EPOW - Ecology Picture of the Week

A Tree Needs a Rhino

Kayu Tanah Tree (Trewia nudiflora), Family Euphorbiaceae
Greater One-horned Rhinoceros (Rhinoceros unicornis), Family Rhinocerotidae
Rhino Latrine
Dudhwa National Park, India

Explanation:  Here is a fascinating case of coevolution, symbiosis, and an unexpected relationship between a tree and a rhino.

Welcome to the terai wetlands and woodlands of northern India along the foothills of the Himalayas.  This is one of the few homes of the dangerous, massive, and endangered greater one-horned rhinoceros.  Massive efforts have been made to prevent this ungulate's extinction, and in this park it thrives, although in low numbers.  

But its woodland home here, and much of its wildlife, are, surprisingly, dependent on the rhino's existence.  This is a mutualism, a symbiosis, that benefits both tree and rhino.  

These rhinos seem to be critical dispersal agents of viable seeds of the kayu tanah tree (Trewia nudiflora), shown in the main photo above, and below. 

This is the kayu tanah tree, Trewia nudiflora -- a common component of the northern India sal (Shoria robusta) woodlands.  

The Trewia nudiflora tree also has high economic importance.

Its wood can be used as a minor source of timber, and is used for crafting chests, furniture, packing cases, yokes, and other items.

The fruits are edible by people, and the roots can be used to provide a medical poultice to relieve gout and rheumatism.

These trees drop their fruit (a drupe -- a fleshy fruit with a stony pit), which then are eaten by the rhinos (and lots of other species) who then defecate in nutrient-rich "latrine" piles in the grasslands. 
  

A rhino "latrine" -- where the rhino defecates into piles
that provide nutrients to feed the seeds that
pass through the rhino's digestive system
and then sprout.
  

There, in summer, the Trewia seeds germinate profusely and, along with other herbs and plants, eventually form small woodland stands or riverine forest patches. Such mosaics of grassland and riverine forest then provide key habitat for abundant spotted deer populations, which are the primary prey for tigers. 

Rhinos, deer, and other herbivores are the key dispersers of other plant seeds as well. Thus, the ecological roles of rhinos and their latrines help maintain vegetation and habitat diversity for a number of species. 

Moreover, this seems to be a case of coevolution; the seeds of Trewia actually may need to pass through the rhino to germinate.  

So … whew … the presence of rhinos serves as a surrogate to the potential presence and viability of Trewia trees and their riverine forest patches that support quite a web of life.