Dietary niche differentiation among three species of invasive rodents (Rattus rattus, R. exulans, Mus musculus)

Abstract

The diets of sympatric rodents partially define their realized niches. Identifying items in stomachs of introduced rodents helps determine rodents' trophic positions and species most at risk of consumption. In the Hawaiian Islands, which lacked rodents prior to human arrival, three rodents (Rattus rattus or black rat, R. exulans or Pacific rat, Mus musculus or house mouse) commonly coexist in native habitats where they consume a wide range of plants and animals. These three rodent species were trapped in montane forest for 2.5 years; their stomach contents were analyzed to determine short-term diets (n = 12-95 indiv. per species), and isotopic fractions of d 15 N and d 13C in their bone collagen were analyzed to further estimate their trophic positions (n = 11-20 indiv. per species). For all three species, [75 % of individuals had plants and [90 % had arthropods in their stomachs, and significant differences in mean relative abundances were found for food items in stomachs among all three rodents. Rodents may be dispersing some native and non-native seeds, including the highly invasive Clidemia hirta. Most identifiable arthropods in rodent stomachs were non-native, and no stomachs contained birds, snails, or lizards. The d 15 N and d 13 C signatures were consistent with trophic feeding differences revealed from stomach contents. Dietary niche differentiation by coexisting rodent species is evident in this forest, with Pacific rats being intermediate between the mostly carnivorous house mouse and the mostly herbivorous black rat; such findings can help forecast rodent impacts and direct management efforts in ecosystems where these invasive animals coexist.

Dental Shape Variation and Phylogenetic Signal in the Rattini Tribe Species of Mainland Southeast Asia

“…Sympatry of related species is, therefore, expected to drive character displacement such as body size differences, as is seen in other species (Dayan and Simberloff 1998). For example, R. exulans and R. rattus successfully niche partition when living sympatrically, but population sizes appear to be are smaller than when similar niche partitioning occurs between the morphologically more different R. rattus and Mus musculus, where population sizes remain relatively high, indicating R. rattus and Mus musculus can niche partition more successfully than R. rattus and R. exulans can (Shiels et al 2012). There is some tentative evidence from the archaeological record of dramatic changes in size (primarily body size) for individual Rattus species in the absence of competition (Armitage et al 1984;Armitage 1994 due to lack of interspecific competition (Armitage 1994).…”

A Novel Multiscale Assessment of Community Assembly across Time, Space, and Functional Niche

“…In mammals, examples of niche differentiation in closely related groups might include differences in dietary and/or locomotor specialization (Hutchinson 1959;Shiels et al 2013). Competition can also result in size segregation, and in extreme cases, this phenomenon could result in traits that are evenly dispersed from each other (Rosenzweig 1966).…”

Invasive rodents, an overlooked threat for skinks in a tropical island hotspot of biodiversity

“…We believe the small differences observed might be explained simply by the foraging behaviour of each rat species. The ship rat is arboreal with a diet mostly made of fruits and plant items (Shiels et al 2014), on the other hand, the Pacific rat is a ground forager that consumes more invertebrates and fewer plants than the ship rat (Shiels et al 2013). Our dietary analysis reveals the same pattern and accurately describes the differences in the diet of the two species; for example, feather remains were found in ship rats only, whereas earthworms were more abundant in Pacific rat guts.…”

“…In 1990, Newman and McFadden (1990) analysed the stomachs of 134 Pacific rats on offshore islands in New Zealand: only three of them contained skink remains. More recently in Hawaiian forests, a diet study on R. rattus, R. exulans and M. musculus conducted by Shiels et al (2013) revealed the complete absence of any skink remains in the stomachs analysed (n = 12-95 individuals per species). Our result can be explained by the high skink species richness and abundance in the archipelago (Bauer & Sadlier 2000) combined with the likely improved estimation of predation rates in our study due to caecum content analysis.…”