Herbivory and resource availability shift plant defense and herbivore feeding choice in a seagrass system
Numerous hypotheses have been posited to explain the observed variation in plant defense strategies against herbivory. Under resource-rich environments, plants are predicted to increase their tolerance (limiting resource model; LRM) and, while the resource availability hypothesis (RAH) predicts a decrease in constitutive resistance in plant species growing in resource-rich environments, at the intraspecific level, plants are predicted to follow an opposite pattern (intraspecific RAH). Furthermore, the effect of multiple factors in modulating plant defense strategies has been scarcely explored and is more difficult to predict. Our aim was to understand how plant defense traits respond to herbivory, resource availability and their interactions, and to assess the effects on plant palatability. To this end, we performed an in situ factorial experiment at two sites simulating three herbivory levels and two nutrient availability conditions with the seagrass Posidonia oceanica. Additionally, we performed a series of feeding experiments with its two main herbivores. While plants decreased their constitutive resistance under nutrient fertilization (contrary to intraspecific RAH but in accordance to the RAH), and did not increase allocation to tolerance (likely due to resource limitation, LRM), simulated herbivory induced resistance traits. However, we found no interactive effects of nutrient fertilization and herbivory simulation on plant defense. Both herbivores responded similarly to changes in plant palatability, strongly preferring nutrient-enriched plants and non-clipped plants. This work highlights the need to better understand the drivers of plant defense intraspecific variability in response to resources, particularly in habitat-forming species where changes in plant traits and abundance will cascade onto associated species.
KeywordsPlant–herbivore interactions Limited resource model Resource availability hypothesis Nutrients Posidonia oceanica
E. Oliver, D. Rita, C. Sangil, J. Grimalt and C. Casas helped with fieldwork experiments.
Author contribution statement
GH, FT and JT conceived the experiment. GH, JT and IC performed the field experiment. IC performed the phosphorus analysis. GH performed plant size, plant chemical traits and statistical analysis. FT and JT funded field and laboratory material and analyses. GH and FT prepared the manuscript. All authors discussed and reviewed the manuscript.
GH was supported by the research personnel program co-funded by the European Social Fund and the Government of the Balearic Islands (Conselleria d´Educació, Cultura i Universitats). This study was supported by POSIPLANT (CTM2011-27377), RESIGRASS (CGL2014-58829-C2-2-R) to FT and JT, and the Ramón y Cajal Program to FT.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- Agrawal AA, Karban R (1999) Why induced defenses may be favored over constitutive strategies in plants. In: Tollrian R, Harwell CD (eds) The ecology and evolution of inducible defenses. Princeton University Press, Princeton, pp 45–61Google Scholar
- Arjonilla M, Forja JM, Gómez-Parra A (1991) Efecto de la materia en suspensión en el análisis de nutrientes con un analizador de flujo continuo de tercera generación. Sem Quim Mar 5:112–120Google Scholar
- Borowitzka MA, Lavery P, van Keulen M (2006) Epiphytes of seagrasses. In: Larkum A, Orth RJ, Dua (eds) Seagrasses: biology, ecology and conservation, Springer, New York, pp 441–461Google Scholar
- Burnham KP, Anderson DR (2002) Model selection and multimodel inference: a practical information-theoretic approach, 2nd edn. Springer, New YorkGoogle Scholar
- Fourqurean J, Zieman J, Powell G (1992) Relationships between porewater nutrients and seagrasses in a subtropical carbonate environment. Mar Biol 114:57–65Google Scholar
- Hemmi A, Jormalainen V (2002) Nutrient enhancement increases performance of a marine herbivore via quality of its food alga. Ecology 83:1052–1064. https://doi.org/10.1890/0012-9658(2002)083%5b1052:NEIPOA%5d2.0.CO;2 CrossRefGoogle Scholar
- Lehtilä K, Boalt E (2008) The use and usefulness of artificial herbivory in plant-herbivore studies. In: Weisser WW, Siemann E (eds) Insects and ecosystem function. Ecological studies (analysis and synthesis), Springer, BerlinGoogle Scholar
- McKey D (1979) The distribution of secondary compounds within plants. In: Rosenthal GA, Janzen DH (eds) Herbivores: their interaction with secondary plant metabolites. Academic Press, New York, pp 55–133Google Scholar
- Ralph P, Tomasko D, Seddon S et al (2006) Human impact on Seagrasses: contamination and eutrophication. In: Larkum A, Orth R, Duarte C (eds) Seagrasses: biology, ecology and conservation. Springer, BerlinGoogle Scholar
- Romero J, Lee K, Pérez M et al (2006) Nutrient dynamics in seagrass ecosystems. In: Larkum A, Orth R, Duarte C (eds) Seagrasses: biology, ecology and conservation. Springer, New York, pp 227–254Google Scholar
- Stumm W, Morgan JJ (1996) Aquatic chemistry: chemical equilibria and rates in natural waters, 3rd edn. Wiley, New YorkGoogle Scholar