By Jonny Lupsha, Wondrium Staff Writer
The pandemic has worsened a “baby bust,” or notable decline in the birth rate. Younger generations are choosing to have fewer, if any, children, and an expected pandemic shutdown-induced baby boom failed to materialize. Population growth is affected by many factors.
A decades-long dip in fertility has accelerated since the novel coronavirus pandemic struck, contrary to expectations. Concerned with the cost of living and child-rearing amid multiple recessions—not to mention, a cultural shift away from the mandate of the nuclear family and fears of exposing an infant to the coronavirus—younger generations are simply having fewer children.
Overpopulation is still a concern globally, but the rate of deceleration in human fertility in some countries, including the United States, alarms some experts.
The study of population growth involves extrapolating meaning from tremendous amounts of data. In his video series Biology: The Science of Life, Dr. Stephen Nowicki, Bass Fellow and Professor of Biology at Duke University, explained factors that limit population growth.
Population Related to Carrying Capacity
Dr. Nowicki said that populations of any species can reach a number called a carrying capacity. He defined a carrying capacity as “the maximum size a population should be able to achieve given the amount of resources available in the environment in which it lives.”
So what happens when a population nears that number? This is one of the reasons that a reproductive rate drops in a species. It slowly realizes that its numbers are unsustainable and finds a way to stabilize itself within its limits before all the resources, such as food, are gone. It’s just one of the factors affecting population growth.
“Population ecologists separate the mechanisms that might regulate population size into two general categories,” Dr. Nowicki said. “These categories are referred to as density-dependent effects and density-independent effects.”
The logistic model of population growth, which deals with carrying capacity, is a model of density-dependent population regulation because for every new member of the population, resources must be divided on a per-individual basis to accommodate them. Aside from resources, density-dependent effects may include the faster and further spread of diseases among a denser population or the allure of a dense population to predators.
What We Learn from Thrips
Density-independent effects on population growth are, as the name implies, unrelated to how dense the population of a species is. For example, Dr. Nowicki said, the first freeze of the autumn season frequently leaves large number of insects dead, having nothing to do with how many or how few there were beforehand. Another example comes from an Australian insect species commonly known by its genus name, Thrips.
“Thrips are small insects that feed on pollen, or leaves, or flower tissues of plants,” he said. “What you see if you monitor the size of a population of Thrips is that during the winter—the Australian winter, so this would be during what we consider the summer months, around June—the temperature is fairly cool. This cool temperature actually impedes the development of individual Thrips.”
As a result of this, many Thrips mature too slowly and the flowers they depend on die before the insects can reproduce. So if the temperatures are cold, the Thrips populations stay low enough that they won’t approach carrying capacity.
The world will have to wait to see how long—and how severely—the current baby bust affects us.