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1 The Web of Life Chapter 1 The Web of Life CONCEPT 1.1 Events in the natural world are interconnected. CONCEPT 1.2 Ecology is the scientific study of interactions between organisms and their environment. CONCEPT 1.3 Ecologists evaluate competing hypotheses about natural systems with observations, experiments, and models. Deformity and Decline in Amphibian Populations: A Case Study There is a high incidence of deformities in amphibians. place fig. 1.1 here Amphibian populations are declining worldwide. Figure 1.2 Amphibians in Decline Deformity and Decline in Amphibian Populations: A Case Study Amphibians are “biological indicators” of environmental problems. • Skin is permeable; pollutant molecules can pass through easily. • Eggs have no protective shell. • They spend part of their life on land and part in water—exposed to pollutants and UV in both environments. Introduction Humans have an enormous impact on the planet. It is important that we try to understand how natural systems work. Ecology is the scientific study of how organisms affect, and are affected by, other organisms and their environment. Concept 1.1 Events in the natural world are interconnected. Concept 1.1 Connections in Nature Even species that do not interact directly can be connected by shared environmental features. Ecologists ask questions about the natural world in order to understand these connections. Concept 1.1 Connections in Nature Controlled experiment: Experimental groups are compared with a control group that lacks the factor being tested. Tree frog eggs were exposed to Ribeiroia parasites in the lab. Four treatments: 0 (the control group), 16, 32, or 48 Ribeiroia parasites. Figure 1.4 Parasites Can Cause Amphibian Deformities Figure 1.5 Do the Effects of Ribeiroia and Pesticides Interact in Nature? Concept 1.1 Connections in Nature Hypothesis: Pesticides decrease the ability of frogs to resist infection by parasites. In another lab experiment, tadpoles reared in the presence of pesticides had fewer white blood cells (indicating a suppressed immune system) and a higher rate of Ribeiroia cyst formation. Figure 1.6 Pesticides May Weaken Tadpole Immune Systems (Part 2) Concept 1.2 Ecology is the scientific study of interactions between organisms and their environment. Concept 1.2 What Is Ecology? Ecology is the scientific study of interactions between organisms and their environment. Environmental science incorporates concepts from the natural sciences (including ecology) and the social sciences and focuses on how people affect the environment and how to address environmental problems. Concept 1.2 What Is Ecology? Early ecological views: 1. There is a “balance of nature” in which natural systems are stable and tend to return to an original state after disturbance. 2. Each species has a distinct role to play in maintaining that balance. Concept 1.2 What Is Ecology? Ecologists now recognize that natural systems do not necessarily return to their original state after a disturbance, and seemingly random perturbations can play an important role. Evidence suggests that different species often respond in different ways to changing conditions. Concept 1.2 What Is Ecology? Scientists now recognize that ecological interactions are more complex than previously thought. One view that has stood the test of time: Events in nature are interconnected. A change in one part of an ecological system can alter other parts of that system. Table 1.1 (Part 1) Table 1.1 (Part 2) Figure 1.8 An Ecological Hierarchy Concept 1.2 What Is Ecology? Population: A group of individuals of a species that are living and interacting in a particular area. Community: An association of populations of different species in the same area. Ecological studies often include both the biotic (living) and abiotic (physical) components of natural systems. Figure 1.9 A Few of Earth’s Many Communities Concept 1.2 What Is Ecology? Ecosystem: A community of organisms plus their physical environment. Landscapes: Areas with substantial differences, typically including multiple ecosystems. All the world’s ecosystems comprise the biosphere—all living organisms on Earth plus the environments in which they live. Table 1.2 Concept 1.2 What Is Ecology? All living systems change over time. Evolution: 1. Change in genetic characteristics of a population over time. 2. Descent with modification— organisms gradually accumulate differences from their ancestors. Concept 1.2 What Is Ecology? Adaptation: A characteristic that improves survival or reproduction. Natural selection: Individuals with certain adaptations tend to survive and reproduce at a higher rate than other individuals. If the adaptation is heritable, the frequency of the characteristic may increase in a population over time. Figure 1.10 Natural Selection in Action Concept 1.2 What Is Ecology? Ecosystem processes: Producers use energy from an external source (e.g., the sun) to produce their own food. Net primary productivity (NPP): Energy captured by producers minus the amount lost as heat in cellular respiration. Consumers get energy by eating other organisms or their remains. Concept 1.3 Ecologists evaluate competing hypotheses about natural systems with observations, experiments, and models. Concept 1.3 Answering Ecological Questions No single approach works in all situations, so ecologists use a variety of methods: • Observational studies in the field • Controlled experiments in the laboratory • Experiments in the field • Quantitative models Concept 1.3 Answering Ecological Questions Experimental design: 1. Replication—performing each treatment more than once; reduces possibility that results are due to a variable that was not measured or controlled in the study. 2. Assign treatments at random—also limits the effects of unmeasured variables. Concept 1.3 Answering Ecological Questions 3. Analyze results using statistical methods; standardized ways to determine whether observed differences are significant (great enough to be of biological importance).