Summary of the Chapter

Biogeography can be simply defined as the academic study of the factors that control the spatial distribution of organisms. Scientist believe that life first appeared on the Earth about 3.5 billion years ago. At first, life was biologically simple and consisted of one celled organ's that are similar to bacteria. However, as time went on life become more complex and diversified because of evolution. Species are being continually modified genetically as spontaneous mutations create new adaptations to the environment. Some of these new adaptations replace old adaptations through natural selection. Scientists estimate that about 10 to 40 million different organisms inhabit the Earth's surface, sky, and waters. Scientists classify organisms using a hierarchical system first developed several centuries ago by the biologist Linnaeus.

Biologists recognize four general types of life: Archaea; Bacteria; Eukaryota; and Viruses. Scientists have developed a hierarchical system for the classification of these organisms into groups of similar individuals. It is based on the taxonomic (classification based on physiology) and phylogenic (classification based on genetics) characteristics of the organism. At the finest scale, organisms that share similar characteristics are called a species. At the second level of the classification similar organisms belong to a particular Genus. For example, trees that are red maples are classified as Acer rubrum.

Evolution is the process by which organisms come to possess genetic adaptations to their environment by way of natural selection. Adaptations are the various biological characteristics of a species. Adaptations are always changing in a population of organisms because of mutations. Mutations result in an alteration of an organism’s genetic code and therefore can create new traits. However, most mutations are fatal. The few that are not fatal may provide an individual with an adaptation that gives them a competitive advantage in terms of survival. Over time reproduction can spread this adaptation to numerous offspring resulting in evolution.

Scientists have recognized that organisms can be organized according to several different functional levels. The functional level known as species refers to a group of organisms that are similar in morphology and physiology and have the ability to interbreed. All of the different organisms of a single species occupying a specific area on the Earth represents a population. A community is defined as all of the populations of different species inhabiting a particular region of the Earth. The most complex functional level of organization is the ecosystem. An ecosystem consists of the community and its relationship to abiotic factors found in the environment.

Most organisms have the ability to move. Through movement species have the ability to colonize new habitats and expand their geographic range. Evolutionary adaptations that allow a species to expand their geographic range may also make a species more resilient to environmental change. Once dispersed, a species can colonize a habitat if a vacant site for colonization is available and on if the abiotic conditions are right. Finally, colonization leads to establishment. The establishment phase can end for species because of temporal changes in the site's abiotic or biotic characteristics.

A geographic range describes the distribution of a species across space. Geographic ranges are never fixed over time. Instead we find that the geographic range of a species can shift, expand and contact because of changes in a abiotic and biotic factors that influence fitness. Many species are limited in some part of their range by abiotic factors. For each of these abiotic factors, species exhibits variations in its ability tolerate the variable when its quantity in the environment changes. When the abiotic variable is too available or too scarce the species may not be able to survive. In this situation, the species is said to have met its limits of tolerance to this variable. In most situations, the individuals of a species in a particular area are limited by a single abiotic factor that controls the fitness and growth of species.

Species can interact with other species in a variety of different ways. Interactions where neither species directly influences the fitness of the other are called neutralism. Competition occurs when both interacting species are negatively effected in terms of fitness. Competition usually occurs when two or more species are using the same common limiting resource for survival. In an amensalism, one species suffers while the other is not influenced in a positive or negative fashion. Mutualism is an interspecific association where the fitness of the interacting species is positively effected. In many cases mutualisms are necessary for the survival of both interacting species. The final common interaction in nature is one where one species gains while the species suffers. Ecologists call these interactions either parasitism, predation or pathogenic disease.

The ecological niche concept extends the tolerance idea described above. The ecological niche models the effect of all abiotic variables and biotic interactions on the distribution of species. Ecologists often refer to two types of niche: the realized and fundamental niche.

Scientists estimate that between 2 to 100 million species currently inhabit the Earth. Most of these species are found in the tropics. All species will eventually go extinct. In most cases, the extinction of a species is caused by a change in the environment or by the presence of new evolved species. Over the Earth's long history, there have been about 5 or 6 period of time where more than 35% of the species existing become extinct over a relatively short period of time. We call these events mass extinctions. Because of the actions of humans, a large number of this species may become extinct in the immediate future. Since the beginning of the Industrial Revolution, about 700 biologically classified species have gone extinct.

Biodiversity is a term used to describe the diversity of life. This term has a much broader definition than the species concept. Biodiversity describes the diversity of life at the genetic, species, and ecosystem levels. Many scientists like to use the biodiversity concept to describe the abundance of forms of life found on the our planet because of definitional problems that exist with the species concept.

