(Solved): Suppose that researchers wanted to examine the combined effects of an introduced predator (a trout) ...

Suppose that researchers wanted to examine the combined effects of an introduced predator (a trout) and the trematode parasite Ribeiroia on amphibian populations. To do this, they established frog populations in each of 40 artificial ponds. Each pond was assigned at random to one of four treatments ( 10 ponds per treatment): 1) neither trout or parasites were added to the pond (the "No trout, no parasite" treatment); 2) no trout were added but parasites were added ("No trout, parasite added"; 3) trout were added but parasites were not added ("Trout added, no parasite"); and 4) both trout and parasites were added ("Trout added, parasite added"). Each pond contained refugia where tadpoles could avoid attack by trout, to avoid fish predators driving frog populations to extinction in an artificial pond, unlike what typically occurs in a natural pond. After two breeding seasons, the researchers estimated the density of frogs in each pond. The results are shown in the table and the figure. Use the information above to answer this question and the following questions. In this experiment, what is(are) the independent factor(s)? The addition of trout The addition of parasites The addition of trout and the addition of parasites Frog density