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GCE III - Key Finding in 2014

    Examining latitudinal variation in salt marsh herbivory

    GCE investigator S. Pennings has been working for over a decade on the interactions between predators, herbivores and plants in salt marsh sites distributed along the east coast (including study sites within the PIE, VCR and GCE domains), in what represents the most extensive study of latitudinal variation in community ecology for any system. Although herbivores are more abundant and do more damage to plants at low versus high latitudes (Pennings et al. 2009), low latitude plants are tougher and less palatable (e.g. Pennings et al. 2001), perhaps as an evolutionary response. Differences in plant palatability affect the performance of individual herbivores, which exhibit poorer growth on low-latitude plants (Ho and Pennings 2013). However, latitudinal variation in plant quality is less important than latitudinal variation in top consumers and competition in mediating variation in food web structure (Marczak et al. 2011, Marczak et al. 2013). The most recent paper on this topic (Wieski and Pennings 2014) examined herbivory, plant defenses and tolerance to herbivory of the shrub Iva frutescens across the entire latitudinal gradient. Herbivory, and spatial and temporal variation in herbivory, was greatest at low latitudes, as were both constitutive and induced defenses in plants (Fig. 1). However, plant tolerance to herbivory did not depend on geographic origin. These findings underscore the importance of considering multiple ways in which plants can respond to herbivores when examining geographic variation in their interactions.

    2014_Accomplishments_Fig3

    Fig. 1 Latitudinal variation in herbivory patterns and plant defenses in marsh elder (Iva frutescens); a: both average herbivore leaf damage (black bar; error bar = SE) and temporal variation in standard deviation (grey bar; error bar = SE) in leaf damage in I. frutescens are higher in low latitudes; b: in 2-choice feeding assays P. aterrima beetles consumed more leaf area of I. frutescens from high over low latitudes; c: P. aterrima preferred leaves from undamaged I. frutescens from both high and low latitudes; however, in lower latitudes this preference developed faster and lasted longer. From Wieski and Pennings (2014).



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This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959, OCE-1237140 and OCE-1832178. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.