ecology as a scientific discipline distinct from biology and other related areas of study. Through vivid examples and accessible explanations, Professor Strauss explicates the field's key theories and raises thought-provoking questions that motivate scientists in this vital area of study.

Next, you move into the fundamental topics covered in the field, which are explored in three units:

  • In lectures 5 through 18, you examine the important forces that impact ecosystems, such as the way energy, nutrients, and water are used and recycled in these systems.
  • In lectures 19 through 32, you focus on specific ecological interactions and processes, including microevolution, population growth, migration, disease, and coevolution.
  • In lectures 33 through 36, you consider some of the latest scientific contributions that suggest how we can intervene in ecosystems in a beneficial way.

Throughout the course, you also learn about the remarkable and often surprising ways that organisms compete, coexist, and cooperate:

  • The interaction of ants and aphids: Living in a relationship not unlike that of the farmer and the dairy cow, ants harvest the nutritious fluid that aphids suck from plants while protecting their wards from predators.
  • The survival strategies of the Monarch butterfly and its imitators: Monarchs feed on poisonous milkweed, which makes them toxic to predators, a fact they signal with their bright coloration. Other species have developed similar markings to "trick" predators into leaving them alone.
  • The surprising relationship between wolves, elks, and river ecosystems in Yellowstone National Park: When the park's wolves were almost hunted to extinction, populations of elk skyrocketed while nearby river ecosystems declined. Freed from the pressure of predation, the elk were able to graze these fragile ecosystems, damaging them significantly. When wolf populations were restored, the elk returned to their traditional habitats, and the river systems revived.
  • The paradoxical relationship between humans and bacteria: As people increasingly use antibacterial soaps, antibiotics, and disinfectants to protect themselves against microbial disease, they drive these organisms to develop a tolerance to these products, putting human beings at an even greater risk of infection by "superbugs."

As you explore these fascinating examples, you experience the sense of wonder that is at the heart of the study of ecology.

The Whole Earth: City and Country

Delving deeply into ecology, you quickly see that this field of study extends beyond what we usually think of as "nature." Ecologists espouse a "whole Earth" view that incorporates both pristine wilderness regions and modern urban settings. From this perspective, the city is simply another form of ecosystem, alive with organisms that are interconnected in complex relationships.

You examine how wildlife adapts to new urban settings, as seen in the example of hawks that thrive on the tops of skyscrapers and feed on urban pigeons. Earth at the Crossroads also illuminates how city settings can generate their own microclimates, evidenced in the "heat island effect," in which the reduced greenery and increased hot, bare surfaces produce higher urban temperatures.

This examination of life in the modern world also takes you to the suburbs, where you'll discover an abundance of life forms dwelling in complicated relationships that rival the complexity of wilderness communities.

Professor Strauss is the perfect guide for exploring the ecological implications of our modern world. As a specialist in urban ecology, he brings classic and cutting-edge scientific studies to bear on his consideration of urban populations, suburban spread, and the ways in which human populations affect and are affected by the ecosystems in which they live.

Humankind's Place in the Biosphere

As you ponder life in these varying ecosystems—both wilderness and urban—you ultimately arrive at an intriguing question: What role does humankind play in this great web of life?

As Professor Strauss explains, humanity has a unique role in the world. We have an unprecedented capacity to shape the biosphere and make thoughtful, informed choices about the actions we take.

In this course, you see how human history is full of examples of how we as a species have changed the world around us, from the development of agriculture to the spread of often-dangerous chemicals that can alter the genetic material of living organisms. But it's also a history of successes and solutions, as innovative scientists and engineers have developed new technologies and practices that allow humankind to thrive while reducing our impact on other species.

As Professor Strauss considers the role humans play in the biosphere, he provides examples of both humankind's mistakes and innovations. The result is a thoughtful and balanced consideration of the role of humanity within Earth's living communities—one that will allow you to develop better-informed opinions regarding crucial questions about the world in which we live.

The Great Web of Life Made Accessible

The goal of ecology is to provide a comprehensive view of the world as an interconnected complex of relationships. In Earth at the Crossroads, this complicated topic is made accessible by an experienced and accomplished instructor. Professor Strauss provides an engaging and thorough overview of this intriguing field of study through the use of compelling anecdotes, easy-to-follow explanations, and helpful visual aids. A leading scholar and researcher in urban ecology, Professor Strauss presents cutting-edge findings that encourage a "whole world" perspective on life on this planet.

Join Professor Strauss as he traces the fascinating links that are at the heart of the study of ecology. You'll discover new ways to view the world of surprise and wonderment that exists all around us in this great web of life.

