Double Feedback Loops

figure 8.11 diagrams the feedback loops that led to the Cambrian explosion. Both extrinsic (environmental) and intrinsic (due to the animals themselves) factors are addressed, and they are inextricably linked in the creation of a more complex marine biosystem, through food chain lengthening and increase in the height of the trophic pyramid. For instance, as available environmental niches are filled, more biotic resources are available and a new predator can evolve to take advantage of the newly evolved prey. These changes are fed back into the evolution of the organisms themselves. Skeletoniza-tion and other defenses such as burrowing can occur in response to increases in predation pressure. Burrowing can uncover new sources of food and change the sea floor in ways beneficial for other hetero-trophic animals. Behavioral changes in animals can occur via both predator-prey escalation and improved efficiency of low-level heter-otrophic feeding strategies, for instance, as when deposit feeders

Garden of Ediacara Heterotrophic Pyramids

Dominant

Autotrophy

Predation

trophic strategies

Filter feeding

Grazing

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