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Unlock This CourseFood webs are like nature's version of "who eats whom" - but much more complex than simple food chains. While a food chain shows a straight line of feeding (grass → rabbit → fox), food webs show the reality: most animals eat multiple things and get eaten by multiple predators. Think of it as a tangled web of relationships where every thread matters.
Understanding food webs helps us see how ecosystems work and why removing even one species can cause dramatic changes throughout the entire system.
Key Definitions:
Plants and algae form the base of all food webs. They capture energy from sunlight through photosynthesis, converting it into chemical energy stored in glucose. Without producers, no other life could exist - they're literally the foundation that supports everything else.
Energy doesn't flow perfectly through food webs - most of it gets lost along the way. This is why food webs have a pyramid shape, with fewer organisms at each higher level.
When a rabbit eats grass, it doesn't get all the energy the grass contained. Much of that energy was already used by the grass for its own life processes like growing, reproducing and staying alive. The rabbit only gets about 10% of the original energy - the rest is lost as heat, movement and waste.
Convert sunlight into chemical energy. Store the most energy in the ecosystem - typically 100% of available energy starts here.
Herbivores that eat plants. Only receive about 10% of the energy from producers due to energy loss through respiration and waste.
Carnivores that eat herbivores. Receive only 1% of the original energy from producers, explaining why there are fewer predators.
When wolves were reintroduced to Yellowstone National Park in 1995, they didn't just affect deer populations. The wolves reduced deer numbers, which allowed trees and shrubs to recover. This brought back birds and beavers, which changed river patterns. One species affected the entire ecosystem - this is called a trophic cascade.
The relationship between predators and prey creates natural population cycles. When prey is abundant, predator numbers increase. As predators increase, they eat more prey, causing prey numbers to drop. With less food available, predator numbers then decrease, allowing prey to recover.
These cycles happen constantly in nature. Lynx and snowshoe hare populations in Canada have been tracked for over 100 years, showing regular 10-year cycles where both populations rise and fall in a predictable pattern.
More food becomes available for predators. Predator survival rates improve and reproduction increases. Predator populations grow, but with a slight delay as it takes time for young to mature.
More predation pressure reduces prey populations. Competition between predators increases. Eventually, food becomes scarce and predator numbers decline, starting the cycle again.
Not all interactions in food webs involve eating. Competition happens when different species need the same resources - food, water, shelter, or mates. This competition shapes how species evolve and where they can live.
Interspecific competition occurs between different species, while intraspecific competition happens within the same species. Both types influence population sizes and distribution patterns.
In Britain, grey squirrels introduced from America have largely replaced native red squirrels. Grey squirrels are better at digesting acorns, can live in deciduous forests and carry a virus that doesn't affect them but kills red squirrels. This shows how competition can lead to local extinctions.
Human activities significantly disrupt natural food webs through habitat destruction, pollution, overfishing and introducing non-native species. Understanding these impacts helps us make better conservation decisions.
Removing large numbers of fish disrupts marine food webs. When cod were overfished in the North Atlantic, seal populations increased, which then affected other fish species.
Destroying habitats breaks food web connections. When forests are cleared, both plants and animals lose their homes, disrupting feeding relationships.
Non-native species can dominate food webs. Cane toads in Australia have no natural predators and poison native animals that try to eat them.
Climate change adds another layer of complexity, shifting where species can live and when they reproduce, potentially mismatching predators and prey timing.
Protecting food webs requires understanding the connections between species. Conservation efforts now focus on maintaining these relationships rather than just protecting individual species.
Some species have disproportionate effects on their ecosystems. Protecting these keystone species, like wolves or sea otters, can maintain entire food webs more effectively than trying to protect every species individually.
Sea otters in California nearly went extinct due to hunting. Their recovery has restored kelp forests because otters eat sea urchins that would otherwise destroy the kelp. The kelp forests now support hundreds of other species, showing how one species can rebuild an entire ecosystem.
Today's conservation strategies consider entire ecosystems rather than individual species. This includes creating wildlife corridors to connect habitats, controlling invasive species and restoring natural predator-prey relationships.
Marine protected areas demonstrate this approach by allowing fish populations to recover, which then supports the entire ocean food web. When fishing pressure is removed, not only do fish populations increase, but the entire ecosystem becomes more stable and productive.
Scientists use various indicators to assess food web stability, including species diversity, population sizes and energy flow efficiency. Healthy food webs typically have high biodiversity and stable population cycles.
The number and variety of species in an ecosystem indicates its health. More diverse food webs are generally more stable because they have multiple pathways for energy flow, making them resilient to disruptions.
Understanding food web interactions helps us predict how ecosystems will respond to changes and guides our efforts to protect the natural world. Every species plays a role and maintaining these complex relationships is essential for healthy ecosystems that can support both wildlife and human needs.