Resources and population growth | Middle school Biology | Khan Academy

For millennia, accounts describe locust swarms appearing, consuming crops, and then vanishing. This phenomenon is explained by the availability of resources, which are essential for all living things to survive and reproduce. Resources can be biotic, like food, or abiotic, such as water, air, shelter, and space. When organisms have sufficient resources, they thrive, grow, and reproduce, leading to population growth. However, most resources are limited. A field can only yield so much food, a pond holds a finite amount of water, and a forest offers limited living spaces. When a population expands while resources remain constant, competition ensues. Imagine rabbits in a meadow: initially, ample grass and water allow their population to boom. As their numbers increase, they must share resources, eventually leading to scarcity. This triggers competition for food and space, causing some rabbits to struggle for survival, fewer births, and ultimately, a slowdown or even a decline in the rabbit population. This pattern is universal in nature. Abundant resources fuel population growth, but as populations swell, resources become limited, intensifying competition and curbing further growth. Competition can also occur between different species, like birds and squirrels vying for seeds, or plants competing for sunlight and water. This isn't aggression but a natural outcome when many organisms depend on the same finite resources, influencing survival and reproduction rates. Locust plagues, for instance, often follow heavy rainfall, which promotes rapid plant growth, providing a bounty of food. This allows locust populations to multiply rapidly. Uniquely, when locust numbers become high and they are crowded, their bodies and behavior change. They transition from solitary living to forming massive swarms that devour crops. This extreme population growth is unsustainable; as the locusts deplete available plants, food becomes scarce, competition intensifies, and the population inevitably crashes, causing the swarms to dissipate. Thus, resource availability directly dictates a population's size.