Fire effects in a landscape of fear : food availability and perceived predation risk as potential determinants of patch utilization by herbivore prey
Abstract: Context: A major effect of climatic change is the global increase in forest fires, which potentially creates an increase in food availability for herbivorous species. Also vegetation density and the numbers of tree logs increase in burned sites, and this is thought to influence the perceived risk of herbivore prey species, which affects their anti‐predator behaviour and thereby the patch utilization. This cascading effect of forest fires might have implications on future ecosystem functioning in the burned area, and more knowledge about the effects of landscape features on predator‐prey interactions is needed to adapt conservation and wildlife management policies, to the changing climate. Aim: This study aims to gain insight into how varying food availability, visibility and escape impediments in burned and unburned forest sites, influence patch utilization by two herbivore species, mountain hare (Lepus timidus) and moose (Alces alces). I predicted that i) animals that are under high predation pressure will have a higher utilization of ‘save’ patches in the control sites where perceived risk is lower, and that ii) animals that experience no or low predation pressure will have a higher patch utilization in the burned areas where food availability is high. Methods: I tested these predictions by conducting a correlative cross‐sectional study in three different boreal forests in the north of Sweden, each with a burned site that burned in 2006 and an equal sized unburned control site. The herbivore community there is predominantly comprised of moose and mountain hare. Measurements on species passage rates and the time they spend in front of the camera are derived from footage obtained from remotely triggered cameras with a PIR sensor. Data on food availability, visibility and number of tree logs and other plot characteristics are collected by taking field measurements around each camera trap. I tested the relations between these variables using a multiple regression analysis with zero‐inflated generalized linear models. Results & discussion: In two of the three areas I did not find a difference in patch utilization between the burned and the control site for mountain hare. In one area there even was a significantly higher patch utilization in the burned site instead of the control, and this made sense since mountain hare utilization was positively correlated to the number of tree logs in two of the three areas. The positive correlation of tree logs could be explained by the fact that birds of prey are a dominant predator for mountain hare, in which case tree logs provide cover for the hares instead of increasing their perceived predation risk. For moose there was no significant difference in utilization between the burned and control site per area. However, in the areas with the highest number of moose passages the difference was almost significant. In this area the multiple regression model also showed the predicted positive correlation of patch utilization and food availability. Conclusions: I conclude from the reflections on the results for mountain hare, that depending on the composition of the predator community, the landscape features will have a different effect on the patch utilization of the prey species. In a study area with many different predator types present, it is difficult to find strong correlations between the landscape features and patch utilization, since these features are ambiguous in their effect on perceived predation risk. Therefore, on the basis this study, it remains difficult to draw clear conclusions about the actual effects of forest fires on predator‐prey interactions, since they are very predator specific. For moose it seems plausible that their patch utilization is indeed predicted by food availability, but that this correlation was not found two of the three areas because of the lack of data points there and/or the possible inaccurate proxy for food availability that was used in this study.
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