Dietary changes in response to population reduction in the possum Trichosurus vulpecula in New Zealand

Abstract

Context Efforts to protect or restore degraded plant communities by population control of invasive herbivores frequently fail to achieve their goals. Aims We seek to quantify changes in diet of an introduced herbivore, the brushtail possum (Trichosurus vulpecula), following population control, and determine how these may contribute to variable responses in plant condition. Methods Stomach contents of possums from five areas of indigenous forest in northern New Zealand were analysed to measure diet before and after the application of possum control. Key results The contribution of fruit, and foliage of some early successional forest species, to total possum diet increased up to 27-fold following possum population control. This was accompanied by declines in consumption of the main pre-control possum foods (foliage from common canopy trees). Dietary changes were a combination of an immediate response to control (1 year) and a strengthening of these initial changes with increasing time since control. Conclusions Possums in the study areas changed diet following population control, from a diet dominated by foliage of common canopy tree species to one dominated by fruits, and foliage of uncommon early successional plants. Pest control instantaneously increased the per capita availability of all foods, and probably permitted absolute increases in some foods through plant recovery, enabling possums to substitute scarce, high-preference foods for abundant but less preferred canopy foliage. Implications Following control of a pest herbivore, dietary changes reduce benefits for the most vulnerable preferred plant foods, but enhance benefits for less favoured plants. Intense pest control can permit some recovery of highly preferred foods, despite increased per capita consumption of these foods by survivors of control.

Long‐term response of temperate canopy trees to removal of browsing from an invasive arboreal herbivore in New Zealand

“…Three of these, Hall's totara, kamahi and toro, were known to be important components of possum diet at Waihaha (totaling 63% of diet in 1991–1992; Sweetapple et al . ). The fourth species, tāwheowheo ( Quintinnia serrata ), is not eaten by possums but was selected to help track changes in foliage cover scores not related to possum browsing.…”

“…The effects of reduced possum abundance on browse pressure at Waihaha were further enhanced by post‐control possums, reducing their intake of foliage from the monitored species, as evidenced by browsing frequencies declining by a greater extent than trap‐catch rates, and by recorded dietary changes (Sweetapple et al . ). Therefore, crown recovery rates are unlikely to have been compromised by insufficient pest‐control intensity.…”

“…, ; Sweetapple et al . ). Possums were controlled over the whole area in winter 1994, 2000, 2005 and 2011, providing the opportunity to extend the assessment period of tree recovery from possum browsing to 20 years, making this the longest running study of its type to date.…”

Snacks in the city: the diet of hedgehogs in Auckland urban forest fragments

“…Predation is often difficult to observe directly, but it can be evaluated indirectly using dietary analysis, which often involves examining the contents of the stomach, other parts of the gastrointestinal tract or faeces (e.g. Klare et al 2011;Sweetapple et al 2013). Dietary analysis can provide important information on the ecological niche of a predator, the level of invasiveness of a species and its potential severity of impact.…”

“…Dietary analysis can provide important information on the ecological niche of a predator, the level of invasiveness of a species and its potential severity of impact. Stomach content analysis has been used to describe the diets of a number of vertebrate species, such as rodents, frogs and possums (Trichosurus vulpecula) (Sweetapple et al 2013;Hervías et al 2014;Courant et al 2017). In hedgehogs (Erinaceus europaeus), stomach content analysis has been used to determine: the composition of the diet in different habitats; the presence of endangered species in the diet; and dietary overlap with native species (Hendra 1999;Jeffries 2011).…”