Last updated May 3, 2018 at 3:03 pm
A type of dunnart eats its competitors to better increase its own food supply.
A lesser hairy-footed dunnart snacks on a grasshopper. Credit: Tamara Potter
How do you stop a competitor eating your food? Easy. Eat the competitor.
That’s the lesson learned from new research investigating the diet of a small marsupial insectivore called the lesser hairy-footed dunnart (Sminthopsis youngsoni), which lives in Australia’s Simpson Desert.
In a paper published in the journal Royal Society Open Science, a team led by ecologist Tamara Potter from the University of Sydney reveals that the dunnart makes a point of eating wolf spiders (members of the genus Lycosa) and suggests that they do so not for nutritional reasons but to prevent the arachnids eating the dunnarts’ preferred food, insects.
If this is, in fact, the case, then it represents the first recorded instance of what is known as “intraguild predation (IGP)” occurring between vastly different species.
IGP – where one species is targeted by another to reduce competition for shared food resources – is quite common, but in most cases the animals involved in the conflict are members of the same phylum.
Killing off the competition
In Australia, for instance, dingoes have been observed killing foxes, thereby reducing competition for smaller prey animals.
In order for a predator-prey relationship to be classified as an example if IGP, the two species must first be identified as members of the same guild, a term which ecologists use to describe groups of species that share resources, regardless of their relationship to each other.
Insect-eating animals thus comprise a guild, while those which eat fruit and live in trees comprise another. The other two critical factors that need to be in play are time and space: the two species must share an environment and be active at the same time of day (or night).
Potter and her colleagues establish that dunnarts and the wolf spiders tick all three boxes. Both are generalist insectivores, both inhabit arid areas, and both are nocturnal.
To determine the diets of both species, the researchers first caught several of each. To each dunnart they attached a small glow-stick (of the type popular at electronic dance parties), which allowed them to be easily observed after release at night. The wolf spiders each had a small piece of reflective tape attached to their backs, for the same purpose.
Pitfall traps
(In all cases, the attachments did not affect movement, and were expected to fall off after a day or so.)
In addition, several pitfall traps were built – small holes into which passing insect and arachnid life fell, allowing the scientists to determine species mix and population density.
The results showed that the diets of dunnarts and wolf spiders overlap by more than 80%. About 13% of the dunnart diet, however, comprised wolf spiders themselves.
This, the researchers suggest, is a much larger percentage than chance would predict. The marsupials also did not eat members of another genus of spider in the area.
The wolf spiders, the scientists write, “are unlikely to be targeted for nutritional reasons; levels of water, energy and nutritional composition vary little between lycosids and other invertebrates that are eaten”.
Thus, they conclude, there is “reasonably strong potential” for intraguild predation to be occurring between the two species. If so, then it represents the most disparate example of the phenomenon ever recorded.
