Bottom-up factors

Verity and Smetacek (1996) have argued that predation or top-down trophic effects are as important as resource-driven or bottom-up factors in structuring planktonic ecosystems. However, grazing control of phytoplankton floristic composition will only occur if secondary consumers are selective for particular algal types. Initial evidence was against such selection. Marshall (1973) reviewed the evidence for dietary restriction in copepods ... 

Phrasing is used to group words together in the utterance, and is influenced by top down factors such as syntax, and bottom up factors which place phrase breaks at roughly equal intervals. 

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