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Ecology - Food Webs


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Trophic Cascade
When changes in one trophic level indirectly has much larger changes to all the trophic levels.
a group of species that co-occur in time and space
Energetic Hypothesis
The length of a food chain is limited by the inefficiency of energy transfer along the chain. (10% rule) = a reason why food chains are short.
Dynamic Stability Hypothesis
Long food chains are less stable than short food chains, in recovering from environmental setbacks = a reason why food chains are short.
Food Chain Theory
The world is green because predators hold herbivores in check (Odd # of trophic levels). The world would be barren if the grazers highly suppressed plant growth (Even # of trophic levels)
Faults of Food Chain Theory
-The greens could be inedible.
-Consumers are co-limited by predators and food (or other factors)
-Omnivory blurs trophic levels
-Factors other than consumers or food limit populations
Keystone species
A species not necessarily abundant, but without them the entire trophic system would undergo huge imbalance.
Facilitation (founder species)
These alter the structure or dynamics of the environment, having positive effects on the survival and reproduction of some of the other species in the community.
The total mass of all individuals in a population:
-dominant species are the most abundant, with the most biomass
Reasons for species dominance
1. The dominant species are most competitive in exploiting limited resources such as water or nutrients
2. They are the most successful at avoiding predation or the impact of disease.

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