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28: Ecosystems and the Biosphere - Biology

28: Ecosystems and the Biosphere - Biology


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  • 28.1: Energy Flow through Ecosystems
    Grazing food webs have a producer at their base, which is either a plant for terrestrial ecosystems or a phytoplankton for aquatic ecosystems. The producers pass their energy to the various trophic levels of consumers. At the base of detrital food webs are the decomposers, which pass their energy to a variety of other consumers. Detrital food webs are important for the health of many grazing food webs because they eliminate dead and decaying organic material, clearing space for new organisms.
  • 28.2: Biogeochemical Cycles
    Mineral nutrients are cycled through ecosystems and their environment. Of particular importance are water, carbon, nitrogen, phosphorus, and sulfur. All of these cycles have major impacts on ecosystem structure and function. As human activities have caused major disturbances to these cycles, their study and modeling is especially important. Ecosystems have been damaged by a variety of human activities that alter the natural biogeochemical cycles.
  • 28.3: Terrestrial Biomes
    Earth has terrestrial and aquatic biomes. Aquatic biomes include both freshwater and marine environments. There are eight major terrestrial biomes: tropical rainforests, savannas, subtropical deserts, chaparral, temperate grasslands, temperate forests, boreal forests, and Arctic tundra. The same biome can occur in different geographic locations with similar climates. Temperature and precipitation are key abiotic factors that shape the composition of animal and plant communities in biomes.
  • 28.4: Aquatic and Marine Biomes
    Aquatic biomes include both saltwater and freshwater biomes. The abiotic factors important for the structuring of aquatic biomes can be different than those seen in terrestrial biomes. Sunlight is an important factor in bodies of water, especially those that are very deep, because of the role of photosynthesis in sustaining certain organisms. Other important factors include temperature, water movement, and salt content. Oceans may be thought of as consisting of different zones.
  • 28.E: Ecosystems and the Biosphere (Exercises)

Human Activity, Biosphere and Ecology

Human activity leading to waste generation and pollution is shown schematically in Fig. 1.1. The waste produced may be in different state of aggregation, such as solid particles, particles suspended in a fluid, dissolved solutes, vapor and gas.

Some of the wastes, discharged into the biosphere are directly or indirectly harmful to some living species or other, or to the entire biotic community. These wastes are referred to as pollutants. The biotic community is made up of all the living beings: the tiniest members being microbes and the largest members being certain species of whales and trees. Man is the most important member of this community. He is responsible for causing pollution and he is capable of combating pollution.

Man has realized rather recently that his existence on earth is neither independent of the other living beings nor of the abiotic environment. It has also dawned on him that nature (the biosphere) cannot assimilate all the wastes generated by him. Pollution resulting from his activities, particularly from industrial activities has now reached a staggering magnitude. This not only concerns the developed countries, but it is also causing anxiety to the developing countries.

This realization has led man to study the inter-relation (dependence) between the different living beings and their surrounding environment. The environment is made up of land, water, air and the physical factors in the immediate vicinity of a biotic community. This branch of study is known as ecology.

Pollutants are those wastes, which cause adverse effects on the biotic community of an ecosystem by interfering with the growth or health or comfort of different species. In a narrow sense, Pollutants are those substances or effects, which are produced as a result of natural processes and or human activities, that are harmful to man directly or indirectly or prejudicial to his amenities and property.

Ecology is a branch of science, which deals with the distribution, and the population of living beings and their dependence and interaction with surrounding environment. The composition of the biotic community is not uniform throughout the biosphere. The different species making up a community, and the population of each species in a locality, depend on the local abiotic environment, including the weather.

Pollutants, discharged in a locality, affect the biotic community in the neighborhood immediately after the discharge and may affect the entire biotic community in the long run. Hence, for ecological studies selected portions of the biosphere (termed as ecosystems) are considered at a time, and the effects of pollutants (which are likely to be discharged as a result of a proposed activity) on the local flora and fauna of these ecosystems are investigated. Such studies are known as “Environment Impact Assessment” (EIA). The aspects, which need’ examination, for preparation of an EIA report depend on the activity being planned.

