It is easy to look at a forest and think it is inevitable: that trees come into being through a dignified process of seasons, seeds and soil, and will regenerate themselves as long as conditions environment allows.
Hidden from view are the creatures whose labors make up the forest – countless microorganisms and invertebrates involved in maintaining that soil, and the animals responsible for its transport. Move seeds that are too heavy to be carried by the wind to where they will germinate.
If one is concerned with the future of a forest — which tree species will thrive and which will decline, or whether species threatened by rapidly changing climates will successfully migrate to other lands. hospitable or not — then one should consider these seed-dispersing animals.
“All the oaks trying to move north are trying to move north,” said Ivy Yen, a biologist at the University of Maine who can be found on a recent afternoon at the reserve. Try to keep track of the habitable range. Penobscot Experimental Forest in nearby Milford, arrange the acorns on a tray for mice and hamsters to find.
“The only way for them to move with changing temperatures is with animals,” Yen said of trees. “Does personality affect that? Will there be individuals more likely to help?”
Yen is a doctoral student in the lab of Alessio Mortelliti, a wildlife ecologist who arrived in Maine nearly a decade ago with a particular interest: seed dispersal that interferes with research. How emerging is the animal personality.
Although researchers have studied how animals move seeds through landscapes, the possible role in their personalities is largely untested. The Penobscot Experimental Forest, with its 1,800 acres of closely monitored woodland, managed according to different forestry techniques, provided a landscape-scale context in which to explore this question.
For the past seven years, every summer, Dr. Mortelliti’s students have trapped deer and southern red-backed hamsters in their study plots — about 2,000 in total — and given them tests. measure where they fall on the spectrum between daring and shy. . Before being released, each was fitted with a microchip, unlike the animals used to identify lost pets.
Tags activate sensors, like the one Yen has mounted above her tray of acorns. Each acorn is painted with bands of color to indicate its species: red oak, red oak, black oak, white oak, marsh white oak, scarlet oak, pin oak, willow oak. Red oaks are already abundant in the area, but other species have only recently emerged or are expected to emerge as rising temperatures push their range northward.
Will these trees succeed in this slow-moving migration — and eventually create new landscapes with aristocratic presence, absorb carbon, provide shelter, nurture animals? wild — would be the function of countless encounters between the rat or the hamster and the acorn.
Does the animal take seeds? If so, are the seeds eaten right away or saved for later? Where does the animal store it? How many times did they not return, either because they forgot where they were or — as often happens with creatures the size of a bite in a forest full of hungry predators — because they were eaten first. , thus giving the caviar a chance to germinate?
“People see that a forest is regenerating,” Dr. Mortelliti said. “But what people don’t see is that the forest is regenerating at the discretion of the small mammals.”
At Dr. Mortelliti’s research sites, each such encounter is recorded. When a mouse or a hamster approaches a tray full of chestnuts; a sensor reads their microchip, identifying the animal; a motion-activated camera captures the moment, capturing the kind of grain they’ve captured. Yen said that in this crop, she will produce more than 1,800 fruits.
On this Mid-Autumn Festival, Ms. Yen presented five trays, each about 100 feet apart. Around each lady spread a non-toxic fluorescent powder, which temporarily sticks to the visitor’s feet. When she returned before dawn, armed with an ultraviolet flashlight whose powder fluoresces, constellations of tiny footprints surround each tray and descend into darkness.
Yen said people don’t realize how many mice and hamsters there are. She estimates that, every 13 steps on her way to the site, she passes a mouse or hamster — not outdoors but hidden under a leaf or cozy in a grassy burrow. Under the light of the twinkling stars and toenail moon, the rodent had completed its silent work. All the acorns have disappeared.
In turn, Ms. Yen followed each trace. Tiny footsteps glowed in the light of her flashlight, going around mossy mounds and under fallen branches, up tree trunks and down again. When the rat walks the opposite way when the crow flies: Some streaks get smaller, the powder is exhausted. Others end up in a buffer – a hole beneath a root, a rotting stump, a hole dug into the ground and carefully covered. Ms. Yen marks the final points with small orange flags.
Some of the acorns stored for the coming winter are still intact. Others were consumed, but from pieces of painted shells, Ms. Yen was able to identify this species. With the help of Elizabeth Pellecer Rivera, a graduate research assistant, she took notes on each one. Sensor data and camera recordings then showed that much of the collection was done by a remarkably industrious deer rat the researchers called 98209062973077, a trapped 13-gram male. at the end of September and was revealed through examinations to be rather shy, despite the cautious probing streak.
When the season ends, Ms. Yen, Dr. Mortelliti, and two graduate students, Maisie Merz and Brigit Humphreys, will analyze all of this data and look for patterns.
It is possible that certain personality types will prove more likely than others to choose certain oak trees. It may take a particularly daring rodent to lift a giant acorn, then stagger under its weight, vulnerable to predators, until it finds cover. Perhaps shy mice would be more likely to hide them in the most suitable places to germinate a forgotten nut.
The results will join a series of studies that have emerged from the experiment over the past few years, most of them led by Allison Brehm, Dr. Mortelliti’s first doctoral student and who has taught Ms. Yen way of tracking.
In a 2019 study in the journal Ecology Letters, which Dr Mortelliti described as a “proof of concept”, researchers showed that Small mammals’ personalities influence their seed choice. Earlier this year, the team described several deer mice, depending on their personality, are more likely than others to store red oak, white pine, and American oak seeds in a way that promotes germination.
In turn, rodent personality-specific feeding strategies change when predators are aroundthe researchers presented in an Oikos paper in 2021.
And land use changes these dynamics. For example, a 2019 study found that, in areas that had been exploited for many years, small mammals tended to be bolder. A study the following year revealed that a more natural forest, with a mix of habitats more than the homogeneity favored by most commercial logging operations, contains more variety of personality.
“This diversity of personality types is perpetuated in populations because that is a good thing, just as genetic diversity is a good thing,” says Dr Brehm.
Rafał Zwolakan ecologist at Adam Mickiewicz University in Poland who studies seed dispersal and animal characterization, called the study “absolutely pioneering.”
“I hope their work will inspire researchers in other laboratories, working in other ecological systems, to focus on this topic,” he said.
When asked to determine the practical implications of his research, Dr. Mortelliti said, “Preserving the diversity of personalities.” There is no such thing as an ideal personality; rather, different individuals perform different roles. Depending on the circumstances – drought, natural disturbances, fluctuations in predator populations – different personality types can stand out. These nuanced dynamics don’t preclude logging, says Dr. Brehm, but they do argue for being careful.
“If you have to manage a landscape, you don’t want to manage it the same way,” she says. “You want to manage the different sections differently so you have a heterogeneous landscape.” Techniques can be used to maintain a variety of tree species, ages and sizes, trying to mimic what would happen naturally.
Mortelliti notes that much of it remains unresearched. Measures of shyness and boldness are not the entire character of the animal; they are relatively characteristic and easy to measure in the field. That aside, hundreds of other plant species are changing their ranges, each following an intermediate animal trajectory.
When Yen finished her work, night gave way to pre-dawn sunsets. A blue jay called; a red squirrel squeaked. Both are seed spreaders with personalities that can influence their contributions to the forest. The same can be said of bears, foxes, crows, turtle, even ants — the entire herd of animals is still untested, affecting not only plants but also even mushrooms.
“I only look at two species at night,” Yen said. “It’s a very small snapshot of what’s happening.” A full picture may not emerge for decades, but the outlines are clear: It takes a lot of individuals to nurture a forest.
