When teaching ecology classes I frequently apply a method called concept-mapping. In concept-mapping assignments students are asked to connect different concepts on a sheet of paper with labeled arrows, thus outlining the interrelations among these concepts. I noticed that, if you wait long enough, every concept will be connected to every other. In addition to initially drawn solid arrows, over time, there are more and more dashed arrows drawn. Students like to expand the assignment to include dashed arrows that indicate indirect interactions and feedbacks among concepts.
|Lake Erken’s shoreline and all the other lakes in our survey are near-pristine except for the introduction of the zebra mussel (Photo credit: PE Hirsch).
|Zebra mussels are numerous in Lake Erken and in the other studied mussel-lakes (Photo credit: PE Hirsch)
|Phenotypic divergence between pelagic (top individuals) and littoral (individuals below) was higher in lakes with zebra mussels (Photo credit: PE Hirsch)
|Perch feeding on zebra mussels on the underside of a foot bridge in one of the study lakes (Photo credit: PE Hirsch)