Author: Théophile Niyitegeka

In dry southern Morocco, domesticated goats climb to the precarious tippy tops of native argan trees to find fresh forage. Local herders occasionally prune the bushy, thorny trees for easier climbing and even help goat kids learn to climb. During the bare autumn season, goats spend three quarters of their foraging time “treetop grazing.”

Spanish ecologists have observed an unusual way in which the goats may be benefiting the trees: the goats spit the trees’ seeds. Miguel Delibes, Irene Castañeda, and José M Fedriani reported their discovery in the latest Natural History Note in the May issue of the Ecological Society of America’s journal Frontiers in Ecology and the Environment. The paper is open access.

Argan may be familiar from popular beauty products that feature argan oil, made from the tree’s nuts. The nut is surrounded by a pulpy fruit that looks a bit like a giant green olive. For goats, the fruits are a tasty treat worth climbing up to 30 feet into the branches to obtain.

But the goats don’t like the large seeds. Like cows, sheep, and deer, goats re-chew their food after fermenting it for a while in a specialized stomach. While ruminating over their cud, the goats spit out the argan nuts, delivering clean seeds to new ground, wherever the goat has wandered. Gaining some distance from the parent tree gives the seedling a better chance of survival.

This novel seed dispersal effect is a variation on the mechanism ecologists call endozoochory, in which seeds more commonly pass all the way through the animal’s digestive system and out the other end (or sometimes through two digestive systems). The authors suspected that reports of goats dispersing argan seeds by this more common mechanism were mistaken, because goats do not usually poop large seeds.

The researchers have witnessed sheep, captive red deer, and fallow deer spitting seeds while chewing their cud, and suspect this spitting variation on endozoochory may actually be common — and perhaps an essential route of seed spread for some plant species.

Source:Science Daily

Zebras may use memory to guide their migration each year. Memory based on past average conditions provides a clear signal that best directs zebras to their destination. In contrast, current vegetation conditions along the way are less important for the direction of the migration according to a computer simulation by researchers from Senckenberg. The study, published in Proceedings of the Royal Society B, highlights that migration routes of large terrestrial mammals such as zebras could be more inflexible than previously thought.

It’s incredible to watch: each year thousands of animals, including zebras, wildebeests and gazelles, migrate in turn with the seasons between foraging grounds. The animals migrate long distances in their search for sufficient and highly nutritious forage. While science has explained certain aspects of this migration, it is not fully understood how the animals know where to go.

Chloe Bracis, a researcher at the German Senckenberg Biodiversity and Climate Research Centre and the Goethe University Frankfurt, has found that memory is the key to directing zebra migration: “Zebras appear to migrate to the location where foraging conditions were best in the past. They seem to navigate to their destination based on memory, and importantly, forecast conditions several months after arrival.”

As part of the study, Bracis and her colleague Thomas Mueller modelled migration routes of zebras using computer simulations. Zebras migrate around 250 kilometers from the Okavango Delta, Botswana to the Makgadikgadi grasslands in November. “We tested two mechanisms which can influence the direction. Simulated zebras could use perception and sense, for example, the vegetation green up in their current surroundings. Alternatively, zebras could use memory, i.e. information from previous migrations, to forecast where to go ,” explains Mueller.

The researchers compared the simulated tracks with real-life tracks from GPS-tagged zebras which were collected by other researchers. Memory using past average conditions was able to predict the migration destination of the modelled zebras up to four times closer than those modelled using perception to find their way. “Memory even beats perception at the largest — that is omniscient — perceptual ranges,” says Bracis and adds “However perception is still important. Other studies have shown the importance of perception of current local conditions on the timing and speed of the zebra migration, but these may be less important for zebras in terms of direction.”

Migration routes of zebras are threatened by climate change and land use change in southern Africa. The zebra migration examined in this study, for instance, was blocked by a fence from the late 60’s until 2004. The researchers therefore see the study as contributing to the conservation of large migratory terrestrial mammals such as zebras. “One can only protect migration routes efficiently if one knows how the animals migrate. If memory of past conditions informs the direction migrating animals take, this suggests migration routes could be relatively inflexible,” concludes Mueller.

Source:Science Daily