Abstract Detail

Interactions of White-Tailed Deer and Invasive Plants in Forests of Eastern North America

Heberling, J. Mason [1], Brouwer, Nathan L. [2], Kalisz, Susan [1].

Plant invasion mediated by deer overabundance: linking demographic patterns and ecophysiological mechanisms.

Leading invasion hypotheses are often framed in terms of community invasibility (e.g., species interactions) or species invasiveness (e.g., “invasive traits”), but the two concepts are not necessarily mutually exclusive. Interactions with generalist herbivores such as white-tailed deer (Odocoileus virginianus) can facilitate exotic plant invasions through modifications to the abiotic and biotic environment, but it is unclear whether deer are necessary for a given plant species invasion or merely exacerbate it. Deer populations in Eastern North America have surged well above historic densities, causing marked impacts to community structure and function. Deer may facilitate plant invasion through biased foraging on natives (trophic effects that reduce biotic resistance) or act as ecosystem engineers to transform the abiotic understory environment that benefit invaders’ physiology (non-trophic effects). Here we report on a 13 yr demography experiment in a deciduous forest with deer exclusion, invader Alliaria petiolata (garlic mustard) removal, and both treatments crossed. We analyze the main and interactive effects of deer on the success of invasives as well as the roles of deer and invasion on native species demography. We uniquely combine long-term demographic data with recent physiological measurements to understand the degree to which deer facilitate Alliaria population growth and further, how the presence of deer influence Alliaria physiology. We found that Alliaria abundance was significantly greater in deer access compared to deer exclusion plots, but this difference varies across years. Our estimates of population growth of Alliaria indicate that this invader is actively spreading in deer access (λ>1) plots but declining (λ<1) in deer exclusion plots. Our physiological data provide a mechanism for these demographic results, Alliaria exhibited higher photosynthetic rates in deer access plots compared to deer exclusion plots. These differences are expressed during months with significant leaf overstory canopy coverage (June-Aug, P<0.001), with no differences before overstory leaf out (March, May) or after canopy leaf senescence (Sept-Jan). After overstory canopy closure, the higher photosynthetically active radiation (PAR) of plants in deer access areas indicates that deer modify understory light levels. PAR increases are likely the combination of high herbivory rates on native understory species (can exceed 75% of native stems) and modification to the sapling and midstory layers. Importantly, deer never consumed Alliaria, contributing to its high fitness. Our results provide the first physiological evidence by which generalist herbivores alter the abiotic and biotic environment to facilitate plant invasion and highlight the utility in the combining demography with physiology.

1 - University of Tennessee, Ecology and Evolutionary Biology, Knoxville, PA, 37996, USA
2 - The National Aviary in Pittsburgh, Pittsburgh, PA, 15212, USA

Keywords:
Alliaria
deer
Ecophysiology
demography
forest ecology
invasion biology.

Presentation Type: Colloquium Presentations
Session: C1, Interactions of white-tailed deer and invasive plants in forests of eastern North America
Location: Chatham Ballroom - C/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 2:15 PM
Number: C1003
Abstract ID:344
Candidate for Awards:None