Disentangling the roles of bottom‐up and top‐down drivers in the trade‐off between food acquisition and safety in prey with multiple predators

Abstract

Disentangling the roles of bottom-up and top-down drivers in the trade-off between food acquisition and safety in prey with multiple predators Abstract 1. Prey face a trade-off between acquiring food and avoiding predation, but food availability, and therefore its effect, is rarely measured in field studies investigating non-lethal effects of predation. The main aim of this study is to investigate the role of the presence of predators in the functional adjustments of feeding parameters with patch quality in a medium-size herbivore. 2. In Hwange National Park (Zimbabwe), we set up an experiment by manipulating, over two years, patch quality for impala (Aepyceros melampus), a medium-sized herbivore. We assess predation risk by monitoring the presence of three GPS-equipped predators: African lions (Panthera leo), spotted hyaenas (Crocuta crocuta) and African wild dogs (Lycaon pictus). 3. In enriched, fertilised plots the impalas reduced step rates (i.e. the rates of change in feeding stations), and increased their number of bites per feeding station while bite rates were not affected. Thus, the main adjustment of their feeding was the step rate. The total time the impalas spent vigilant appeared to be a good predictor of the variation of their bite rate. Although vigilance caused a reduction in bite rate when at a feeding station, the impalas reduced the relative costs of vigilance by continuing chewing and processing their food when scanning for predators. 2 4. When predators were in the vicinity, the impalas increased their exclusive vigilance (high-cost vigilance) but not their vigilance while chewing (low-cost vigilance) and decreased their bite rate while their step rate and the number of bites per feeding station did not change significantly. The impalas were thus visually disconnected from their patch, and reduced their bite rate when actually foraging. Exclusive vigilance increased when both lions and hyaenas were in the vicinity, and when wild dogs were nearby. 5. Patterns of vigilance that altered bite rate were linked to the presence of predators during the previous 24h. Over the long term patch quality was the main determinant of the feeding parameters (step rate and bite rate). This study shows how predators, by affecting the time prey devote to predator detection, shape the functional adjustments of food acquisition by prey to local patch quality.

Grouping behaviour and activity patterns of impala (Aepyceros melampus) in a nutrient –rich and a nutrient-poor savanna in Tanzania

“…Family groups with juveniles tend to reduce exposure to temperature extremes by staying under shade ( Shrestha et al., 2014 ) and to avoid predators ( Shukla et al., 2021 ). Females with young offspring select sub-optimal forage habitats to reduce predation risks and to save energy ( Ahmad et al., 2016 ; Pays et al., 2021 ). In addition, females have higher energy requirements than males due to their small body size and reproduction demands ( Szemán et al., 2021 ).…”

“…Grouping behaviour and activity patterns of herbivores tend to vary in relation to differing food quality and availability ( Fryxell, 1991 ; Smith and Cain, 2009 ; Koenig et al., 2013 ). Forage quality had shown to reduce impala movement ( Pays et al., 2021 ) time spent vigilant ( Pays et al., 2012 ), and influence feeding behaviour ( Blanchard and Fritz, 2008 ). Furthermore, group size tends to differ between habitats ( Szemán et al., 2021 ).…”

Habitat but not group size or recent predator activity affect corvid collective vigilance at carcasses

“…As meso-scavengers, corvids are at risk of being preyed upon or attacked by larger scavengers, potentially when competing over the shared resource of a carcass. In Australia, larger scavengers that may attack or exclude corvids from carcasses include dingoes (Canis dingo), wedge-tailed eagles (Aquila audax), red foxes (Vulpes vulpes) and feral cats (Felis catus) (Doherty et al, 2019(Doherty et al, , 2015Olsen, 2005;Rowley, 1973b). Understanding the influence of these larger scavengers, and other factors, on corvid vigilance behaviour will provide novel insight into the scavenging dynamics of corvids and deepen our understanding of predation effects around carcasses.…”

“…It is also important to consider the species-specific interactions between corvids and their predators and the important influence on the landscape of fear (Creel et al, 2014(Creel et al, , 2019Makin et al, 2018). For example, eagles hunt more effectively in open habitat (Olsen, 2005) and thus corvids would likely be more vigilant when eagles are present in these areas. However, dingoes may be more effective predators in closed habitats, with corvids likely more vigilant there when dingoes are present.…”

Anchoring grassland sustainability with a nature‐based small burrowing mammal control strategy

“…Another important density‐dependent factor controlling burrowing mammal density is predation (Hoy et al, 2016; Krebs et al, 1995; Majchrzak et al, 2022; Pays et al, 2021). If the predator density is low, the prey will have a low predation rate and high survival.…”