Jasper C. Croll and Hal Caswell: Read the article
Does family matter? Croll and Caswell develop a new approach to integrate family interactions in matrix population models. With this approach, they show that the disruption of African elephant families accelerates the decrease in population growth due to poaching.
While your family members might drive you a little crazy during Thanksgiving dinner or by the end of your two-week vacation, they also likely kept you alive during your childhood and continue to impact your life today. That is because you – like all organisms on earth – are part of a “kinship network”: a group that includes your parents, grandparents, children, grandchildren, siblings, aunts, uncles, and cousins. How this network functions impacts how an individual organism survives and reproduces, a concept termed “life history”. Imagine how you might have been a different person had you grown up within a different family or entirely alone!
Despite the significant role that these familial interactions play in an organism’s life, many current models for the viability of populations only account for interactions at a population level or with direct kin, disregarding the impacts of more distant and complex familial interactions. Jasper Croll and Hal Caswell set out to develop a framework that integrates these crucial feedback mechanisms between the kinship network and an individual’s life history.
Croll and Caswell generated a mathematical model in which an individual’s survival and fertility matrices depend on the kin network. The model frames the kinship network around a single individual named Focal. The kinship network functions as an intermediate level between the individual and the population; imagine a sandwich, where kinship is the meat between two slices of bread.
To demonstrate the utility of this model, Croll and Caswell examined female African elephants as a case study. African elephants are highly social animals, and the females live in family groups led by a matriarch. Previous studies on this species have identified several core familial interactions that Croll and Caswell incorporated into their own model: the presence of a mother improves the juvenile elephant’s survival, the presence of sisters increases the fertility of young female elephants, and older matriarchs increase juvenile survival. The researchers used this model to evaluate how familial interactions impact the effect of poaching on population growth.
The researchers found that the positive effect of family interactions amplifies the negative effect of poaching on population growth because poaching damages the family structure. Essentially, the impact of poaching is actually worse than previous calculations might have predicted because it affects not only the elephant that died, but also all of her family members. For example, one can imagine a young elephant whose mother has died from poaching; this child would have a decreased likelihood of survival. Perhaps less intuitively, even if this young elephant’s sister died, the elephant would have decreased fertility, thereby further reducing the population size.
Croll and Caswell’s work has far-reaching implications in improving future models for ecological predictions and conservation of animal populations. Similar models have even been used to explore the impact of family member’s deaths from COVID-19 in the United States. The significance of the kinship network is applicable across diverse fields, and improving our understanding of these interactions continues to highlight the complex ways in which all life is connected.