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36 lectures
 |  Average 30 minutes each
  • 1
    An Ecological Diagnosis of the Living Earth
    What is ecology? This introductory lecture considers key topics and concepts you'll encounter as you study the complex interactions of Earth's biosphere—and raises the question of humankind's place within this great network of relationships. x
  • 2
    Humanity and the Tragedy of the Commons
    Although human beings are a relatively young species, we have had a huge impact on the planet we inhabit. Here, consider some of the ramifications of this effect, focusing on a fundamental principle of ecology, the Tragedy of the Commons, and see this principle at work in the fishing industry. x
  • 3
    Ecology—Natural History to Holistic Science
    In the last century, ecology emerged as a new area of study that draws from diverse disciplines, including natural history, biology, botany, and zoology, to forge a holistic understanding of life on earth. Chart the history of this burgeoning field and the great minds that shaped its development. x
  • 4
    Ecology as a System—Presses and Pulses
    All ecosystems are constantly in flux. Begin to explore the biological, geological, and physical forces that drive change in the Earth's ecosystems, and develop an appreciation of the important role played in ecology by social factors, including public policy and shifts in human demography. x
  • 5
    Climate and Habitat—Twin Ecological Crises
    Apply what you learned in the last lecture about the forces of change within the Earth's ecological system to understand two crucial aspects in today's world: climate change and habitat destruction. x
  • 6
    Human Society as Ecological Driver
    Human power structures, social organization, information flow, and cultural practices can profoundly change the shape of ecosystems. Examine the role of humans as "ecosystem engineers" as you look more closely at some of the social forces and practices that affect the ecology of our planet. x
  • 7
    Movement of Energy through Living Systems
    Begin your consideration of specific forces that cause ecosystem change by examining the flow of energy. You trace how energy moves through ecosystems, from sunlight through the transitions of food production, consumption, and decomposition. x
  • 8
    Humans as Energy Consumers
    Humans are the most voracious consumers of energy on the planet, and our appetite for energy produces enormous short- and long-term challenges to ecological sustainability. Investigate human energy consumption habits and examine alternatives to traditional ways of accessing energy. x
  • 9
    Nutrient Cycling in Ecosystems
    While energy moves from the sun through organisms and is ultimately lost to the atmosphere, crucial organic molecules are recycled endlessly. Learn how two of these essential building blocks of life—carbon and nitrogen—move through the ecosystem. x
  • 10
    The Challenges of Waste and Disposal
    Just as organic nutrients remain in the environment, so too do the byproducts of human life. Consider the impact of human trash on the environment and examine alternatives to the current strategies of waste disposal. x
  • 11
    The Water Cycle and Climate
    Water, like all other molecules in ecosystems, is recycled endlessly. Investigate the process by which water circulates through the ecosystem and examine the role water plays as a living system in pollution abatement and long-term sustainability. x
  • 12
    Human Water Use and Climate Change
    Human water consumption is growing at an astounding rate. The depletion of water resources threatens ecosystems, contributes to changes in climate, and renders human communities more vulnerable to disaster and disease. Examine how human behavior is affecting water reserves and explore strategies for conserving this precious resource. x
  • 13
    Rain and Heat—Forces That Shape Climate
    Why do some regions develop desert climates, while others become rainforests? What adaptations must organisms make to survive in these habitats? Examine the role of water and weather in determining the characteristics of different ecosystems, and learn how organisms develop mechanisms to thrive in extreme environments. x
  • 14
    The Ecology of Global Climate Change
    Most experts in climatology agree: The Earth is rapidly warming, and while the causes are complex, human technology is most likely contributing to this trend. Investigate the role of climate change on shifting animal migratory patterns, life-cycle fluctuations in plants, and the disappearance of marine habitats, and consider ways to reduce the impact of climate change on the Earth's ecosystems. x
  • 15
    How Living Organisms Acquire Food
    Return to the topic of energy flow within ecosystems to consider the interaction between producers and consumers within a complex pattern called the food web. Examine how this relationship shapes plant distribution and animal behavior, and consider what happens when these systems experience stress due to ecosystem fragmentation and species extirpation. x
  • 16
    The Ecological Consequences of Agriculture
    The current model for food production and distribution in developed countries creates a large and growing burden on the Earth's biosphere. Explore the role of modern large-scale agriculture in the dynamics of ecosystems, and consider alternative models for food production and delivery. x
  • 17
    Food, Energy Flows, Biomagnification
    One effect of the food web is that nutrients and chemicals become concentrated in organisms at the top of the food chain. In this lecture, learn how this process, called biomagnification, both benefits living organisms and leads to the concentration of toxic substances, including DDT and PCBs. x
  • 18
    The Human Ecology of Biomagnification
    Take a closer look at some of the negative effects of biomagnification that can be traced to human activity. Examine several examples of human-influenced biomagnification, including the appearance of organic pollutants in human breast milk and the notorious case of mercury poisoning in the human and animal populations of Minamata Bay, Japan. x
  • 19
    The Ecological Community as a Living Mosaic
