Keystone Predation and Plant Species Coexistence: The Role of Carnivore Hunting Mode

Abstract

Plant communities are shaped by bottom-up processes such as competition for nutrients and top-down processes such as herbivory. Although much theoretical work has studied how herbivores can mediate plant species coexistence, indirect effects caused by the carnivores that consume herbivores have been largely ignored. These carnivores can have significant indirect effects on plants by altering herbivore density (density-mediated effects) and behavior (trait-mediated effects). Carnivores that differ in traits, particularly in their hunting mode, cause different indirect effects on plants and, ultimately, different plant community compositions. We analyze a food-web model to determine how plant coexistence is affected by herbivore-consuming carnivores, contrasting those causing only density-mediated effects with those causing trait-mediated effects as well. In the latter case, herbivores can adjust their consumption of a refuge plant species. We derive a general graphical model to study the interplay of density- and trait-mediated effects. We show that carnivores eliciting both effects can sustain plant species coexistence, given intermediate intensities of behavioral adjustments. Coexistence is more likely, and more stable, if the refuge plant is competitively dominant. These results extend our understanding of carnivore indirect effects in food webs and show that behavioral effects can have major consequences on plant community structure, stressing the need for theoretical approaches that incorporate dynamical traits.

Keystone nonconsumptive effects within a diverse predator community

“…Likewise, defenses that require prey traits to move in one direction to protect against one predator species, but another direction to defend against a second predator, can lead to intermediate strategies/morphologies not fully protective against either predator species (e.g., McIntosh & Peckarsky, ). Our results support the argument that recreating natural variation in predator biodiversity, and thereby portraying the broad ranges of predator community compositions typical of many field situations, provides an opportunity to capture the full diversity of multipredator effects through nonconsumptive mechanisms (Calcagno, Sun, Schmitz, & Loreau, ; Davenport & Chalcraft, ; Hoverman & Relyea, ). Although we believe it is clear Aeshna is altering NCEs imposed by mesopredator communities, some of the patterns we observed (e.g., increased C. pipiens larval survival, but decreased adult longevity in Aeshna communities) are difficult to describe mechanistically with our design, which did not take any physiological measurements such as respiration rate or stress hormone measurements.…”

Scientific Foundations for an IUCN Red List of Ecosystems

“…Decoupling of interactions may reduce diversity by preventing some species from completing their life cycles [126], [129]. Trophic diversity (Table 5), a special case of interaction diversity where interactions are directional and hierarchical [141], can mediate co-existence, resilience and function in contrasting ecosystems [15], [58], [139], [142].…”

Lignes directrices pour l’application des critères et catégories de la Liste Rouge des Écosystèmes de l’UICN version 1.0

“…Les assemblages de carnivores divers (de comportement et densité variés) favorisent la coexistence des espèces végétales (Calcagno et al 2011). Le déclin de la proie primaire précipite le changement de régime et de phase (Springer et al 2003).…”