Explain primary and secondary succession, and evaluate how human activities such as pollution, habitat destruction, and resource use affect ecosystems and biodiversity (TEKS Biology, Reporting Category 5; stability and change; cause and effect).

What this topic is asking

The Biology TEKS ask you to explain succession (how communities change over time) and to evaluate human impacts on ecosystems and biodiversity. For STAAR Reporting Category 5 you need to tell apart primary and secondary succession, describe how human activities affect ecosystems, and suggest ways to reduce harm. This is a stability and change and cause-and-effect topic, and the human-impact items often ask you to weigh a problem and a solution.

Ecological succession

There are two types:

• Primary succession begins where there is no soil and no community, such as bare rock left by a retreating glacier or cooled lava. Pioneer species (like lichens and mosses) arrive first and slowly help form soil, allowing larger plants and then animals to follow. Because soil must be built from scratch, primary succession is slow.
• Secondary succession begins where a disturbance (a fire, flood, or clearing) has removed the community but left the soil. Because the soil and seeds are already there, recovery is faster than primary succession.

The key distinction STAAR tests is whether soil is already present: present means secondary, absent means primary.

How human activities affect ecosystems

The common thread is cause and effect: a human action changes a part of the ecosystem, which ripples through the connected food webs and cycles. For example, clearing a forest removes habitat (so species decline), reduces the producers that capture energy and carbon, and can disrupt the water and carbon cycles. Pollution can poison organisms or upset the balance of nutrients.

Biodiversity and why it matters

A loss of biodiversity makes an ecosystem more fragile, because there are fewer species to maintain its functions. This is why human impacts that reduce biodiversity are a concern, and it links to the genetic variation that lets populations adapt (see mechanisms of genetic change).

Reducing the impact: conservation

The TEKS ask you to evaluate human impact, which means suggesting solutions as well as problems. Conservation measures include:

• Protecting habitats (reserves, national parks) so species have places to live;
• Reducing pollution (cleaning emissions and waste, reducing fossil-fuel burning);
• Using resources sustainably (limiting fishing and logging to rates that allow recovery);
• Restoring damaged ecosystems (replanting forests, cleaning waterways).

A strong STAAR answer names a specific impact and a specific way to reduce it, showing the cause-and-effect link between the action and the ecosystem.

Try this

Q1. State the difference between primary and secondary succession. [2]

• Cue. Primary succession starts where there is no soil (bare rock) and is slow; secondary succession starts where soil remains after a disturbance and is faster.

Q2. Describe one human activity that reduces biodiversity and one way to reduce its impact. [2]

• Cue. For example, habitat destruction (clearing forest) reduces biodiversity; protecting or restoring habitat reduces the impact.