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Introduction Homeostasis: Maintaining Stability Negative Feedback Positive Feedback Change in Populations: Evolution Natural Selection Adaptation: Response to Environmental Change Population Dynamics: Stability and Change in Ecosystems Succession: Changes Over Time Biodiversity and Change Fossil Record Comparative Anatomy Molecular Evidence Human Influence on Stability and Change Summary
Earth's living systems have stability, and they interact with the rest of the physical world, which is constantly changing. Systems live in changing environments. Temperature and food availability change regularly. Systems are constantly changing. Systems have to balance stability and change.
Stability is the system's ability to maintain an internal state, or an internal structure, in the face of external changes.
Change is the system's ability to maintain internal stability while having external changes.
This lesson is about how the system maintains stability, the system's response to internal changes, and the changes to the system driven by the system's external environment over a long period of time.
Homeostasis is the process of internal stability employed by living systems. Homeostasis regulates system variables, such as body temperature, the pH of blood, the concentration of glucose in the blood, and the system's osmotic equilibrium.
Feedback is the most popular and widely used mechanism. It maintains homeostasis by counteracting any changes from the normal, or set point, state.
Example: The regulation of blood glucose. The blood glucose levels rise after you eat. The pancreas releases insulin. Your cells absorb glucose, which lowers blood sugar levels, and then, when normal levels are restored, insulin secretion stops.
Other examples of negative feedback include:
Positive feedback is the opposite of negative feedback. It occurs when there is an amplification of change, instead of a reduction. It is less common and usually occurs in processes that require a rapid and decisive change.
Example: Blood clotting. In an injury, platelets release certain chemicals, and more platelets are attracted, which accelerates the formation of the clot. Once the clot is formed, the entire process stops.
Other examples include:
While homeostasis maintains stability in individuals, in populations, change occurs over generations. It is driven by evolution, which is the process by which populations adapt to their environment over time.
Without genetic variation in populations, there wouldn't be evolution. Variation occurs from:
Gene variations affect how individuals in a population will survive in a certain environment, which theory of evolution is based upon called natural selection.
Natural selection is a process that takes place when individuals with preferred traits are able to live longer because of those traits.
Example: In England's peppered moths population, natural selection in response to environmental changes occurred. England experienced an industrial revolution, which led to pollution and a change in the color of the trees. It originally had a lot of light colored moths that blended into the light colored trees and therefore were not predated upon. When the tree color changed to a darker color, there was a moth that had a mutation to be dark colored, and that mutation survived longer and was able to reproduce in larger numbers than the remaining light moths, leading to a change in the population of colored moths from naturally selected light colored moths to a population of dark colored moths.
An adaptation is a trait in an organism that makes it more likely to survive and reproduce in a given environment.
For a long time, the species has slowly evolved coping mechanisms for pressures from the environment, through the process of natural selection. These are called adaptations.
Ecosystems also experience stability and change. Population dynamics help us understand the change in numbers, the interactions between organisms in a population, and the effects of those interactions.
Both processes will eventually lead to the stabilization of the ecosystem by reaching a climax community.
Biodiversity is defined as the different types of organisms in an ecosystem, and at the genetic and species levels. Stability is supported by biodiversity in the following ways:
Change in biodiversity has either a natural reason from the environment, or an anthropogenic reason from human activity.
Some ecosystems, like tropical rainforests, are quicker to recover from disturbances than others, like deserts, which take longer to recover.
Fossils are evidence of gradual changes in a species that support evolution. The fossils bridge the gaps in the timeline and show how modern species descend from their ancestors.
Example: Archaeopteryx is a species that perfectly combines the features of a dinosaur and a bird and is a great example of evolution.
Structures that are similar in several species indicate a common ancestor.
The closer the organisms, the more similar the DNA and protein sequences they have. The conserved genes are evidence for stability, while the changes and mutations that are present are evidence for change.
The impact humans have on nature's balance of stability and change is profound.
In a growing environment, humans can either facilitate the ecosystem's long-term stability (through conservation) or alter and accelerate the ecosystem's change and promote extinction.
In the study of biology, some of the main themes of study are stability and change.
This process has provided a fundamental understanding that is necessary to aid a population of organisms in a new home to live, while also avoiding the collapse of ecosystems.