Plant succession is a repeatable, directional change in the types of plant species that occupy a habitat through time after a disturbance. Scientists have classified many different types of succession. In the majority of these successions types, the initial plant community is dominated by small, short lived weed species that have the ability to produce many seeds. The species found the late stages of succession tend to huge, long lived species that produce only a few large well developed seeds. A number of mechanisms have been identified as the causal mechanisms responsible for succession. The mechanisms involved in succession include: facilitation, abiotic modification and resource competition; differential competition of resources by the plant species; and differential competition of space by the plant species.

Ecosystems are dynamic entities composed of a mosaic of biotic and abiotic components that interact in some fashion. Some of the more important components include soil, atmosphere, solar radiation, water, and living organisms. Soil provides the living organisms found in an ecosystem with nutrients, water, a home, and a structural medium for the roots of many types of plants. The atmosphere is an important sink for oxygen, carbon dioxide, and water. These substance cycle from the atmosphere to life and back to the atmosphere mainly through the processes of photosynthesis, respiration, evapotranspiration, and precipitation. The Sun provides ecosystems with energy in the form of radiation which is used to generate heat and power photosynthesis. Water also plays and important role in the functioning of an ecosystem. Water is incorporated into the bodies of organisms, is a medium fro nutrient exchange between soil and life, and is used in photosynthesis.

Ecosystem can also be modeled in terms of energy and matter flow. Plants are the only organisms found in ecosystems that can chemically fix energy. Using the Sun's light and nutrients and water from the environment, plants can create a variety of organic materials. Organic matter is then passed on to heterotrophic forms of life through consumption. A special group of heterotrophs, know as the decomposers, play an important ecosystem function by converting organic matter back into its inorganic constituents. This process also provides the decomposers with energy to run their metabolism. Energy and matter can also move from one ecosystem to another. This movement is done through processes like seed dispersal, animal migration, leaching, and erosion.

A biome is a major ecosystem type that can be found in different regions of the planet where similar environmental conditions exist. The types of species found in a single biome type are often genetically distinct from each other from region to region. However, these species are similar in terms of the morphological and physiological adaptations that they possess indicating similar natural selection processes. The major biomes found on the Earth's surface are: tundra, boreal forest, temperate deciduous forest, grassland, chaparral, desert, tropical savanna, and tropical rainforest. Each of these biomes is described generally in terms of environmental characteristics and the types of plants and animals that dominate these ecosystems.

A portion of the solar energy that enters ecosystems is used by plants to create organic chemical energy. Through photosynthesis, carbon dioxide, water and sunlight are converted into glucose (form of organic chemical energy) and oxygen. Glucose can then be altered, through the addition of other chemicals, into pigments, lipids, sugars, proteins and nucleic acids. This organic energy can then be passed on to other organisms, the heterotrophs, through consumption and assimilation. Energy is freed for use by life through respiration which operates both in plants and animals. The amount of energy fixed by organisms in ecosystems is usually less than 3% of energy received as sunlight. Some ecosystems that are photosynthetically limited because of scarce water or cold temperatures fix less than 1% of the energy available for photosynthesis.

The grazing food chain models the movement of energy in producers and consumers at the trophic level. It begins with the photosynthetic fixing of energy by plants. These plants are then consumed by the herbivores, and the herbivores are consumer by carnivores. Note that you can have several levels of carnivores. The number of levels in the grazing food chain is determined by the productivity of the habitat. More productive habitats have more trophic levels. The detritus food chain models the consumption of waste or dead organisms by the decomposers. The organisms found in this food chain gain their energy either through respiration or fermentation. Consumption of organic matter by decomposers also converts this material into its original inorganic components.

Trophic pyramids are used by scientists to model the flow of energy and organic matter through ecosystems. In most ecosystems, the amount of energy and matter found in each successive trophic level decreases in quantity. This observation is related to assimilation efficiencies and the fact that many organisms have defense mechanisms to reduce the chance of being consumed. A food web is a model that describes who eats who in an ecosystem.

Within an ecosystem nutrients can cycle between the biosphere, hydrosphere, lithosphere, and atmosphere. For each element, the exact pattern of cycling is quite unique and may involve a number of abiotic and biotic processes. About 20 to 30 nutrients are required for the metabolic processes in the various types of life. The most frequently used nutrients are referred to as macronutrients. Carbon, oxygen, hydrogen, nitrogen and phosphorus are the most common macronutrients and they ordinarily constitute more than 1% of the dry weight of an organism. Elements required in very small amounts are called micronutrients. Nutrients can enter or leave the nutrient store of an ecosystem through a variety of processes. In a stable ecosystem, losses of nutrients are normally small in amount. Disturbance can increase the quantity of nutrients removed from an ecosystem substantially. The main processes that add nutrients to ecosystems are weathering, atmospheric input, and biological fixation. Losses of nutrients to ecosystems can occur by way of erosion, leaching, gaseous emission, and the emigration and harvesting of biomass. The magnitude of nutrient loss to ecosystems can often be greater than inputs.

