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Unit 4 Ecosystems Background
Introduction
The abundance of a species and species diversity affect how natural resources are processed within an ecosystem. This pattern of processing contributes to functional and compositional characteristics of an ecosystem. But many ecosystems around the world are currently experiencing significant changes in species composition, abundance, and diversity due to the influence of human activity. These changes have, more often than not, led to a reduction in species diversity. Changes in species composition, species richness, and/or functional type affect the efficiency with which resources are processed within an ecosystem, raising the issue of whether the biogeochemical functioning of an ecosystem will be impaired by a loss of species or the introduction of a new species.

Essential Questions
Why do ecosystems like Tropical Rainforests have such immense diversity? What have scientists discovered that determines how many individuals of a species can be supported within an ecosystem? How does science restore the diversity to areas where human activity has interfered with the natural structure of a habit/ecosystem?

Content
Unit 4 addresses two fundamental questions that ecologists seek to answer: Why is there so much diversity within ecosystems and why are so many species in such abundance? Today ecosystems are shaped and characterized by complex interactions among social, economic, institutional, and environmental variables. The effects of anthropogenic habitat loss or degradation on the numbers and types of species in an ecosystem are still unfolding. The video introduces us to Stuart Davies, director of the Center for Tropical Forest Science (Smithsonian Tropical Research Institution), who studies tropical rain forests, one of the most diverse biomes on Earth. Davies and his research team are conducting a worldwide tree census in an attempt to discover how such a wide range of species competing for the same resources can successfully co-exist. These scientists are trying to understand this by studying energy flow and biogeochemical cycling concepts, niche evolution and partitioning in forests, and the role of predators and pathogens in maintaining diversity (Janzen-Connell effects) and species abundance. The second case study focuses on the rise and fall of different populations in a riparian habitat as a result of a wolf reintroduction project in a temperate ecosystem. Robert Crabtree, chief scientist and founder of The Yellowstone Ecological Research Center, untangles the cascading effect in Yellowstone National Park after the wolf was removed and 70 years later reintroduced. By looking at the balance that exists between species, both scientists wish to learn how to manage and protect any ecosystem from becoming permanently and irreversibly destroyed. Unit 4 - 53 The Habitable Planet

Background
Learning Goals
During this session you will have an opportunity to build understandings of the following. a. Knowledge i. Global circulation patterns and geography create the basic conditions that determine abundance and diversity. ii. Decomposers are more important than organisms at any trophic level when it comes to flow of energy through a food chain or food web. iii. Bioaccumulation of a toxin in the lower trophic levels can lead to biomagnifications in a predator. iv. Living organisms have the capacity to produce populations of infinite size, but environments and resources are finite (carrying capacity). v. Organisms with a narrow niche are the most sensitive to environmental changes. vi. A disruption of ecosystem interactions impacts the natural selection process. b. Skills i. Ability to recognize the mechanism responsible for the elevated absorption of carbon by land ecosystems. ii. Ability to understand how to “harvest” a population without disrupting its natural growth rate. c. Dispositions i. Alteration of ecosystem interaction has a direct impact on social, economic, and...
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