Explain how the interactions among organisms and biodiversity contribute to ecosystem stability and resilience (North Carolina Standard Course of Study, Biology, LS.Bio.5).

What this topic is asking

North Carolina LS.Bio.5 asks how interactions among organisms and biodiversity contribute to ecosystem stability and resilience. For the Biology EOC you need to know the main species interactions (competition, predation, and symbiosis: mutualism, commensalism, parasitism), why biodiversity increases stability, the idea of a keystone species, and how ecosystems recover through succession. Items often ask you to classify an interaction or explain a recovery.

Species interactions

The symbiotic relationships are a frequent EOC item, so learn the three types by who benefits:

• Mutualism: both benefit. Bees get nectar while pollinating flowers; both species gain.
• Commensalism: one benefits, the other is unaffected. Barnacles on a whale get transport and feeding opportunities; the whale is essentially unaffected.
• Parasitism: one benefits, the other is harmed. A tapeworm gains nutrients while harming its host.

Predation and competition shape populations too: predators help control prey numbers (a density-dependent factor), and competition limits how many of each competing species the ecosystem can support. These interactions help keep the ecosystem in balance.

Biodiversity and stability

A related idea is the keystone species: a species that has an unusually large effect on its ecosystem relative to its abundance. Removing a keystone species (for example, a top predator that keeps a prey population in check) can cause the whole community to change dramatically, so keystone species are important to stability out of proportion to their numbers.

Disturbance, recovery, and succession

Ecosystems experience disturbances, such as fires, floods, storms, and human activity. A resilient ecosystem can recover from these. The recovery process is ecological succession: the gradual, ordered change in the community over time. After a disturbance that clears an area, pioneer species (such as grasses) colonize first, followed by shrubs, then trees, until a mature, stable community returns. Succession shows that an ecosystem can rebuild its community, a direct demonstration of resilience. The faster and more completely an ecosystem recovers, the more resilient it is, and biodiversity supports that recovery.

Try this

Q1. Name the three types of symbiosis and state who benefits in each. [3]

• Cue. Mutualism (both benefit); commensalism (one benefits, the other unaffected); parasitism (one benefits, the other harmed).

Q2. Explain why a more biodiverse ecosystem is usually more resilient. [2]

• Cue. A wider variety of species and genes means some are more likely to survive a disturbance and keep the ecosystem functioning, so it recovers better.