Presentation Information
[C01-01]Modeling Irreversible Population Decline Triggered by Social Behavior Change
*Sunhee Chae1, Hye Jin Park1, Hyeong-Chai Jeong2,3 (1. Inha University (Korea), 2. Sejong University (Korea), 3. Korea Institute for Advanced Study (Korea))
Keywords:
Structured population dynamics,Irreversible population decline,Stress-response behavior,Transgenerational inheritance
John B. Calhoun provided mice with an ideal environment—known as "mouse utopia"—offering unlimited food, water, and safety in a limited space to study how population density affects social behavior in a controlled environment [1]. While the population initially grew rapidly, it ultimately collapsed after peaking due to overcrowding. Remarkably, the decline continued even as the population shrank. Mice showed behavioral breakdowns during this phase: mice became increasingly aggressive, withdrawn, and ceased reproduction. These behavioral disruptions persisted across generations, suggesting a possible transgenerational effect, though its existence remains debated.
Inspired by these observations, we propose a minimal model to investigate the underlying mechanisms of irreversible population decline, focusing on transgenerational effects. In the model, genetically identical mice exhibit one of two behavioral types: "social" mice, which engage in normal reproduction, and "unsocial" mice, which display abnormal, non-reproductive behavior. Only social mice reproduce, while unsocial mice emerge when social individuals become desocialized under environmental stress. As the population size increases, the desocialization rate rises. Crucially, we assume this rate retains a memory of past high population densities: even if the population decreases, the desocialization rate remains elevated. Moreover, social mice can pass on a high desocialization rate to their offspring, even if the offspring themselves were not exposed to high stress. Incorporating a memory-length parameter enables us to investigate the conditions that lead to irreversible population decline.
We systematically explore the model’s parameter space and identify two distinct mechanisms driving population collapse. The first stems from a non-zero memory length, reflecting transgenerational inheritance of social behavior. The second arises from extremely high desocialization rates at large population sizes, leading to collapse through an abrupt, memory-independent response to environmental stress. These two scenarios emerge in different regions of the parameter space, distinguished by the presence or absence of memory effects. Accordingly, once key model parameters are determined experimentally, our framework provides a concrete basis for testing the existence and impact of transgenerational inheritance.
[1] Calhoun, John B. ''Death squared: the explosive growth and demise of a mouse population." (1973): 80-88.
Inspired by these observations, we propose a minimal model to investigate the underlying mechanisms of irreversible population decline, focusing on transgenerational effects. In the model, genetically identical mice exhibit one of two behavioral types: "social" mice, which engage in normal reproduction, and "unsocial" mice, which display abnormal, non-reproductive behavior. Only social mice reproduce, while unsocial mice emerge when social individuals become desocialized under environmental stress. As the population size increases, the desocialization rate rises. Crucially, we assume this rate retains a memory of past high population densities: even if the population decreases, the desocialization rate remains elevated. Moreover, social mice can pass on a high desocialization rate to their offspring, even if the offspring themselves were not exposed to high stress. Incorporating a memory-length parameter enables us to investigate the conditions that lead to irreversible population decline.
We systematically explore the model’s parameter space and identify two distinct mechanisms driving population collapse. The first stems from a non-zero memory length, reflecting transgenerational inheritance of social behavior. The second arises from extremely high desocialization rates at large population sizes, leading to collapse through an abrupt, memory-independent response to environmental stress. These two scenarios emerge in different regions of the parameter space, distinguished by the presence or absence of memory effects. Accordingly, once key model parameters are determined experimentally, our framework provides a concrete basis for testing the existence and impact of transgenerational inheritance.
[1] Calhoun, John B. ''Death squared: the explosive growth and demise of a mouse population." (1973): 80-88.