The independent and dependent variables for the study of herbivore performance.

<p>The independent and dependent variables for the study of herbivore performance.</p

Patterns of herbivore body size in the field.

<p>Latitudinal variations in body size of <i>U. pieloui</i> and <i>Paroxya</i> on <i>Solidago</i> plants (A, B), <i>U. ambrosiae</i> and <i>Ophraella</i> on <i>Iva</i> plants (C, D), and <i>Prokelisia</i> and <i>Orchelimum</i> on <i>Spartina</i> plants (E, F). Each point represents a single study site.</p

Plant and herbivore species studied.

<p>Plant common name, family, growth form, herbivore taxonomic group, feeding guild, and diet range are indicated in parentheses.</p

Preference and Performance in Plant–Herbivore Interactions across Latitude–A Study in U.S. Atlantic Salt Marshes

<div><p>High-latitude plants are often more palatable to herbivores than low-latitude conspecifics. Does increased plant palatability lead to better herbivore performance? Our field and laboratory work investigated (A) whether high-latitude plants have traits indicating that they should be higher-quality foods for herbivores; (B) whether geographic differences in plant quality are more important than local adaptation of herbivores. We studied 3 plant species and 6 invertebrate herbivores in U.S. Atlantic Coast. Past studies had shown high-latitude individuals of these plants are more palatable than low-latitude conspecifics. We documented plant traits and herbivore performance (body size) in the field across latitude. We collected individuals from different latitudes for factorial (plant region x herbivore region) laboratory experiments, examining how herbivore performance was affected by plant region, herbivore region, and their interaction (i.e., local adaptation). Field surveys suggested high-latitude plants were likely of higher quality to herbivores. Leaf nitrogen content in all plant species increased toward high latitudes, consistent with lower leaf C/N and higher leaf chlorophyll content at high latitudes. Furthermore, leaf toughness decreased toward higher latitudes in 1 species. The body size of 4 herbivore species increased with latitude, consistent with high-latitude leaves being of higher quality, while 2 grasshopper species showed the opposite pattern, likely due to life-history constraints. In the laboratory, high-latitude plants supported better performance in 4 herbivore species (marginal in the 5th). The geographic region where herbivores were collected affected herbivore performance in all 6 species; however, the pattern was mixed, indicating a lack of local adaptation by herbivores to plants from their own geographic region. Our results suggest that more-palatable plants at high latitudes support better herbivore growth. Given that geographic origin of either plants or herbivores can affect herbivore performance, the nature of plant-herbivore interactions is likely to change if climate change “reshuffles” plant and herbivore populations across latitude.</p> </div

Study locations on the Atlantic Coast of the United States.

<p>Two sites >1 km apart were established at each location for geographic sampling; laboratory experiments used only one of the sites from each location.</p

Appendix A. Iva food web based on observations on Sapelo Island, Georgia, USA.

Iva food web based on observations on Sapelo Island, Georgia, USA

The impact of plant region on herbivore performance.

<p>The impact of <i>Solidago</i> plant regions on <i>U. pieloui</i> population growth and <i>Paroxya</i> growth rate (A, B); the impact of <i>Iva</i> plant regions on <i>U. ambrosiae</i> population growth and <i>Ophraella</i> growth rate (C, D); the impact of <i>Spartina</i> plant regions on <i>Prokelisia</i> body size and <i>Orchelimum</i> growth rate (E, F).</p

Patterns of plant traits in the field.

<p>Leaf C:N and toughness of <i>Solidago sempervirens</i> (A, B), <i>Iva frutescens</i> (C, D) and <i>Spartina alterniflora</i> (E, F) versus latitude. Each point represents a single study site.</p

Map of study site.

<p>Infrared aerial images taken during a flyover of the marsh restoration project in the Lower Neches Wildlife Management Area (LNWMA) in September 2009, and ground-level pictures of terraces (large patches) and mounds (small patches).</p

Disturbance and patch size effects on plant characteristics.

<p>Effects of disturbance treatments in large (terraces) and small (mounds) patches on plant characteristics: a) total plant cover, b) total live stem density, c) <i>Spartina alterniflora</i> stem height, d) relative <i>Spartina alterniflora</i> chlorophyll <i>a</i> content. Error bars represent standard error. Significant treatment effects from two-way ANOVA are noted; D = Disturbance, H = Habitat patch size.</p