Resource-ratio theory applied to large herbivores

Area of Science:

• Ecology
• Zoology
• Theoretical Ecology

Background:

• Resource competition theory (RCT) is well-established for plants and microbes but rarely applied to animals.
• Classical animal competition studies differ in resource description from RCT.
• Applying RCT to animal ecology requires novel resource attribute definitions.

Purpose of the Study:

• To present the first fully specified RCT models for terrestrial animals.
• To distinguish between positive (mineral elements) and negative (plant defenses) resource attributes for animal quality.
• To apply RCT to ungulate communities exploiting plant cell wall and cell contents.

Main Methods:

• Developed novel Resource-Ratio Theory (RCT) models for terrestrial animals.
• Defined animal resources by positive (mineral elements) and negative (plant defenses) attributes.
• Applied RCT to ungulate communities using plant cell wall and cell contents as resources.

Main Results:

• Ungulate species with different body sizes coexist via a "demand-minimizing" strategy, taking less of a competitor's limiting resource.
• Ungulates with different mouth widths experience competitive exclusion with an "extraction-maximizing" strategy, taking more of a competitor's limiting resource.
• Differential resource utilization explains coexistence in grazing herbivores.

Conclusions:

• Body size variation enables grazing herbivores to coexist in grasslands through resource competition.
• Spatial heterogeneity in plant defenses is crucial for maintaining the full diversity of grazing communities.
• Resource competition theory provides a framework for understanding animal community structure and coexistence.