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Community & Population Ecology

Nature's medicines Nature's medicines The rosy periwinkle (pink) and Pacific yew(red) are plants that save lives. Both provide substances used in chemotherapy to inhibit the cell division of cancerous cells. Vincristine and vinblastine, two drugs derived from the plant (periwinkle), are used to treat childhood leukemia and cases of Hodgkin's disease respectively. Taxol was initially extracted from the bark of the Pacific yew which is involved in treating ovarian cancer. This topic introduces the science of different plant and animal communities.

Learning Objectives

After completing the topic, the student will be able to:

  • Define, discuss and distinguish the terms “community” and “population ecology”.
  • Illustrate the different types of community interactions.
  • Explore the interesting facts about animal mimicry to prevent themselves from enemies.
  • Define the term trophic level and list the various trophic levels in food chain.
  • Understand the mechanism of how energy is transferred between food chains.
  • Define and describe the term “biological magnification” and analyze the causes, threat and prevention for it.
  • Define and discuss the term “ecological succession” and choose the correct sequence of events that occur during this phenomenon.
  • Define and discuss the term “Biomes” and list different types of biomes.
  • Define and describe the term “Biogeochemical cycles” and list different types of chemical cycles.
  • Describe and analyze the exponential population growth and the circumstances that encourage it.
  • Identify the features of logistic growth and the carrying capacity of a population.
  • Compare density–independent and density–dependent factors that affect population size.
Coral reefs are extensive and diverse marine ecosystems Coral reefs are extensive and diverse marine ecosystems Corals themselves are tiny animals that live in colonies. Corals may be soft or hard (strengthened by secretions of calcium carbonate). Coral reefs are made up of hard and soft corals, sponges, ascidian and algae, all combining to hold the physical structure of the reef together.
Community Ecology

Communities are made of populations that interact with the environment and with each other. An ecological community is a group of actually or potentially interacting species living in the same location. Communities are bound together by a shared environment and a network of influence each species has on the other.

Community ecology is an expanding and rich sub field of ecology. Ecologists investigate the factors that influence biodiversity (variations of life forms), community structure, and the distribution and abundance of species.

These factors include interactions with the abiotic (nonliving chemical and physical factors) world and the diverse array of interactions that occur between species. Species interactions, including competition, predation, herbivory, parasitism and mutualisms, commensalism, are the basis for most of the research in community ecology.

Questions of interest include: What are the feeding relationships among species? Who competes with whom and for what resources? Does the presence of some species benefit others?

A simplified food web A simplified food web Food webs are a graphical depiction of the interconnections among species based on feeding relationships.
Food webs

Food webs are a graphical depiction of the interconnections among species based on feeding relationships, and are a core concept of the field. The role of keystone species in communities is another important tenet, and one of the best–known ideas in community ecology. Keystone species are those whose presence or absence profoundly affects other species in the community, disproportionately to its abundance (relative representation of species).

Community ecologists not only study the structure of communities but also changes in that structure. What do volcanoes, glaciers, sand dunes, storms, agriculture, and fire have in common? They all initiate the process of change in communities.

In the adjacent figure, illustrating a three trophic food chain (producers–herbivores–carnivores) linked to decomposers. A food web is a set of interconnected food chains by which energy and materials circulate within an ecosystem. The movement of mineral nutrients is cyclic, whereas the movement of energy is unidirectional and noncyclic. Trophic species are encircled as nodes and arrows depict the links.

In this chapter, we will examine the factors that are most significant in structuring a community – in determining how many species there are overall, which particular species are present, and the relative abundance of these species. We begin with a fundamental factor influencing community structure: the interactions between the organisms in a community.

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