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Biology LibreTexts

Table of Contents

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  • This collection provides an overview of what is meant by the term ‘biodiversity,’ and how we measure it. The collection reviews the different levels of biodiversity, or the ‘biodiversity hierarchy’ including: genetic and phenotypic diversity; population diversity; species diversity; community diversity; ecosystem diversity; landscape diversity; and historical and ecological biogeographic diversity.
    • 11: Ecosystem Diversity

      An ecosystem is a community plus the physical environment that it occupies at a given time. An ecosystem can exist at any scale, for example, from the size of a small tide pool up to the size of the entire biosphere. However, lakes, marshes, and forest stands represent more typical examples of the areas that are compared in discussions of ecosystem diversity.
    • 12: Population Diversity

      A population is a group of individuals of the same species that share aspects of their genetics or demography more closely with each other than with other groups of individuals of that species (where demography is the statistical characteristic of the population such as size, density, birth and death rates, distribution, and movement of migration). Population diversity may be measured in terms of the variation in genetic and morphological features that define the different populations.
    • 13: Biogeographic Diversity

      Biogeography study's the distribution of organisms in space and through time. Analyses of the patterns of biogeography can be divided into historical biogeography and ecological biogeography. Historical biogeography uses past events in the geological history of the Earth and ecological biogeography examines the dispersal of organisms (usually individuals or populations) and the mechanisms that influence this dispersal to explain patterns in the spatial and temporal distributions.
    • 14: Community Diversity

      A community comprises the populations of different species that naturally occur and interact in a particular environment. Some communities are relatively small in scale and may have well-defined boundaries. Some examples are: species found in or around a desert spring, the collection of species associated with ripening figs in a tropical forest, and those clustered around a hydrothermal vent on the ocean floor. Other communities are larger, more complex, and may be less clearly defined.
    • 15: Ecoregions

      An ecoregion is a relatively large unit of land or water containing a geographically distinct assemblage of species, natural communities, and environmental conditions. Several standard methods of classifying ecoregions have been developed, with climate, altitude, and predominant vegetation being important criteria. Bailey's classification is one of the most widely adopted. It is a hierarchical system with four levels: domains, divisions, provinces and sections.
    • 16: Extinction

      Extinction (the complete disappearance of a species from Earth) is an important part of the evolution of life on Earth. The current diversity of species is a product of the processes of extinction and speciation throughout the previous 3.8 billion year history of life. There might be 40 million species alive today, but between 5 and 50 billion species have lived at some time during the history of the Earth.
    • 17: Landscape Diversity

      A landscape is "a mosaic of heterogeneous land forms, vegetation types, and land uses" (Urban et al., 1987). Therefore, assemblages of different ecosystems (the physical environments and the species that inhabit them, including humans) create landscapes on Earth. Although there is no standard definition of the size of a landscape, they are usually in the hundred or thousands of square miles.
    • 2: Definition of Biodiversity

      Biodiversity is a complex topic, covering many aspects of biological variation. In popular usage, the word biodiversity is often used to describe all the species living in a particular area. If we consider this area at its largest scale - the entire world - then biodiversity can be summarized as "life on earth." However, scientists use a broader definition of biodiversity, designed to include interactions with the abiotic aspects of their environment.
    • 3: Spatial Gradients in Biodiversity

      Generally speaking, warm tropical ecosystems are richer in species than cold temperate ecosystems at high latitudes. A similar pattern is seen for higher taxonomic groups (genera, families). Various hypotheses (e.g., environmental patchiness, solar energy, productivity) have been raised to explain these patterns.
    • 4: Introduction to the Biodiversity Hierarchy

      To effectively conserve biodiversity, we need to be able to define what we want to conserve, determine where it currently occurs, identify strategies to help conserve it, and track over time whether or not these strategies are working. The first of these items, defining what we want to conserve, is complicated by the remarkable diversity of the organisms themselves. This is a product of the genetic diversity of the organisms.
    • 6: Species Diversity

      Strictly speaking, species diversity is the number of different species in a particular area (species richness) weighted by some measure of abundance such as number of individuals or biomass. However, it is common for conservation biologists to speak of species diversity even when they are actually referring to species richness.
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