Ecology Lab Spring 2024

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Figure 2.1. Energy pyramid Created by Tara Scully The George Washington University tscully@gwu.edu Ecology Lab Lesson I NTRODUCTION Living organisms do not exist in a vacuum. They interact with individuals of their own species ( population ) and with individuals from other species ( community ). These are the living, or biotic , components of an ecosystem. Organisms also interact with all the nonliving, or abiotic , components of the ecosystem—factors like temperature, water availability, nutrients, and energy. An ecosystem is therefore a community of organisms interacting with their physical environment. These interactions are dynamic and complex, changing in space and through time. Ecosystems are not closed systems operating independently of neighboring ecosystems. They are open systems, receiving inputs (organisms, nutrients, energy) from other ecosystems (both neighboring and distant) and providing inputs (organisms, nutrients, energy) to other ecosystems. This characteristic ensures that all ecosystems are interconnected either directly or indirectly and at different scales and times. Ecology is one of the youngest branches of biology. Ecologists try to understand two basic characteristics of any ecosystem: 1. How energy flows through the ecosystem 2. How nutrients are cycled within the ecosystem Almost all ecosystems receive their energy from the sun: Photosynthetic organisms known as producers use the sun’s energy to make sugars. This energy can then be passed upward through food chains to many different consumers ranging from primary consumers like insects that feed on plants, to secondary consumers that feed on primary consumers, to tertiary consumers that in turn feed on secondary consumers. Each feeding level is known as a trophic level . Initial energy from the sun is passed upward in steps, with only about 10% of the energy being passed from one trophic level to the next—as illustrated in Figure 2.1, where an insect-eating bird is a secondary consumer and a bird-eating bird is a tertiary consumer.

Created by Tara Scully The George Washington University tscully@gwu.edu Ecologists study changes in ecosystems through time and are therefore interested in the amount of energy that producers make each year and can pass on to consumer animals. They use a measurement called net primary productivity (NPP): essentially, how much additional plant biomass (weight of organisms per unit of area) is made each year or season in a given area. NPP is clearly different in summer and winter in temperate ecosystems, but it does not change very much in tropical ecosystems. Nutrient availability in temperate ecosystems will also change in different seasons, as factors like temperature and available biomass determine the activity of decomposer organisms, consumers that break down dead animal and plant tissues, making their chemical components available to the ecosystem again. A positive or negative change in the amount of plant biomass available each year will affect the entire food web. O VERVIEW These lab assignments and experiments will explore the ecosystem structure around you, the process of tracking population change, and detect and analyze the impact of synthetic material in your ecosystem. Please read through the entire lab plan and do the Prior to performing the lab instructions before starting any of your lab assignments. All figures in the lab are adapted from Discover Biology. Objective s Student Worksheets Experimental objectives and submissions ■ Construct a local food web. ■ Determine population estimates using the mark–recapture method. ■ Identify the range of factors that affect diversity of life and pollution in ecosystems. ■ Test how variables such as location, vehicle, and pedestrian traffic affect the amount of trash. Worksheet 1: Food webs of your region Worksheet 2: Mark and recapture activity Worksheet 3: Trash analysis and ecosystem health Food webs of your ecosystem I NTRODUCTION Energy in ecosystems passes up the food chain, from producers, to primary consumers, to secondary consumers, finally ending with tertiary consumers as exemplified in Figure 2.1. Note that while most food chains have at least three trophic levels, some complex ecosystems have more. However, individual food chains have many cross-connections to other organisms, creating interconnected food webs (Figure 2.2). A food web connects all of the food chains in a community. To understand complex food webs, ecologists may simplify matters by focusing on just one species population in a specific trophic level. Making annual counts of an individual population over long periods of time enables ecologists to learn what factors might be causing population increases and decreases and, possibly, to predict how a change will cascade through an ecosystem.

Created by Tara Scully The George Washington University tscully@gwu.edu 3 Energy in ecosystems passes up the food chain, from producers, to primary consumers, to secondary consumers, finally ending with tertiary/quaternary consumers. However, individual food chains have many cross-connections to other organisms, creating interconnected food webs. Prior to performing the lab , you should search for the definitions of the following terms: food web, producers, consumers, communities, ecosystems, and biomes. I NSTRUCTIONS CREATE THREE FOOD WEBS: 1. In lab, you will have a selection of producers located throughout the lab. Identify 3 producers that you want to research and take a picture. If you know what they are great! Place these at the base of your foodweb. Label the producers with their genus and species. If you don’t know what they are either google it or use the app: Seek. 2. Next do some digging, identify 2 primary consumers who consume each of your producers (hint – see if there are any consumers located in the lab). Capture/download pictures but be sure to note the website they come from (attach a link to the picture) online. Label each primary consumer with their genus and species. Place these in the next level of your food web and draw a line connecting each primary consumer to the producer they eat. Consider if any of your primary consumers consume both of your producers and make those connections in your food web. 3. From those 6 primary consumers, choose 3 primary consumers and identify 1 secondary consumer that consumes each of the 3 chosen primary consumers you selected (3 total secondary consumers for the entire food web). Capture/download pictures but be sure to note the website they come from (attach a link to the picture) online. Label each secondary consumer with their genus and species. Place these in the next level of your food web and draw a line connecting each secondary consumer to the primary consumer they eat. Consider if any of your secondary

Created by Tara Scully The George Washington University tscully@gwu.edu consumers consume more than one of your primary consumers or producers or each other and make those connections in your food web. 4. Lastly, find 1 tertiary consumer. Capture/download pictures but be sure to note the website they come from (attach a link to the picture) online. Label the tertiary consumer with their genus and species. Place this in the next level of your food web and draw a line connecting the tertiary consumer to the organisms in the lower trophic levels that they eat. Consider if your tertiary consumer consumes more than one of your secondary/primary consumers or producers and make those connections in your food web. Cheat sheet for Food Web Structure Producer level = 3 producers Primary consumer level = each producer should have two primary consumers eating them for a total of 6 primary consumers Secondary consumer level = each primary consumer should have 1 secondary consumer eating them for a total of 3 secondary consumers Tertiary consumer level = only 1 tertiary consumer is necessary, but it must eat all the 3 secondary consumers, or you can have one for each or one that eats two and one that eats that last secondary consumer Mark and Recapture Activity I NTRODUCTION Counting the number of individuals of a species may be relatively easy when we’re dealing with immobile organisms like plants or barnacles or mushrooms, but what about highly mobile animals or protists like Paramecium that can easily move from one area to another? One method that ecologists use is called mark–recapture. Using this method, ecologists capture and tag or mark a certain number of individual animals from a species’ population. The marked animals are then returned to the wild. On a second visit, animals of the same species are captured and the number carrying markings from the first visit is noted. From this information the population size can be estimated by the following formula (the Lincoln– Petersen method): N= MC/R where N = the estimate of total population size M= the number of animals captured and marked initially C = the number of animals captured the second time R = the number of animals that were found to be marked the second time This worksheet expands your food web research to determine how populations change and what influences those changes. Prior to performing the lab , you should search the following terms: population, immigration, emigration, biotic and abiotic factors.

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