When Food Webs Get Disrupted

By the end of this lesson, you will be able to explain how changes like population shifts, natural disasters, and human activity change the way energy moves through a food web.

Energy in an ecosystem starts with the Sun. Plants and other producers, which are organisms that make their own food using sunlight, capture that energy. When a grasshopper eats grass, some of that energy moves to the grasshopper. When a lizard eats the grasshopper, and a hawk eats the lizard, the energy keeps moving. A food web is a model that shows all of these overlapping feeding connections in one ecosystem. Only a small part of the energy passes to the next level, so each step depends on the ones below it.

Picture a Texas prairie near a ranch outside Austin. Grasses feed grasshoppers and rabbits, which feed snakes and hawks, and decomposers like fungi break down whatever dies and return nutrients to the soil. Everything stays fairly steady as long as each population, meaning the number of one kind of organism living in an area, stays balanced.

Now add a disruption. A long drought kills much of the grass, so less energy enters the web. Rabbit numbers drop, and hawks either go hungry or move away. A wildfire or flood can do the same thing quickly. Human intervention matters too: building a shopping center over the prairie removes producers entirely, while planting native grasses or controlling an invasive species can help energy flow return to normal.

Notice that a change at one point never stays at one point. Removing a predator can let prey populations explode and strip the plants bare, which then starves those same prey. Food webs are connected, so energy transfer shifts throughout the whole system.

Try it: if a disease sharply reduced the snake population on that prairie, what would likely happen to the grasshopper population and to the grasses?