Evolution of territoriality by herbivores in response to host plant defenses

Plant defenses limit resource availability and concentrate herbivores at specific sites where they then suffer from induced plant defenses, increased predation and competition. Plant traits that enhance the negative effects of competition and increased predation must be included in the suite of plant defenses against herbivory. In an example with Pemphigus gall aphid, plant defenses result in a strong selection pressure favoring territorial behavior. The negative effects of competition give territorial individuals a 2.3-fold advantage over non-territorial individuals. Induced defenses (density dependent leaf abscission) can be just as important as competition as a selection pressure for territorial behavior. With the addition of induced plant defenses territorial individuals realize a 4.4-fold advantage. In the absence of territorial behavior, predation would probably increase by 52%. The same traits which promote territoriality also encourage cannibalism, a common herbivore behavior. -from Author