The most active interface of nutrient cycling within an ecosystem is the uppermost layers of the soil. In the soil layer, numerous types of organisms are found whose primary function in the ecosystem is to decompose organic matter. Decomposition breaks down complex organic molecules into much smaller inorganic molecules and atoms. This inorganic matter can then reenter the ecosystem when absorbed by plant roots for metabolism and growth. The soil also receives inputs of nutrients through biological fixation, atmospheric input, and weathering.

The carbon cycle models the movement and storage of carbon in the biosphere, lithosphere, hydrosphere and atmosphere. Carbon is stored in the biosphere as living organisms; in the atmosphere as carbon dioxide gas; in the lithosphere as soil organic matter, as fossil fuel deposits, and as sedimentary rock deposits; and in the oceans as dissolved carbon dioxide gas and as calcium carbonate shells in marine organisms. Processes the move carbon from one store to another include photosynthesis, respiration, oceanic diffusion, biomass combustion, fossil fuel burning, fossil fuel creation, and sedimentary rock formation. Humans have altered the carbon cycle through fossil fuel burning, deforestation, and land-use change. The net result of these processes is an increasing concentration of carbon dioxide in the atmosphere.

The nitrogen cycle is one of the most important nutrient cycles in relation to terrestrial ecosystems. Most plants are limited in their growth by the availability of nitrogen despite the fact that the atmosphere is 78% nitrogen gas. Only a few organisms have the ability to use atmospheric nitrogen. Most organisms prefer nitrogen in the solid nitrate form. Besides the atmosphere, the other important stores of nitrogen are the soil and the organic molecules of life. Nitrogen is added to ecosystems in solid form primarily through biochemical fixation by specialized microorganisms like bacteria, actinomycetes, and cyanobacteria. The conversion of organic nitrogen to inorganic nitrogen within the soil is a complex process that involves a number of organisms and chemical processes. Humans have also severely altered the nature of this nutrient cycle by generally making solid forms nitrogen more available.

 

List of Key Terms

Abiotic, Acidic, Actinomycetes, Adaptation, Algae, Alkaline, Allelopathy, Allogenic Succession, Amensalism, Amino Acid, Ammonia, Ammonium, Amphibian, Anaerobic, Angiosperm, Archaea, Archaebacteria, Asexual Reproduction, Assimilation, Atmosphere, Autogenic Succession, Autotroph,

Bacteria, Biogeochemical Cycling, Biomass, Biome, Biosphere, Biotic,

Calcium Carbonate, Cambrian Explosion,Carbohydrate, Carbonate, Carbon Dioxide, Carnivore, Cation Exchange, Cell, Cellular, Cellulose, Chalk, Chaparral, Chemical Weathering, Chlorophyll, Clay, Climax, Climax Community, Coal, Colonization, Community, Community Boundaries, Competition, Coniferous, Consumer, Cyanobacteria,

Deciduous, Decomposer, Decomposition, Denitrification, Dispersal, Dissociation, Distributional Limit, Disturbance, Detritivore, Detritus, Detritus Food Chain, Dispersal, Divergent Evolution, Diversity, Dolomite, DNA,

Ecological Niche, Ecosystem, Ecotone, Electromagnetic Energy, Element, Eluviation, Energy, Environmental Gradient, Epiphytic, Erosion, Establishment, Eukaryota, Eukaryote, Evolution, Exploitation, Extinction, Evapotranspiration, Evaporation, Evolution,

Facilitation, Facilitation Model of Succession, Fermentation, Fixation, Fixed Energy, Foliar Leaching, Food Chain, Food Web, Fossil Fuel, Fundamental Niche, Fungi,

Gene, Gene Frequency, Gene Pool, Genetic Diversity, Genus, Geographic Range, Glucose, Grazing Food Chain, Gravity, Gross Primary Productivity, Gross Secondary Productivity,

Haploid, Heterogeneity, Heterotroph, Homeostatic, Herbivore, Holistic, Host, Humus, Hurricane, Hydrosphere, Hyphae,

Inhibition Model of Succession, Inorganic, Interaction, Interference, Interspecific Interaction, Intraspecific Interaction,

