The Relative Concentrations of Nutrients and Toxins Dictate Feeding by a Vertebrate Browser, the Greater Glider Petauroides volans

Abstract

Although ecologists believe that vertebrate herbivores must select a diet that allows them to meet their nutritional requirements, while avoiding intoxication by plant secondary metabolites, this is remarkably difficult to show. A long series of field and laboratory experiments means that we have a good understanding of the factors that affect feeding by leaf-eating marsupials. This knowledge and the natural intraspecific variation in Eucalyptus chemistry allowed us to test the hypothesis that the feeding decisions of greater gliders (Petauroides volans) depend on the concentrations of available nitrogen (incorporating total nitrogen, dry matter digestibility and tannins) and of formylated phloroglucinol compounds (FPCs), potent antifeedants unique to Eucalyptus. We offered captive greater gliders foliage from two species of Eucalyptus, E. viminalis and E. melliodora, which vary naturally in their concentrations of available nitrogen and FPCs. We then measured the amount of foliage eaten by each glider and compared this with our laboratory analyses of foliar total nitrogen, available nitrogen and FPCs for each tree offered. The concentration of FPCs was the main factor that determined how much gliders ate of E. viminalis and E. melliodora, but in gliders fed E. viminalis the concentration of available nitrogen was also a significant influence. In other words, greater gliders ate E. viminalis leaves with a particular combination of FPCs and available nitrogen that maximised the nutritional gain but minimised their ingestion of toxins. In contrast, the concentration of total nitrogen was not correlated with feeding. This study is among the first to empirically show that browsing herbivores select a diet that balances the potential gain (available nutrients) and the potential costs (plant secondary chemicals) of eating leaves. The major implication of the study is that it is essential to identify the limiting nutrients and relevant toxins in a system in order to understand feeding behaviour.

The importance of protein in leaf selection of folivorous primates

“…A number of studies have pointed out that selection of high protein food would only be required if the food items in the environment have average protein concentrations below the required needs [e.g., Ganzhorn et al, 2009;Mowry et al, 1996;Simmen et al, 2014;Yeager et al, 1997] and that, once average protein concentrations are above requirements, selection could be based on other components and criteria, such as the availability within the environment [e.g., Fashing et al, 2007;Oftedal, 1991] or secondary plant chemicals [Moore & Foley, 2005]. While this idea has been around for some time, it has rarely been tested in folivores [Jensen et al, 2015;Marsh et al, 2014]. Instead, studies started to focus on long-term nutrient budgets and nutrient balancing using the conceptual approach of geometric frameworks [e.g., DeGabriel et al, 2014;Felton et al, 2009;Irwin et al, 2014;Johnson et al, 2013;Rothman et al, 2011], on new methods on how to measure protein that is actually available [DeGabriel et al, 2008], or on an understanding of other confounding variables [Wallis et al, 2012].…”

Craniomandibular Variation in Phalangeriform Marsupials: Functional Comparisons with Primates

“…Folivore Predominantly feeds on young leaves of Eucalyptus species, stomach contents included fragments of bark and buds Marples (1973), Comport et al (1996), Harris and Maloney (2010), and Jensen et al (2015)…”

Folivory with leaf folding by giant flying squirrels: its patterns and possible function

“…Folivorous mammals generally avoid foods with higher concentrations of secondary metabolites (Glander 1982;Garber 1987). For example, the greater glider Petauroides volans varies its consumption of Eucalyptus leaves to minimize ingestion of toxins unique to that tree genus (Jensen et al 2015). In addition, the giant tree squirrel Ratufa indica feeds on leaf centers in some tropical tree species to avoid consuming alkaloids abundant in leaf margins (see Kawamichi 2015).…”