Community Ecology Chapter 54 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

avoiding direct competition. encouraging mutualistic interactions. Two-species interactions are classified by the impact each species has on the other species. Thus, a competitive interaction is one where the populations of each species are hurt by the presence of the other species, usually because each species consumes the same resources. Niche partitioning enables species to coexist by avoiding direct competition. encouraging mutualistic interactions. providing prey with a place to hide from predators. creating new resources. allowing abiotic factors, such as climate or nutrient availability, to influence the community. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

What is one difference between the fundamental niche and the realized niche? The realized niche is larger. The fundamental niche is determined by competitors. The realized niche is determined by abiotic resources. If you want to find the species, look in the realized niche. The difference is called the occupied niche. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Look at Figure 54. 3 in the textbook Look at Figure 54.3 in the textbook. Joseph Connell showed that when Balanus are removed from the intertidal zone, Chthamalus expand their niche. What would you predict if he removed Chthamalus? Since Balanus is the superior competitor, it probably would move up into the space Chthamalus occupied. Since Chthamalus is the superior competitor, it probably would move down into the space Balanus occupied. Since Balanus is the superior competitor, it probably cannot live in the high intertidal zone. Balanus would disappear as well, since it preys on Chthamalus. none of the above Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Figure 54.4 shows that when two species of finch coexist, their beak sizes diverge, which is character displacement. If the two species colonized an island on which there were seeds of only one size, what would Gause’s principle of competitive exclusion (page 1199 in the textbook) predict? The finches would hybridize and become one species. G. fuliginosa would evolve small beaks, and G. fortis would evolve large beaks. One of the finch species would probably disappear from the island. The plants would evolve seeds of different sizes. It is impossible to predict the outcome Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

An obligate mutualism is an interaction in which at least one species cannot survive without the presence of the other species; a facultative mutualism is an interaction that benefits both species but is not required by either species. One reason facultative mutualisms are more common is in an obligate mutualism, if the partner becomes extinct, the obligate mutualist will also become extinct. in a facultative mutualism, if the partner becomes extinct, the obligate mutualist will also become extinct. in an obligate mutualism, the obligate mutualist is obliged to support its partner. in a facultative mutualism, neither partner can depend on the other partner. obligate mutualisms can occur only in tropical environments. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

This graph (Figure 54.10 in the textbook) shows the effect of soil pH on microbial diversity. One conclusion you should draw from this figure is the higher the soil pH, the higher the microbial diversity. the lower the soil pH, the higher the microbial diversity. microbes eat pH. the scientists couldn’t find any acidic or basic soils. there appears to be an optimal pH value for maximizing microbial diversity. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Look at the following figure (Figure 54 Look at the following figure (Figure 54.13 in the textbook), which shows a partial Chesapeake Bay food web. If sea nettles disappeared, this figure predicts that there would be fewer fish eggs. there would be more striped bass. there would be fewer zooplankton. striped bass would have less food to eat. sea nettles would reinvade from the ocean. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Look at the following graph (Figure 54. 15 in the textbook) Look at the following graph (Figure 54.15 in the textbook). Robert Paine removed Pisaster, an uncommon starfish, and measured species diversity. He found species diversity dropped dramatically when Pisaster was not present. From this, we can conclude that uncommon species are more important than common species. predators are more important than prey. Pisaster probably preferred to consume the dominant competitors. Robert Paine’s experiment was poorly designed. removing one species always hurts the community. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Disturbance is an important component of succession because it removes keystone species. changes the biome from one kind to another. introduces invasive species. is associated with humans. tends to promote earlier-successional stages. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

The fact that vertebrate species richness is correlated with potential evapotranspiration indicates that temperature is more important than rainfall. humidity is more important than temperature. humidity is more important than rainfall. rainfall is more important than temperature. mammals prefer stable climates. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

The intermediate disturbance hypothesis predicts that most disturbances are intermediate in intensity. species richness is highest when disturbances are intermediate. most communities are at an intermediate stage of succession. intermediate disturbances maximize competitive exclusion. because species richness corresponds to geographic area, intermediate disturbances increase species richness. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.