Lecture 1 Introduction to Ecology PDF

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Lecture 1: Ecology Introduction Ecology 1. The scientific study of interactions between organisms and their environment 2. The scientific study of interactions that determine the distribution (geographic location) and abundance of organisms ● ●

Other meanings in public usage Differs from environmental activism and environmental science (solutions to environmental problems)

General Misconceptions 1. Balance of nature – return to original preferred state after disturbance 2. Each species has a distinct role to play in maintaining that balance Ecological Maxims (Guiding Principles) 1. Organisms interact and are interconnected 2. Everything goes somewhere 3. No population can increase in size forever 4. Finite energy and resources result in tradeoffs a. Tradeoffs can be thought of as an investment of energy by species 5. Organisms evolve 6. Communities and ecosystems change over time a. Change can happen either very rapidly or very slowly, depending on the species; biased/limited by our own perception because of our own lifespan so we overlook changes 7. Spatial scale matters Evolution: a change in allele frequencies within a population over time Adaptation: a characteristic of an organism that improves its ability to survive or reproduce Natural Selection: the process by which individuals with certain traits tend to survive and reproduce at a higher rate than other individuals because of those traits Ecological Hierarchy ORGANISM → POPULATION → COMMUNITY → ECOSYSTEM → LANDSCAPE → BIOSPHERE Population: group of individuals of a species that are living and interacting in a particular area Community: association of populations of different species in the same area Ecological studies often include both the biotic (living components), and abiotic (physical components) of natural systems ● Ecosystems, landscapes, and biospheres include both biotic and abiotic components Ecosystem: the community and the physical environment

Landscape: areas that vary substantially from one place to another and typically include more than one ecosystem Biosphere: all living organisms on Earth plus the environments in which they live Producers: capture energy from an external source (e.g. the sun) and use it to produce food Consumers: get energy by eating other organisms or their remains Ecological Studies 1. Observational studies 2. Experimental Manipulation studies Ecological experiments can be done at different scales: A. Laboratory: not realistic and very tightly controlled, less expensive B. Small-scale field (Mesocosm): a lot of control – less than lab but more than large-scale, not as realistic as large scale, balance between lab and large-scale, done after lab study but before large-scale C. Large-scale field: very realistic, very difficult to get large sample sizes and very expensive

Laboratory

Realism Number of Replications Cost

Small-scale (Mesocosm)

Large-Scale

Not very realistic

A little realistic

Very realistic

Many (very controlled)

Medium (less controlled than lab)

Little

Least expensive

A little expensive

Very expensive

Ecological Experiments: Design and Analysis 1. Assignments of treatments and control 2. Replication 3. Random assignment of treatments 4. Statistical analyses (statistical vs. biological significance) Scientific Method ● Scientists use a series of steps called the scientific method: 1. Make observations and ask questions 2. Use previous knowledge or intuition to develop hypotheses 3. Evaluate hypotheses by experimentation, observational studies, or quantitative models 4. Use the results to modify the hypotheses, pose new questions, or draw conclusions about the natural world ●

The process is iterative and self-correcting

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Sometimes experiments cannot be done due to scope or scales, so instead, modeling approaches are used (e.g. computerized simulations)

Case Study: Deformity and Decline in Amphibian Populations ● High incidence of deformities in amphibians ● Declining populations of amphibians worldwide ● Amphibians are especially vulnerable to environmental toxins, making them useful biological indicators ○ Skin is permeable; pollutant molecules can pass through easily ○ Eggs have no protective shell ○ They spend part of life on land and part in water—exposed to pollutants and UV in both environments. ● Observation of Pacific tree frogs suggested that a parasite could cause deformities ● Small glass beads implanted in tadpoles to mimic the effect of cysts of Ribeiroia ondatrae, a trematode flatworm, also produced deformities ● Further studies: deformities of Pacific tree frogs occurred only in ponds, which also had an aquatic snail, Planorbella tenuis, the intermediate host of the parasite The Life Cycle of Ribeiroia ● More complex life cycle for parasite in comparison to other species ● Contingent on other species that need to be present in the environment for them to cleave their lifecycle properly ● A controlled experiment: ○ Tree frog eggs were exposed to Ribeiroia parasites in the lab ○ Four treatments: 0 (the control group), 16, 32, or 48 Ribeiroia parasites ● A field experiment: ○ Six ponds, three with pesticide contamination ○ Six cages in each pond, three with mesh size that allowed parasite to enter

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Hypothesis: pesticides decrease the ability of frogs to resist infection by parasites Another lab experiment: Effect of Ribeiroia infection on immune response and cyst formation

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Other experiments have shown that a wide range of factors are responsible for the decline in amphibian populations The relative importance of factors such as habitat loss, parasites and disease, pollution, UV exposure, introduced species, and others are still being investigated

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Removal of introduced species allows frogs to recover...