Abstract
While constrained by endogenous rhythms, morphology and ecology, animals may still exhibit flexible activity patterns in response to risk. Temporal avoidance of interspecific aggression can enable access to resources without spatial exclusion. Apex predators, including humans, can affect mesopredator activity patterns. Human context might also modify temporal interactions between predators. We explored activity patterns, nocturnality and the effects of human activity upon a guild of carnivores (grey wolf, Canis lupus; Eurasian lynx, Lynx lynx; red fox, Vulpes vulpes) using travel routes in Plitvice Lakes National Park, Croatia. Humans were diurnal, foxes nocturnal and large carnivores active during the night, immediately after sunrise and before sunset. Carnivore activity patterns overlapped greatly and to a similar extent for all pairings. Activity curves followed expectations based on interspecific killing, with activity peaks coinciding where body size differences were small (wolf and lynx) but not when they were intermediate (foxes to large carnivores). Carnivore activity, particularly fox, overlapped much less with that of diurnal humans. Foxes responded to higher large carnivore activity by being more nocturnal. Low light levels likely provide safer conditions by reducing the visual detectability of mesopredators. The nocturnal effect of large carnivores was however moderated and reduced by human activity. This could perhaps be due to temporal shielding or interference with risk cues. Subtle temporal avoidance and nocturnality may enable mesopredators to cope with interspecific aggression at shared spatial resources. Higher human activity moderated the effects of top-down temporal suppression which could consequently affect the trophic interactions of mesopredators.Significance statementTemporal partitioning can provide an important mechanism for spatial resource access and species coexistence. Our findings show that carnivores partition the use of shared travel routes in time, using the cover of darkness to travel safely where their suppressors (large carnivores) are more active. We however observed fox nocturnality to be flexible, with responses depending on the activity levels but also the composition of apex predators. High human activity modified the top-down temporal suppression of mesopredators by large carnivores. The use of time by predators can have demographic and trophic consequences. Prey accessibility and susceptibility can be temporally variable. As such, the ecosystem services and the ecological roles of predators may be affected by human time use as well as that of intraguild competitors. Temporal interactions should not be overlooked when evaluating human use and conservation priorities in protected areas.
Highlights
Top-down regulation and the suppression of mesopredators by large carnivores can be elicited via direct killing, harassment and the risk associated with such encounters (Crooks and Soulé 1999; Palomares and Caro 1999; Ritchie and Johnson 2009)
Using generalized linear models, we examined if human photo capture rate indices (PCRI) affected whether each carnivore’s activity records occurred at night
We examined the effect of large carnivore PCRI and the interaction between large carnivore PCRI and human PCRI
Summary
Top-down regulation and the suppression of mesopredators by large carnivores can be elicited via direct killing, harassment and the risk associated with such encounters (Crooks and Soulé 1999; Palomares and Caro 1999; Ritchie and Johnson 2009). Ecological differentiation along a niche axis is deemed necessary for coexistence between competitors (Hardin 1960). Carnivores may spatially avoid competitors or differentiate dietary niche (Azevedo et al 2006; Bassi et al 2012; Newsome and Ripple 2014). Regardless of diet, intraguild aggression can still present risk for mesopredators and some spatial resources such as linear travel routes may exacerbate this risk because of their frequent use by apex predators (Shannon et al 2014; Haswell et al 2018). An animal’s circadian activity pattern may provide an important dimension for minimising the likelihood of aggressive encounters
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