Let me quickly review for you how this works. So again, the surface of the Earth is heated by the sun. The amount of energy that comes out of the Earth, geothermal energy, is a few thousand times less than what actually comes from the sun. So, in certain places it can be important, but overall, it’s the sun that sets the Earth’s surface temperature, not the internal temperature of the Earth. And when the sun shines on the Earth, some of it is actually reflected back to space, again more of it if it’s on an ice- covered part of the Earth or where there’s lots of clouds. And some of it is absorbed by the Earth and when it absorbs energy in the visible spectrum what happens is the Earth heats up in response because it’s absorbing energy. And when objects heat up they emit their own radiation but in a longer wave length and so that radiation then heads back towards space. If the Earth had no atmosphere it would be about 30 degrees colder. So we would actually have a frozen planet. We are habitable because of our atmosphere, and because our atmosphere has some greenhouse gases in particular carbon dioxide and methane, the most important of which is actually water vapor. Water vapor is interesting, we don’t often talk about it as a greenhouse gas, but the reason it’s important is it’s like an amplifier. It turns over quickly. It lasts in the atmosphere hours to days to weeks. And so, as a result you can think of the other greenhouse gases, carbon dioxide and methane, as the dial say on your stereo but it’s the water vapor that amplifies the effect because it turns over so quickly. And so, what happens is that these greenhouse gases, they absorb some of the infrared radiation, the long wave radiation, and re-radiate it both back to space and downward, but they act like a thermal blanket. So, they essentially keep the Earth’s surface warmer than it would be otherwise. And that’s how the greenhouse effect works. And again, this isn’t just a theory, we can actually say this is what causes Venus to be 460 degrees Celsius. We know this in fact in the laboratory we measure carbon dioxide by looking at how it absorbs long wave radiation.
Ecosystem feedback is the effect that change in one part of an ecosystem has on another and how this effect then feeds back to affect the source of the change inducing more or less of it. These feedback loops form the basic dynamics for regulating the state of the ecosystem.
A negative feedback loop is where the state of one element affects the other in the opposite direction, with the net result of this being a stable system where different forces are counterbalancing each other out creating some equilibrium
Positive feedback stimulates change and it is responsible for the sudden appearance of rapid changes within ecosystems. Positive feedback is a circular link of effects that are self-reinforcing. When part of the system increases, another part of the system also changes in a way that makes the first part increase even more. Positive feedback is a source of instability and strong force of change as it can drive the system outside of its normal operating parameters.
Positive Feedback Loop Examples
The melting of the polar ice caps is an example of a vicious cycle, as the reflective ice caps melt they reflect less sunlight and heat back to the atmosphere, with more of this heat being trapped by the dark ocean which is now exposed by the loss of ice cap. This retained heat then increases the temperature feeding back to induce the melting of more ice caps creating what we would call a vicious circle.
We might cite the pollution of the lagoons that surround small South Pacific islands. Many South Pacific communities now consume imported packaged and canned foods, disposing of the empty cans and other waste in dumps. Rainwater runoff from the dumps pollutes the lagoons, reducing the quantity of fish and other seafood. With less seafood, people are forced to buy more and more cheap canned food, the pollution becomes worse and the lagoon has fewer fish. This positive feedback loop changes the lagoon ecosystem while also degrading the people’s diet again creating a vicious circle.
Negative Feedback Loop Example
Look at the succession of an ecosystem from grass to shrub community, beginning with an ecosystem in which the ground is covered with grasses. Shrubs may be present, but they are young and scattered. The ecosystem may stay this way for five to ten years, or possibly longer, because shrub seedlings grow very slowly. They grow slowly because grass roots are located in the topsoil, while most of the shrub roots are lower down. Grasses intercept most of the rainwater before it reaches the roots of the shrubs. Because the grasses limit the supply of water to the shrub seedlings, they maintain the integrity of the ecosystem as a grass ecosystem. At this stage, negative feedback is acting to keep the biological community the same.
Various sources used for this post
Nature is not simply a warehouse of resources to serve human needs. Rather, it is a highly integrated, interdependent functioning system upon which all life forms, including the soil, water, plants, animals and humans depend for survival. In fact, Modern science has provided extensive empirical evidence which indicated that nature was a complex collection of water, air, soil, animal, plants and human beings. The components were sufficiently interdependent that the failure of one part of the system could undermine the productivity of other parts. As a result, it is necessary for us to treat the natural environment with love and respect because the failure of the system would ultimately threaten the subsistence of human beings.