Prior to carrying out an activity which is likely to affect an ecosystem, it is desirable to take a stock of the local environment, that is, to prepare an environmental inventory. Based on the environmental inventory, and the EIA Report, an Environmental Impact Statement (EIS) is prepared to highlight the environmental changes expected as a result of a proposed activity. It is to be presented in a specified format as laid down by the national/state/local authority that finally decides about the implementation of the activity.

An Ecosystem:

An Ecosystem in the broadest sense is the entire biosphere with all the living beings and physical factors and chemical environment, which makeup the non-living surroundings sustaining life. Since it is not possible to consider the entire biosphere in an investigation, an ecosystem implies a portion of the biosphere where some living beings are in co­existence with their immediate surrounding environment. An ecosystem is more or less a closed system from which a small amount of material may leave or into which a small amount may enter compared to the amount in internal circulation.

An EIA Report should be prepared to predict the biological and physical changes, which are likely to occur as a result of any proposed activity. It should include suggestions about a new legislation/a change in the existing policies and programmes related to (a) land use pattern, (b) industrialization and (c) operational procedures.

Expected effects on human health and well-being, as a consequence of the proposed activity, should also be mentioned in the report. The report would help in understanding the social, cultural and aesthetic changes in the surroundings, which may occur as a result of the proposed activity.

An Environmental Inventory:

An Environmental Inventory is a compilation of the abiotic environmental information in a locality, prior to implementation of a proposed activity.


What is an ecosystem?

Click to enlarge image Toggle Caption

The word ecosystem means ecological systems. Ecology is the study of ecosystems

An ecosystem includes all the living things (plants, animals and organisms) in a given area, interacting with each other, and with their non-living environments (weather, earth, sun, soil, climate, atmosphere). In an ecosystem, each organism has its own niche or role to play.

Ecosystems are the foundations of the Biosphere and they determine the health of the entire Earth system.

Sir Arthur George Tansley (1871 –1955) was an English botanist who introduced the concept of the ecosystem into biology

Ernst Heinrich Philipp August (1834 –1919) was a German biologist, naturalist philosopher, physician, professor, marine biologist, and artist who discovered, described and named thousands of new species mapped a genealogical tree relating all life forms invented many words commonly used by biologists today, such as phylum, phylogeny, and ecology.

An ecosystem is a community of living organisms (plants, animals and microbes) in a particular area.

The term `eco' refers to a part of the world and `system' refers to the co-ordinating units. An ecosystem is a community of organisms and their physical environment interacting together. Environment involves both living organisms and the non-living physical conditions. These two are inseparable but inter-related. The living and physical components are linked together through nutrient cycles and energy flows.

The organisms in an ecosystem are usually well balanced with each other and with their environment. An ecosystem may be natural or artificial, land-based or water-based. Artificial systems may include a cropland, a garden, a park or an aquarium. Introduction of new environmental factors or new species can have disastrous results, eventually leading to the collapse of an ecosystem and the death of many of its native species. Some of the major non-living factors of an ecosystem are: Sunlight Water Temperature Oxygen Soil Air

How big is an ecosystem?

Ecosystems can be of any size, but usually they are places. An ecosystem may be of very different size. It may be a whole forest, as well as a small pond. An ecosystem may be as large as the Great Barrier Reef or as small as the back of a spider crab's shell, which provides a home for plants and other animals, such as sponges, algae and worms.

Ecosystem boundaries are not marked (separated) by rigid lines. Ecosystems are often separated by geographical barriers such as deserts, mountains, oceans, lakes and rivers. As these borders are never rigid, ecosystems tend to blend into each other. Therefore, a lake can have many small ecosystems with their own unique characteristics. As a result, the whole earth can be seen as a single ecosystem, or a lake can be divided into several ecosystems, depending on the used scale. Scientists call this blending “ecotone”

Ecosystem diversity

Ecosystem diversity is the variety of ecosystems in a given place. An ecosystem is a community of organisms and their physical environment interacting together. For food, shelter, growth and development, all life systems interact with the environment. This is why it is necessary to preserve the ecosystems.

Scales of Ecosystems

Ecosystems come in indefinite sizes. It can exist in a small area such as underneath a rock, a decaying tree trunk, or a pond in your village, or it can exist in large forms such as an entire rain forest. Technically, the Earth can be called a huge ecosystem.

