Experimental design: controlling variablesdamschen and her team were able to conduct a manipulative experiment to test their hypothesis: connecting patches promotes plant species richness in the patches. they cleared 30 large patches of forest at the savannah river site so that the patches all started with a plant species richness of zero. then they set up different treatments to simulate connectedness and lack of connectedness. they used strips of cleared land, called corridors, to connect patches. to control for the many variables present in a field experiment, it was critical that the experiment was designed properly. if the patches differed in more than the presence or absence of a corridor, it would not be properly controlled, and they could not be certain if their results were caused by the corridor, or some other variable. to test the hypothesis that corridors promote plant species richness, they created two types of patches, shown below. one patch, called the connected patch, was connected to a central patch by a 150-m corridor. a second patch, called the unconnected "winged" patch, was 150 m from the central patch but not connected by a corridor. this design enabled them to control for several factors. the total area of the patch plus the corridor, or the patch plus the wings was the same. the total amount of edge (perimeter of each patch) was similar between the two treatments. both patch types were the same distance from the central patch. below are 4 examples of ways damschen and her colleagues could have designed their experiment. identify what is wrong with each design.