Forager‐mediated cascading effects on food resource species diversity

Abstract

Perceived predation risk varies in space and time. Foraging in this landscape of fear alters forager‐resource interactions via cascading nonconsumptive effects. Estimating these indirect effects is difficult in natural systems. Here, we applied a novel measure to quantify the diversity at giving‐up density that allows to test how spatial variation in perceived predation risk modifies the diversity of multispecies resources at local and regional spatial levels. Furthermore, we evaluated whether the nonconsumptive effects on resource species diversity can be explained by the preferences of foragers for specific functional traits and by the forager species richness. We exposed rodents of a natural community to artificial food patches, each containing an initial multispecies resource community of eight species (10 items each) mixed in sand. We sampled 35 landscapes, each containing seven patches in a spatial array, to disentangle effects at local (patch) and landscape levels. We used vegetation height as a proxy for perceived predation risk. After a period of three nights, we counted how many and which resource species were left in each patch to measure giving‐up density and resource diversity at the local level (alpha diversity) and the regional level (gamma diversity and beta diversity). Furthermore, we used wildlife cameras to identify foragers and assess their species richness. With increasing vegetation height, i.e., decreasing perceived predation risk, giving‐up density, and local alpha and regional gamma diversity decreased, and patches became less similar within a landscape (beta diversity increased). Foragers consumed more of the bigger and most caloric resources. The higher the forager species richness, the lower the giving‐up density, and alpha and gamma diversity. Overall, spatial variation of perceived predation risk of foragers had measurable cascading effects on local and regional resource species biodiversity, independent of the forager species. Thus, nonconsumptive predation effects modify forager‐resource interactions and might act as an equalizing mechanism for species coexistence.

So many choices, so little time: Food preference and movement vary with the landscape of fear

“…However, bigger seeds also have proportionally more nutrient content per seed than smaller ones, making them more profitable food (Hou et al, 2021 ; Wang & Corlett, 2017 ; Wang & Yang, 2014 ), and this preference might therefore not be affected by varying perceived predation risk (Sivy et al, 2011 ). A preference for maximizing energetic gains is also evident by the removal of the larger and most nutritious seeds first, while smaller and less nutritious seeds are left in higher densities in the patch, or consumed only after the most preferable seeds are depleted in safer landscapes (Figures 4 and 5 ; see also Eccard et al, 2022 ; Ferreira et al, 2022 ).…”

“…Therefore, functional traits of resources and dietary preferences of foragers are often interlinked, but as perceived predation risk also affects the forager's behavior, it can alter the choice for certain resource traits. Ultimately, the landscape of fear generates behavioral-mediated cascading effects that alter the final composition of communities of resource species (Eccard et al, 2022), and foragers can affect the coexistence of plant species (Ferreira et al, 2022;Garb et al, 2000;Stump & Chesson, 2017).…”

“…Therefore, functional traits of resources and dietary preferences of foragers are often interlinked, but as perceived predation risk also affects the forager's behavior, it can alter the choice for certain resource traits. Ultimately, the landscape of fear generates behavioral‐mediated cascading effects that alter the final composition of communities of resource species (Eccard et al, 2022 ), and foragers can affect the coexistence of plant species (Ferreira et al, 2022 ; Garb et al, 2000 ; Stump & Chesson, 2017 ). To better understand the complex demographic and biodiversity effects of foraging in different landscapes of fear—especially at the community level of the resources—it becomes important to understand forager's dietary preferences for specific functional traits, and how perceived predation risk modifies these preferences.…”