Question

The barnacle species, Chthamalus stellatus (CS), is found only in the high intertidal zone whereas Balanus glandula (BG) is found only in the low intertidal zone. A researcher transplanted CS from the high to low (T-CS), and BG from the low to high (T-BG) intertidal zones. Additionally, they allowed the species to grow alone or in competition with each other, and quantified survival. Which one or more of the following inferences is/are consistent with the experimental results shown below?

• A. Only abiotic conditions increase mortality of BG in the high intertidal zones
• B. Only abiotic conditions increase mortality of CS in the low intertidal zones.
• C. Interspecific competition increases mortality of BG in the high intertidal zone.
• D. Interspecific competition increases mortality of CS in the low intertidal zone

Hint:

In patch dynamics: big stable patches act as sources; isolated small patches face high extinction risk; multiple connected patches form a metapopulation; inbreeding is lowest where dispersal is high.

Answer 1

The Correct Option is A, D

Step 1: Read the “grown alone” bars (abiotic filter).
- High intertidal: CS has high survival; T–BG has low survival.
- Low intertidal: BG has high survival; T–CS has high survival.
\(\Rightarrow\) BG fails in the \emph{high} zone even without competitors (abiotic stress), whereas CS can survive in the \emph{low} zone when alone (abiotically suitable).

Step 2: Read the “both species together” bars (competition effect).
- High intertidal: CS still high; T–BG still very low \(\Rightarrow\) competition does not further depress BG — mortality there is due to \emph{abiotic} conditions.
- Low intertidal: BG high; T–CS drops from high (alone) to low (together) \(\Rightarrow\) strong \emph{interspecific competition} against CS in the low zone.

Step 3: Evaluate statements.
(A) \emph{Only abiotic conditions increase BG mortality in high zone} — True: BG is already low when alone; competition adds little/no extra effect.
(B) \emph{Only abiotic conditions increase CS mortality in low zone} — False: CS survives well alone in low zone; mortality increases only when BG is present (competition).
(C) \emph{Competition increases BG mortality in high zone} — False: mortality is high even when alone.
(D) \emph{Competition increases CS mortality in low zone} — True: big drop when BG is present. Final Answer:\quad \(\boxed{\text{(A) and (D)}}\)