Define ecosystem.
The term species may be described using different concepts, including the biological species concept and the morphological species concept. The morphological species concept is based on appearance or observable features. Describe what is meant by the biological species concept.
The populations of E. eschscholtzii are split by the Central Valley, shown in Fig. 6.2, which has conditions that are unsuitable for salamanders. Some scientists believe that the separated populations of E. eschscholtzii have evolved into different species of salamander. Individuals from different salamander populations may be unable to reproduce with one another, even when they are able to interact. Explain how salamanders from different populations have evolved to be unable to reproduce with each other.