Foliar Nutritional Quality Explains Patchy Browsing Damage Caused by an Invasive Mammal

Abstract

Introduced herbivores frequently inflict significant, yet patchy damage on native ecosystems through selective browsing. However, there are few instances where the underlying cause of this patchy damage has been revealed. We aimed to determine if the nutritional quality of foliage could predict the browsing preferences of an invasive mammalian herbivore, the common brushtail possum (Trichosurus vulpecula), in a temperate forest in New Zealand. We quantified the spatial and temporal variation in four key aspects of the foliar chemistry (total nitrogen, available nitrogen, in vitro dry matter digestibility and tannin effect) of 275 trees representing five native tree species. Simultaneously, we assessed the severity of browsing damage caused by possums on those trees in order to relate selective browsing to foliar nutritional quality. We found significant spatial and temporal variation in nutritional quality among individuals of each tree species examined, as well as among tree species. There was a positive relationship between the available nitrogen concentration of foliage (a measure of in vitro digestible protein) and the severity of damage caused by browsing by possums. This study highlights the importance of nutritional quality, specifically, the foliar available nitrogen concentration of individual trees, in predicting the impact of an invasive mammal. Revealing the underlying cause of patchy browsing by an invasive mammal provides new insights for conservation of native forests and targeted control of invasive herbivores in forest ecosystems.

New approaches to tannin analysis of leaves can be used to explain in vitro biological activities associated with herbivore defence

“…Using this method, DeGabriel et al (2009) showed that the in vitro digestible N concentration of eucalypt foliage influenced the reproductive success of female common brushtail possums (Trichosurus vulpecula). As a consequence, in vitro digestible N concentrations have been used as indicators of the nutritional quality of habitat for marsupial folivores (DeGabriel et al, 2009;Youngentob et al, 2011;Windley et al, 2016).…”

Cold temperature improves tannin tolerance in a granivorous rodent

“…Plant–herbivore interactions shape community dynamics and support ecosystem function in virtually all natural systems. Herbivores have evolved to avoid or tolerate potentially toxic plant secondary metabolites (PSMs) in their diet (Foley & Moore, ; Torregrossa & Dearing, ), the effects of which can influence their distribution and abundance (Cork & Catling, ), reproductive success (DeGabriel, Moore, Foley, & Johnson, ) and the impact of invasive species (Windley et al, ). At least part of the variation in PSM tolerance observed within and among herbivores can be attributed to their detoxification capability (Freeland & Janzen, ; Marsh, Wallis, & Foley, ).…”

The potential of using Unmanned Aerial Vehicles (UAVs) for precision pest control of possums (Trichosurus vulpecula)

“…Detection of foliage damage using hyperspectral signatures is now achievable and could be used to enable rapid detection of pest activity (Lehmann et al 2015;Windley et al, 2016), or even of the pests themselves (Chrétien et al 2016;Gonzalez et al 2016). Possums are known to selectively defoliate tree species including kamahi (Weinmannia racemosa), northern rātā (Metrosideros robusta), kohekohe (Dysoxylum spectabile), tree fuchsia (Fuchsia excorticata), and other plant species (Pekelharing et al 1998;Sweetapple and Nugent 1999;Gormley et al 2012;Holland et al 2013).…”