University:
Massachusetts Institute of Technology
Course:
12.00 | Frontiers and Careers in Earth, Planets, Climate, and Life
Academic year:

2022
Views:

366

Pages:

1
Author:

StellarStrategist

Communities and Ecosystems Define the following terms Distinguish between Species: A group of organisms that can interbreed and produce fertile offspring Autotroph: An organism that synthesises its organic molecules from inorganic substances Habitat: The environment in which a species Heterotroph: An organism that obtains its normally lives or the location of a living organism organic molecules from other organisms Population: A group of organisms of the same species who live in the same area at the same time Consumer: An organism that ingests other Community: A group of populations living and organic matter that is living or recently killed interacting with each other in an area Detritivore: An organism that ingests non- Ecosystem: A community and its abiotic living organic matter environment Saprotroph: An organism that lives on or in Ecology: The study of the relationships between living organisms and between organisms and the environment non-living organic matter, secreting digestive enzymes into it and absorbing the products of digestion Food chains versus food webs • Food chains and food webs both describe the feeding relationships in a community • Arrows represent the transfer of energy and matter (point in the direction of energy flow) • The position an organism occupies is it’s trophic level (1st = producer; 2nd = 1° consumer, etc.) • Food chains show linear relationships food webs show interconnected relationships Food Chains Food Webs Algae → Carp → Kingfisher → Water Snake Algae Waterweed → Pond Flies → Frog → Snake Waterweed Carp Frog Pond Flies Phytoplankton → Zooplankton → Tuna → Orca Kingfisher Snake Explain energy flow in a food chain • The initial energy source for (almost) all communities is sunlight • Autotrophs (producers) convert light energy into organic matter via photosynthesis • Heterotrophs consume this organic matter in order to meet their energy requirements • Only ~10% of the energy is passed from one trophic level to the next, the rest is lost (as heat, used in cellular respiration, lost in faeces, etc.) • Because of this, the length of a food chain is limited (terminates with a saprotroph) Pyramids of energy • Pyramids of energy show the energy flow across trophic levels in a community (with producers at the bottom) • They are expressed in units of energy per area per time (e.g. kJ/m2/year) • They will always appear as a pyramid, as energy transformations are not 100% efficient, so higher trophic levels always have less energy (~90% less) than preceding levels Nutrients Energy flows, nutrients recycle 1 J/m2/year 10 J/ m2/year 100 J/ m2/year 1,000 J/m2/year • Energy flow is limited as it cannot be recycled and must be replaced by a continuous external source (the sun) • Nutrients (material required by an organism) are constantly being recycled within an ecosystem as food • Decomposers (saprotrophic bacteria and fungi) recycle nutrients by returning them to the soil for plants to use