ACTIVITY 2: INTRODUCTION TO POND ECOLOGY STUDY

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1 ACTIVITY 2: INTRODUCTION TO POND ECOLOGY STUDY Introduction Ecology, as a science, deals with interactions of all organisms within the environment. These interactions not only encompass between-species interactions (e.g., plant-animal interactions), but also interactions between individuals of the same species (e.g., sibling relations; competition for mates; etc.). Another aspect of ecology deals with the environmental conditions that result from abiotic factors (environmental conditions produced by organisms are termed biotic factors). The biotic factors that affect an ecosystem might include the weather, how much water is available for consumption, what type of soil is present, and whether there is enough oxygen to support aerobic respiration. Each species within an ecosystem has slightly different requirements for maintaining life. The earth presents a mosaic of different combinations of abiotic factors, providing a myriad of habitats for biotic organisms. As a result, most organisms are restricted to habitats that have a combination of abiotic factors that allow them to survive. Ecologists term the different areas biomes and the groups of organisms living there communities. Although the terms are new to most people, the concept is already present in their minds. The ecosystems (with their characteristic communities, bigeochemical cycles, and energy flow patterns) are not static entities. Depending on how the environment changes, the biomes in that environment will also change. In fact, starting with new, bare soil or rock, there is a predictable progression of communities and abiotic conditions. This progression is known as succession. An ecosystem is maintained by a delicate balance of interactions between living organisms (biotic factors) and abiotic factors. All organisms, including humans, are subject to the ecological laws that govern the relationships of organisms and their environment. Humans, more than other organisms, have the ability to modify the environment to their own choosing. Such power must be used with care because its misuse can yield disastrous results. Acid rain is a side effect of air pollution. Sulfur oxides and nitrogen oxides react with water in the atmosphere to form sulfuric acid and nitric acid, respectively, which ultimately are returned to earth in rain. The burning of oil and gasoline produces nitrogen oxides. Sulfur oxides are produced by pollutants from burning coal. Pure rainwater has a ph of 5.6 Rainwater with a ph less than 5.6 is classified as acid rain, but rainwater has been recorded with a ph as low as 1.5. Lakes subjected to acid rain have a lowered ph that severely interrupts the normal functioning of the aquatic ecosystem. Few organisms can tolerate such conditions. Organic pollution is largely the result of human activity that increases the quantity of fertilizers, sewage, nitrates, and phosphates in lakes and streams. Organic pollution provides an excess of nutrients for the ecosystem and leads to changes in the community of organisms. Polluted waters tend to have a reduced oxygen content, which kills off desirable heterotrophic species, especially game fish. Aquatic organisms vary in their ability to tolerate organic pollution. Pond Ecology Experiment In a few weeks, we will set up a long-term experiment to simulate three different lake environments: normal, polluted with acid rain, and polluted with organic nutrients. Your task will be to follow and compare these ecosystems to ascertain the effects of acid and organic pollution on a.) the diversity (the number of species present) and density (number of individuals of each species) of organisms, b.) the population growth rates of each organism, and c.) how our manipulations affect the biological community over time. For this experiment, you will work in groups of six (two lab tables per group). Each group will set up three simulated aquatic environments with different abiotic conditions: 1. Normal Ecosystem (control; using tap water) 2. Acid pollution (ph adjusted to 3 with sulfuric acid to simulate acid rain) 1

2 3. Organic pollution (fertilizer added to ecosystem to simulate fertilizer run-off) A functioning ecosystem must also include biotic factors. Since we are interested in examining the effects of abiotic factors on the biotic organisms, we will add the same organisms to each of these three ecosystems. Although our ecosystems will focus on members of Kingdom Protista (common in pond ecosystems), we will also include one plant to provide oxygenation for the ecosystem, and one animal to serve as a predator. Notice that the list of organisms to be included below includes both autotrophic and heterotrophic Protistans. After establishing the appropriate abiotic conditions, we will be adding (stocking) each ecosystem with the same biotic organisms. These organisms will include the following six species: 1. Mixed ciliates (Alveolates; heterotrophic) 2. Euglena (a Euglenozoan; myxotrophic) 3. Diatoms (A photosynthetic Protistan; autotrophic) 4. Desmids (A photosynthetic Protistan; autotrophic) 5. Rotifers (Ph. Rotifera; nearly microscopic, heterotrophic animals) During the laboratory today, you should examine cultures of each of these species by making wet mounts so that you can recognize all of these in future weeks. In addition, you have prepared slides to create your own cheat sheet during the first portion of this laboratory. For this study, each person will be responsible for developing two hypotheses that you can test with the data that we are collecting. The lab report that you will write in this course will address only these hypotheses. We will be discussing the structure and format of scientific papers throughout this course. Before you begin, consider developing your hypotheses to aid you in effective data collection during the course of the experiment. Examples of hypotheses (do not use these): I hypothesize that diatoms will be in higher abundance than heterotrophic organisms in the organic pollution ecosytem relative to the control ecosystem. I hypothesize that ciliates will be more abundant in the organic ecosystem relative to the control ecosystem. Write down your hypotheses here: On the next several pages, you will find examples of some of the hypotheses that students have tested in previous semesters. We will refer to these today, and throughout the semester as examples for this experiment. If you would like, you may also consider some of these results in developing your own hypotheses. 2

