Shrub cover homogenizes small mammals’ activity and perceived predation risk

Abstract

Altered disturbance regimes, increasing atmospheric CO2, and other processes have increased woody cover and homogenized vegetation in savannas across the planet. African savannas with extensive versus minimal woody cover often have vastly different animal communities. However, we lack a clear mechanistic understanding of why animal communities are changing with vegetation structure. Our goal for this study was to understand how vegetation structure in an African savanna shaped the perceived predation risk of small mammals, hence affecting their activity. Using a reciprocal measure of standard giving-up-densities, amount of food eaten, we found sharp declines in rodents’ perceived predation risk and increased rodent activity underneath shrub cover. This response was consistent across species; however, species showed subtle differences in their responses to grassy vegetation. Our findings suggest that areas of minimal or extensive shrub cover (shrub encroachment) may be homogenizing rodents’ perceptions of predation risk and thus shaping their use of space.

Fear of large carnivores is tied to ungulate habitat use: evidence from a bifactorial experiment

“…Whereas, as our results experimentally demonstrate, fear mediates the avoidance of shrubby areas by large ungulates, other evidence indicates that smaller mammals show reductions in fear as shrub cover increases 65 . As shrub encroachment increases, these inter-specific differences in the perception of predation risk may exacerbate the ongoing patterns of global loss and replacement of large mammals with smaller ones 11 , 65 .…”

“…Whereas, as our results experimentally demonstrate, fear mediates the avoidance of shrubby areas by large ungulates, other evidence indicates that smaller mammals show reductions in fear as shrub cover increases 65 . As shrub encroachment increases, these inter-specific differences in the perception of predation risk may exacerbate the ongoing patterns of global loss and replacement of large mammals with smaller ones 11 , 65 . More than the reduction of larger ungulates alone, the replacement of large consumers with smaller ones is likely to have important trophic consequences that reshape the structure and demographics of plant communities 2 , 11 , 66 .…”

Savanna Rodents’ Selective Removal of an Encroaching Plant’s Seeds Increased With Grass Biomass

“…At each sampling site (50 × 50 m plot, 0.25 ha) we established four seed stations around the center of the site. We placed the seed stations (30 cm diameter tray) halfway under shrubs to increase foraging rates (Loggins et al, 2019b). Prior to trials, we pre-baited trays for 24 h with oats and peanut butter.…”

“…We set the motion-sensitive camera to photo, three bursts, with a 5 s trigger interval. To calculate the length of foraging bout we measured the duration of time each individual rodent first and last appeared on camera, with new bouts starting after 20 min of non-detection (Loggins et al, 2019b). When multiple individuals of the same species appeared on camera simultaneously, we noted a foraging bout for the maximum number of individuals seen in the frame.…”

“…The extent of rodents' predation and dispersal of seeds is likely a function of environmental conditions. At a local scale, rodents' movements are shaped by vegetation structure, such as grass biomass and shrub cover, which provide cover from predators (Hulme, 1993;Monadjem, 1999a;Loggins et al, 2019b). While less pronounced, rodent activity may also be influenced by different types and configurations of surrounding landscapes (Nupp and Swihart, 2000;Orrock and Damschen, 2005;Ness and Morin, 2008).…”