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Chapter 55

Chapter 55


Department
Biological Sciences
Course Code
BIOA02H3
Professor
Kamini Persaud
Chapter
55

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Chapter 55 Community Ecology
55.1 What Are Ecological Communities?
- CHARLES DARWIN ALSO A PIONEERING ECOLOGIST WHO UNDERSTOOD THE NATURE AND COMPLEXITY OF THE
INTERACTIONS AMONG A COMMUNITY.
COMMUNITIES ARE LOOSE ASSEMBLAGES OF SPECIES
- HENGRY GLEASON ARGUED THAT PLANT COMMUNITIES WERE LOOSE ASSEMBLAGES OF SPECIES, EACH OF WHICH WAS
INDIVIDUALLY DISTRIBUTED ACCORDING TO ITS UNIQUE INTERACTION WITH THE PHYSICAL ENVIRONMENT.
- FREDERICK CLEMENTS ARGUED THAT PLANT COMMUNITIES WERE TIGHTLY INTEGRATED SUPERORGANISMS AND THAT
COMMUNITIES IN SIMILAR ENVIRONMENTS WOULD HAVE THE SAME SPECIES COMPOSITION UNLESS THEY HAD BEEN
RECENTLY DISTURBED.
- HENRY WAS RIGHT ECOLOGICAL COMMUNITIES ARE NOT ASSEMBLAGS OF ORGANISMS THAT MOVE TOGETHER AS UNITS
WHEN ENVIRONMENTAL CONDITIONS CHANGE; RATHER EACH SPECIES HAS UNIQUE INTERACTION WITH ITS BIOTIC AND
ABIOTIC ENVIRONMENTS.
The organisms in a community use diverse sources of energy
- Organisms in a community can be divided into trophic levels based on the source of their energy.
- A trophic level consists of the organisms whose energy source has passed through the same number of
steps to reach them.
- Plants and other autotrophs = photosynthesizers or primary producers.
- All heterotrophs directly or indirectly consume energy-rich organic molecules produced by primary
producers.
- Organisms that eat plants directly = herbivores or primary consumers.
- Organisms that eat herbivores = secondary consumers.
- Those that eat secondary consumers = tertiary consumers, and so on.
- Organisms that eat the dead bodies of organisms or their waste products = detritivores or
decomposers. Ex: bacteria, fungi, worms, mites, insects. They transform the dead remains (=detritus)
intro free mineral nutrients that can again be taken up by plants. Without these, most nutrients would
eventually be tied up in dead bodies, where they would be unavailable to plants. Continued ecosystems
productivity depends on the rapid decomposition of detritus.
- Organisms that obtain their food from more than one trophic level = omnivores.
- BECAUSE MANY SPECIES ARE OMNIVORES, TROPHIC LEVELS ARE OFTEN NOT CLEARLY DISTINCT, BUT WE TAKE THE
FUZZINESS OF TROPHIC LEVELS INTO ACCOUNT AND THEY ARE THEREFORE STILL USEFUL FOR THINKING OF ENERGY FLOW
THROUGH COMMUNITIES.
- FOOD CHAIN INTERCONNECTED TO MAKE A FOOD WEB BECAUSE MORE SPECIES EATEN BY/EAT MORE THAN ONE SPECIES.
- MOST COMMUNITIES HAVE 3 5 TROPHIC LEVELS BECAUSE OF ENERGY LOSS B/W LEVELS.
- EXPLANATION OF DIAGRAM FROM LECTURE:
- IN MOST TERRESTRIAL ECOSYSTEMS, PHOTOSYNTHETIC PLANTS DOMINATE, BOTH IN TERMS OF THE ENERGY THEY
REPRESENT AND THE BIOMASS THEY CONTAIN.
- IN FORESTS, THE BIOMASS FOR PRIMARY PRODUCERS IS MOSTLY WOOD HARD TO DIGEST.
- IN GRASSLANDS, PLANTS ARE EASIER TO DIGEST.
- THEREFORE, BIOMASS OF HERBIVORES IS LARGER IN GRASSLANDS THAN IN FORESTS.
- IN ACQUATIC ECOSYSTEMS, DOMINANT PHOTOSYNTHESIZERS ARE BACTERIA AND PROTISTS. THOSE UNICELLULAR
ORGANISMS HAVE SUCH HIGH RATES OF CELL DIVISION THAT A SMALL BIOMASS OF PHOTOSYNTHESIZERS CAN FEED
A MUCH LARGE BIOMASS OF HERBIVORES.
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