Use mathematical representations to support claims about how biodiversity and interactions affect the stability and resilience of ecosystems (Louisiana Student Standards for Science, High School Biology, HS-LS2-2).

What this topic is asking

Louisiana's LS2 standards (HS-LS2-2) ask you to support claims about how biodiversity and interactions affect the stability and resilience of ecosystems. For LEAP 2025 Biology you should understand what makes an ecosystem stable, how biodiversity increases resilience, the special role of keystone species, and how ecosystems respond to and recover from disturbance. The test often gives two ecosystems and asks which is more resilient, with a reason.

Stability and resilience

A disturbance tests an ecosystem: a stable, resilient ecosystem absorbs the shock and recovers, while a fragile one can be permanently changed or collapse. The standard asks you to explain what gives an ecosystem this resilience.

Why biodiversity supports stability and resilience

This is the same argument made in the biodiversity topic, applied specifically to how ecosystems respond to disturbance: diversity is a kind of insurance.

Keystone species

A keystone species is one whose effect on the ecosystem is far greater than its abundance would suggest. It often controls the populations of other species, so removing it causes a cascade of changes. A classic example is a top predator that keeps a prey species in check: remove the predator, and the prey can overgraze and reduce the diversity of the whole community. Identifying that the loss of a keystone species causes large, far-reaching changes is a common test point.

Species interactions

The interactions between species help keep an ecosystem balanced:

• Predation keeps prey populations in check (and prey availability limits predators).
• Competition for resources limits how large each population can grow.
• Symbiosis (close relationships such as mutualism, where both benefit) links species together.

These interactions, together with limiting factors, regulate populations around their carrying capacities and contribute to overall stability.

Try this

Q1. Explain why an ecosystem with high biodiversity is generally more resilient than one with low biodiversity. [2]

• Cue. More species and genetic variety mean some are likely to survive a disturbance and keep the ecosystem functioning, and there are more alternative pathways if one species declines.

Q2. State what a keystone species is and what happens when one is removed. [2]

• Cue. A species whose effect on the ecosystem is far greater than its numbers; removing it causes large, far-reaching changes throughout the community.