recap

56.2 recap

Community membership is a consequence of regional species pools, environmental conditions, and species interactions. These three factors act as “filters” that control community membership. Biotic resistance—the process by which species interactions exclude or slow the population growth of colonizing species—is rarely documented.

learning outcomes

You should be able to:

  • Name the three factors that determine community membership, and evaluate their relative importance in given situations.

  • Explain and illustrate with examples how environmental factors can act as a filter or barrier affecting community structure.

  • Explain why studying introduced non-native species provides a unique test of community membership.

Question 1

Refer to Figure 56.6. Which factor is most limiting to the species membership of the local community? Explain.

The most important factor limiting species membership in the local community is dispersal and immigration. Seven species did not pass through the species supply filter, while 4 species and 3 species, respectively, did not pass through the abiotic and biotic filters.

Question 2

If you were trying to reduce the number of non-native species colonizing Mount St. Helens, what one best general management action would you employ?

Given that the species supply filter has the most potential to exclude species from a local community, the best management action would be to exclude, as much as possible, non-native species from entering the mountain in the first place.

Once a species is part of a community, how is it able to coexist with other species there? In the next section we will consider theories and examples that seek to explain how species interactions help form communities of varying composition and diversity.