Explanation:

- The underlined segment "means an accelerated rate of change in habitat" is clear and grammatically correct. It indicates that increased human activity currently results in a faster change in habitats.

- Option 1: No improvement - This is the original sentence, which is already clear and grammatically correct.

- Option 2: "human activity meant a accelerated rate in change" - This suggests a past action, which is not suitable here, and "a accelerated" should be "an accelerated."

- Option 3: "human activities mean an acelerated rate from change" - "Activities" is plural, but "means" should be used, and "rate from change" is not correct wording.

- Option 4: "human activity is meaning an acelerated rate of change" - "Is meaning" is an incorrect tense.