Ingestion Rates of Deposit Feeders

Aquatic deposit feeders are organisms that feed on organic material in the bottoms of lakes and oceans. Display 9.21 shows the typical dry weight in mg, the typical ingestion rate (weight of food intake per day for one animal) in mg/day, and the percentage of the food that is composed of organic matter for 19 species of deposit feeders. The organic matter is considered the "quality" part of their food. Zoologist Leon Cammen wondered if, after accounting for the size of the species as measured by the average dry weight, the amount of food intake is associated with the percentage of organic matter in the sediment. If so, that would suggest that either the animals have the ability to adjust their feeding rates according to some perception of food "quality" or that species' ingestion rates have evolved in their particular environments. Ana- lyze the data to see whether the distribution of species' ingestion rates depends on the percentage of organic matter in the food, after accounting for the effect of species weight. Also describe the association. Notice that the values of all three variables differ by orders of magnitude among these species, so that log transformations are probably useful. (Data from L. M. Cammen, "Ingestion Rate: An Empirical Model for Aquatic Deposit Feeders and Detritivores," Oecologia, 44 (1980): 303-10.)