Every year tourists from around the world pay thousands of dollars to catch a glimpse of The Great Migration on an East African safari (I was one of these tourists) where 2 million wildebeests, zebras, and gazelles migrate in a circular route covering 1800 miles, trampling each other as they run straight into predator territories.
One of every six wildebeests will die during this strenuous migration. The herds face the greatest danger when they cross the Mara River, where many are attacked by crocodiles and others drown. Once out of the river, predatory animals lurk eagerly for meals – the lions, cheetahs, and leopards, each with their own weapons.
The chart below shows the exponential wildebeest population growth after 1955. But after reaching 1.4 million in 1975, there is a leveling off to 1.2 million as the population comes into equilibrium with its expanded carrying capacity and strenuous lifestyle. If we told you that the Great Migration wasn’t always around, can you guess when it started based on the graph behavior below?
Earlier in the late 1800’s, the wildebeest population had depleted by 90% due to a virus called rinderpest. Humans developed a vaccine to eliminate this virus in the 1950s, leading to the growth we see above. But this led to a new problem: overpopulation. Suddenly there were too many mouths feeding on one pasture, and so migrate they must.
These animals follow the highly seasonal rainfall patterns for water and food, creating the circular pattern of the Great Migration we observe today. In addition to increasing the size of the herd’s dinner plate, the migration gives the eroded food resources at the origin a chance to recover. Thus the herds escape resource constraints by giving the grass time to grow as they search for new grass.
It is worth noting that once the cycle of migration begins, it is difficult to stop. If the wildebeests decided the life of the wanderer was not for them and stopped in their tracks, their effective carrying capacity would immediately drop. They would deplete their local food resources and the rate of death from starvation would soar until the herd was in balance with their available grazing fields. Even if they were happier in general when they could graze lazily in their hometown, their individual survival instincts will drive them to migrate on and on to satiate their hunger for grass.
These great herds of instinctual beasts may seem dumb or mechanistic to lead such a Sisyphean existence always in search of food. But humanity is similarly locked into a trajectory of constant production and consumption growth driven not just by food, but also more cars and bigger houses, as we deplete our resources of clean water and oil reserves and risk exceeding our natural carrying capacity, relying on technological innovation to allow us to deplete these resources more efficiently. Americans accept longer and longer work weeks and looming social and economic consequences lest we succumb to the fate of a wildebeest herd that simply chooses to stop moving.
Tourists on safaris notice almost immediately that wildebeests and zebras are everywhere, but the predator lions are harder to spot. If lions are the dominant and vicious hunters seen on National Geographic, why are there so few of them?
Lions don’t just kill their food, they kill each other. Lion prides will consist of one or two dominant male lions, many females, and their cubs. When these male cubs grow to 2-3 years of age, their time has come to be a lion king – they must kill another pride’s king in order to take over that throne. After seizing this new power, these kings will murder all the cubs not a spawn of their own, and court the female lions of that pride to pass on their genes. Similar to the wildebeests’ situation, we may find it illogical and stupid that rather than cooperate, male lions will kill other lions with the goal of producing cubs that may one day kill their own fathers when it is their turn to follow the instinctual cycle. But this violent killing and conquering of its own kind is not unique to lions. We see this in our own history through Christopher Columbus’s enslavement and massacre of Native Americans during his quest for more gold and power. Human civilizations have engaged in conquests over territories and resources for thousands of years.
No one population can grow exponentially forever – each will hit a limiting factor at some point due to too many players competing for the same resources. The causal loop diagram, or systems model below, is a simplified representation of how living things interact with their resources, driven by the purpose of surviving and passing on genes to ensure the survival of their offspring.
As a population grows, so does resource consumption. As available resources fall, the average lifespan of each population will fall, leading to higher death rates and a smaller population. In order for a population to maintain growth, it must find new resources, fight its own kind, or eliminate competitor populations (see model below). We see populations search for new resources when wildebeests begin migration or when human explorers colonized and develop new lands. We see populations fight their own through lion pride takeovers or when one human civilization fights another for control over gold and oil. We see competitors eliminate each other when cheetahs and leopards kill unattended lion cubs, and when humans hunt wolves to protect livestock or when humans kill each other, focusing on skin color or religious differences to make enemies seem alien and inhuman.
Some populations become smarter and devise new ways to mute the effect of resource consumption on population decline. Humans have created technological advancements such as agricultural innovations that allow the resource variable to regenerate faster, or be more efficiently used (lowering the rate of Resource Consumption per person). As long as the rate of resource growth keeps up with the rate of population growth, there will be enough to feed all the human population (although we would still run into food distribution challenges). However, overpopulation today creates a new problem: human actions affect climate change, which leads to ecological and environmental challenges ahead.
Another unique property of humans is our ability to ask questions about the state of humankind, envision the type of world we want to live in, and plan for our futures. Therefore, responsible citizens have led environmental and sustainability movements today focused on educating people about responsible growth in population, industrialization, pollution, food production, and resource depletion so that we aren’t like the animals who behave in instinctive patterns driven purely by selfish needs for survival and reproduction.
By Jenny Zhou and Andrew Frangos