Plant-herbivore interactions

   

Photo: Caterpillar eating Spartina alterniflora in Maine.

Photo: Paroxya grasshopper eating Iva frutescens in Georgia.

Photo: Orchelimum grasshopper eating Spartina alterniflora in Georgia.

Photo: Omnivorous Armases crab, common in southeastern U.S. salt marshes.

Photo: Trirhabda beetle feeding on Baccharis in Texas.

I am interested in the factors that mediate herbivore feeding choices.  Despite decades of interest, we do not have a general, predictive understanding of why herbivores eat the particular plants that they do.  A variety of plant traits, including toughness, nitrogen content, minerals (silica in higher plants, calcium carbonate in seaweeds), and chemical defenses may all affect the palatability of plants, but it is difficult to predict which plant traits will matter to particular herbivores in particular cases.  I have studied this issue using a variety of organisms, including gastropods, isopods, sea urchins, fish and insects.  I am also interested in the possibility that feeding specialization may be selected against in some organisms because a mixed diet is more nutritious than any single food.

 

I am also interested in how plant-herbivore interactions change across gradients.  Much of my recent research focused on latitudinal gradients in plant-herbivore interactions in salt marshes along the Atlantic coast of the U.S.  A major dogma of biogeography is that consumer-prey interactions are more intense at lower latitudes.  If this is true, prey should have evolved increased defenses (i.e., be less palatable) at low versus high latitudes.  My students and I examined these hypotheses using a suite of plant species that occur in coastal salt marshes from Florida into New England.  Results to date indicate that 1) there is a community-wide pattern for southern plants to be less palatable than northern plants, 2) that a variety of plant traits may contribute to this pattern, 3) that this pattern has a strong genetic component, 4) that herbivore pressure may be one selective factor contributing to this pattern, 5) that latitudinal variation in plant quality affects herbivore growth rates and body size, and 6) that similar patterns occur in European salt marshes.

 

Our recent work in this area focused on putting the plant-herbivore interaction into a broader trophic context.  In collaboration started with Dr. Robert Denno, we examined latitudinal variation in top-down and bottom-up interactions in Atlantic coast salt marshes.  We tested a variety of hypotheses about how latitudinal variation in plant quality, predator abundance and omnivore abundance mediates herbivore abundance and herbivore damage to plants.

 

I am also interested in how interactions between parasitic plants and host plants parallel or contrast with interactions between herbivores and host plants (see parasitic plant link).

 

Some recent plant-herbivore publications:

 

Marczak, L. B., K. Więski, R. F. Denno and S. C. Pennings. 2013. Importance of local versus geographical variation in saltmarsh plant quality for arthropod herbivore communities. Journal of Ecology 101:1169-1182.

Ho, C.-K. and S. C. Pennings. 2013. Preference and performance in plant-herbivore interactions across latitude—a study in U.S. Atlantic salt marshes. PLOS One. doi: 10.1371/journal.pone.0059829.

McCall, B. D. and S. C. Pennings. 2012. Geographic variation in salt marsh structure and function. Oecologia 170:777-787.

Jimenez, J. M., K. Wieski, L. B. Marczak, C.-K. Ho, S. C. Pennings. 2012. Effects of an omnivorous katydid, salinity, and nutrients on a planthopper-Spartina food web. Estuaries and Coasts 35:475-485.

Marczak, L. B, C.-K. Ho, K. Wieski, H. Vu, R. F. Denno and S. C. Pennings.  2011.  Latitudinal variation in top-down and bottom-up control of a salt marsh food web.  Ecology 92:276-281.

Ho, C.-K., S. C. Pennings and T. H. Carefoot.  2010.  Is diet quality an overlooked mechanism for Bergmann’s rule?  American Naturalist 175:269-276.

Pennings, S. C., C.-K. Ho, C. S. Salgado, K. Więski, N. Davé, A. E. Kunza, E. L. Wason.  2009. Latitudinal variation in herbivore pressure in Atlantic Coast salt marshes.  Ecology 90:183-195. 

Ho, CK and SC Pennings.  2008. Consequences of omnivory for trophic interactions on a salt-marsh shrub.  Ecology 89:1714-1722.

Wason, E. L. and S. C. Pennings.  2008.  Grasshopper (Orthoptera: Tettigoniidae) species composition and size across latitude in Atlantic Coast salt marshes.  Estuaries and Coasts 31:335-343.

Pennings, S. C., Zimmer, M., Dias, N., Sprung, M., Davé, N., Ho, C.-K., Kunza, A., McFarlin, C., Mews, M., Pfauder, A., Salgado, C.  2007.  Latitudinal variation in plant-herbivore interactions in European salt marshes.  Oikos 116:543-549.

 Pennings, S. C., Silliman, B. R. 2005.  Linking biogeography and community ecology: latitudinal variation in plant-herbivore interaction strength.  Ecology 86:2310-2319.

Salgado, C. S., Pennings, S. C.  2005.  Latitudinal variation in palatability of salt-marsh plants: are differences constitutive? Ecology 86:1571-1579.

Siska, E. L., S. C. Pennings, T. L. Buck and M. D. Hanisak.  2002.  Latitudinal variation in palatability of salt-marsh plants: which traits are responsible?  Ecology 83:3369-3381.

Pennings, S. C., E. L. Siska and M. D. Bertness.  2001.  Latitudinal differences in plant palatability in Atlantic coast salt marshes.  Ecology 82:1344-1359.

Updated 1/2014