Small mammals as potential seed dispersers in New Zealand

Abstract

Weed invasion success is strongly influenced by availability of seed dispersal vectors, which may include animals. We examined the potential of several small introduced mammals (mice, kiore, ship rats and possums) to disperse germinable seeds in New Zealand. Captive animals were fed fleshy fruit of weeds (Berberis glaucocarpa, Cotoneaster spp., Crataegus monogyna, Ilex aquifolium, Leycesteria formosa, Ligustrum sinense, Lonicera japonica, Passiflora mollissima, Pyracantha angustifolia, Sorbus hupehensis) and native species (Coprosma spp., Prumnopitys ferruginea and Solanum aviculare). We recorded the percentage of fruit consumed, seed ingested and gut passage time. Faeces were collected and the seeds extracted and tested for germination potential in an unheated glasshouse (two weed species) or under controlled conditions (11 species). The smallest rodents (mice and kiore) generally destroyed all seeds eaten. Large numbers of viable seeds of the small‐seeded (<1 mg) species, L. formosa and S. aviculare, passed through ship rats. Possums consumed the seeds of all adventive and native fruits except P. ferruginea. The proportion of seeds recovered intact from possum faeces varied with plant species and ranged from 6 to 83%. The time required for 50% of all seeds to be passed by possums ranged from 2.5 to 5.5 days with an average of 3.7 days, and was generally unrelated to simple fruit parameters such as percentage pulp and moisture content. For seeds where germination also occurred in the uneaten controls, the germination of seed from possums ranged from 3 to 78%. Germination was mostly lower in seeds from possums than in the controls, where differences were significant. Possums have major potential to disperse a wide range of fleshy fruit‐producing native and introduced plant species. Ship rats have the potential to disperse those with very small seeds.

Facilitative interactions between an exotic mammal and native and exotic plants: hog deer (Axis porcinus) as seed dispersers in south-eastern Australia

“…Increased propagule supply can increase the probability of recruitment at the invasion front (Masters and Sheley 2001) and facilitate the invasion of new sites (Gosper et al 2005), particularly when dispersal is directed to sites that favour seedling establishment and survival (Briggs et al 2009) following non-random habitat selection by herbivores (Cosyns et al 2005). However, these effects are not restricted to exotic plant species and may also facilitate native plants (Williams et al 2000). In particular, endozoochory may facilitate the re-establishment of plant species that have been displaced from habitat fragments (Cosyns et al 2005;Shiponeni and Milton 2006) in situations where plant community conservation is constrained by seed availability (Bakker and Berendse 1999).…”

“…Endozoochory by exotic mammalian herbivores has the potential to facilitate the invasion of exotic plant species (Williams et al 2000). The ingestion and excretion of seeds by animals (Wang and Smith 2002) can accelerate plant invasions by providing a long-distance dispersal mechanism (Myers et al 2004;Trakhtenbrot et al 2005).…”

Multiple factors determine the rate of increase of an invading non-native tree in New Zealand

“…Possums are probably in the study area but we have no evidence of them dispersing hawthorn there, although they ingest and defecate germinable hawthorn seed in Australia (Bass 1990) and under New Zealand laboratory conditions (Williams et al 2000). There is also the possibility of accidental ingestion by stock, although we have no evidence.…”

“…All hawthorn seedlings (\30 cm) and juveniles ([30 cm, non-fruiting) within the plots were counted. The non-native brushtail possum (Trichosurus vulpecula) is a potential disperser of hawthorn seed (Bass 1990;Williams et al 2000) and has been observed in the area (Davidson 1969), so we searched for them using a spotlight on two late autumn nights when the hawthorns were in full fruit.…”

Hoarding behavior by ship rats (Rattus rattus) in captivity and its relevance to the effectiveness of pest control operations

“…Here, we have reported the hoarding of cereal-based bait pellets among wild-caught/captivemaintained ship rats, confirming unpublished observations from field-based studies that ship rats will raid and hoard bait in defined cache sites (e.g., in a study using motion-triggered video, we have previously recorded a single ship rat in the wild removing six 12-g RS5 baits from a cage within 15 min; Bruce Warburton, unpublished data). Similarly, Williams et al (2000) reported hoarding behavior among both captive ship rats and kiore (R. exulans) when these animals were offered native or exotic fleshy seeds, with average hoarding rates of approximately 30% for both species. In our study, we observed variable hoarding rates, but overall 78% of ship rats (31/40) showed at least one hoarding event, indicating that the majority of ship rats will hoard food when offered a supply of highly palatable cereal bait in excess.…”