How did the ant steal the lion’s dinner? This isn’t the start of considered one of Aesop’s Fables. It’s the discovering of a brand new examine exhibiting how the disruption of 1 tiny mutual relationship on the African savanna has massive impacts on the meals net — all the way in which to the lion’s den.
When big-headed ants (Pheidole megacephala) invade the savanna, they kill off native acacia ants (genus Crematogaster), robbing native whistling thorn timber of their valiant defenders towards hungry elephants. With out ants to chew them, the elephants rip up the thorn timber, opening up the grassland, which makes it more durable for lions to catch their most popular zebra meals. Lions find yourself looking buffalo as a substitute. The findings, revealed on-line January 25 in Science, present that invasive species’ results may be very oblique — and recommend that modifications in numerous low-level mutualisms may additionally echo up meals webs in different ecosystems.
Over the previous 15 years or so, wildlife ecologist Jake Goheen and his colleagues on the College of Wyoming in Laramie and the Ol Pejeta Conservancy in Laikipia, Kenya, have been learning how acacia ants shield whistling thorn timber (SN: 6/15/10). When an elephant tries to eat the tree, “ants swarm up inside its nostrils and chew from the within out,” Goheen says.
The scientists have been additionally inspecting what the lions within the conservancy eat as a part of a separate examine. “One of many issues that we discovered … was that lions are way more efficient, they’re extra profitable with their hunts in areas the place tree cowl is excessive,” Goheen says.
However what occurs when tree cowl is all of a sudden low? To seek out out, Goheen and his colleagues collared six lionesses from the native prides to trace their exercise and kills. The crew additionally arrange experimental plots the place big-headed ants had invaded, and the place the native ants nonetheless held sway.
The large-headed ant arrived within the conservancy between 2002 and 2005, Goheen says. “We expect it in all probability was imported on produce,” introduced into the homes or vacationer camps within the space. The invading bugs kill native acacia ants wherever they discover them. And different research have proven that with out defending ants, pachyderms tore down the thorn timber 5 to seven occasions extra usually.
Within the new examine, the scientists may have used drones or satellite tv for pc photos to check tree cowl, however “we don’t have that sort of cash,” Goheen says. As a substitute, the researchers tracked their collared lions, after which obtained down on fingers and knees close to the lions’ current kills, utilizing a spread finder to measure the openness of the world. Areas with big-headed ants, the crew confirmed, had 2.67 occasions larger visibility than areas with out — that means that lions may see farther, however so may their prey.
Lions relied on the quilt of timber to pounce on hapless zebras close by: The place visibility was low, the chance of a zebra kill was 62 p.c. However when visibility was excessive, the lion’s probability of taking down a zebra dropped to solely 22 p.c.
Over the three years of the examine, zebra dinners decreased from 67 p.c to 42 p.c of lion kills. However the lions didn’t go hungry. As a substitute, they went for beef. Buffalo kills elevated from zero to 42 p.c of kills over the examine interval. It’s a dangerous eating regimen, Goheen says. Buffalo “are massive and feisty,” and lions looking buffalo usually tend to be injured.
The examine exhibits that “the disruption of a mutualism can have cascading results on different species in the neighborhood,” says Emilio Bruna, a plant ecologist on the College of Florida in Gainesville. “These results may be sudden and oblique.”
It’s a clue, Bruna says, that ecologists must be searching for different pairs just like the acacia ant and the thorn tree, the place a single particular relationship is a basis for an ecosystem and a single anthill may trigger a savanna-wide shift in who’s consuming who.
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