Biodiversity & Ecosystem Disruption
- Explain why biodiversity strengthens ecosystem stability and resilience
- Describe how invasive species and human activity disrupt ecosystems
- Predict how populations and communities respond to environmental change
Why biodiversity matters
Biodiversity is the variety of life in a system — the number of different species and the genetic variation within them. It is not just a tally; it is what makes an ecosystem stable and resilient. A diverse community has redundancy: if one species is lost, others can fill a similar role, so the whole system keeps functioning. Diverse communities also resist invasion and recover faster from disturbance. Genetic diversity within a species is just as important — it is the raw material for natural selection, letting a population adapt when the environment changes.
Invasive species
An invasive species is one introduced (usually by humans) to a new area where it is not native and where it causes ecological harm. Freed from the predators, parasites, and competitors that held it in check back home, it can grow almost exponentially and outcompete native species for resources. Zebra mussels clogging waterways, kudzu smothering forests, and brown tree snakes wiping out native birds on Guam all show the pattern: an unchecked newcomer collapses native populations and slashes biodiversity.
A fast-reproducing plant is introduced to an island that has no herbivores or diseases able to attack it. Predict its short-term population growth and its effect on native plants, and name the two ecological principles involved.
- 1.With no predators, parasites, or competitors adapted to control it, the plant faces no density-dependent brakes and its resources are effectively unlimited at first — so it grows exponentially (J-shaped, dN/dt = rN).
- 2.As it spreads it competes with native plants for light, water, and soil nutrients — a −/− interaction in which the aggressive newcomer usually wins.
- 3.By competitive exclusion, the invader outcompetes natives for shared resources, so native populations shrink and local biodiversity falls.
Why do introduced invasive species often grow explosively in their new range?
A species being non-native is not enough to make it invasive — many introduced species are harmless. "Invasive" requires that it also spreads and causes ecological or economic harm. Watch for exam choices that call every introduced species invasive.
Human impact
Humans disrupt ecosystems on a global scale. Habitat destruction and fragmentation (deforestation, urban sprawl) is the leading cause of biodiversity loss, shrinking and isolating the areas species need. Pollution poisons air, water, and soil — and can bioaccumulate, concentrating toxins up the food chain so top predators are hit hardest. Burning fossil fuels raises atmospheric CO₂, driving climate change that shifts temperature and rainfall faster than many species can adapt. Overexploitation — overfishing, overhunting — removes species faster than they can reproduce.
A pesticide is present at low concentration in lake water but is found at dangerously high levels in the fish-eating eagles at the top of the food chain. What explains this pattern?
Responses to environmental change
When the environment changes, populations respond in a few ways. Individuals may acclimate through short-term physiological adjustment. Populations can shift their range — moving toward the poles or up mountains as the climate warms — or shift the timing of events like flowering and migration (phenology). Over generations, populations with enough genetic diversity can adapt by natural selection. If the change is too fast or too severe and none of these keep pace, the population declines toward local extinction. This is exactly why genetic diversity is such valuable insurance.
Two beetle populations face a rapidly warming climate. Population A has high genetic diversity; population B is genetically nearly uniform. Which is more likely to persist, and why?
The unifying thread of this unit: diversity buys stability. High species and genetic diversity lets ecosystems absorb disturbance and lets populations adapt to change; losing it — through invasion, habitat destruction, or pollution — makes systems fragile. On free-response, connect a specific disruption to reduced biodiversity to reduced resilience.
Answer the 3 checkpoints as you read.
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