Ecosystems can be classified into three main scales.
Micro: A small scale ecosystem such as a pond, puddle, tree trunk, under a rock etc.
Messo: A medium scale ecosystem such as a forest or a large lake.
Biome: A very large ecosystem or collection of ecosystems with similar biotic and abiotic factors such as an entire Rainforest with millions of animals and trees, with many different water bodies running through them.


Chapter 50 - An Introduction to Ecology and the Biosphere

  • Ecologists ask questions about factors affecting the distribution and abundance of organisms.
  • Ecologists might study how interactions between organisms and the environment affect the number of species living in an area, the cycling of nutrients, or the growth of populations.

Ecology and evolutionary biology are closely related sciences.

  • Ecology has a long history as a descriptive science.
  • Modern ecology is also a rigorous experimental science.
  • Ecology and evolutionary biology are closely related sciences.
  • Events that occur over ecological time (minutes to years) translate into effects over evolutionary time (decades to millennia).
    • For example, hawks feeding on field mice kill certain individuals (over ecological time), reducing population size (an ecological effect), altering the gene pool (an evolutionary effect), and selecting for mice with fur color that camouflages them in their environment (over evolutionary time).

    Ecological research ranges from the adaptations of individual organisms to the dynamics of the biosphere.

    • The environment of any organism includes the following components:
      • Abiotic components: nonliving chemical and physical factors such as temperature, light, water, and nutrients.
      • Biotic components: all living organisms in the individual’s environment.
      • Each landscape or seascape consists of a mosaic of different types of patches, an environmental characteristic ecologists refer to as patchiness. Landscape ecological research focuses on the factors controlling exchanges of energy, materials, and organisms among ecosystem patches.

      Ecology provides a scientific context for evaluating environmental issues.

      • It is important to clarify the difference between ecology, the scientific study of the distribution and abundance of organisms, and environmentalism, advocacy for the protection or preservation of the natural environment.
      • To address environmental problems, we need to understand the interactions of organisms and the environment.
      • The science of ecology provides that understanding.
      • In 1962, Rachel Carson’s book Silent Spring warned that the use of pesticides such as DDT was causing population declines in many nontarget organisms.
      • Today, acid precipitation, land misuse, toxic wastes, habitat destruction, and the growing list of endangered or extinct species are just a few of the problems that threaten the Earth.
      • Many influential ecologists feel a responsibility to educate legislators and the general public about decisions that affect the environment.
        • It is important to communicate the scientific complexity of environmental issues.

        Concept 50.2 Interactions between organisms and the environment limit the distribution of species

        • Ecologists have long recognized distinct global and regional patterns in the distribution of organisms.
        • Biogeography is the study of past and present distributions of individual species in the context of evolutionary theory.
        • Ecologists ask a series of questions to determine what limits the geographical distribution of any species.

        Species dispersal contributes to the distribution of organisms.

        • The movement of individuals away from centers of high population density or from their area of origin is called dispersal.
        • The dispersal of organisms is crucial to understanding geographic isolation in evolution and the broad patterns of geographic distribution of species.
        • One way to determine if dispersal is a key factor limiting distribution is to observe the results when humans have accidentally or intentionally transplanted a species to areas where it was previously absent.
          • For the transplant to be considered successful, the organisms must not only survive in the new area, but also reproduce there.
          • Consequently, ecologists rarely conduct transplant experiments today.
          • Instead, they study the outcome when a species has been transplanted accidentally or for another purpose.

          Behavior and habitat selection contribute to the distribution of organisms.

          Biotic factors affect the distribution of organisms.

          • Do biotic factors limit the distribution of species?
            • Negative interactions with other organisms in the form of predation, parasitism, disease, or competition may limit the ability of organisms to survive and reproduce.
              • Predator-removal experiments can provide information about how predators limit distribution of prey species.
              • For example, the absence of a specific pollinator or prey species may limit distribution of an organism.

              Abiotic factors affect the distribution of organisms.

