You suggest a totally different model as
a possible explanation for your observations and maintain that the two
species exist in different environments because of differences
in salinity. One species needs a higher salinity, otherwise its body
tissues absorb too much water, swell up and become damaged, while the other
species prefers a lower salt content or it will loose too much water
to the more salty environment. The presence of one of the species does therefore
not influence the survival of the other.
Your explanation is as good as your friends in one major respect.
Both opinions explain why the different species dominate in different areas.
Both models also make a viable attempt to explain the observed patterns,
but the explanations as such are totally different. One explanation implies
that the different species of mussels affect one another so that they don't
coexist optimally. The other emphasizes environmental variations: The two species
of mussels cannot grow well in the same salt concentration.
We now have a problem, we have two models
that can explain what we have observed and there might even be several
other possible explanations. Therefore, we really need a reasonable method that
can help us decide which model is the correct one. We can use argumentation and discussion (the usual method of dealing with differences of opinion), or we can
attempt a more scientific procedure.
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