We now know that mountain treeshrews and summit rats feed on the nectar secreted by the giant pitcher plant – Nepenthes rajah – then defecate into its pitchers, providing it with much needed nutrients deficient in the soils in which it grows.
This recent finding, by researchers at Monash University in Melbourne and Kuala Lumpur – including the two authors of this article – sits squarely in the field of “mutualism”.
Mutualisms are mutually beneficial relationships found in nature – often, but not always, between a plant and an animal.
Such relationships were first described more than 130 years ago when it was discovered that fungi and algae live together in “symbiosis” to form another organism: the lichen.
Many of the mutualisms we know about result in one species receiving a much needed service – such as pollination or protection from predators – while the other species gains a reward – normally food or somewhere to live.
Gaining an understanding of mutualisms can make a significant contribution to species conservation, as the following examples demonstrate.
Mutualism ecology – the way mutualistic species interact in their habitats – has enriched our understanding of ecology with some exciting finds in recent decades.
Our recent “pitcher” discovery is the only known instance where multiple small mammals interact in a mutually beneficial way with a carnivorous plant. The finding provides the most plausible explanation yet as to why Nepenthes rajah produces some of the largest pitchers in the genus.
The pitchers are shared between the animals in time – mountain treeshrews visit pitchers during the day, and summit rats visit at night, meaning both small mammals get their fill of nectar from the pitchers. At the same time the pitchers get a round-the-clock source of nutrients that no other pitchers appear to have access to.
This is a unique and seemingly simple relationship, but it characterises the complexity in nature that may so easily be overlooked.
Mutualisms are not new to science, nor are they a novel method of human-animal interaction.
Take for example a small bush bird known as the greater honeyguide (Indicator indicator). When searching for honey, Boran people in eastern Africa traditionally used honeyguides to dramatically increase their chances of finding a colony.
The birds consume larvae and wax from discarded honeycomb, which they can only access after humans have opened the hive using tools and smoke to stun the bees.
Anecdotal records indicate humans have had a mutualistic relationship with the honeyguide since prehistory, and further research has shown honeyguides form similar mutualistic relationships with other mammals such as honey badgers – Mellivora capensis – in the absence of humans.
Badgers are encouraged to pursue the honeyguide to a bee colony and, taking advantage of their sting-resistant hide, rob the honeycomb.
In much the same way as humans discard a portion of honeycomb for the birds, badgers also leave some behind that benefit their “guide”.
In these two examples, the importance of mutualism ecology to conservation is evident. Honeyguides interact in a mutualism with humans where the potential impact of one species far outweighs the other.
Honeyguides have demonstrated a capacity to moderate their behaviour in the absence of humans, negotiating a mutualism with other mammals in order to obtain bee larvae.
But humans retain the ability to moderate their behaviour and find an alternative resource (sugar, commercial honey), and the capacity of other mammals to completely fill the void is unknown.
Understanding the ecology of the relationship formed between the species enables us to predict the impact of human withdrawal from such a mutualism, and observe how the birds respond.
On the contrary, in the carnivorous plant/small mammal example, there is far less potential for one species to obtain resources elsewhere and thus, the impact of losing one or more species from the mutualism is unknown.
Apportioning conservation resources to a single species based on rarity or species traits, for example, may have little conservation value if one or more of its mutualists are not also preserved.
In this way, mutualism ecology contributes to our understanding of the way species interact and their important conservation values.
Our understanding of mutualisms has come a long way since the first scientific documentations of beneficial interactions between species.
Learning more about the way species interact in nature helps us learn how things are connected and depend on each other, and this can have big repercussions on decisions relating to species conservation.
Increasing knowledge on mutualisms in nature and considering mutualisms in a larger, integrated network is an important way forward in approaching our view of the world.