Sign up to access the complete lesson and track your progress!
Unlock This CourseImagine a perfectly balanced seesaw - that's what a stable ecosystem looks like! When everything is working properly, populations of different species stay roughly the same size over time. But what happens when something tips the balance? Let's explore how ecosystems maintain their stability and what can go wrong.
Key Definitions:
In a stable ecosystem, birth rates roughly equal death rates. When populations get too large, competition for resources increases, leading to higher death rates. When populations get too small, there's less competition and more resources available, allowing populations to recover.
Several factors work together to control how many organisms can live in an ecosystem. Understanding these helps us predict what might happen when conditions change.
These factors become more important as population density increases. Think of them as nature's way of putting on the brakes when things get too crowded.
More individuals means less food per animal. Weaker animals may starve, reducing population size naturally.
Crowded conditions help diseases spread faster, increasing death rates in dense populations.
Limited nesting sites and territories lead to fighting, stress and reduced breeding success.
One of the most fascinating examples of ecosystem stability comes from predator-prey cycles. These relationships create natural population controls that keep ecosystems balanced.
For over 200 years, scientists have tracked lynx and snowshoe hare populations in Canada. The data shows a clear pattern: when hare numbers are high, lynx numbers increase about 2 years later. When hares become scarce due to predation, lynx numbers crash, allowing hare populations to recover. This cycle repeats roughly every 10 years, demonstrating natural population control.
The relationship follows a predictable pattern that maintains long-term stability:
With few predators around, prey animals reproduce rapidly. Food is plentiful and competition is low, leading to population growth.
Abundant prey means easy hunting for predators. Well-fed predators reproduce more successfully, increasing predator numbers.
More predators mean higher predation pressure. Prey numbers start falling as death rates exceed birth rates.
With scarce prey, predators struggle to find food. Starvation and reduced breeding cause predator numbers to crash and the cycle begins again.
Every environment has limits. Carrying capacity represents the maximum population size that can be sustained long-term without damaging the environment.
Multiple environmental factors work together to set population limits:
The amount of available food often sets the ultimate limit on population size.
All life needs water. Drought conditions can dramatically reduce carrying capacity.
Animals need places to live, nest and raise young. Limited space means limited populations.
Humans are incredibly powerful ecosystem engineers. Our activities can either support or destroy ecosystem stability, often with far-reaching consequences.
In 1995, wolves were reintroduced to Yellowstone National Park after being absent for 70 years. The results were dramatic: deer populations decreased and changed their behaviour, avoiding areas where wolves hunted. This allowed trees and shrubs to recover, which brought back birds and beavers. Rivers even changed course as vegetation stabilised riverbanks. This shows how one species can affect an entire ecosystem's stability.
When done thoughtfully, human actions can help restore ecosystem stability:
Protected areas, breeding programs and habitat restoration help endangered species recover and maintain stable populations.
Fishing quotas and protected breeding areas prevent overfishing and allow fish populations to maintain stable numbers.
Unfortunately, many human activities disrupt ecosystem stability:
Clearing forests and draining wetlands removes the homes that animals need to survive and reproduce.
Chemical pollution can poison organisms directly or disrupt food chains, causing population crashes.
Changing temperatures and weather patterns force species to adapt quickly or face extinction.
Scientists use several indicators to assess whether ecosystems are stable and healthy. These measurements help us understand when intervention might be needed.
Researchers look for specific signs that indicate whether an ecosystem is thriving or struggling:
Stable ecosystems show relatively steady population sizes over time, with natural fluctuations around average levels rather than dramatic crashes or explosions.
Healthy ecosystems typically have many different species. High biodiversity provides stability because if one species struggles, others can fill similar roles.
Coral reefs demonstrate how quickly ecosystem stability can collapse. When water temperatures rise by just 1-2°C, corals expel their symbiotic algae and turn white (bleach). Without these algae, corals starve and die, destroying habitat for thousands of fish species. The Great Barrier Reef has experienced several major bleaching events since 1998, showing how climate change threatens ecosystem stability worldwide.