Fox abundance and dynamics are linked to the amount of arable land and to the abundance of their main prey, voles ( Microtus spp.) 28, 29. During this time, the fox has remained ubiquitous throughout Europe, including Sweden 28. The lynx returned to south-central Sweden in the 1950’s after 50 years of absence 26, and the wolf returned in the 1980’s after having been absent for more than a century 27. Thus, mesopredators are confronted with a dilemma: should they avoid these larger guild members to avoid being killed, even if this means missing scavenging opportunities, or should they take the risk to obtain a free meal? We studied this question in a boreal ecosystem in Sweden where red fox ( Vulpes vulpes, hereafter fox) was the dominant mesopredator, and Eurasian lynx ( Lynx lynx, hereafter lynx) and grey wolf ( Canis lupus, hereafter wolf) were the apex predators.īoth lynx and wolves have been extirpated from most of Europe for several centuries, but recently they have followed a world-wide pattern of large carnivore recovery 25. Much of the carrion available to scavengers is provided by apex predators because of their habit of killing large prey, which they often cannot completely consume by themselves 20, 21, 22, 23, 24. There is an increasing amount of literature on the role and importance of scavenging 15, 16, 17, 18, some even suggesting that scavenging may buffer the effects of climate change 19. Most vertebrate carnivores are not only predators, but also facultative scavengers, and scavenging is a prevalent phenomenon in most terrestrial systems 15. There may also be reasons for mesopredators to be attracted to apex predators. It has been suggested that fear of being killed makes mesopredators avoid not only direct proximity to apex predators, but also the habitats used by them which in turn may influence the demography of mesopredator populations 14. Although there is ample anecdotal evidence of apex predators killing mesopredators 4, 13 there are few studies that have been able to demonstrate that this mortality is additive and strong enough to limit mesopredator population growth 14. The empirical evidence for negative effects of apex predators on mesopredator abundance is strong in both aquatic 6, 7 and terrestrial systems 8, 9, 10, 11, 12. According to the Mesopredator Release Hypothesis, the human-caused worldwide reduction of apex predators has not only reduced their impact on herbivores, but also “released” mesopredators from top-down control, allowing them to thrive. However, the discovery that predators kill, and even consume, not only their herbivore prey, but also members of other competing predator species within their own guild 2, 3, 4, introduced more complexity to ecosystem theory, and supported the Mesopredator Release Hypothesis 5. Classic ecosystem theory predicts that predators control herbivores, restricting their grazing effect on the vegetation and thereby keeping “the world green” 1. This study shows that different apex predator species may affect mesopredator abundance in different ways and that the results may be dependent on the spatiotemporal scale and resolution of the data.Īpex predators may have multiple top-down effects on lower trophic levels in the ecosystem. In contrast, at the wolf territory level there was a negative effect of wolves on fox abundance when including detailed information of pack size and time since territory establishment, whereas there was no effect of lynx abundance. At this spatial scale, there was no effect of wolf abundance on fox abundance, whereas lynx abundance had a positive effect. Bottom-up processes were more influential than top-down effects as the proportion of arable land was the key indicator of fox abundance at the landscape level. Data from the Swedish wolf-monitoring system and VHF/GPS-collared wolves were used to study the effect of wolf pack size and time since wolf territory establishment on fox abundance. We used wildlife triangle snow-tracking data to investigate the abundance of red fox ( Vulpes vulpes) in relation to lynx ( Lynx lynx) and wolf ( Canis lupus) occurrence as well as land composition and vole ( Microtus spp.) density. Apex predators may affect mesopredators through intraguild predation and/or supply of carrion from their prey, causing a trade-off between avoidance and attractiveness.
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