Outsourcing, i.e. the obtaining of goods or a service from an outside supplier, makes it possible for commercial companies to increase their own efficiency. Delegating services to more efficient partners can also make sense in nature. The team around Dr. Caroline Schöner from the research group Applied Zoology and Nature Conservation at the University of Greifswald wanted to examine why some species of pitcher plants no longer catch insects, but let mammals do this for them, which they “pay” with high quality shelters or nectar. When the mammals take shelter or drink the nectar, they drop their nitrogen-rich faeces, which is then digested by the pitcher plants. The animals thus provide their plant interaction partners with pre-digested and assimilated nutrients and extend the food spectrum of the plants to prey which they would not otherwise catch. The plant itself can save costs, because, for example, it doesn’t have to produce scents for attracting insects. Ultimately, this leads to the loss of an evolutionary characteristic which is no longer needed.
As an example of this kind of ecological outsourcing, the team examined the mutualism (a partnership determined by mutual use) between the pitcher plant, Nepenthes hemsleyana, and the bat, Kerivoula hardwickii. “The plant interacts with insect-eating bats, which fertilise the plant with their faeces, whilst using the plants as shelter during the day,” explains Caroline Schöner. By using feeding experiments in both the natural habitat of the plants on the island of Borneo, as well as in the greenhouse of the Botanical Garden in Greifswald, the team was able to prove, that the plants profit much more from the bats’ faeces than from the more natural insect diet. “Nepenthes hemsleyana does not just show higher levels of photosynthesis when it has access to the faeces of the mammal interaction partner, one can also recognise advantages with regard to the growth and nutrient content in its leaves,” explains Michael Schöner, who was part of the research team. And the leader of the research group, Applied Zoology and Nature Conservation, and senior author of the study, Prof. Gerald Kerth from the University of Greifswald, adds: “This of course also makes the plant very reliant on the faeces of the bats. This means that the plants are not any different, for example, to car manufacturers; they cannot continue to produce without the cooperation of their suppliers.”
In earlier investigations, the researchers were able to prove that the pitcher plants cover approximately a third of their nitrogen requirements via the bats’ faeces. However, especially after periods of extreme nutrient deficiency, the plants can absorb the nitrogen from bat faeces considerably faster than from insects, as shown by the results of this new study. Dr. Charles Clarke from the Australian James Cook University Cairns has looked at the interaction between species of pitcher plants and tree shrews and rats for years. He suspects that this evidence is also applicable for other types of pitcher plants and a large amount of further mutualist interactions in nature. This could be a key for understanding such interactions themselves and their evolution.
The study was financed by the Deutsche Forschungsgemeinschaft, the German Academic Exchange Service, the University of Brunei Darussalam and the University of Greifswald.
Further Information
Original Article Ecological outsourcing: a pitcher plant benefits from transferring pre-digestion of prey to a bat mutualist. Caroline R. Schöner1, Michael G. Schöner1, T. Ulmar Grafe2, Charles Clarke3, Linda Dombrowski1, Moi Chan Tan2 and Gerald Kerth1
Journal of Ecology on 7 December 2016, doi: 10.1111/1365-2745.12653
Contact at the University of Greifswald
Caroline R. Schöner
1 Applied Zoology and Nature Conservation
Zoological Institute and Museum
Johann-Sebastian-Bach-Straße 11/12
17489 Greifswald
Tel.: +49 3834 86-4273
Fax: +49 3834 86-4252
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