Revisiting the Jarman–Bell Principle

Environmental context shapes the relationship between grass consumption and body size in African herbivore communities

“…Still, the mechanism behind this relationship remains elusive, and further research should attempt to disentangle whether high grass dependence is possible for large herbivores due to the comparatively homogeneous distribution of grasses (Bhat et al, 2020;Staver, Asner, et al, 2019) or shallower nutrient gradients across grass tissues (Güsewell, 2004;Potter & Pringle, 2023;Reich & Oleksyn, 2004).…”

“…That the positive relationship between body mass and grass dependence manifests across a diversity of herbivore communities is encouraging, as it suggests that some general (and scale‐independent) principles do underlie herbivore foraging behavior (Abraham et al., 2022 ; Olff et al., 2002 ) and therefore also their impacts on plants (Karp et al., in revision ; Staver et al., 2021 ). Still, the mechanism behind this relationship remains elusive, and further research should attempt to disentangle whether high grass dependence is possible for large herbivores due to the comparatively homogeneous distribution of grasses (Bhat et al., 2020 ; Staver, Asner, et al., 2019 ) or shallower nutrient gradients across grass tissues (Güsewell, 2004 ; Potter & Pringle, 2023 ; Reich & Oleksyn, 2004 ).…”

“…As such, large herbivores can minimize search costs and therefore lessen starvation risk by specializing in grass (Bhat et al., 2020 ). The second mechanism derives from metabolic theory, which suggests that small herbivores require high‐quality forage but in small quantities, whereas large herbivores can tolerate lower‐quality forage but require large quantities of it (the Jarman‐Bell Principle; Bell, 1971 ; Hopcraft et al., 2010 ; Jarman, 1974 ; Olff et al., 2002 ; Potter & Pringle, 2023 ). Because woody plants have steeper nutrient gradients across tissues than do grasses (Güsewell, 2004 ; Reich & Oleksyn, 2004 ), small herbivores can meet their nutritional needs by selectively feeding on only the high‐quality parts of woody plants, such as fruit, buds, and young leaves.…”

“…Because woody plants have steeper nutrient gradients across tissues than do grasses (Güsewell, 2004 ; Reich & Oleksyn, 2004 ), small herbivores can meet their nutritional needs by selectively feeding on only the high‐quality parts of woody plants, such as fruit, buds, and young leaves. In contrast, larger herbivores can satisfy their greater forage requirements by eating grass in bulk (Abraham et al., 2022 ; Potter & Pringle, 2023 ). Regardless of the mechanism, the pattern of increasing grass dependence with increasing body size has emerged as a robust pattern across tropical herbivore species (Abraham et al., 2022 ).…”