1 Dynamics of Ecosystems Chapter Biology Raven and Johnson 7 th Ed

2 Mimicry Batesian mimicry – Palatable insects resemble brightly colored, distasteful species. Mullerian mimicry – Unrelated protected species resemble one another.  predators learn more quickly

3 Mimicry Batesian mimicry – Palatable insects resemble brightly colored, distasteful species. Mullerian mimicry – Unrelated protected species resemble one another.  predators learn more quickly

4 Coevolution and Symbiosis Coevolution involves long-term mutual evolutionary character adjustments of two or more species. – predator-prey interactions – symbiotic relationships  two or more kinds of organisms live together in permanent relationships  commensalism, mutualism, and parasitism

5 Interactions Among Ecological Processes Keystone species – Species that have a particularly strong effect on community composition.  top predators

6 Succession Succession is the process of ecosystems changing from a simple to a more complex structure. – primary succession - occurs in bare or open areas  eutrophication of oligotrophic lakes  Lichens first, then mosses, then larger plants. – secondary succession - occurs following only when soil is already present

7 Carbon Cycle CO2 is formed in many ways, but only photosynthesis can break it down.

8 The Nitrogen Cycle Relatively few types of organisms can fix nitrogen into forms that can be used for biological processes. Nitrogen fixation: N 2 + 3H 2  2NH 3 – Only symbiotic bacteria fix enough nitrogen to be of major significance in nitrogen production. – ammonification – denitrification

9 Nitrogen Cycle

10 The Phosphorus Cycle Phosphates weather from soils into water, enter plants and animals, and are re- deposited in the soil when plants and animals decompose. – Millions of tons are added to agricultural land annually to increase crop production.  Superphosphate- can cause oligotrophication of water sources by “choking”.

11 Phosphorus Cycle

12 Trophic Levels Autotrophs - capture light energy and manufacture own chemical energy – primary producers Heterotrophs - must obtain organic molecules that have been synthesized by autotrophs – consumers

13 Trophic Levels – Primary consumers - herbivores – Secondary consumers - organisms that feed on herbivores – Decomposers - break down complex organic material into simpler compounds – Detritivores - live on refuse of an ecosystem

14 Trophic Levels

15 Trophic Levels Trophic level refers to the feeding level of an organism. – Organisms from each trophic level constitute a food chain.  Interconnected food chains constitute a food web. On average, 10% of the organic matter (energy) transfers from one trophic level to the next.

16 Primary Productivity Primary productivity refers to the amount of organic matter produced from solar energy in a given area during a given period of time. – Gross primary productivity is the total organic matter produced. – Net primary productivity is the amount of organic matter produced that is available to heterotrophs. Secondary productivity - rate of production by heterotrophs

17 The Energy in Food Chains Due to the Second Law of Thermodynamics, food chains are generally limited to three or four steps (trophic levels). – A community’s productivity is ultimately determined by the amount of sunlight it receives. – In northern climates, net primary productivity often increases as the growing season lengthens.

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