Connell’s Barnacle Case Study

Who conducted the famous barnacle experiment on niches in the intertidal zone?

Joseph Connell (1961). He studied the distribution of Chthamalus Stellatus and Semibalanus Balanoides on rocky shorelines in Scotland.

What is the intertidal zone?

The intertidal zone is the zone that is exposed to air at low tides, and submerged underwater at high tides.

Which barnacle was found in the upper intertidal zone (above the low tideline)?

Chthamalus Stellatus. It survives in areas exposed to air, but is forced to remain above the low tide line because it is outcompeted by the Semibalanus below.

Which barnacle was found in the low intertidal zone (below the low tideline)?

Semibalanus Balanoides. It thrives underwater, but cannot survive prolonged exposure to air, so it stays underwater.

What happened when Semibalanus Balanoides was removed from the Connell experiment?

Chthamalus Stellatus was able to spread downward into the lower intertidal zone (underwater). This showed that the Chthamalus fundamental niche areas included underwater areas, but competition normally excluded it.

What happened when Chthamalus Stellatus was removed? 

Semibalanus Balanoides did not spread upward into the upper intertidal zone, because it cannot tolerate air exposure. This showed that its distribution was limited by physiological stress, and not competition. 

What compeititon was observed when Semibalanous Banaloides pushed Chthamalus Stellatus off the rocks?

This was interference competition. Semibalanus undercut and pried off Chthamalus, directly excluding it from lower rocks.

Define fundamental niche and give examples in relation to the Barnacle study.

The fundamental niche is the full range of conditions and habitats a species could occupy based on its physiology.

• Chthamalus Stellatus fundamental niche: both lower and upper intertidal zones

• Semibalanous Balanoides fundamental niche: only lower intertidal zones (dies if exposed to air)

Define realized niche and give examples in relation to the Barnacles study

The realized niche is the actual range a species occupies in nature, after competition and other interactions. 

• Chthamalus Stellatus realized niche: only the upper intertidal zone (excluded from lower due to competition from Semibalanous Balanoides)

• Semibalanous Balanoides realized niche: the entire lower intertidal zone (same as its fundamental niche)

What ecological principle did the Connell's Barnacle experiment demonstrate?

It showed the distinction between fundamental and realized niches, and how competition (especially interference competition) restricts many species to realized niches smaller than their potential fundamental niches.

Compare and contrast the terms “individual niche” and “realized niche”

The fundamental niche is defined as the entire niche that a species is potentially capable of using. This includes all of the interactions a species has within its habitat and community, its pattern of living, and its use of resources. It can be described using the times and locations where the species is active, where and how it gets its energy, which other species it interacts with, and so on.

• While the realized niche is the actual niche that a species occupy based on local competitive conditions. It is usually smaller than the fundamental niche due to the effects of competition with other species.