Tag Archives: Connell

Community Development and Persistence in a Low Rocky Intertidal Zone. Jane Lubchenco and Bruce Menge (1978)

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Though I had to read through Community Development in a Low Rocky Intertidal Zone, in part or in full, several times before I feel I came to approach understanding, I feel the central idea is one of the more useful ones I’ve yet to read about for Ecological Thought and Practice. In the essay’s introduction the authors state that while communities have several characteristics, it is a mistake to study them as separate phenomena when in reality they are interconnected. In my notes, I wrote the following in order to clarify for myself what I was reading about: “Succession depends on competition (Connell) but also predation (Paine), dispersal rates and reproductive output (Gleason), life histories and persistence (Clements).

I think that due to their more holistic approach Lubchenco and Menge were able to add to ecological thought of the day by confirming and documenting the interactions among the ideas that their predecessors had proven. Though their results stated that “the role of consumers in determining the pattern followed during community development, or succession, seemed of overriding importance” which primarily confirms Paine’s 1966 essay, but predation, they found was largely inversely proportional to wave energy. They also documented, through denudation of patched of the rocks, the importance of dispersal and growth rates in determining which species became dominant, but because their study took place over several years, they were able to show the persistence of the communities and how quickly those patches returned to the state at which they had been before the experiment. This persistence supports Clements theory of a tendency toward climactic climax.

Today in class we were asked whether or not Connell and Paine’s studies contradicted one another, here Lubchenco and Menge showed that at least in some communities, the two ideas are both valid. I thought the reading was helpful in understanding other ideas we’ve already covered in class. The use of so many variables and controls including not only the exclusion of predators but the enclosure of predators were useful in illuminating the authors’ points.

The Influence of Interspecific Competition and Other Factors on the Distribution of the Barnacle Chthamalus Stellatus. Joseph Connell (1961)

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Upon witnessing that two species of barnacles seemed to have the adults of their species segregated into horizontal bands on a rocky intertidal shore but that the youth of the higher species could be found in the lower band with the other species, Connell set out to study the primary reason for that segregation. His theory was that the completion for space between the two species bore at least some responsibility for the separation. This theory was supported by the following studies; two species will either compete for resources with one species becoming more dominant in an area (Beauchamp and Ullyott 1932) (Kenny and Stevenson 1956), equal distribution of one species is due to that species competing primarily with itself (Holme 1950) (Clark and Evans 1954), and if two species with similar needs are living in the same area it is because they are not competing for resources (Lack 1954) (MacArthur 1958).

The method Connell used to test this theory was to map the locations of the barnacle species Chthamalus Stellatus, hereafter referred to at C.S., in the period of the year before what he hypothesized to be C.S.’s competitor Balanus Balanoides, hereafter referred to as B.B.. After mapping the locations of C.S. it was possible to control the height above or below mean tide level so that the effects of competition could be seen in environments where both C.S. and B.B. were primarily observed. One half of all clusters of C.S.  growth were kept from being interfered with by B.B.. The growth and mortality rates in each case were recorded.

The results showed that C.S. was fully capable of growing to maturity at the levels on which B.B. was typically dominant, implying that the competition for space is what was preventing C.S.’s proliferation at the lower levels. In fact, while the hypothesis was that competition was at least somewhat responsible for the distribution of the two species, the study found that predation by carnivorous aquatic snails, battery by waves, and intraspecies crowding combined were not much more likely to be responsible for the death of an individual C.S. than was crowding of some sort by B.B..

I read this essay about two hours ago and have been idly trying to come up with an example of competitors coexisting. None come to mind except in the case of lions and tigers and bears coexisting in Oz. Given this, I can’t find fault in Connell’s reasoning. His experiment took into account as many variables as I could think of and the information gained fulfilled his hypothesis without assumption. In the case of this essay the limited resource in question was space, but it is easy to imagine that if the same experiment were performed on species competing for water or a nutrient source like meat the results would show that at least some of the reason for animal dispersion was due to interspecific competition. As a follow up to this study, I would be interested to see if there were more studies done on intraspecific competition and what its causes may be.