Zooming in on mechanistic predator-prey ecology: Integrating camera traps with experimental methods to reveal the drivers of ecological interactions.

Camera trap technology has galvanized the study of predator-prey ecology in wild animal communities by expanding the scale and diversity of predator-prey interactions that can be analysed. While observational data from systematic camera arrays have informed inferences on the spatiotemporal outcomes of predator-prey interactions, the capacity for observational studies to identify mechanistic drivers of species interactions is limited. Experimental study designs that utilize camera traps uniquely allow for testing hypothesized mechanisms that drive predator and prey behaviour, incorporating environmental realism not possible in the laboratory while benefiting from the distinct capacity of camera traps to generate large datasets from multiple species with minimal observer interference. However, such pairings of camera traps with experimental methods remain underutilized. We review recent advances in the experimental application of camera traps to investigate fundamental mechanisms underlying predator-prey ecology and present a conceptual guide for designing experimental camera trap studies. Only 9% of camera trap studies on predator-prey ecology in our review use experimental methods, but the application of experimental approaches is increasing. To illustrate the utility of camera trap-based experiments using a case study, we propose a study design that integrates observational and experimental techniques to test a perennial question in predator-prey ecology: how prey balance foraging and safety, as formalized by the risk allocation hypothesis. We discuss applications of camera trap-based experiments to evaluate the diversity of anthropogenic influences on wildlife communities globally. Finally, we review challenges to conducting experimental camera trap studies. Experimental camera trap studies have already begun to play an important role in understanding the predator-prey ecology of free-living animals, and such methods will become increasingly critical to quantifying drivers of community interactions in a rapidly changing world. We recommend increased application of experimental methods in the study of predator and prey responses to humans, synanthropic and invasive species, and other anthropogenic disturbances.

Interplay of competition and facilitation in grazing succession by migrant Serengeti herbivores.

Competition, facilitation, and predation offer alternative explanations for successional patterns of migratory herbivores. However, these interactions are difficult to measure, leaving uncertainty about the mechanisms underlying body-size-dependent grazing-and even whether succession occurs at all. We used data from an 8-year camera-trap survey, GPS-collared herbivores, and fecal DNA metabarcoding to analyze the timing, arrival order, and interactions among migratory grazers in Serengeti National Park. Temporal grazing succession is characterized by a "push-pull" dynamic: Competitive grazing nudges zebra ahead of co-migrating wildebeest, whereas grass consumption by these large-bodied migrants attracts trailing, small-bodied gazelle that benefit from facilitation. "Natural experiments" involving intense wildfires and rainfall respectively disrupted and strengthened these effects. Our results highlight a balance between facilitative and competitive forces in co-regulating large-scale ungulate migrations.

Fear of the human "super predator" pervades the South African savanna.

Lions have long been perceived as Africa's, if not the world's, most fearsome terrestrial predator,1,2,3,4,5,6,7,8,9 the "king of beasts". Wildlife's fear of humans may, however, be far more powerful and all-prevailing1,10 as recent global surveys show that humans kill prey at much higher rates than other predators,10,11,12 due partly to technologies such as hunting with dogs or guns.11,13,14,15 We comprehensively experimentally tested whether wildlife's fear of humans exceeds even that of lions, by quantifying fear responses1 in the majority of carnivore and ungulate species (n = 19) inhabiting South Africa`s Greater Kruger National Park (GKNP),9,15,16,17 using automated camera-speaker systems9,18 at waterholes during the dry season that broadcast playbacks of humans, lions, hunting sounds (dogs, gunshots) or non-predator controls (birds).9,19,20,21,22 Fear of humans significantly exceeded that of lions throughout the savanna mammal community. As a whole (n = 4,238 independent trials), wildlife were twice as likely to run (p < 0.001) and abandoned waterholes in 40% faster time (p < 0.001) in response to humans than to lions (or hunting sounds). Fully 95% of species ran more from humans than lions (significantly in giraffes, leopards, hyenas, zebras, kudu, warthog, and impala) or abandoned waterholes faster (significantly in rhinoceroses and elephants). Our results greatly strengthen the growing experimental evidence that wildlife worldwide fear the human "super predator" far more than other predators,1,19,20,21,22,23,24,25,26,27,28 and the very substantial fear of humans demonstrated can be expected to cause considerable ecological impacts,1,6,22,23,24,29,30,31,32,33,34,35 presenting challenges for tourism-dependent conservation,1,36,37 particularly in Africa,38,39 while providing new opportunities to protect some species.1,22,40.