Psychologists know that childhood trauma, or the experience of harmful or adverse events, can have lasting effects on people’s health and well-being well into adulthood. But while the consequences of early adversity in humans have been well researched, humans are not the only ones who can experience adversity.
If you have a rescue dog, you’ve probably witnessed how the abuse or neglect he experienced earlier in life now affects his behavior – these pets tend to be more skittish or reactive. Wild animals also experience adversity. While their negative experiences can easily be dismissed as part of life in the wild, they still have lifelong consequences – just like traumatic events in people and pets.
As behavioral ecologists, we are interested in how adverse experiences early in life can influence animals’ behavior, including the types of decisions they make and the way they interact with the world around them. In other words, we want to see how these experiences influence the way they behave and survive in the wild.
Many studies in humans and other animals have shown the importance of early life experiences in shaping the way individuals develop. But researchers know less about how multiple, different instances of adversity or stressors can build up in the body and what their overall impact is on an animal’s well-being.
Wild populations face many types of stressors. They compete for food, risk being eaten by a predator, suffer from disease and have to contend with extreme weather conditions. And as if living in the wild wasn’t hard enough, humans are now adding additional stressors like chemical pollution, light and sound pollution, and habitat destruction.
Given the widespread loss of biodiversity, understanding how animals respond to and are harmed by these stressors can help conservation groups better protect them. But it is not easy to take such a diversity of stressors into account. To address this need and demonstrate the cumulative impact of multiple stressors, our research team decided to develop a wildlife index based on psychological research on human childhood trauma.
A cumulative adversity index
Developmental psychologists began developing what psychologists now call the Adverse Childhood Experiences score, which describes the amount of adversity a person experienced as a child. Briefly, this index adds up all adverse events—including forms of neglect, abuse, or other household dysfunctions—that an individual experienced during childhood into a single cumulative score.
This score can then be used to predict health risks later in life, such as chronic health conditions, mental illness or even economic status. This approach has revolutionized many human health intervention programs by identifying children and adults at risk, allowing for more targeted interventions and preventive efforts.
What about wild animals? Can we use a similar type of score or index to predict negative survival outcomes and identify high-risk individuals and populations?
These are the questions we set out to answer in our latest research paper. We developed a framework for creating a cumulative adversity index – similar to the adverse childhood experience score, but for wildlife populations. We then used this index to gain insight into the survival and longevity of yellow-bellied marmots. In other words, we wanted to see if we could use this index to estimate how long a marmot would live.
A groundhog case study
Yellow-bellied marmots are a large ground squirrel closely related to groundhogs. Our research group has been studying these marmots in Colorado at the Rocky Mountain Biological Laboratory since 1962.
Yellow-bellied marmots are an excellent study system because they are active during the day and have an address. They live in burrows spread over a small, defined geographic area called a colony. The size of the colony and the number of individuals residing there varies greatly from year to year, but they are normally composed of matrilines, meaning that related females tend to remain within the natal colony, while male relatives move to form a colony. to look for a new colony. .
Yellow-bellied marmots hibernate most of the year, but become active between April and September. During this active period, we observe each colony daily and regularly capture every individual in the population – that’s over 200 unique individuals in 2023 alone. We then mark their backs with a clear symbol and give them a uniquely numbered ear tag, so they can be identified later. .
Although they can live up to 15 years, we have detailed information about the life experiences of individual marmots spanning nearly 30 generations. They were the perfect test population for our cumulative adversity index.
Among the sources of adversity, we included ecological measures such as a late spring, summer drought, and a high presence of predators. We also included parental measures such as having an underweight or stressed mother, being born or weaned late, and losing one’s mother. The model also included demographic measures, such as being born in a large litter or having many male siblings.
Importantly, we only looked at women because they are the ones who tend to stay at home. Therefore, some of the adversities mentioned only apply to women. For example, females born in litters with many males become masculinized, likely due to high testosterone levels in the mother’s womb. The females behave more like males, but this also reduces their lifespan and reproductive output. Therefore, having many male siblings is harmful for women, but perhaps not for men.
Does our index, or the number of side effects a marmot experiences initially, explain the differences in marmot survival? We discovered that this is indeed the case.
Experiencing even one adversity before the age of 2 almost halved an adult marmot’s chances of survival, regardless of the type of adversity they experienced. This is the first record of lasting negative consequences of maternal loss in this species.
So what?
Our study is not the only one of its kind. A few other studies have used an index similar to the human adverse childhood experience score in wild primates and hyenas, with broadly similar results. We are interested in broadening this framework so that other researchers can adopt it for the species they study.
A better understanding of how animals can and cannot cope with multiple sources of adversity can contribute to wildlife conservation and management. For example, an index like ours could help identify at-risk populations that require more immediate conservation action.
Rather than addressing the one stressor that appears to have the greatest effect on a species, this approach could help managers think about the best way to reduce the total number of stressors a species experiences.
For example, changing weather patterns due to global warming trends can create new stressors that a wildlife manager cannot address. But it may be possible to reduce the number of times these animals come into contact with humans during key times of the year by closing trails or providing additional food to replace the food they lose due to harsh weather.
Although this index is still in its early stages, it could one day help researchers ask new questions about how animals adapt to stress in the wild.
This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. It was written by: Xochitl Ortiz Ross, University of California, Los Angeles
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Xochitl Ortiz Ross has received funding from the National Science Foundation, the University of California, Los Angeles, the Rocky Mountain Biological Laboratory, the Animal Behavior Society, the American Society of Mammaologists, and the American Museum of Natural History.
Daniel T. Blumstein received funding from the National Science Foundation, the University of California Los Angeles, the Rocky Mountain Biological Laboratory, and the National Geographic Society.