Mzima Springs: Where fish groom hippos

US President Barack Obama's new documentary on Netflix, Our Great National Parks, features eight of the world's most unique, with Kenya's Tsavo National Park on the cards.

The uniqueness of Tsavo lies in its dry unforgiving landscape and the symbiotic way in which animals survive: A family of dwarf mongoose help the hornbills get food.

While natural water sources in Tsavo disappear during the dry seasons, Mzima Springs is a permanent oasis and the national park's iconic attraction.

The crystal-clear water of this chain of lakes is filtered through the volcanic rocks of the Chyulu Hills to the north; over 50 million gallons seeping from the ground every day into crystal clear pools buzzing with activity.

At Mzima Springs, hippo's poop provide natural fertiliser that is the heart of the diversity of life in this ecosystem. The hippo fertiliser helps in growing date and raffia palms, water berries and figs whose falling fruits provide food for velvet monkeys and birds.

Hippo's poop also provides nutrients for plants, food for insects and arthropods, mollusks, annelids, echinoderms and cnidarians beneath the waters of Mzima Springs.

Fish in the springs feed on the poop while providing the hippo with 'house help' duties; cleaning hippo's teeth whenever they open the mouth, foraging for scraps stuck between the hippo's teeth in an unusual mutuality of trust.

Rasping mouthparts from fish also cleans the hippo's hide, toenails, the cracked feet and butt. Others cover the bristles of its tail. A whole community of fish functioning as hippo cleaners; skin-cleaning and tick-picking in what biologists call mutualism - a relationship between two species from which both benefit: fish get a full meal of hippo's poop in exchange for a pedicure and polish.

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Writing for Ecology Centre in 2002, Joe Eaton notes that Mzima Springs has a mutualism "running along a continuum from the intimate symbiotic partnership between alga and fungus that makes a lichen, to the loose association of songbirds in a multispecies feeding flock.

"Mutualist relationships cross the boundaries of phylum and kingdom, linking plants with fungi that nourish their roots and animals that pollinate their flowers and disperse their seeds," Eaton writes.

Eaton concurred with distinguished biologist Lynn Margulis, who saw the very origin of complex life as the result of symbiosis between single-celled organisms (endosymbiosis) and "the prevalence of mutualism seems at odds with the notion, going back to Darwin's Origin of Species, of nature as an arena of fierce competition."

Russian evolutionary biologist Pyotr Kropotkin, the prince turned anarchist, argues in his classic, Mutual Aid, that cooperative behaviour is more central than competition, citing the wolf pack or the termite colony as examples where organism gain "inclusive fitness" by aiding the survival of close relatives whose genes it shares.

But competition did occur during the prolonged drought of 2009 when starving game animals were driven to the Mzima Springs in their thousands and the competition with resident hippos saw most starving to death: only five are remaining, down from 70 in 2003.

While Mzima Springs is a small green oasis, it's a different story in other arid parts of Tsavo where the incredible memory and sense of smell from millions of receptors in their trunks help the elephants to guide other animals to where there is water and food - until the dry season ends around September.

But long before Obama, documentary filmmaker, Alan Root, shot Mzima: Portrait of a Spring, in 1969.