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. 2020 May 26;10(13):6385-6394.
doi: 10.1002/ece3.6374. eCollection 2020 Jul.

Weak latitudinal gradients in insect herbivory for dominant rangeland grasses of North America

Dylan R Kent  1 , Joshua S Lynn  1   2 , Steven C Pennings  3 , Lara A Souza  4 , Melinda D Smith  5 , Jennifer A Rudgers  1
Affiliations

Weak latitudinal gradients in insect herbivory for dominant rangeland grasses of North America

Dylan R Kent et al. Ecol Evol. .

Abstract

Patterns of insect herbivory may follow predictable geographical gradients, with greater herbivory at low latitudes. However, biogeographic studies of insect herbivory often do not account for multiple abiotic factors (e.g., precipitation and soil nutrients) that could underlie gradients. We tested for latitudinal clines in insect herbivory as well as climatic, edaphic, and trait-based drivers of herbivory. We quantified herbivory on five dominant grass species over 23 sites across the Great Plains, USA. We examined the importance of climate, edaphic factors, and traits as correlates of herbivory. Herbivory increased at low latitudes when all grass species were analyzed together and for two grass species individually, while two other grasses trended in this direction. Higher precipitation was related to more herbivory for two species but less herbivory for a different species, while higher specific root length was related to more herbivory for one species and less herbivory for a different species. Taken together, results highlight that climate and trait-based correlates of herbivory can be highly contextual and species-specific. Patterns of insect herbivory on dominant grasses support the hypothesis that herbivory increases toward lower latitudes, though weakly, and indicates that climate change may have species-specific effects on plant-herbivore interactions.

Keywords: biogeography; climate change; grass; herbivory; latitudinal gradient; plant–insect interactions; rangeland.

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Conflict of interest statement

The authors have no conflicts of interest to declare.

Figures

Figure 1
Figure 1
Map of sampling locations across the North American plains indicating the gradient of sampling and an inset of the study region within the greater continental USA. Geographic coordinates and further site details are provided in Table S1
Figure 2
Figure 2
Percentage herbivore damage (mean per site) over latitude for all species combined and for each focal species individually. Each point represents average damage for at species × site combination. A solid best‐fit line indicates a relationship with latitude for which p < .05 and a dashed line represents a nonsignificant trend (0.98 > p> .05). (a) All species, (b) Andropogon gerardii (c) Bouteloua dactyloides, (d) Bouteloua eriopoda, (e) Bouteloua gracilis, and (f) Schizachyrium scoparium
Figure 3
Figure 3
Relative effects (standardized slopes) of abiotic factors (growing degree days as GDD, growing season precipitation (PPT), nitrogen (N), phosphorous (P), pH, soil organic matter (SOM), specific leaf area (SLA), or specific root length (SRL) on herbivore damage for all species combined, and for each focal species individually. A positive value indicates an increase in herbivory with the factor, *indicates p < .05., and • indicates 0.1 > p> .05
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