Population dynamics and resource availability drive seasonal shifts in the consumptive and competitive impacts of introduced house mice (Mus musculus) on an island ecosystem

Abstract

Background House mice (Mus musculus) are widespread and invasive on many islands where they can have both direct and indirect impacts on native ecological communities. Given their opportunistic, omnivorous nature the consumptive and competitive impacts of house mice on islands have the potential to vary over time in concert with resource availability and mouse population dynamics. Methods We examined the ecological niche of invasive house mice on Southeast Farallon Island, California, USA using a combination of mouse trapping, food resource surveys, and stable isotope analysis to better understand their trophic interactions with native flora and fauna. Specifically, we coupled the analysis of seasonal variation in resource availability over a 17-year period (2001–2017), carbon (δ13C) and nitrogen (δ15N) stable isotope values of mouse tissue and prey resources in a single year (2013), and isotopic niche and mixing models to quantify seasonal variation in mouse diets and the potential for resource overlap with native species. Results We found that plants were the most important resource for house mice during the spring months when vegetation is abundant and mouse populations are low following heavy precipitation and declines in mouse abundance during the winter. While still consumed, plants declined in dietary importance throughout the summer and fall as mouse populations increased, and seabird and arthropod resources became relatively more available and consumed by house mice. Mouse abundance peaks and other resource availability are low on the island in the fall months when the isotopic niches of house mice and salamanders overlap significantly indicating the potential for competition, most likely for arthropod prey. Discussion Our results indicate how seasonal shifts in both mouse abundance and resource availability are key factors that mediate the consumptive and competitive impacts of introduced house mice on this island ecosystem. As mice consume and/or compete with a wide range of native taxa, eradication has the potential to provide wide-reaching restoration benefits on Southeast Farallon Island. Post-eradication monitoring focused on plant, terrestrial invertebrate, salamander, and seabird populations will be crucial to confirm these predictions.

Small mice create big problems: Why Predator Free New Zealand should include house mice and other pest species

“…In contrast, densities after mammal eradications in NZ have increased to > 150 mice/ha (Goldwater, 2007). On islands where mice lack competitors and predators, densities of > 1000 mice/ha have been recorded (Polito et al., 2022). In dry agricultural areas of Australia, despite a diverse assemblage of potential predators of mice, densities have been documented at 2716/ha (Singleton et al., 2007), illustrating the degree to which dynamics are bottom‐up (cf.…”

An invasive appetite: Combining molecular and stable isotope analyses to reveal the diet of introduced house mice (Mus musculus) on a small, subtropical island

“…Our models consisted of three Markov Chain Monte Carlo (MCMC) chains of 1,000,000 iterations, thinned by 500, and with a burn-in of 500,000 [42]. We checked model convergence and fit by plotting the posterior predictive distributions and assessing Gelman-Rubi diagnostic values (i.e., Gelman-Rubin statistics < 1.1; sensu [19,88]). A posteriori, we combined the original eight sources into four source groups for summarizing and reporting source proportion in diet; similarly for our model excluding mōlī as a source, we combined the original seven sources into three source groups.…”

“…In such a non-native dominated ecosystem, it is unsurprising to find mouse diet dominated by non-natives. Indeed, other studies from island systems with a history of disturbance and introduced species (such as the Main Hawaiian Islands and Southeast Farallon Island) also report that mice consume a mix of native and non-native taxa [17,19,92]. As opportunistic omnivores, mice will likely eat accessible and abundant taxa [16].…”

“…Previous research of house mice on islands shows that mice have complex, omnivorous diets but tend to prefer arthropods (especially Lepidopteran larvae), followed by seeds and vegetative materials [2,5,6,9,[12][13][14][15][16][17][18][19][20][21][22][23][24]. Beyond arthropods and plants, mice have been documented to consume a variety of other foods, including seabirds (via depredation and/or scavenging; [1,4,10,16,[25][26][27]), landbirds [28], skinks, and possibly other reptiles [29].…”

“…While these studies have contributed important information about mouse diet and ecology, nearly all document challenges owing to diet determination methods used. For example, some studies mention biases in identifying prey species (i.e., microhistological surveys; [17]) or make assumptions about mouse diet in estimates of food source contributions (i.e., stable isotope analysis; [19,21]). Combining dietary determination methods-especially for cryptic, understudied taxa, such as insular house mouse populations-is a more informative and robust approach that can reduce biases and increase taxonomic resolution [31].…”