Answer:
1. A forest of pine trees is burned over a 10 mile area when lightning strikes a tree. In the spring, a few seedlings are beginning to sprout → secondary succession.
2. A glacier has scraped all soil from a rocky area. As it slowly retreats, some of the rock is broken down by weathering. Some moss begins to grow → primary succession.
3. A small symbiotic organism secretes acid into the rock to anchor itself in place → lichens - pioneer organisms.
Explanation:
The succession is the colonization of an open area and includes all the changes the area suffers since then. It is a sequence of events that involves the establishment of different species through time. A sequence of changes that occur in a community temporally and spatially. Local colonizations and extinctions occur while ecosystems evolve at a more complex level.
Ecological succession occurs in stages. The first stages are represented by communities of simple trophic levels and few species. With time, the communities go through different stages. They transform into more complex ecosystems that are much richer in diversity, showing more interaction among the different species that compose it. The final stage is known as the climax and represents a mature and stable system.
While the community is going through these changes, many species get extinct while many others get to emerge and survive. It occurs overlapping of different taxonomic groups that interact with each other competing or beneficiating other groups.
There are two types of succession, primary and secondary, depending on the magnitude of the alteration.
- <u>Primary succession </u>refers to an open space with no living organisms, such as a bare rock exposed due to a retreating glacier, a volcanic activity, or an intense fire. If previous species were inhabiting this area, after the event, nothing is left.
In those cases where there is an alteration or disturbance at a site that opens the area, it allows new species to grow. With time, new species arrive and manage to establish again. The order of the establishment depends on the strategies of each of the species to survive.
First, pioneer species arrive. These are the first inhabitants, mostly lichens or plants with the capability of surviving in such an environment. Only a few pioneers can establish in the open space. Pioneers modify the habitat, making it more suitable for the establishment of later species, converting rock into fertile soil. As conditions get better, new species arrive like grasses. Grasses and pioneers keep modifying the soil, making it better with time. New species arrive. Habitat modification keeps on going while new species establish. They produce shadows, alter the temperature, and humidity, fertilizing the soil, competing for resources. Competition becomes more frequent between species. The first species are eventually eliminated by competition, but new species keep appearing and competing for resources. This sequence continues until the commuting reaches a climax, becoming stable and lasting for hundreds of years until another disturbance occurs.
- <u>Secondary succession</u> refers to an open space left after a perturbation that might have removed all or some of the vegetable forms of life that used to inhabits that area. But the soil remains good and fertile. It has spores and seeds that will emerge when the conditions are appropriate. The disturbance occurred but vegetable species have strategies to survive the event and grow once it´s over. Pine trees are adapted to fire, and some species need fire to germinate.
