Chapter 8 Biogeographic Processes Chapter Objectives Upon completion of this chapter the student will be able to: 1. Define the terms ecosystem, habitat, ecological niche, and community. 2. Outline how plants and animals adapt to the abundance and scarcity of water. 3. Discuss how plants and animals adapt to temperature variations. 4. Comment on the impact of light and wind on plant distributions. 5. Discuss the impact of geomorphic and edaphic factors on the distribution of species. 6. Discuss the positive, negative, and neutral interactions between species that determine distribution patterns. 7. Explain the process of succession. 8. Outline how historical biogeography can contribute to the distribution of species 9. Explain the different distribution patterns of species. 10. Describe how biogeographic regions are determined. 11. Discuss the importance of biodiversity and the direction of change on Earth. Chapter Lecture Biogeography is a branch of geography that focuses on the distribution of plants and animals over the Earth. Ecological Biogeography is concerned with how the distribution patterns of organisms are affected by the environment, including both the physical and biological environment. Historical biogeography focuses on how spatial distribution patterns of organisms arise over time and space. I. Energy and Matter Flow in Ecosystems Ecology is the study of the interactions between life-forms and their environment. An ecosystem is defined as a group of organisms and the environment with which they interact. Ecosystems have inputs of matter and energy that plants an animals use to grow, reproduce and maintain life. Matter and energy are also exported from ecosystems. A. The Food Web This describes how food energy flows from organism to organism within an ecosystem. Primary producers support primary, secondary and higher-level consumers. Decomposers feed on dead plant and animal matter from all levels. B. Photosynthesis and Respiration Photosynthesis is the process in which plants combine water, carbon dioxide, and solar energy to produce carbohydrates. Respiration is the reverse process, in which carbohydrates are oxidized in living tissues to yield the energy that sustains life. Gross photosynthesis is the total amount of carbohydrates produced by photosynthesis. Net photosynthesis is the amount of carbohydrates remaining after respiration has broken down sufficient carbohydrates to power the plant.
Net photosynthesis = Gross photosynthesis Respiration C. Net Primary Production This measures the rate of accumulation of carbohydrates by primary producers. Equatorial rainforests and freshwater swamps and marches are among the most productive ecosystems, while deserts are the least productive. D. Net Production and Climate Day length, air and soil temperature, and water availability are the most important climatic factors that control net primary productivity. E. Biomass as an Energy Source The use of biomass as an energy source involves releasing solar energy that has been fixed in plant tissues through photosynthesis. This process can take place in a number of ways; direct burning of plant matter as fuel, and the generation of intermediate fuels from plant matter. F. The Carbon Cycle The carbon cycle is a biogeochemical cycle in which carbon flows among storage pools in the atmosphere, ocean, and on the land. Human activity has affected the carbon cycle, causing carbon dioxide concentrations in the atmospheric storage pool to increase. G. The Nitrogen Cycle The Nitrogen cycle is a biogeochemical cycle in which much of the nitrogen fixed by human activities is carried away from the soil into rivers and lakes and ultimately reaches the ocean, Major water pollution problems can arise when nitrogen stimulates the growth of algae and phytoplankton. The respiration of these organisms can then reduce quantities of dissolved oxygen to levels that are detrimental to desirable forms of aquatic life. II. Ecological Biogeography This examines the distribution patterns of plants and animals from the viewpoint of ecological factors and interrelationships between species. The habitat of a species describes the physical environment that harbors its activities. The ecological niche of a species describes how it obtains its energy and how it influences other species and its own environment. The community is a group of interacting organisms that occupy a particular habitat. Specific types of communities are called associations. Important physical environmental factors such as temperature and moisture limit where organisms can live. Other factors such as light and wind also play a role. A. Water Need Both plants and animals show a variety of adaptations that enable them to cope with the abundance or scarcity of water. Plants that are adapted to drought conditions are xerophytes. Trees and shrubs that shed their leaves seasonally are deciduous, while evergreen plants retain most of their leaves in a green state through one or more years. Mammals are by nature poorly adapted to desert environments. To cope with water shortages, xeric animals may become dormant during dry periods, nest during the wetter periods of the year and rely on various methods of cooling.
