Landscape simplification and plant tolerance responses to herbivory affect the outcome of plant-herbivore interactions

Background/Question/Methods

The transition from agricultural landscapes dominated by natural habitats to landscapes dominated by agricultural areas, also known as landscape simplification, has been shown to directly affect herbivore abundance and plant herbivore damage. Those changes in the second trophic level can have vast consequence on plant biomass and productivity.  Tolerance, a compensatory plant response to herbivore damage, decreases the negative effects imposed by herbivores on plants. However, the effect of plant compensatory responses to herbivory in landscapes differing in their simplicity (i.e. percentage of agricultural area) has not been explored. In one Colombian potato variety we previously found that plants attacked by low numbers of Guatemalan potato moth, Tecia solanivora Povolny (Lepidoptera: Gelechiidae) larvae produce a 2.5 fold higher marketable potato yield than undamaged plants, providing a model example of herbivore-mediated overcompensatory plant responses. Previous work also showed that landscape simplification increased potato moth density and decreased plant biomass. In this project we wanted to assess if the induction of compensatory responses would decrease the negative effect of landscape simplification on plant biomass mediated by changes in herbivore abundance. We chose 15 sites differing in the percentage of agricultural area and altitude where we set up plots of overcompensating plants and non-compensating plants under insecticide and non-insecticide treatments to quantify the effect of landscape simplification mediated through changes in herbivore abundance on plant biomass.

Results/Conclusions

As predicted, landscape simplification increased potato moth abundance and the amount of plant tissue damaged by herbivores. Across all varieties and treatments, moth abundance had a negative effect on plant biomass.  In the compensating variety, plant biomass decreased more steeply in control plots than in insecticide-sprayed plots as moth abundance increased.  Despite the negative effect of moth abundance on plant biomass, the overall biomass of the compensating variety in control plots was greater than in insecticide-sprayed plots, while the non-compensating plants had a higher biomass in insecticide sprayed plots than in control plots. Our results show that although compensatory plant responses can increase the negative effect of landscape simplification on plant biomass, these plant responses can also help maintain a higher overall biomass in the presence of herbivores, making the system more productive and less reliable on external inputs.

In conclusion our data suggest that life history traits of plants, such as compensatory responses could play an important role in maintaining ecosystem services such as biomass production under changing environments, with important implications for agricultural production.