On May 18, 1980, Mount St. Helens in the state of Washington erupted with the force of a hydrogen bomb. The volcano had been dormant for over 120 years, but now 57 people were dead and forests and lakes were totally destroyed, including nearby Spirit Lake, which became a mud hole. The blast leveled trees in areas over 10 miles from the crater and ash deposits suffocated life on the mountain. However, within weeks, mammals that had taken shelter underground started to reappear in the area, and now, over thirty years later, many areas of the mountain are colonized with a large variety of plant and animal life. How does an area move from a sterile, barren wilderness to one full of life?
Primary Succession
Question 1
1.
What does primary succession start with?
Secondary Succession
Question 2
2.
What does secondary succession start with?
The term pioneer speciesis used to describe the species that first colonize new habitats created by disturbance. Although the term is usually applied to plants, microbial and invertebrate pioneer species are also sometimes recognized. For terrestrial habitats two groups of pioneers can be distinguished: those that colonize siteslacking developed organic soil and initiate primary succession and those that initiate secondary succession, often via recruitment from species that are transported from far away.
Primary succession begins in barren areas, such as on bare rock exposed by a retreating glacier. The first inhabitants are lichens or plants—those that can survive in such an environment. Over hundreds of years these “pioneer species” convert the rock into soil that can support simple plants such as grasses. These grasses further modify the soil, which is then colonized by other types of plants. Each successive stage modifies the habitat by altering the amount of shade and the composition of the soil. The final stage of succession is a climax community, which is a very stable stage that can endure for hundreds of years.
Question 3
3.
Describe a pioneer species.
Question 4
4.
Describe the importance of a keystone species.
We define an indicator in biology as an organism that the presence, or lack thereof, provides a clear signal about the environmental conditions. Depending on the organism, its appearance can signal both a healthy ecosystem or an unhealthy one. These indicators can reveal information about many factors in an environment, including pollution levels, salinity, temperature, and nutrient or food availability.
Indicator species, —often a microorganism or a plant—that serves as a measure of the environmental conditions that exist in a given locale. For example, greasewood indicates saline soil; mosses often indicate acid soil. Tubifex worms indicate oxygen-poor and stagnant water unfit to drink. The presence of certain species of plants suggests how well other species might grow in the same place.