    Local ecological communities are complex aggregations of living and nonliving forces. Take a look at these living mosaics by exploring predator and prey relationships, interactions of competition and cooperation, and the effect of large-scale disturbances such as fires and flood. x
  • 20
    Wildlife Adaptation to Human Landscapes
    Following World War II, suburban living spread in human populations, fragmenting wildlife habitats and disrupting ecosystems near urban landscapes. Examine the effects of increasing urbanization and the strategies species develop to adapt to ecosystems now dominated by human communities. x
  • 21
    Biodiversity, Disturbance, Invasive Species
    One of the elements that can help bring stability to an ecosystem is biodiversity, or the diversity of life within an ecosystem. Here, begin to consider the phenomena that impact biodiversity, including forest fires, deforestation, and competition posed by the invasion of nonnative species. x
  • 22
    Biodiversity Decline and Restoration Ecology
    As human populations have soared, urban areas have expanded to accommodate more residents. In this lecture, explore the effects of urbanization on local and regional biodiversity as well as actions that can mitigate negative impact and enhance local ecosystems. x
  • 23
    Microevolution and Biological Variation
    Healthy populations of organisms have enough genetic variability to withstand ecological change. Examine the processes and conditions that contribute to the production of biological variation within a population and how that variation can help stabilize the entire ecosystem. x
  • 24
    Human Impacts on Ecological Space and Time
    As humans carve up landscapes and reshape them with nonnative plants and animals for their own use, biodiversity in those areas decreases, leaving native species subject to extinction. Consider what is lost when the biodiversity is suppressed, and explore ways in which humans can coexist with healthy local ecosystems. x
  • 25
    Population Growth and Its Natural Limits
    No aspect of ecology is more fundamental to resiliency than the way in which natural populations grow. Examine the models that help describe population growth, and review the different strategies and behaviors that species have developed to maintain population size and support the resiliency of their habitats. x
  • 26
    The Human Shift to an Urban Lifestyle
    Humans have undergone a massive demographic transition as over half of the human population has moved from rural to urban lifestyles. Investigate how this shift has created a unique set of ecological characteristics, and consider the challenges posed by urban infrastructure on environmental sustainability. x
  • 27
    The Ecology of Dispersal and Migration
    In response to seasonal conditions, the threat of predators, mating behaviors, and the availability of food, some organisms have to move long distances in order to complete their lifecycles. Here, explore the costs and benefits of migration and consider the challenges organisms face during these long, dangerous treks. x
  • 28
    Human Impacts on Animal Migration
    Human land-use practices have disrupted the migratory patterns of many species, which are now threatened with extinction as a result of this disruption. Investigate the unique ecological requirements of migratory species, as well as some of the management strategies to facilitate animal movement across urbanized landscapes and agricultural ecosystems. x
  • 29
    Ecology and Economy of Sex and Reproduction
    Why do organisms reproduce sexually? What is gained by this costly and often risky form of reproduction? What behaviors have species developed to mitigate those risks? Explore these questions and develop an understanding of the ecology of reproduction and its implication for ecological sustainability and biodiversity. x
  • 30
    Cities and the Human Demographic Transition
    Shifting demographic patterns toward industrialization and urbanization have dramatically reduced the size of nuclear families all over the world. Explore the ecological forces that select for large and small families among the human species and what this phenomenon suggests for our future sustainability. x
  • 31
    Coevolution among Species
    Many species live so close to each other that they affect each other's evolutionary trajectories through a process called coevolution. Analyze the many forms of coevolution, including mutualism, predator-prey arms races, mimicry, camouflage, and deception, and consider how the rapid decline of the world's ecosystems places these relationships in peril. x
  • 32
    The Coevolution of Human Diseases
    Take a closer look at a particular example of coevolution: the development of zoonotic diseases (diseases that spread from animals to people) in human beings, including Lyme disease and West Nile fever. Also, learn how climate change and habitat fragmentation affect the spread of infectious diseases. x
  • 33
    Strategies for Reversing Ecosystem Decline
    In conservation biology and restoration ecology, scientists study how to sustain natural ecosystems and preserve the populations of declining species. Review some of the ways experts have sought to rebuild damaged habitats as you consider current debates about the efficacy and ethics of these interventions. x
  • 34
    Designing Spaces for Wildlife
    Continue your examination of conservation biology with a consideration of park design and the effort to preserve green spaces. Since precious resources go into conservation, scientists and policymakers must make difficult decisions about which species to include in recovery plans. x
  • 35
    Toward Sustainable Urban Ecosystems
    As human populations grow and evolve, the need to make conscious, positive transformations in the way people live becomes increasingly important. Explore the new field of urban ecology as it seeks to understand and improve the ecology of cities around the world. x
  • 36
    Recovering Ecosystems—Hope for the Future
    While human activity has put many habitats at risk, much is being done to heal damaged and threatened ecosystems. Examine some of the ways ecological thinking and action can simultaneously preserve these habitats and enhance the health and well-being of human communities. x