3 EXAMPLE 1: Hypotheses: compared to all other organisms, Euglena will have a higher rate of survival in the acid environment. This is because Euglena is resistant to extreme conditions; therefore it is expected to thrive in the acid environment. Second, all of the autotrophs including Euglena will have optimum conditions in the organic environment creating a higher survival rate compared to the normal ecosystem. This is because the organic ecosystem has ideal conditions for autotroph survival because of the overabundance of nutrients. EXAMPLE 2: Hypotheses: Adding fertilizer to an ecosystem will increase the population abundance of all autotrophs including Euglena, and adding acid to an ecosystem will decrease the abundance of all heterotrophs, excluding Euglena 3

4 EXAMPLE 3: Hypotheses: Euglena will be in higher abundance than autotrophic or heterotrophic organisms in the acid pollution ecosystem relative to the control ecosystem. This is because of the mixotrophic characteristics of Euglena. The second hypothesis is that the ratio of all organisms will decline in organic pollution ecosystem relative to the control ecosystem because of the decrease in oxygen concentration in the water. EXAMPLE 4: Hypotheses: In the organic ecosystem, there would be a bottom-up community organization. Therefore, increasing nutrients would increase the autotroph population, and therefore there would be an increase in heterotrophs as well. The second hypothesis is that rotifers would be more abundant in the normal ecosystem relative to the acid ecosystem. This is because the acid ecosystem is hypothesized to have fewer organisms than the normal ecosystem. 4

5 EXAMPLE 5: Hypotheses: Heterotrophs will be more abundant in the organic ecosystem than in the control ecosystem. Fertilizer will result in an increase in abundance of algae, and this will therefore result in an increase in heterotrophs. Second, Euglena will be more abundant in the acidic ecosystem than in the normal ecosystem because Euglena is mixotrophic and more resistant to acidic environments. EXAMPLE 6: Hypotheses: Euglena will be more abundant in the organic ecosystem than in the normal ecosystem. This is because the fertilizer in the organic ecosystem will promote growth. Second, Euglena would be more abundant in the acid ecosystem than in the normal ecosystem. Since Euglena is mixotrophic, it should be able to thrive in the acid ecosystem. 5

6 EXAMPLE 7: Hypotheses: In the organic ecosystem, the autotrophs will be higher in abundance initially and then decrease in abundance compared to Euglena, which we expect to increase in abundance and become the dominant organism. Second, In the acid ecosystem, Euglena will be more abundant than in the control ecosystem. EXAMPLE 8: Hypotheses: Euglena will be more abundant in the acid ecosystem relative to the control ecosystem. Second, in the organic ecosystem, Euglena will initially increase and then level off, whereas other autotrophs will increase and then decrease. In the control ecosystems, both will increase steadily. 6

7 EXAMPLE 9: Hypotheses: There will be a lower abundance of autotrophs and Euglena in the acid rain ecosystem as compared to their abundance in the normal ecosystem. This is because the acidity of the water will limit the types of organisms that can grow. Second, the abundance of heterotrophs and Euglena in the organic pollution ecosystem will be lower than the abundance in the normal ecosystem. This is because organic pollution will decrease oxygen levels in the ecosystem needed for the heterotrophs and Euglena to survive. EXAMPLE 10: Hypotheses: Acid pollution will have a negative effect on the growth of all organisms because most organisms have a narrow ph range in which they can survive. Second, Euglena will have a better survival rate in the acid environment than any other organisms being studied. This is because of the ability of Euglena to utilize different nutritional modes. 7