Lecture Nine Flashcards
What are the three models that provide a generalized framework for how succession is known to occur?
Facilitation model, inhibition model, and tolerance model.
What is the Facilitation model?
Early successional species change the environment, making it more suitable for later successional species to invade and grow. Only certain pioneers can be started with because the habitat is not yet suitable for later species. The early species modify the environment to make it suitable for later species, and then the early species are eliminated through competition for resources by the later arrivals. This continues until current residents no longer facilitate the invasion and growth of the next species.
What is the Inhibition model?
Involves strong competitive interactions, no species is completely superior to another. These species maintain position as long as they live and reproduce, and can only be replace if injured or dead. Modification of the environment by early occupants makes it less suitable for the recruitment of later successional species. There is no climax, per se.
What is an example of the Inhibition model?
Allelopathy plants. Once the white sage moves into an area, it grows and makes the soil toxic for other plants - making it hard for more succession to occur.
What is the Tolerance Model?
Species in earlier successional stages neither aid nor inhibit later successional species. Later successional stage species can invade a newly exposed site, become established, and reach maturity without the influence of pioneer species. Modification of environment has little to do with the subsequent recruitment of later successional species. Early species are eliminated through competition for resources by later arrivals.
Why two factors related to succession impact diversity?
The time/age of the environment and the frequency of disturbance.
Does diversity always increase with time?
No. The site can fluctuate and even go backwards, such as an oak-pine forest in New York.
When is the peak in diversity of an environment?
During mid-successional stages in a transition period, where the climax species have arrived by the pioneer species have not been replaced.
Does the growth rate of competitors affect diversity?
Yes, it may be the thing that affects diversity the most. If the growth rate of competitors is slow, the period of coexistence between climax and pioneer species is extended.
What happens when an area is frequently re-disturbed?
Pioneering species will never give way to climax species.
What is the Intermediate Disturbance Hypothesis?
The idea that higher diversity is maintained at intermediate levels of disturbance because disturbance can increase diversity by reducing the abundance of competitively dominant species, but can decrease diversity by being too frequent.
Why is there a direct link between plant succession and the type of animal diversity?
Because as the species composition and structure of vegetation change, animals can lose or gain habitat. Bird and insect diversity changes with increase of trees and leaf litter.
What are four broadly defined successional stages?
Herbs, shrubs, pines, hardwoods.
How many glacial cycles have occurred over the last 2.6 million years?
About 20, at the glacial maximum ice covered 30% of Earth’s surface. NA ice sheet reached maximum size about 18,000 years ago. We are still technically in an ice age.
When did ice become restricted to northern Canada?
8,000 years ago.
