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An Introduction to Ecology (Selected concepts from Ch 18, 19, and 20) Biology 160, Murkowski Overview: We’ll use a few excerpts from these chapters to help orient us to an exciting area of specialty within the field of biology, ecology! As you read, remember that the words in bold are vocabulary terms I would expect you to understand in a quiz or exam. If they’re not clear as you read, check your textbook, ask a colleague, or drop me a note! Introduction: Once you’re familiar with the diversity of life, you’re well-equipped to start asking questions about how organisms interact with each other and the environment. This is ecology! There are several levels at which you can study ecology. I’ll highlight a few in the sections that follow. Levels of Ecology: Ecologists work at many different levels. Some ecologists, for example, are concerned with questions of organismal ecology. These folks want to know how a particular species or population adapts to their abiotic environment. This is a big area of study in these days of rapid climate change! The ecologists tracking the so-called “killer bees” are, for example, very interested in how abiotic factors like temperature affect the spread of these aggressive creatures! Population ecology is the next level up. These ecologists study the factors (both biotic and abiotic) that regulate populations over time. The growth of populations can usually be characterized by one of two types of growth curves, exponential and logistic, as shown at left. (Ignore the equations, unless you like that sort of thing!!) Exponential growth is typical in an ideal environment with unlimited resources. As you can imagine, this type of growth is pretty rare in healthy ecosystems. Instead, populations usually start to run out of resources, slowing their growth rate. This results in a logistic growth model where the population gradually approaches its carrying capacity (K). The carrying capacity is the number of individuals in a population that the environment can sustainably support. When we look around the natural world, we see that some populations over-shoot their carrying capacity, causing sharp die-offs that bring population numbers back down. Others experience a more gradual decrease in their growth rate, gently leveling off at their carrying capacity. These reductions in a population’s growth rate can be caused by both density-dependent, and density-independent factors. The density-dependent factors, as their name suggests, depend on the number of individuals in the population. One of the most common forms of a densitydependent limit on growth is intraspecific competition. (Remember that the prefix “intra” tells us within!) This is competition from other members within your species for the same limited resource. Resources like food supply, nesting sites, predation, and even toxic waste products can all limit a population’s growth in a density-dependent fashion. In contrast, densityindependent factors limit a population’s growth regardless of the size of that population. Weather is often a factor as either heat or cold can reduce a population’s growth regardless of its size (as can floods, fires, and other natural disasters). This observation begs the question, “where are humans at in terms of our carrying capacity?” There are lots of ways to begin to ask this question. One common approach to answering this question is to begin to quantify the amount of resources used by each of us, and compare it to the amount of resources available in a given area. As the image at right shows, much of the world, including those of us in the USA are above the “break-even” red line, meaning we use more resources than our environment can sustainably provide. This is, of course, an average. There are lots of factors that contribute to your overall resource use. It can be an eye-opening experience to calculate your own “ecological footprint” and see how you stack up based on your everyday choices! We’ll try an example of this on our in-class activity this week! A Few Other Final Thoughts: Our ecology lab introduced several other important ecological concepts, including trophic levels, energy pyramids, and a variety of ecological roles species can play in their community. I encourage you to read through the handout a second time and make sure these roles are clear: Keystone Species: This is a term we borrow from architecture. It describes the uppermost stone in an arch. As you can probably imagine from the image at left, if you remove this stone, the entire arch collapses. In ecology, we use this idea to describe not the most abundant species, but one whose presence is required to stabilize the entire species. Hint: As you think back on the Yellowstone video, consider how many different species were impacted by the reintroduction of the wolves. Foundation Species: Ecologists use this term to describe species that have a disproportionate role in supporting other members of the community. You can also often think of these species as literally providing a foundation (the habitat) for a wide variety of other species in the community. If you think about our little friend on the left, for example, his presence creates freshwater ponds, marshes, and wetlands that provide habitat for an enormous assortment of other plants and animals.