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

 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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

This lecture spotlights the fascinating variety of instruments that have unveiled the universe in the course of the 20th century, from ground-based optical, radio, and neutrino telescopes to spacecraft that are surveying the cosmos at x-ray, gamma ray, infrared, and other wavelengths.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

Is history a science? This lecture follows the shifting fortunes of objectivity and relativism as historical methodologies. The latter culminated in the extreme form of relativism known as post-modernism, which attacked the foundations of science itself.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.