The relative importance and the role of predation risk for prey is still subject of debate, especially the relative strength of top-down versus bottom-up processes. European hare are thought to respond particularly strong to predation risk, which possibly contributed to the decline in population numbers in north-west Europe. Therefore the objective of this thesis was to investigate the effects of predation risk and habitat characteristics on European hare.
On a predator-free island, I subjected European hares to the elevated predation risk of a leashed dog, and tested how habitat characteristics affected the movement response of hares (chapter 2). Movement responses of GPS-collared hares were measured in patches with different vegetation structure on a short (i.e., several hours) and a long (i.e., 24 hours) timescale. The movement response of European hare to elevated predation risk was best explained by a model that included the interaction between predation risk and vegetation structure. On the short time scale, a strong immediate movement response was found in open habitat with low cover. However, on the long timescale, the effect of the treatment synchronized with the daily rhythm of the hare. The distance covered between resting and foraging grounds was negatively affected by elevated predation risk, while use of less risky (often low-quality) vegetation during resting and foraging was favoured.
Secondly, I tested the effects of predators (i.e., red fox (Vulpes vulpes)), fellow prey and habitat characteristics on the space use of two sympatric prey species, the European hare and European rabbit (Oryctolagus cuniculus) using camera traps (chapter 3). The response of hare and rabbit to space use by predators, space use by fellow prey, and habitat characteristics was different for both prey species investigated. The level of activity by rabbits, which make use of a refuge for escape (i.e., central-place forager), was positively correlated with the level of activity by predators over time, however, space use of rabbits was uncorrelated to space use by predators. The level of activity by hares, which do not make use of a refuge (i.e., free-ranging), was uncorrelated with the level of activity by predators over time, however, space use of hares was correlated with space use by predators. Predator absence possibly led to avoidance behaviour between hare and rabbit, while predator presence promoted coexistence between the two species. Competition for predator free space may have reversed the relationship between the space use by predators and habitat characteristics on the space use by hare and rabbit.
In chapter 4, I tested the relative importance of predator (fox) and competitor (rabbit) activity and forage quality and quantity for the proportion of time spent in a vegetation type, and the proportion of time spent foraging by European hare. Space use and foraging behaviour was investigated by equipping hares with GPS and accelerometers. Hand-plucked samples of plant species were used to analyse forage quality and quantity. The activity of predators and competitors was investigated using camera traps. During days that predators were more active, hares spent a higher proportion of time in low-risk patches, and in patches with low-quality food and low-quantity food. Overall, habitat characteristics (i.e., forage quality and vegetation height) more strongly affected hare space use than the activity of predators. The activity of competitors was not related to space use. During days that competitors were more active, hares spent a higher proportion of time foraging in patches of low-quality food. Overall, habitat characteristics (i.e., forage quality, vegetation height and edible biomass) more strongly affected hare foraging time than the activity of predators, and the activity of competitors was least important.
In chapter 5, I tested the correlation between chronic exposure to predation risk of multiple predators and body condition and reproductive output of European hare. Density of all predators year-round present was estimated. To describe body condition, I extracted four components of the body measurements of shot hares by a principal component analysis. Reproductive output of hares was estimated as the number of placental scars. Predation risk was negatively correlated with the number of placental scars and the ‘health’ component of body condition of European hare (i.e., weight of liver, kidney, heart and body).
In this thesis I showed that both bottom-up and top-down forces modulate prey species behaviour and distribution simultaneously. Overall, predators seemed less important than habitat characteristics in affecting space use and foraging behaviour on the scale of the food patch and the scale of the daily range. Nevertheless, the effect of predators per se on space use and foraging behaviour was more important at the scale of the food patch than at the scale of the daily range. My conclusion is that the relative importance of predators for the behavioural response of prey is negatively correlated with the scale of the processes. Additionally, predators seemed fairly important in affecting body condition and reproductive output at the scale of the home range. I expect the relative importance of predators for prey fitness to be positively related with the scale of the processes. Insight into the effects of predation risk and habitat characteristics on European hare, helps us to understand the responses of hares to the changes in the north-west European landscape. The increased numbers, accessibility and distribution of predators has probably contributed to the decline in population numbers of the European hare in north-west Europe.