Species’ traits help predict small mammal responses to habitat homogenization by an invasive grass

Abstract

Invasive plants can negatively affect native species, however, the strength, direction, and shape of responses may vary depending on the type of habitat alteration and the natural history of native species. To prioritize conservation of vulnerable species, it is therefore critical to effectively predict species' responses to invasive plants, which may be facilitated by a framework based on species' traits. We studied the population and community responses of small mammals and changes in habitat heterogeneity across a gradient of cheatgrass (Bromus tectorum) cover, a widespread invasive plant in North America. We live-trapped small mammals over two summers and assessed the effect of cheatgrass on native small mammal abundance, richness, and species-specific and trait-based occupancy, while accounting for detection probability and other key habitat elements. Abundance was only estimated for the most common species, deer mice (Peromyscus maniculatus). All species were pooled for the trait-based occupancy analysis to quantify the ability of small mammal traits (habitat association, mode of locomotion, and diet) to predict responses to cheatgrass invasion. Habitat heterogeneity decreased with cheatgrass cover. Deer mouse abundance increased marginally with cheatgrass. Species richness did not vary with cheatgrass, however, pocket mouse (Perognathus spp.) and harvest mouse (Reithrodontomys spp.) occupancy tended to decrease and increase, respectively, with cheatgrass cover, suggesting a shift in community composition. Cheatgrass had little effect on occupancy for deer mice, 13-lined ground squirrels (Spermophilus tridecemlineatus), and Ord's kangaroo rat (Dipodomys ordii). Species' responses to cheatgrass primarily corresponded with our a priori predictions based on species' traits. The probability of occupancy varied significantly with a species' habitat association but not with diet or mode of locomotion. When considered within the context of a rapid habitat change, such as caused by invasive plants, relevant species' traits may provide a useful framework for predicting species' responses to a variety of habitat disturbances. Understanding which species are likely to be most affected by exotic plant invasion will help facilitate more efficient, targeted management and conservation of native species and habitats.

Group effects of a non‐native plant invasion on rodent abundance

“…Our observation of a negative linear trend for abundance of cricetids in relation to cheatgrass cover is in agreement with the majority of investigations examining effects of cheatgrass on rodents at the individual species (Hall ) and community levels (Ostoja and Schupp , Freeman et al. , but see Ceradini and Chalfoun ). The species comprising the family Cricetidae in our study area represented several foraging guilds (e.g., granivores, folivores, and carnivores), but were similar in that they were all relatively small and reliant upon quadrupedal motion.…”

“…This finding for Ord's kangaroo rats is not entirely unique for rodents. For example, Ceradini and Chalfoun () observed that deer mice abundance increased marginally with cheatgrass abundance. In addition, Pearson and Fletcher () and Malick et al.…”

“…). We suspect that each of these factors, and possibly indirect effects receiving less attention, such as increased predation risk (Mattos and Orrock , Ceradini and Chalfoun ), was responsible for a reduction in abundance of cricetids. For example, it has been speculated that the cricetid species we investigated are more vulnerable to predation because they do not engage in long ricochetal, erratic jumping as a means of escaping predators (Degen ), though this groups’ preference for more closed habitat types likely also influences their locomotor style.…”

“…For example, though Litt and Steidl () reported that presence and abundance of heteromyids decreased with increasing dominance of Lehmann lovegrass ( Eragrostis lehmanniana ), whereas abundance of murids decreased, their analytical framework was individual species based. A recent exception to the pattern of examining plant invader effects on rodents at the species or community level was put forth by Ceradini and Chalfoun (), where authors examined cheatgrass ( Bromus tectorum ) effects on rodent occupancy based on species’ natural history traits, such as habitat associations (i.e., open vs. closed).…”

Enemy release from the effects of generalist granivores can facilitate Bromus tectorum invasion in the Great Basin Desert

“…However, the extent that novel weapons influence the feeding preferences of generalist vertebrates (e.g., Kalisz, Spigler, & Horvitz, 2014) in invaded communities is generally unclear. Alternatively, native rodents in the Great Basin could avoid cheatgrass seeds relative to seeds from native competitors due to inferior nutritional quality (Kelrick & MacMahon, 1985) and/or effective physical defenses (e.g., persistent awns) (Ceradini & Chalfoun, 2017).…”