When perception reflects reality: Non‐native grass invasion alters small mammal risk landscapes and survival

Abstract

Modification of habitat structure due to invasive plants can alter the risk landscape for wildlife by, for example, changing the quality or availability of refuge habitat. Whether perceived risk corresponds with actual fitness outcomes, however, remains an important open question. We simultaneously measured how habitat changes due to a common invasive grass (cheatgrass, Bromus tectorum) affected the perceived risk, habitat selection, and apparent survival of a small mammal, enabling us to assess how well perceived risk influenced important behaviors and reflected actual risk. We measured perceived risk by nocturnal rodents using a giving‐up density foraging experiment with paired shrub (safe) and open (risky) foraging trays in cheatgrass and native habitats. We also evaluated microhabitat selection across a cheatgrass gradient as an additional assay of perceived risk and behavioral responses for deer mice (Peromyscus maniculatus) at two spatial scales of habitat availability. Finally, we used mark‐recapture analysis to quantify deer mouse apparent survival across a cheatgrass gradient while accounting for detection probability and other habitat features. In the foraging experiment, shrubs were more important as protective cover in cheatgrass‐dominated habitats, suggesting that cheatgrass increased perceived predation risk. Additionally, deer mice avoided cheatgrass and selected shrubs, and marginally avoided native grass, at two spatial scales. Deer mouse apparent survival varied with a cheatgrass–shrub interaction, corresponding with our foraging experiment results, and providing a rare example of a native plant mediating the effects of an invasive plant on wildlife. By synthesizing the results of three individual lines of evidence (foraging behavior, habitat selection, and apparent survival), we provide a rare example of linkage between behavioral responses of animals indicative of perceived predation risk and actual fitness outcomes. Moreover, our results suggest that exotic grass invasions can influence wildlife populations by altering risk landscapes and survival.

Mechanisms underlying increased nest predation in natural gas fields: a test of the mesopredator release hypothesis

“…Mesopredators in our system may therefore have somewhat complementary local distributions (Sozio and Mortelliti ), with deer mice and ground squirrels displacing chipmunks in more fragmented areas. Generalist species such as deer mice tend to thrive near human disturbance, often at the expense of more sensitive or specialist species which are unable to adapt as quickly to novel environments (Crooks , Ceradini and Chalfoun ).…”

“…For tray construction details, see Appendix S2: Fig S2. We opened trays after sunset and closed trays the following morning before sunrise to ensure that only nocturnal rodents accessed stations. We recorded any signs of visitation at foraging trays (see Ceradini and Chalfoun 2017) and observed no sign of animals other than rodents foraging in trays. We sifted sand from visited trays to collect remaining seeds and dried all seed in an oven for 24 h at 60°C before weighing.…”

Do or do not. There is no try in restoration ecology

“…Nonetheless, we live in a time when nature needs us (Dalby ), and our work will never be done. The work we need to do of course includes more technical endeavors such as adding plants and animals back into systems (Desimone ; James et al ; Perino et al ) or managing for less desirable species such as exotics (Ceradini & Chalfoun ; Bell et al ), but what was much more forward‐oriented thinking at this meeting was that the work in turn changes and educates us—and this process should be lifelong and generational. The old idea of land stewardship was new again.…”

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

“…The majority of investigations on non-native plants and vertebrates have analyzed the effects of invading plant species on either individual species or entire communities , Litt and Steidl 2011, Hall 2012, Horn et al 2012, Malick et al 2012, Litt and Pearson 2013, Freeman et al 2014, Ceradini and Chalfoun 2017a, Smith et al 2017. Though several of the above investigations have reported on non-native plant effects on rodent families Steidl 2011, Smith et al 2017), not all have done so by analyzing data at the actual group level.…”