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Your professor

Eric G. Strauss

About Your Professor

Eric G. Strauss, Ph.D.
Loyola Marymount University
Dr. Eric G. Strauss is Presidential Professor in Ecology at Loyola Marymount University in Los Angeles. He is one of the founding science directors of the Urban Ecology Institute at Boston College, where he previously was Director of the Environmental Studies Program and Research Associate Professor. He received his undergraduate education at Emerson College and earned his Ph.D. from Tufts University. An active researcher,...
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Earth at the Crossroads: Understanding the Ecology of a Changing Planet is rated 3.8 out of 5 by 26.
Rated 5 out of 5 by from Fascinating I like how instead of focusing on just reducing Greenhouse gasses or stop using plastic straws. Professor Strauss talks about over fishing, deforestation, and human displacement as well.
Date published: 2020-10-26
Rated 1 out of 5 by from Elementary school level The presentation was at a very basic level. The presenter droned about simple ideas as if they were monumental concepts including irrelevant information about his personal experiences that did nothing to educate. I learned nothing from it. The data presented was always 10 or more years out of date.
Date published: 2020-09-20
Rated 5 out of 5 by from Hope for the Future I bought this course because I care about the planet and wanted to have a better understanding of its ecosystems. Dr. Strauss delivers his extensive background in ecological theory and practice from his a own field work and case studies in a relaxed and engaging manner. The material he covers is more relevant today then when this course first appeared 10 years ago. His presentation on urban ecology at the end of the 36 lectures I found most poignant. He discusses the impacts mass movement to cities, climate change, waste management, energy cycles and zoonotics (COVID 19, Ebola) have had on the planet and makes suggestions that offer hope for a better future for our natural and urban environments. Since we have entered the anthripocene, it is clearly evident that we need to find a balance in our use of the earths resources. I look forward to and hope for a second edition of this course with Dr. Strauss.
Date published: 2020-09-14
Rated 5 out of 5 by from Excellent Course I bought this course to give me an in-depth view of the changing environment. The DVD format showed the instructor using visual aids which proved useful in better understanding the course content.
Date published: 2019-10-12
Rated 5 out of 5 by from Excellent presentation of complex interactions This is a great course to get a good understanding about all the various factors and elements contained in "ecology" and how they interact - climate change is just one of these. Professor Strauss just lays out the facts, no preaching. The information in this course should receive wide dissemination, particularly to our governing representatives and schools at all levels.
Date published: 2019-10-07
Date published: 2019-09-21
Rated 5 out of 5 by from The professor was very well informed We are really enjoying this series of lectures. This man is telling it as it is. Climate change is here and not "believing" what is going on is a real story of refuting the scientific method. This series should be required in all high school classes. He does a fairly good job of not making us all feel like jerks for not immediately giving up animal protein , leather, all pesticides and fertilizers. We would appreciate a few more photos of some of plants and animals discussed since they sound so interesting. His voice is easy to listen to and does not put me to sleep. We have learned a great deal from the lectures and still have a few more to go. As with virtually every ecologist in the land, there has not yet been any mention of the other side of the equation. Our destructive use of finite resources gets a lot of attention, but very little is said about how to reduce the demand for those resources. How about some mention of the effects of population rates? I am not suggesting anything Draconian, but how about providing all persons of reproductive age with the knowledge and means to prevent the unexpected and unwanted. Parenthood should be voluntary, not an unwelcome burden. This is not to say I expect the professor to lecture on anything involving reproduction. That is not the reason for this course. However, I would think that a comment about supply versus demand in the use of our shared resources by a larger and larger population merits some mention.
Date published: 2019-03-25
Rated 4 out of 5 by from Revieving my classes from college Although many of the lectures are a review for me, there is so much to learn. I enjoy watching the lectures whenever I have time.
Date published: 2019-02-28
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