PART I: Calculating Species Diversity

PART I: Calculating Species Diversity (15 points)

Part I is based on Habit, E. et al. 2006. Response of the fish community to human-induced changes in the Biobío River in Chile. Freshwater Biology 51: 1–11.) YOU WILL NEED TO READ THIS PAPER TO ANSWER SOME OF THE QUESTIONS. IT IS POSTED IN THE HOMEWORK MODULE IF THE LINK DOES NOT WORK.

INTRODUCTION

Species richness and species diversity are important ways of characterizing and understanding the structure of communities. Comparing species richness and diversity through time and among different locations is one way to determine effects of environmental change on communities. In this exercise you will use species richness and diversity to infer effects of industrial developments by humans on the freshwater fishes of a large river in central Chile—the Biobío River (Figure 1).

Figure 1  Upper Biobío River, VIII Region, Chile. (Photo by William M. Ciesla, Forest Health Management International, Bugwood.org/CC BY-NC 3.0 US)

In the Amazon Basin to the north of Chile and east of the Andes Mountains, freshwater fish communities are extremely rich and diverse. Even small drainages may have 200+ species. In contrast, the Biobío River in central Chile has the highest richness of any of the rivers in Chile at 17 native species. Many of these species are endemic to the central Chilean rivers and several are considered threatened or endangered. The 17 native species include catfishes such as Trichomycterus areolatus (Figure 2), and Diplomystes nahuelbutaensis, the percids Percichthys trucha (Figure 3) and Percilia irwini, the lampreys Geotria australis, and Mordacia lapicida, and the galaxiids Aplochiton zebra, and Galaxias maculatus.

Figure 2  The catfish Trichomycterus areolatus. (Photo by Pablo Reyes Lobao-Tello/CC BY 3.0)

Figure 3  The percid Percichthys trucha. (Photo by Pablo Reyes Lobao-Tello/CC BY 3.0)

The Biobío River is also important for human uses such as for drinking water, irrigation, hydroelectric power generation, and industrial uses. Human use of the river has increased dramatically since about 1995. We will compare patterns of richness and diversity from four zones along the river to determine possible effects of human developments on the fish community.

The general pattern of fish species communities in Chilean rivers is increasing richness and diversity as you move downstream. Upstream communities have relatively few species, but those species occur throughout the length of the river. New species are added to the list as you move downstream. For example, in the smaller Andiléan river system located just north of the Biobío drainage, upstream locations have on average 3.2 species of fish. Downstream locations have on average 7.3 species, and the community is composed of the same species found in the upstream locations plus new species found only in the lower locations. We would expect the same pattern of richness and corresponding diversity in the Biobío River.

Species richness is simply the number of fish species in a given location. For our measure of diversity we will calculate the Shannon index as given in Chapter 16 as follows:

Where p_i is the proportion of the total number of individuals in the sample that are species i, and S is species richness, (i.e., the total number of species in the sample). Examples of how to calculate the Shannon Index are found in Chapter 16.

QUESTIONS

The table below (on the following page) is of fish species found in the Biobío River. In columns labeled Zone 1 to Zone 4 are the number of individuals of a given species found in each zone. Zone 1 represents the most upstream locations and Zone 4 is the most downstream location. Using this table you can determine richness and diversity of the fish community in each zone.

Question 1:

Calculate species richness and the Shannon diversity index for each zone in the highlighted table provided below.

Fill in your answers in the table below (1 point each for highlighted calculations/cells). Note: rest of table (i.e., proportions of individuals) must be filled in correctly to get correct answers for calculations of H).

Question 2:

Describe the patters in both species richness and diversity (H) across the zones from upstream to downstream. Are the patterns the same for both richness and diversity? Explain your answer (3 points).

Question 3:

In relatively undisturbed rivers, we expect both richness and diversity to increase from upstream locations to downstream locations. Historically, the Biobío River showed this same pattern. Is the current pattern consistent with this expectation (1 points)? In the paper, what factors did the authors describe that might cause a change in the typical pattern (3 points)?

Continue to Part II Below

PART II: How Do Predation and Dispersal Interact to Influence
Species Richness? (15 points)

As described in the textbook (Analyzing Data 19.1; Page 438), the Shurin (2001) study considered the roles of predation and dispersal on the species richness of zooplankton communities. Shurin also measured the abundance of phytoplankton, which is eaten by the zooplankton. The figure below shows the amount of chlorophyll a (a measure of phytoplankton abundance) in the four predation treatments, with and without dispersal, imposed in the experimental ponds: (1) no predators, (2) fish predators only (juvenile bluegill sunfish, Lepomis macrochirus), (3) insect predators only (the backswimmer bug Notonecta undulata), and (4) both fish and insect predators.

QUESTIONS

Question 1:

How did predation alone affect the abundance of phytoplankton within the ponds (2 point)? Give a plausible explanation for why this occurred. Did fish and insect predators have different effects on phytoplankton abundance without dispersal (2 points)?

Question 2:

How does phytoplankton abundance change with the addition of zooplankton dispersal into the ponds (2 points)? Without knowing anything about zooplankton abundance in the ponds, can you say what these results suggest about the dual effects of predation and zooplankton dispersal on phytoplankton abundance (2 points)?

Question 3:

Was there a difference in the effect of predation and zooplankton dispersal treatments on phytoplankton abundance (1 point)? If so, what does this suggest about the role of different predators on phytoplankton abundance (2 points)?

Question 4:

Suppose an additional treatment, that of doubling the dispersal of zooplankton, was added to this experiment. What would you predict this treatment would do to phytoplankton abundance in the fish-only versus insect-only predation treatments (2 points)? Consider the entire range of zooplankton dispersal, from none to intermediate to heavy. What type of relationship between dispersal and phytoplankton abundance would be produced (2 points)?