The value of nature to people has long been recognized, but in recent years, the concept of ecosystem services has been developed to describe these various benefits. An ecosystem service is any positive benefit that wildlife or ecosystems provide to people. The benefits can be direct or indirect—small or large.
The Millennium Ecosystem Assessment (MA), a major UN-sponsored effort to analyze the impact of human actions on ecosystems and human well-being, identified four major categories of ecosystem services: provisioning, regulating, cultural and supporting services.
Provisioning Services: When people are asked to identify a service provided by nature, most think of food. Fruits, vegetables, trees, fish, and livestock are available to us as direct products of ecosystems. A provisioning service is any type of benefit to people that can be extracted from nature. Along with food, other types of provisioning services include drinking water, timber, wood fuel, natural gas, oils, plants that can be made into clothes and other materials, and medicinal benefits.
Regulating Services: Ecosystems provide many of the basic services that make life possible for people. Plants clean air and filter water, bacteria decompose wastes, bees pollinate flowers, and tree roots hold soil in place to prevent erosion. All these processes work together to make ecosystems clean, sustainable, functional, and resilient to change. A regulating service is the benefit provided by ecosystem processes that moderate natural phenomena. Regulating services include pollination, decomposition, water purification, erosion and flood control, and carbon storage and climate regulation.
Cultural Services: As we interact and alter nature, the natural world has in turn altered us. It has guided our cultural, intellectual, and social development by being a constant force present in our lives. The importance of ecosystems to the human mind can be traced back to the beginning of mankind with ancient civilizations drawing pictures of animals, plants, and weather patterns on cave walls. A cultural service is a non-material benefit that contributes to the development and cultural advancement of people, including how ecosystems play a role in local, national, and global cultures; the building of knowledge and the spreading of ideas; creativity born from interactions with nature (music, art, architecture); and recreation.
Supporting Services: The natural world provides so many services, sometimes we overlook the most fundamental. Ecosystems themselves couldn’t be sustained without the consistency of underlying natural processes, such as photosynthesis, nutrient cycling, the creation of soils, and the water cycle. These processes allow the Earth to sustain basic life forms, let alone whole ecosystems and people. Without supporting services, provisional, regulating, and cultural services wouldn’t exist.
Have you ever heard the story of how coal miners would take canaries down in the coal mines to warn them of danger? Methane gas and other gases can be toxic at high levels and the idea was to take a canary down into the coal mine and if he dies then it was early warning sign for the workers to leave because of toxic gases.
Indicator species (also known as bioindicator species) are a tool which scientists can use to be like the canary in the coal mine. Not just any organism can be used as an indicator species. The absence or presence of an indicator species can alert scientists as to whether or not a particular habitat might be in trouble. Indicator species might not tell us what is the specific problem, but they are an early detection tool.
Stream ecologists can survey a creek or stream searching for indicators species such as mayfly larvae, dragonfly larvae, or crayfish. These specific organisms prefer clean water and if a scientist cannot find them in a stream which they are native it could indicate a problem. When these organisms are not found then the scientist will do further tests such as testing for dissolved oxygen, elevated levels of nitrites or ammonia, and also temperature.
Lichens can be used as an indicator species for air pollution. Certain species of lichen have a low tolerance for air pollution. Amphibians, like the tiger salamander above, are good indicator species because their skin is moist and permeable which allows for a variety of pollutants to enter their body. Lobsters have become indicators of climate change. Warmer ocean temperatures will effect dissolved oxygen levels and salinity levels which lobsters are sensitive.
What are some characteristics of an indicator species? The species is abundant and has a wide distribution. Good indicator species are also easy to identify and sample. Another characteristic is they are sensitive to the stress or disturbance, but they do not die. And a very important characteristics is an indicator species has been well-studied and we are knowledgeable about their life history.
What if in the Spring you did not hear any songbirds singing? What do you think that might indicate?
What is great about AP Environmental Science (APES)? Science is all around us. Some we can see and some of it we cannot. A good portion of APES you can see and this makes it more enjoyable for a student as they think about the world around them and how it works. AP Environmental Science is interdisciplinary. This means it consists of concepts which are taught in other science disciplines such as Biology, Chemistry, Physics, Geology, Oceanography, Human Geography, and even Astronomy. Join me this year as we learn about the complexities of ecosystems and how they respond to the exponential growth of the human population in addition to learning about the many different strategies we use or have tried to use to maintain biodiversity and maintain ecological balance. We will use words such as tragedy of the commons, dead zones, food deserts, acid precipitation, desertification, and yes…global warming. This course is not just about identifying the problems, but we look at the causes and search for possible solutions. We will take this journey together and in the end you will have learned to become problem-solvers and be slightly more science literate.