Tale of two metrics: density and biomass in a desert rodent community

Activity overlap of carnivores, their potential wild prey, and temporal segregation, with livestock in a Biosphere Reserve in the Chihuahuan Desert

Daily activity is an important aspect of animal behavior and depends both on nutritional and reproductive demands. It also can be modified by—among other factors—interspecific competition, the need to minimize the risk of predation, and human disturbance, such as the presence of cattle. We studied the activity patterns and degree of overlap among carnivores, their potential wild prey, and livestock, in a Biosphere Reserve in the Chihuahuan Desert. There was no temporal segregation among the carnivores. Carnivores synchronized their activity with that of their main prey, the black-tailed jackrabbit (Lepus californicus). In contrast, we did observe temporal segregation between the puma (Puma concolor), coyote (Canis latrans), and bobcat (Lynx rufus), with mule deer (Odocoileus hemionus). There was little activity overlap between predators and livestock (Bos taurus, Equus caballus). However, to avoid conflict resulting from livestock predation we suggest increasing and improving surveillance, and that calves and females close to calving be sheltered. More studies on the multi-niche interactions of livestock and their wild predators are needed to understand daily activity overlap in different seasons, and to better understand the mechanisms of coexistence in protected areas in order to make sound management recommendations to cattle growers and park rangers.

The landscape of fear: the missing link to understand top-down and bottom-up controls of prey abundance?

Identifying factors that may be responsible for regulating the size of animal populations is a cornerstone in understanding population ecology. The main factors that are thought to influence population size are either resources (bottom-up), or predation (top-down), or interspecific competition (parallel). However, there are highly variable and often contradictory results regarding their relative strengths and influence. These varied results are often interpreted as indicating "shifting control" among the three main factors, or a complex, nonlinear relationship among environmental variables, resource availability, predation, and competition. We argue here that there is a "missing link" in our understanding of predator-prey dynamics. We explore whether the landscape-of-fear model can help us clarify the inconsistencies and increase our understanding of the roles, extent, and possible interactions of top-down, bottom-up, and parallel factors on prey population abundance. We propose two main predictions derived from the landscape-of-fear model: (1) for a single species, we suggest that as the makeup of the landscape of fear changes from relatively safe to relatively risky, bottom-up impacts switch from strong to weak as top-down impacts go from weak to strong; (2) for two or more species, interspecific competitive interactions produce various combinations of bottom-up, top-down, and parallel impacts depending on the dominant competing species and whether the landscapes of fear are shared or distinctive among competing species. We contend that these predictions could successfully explain many of the complex and contradictory results of current research. We test some of these predictions based on long-term data for small mammals from the Chihuahuan Desert in the United States, and Mexico. We conclude that the landscape-of-fear model does provide reasonable explanations for many of the reported studies and should be tested further to better understand the effects of bottom-up, top-down, and parallel factors on population dynamics.