In most ecosystems, the introduction of non-native plant species disrupts natural food webs and threatens ______ in severely degraded habitats,...

Let's begin by understanding the meaning of this sentence. We'll use our understanding of pause points and segment the sentence as shown - understanding and assimilating the meaning of each segment bit by bit!

Sentence Structure

• In most ecosystems,
  • the introduction of non-native plant species
    • disrupts natural food webs
      • and
    • threatens biodiversity [?]
• in severely degraded habitats,
  • certain invasive plants
    • have been deliberately introduced
      • to prevent soil erosion
        • and
      • to restore ground cover.
• Where [?] varies:
  • A: but
  • B: , but
  • C: ,
  • D: (nothing)

Understanding the Meaning

Let's start reading from the beginning:

"In most ecosystems, the introduction of non-native plant species disrupts natural food webs and threatens biodiversity"

So this part is telling us:

• In most ecosystems, when non-native plants are introduced
  • they cause problems
  • they disrupt food webs
  • they threaten biodiversity

This is where we have the blank.

Let's look at the choices:

• They're asking us whether we need "but," ", but," just a comma, or nothing after "biodiversity"

To see what works here, let's read the rest of the sentence and understand what it's saying!

"in severely degraded habitats, certain invasive plants have been deliberately introduced to prevent soil erosion and restore ground cover."

Now let's understand what this second part is telling us:

• In severely degraded habitats (really damaged ecosystems)
  • invasive plants have been deliberately introduced - on purpose
  • Why? To prevent soil erosion
  • And to restore ground cover

So the complete picture is:

• First part: invasive plants are usually HARMFUL (disrupt, threaten)
• Second part: BUT in badly damaged habitats, invasive plants can be HELPFUL (prevent erosion, restore ground cover)

What do we notice about the structure here?

• The first part is a complete thought
  • "In most ecosystems, the introduction of non-native plant species disrupts natural food webs and threatens biodiversity"
  • This could stand alone as a sentence
• The second part is also a complete thought
  • "in severely degraded habitats, certain invasive plants have been deliberately introduced to prevent soil erosion and restore ground cover"
  • This could also stand alone as a sentence
• These two complete thoughts present CONTRASTING ideas
  • One says invasive plants are bad
  • The other says they can be good in certain situations

So we need:

• The word "but" to show the contrast between these ideas
• A comma before "but" because we're connecting two complete thoughts with a coordinating conjunction

The correct answer is B: , but

GRAMMAR CONCEPT APPLIED

Connecting Two Complete Thoughts with a Coordinating Conjunction

When you want to join two complete thoughts (sentences that could each stand alone) using a coordinating conjunction like "but," you need to place a comma before the conjunction. The coordinating conjunctions are: but, and, or, so, yet, for, nor (these are called FANBOYS in grammar terms: For, And, Nor, But, Or, Yet, So).

The pattern:

• Complete thought + , + coordinating conjunction + complete thought

Example 1:

• Without conjunction: The experiment failed. The researchers learned valuable lessons.
• With comma + but: The experiment failed, but the researchers learned valuable lessons.
• First part = complete thought
• Comma before "but"
• Second part = complete thought

Example 2:

• Without conjunction: The data supported the hypothesis. The team needed to replicate the results.
• With comma + and: The data supported the hypothesis, and the team needed to replicate the results.
• First part = complete thought
• Comma before "and"
• Second part = complete thought

In this question:

• First complete thought: "In most ecosystems, the introduction of non-native plant species disrupts natural food webs and threatens biodiversity"
• Coordinating conjunction showing contrast: but
• Second complete thought: "in severely degraded habitats, certain invasive plants have been deliberately introduced to prevent soil erosion and restore ground cover"
• Correct structure: Complete thought + , but + complete thought