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?
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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.
Only abiotic conditions increase mortality of BG in the high intertidal zones
Only abiotic conditions increase mortality of CS in the low intertidal zones.
Interspecific competition increases mortality of BG in the high intertidal zone.
Interspecific competition increases mortality of CS in the low intertidal zone
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The Correct Option isA, D
Solution and Explanation
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 \(\boxed{\text{(A) and (D)}}\)