              • The global distribution of organisms broadly reflects the influence of abiotic factors such as temperature, water, and sunlight.
              • The environment is characterized by spatial and temporal heterogeneity.
              • Environmental temperature is an important factor in the distribution of organisms because of its effect on biological processes.
                • Very few organisms can maintain an active metabolism at very high or very low temperatures.
                • Some organisms have extraordinary adaptations to allow them to live outside the temperature range habitable for most other living things.
                • Most aquatic organisms are restricted to either freshwater or marine environments.
                • Terrestrial organisms face a nearly constant threat of desiccation and have adaptations to allow them to obtain and conserve water.
                • Intensity of light is not the most important factor limiting plant growth in most terrestrial environments, although shading by a forest canopy makes competition for light in the understory intense.
                • In aquatic environments, light intensity limits distribution of photosynthetic organisms.
                  • Every meter of water depth selectively absorbs 45% of red light and 2% of blue light passing through it.
                  • As a result, most photosynthesis in aquatic environments occurs near the surface.

                  Four abiotic factors are the major components of climate.

                  • Climate is the prevailing weather conditions in an area.
                    • Four abiotic factors—temperature, water, sunlight, and wind—are the major components of climate.
                    • Climatic factors, especially temperature and water, have a major influence on the distribution of organisms.
                    • Annual means for temperature and rainfall are reasonably well correlated with the biomes found in different regions.
                    • The sun’s warming effect on the atmosphere, land, and water establishes the temperature variations, cycles of air movement, and evaporation of water that are responsible for latitudinal variations in climate.
                    • Coastal regions are generally moister than inland areas at the same latitude.
                    • In general, oceans and large lakes moderate the climate of nearby terrestrial environments.
                      • In certain regions, cool, dry ocean breezes are warmed when they move over land, absorbing moisture and creating a hot, rainless climate slightly inland.
                      • This Mediterranean climate pattern occurs inland from the Mediterranean Sea.
                      • In the Northern Hemisphere, south-facing slopes receive more sunlight than north-facing slopes, and are therefore warmer and drier.
                      • These environmental differences affect species distribution.
                      • This temperature change is equivalent to that caused by an 880-km increase in latitude.
                      • On the leeward side of the mountain, cool, dry air descends, absorbing moisture and producing a rain shadow.
                      • Deserts commonly occur on the leeward side of mountain ranges.
                      • Belts of wet and dry air on either side of the equator shift with the changing angle of the sun, producing marked wet and dry seasons around 20° latitude.
                      • Seasonal changes in wind patterns produce variations in ocean currents, occasionally causing the upwelling of nutrient-rich, cold water from deep ocean layers.
                      • During the summer and winter, many temperate lakes are thermally stratified or layered vertically according to temperature.
                      • These lakes undergo a semiannual mixing, or turnover, of their waters in spring and fall. Turnover brings oxygenated water to the bottom and nutrient-rich water to the surface.
                      • Forest trees moderate the microclimate beneath them.
                        • Cleared areas experience greater temperature extremes than the forest interior.
                        • A detailed record of these migrations is captured in fossil pollen in lake and pond sediments.
                        • A major question for tree species is whether seed dispersal is rapid enough to sustain the migration of the species as climate changes.
                        • Consider the American beech, Fagus grandifolia.
                          • Climate models predict that the northern and southern limit of the beech’s range will move 700–900 km north over the next century.
                            • ? The beech will have to migrate 7–9 km per year to maintain its distribution.

                            Concept 50.3 Abiotic and biotic factors influence the structure and dynamics of aquatic biomes

                              Varying combinations of biotic and abiotic factors determine the nature of the Earth’s biomes, major types of ecological associations that occupy broad geographic regions of land or water.

                            Aquatic biomes occupy the largest part of the biosphere.

