Dynamic Landscape of Fear
The Snapshot team have written another paper using the Snapshot data we all help to classify. The paper A ‘dynamic’ landscape of fear: prey responses to spatiotemporal variations in predation risk across the lunar cycle can be found at http://onlinelibrary.wiley.com/doi/10.1111/ele.12832/full for those of you interested in reading the original.
Lead by Meredith Palmer the paper explores how four ungulate species, buffalo, gazelle, zebra and wildebeest respond to predation risk during differing stages of the lunar cycle. These four make up the bulk of the African lion’s diet in the Serengeti along with warthog. Of course warthog are strictly diurnal so are not affected by the lunar cycle as they are tucked up nice and snug in a burrow.
For the other four night time can be a stressful time. None of these animals sleep all night, they snatch rest here and there, keep grazing and most importantly of all keep a watchful eye or ear out for possible attack.
It has long been thought that prey species territory is shaped by fear and that animals have safe areas (where they rest, give birth, etc) and risky areas where they instinctively know predators may be lurking. These areas trigger a risk versus reward response as they often contain better forage/water etc.
What Meredith and the team argue is that this landscape of fear is very much dynamic changing not only with seasons and night and day but on a very much finer scale as influenced by light availability through the moon.
Lions find it so much easier to hunt during nights where the moon gives of least light. It gives them a great advantage to stalking close to their prey using the dark as a kind of camouflage. The prey species, on the other hand, are at a distinct disadvantage, they can’t see the stalker and even if they sense its presence they are reluctant to flee as this presents a great risk in itself if they can’t see.
Meredith and her colleagues took the data from Snapshot Serengeti to quantify nocturnal behaviour of the key species using the presence or absence of relaxed behaviour (defined when we classify a species as resting or eating.) They then overlapped this with data collected through Serengeti Lion Project on lion density and hunting success. This data enabled them to work out what areas where high or low risk to the prey species. Using a clever statistical program, R, the data was analysed to see if lunar cycle had any bearing on animal behaviour, in particular, predator avoidance.
They found that moonlight significantly affected the behaviour of all four species but in a variety of ways. As we mentioned before there is often a good reason to venture into the high risk areas and the trade off in increased risk of predation is a really good feed. Buffalo for instance don’t change their use of space so much but were found to form more herds on dark nights. It seems safety in numbers works well for buffalo. Zebra react similarly in their herding activity but are much more erratic when it comes to space use, moving around a lot more randomly keeping potential predators on their toes.
Each species showed an aversion to using high risk areas at night but, particularly wildebeest and zebra, were found to increase their use of these areas when the moons luminosity was higher and safety increased. It was noted that high risk areas where avoided more frequently in the wet season than the dry. The thought being that there is increased hours of moonlight during the dry season that the animals take advantage of. Perhaps too the drive to find enough good food is a factor.
This paper serves to remind us that although what we do at Snapshot Serengeti is fun it is more than just a way for us classifiers to pass the time. It really has a very significant role in science and that role is ever increasing.