B. Temperature Temperature acts directly to influence the rates at which physiological processes take place in plant tissues. Each plant species has an optimum temperature associated with each of its functions, such as photosynthesis, flowering, fruiting, or seed germination. Fewer species of plants are adapted to cold climates. Cold blooded animals lack a mechanism for temperature regulation and thus are active only during warm periods of the year. Warm blooded animals have adopted methods for maintaining a relatively constant body temperature. C. Other Climatic Factors Light varies with latitude and affects both plant and animal behavior. Ecological factors of light intensity, length of daylight period, length of the growing season, and wind duration and intensity act to determine plant and animal distribution patterns. D. Bioclimatic Frontiers The geographic boundary corresponding with a critical limiting level of climate stress beyond which a species cannot survive. E. Geomorphic Factors Geomorphic factors influencing plant and animal distributions include slope angle, slope aspect, and relief. F. Edaphic Factors These factors include soil particle size and amount and nature of organic matter in the soil. There is a strong coincidence between climate, soil, and biota at the global level. G. Disturbance These factors include fire, flood, volcanic eruption, storm waves, high winds, and other infrequent catastrophic events that damage or destroy ecosystems and modify habitats. It is part of a natural process to which many ecosystems are adapted. H. Interactions Among Species Species interact in a number of ways, including negative interactions; competition, predation and parasitism, herbivory, and allelopathy. Symbiosis refers to a positive interaction between species such as commensalism, protocooperation, and mutualism. III. Ecological Succession Ecological succession refers to the process in which plant communities succeed one another on the way to a stable endpoint. Primary succession occurs on new soil, while secondary succession occurs where disturbances have removed or altered existing communities. A. Succession, Change, and Equilibrium Although succession is the natural tendency for ecosystems to change with time, it is opposed by natural disturbances and limited by local environmental conditions. IV. Historical Biogeography Focuses on how spatial distribution patterns of organisms arise over space and time. It examines four key processes: evolution, speciation, extinction, and dispersal. A. Evolution Life has attained its astonishing diversity through evolution. Natural selection acts on variation to produce populations that are progressively better adjusted to their environment. Variation arises from mutation and recombination. A species is best defined as a population of organisms that are capable of interbreeding successfully, but instead it is usually defined by a typical morphology, or phenotype.
B. Speciation This is the process by which species are differentiated and maintained. Component processes affecting speciation include mutation, natural selection, genetic drift, and gene flow. Isolation, in which breeding populations are separated, enhances speciation. C. Extinction This occurs when populations become very small and thus are vulnerable to chance occurrences of fire, disease, or climate change. Rare but extreme events can cause mass extinctions. D. Dispersal Species expand their ranges by dispersal. Dispersal is the capacity to move from a location of origin to new sites. In diffusion, species extend their range slowly from year to year. In long-distance dispersal, unlikely events establish breeding populations at remote locations. E. Distribution Patterns Spatial patterns of species distribution include: 1. Endemic species are found in one location or region and no where else 2. Cosmopolitan species are widely dispersed and nearly universal. 3. Disjunction occurs when one or more closely related species appear in widely separated regions. F. Biogeographic Regions occur where the same or closely related plants and animals are found together. In these regions species have common histories of evolution and environmental affinity. V. Biodiversity Expresses the variety of biological life on Earth. Human activity has reduced biodiversity by modifying natural habitats and causing extinctions. Extinction rates for many groups of plants and animals are as high or higher today than they have ever been at any time during the past. Preservation of global biodiversity must include strategies aimed at protecting species diversity hotspots. Internet Resources Introduction to biogeography: (http://www.nyu.edu/projects/fitch/courses/evolution/html/biogeography.html) Biogeography.org - An Internet Research Portal: (http://www.biogeography.org/) Ecological succession along the Penn State New Kensington Nature Trail: (http://www.nk.psu.edu/naturetrail/succession.htm) A variety of simple, interactive ecosystem simulation models: (http://www.unicamp.br/fea/ortega/java/index.htm) Environmental biology of grasslands with discussion of succession: (http://www.marietta.edu/~biol/102/grasslnd.html) Plant communities of California: (http://encenter.org/habitat/habitatcontent.html)