A game of cat and mouse is playing out in Panama鈥檚 rainforests, with large rodents called agoutis using their keen sense of smell to avoid ocelots that hunt them. The fear the rodents have for these predators and the ways it directs their behaviour have ripple effects that could alter the diversity of plants around them.
Most research on this 鈥渆cology of fear鈥� has been centred on temperate ecosystems, says at the Smithsonian Tropical Research Institute in Panama City. To see how the phenomenon could play out in the tropics, he and at the University of Panama looked to Central American agoutis (Dasyprocta punctata) and ocelots (Leopardus pardalis).
Agoutis, like many rodents, are prolific seed spreaders. They聽hoard seeds and retrieve them from buried caches later, but many of these will be abandoned and allowed to sprout. This benefits plants by聽dispersing them in a forest.
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To see if fear of ocelots disrupted the agoutis鈥� seed-shuttling habits, G谩lvez and Hern谩ndez attached strings and聽numbered flags to palm seeds so their locations could be聽spotted after being cached by聽agoutis. The pair set the seeds out in the forest in Metropolitan Natural Park in Panama City, both in areas with high and low聽densities of ocelots.
Where ocelots were plentiful 鈥� that is, spotted by trail cameras every week 鈥� the palm seeds were moved 50 to 300 per cent less than in areas of lower ocelot density, depending on the season. The agoutis also didn鈥檛 return to caches as often in areas with a large number of ocelots.
The rodents have a keen sense of smell and were probably reacting to the odours of the ocelots鈥� faeces and urine, says G谩lvez. The team confirmed this聽in a forest near Gamboa, Panama, by setting out palm seeds and trail cameras. In some locations, the seeds were placed next to a rag soaked in ocelot urine and a small pile of faeces. The agoutis were more cautious near the ocelot scents, taking longer to remove the seeds compared with those in places not marked with ocelot waste.
The researchers think this could have knock-on effects on forest vegetation. Seed beetles can infect and kill a palm seed left on the ground. In areas with聽hesitant agoutis, beetles 鈥渉ave a longer window to infect those seeds before the agouti comes and takes the seeds away鈥�, says G谩lvez.
This hasn鈥檛 been directly confirmed, but the team expects that the beetles鈥� effects could influence forest plant diversity. If fewer palms get a foothold, that may allow a wider range of聽plants to compete in places of聽high ocelot density.
Fear-spurred ecosystem cascades have been identified before, says at Western University in Ontario, Canada. She has seen it in her own work on raccoons, which don鈥檛 eat as many seashore creatures when exposed to the聽sound of barking dogs. 鈥淎聽large part of the formidable effect that predators play in ecosystems is driven by the fear聽that predators inspire in聽prey,鈥� she says.
Because of the downstream influence on the food web, she says that restoring fear may play a crucial role in restoring disturbed ecosystems.
Behavioral Ecology
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