Analysis of the characteristics of fruit eaten by possums,Trichosurus vulpecula, in New Zealand

Abstract

The colours and sizes of the fleshy fruits of native trees and shrubs in the New Zealand flora and in the flora of the Orongorongo Valley, southern Rimutaka Range, were compared with those known to be eaten by possums to assess the degree of food selection by possums. Colour and diameter of fruits had little effect on whether they were selected by possums, but the size of the enclosed seed affected feeding behaviour. Fruits with seeds < 10 mm were eaten whole, whereas usually only the skin and flesh were eaten from fruits with larger seeds. An analysis of the wet and dry weights of the flesh and seeds of fruits growing in the Orongorongo Valley suggested that possums could maximise their dry matter intake from fruits by feeding preferentially on the larger fruits. Although this suggestion was supported in general by field observations, other studies suggest that annual variations in the abundance of fruits of the various species and their accessibility are also important in determining the contribution of fruits to the diet of possums. INTRODUCfIONNew Zealand's flora of fleshy-fruited plants evolved on an isolated land mass for over 70 million years without any terrestrial mammals, apart from three species of small bats. The main dispersers of the seeds of fleshy-fruited plants are birds and lizards (Clout 1982;Whitaker 1987;Clout & Hay 1990).About 140 years ago, brushtail possums, Trichosurus vulpecula (Marsupialia), were introduced from Australia (Pracy 1974). Although possums are primarily leaf-eaters, in their native Australia they also eat fleshy fruits, particularly in the tropical parts of their range (Proctor-Gray 1984;Kerle 1985). In New Zealand they supplement their diet in the summer and autumn with large quantities of the fruits of native trees and shrubs (Green 1984;Cowan 1990), and may compete for those resources with native frugivorous birds (Leathwick et al., 1983).Possums are selective browsers, showing clear preferences for the leaves of particular native plants (Fitzgerald 1976(Fitzgerald , 1981. Williams (1982) analysed the protein, lipid, carbohydrate, and energy contents of six fruit species which featured in the diet of possums in native forest, and compared them with the leaf-only component of the diet. He suggested that inclusion of fruit in the diet provided possums with a greater rate of intake of digestible nutrients; however, physical characteristics of some fruits detracted from their value as foods. Cowan (1990) also suggested that factors other than nutritional quality might influence the possums' choice of fruits. The present paper examines the influence of the colour, size of the whole fruit, and the composition of the fruit flesh on the choice of native fruits eaten by possums. A "fruit" was defined as a discrete package consisting of fleshy, edible pulp surrounding or attached to the seed(s) (Willson 1986). Fleshy fruits included arillate structures (such as those of the podocarps) but not "dry" fruits and capsules which are not usually eaten by possums (Cowan 1990)...

Small mammals as potential seed dispersers in New Zealand

“…Possums accepted a wide range of native and adventive fruits just as they are recorded doing in the wild ( Williams 1982; Clout & Gaze 1984; Cowan 1990a, 1992). The absence of a significant correlation between years in the proportion of fruits eaten for possums, and ship rats, suggests several factors are involved in the animals’ choice of food items.…”

“…Whether a seed is destroyed during ingestion depends partly on fruit and seed characteristics such as size ( Cowan 1992; Izhaki et al 1995 ). The fate of an ingested seed and its viability depend both on the way it is handled and masticated and on the treatment received in the animal’s gut.…”

Quantifying seed dispersal by birds and possums in a lowland New Zealand forest

“…Three different studies all present similar numbers: Cowan (1992) found an overall average of 71.5 faecal pellets per night for field-trapped possums held overnight in 12 different months. Fitzgerald (1977) also trapped and held possums overnight and had a very similar average of 69.7 pellets.…”

“…Silvereyes disperse fruits up to 9.9 mm mean diameter (Crataegus monogyna; Williams & Karl 1996), while there is no evidence that possums disperse any fruits greater than 10 mm diameter (Williams 2003). Possums ate only the pulp of six species of fruits >9 mm diameter (Rhopalostylis sapida, mean fruit diameter 9.1 mm; Elaeocarpus dentatus 9.2 mm; Prumnopitys taxifolia 9.4 mm; Hedycarya arborea 9.7 mm; Ripogonum scandens 10.5 mm; Prumnopitys ferruginea 13.0 mm; Cowan 1990Cowan , 1992Williams et al 2000;Kelly et al 2010). Cowan (1990) found one R. scandens seed in possum faeces, apparently the largest fruit recorded as dispersed by a possum, but this fruit is also dispersed by silvereyes (O'Donnell & Dilks 1994).…”

Akodon montensis (Thomas, 1913) (Muridae) as a disperser of endozoochoric seeds in a coastal swamp forest of southern Brazil

“…Seed viability depends on the treatment received in the animal digestive tract (Howe 1986;Price and Jenkins 1986;Schupp 1993) and partly on the characteristics of the fruits and seeds, such as size (Cowan 1992;Schupp 1993;Izhaki et al 1995;Williams et al 2000). Because some small seeds, usually abundant in fruits, are likely to be ingested intact with fruit flesh, they may remain viable even after passing through the consumer digestive system (Howe 1986;Fleming et al 1993).…”