How will level of competition among birds in population b change if many birds from population a join population b

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.        

answer; cindy crawford tina feycarrie underwood///meryl streep;