In ecology, as in comedy, timing is everything.
Hours, minutes or even seconds can make the difference for an animal between stumbling upon a predator and avoiding it, between finding a berry-laden bush and discovering branches that have already been gnawed on. Mere moments can determine if a raccoon comes face to face with a bobcat at night, if a flock of cocky turkeys find their field already occupied by cranes, if a deer disappears into the trees before a coyote appears.
The fortune of an animal and the health of entire ecosystems may depend on these fleeting encounters, or not lucky ones. “An animal must be in the right place, at the right time, to avoid predators, find food, reproduce successfully.,” said Neil Gilbert, a postdoctoral researcher at Michigan State University.
In that way, the interactions between animals in a given ecosystem are like a theatrical production, he said, adding: “For the production to be a success, each actor has to be on stage, in the right place, and they have to act and deliver their lines at the right time.”
Now, a new study reveals how humans could unknowingly rewrite these ecological scripts, altering the way characters interact and fueling more interspecies encounters.
For the study, Dr. Gilbert and his colleagues analyzed images captured by Wisconsin snapshot, a citizen science project run by the Wisconsin Department of Natural Resources. Since 2016, volunteers have deployed more than 2,000 wildlife cameras across the state, capturing tens of millions of images of Wisconsin fields, farms and forests, and the fauna that frequents them.
Wild animals of different species were more likely to lead overlapping lives (appearing at local camera sites in quicker succession) in human-altered landscapes, such as farms, than in quieter places, such as national forests, the researchers reported. scientists. in PNAS last month.
The finding suggests that human disturbance may bring the animals closer, making them more likely to collide with each other. “There’s a little less room to move around,” Dr. Gilbert said.
Although more research is needed, that interspecies squeeze could have effects such as making it harder for prey to evade predators, intensifying competition for resources or increasing the risk of disease transmission between species, the researchers say.
“The compression of species niches will likely lead to new interactions between species with unknown consequences,” Benjamin Zuckerberg, an ecologist at the University of Wisconsin-Madison and an author of the study, said in an email.
strangers on a plain
The Wisconsin Department of Natural Resources created Snapshot Wisconsin in an effort to collect continuous data throughout the state, at all hours of the day and during all seasons of the year, on local wildlife populations. It relies on an army of volunteer camera hosts to set up, monitor and maintain wildlife cameras, both on public and private land throughout the state.
The cameras, which are activated by movement and body heat, have captured a menagerie of animals going about their daily lives: bald eagles scavenging in the snow, bear cubs climbing trees, a newborn fawn, a group of otters frolicking on a grassy path. “That’s so many otters,” said Jennifer Stenglein, a quantitative research scientist at the Wisconsin Department of Natural Resources and an author of the new study.
(The department posts many of the photos on zooniversean online citizen science platform, where volunteers from around the world can help identify the creatures in each shot).
For the new study, the researchers analyzed nearly 800,000 animal photographs captured over the course of four years. To assess the “co-occurrence” of species, they calculated how much time elapsed between when members of 74 species pairs—turkeys and deer, for example, or coyotes and skunks—appeared at a given camera site.
If coyotes and skunks routinely appear in the same place within an hour or day of each other, they are more likely to have overlapping habitats and routines, and to be found in the real world, than if days or weeks pass by. between appearances, the scientists reasoned.
The time intervals between detections varied greatly. Sometimes the cameras captured the odd pairings of animals in the same frame; other times, days or weeks may pass between their appearances.
But overall, across all animal pairs, the trend was clear: In relatively pristine habitats, such as national forests, about six days passed, on average, between detections. In the most human-disturbed habitats, that interval was reduced to an average of four days.
Over a three-month period, the researchers estimated, highly antagonistic pairs — that is, duos in which one species was likely to kill the other — such as bobcats and rabbits or foxes and squirrels. they are found seven times more in the most disturbed landscapes compared to the least disturbed. (Even when animals aren’t face-to-face, simply hearing or smelling a predator can have “dramatic effects” on the behavior of prey species, Dr. Gilbert noted.)
“It will be fascinating to see who will be the winners and who will be the losers in this human-compressed niche space,” said Dr. Zuckerberg.
“For example, will smaller dams and competitors need to adapt new defenses or behaviors?” He asked himself. Can they even do it?
The scientists also found that much of the effect seemed to be driven by differences in relative abundance; Species like raccoons and squirrels tended to be more numerous in human-disturbed landscapes, where garbage dumps overflow and fields are full of grain, than in wilder ones.
But these differences did not fully explain the findings, suggesting that some species might also change their behavior in human-disturbed habitats, becoming active at different times of day or with a less wide distribution. (Animals with less room to roam would be more likely to collide, like gas particles in a shrinking container, Dr. Gilbert noted.)
Still, many questions remain, including whether the findings generalize to other species and ecosystems and what precisely happens when these creatures meet, even when the encounters are caught on camera.
How did the wildcat do? chase the coyote? who won the skunk-raccoon face to face? And why does that deer look like it’s about to kick a snarling possum in the face? (“Like, what did this poor possum do?” Dr. Gilbert wondered.)
More generally, do species like deer and raccoons interact with each other when they are on a dark trail? Or are they just passing through, like conscious ships in the night? “It’s hard to break down completely,” Dr. Zuckerberg said.
But the study illustrates the potential of using wildlife cameras to investigate aspects of animal behavior that might otherwise be difficult to observe, Dr. Stenglein said.
“We don’t sit in the field and watch the animals interact,” he said. “But there is a lot of power in being able to use this tracking camera data to understand how animals behave. It just, for me, opens a floodgate of possibilities.”