Organisms And Populations

Joseph Connell's field experiments on the rocky sea coasts of Scotland showed that on the intertidal zone the dominant and larger barnacle Balanus competitively excludes the smaller Chthamalus from the better, lower regions of the shore. When Balanus was experimentally removed, Chthamalus was able to occupy that zone, proving the exclusion was due to interference competition rather than physical tolerance alone. The deep subtidal zone is incorrect because barnacles in this study inhabit the tidal shore where they are alternately submerged and exposed, not permanently deep water. The freshwater estuary is wrong since these are marine barnacles intolerant of low salinity. The open pelagic zone is inappropriate because barnacles are sessile organisms attached to rock surfaces, not free-floating in open water. As described in NCERT Class 12, Chapter 13 (Organisms and Populations), this experiment is cited as evidence for interspecific competition and partial support for Gause's competitive exclusion principle, which states that two species competing for the same limiting resource cannot coexist indefinitely. The competitively inferior species is eventually eliminated unless it evolves a mechanism such as resource partitioning to reduce the overlap. Plausibility check: the recovery of Chthamalus only after Balanus removal directly links cause (competition) to the intertidal location, confirming the intertidal zone as the correct answer.