Thursday, 25 May 2017

Tree-climbing goats spit out and disperse valuable argan seeds

25 May 2017

Goats climb argan trees to eat their fruit and leaves


By Elizabeth Preston

In south-western Morocco, acrobatic goats climb argan trees to eat their fruit and leaves. A tree full of goats is a striking sight, but the goats’ widely overlooked habit of regurgitating and spitting out the nuts may be important to the life of these forests.

Goat herders lead their flocks through the argan (Argania spinosa) forests, where the animals can clamber up trees 8 to 10 metres high and strip them nearly bare. Popular accounts say the goats defecate the nuts of argan fruits, which can then be retrieved from the goats’ manure.

Cracking these nuts open is the first step in making argan oil, a valuable export to richer countries where it is used in beauty products and foods. People may also harvest the fruits directly, but the goats save them a step.

“Some scientists have accepted the defecation hypothesis, probably because they did not speak to the herders,” says Miguel Delibes, a biologist at Doñana Biological Station in Seville, Spain.

The herders say the goats mostly spit the seeds out.
Seed of a thought

“Goats do not usually defecate large seeds,” Delibes and his co-authors write. This made them sceptical that argan nuts, about 2.2 centimetres long, took this route through the animals.

So they fed Spanish domestic goats fruits with seeds of various sizes, including olives, hawthorn fruits, and carob tree pods. The researchers didn’t have access to argan fruits as the tree doesn’t grow in Spain.

Despite not being able to find all of the seeds afterwards, the authors note, they recovered spat-out seeds from every type of fruit. The largest seeds — still smaller than an argan nut — were most likely to be spat out. Smaller seeds more often wound up in faeces.

Food that a goat swallows travels to the rumen, the first of four stomach compartments. Like other ruminants such as cattle or deer, the goat regurgitates material — the cud — from this compartment for extra chewing.

“The time in the rumen is very variable,” Delibes says, because goats may chew foods several times. A goat might spit out a swallowed seed hours or days later — up to six days in the study.

The researchers tested the viability of regurgitated seeds and found that more than 70 per cent could still grow. That means spitting goats might be an overlooked ecological factor, helping to scatter the seeds of plants they eat.
 

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