Barbary Sheep and Desert Bighorns

Barbary sheep (Ammotragus lervia)  aoudad

This handsome fellow is an aoudad (Ammotragus lervia), aka a Barbary Sheep. These caprids are approximately the same size as domestic goats and weigh from 40 to 140 kg (88 to 300 lb).  Their original range was the desert and arid scrubland of Northern Africa–the northern margins of the Sahara in Algeria, Tunisia, northern Chad, Egypt, Libya, northern Mali, Mauritania, Morocco, Niger and Sudan–however as the Sahara expands and grows hotter and more dry, the aoudad is going extinct in its home range.

Desert Bighorns (Ovis canadensis nelsoni)

This is where the issue becomes morally complex.  Bestiary keepers and gentleman hunters of previous eras imported populations of Barbary sheep to other parts of the world which more closely resemble the now vanished ancestral scrublands of the Sahara.  Thus Aoudads might be going extinct in North Africa, but they are flourishing in Texas.  Their success comes at the expense of the endangered native caprid of Texas, the desert bighorn sheep (Ovis canadensis nelsoni) a desert subspecies of bighorn which once dwelt in Texas in thriving herds before over-hunting, disease, and habitat loss nearly wiped them out.  The Aoudad is larger and more aggressive (and requires less water) than the bighorn.  The invader is out-competing the native, and Texans are up in arms about it–quite literally, since they are renowned as a gun-toting people.  Aoudads, so precious in their original home in North Africa, are being blasted away as invasive pests in Texas.

My interpretation is that climate change is making West Texas more like the Sahara used to be (and making the Sahara more like the Atacama…or like the sunny side of the moon). Although, there are lots of factors at play when it comes  to whether an organism is successful in an ecosystem, climate change affects a lots of these variables.   Aoudads and bighorns have a relationship sort of like the round goby and the mottled sculpin (remember them) although the Aoudads don’t actually eat the bighorns’ eggs, they just run the males off and pointlessly hoard all of the bighorn ewes.  We are going to see more of these situations involving invasive creatures and we are going to have to start thinking now about how to best manage climate refugee species.  Do we want Aoudads to go extinct in the wild? Do we want the deserts of Texas to have no wild caprids?  Maybe we need to start releasing desert bighorns in Arkansas or Rhode Island?  What even is a natural habitat in a world where humankind has changed every habitat?

Ant Farmers

Agriculture is almost unknown in the natural world. Human beings are the only vertebrates known to grow crops or keep livestock (with the possible exception of damselfish which carefully tend little algae gardens).  And yet we were not the first animals to invent the concept.  Ants have farmed fungi within their tunnels for tens of millions of years.  Ants also keep aphids in captivity in order to “milk” them of sugary secretions–or to eat them outright.  It is possible that beetles, termite, or snails came up with the concept first, but most evidence points to ants as the first farmers.

An Ant Milking Aphids

Ants do not have a shabby operation either. Leaf cutter ants form the largest and most complicated animal societies known on Earth (other than our own) and a single colony can have over 8 million individuals.  Leaf cutters are an ideal example of how adept ants are at farming fungi.  Four different castes of worker ants work together to bring back leaf fragments and integrate them into huge fungal gardens. Different species of leafcutters cultivate different fungi from the Lepiotaceae family.  Certain bacteria with antifungicidal and antibacterial properties grow within the metapleural glands of the ants.  The worker ants use these bacteria to “prune and weed” dangerous or unproductive organisms out of their gardens.  Older (more expendable) worker ants carry waste products from the hive to a waste pile where they stir the hive wastes together to aid in decomposition.  The waste-management job brings the danger of fungal or bacterial contamination and contaminated ants are exiled to certain death in order to keep the gardens safe.  Additionally dead ants from within the hive are carefully placed around the waste pile so as to protect the hive from their decomposition.

Leaf Cutter Ants at the Cameron Currie Lab arrange cut-up leaves into their fungal garden.

According to geneticists who study the rates of mutation within the various fungal cultivars, ants began their farm relationship with fungi around 50 million years ago in the warm Eocene epoch (an era which saw many of the critical relationships in modern ecosystems begin).

 

Digital Cut-away of an underground leaf-cutter nest

Scientists are also beginning to understand the means by which ants herd their little flocks of aphids.  The aphids are smaller insects which feed on the saps and juices of plants (which they suck out by means of specialized mouthparts called stylets).  The ants prevent the aphids by flying away by tearing off their wings.  The feet of the ants produce chemicals which tranquilize and subdue the aphids and keep them from escaping the “pastures” near the ant colonies.  It is believed that aphids also derive certain benefits from this arrangement since the aggressive ants protect them from many of their natural predators.

An Ant with a “herd” of Aphids

For years naysayers belittled the farming achievements of ants suggesting they were little more than symbiotic arrangements.  However as entomologists study the ants more carefully they increasingly discover just how complicated and sophisticated those relationships are (involving as they do numerous symbiotic relationships with bacteria in order to produce the chemicals necessary for agricultural control).  Additionally, what are humankind’s relationships with our crops and animals if not huge harrowing examples of symbiosis?