Competition between barnacles

The second study concerns two species of barnacle in Scotland: Chthamalus stel-latus and Balanus balanoides (Figure 8.2) (Connell, 1961). These are frequently found together on the same Atlantic rocky shores of northwest a diversity of examples of competition ...

Figure 8.1 (a) Frequency of aggressive encounters initiated by individuals of each fish species during a 72-day experiment in artificial stream channels with two replicates each of 50 Dolly Varden (Salvelinus malma) or 50 white-spotted charr (S. leucomaenis) alone (allopatry) or 25 of each species together (sympatry). (b) Foraging frequency. (c) Specific growth rate in length. Different letters indicate that the means are significantly different from each other. (From Taniguchi & Nakano, 2000.)

Sympatry

Allopatry

S. malma S. leucomaenis

High

Allopatry

High

High

High

High

High

High

High

High

Temperature treatment

Europe. However, adult Chthamalus generally occur in an intertidal zone that is higher up the shore than that of adult Balanus, even though young Chthamalus settle in considerable numbers in the Balanus zone. In an attempt to understand this zonation, Connell monitored the survival of young Chthamalus in the Balanus zone. He took successive censuses of mapped individuals over the period of 1 year and, most importantly, he ensured at some sites that young Chthamalus that settled in the Balanus zone were kept free from contact with Balanus. In contrast with the normal pattern, such individuals survived well, irrespective of the intertidal level. Thus, it seemed that the usual cause of mortality in young Chthamalus was not the increased submergence times of the lower zones, but competition from Balanus in those zones. Direct observation confirmed that Balanus smothered, undercut or crushed Chthamalus, and the greatest Chthamalus mortality occurred during the seasons of most rapid Balanus growth. Moreover, the few Chthamalus individuals that survived 1 year of Balanus crowding were much smaller than uncrowded ones, showing, since smaller barnacles produce fewer offspring, that interspecific competition was also reducing fecundity.

Figure 8.2 The intertidal distribution of adults and newly settled larvae of Balanus balanoides and Chthamalus stellatus, with a diagrammatic representation of the relative effects of desiccation and competition. Zones are indicated to the left: from MHWS (mean high water, spring) down to MLWS (mean low water, spring); MTL, mean tide level; N, neap. (After Connell, 1961.)

Balanus

Chthamalus

MHWS

MHWN

MLWN

MLWS

Balanus

Chthamalus

MHWS

MHWN

MLWN

MLWS

h

\

i

{

y

*

i

I

\

M

i

I

Adults Larvae

Desiccation Intraspecific competition

Adults Larvae

Desiccation Interspecific competition with Balanus

Distribution

Distribution

Distribution

Relative effects of these factors

Distribution

Relative effects of these factors

Thus, Balanus and Chthamalus compete. They coexist on the same shore but, like the fish in the previous section, on a finer scale their distributions overlap very little. Balanus outcompetes and excludes Chthamalus from the lower zones; but Chthamalus can survive in the upper zones where Balanus, because of its comparative sensitivity to desiccation, cannot.

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Responses

  • Ida
    Is there interspecific competition between cthamalus and barnacle?
    2 months ago

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