Episodic herbivory, plant density dependence, and stimulation of aboveground plant production

• Published in: Ecology and evolution 2020-06, Vol.10 (12), p.5302-5314
• Main Authors: Ritchie, Mark E., Penner, Jacob F.
• Format: Article
• Language: English
• Subjects: aboveground primary production; Biomass; Density dependence; Dependence; Energy transfer; episodic herbivory; grasslands; grazing; Growth rate; Herbivores; Herbivory; herbivory event; Original Research; Parameter estimation; Plant growth; Plant production; Planting density; plants; Primary production; Productivity; relative growth rate; Serengeti; Stimulation; Sustainability
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.6274

Herbivory is a major energy transfer within ecosystems; an open question is under what circumstances it can stimulate aboveground seasonal primary production. Despite multiple field demonstrations, past theory considered herbivory as a continuous process and found stimulation of seasonal production to be unlikely. Here, we report a new theoretical model that explores the consequences of discrete herbivory events, or episodes, separated in time. We discovered that negative density (biomass) dependence of plant growth, such as might be expected from resource limitation of plant growth, favors stimulation of seasonal production by infrequent herbivory events under a wide range of herbivory intensities and maximum plant relative growth rates. Results converge to those of previous models under repeated, short‐interval herbivory, which generally reduces seasonal production. Model parameters were estimated with new and previous data from the Serengeti ecosystem. Patterns of observed frequent and large magnitude stimulated production in these data agreed generally with those predicted by the episodic herbivory model. The model thus may provide a new framework for evaluating the sustainability and impact of herbivory. The issue of whether herbivores can stimulate plant production remains controversial. Here we develop a theoretical framework for understanding how discrete or episodic herbivory events can stimulate plant production under a wide variety of conditions without increasing nutrient availability. The model predictions, based on new data for relative growth rates of grassland plants, agree reasonably well with previously published data for grazing impacts on above‐ground production in the Serengeti.