                            • Ecologists distinguish between freshwater and marine biomes on the basis of physical and chemical differences.
                              • Marine biomes generally have salt concentrations that average 3%, while freshwater biomes have salt concentrations of less than 1%.
                              • The evaporation of water from the oceans provides most of the planet’s rainfall.
                              • Ocean temperatures have a major effect on world climate and wind patterns.
                              • Photosynthesis by marine algae and photosynthetic bacteria produce a substantial proportion of the world’s oxygen. Respiration by these organisms consumes huge amounts of atmospheric carbon dioxide.
                              • The pattern and speed of water flow and the surrounding climate are also important.
                              • There is sufficient light for photosynthesis in the upper photic zone.
                              • Very little light penetrates to the lower aphotic zone.
                              • This zone is made up of sand and sediments and is occupied by communities of organisms called benthos.
                              • A major food source for benthos is dead organic material or detritus, which rains down from the productive surface waters of the photic zone.
                              • As a result, water temperature in lakes is stratified, especially in summer and winter.
                              • In the ocean and most lakes, a narrow stratum of rapid temperature change called a thermocline separates the more uniformly warm upper layer from more uniformly cold deeper waters.
                              • Oligotrophic lakes are deep, nutrient poor, oxygen rich, and contain little life.
                              • Eutrophic lakes are shallow, nutrient rich, and oxygen poor.
                              • The limnetic zone is the open surface water.
                              • They can be saturated or periodically flooded.
                              • Wetlands include marshes, bogs, and swamps.
                              • They are among the most productive biomes on Earth and are home to a diverse community of invertebrates and birds.
                              • Because of the high organic production and decomposition in wetlands, their water and soil are low in dissolved oxygen.
                              • Wetlands have a high capacity to filter dissolved nutrients and chemical pollutants.
                              • Humans have destroyed many wetlands, but some are now protected.
                              • Headwaters are cold, clear, turbulent, and swift.
                                • They carry little sediment and relatively few mineral nutrients.
                                • Many streams and rivers have been polluted by humans, degrading water quality and killing aquatic organisms.
                                • Damming and flood control impairs the natural functioning of streams and rivers and threatens migratory species such as salmon.
                                • The salinity of these areas can vary greatly.
                                • Estuaries have complex flow patterns, with networks of tidal channels, islands, levees, and mudflats.
                                • They support an abundance of fish and invertebrate species and are crucial feeding areas for many species of waterfowl.
                                • The upper intertidal zone experiences longer exposure to air and greater variation in salinity and temperature than do the lower intertidal areas.
                                • Many organisms live only at a particular stratum in the intertidal.
                                • The surface waters of temperate oceans turn over during fall through spring.
                                • The open ocean has high oxygen levels and low nutrient levels.
                                • This biome covers 70% of the Earth’s surface and has an average depth of 4,000 meters.
                                • They are formed by the calcium carbonate skeletons of coral animals.
                                • Mutualistic dinoflagellate algae live within the tissues of the corals.
                                • Coral reefs are home to a very diverse assortment of vertebrates and invertebrates.
                                • Collecting of coral skeletons and overfishing for food and the aquarium trade have reduced populations of corals and reef fishes.
                                • Global warming and pollution contribute to large-scale coral mortality.
                                • Most of the ocean’s benthic zone receives no sunlight.
                                • Organisms in the very deep abyssal zone are adapted to continuous cold (about 3°C) and extremely high pressure.
                                • Unique assemblages of organisms are associated with deep-sea hydrothermal vents of volcanic origin on mid-ocean ridges.
                                  • The primary producers in these communities are chemoautotrophic prokaryotes that obtain energy by oxidizing H2S formed by a reaction of volcanically heated water with dissolved sulfate (SO42?).

                                  Concept 50.4 Climate largely determines the distribution and structure of terrestrial biomes

