Answer to Question 1
The first species to reinvade a disturbed environment are called opportunists or pioneer species. They tend to be fast growing, rapidly reproducing, environmentally tolerant species that can spread across the disturbed area quickly. In colonizing a previously disturbed area, these organisms tend to begin the process of repair, improving the soil or modifying the local climate in ways that can result in their replacement by other, slower growing organisms that ultimately have competitive advantages. In general, succession patterns are predictable, at least in terms of the types of plants that will become prevalent at various stages of succession. If many species are equally well suited to the environmental conditions at a particular stage of succession, however, an element of unpredictability may be introduced into the succession pattern. Thus a diversity of outcomes is possible, and this diversity may be reflected in the biodiversity of a region subject to disturbance. Indeed, we will see in the next section that a modest level of disturbance may be required for high-diversity ecosystems to become established. Succession is one indication that the biosphere has the capacity to heal, that it is resilient to perturbation.
Answer to Question 2
C
A typical eukaryotic cell.
A typical fire extinguisher designed to be used on class A, B, or C fires.
Typical Startup Cost Categories Cont.
Types of ecosystem service vs. total global value per year
Sequence Series Arithmatic Progression Problem
Opener Alignment comparing DNA sequence for the leptin gene from dogs (top) and humans (bottom)