Laterite, Law of the Minimum, Leaching, Lichen, Lightning, Limestone, Limiting Factor, Lipid, Lithosphere, Litter, Litterfall, Litter Layer,

Macronutrient, Mammal, Metabolism, Micronutrient, Migration, Mineralization, Molecule, Mutation, Mutualism, Mycorrhizae,

Natural Gas, Natural Selection, Negative Feedback, Neutralism, Net Primary Productivity, Niche Specialization, Nitrate, Nitrification, Nitrite, Nitrogen Cycle, Nitrogen Fixation, Nonsymbiotic Mutualism, Nucleic Acid,

Oil, Optimum, Organic, Organic Matter, Oxidization,

Parasite, Pathogen, Peat, Permafrost, Photosynthesis, Photosynthetic Autotroph, Phylogenic, Phylum, Pigment, Pioneer Species, Plant, Population, Positive Feedback, Potential Energy, Precipitation, Predator, Prey, Primary Carnivore, Primary Consumer, Primary Producer, Primary Succession, Producer, Productivity, Progressive Succession, Prokaryote, Protein, Protoplasm, Pyramid of Biomass,

Radiant Energy, Realized Niche, Reduction, Reptile, Respiration, Resource, Retrogressive Succession,

Secondary Carnivore, Secondary Consumer, Secondary Substance, Secondary Succession, Sediment, Sedimentary Rock, Seed Dispersal, Sexual Reproduction, Shale, Sink, Soil, Solar Radiation, Spatial Isolation, Species, Species Associations, Succession, Sugar, Symbiotic Mutualism, System State,

Taiga, Taxonomic, Temperature, Tertiary Consumer, Time, Tolerance Model of Succession, Tolerance Range, Transpiration, Trophic Level, Tropical Rainforest, Tundra,

Virus, Volcano,

Weathering,

 

Study Questions, Problems and Exercises

Essay Questions

(1). Discuss the concept that ecosystems are essentially energy systems.

(2). Compare and contrast the function and structure of the grazing and detritus food chain.

(3). What is an ecosystem? How does it differ from a community? What are some of its important components?

(4). Evolution describes the process by which species come to possess adaptations. In an essay, describe how evolution works through natural selection, spatial isolation, and gene mutation.

(5). Explain in detail how energy moves through the grazing food chain and the detritus food chain. Also, discuss how these food chains are related to each other and are necessary for the cycling of nutrients in an ecosystem.

(6). What seven conditions are required to define something as living?

(7). How did life begin? How did it change from its beginnings to the present?

(8). Outline the four recognized different groups of biological entities.

(9). What are some of the major components of ecosystems? How are these components related to each other?

(10). Describe how energy flows through ecosystems.

(11). Discuss the term dispersal. Include in your answer an explanation of why organisms want to disperse, and how organisms accomplish this life-cycle strategy.

(12). Discuss Connell and Slatyer's three mechanisms of succession. Start your answer with a definition and an example of what is succession, and describe how succession begins.

(13). With the aid of a diagram explain the ecological niche concept. Also, discuss in your essay the difference between the fundamental and realized niche, and the relationship between niche and tolerance range.

(14). Compare and contrast the characteristics (climate, plant types, animal life, soil types, etc.) of the following biomes: Tundra, Temperate Deciduous Forest, Desert, and Tropical Rainforest.

(15). Discuss the different types of species interactions. Be sure to include in your essay information on how each type of interaction between two species influences the fitness of each species.

(16).Species vary in abundance both spatially and temporally. Further, we can generalize that a species will occur only where and when:

(a). It is capable of reaching a location;
(b). Appropriate conditions and resources exist for survival; and
(c). Interspecific interactions do not preclude it.

Discuss these statements fully.

(17). Understanding biogeochemical cycling in an ecosystem requires complete knowledge of the inputs and outputs to that ecosystem. With the aid of diagrams and examples, discuss the cycling of a nutrient in a typical ecosystem focusing on the concept of inputs and outputs to a system.

(18). How do the following attributes control the population dynamics of a species: natality, immigration, mortality and emigration.

(19). Organic matter is continually being added to the surface of soils by way of wastes and death. Why is the input of organic matter important in community and ecosystem function?

(20).Discuss in detail the nitrogen or carbon cycle. In your discussion be sure to explain how humans have altered these systems.

(21). Why should we be careful of introducing exotic animals and plants into habitats where they never existed before?

(22). How does competition differ from predation or parasitism?

(23). What is plant succession? What are the differences between a primary and a secondary succession? How does facilitated succession work?

(24). What is an ecological niche? How do fundamental and a realized niches differ?

(25). Why does the nitrogen cycle require bacteria?