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The Ecosystem Perspective

The Ecosystem Perspective. Examines interactions between whole communities and the physical environment. Emphasizes how physical setting influences trophic structure, energy flow and nutrient cycling.

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The Ecosystem Perspective

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  1. The Ecosystem Perspective • Examines interactions between whole communities and the physical environment. • Emphasizes how physical setting influences trophic structure, energy flow and nutrient cycling. • To fully understand the system requires knowledge from all other perspectives: from individual adaptation, to population dynamics, to community processes, to flows of energy and matter.

  2. An example from the book: energy flows in a temperate forest

  3. Deep SeaHydrothermal Vent Communities: An Example of the Ecosystems Perspective

  4. A New Age of Exploration • In the last 30 years, the development of highly durable and maneuverable deep submersible vessels has opened up the abyss to exploration. • Scientists were able to study the behavior and interactions of midwater organisms and the community structure and physiology of deep water benthic organisms

  5. In the late 1970s, the deep submersible Alvin descended over oceanic ridges near the Galapagos Is. to study hydrothermal vents > 8,000 ft below the surface. • Oceanic ridges are ripples on the sea bottom at the sites of sea floor spreading. • Because the earths crust is thin at the ridges, geothermal activity is high.

  6. One type of hydrothermal vent: a “black smoker” • Hydrothermal vents discharge super heated water, > 4000C. It mixes with ambient sea (40C) forming a temperature gradient away from the opening of the vent. • The discharge is laden with dissolved minerals and gases, including hydrogen sulfide, H2S. Minerals precipitate forming chimneys and ridges around the discharging water.

  7. A Startling Discovery • In the warm waters near the vents, a unique benthic community was discovered. • The most abundant members were crabs, limpets, clams, eel-like fish, and an unusual worm. • The fauna included species of gigantic invertebrates representing previously unknown taxa.

  8. Galotheid crabs

  9. A hydrothemral vent clam and limpets • The limpets graze on free living bacteria on the. • The clams, Calyptogena sp., gain nutrition from internal bacterial symbionts.

  10. Riftia is in the phylum Vestimentifera, endemic to the vents. Large individuals are about 1 meter long. They obtain nutrition only by digesting bacterial symbionts. The bacteria derive all their nutrition from oxidizing hydrogen sulfide.

  11. Riftia has no gut. • The gills (plume) extract oxygen and H2S from the sea water. • Both gases are transported on a form of hemoglobin through the circulatory system to the tissues. The ultimate destination of the H2S and most of the oxygen is the trophosome (feeding body) • Capillary beds in the trophosome distribute the H2S to symbiotic bacteria, which oxydize the H2S, grow and are phagositized by the tissues of the trophosome.

  12. A deep-sea respirometer held in place by the Alvin • The physiology of these organisms is remarkable. • They live at elevated temperatures, but can withstand wide temperature fluctuations. • Ambient pressure can exceed 100 atmospheres.

  13. Most vent communities (white dots) have been found along oceanic ridges, which are zones of sea floor spreading and hydrothermal actvity.

  14. Convection cells deep within the earth bring molten magma to the thin crust at the spreading ridges.

  15. Black smokers and chimneys

  16. Stages of formation and loss of a hydrothermal vent Remarkably, the rock contains life. Bacteria that may be the direct ancestors of the earliest life forms respire chemicals in the rocks.

  17. Stages of vent formation and loss • At the site of a forming vent the sea floor is thin and geothermal activity heats the surface rock and water permeating the rock. • Two groups of bacteria live below the surface in the porous rock and sediments: mesophiles which live in the top few meters in temperature around 500C, and thermomphiles, which live in deeper layers at temperatures approaching 1500C. • An diking event (mini eruption) brings molten magma near the surface. Through convection, water is drawn through the sediments, up along the sides of the dike, and expelled at a fissure, the vent. • It is estimated that the entire volume of the ocean is drawn through the vents in the oceanic ridge systems every 8,000,000 yr.

  18. Marine “Snow” • The water expelled at the vent soon after the diking event carries high concentrations of the two types of bacteria. • The bacteria agglomerate into particles called “snow”

  19. Tropic Structure • The food web is similar to other marine ecosystems -- with filter feeders, grazers, and predators. • The major difference is that all energy derives ultimately from inorganic chemicals, rather than the sun. Chemosynthetic bacteria, either free-living or symbiotic, take the place of the photosynthetic autotrophs of other systems.

  20. A Succession at a vent site B A. When the vent erupts, marine snow falls, an initial bounty. B. After some months, the site is colonized by dispersive species, analids, isopods, etc. C. After several years, Riftia colonies have taken over the site. D. Over time, the composition of the expelled water changes. Additions of iron oxides sometimes stain the Riftia tubes. E. As the concentrations of H2S in the discharge diminish, so does the biomass of the Riftia assemblages. Eventually, the vent fauna becomes at the site. C D E

  21. The colonization problem • Vents are unstable. The appear and disappear in time courses of a few decades to centuries at most. • Therefore, the vent communities must disperse juveniles to find newly formed vents. • Most species have dispersing larvae provisioned with yolky eggs. They swim and ride bottom currents to colonize new vents.

  22. More than one variation on a theme. • Since the discovery of the hot vent communities, cold vent and seepage communities have been discovered in the deep sea. • Any reduced compound appears to provide a suitable energy source. For example, some communities thrive on methane that erupts as organic sediments are subducted under techtonic plates.

  23. Discovery of the hydrothermal vent fauna has spawned a new field of study, “extremophiles”, and transformed our thinking about extraterrestrial life.

  24. Question: In what major way might the energy flow diagram of the hydrothermal vent communities look different from tha of a deciduous forest?

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