Frugivory by introduced black rats (Rattus rattus) promotes dispersal of invasive plant seeds

Abstract

Oceanic islands have been colonized by numerous non-native and invasive plants and animals. An understanding of the degree to which introduced rats (Rattus spp.) may be spreading or destroying seeds of invasive plants can improve our knowledge of plant-animal interactions, and assist efforts to control invasive species. Feeding trials in which fruits and seeds were offered to wild-caught rats were used to assess the effects of the most common rat, the black rat (R. rattus), on 25 of the most problematic invasive plant species in the Hawaiian Islands. Rats ate pericarps (fruit tissues) and seeds of most species, and the impacts on these plants ranged from potential dispersal of smallseeded (B1.5 mm length) species via gut passage (e.g., Clidemia hirta, Buddleia asiatica, Ficus microcarpa, Miconia calvescens, Rubus rosifolius) to predation where \15% of the seeds survived (e.g., Bischofia javanica, Casuarina equisetifolia, Prosopis pallida, Setaria palmifolia). Rats consumed proportionally more seed mass of the smaller fruits and seeds than the larger ones, but fruit and seed size did not predict seed survival following rat interactions. Although invasive rat control efforts focus on native species protection, non-native plant species, especially those with small seeds that may pass internally through rats, also deserve rat control in order to help limit the spread of such seeds. Black rats may be facilitating the spread of many of the most problematic invasive plants through frugivory and seed dispersal in Hawaii and in other ecosystems where rats and plants have been introduced.

Biology and Impacts of Pacific Island Invasive Species. 11.Rattus rattus,the Black Rat (Rodentia: Muridae)

“…data). Adult male R. rattus are larger in both mass and body length than adult females (Innes 2005a, Shiels 2010, whereas average tail length has been recorded as similar between sexes (Innes 2005a) or slightly greater in males than in females (Shiels 2010).…”

“…Instead of body size, features that distinguish R. rattus from other coexisting rodents (e.g., R. exulans, R. norvegicus, and Mus musculus [house mouse]) include tail length and ear length. The tail of R. rattus is approximately 27 ± 2 mm (or 16% ± 1%) longer than the rest of its body (Innes 2005a, Shiels 2010, whereas R. exulans, R. norvegicus, and M. musculus all have tails approximately equal to or shorter than their body length exclusive of the tail (Atkinson and Towns 2005). The longer tail and sleek body shape of R. rattus may be adaptations related to their arboreal activity ( Figure 1), which is more frequent than that of other introduced Rattus spp.…”

“…The longer tail and sleek body shape of R. rattus may be adaptations related to their arboreal activity ( Figure 1), which is more frequent than that of other introduced Rattus spp. and mice (Shiels 2010, Foster et al 2011, King et al 2011a. Ear length of R. rattus (19.0 -26.0 mm) is generally the largest among the four main invasive rodents introduced to Pacific islands, including R. exulans (15.5 -20.5 mm), R. norvegicus (14.0 -22.0 mm), and M. musculus (12.0 -15.0 mm).…”

Trait-based plant mortality and preference for native versus non-native seedlings by invasive slug and snail herbivores in Hawaii

“…Leaf hairs occur on C. hirta (long hairs) and P. albidus (short hairs), and C. parviflora exudes white latex sap when damaged. Aside from F. uhdei, which is common within and adjacent to F. uhdei plantation forests in Hawaii, the non-native species included in our study are recognized as important threats to native forests and are among the top 25 most problematic invasive plant species in Hawaii (Shiels 2011).…”

Nicodemia madagascariensis(Lam.) R. Parker (Family Scrophulariaceae), a casual alien plant new to Italy

“…The black rat (Rattus rattus L., 1758), which is very common within Fossa della Garofala, has already been proved to disperse the seeds of Buddleja asiatica Lour. (Shiels 2011).…”