                                  • Because there are latitudinal patterns of climate over the Earth’s surface, there are also latitudinal patterns of biome distribution.
                                  • A climograph denotes the annual mean temperature and precipitation of a region.
                                    • Temperature and rainfall are well correlated with different terrestrial biomes, and each biome has a characteristic climograph.
                                    • The canopy of the tropical rain forest is the top layer, covering the low-tree stratum, shrub understory, ground layer, litter layer, and root layer.
                                    • Grasslands have a canopy formed by grass, a litter layer, and a root layer.
                                    • Stratification of vegetation provides many different habitats for animals.
                                    • Hurricanes create openings for new species in tropical and temperate forests.
                                    • In northern coniferous forests, snowfall may break branches and small trees, producing gaps that allow deciduous species to grow.
                                    • As a result, biomes exhibit patchiness, with several different communities represented in any particular area.
                                    • For example, natural wildfires are an integral component of grasslands, savannas, chaparral, and many coniferous forests.
                                    • Fires are now controlled for the sake of agricultural land use.
                                    • Tropical rain forests receive constant high amounts of rainfall (200 to 400 cm annually).
                                    • In tropical dry forests, precipitation is highly seasonal.
                                    • In both, air temperatures range between 25°C and 29°C year round.
                                    • Tropical forests are stratified, and competition for light is intense.
                                    • Animal diversity is higher in tropical forests than in any other terrestrial biome.
                                    • Deserts have low and highly variable rainfall, generally less than 30 cm per year.
                                    • Temperature varies greatly seasonally and daily.
                                    • Desert vegetation is usually sparse and includes succulents such as cacti and deeply rooted shrubs.
                                    • Many desert animals are nocturnal, so they can avoid the heat.
                                    • Desert organisms display adaptations to allow them to resist or survive desiccation.
                                    • Rainfall is seasonal, averaging 30–50 cm per year.
                                    • The savanna is warm year-round, averaging 24–29°C with some seasonal variation.
                                    • Savanna vegetation is grassland with scattered trees.
                                    • Large herbivorous mammals are common inhabitants.
                                      • The dominant herbivores are insects, especially termites.
                                      • Annual precipitation ranges from 30 to 50 cm.
                                      • Chaparral is dominated by shrubs and small trees, with a high diversity of grasses and herbs.
                                      • Plant and animal diversity is high.
                                      • Adaptations to fire and drought are common.
                                      • Large grazers and burrowing mammals are native to temperate grasslands.
                                      • Deep fertile soils make temperate grasslands ideal for agriculture, especially for growing grain.
                                      • Most grassland in North America and Eurasia has been converted to farmland.
                                      • Coniferous forests have long, cold winters and short, wet summers.
                                      • The conifers that inhabit these forests are adapted for snow and periodic drought.
                                      • Coniferous forests are home to many birds and mammals.
                                      • These forests are being logged at a very high rate and old-growth stands of conifers may soon disappear.
                                      • A mature temperate broadleaf forest has distinct vertical layers, including a closed canopy, one or two strata of understory trees, a shrub layer, and an herbaceous layer.
                                      • The dominant deciduous trees in Northern Hemisphere broadleaf forests drop their leaves and become dormant in winter.
                                      • In the Northern Hemisphere, many mammals in this biome hibernate in the winter, while many bird species migrate to warmer climates.
                                      • Humans have logged many temperate broadleaf forests around the world.
                                      • Alpine tundra is found on high mountaintops at all latitudes, including the tropics.
                                        • The plant communities in alpine and Arctic tundra are very similar.

                                        Lecture Outline for Campbell/Reece Biology, 7th Edition, © Pearson Education, Inc. 50-1


                                        To understand the levels of belonging in an ecosystem, let us consider the diagram below.

                                        Levels of organisation in an ecosystem

                                        Individual, Species, Organism:

                                        An individual is any living thing or organism. Individuals do not breed with individuals from other groups. Animals, unlike plants, tend to be very definite with this term because some plants can crossbreed with other fertile plants.
                                        In the diagram above, you will notice that Gill, the goldfish, is interacting with its environment, and will only crossbreed with other goldfish just like her.

                                        Population:

                                        A group of individuals of a given species that live in a specific geographic area at a given time. (an example is Gill, her family, friends, and other fish of Gill’s species) Note that populations include individuals of the same species, but may have different genetic makeup such as hair/eye/skin color and size between themselves and other populations.

                                        Community:

                                        It includes all the populations in a specific area at a given time. A community includes populations of organisms of different species. In the diagram above, note how populations of goldfish, salmons, crabs, and herrings coexist in a defined location. A great community usually includes biodiversity.

                                        Ecosystem:

                                        As explained in the pages earlier, ecosystems include more than a community of living organisms (biotic) interacting with the environment (abiotic). At this level, note how they depend on other abiotic factors such as rocks, water, air, and temperature.

                                        Biome:

                                        A biome, in simple terms, is a set of ecosystems sharing similar characteristics with their abiotic factors adapted to their environments.

                                        Biosphere:

                                        When we consider all the different biomes, each blending into the other, with all humans living in many different geographic areas, we form a huge community of humans, animals and plants, and micro-organisms in their defined habitats. A biosphere is the sum of all the ecosystems established on planet Earth. It is the living (and decaying) component of the earth system.


                                        Watch the video: The Biosphere (December 2022).