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Here are three pairs
of species in the same genera, plotted again with months on the x axis and
density per cubic meter on the y axis.
Note, though, that each chart now shows both depths, with the light
color representing water above the pycnocline, and the dark color
representing water below it. Note also
that the scales are not standardized.
These graphs show some very interesting results.
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The two species of Centropages show incredibly sharp temporal
differentiation, with hamatus declining just as typicus appears in the water
column. Contrast this with Acartia, in
which both species have peak abundances in the same month. However, look at the vertical distributions
of Acartia: longeremis is much more prevalent in the sub-pycnocline waters,
while hudsonica shows slightly higher numbers above the thermocline.
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Lastly, both species
of pseudocalanus show the same pattern: newmani is much more abundant in
surface waters, while moultoni is almost absent from surface waters until the
fall. These species show strong
affinities for certain depths, which in turn has large consequences in how
they are differentially transported by currents in the gulf of maine.
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Now I want to
broaden our view again, and re-address the entire community. The graphs I showed before are nice for
picking out the dominant species, but it is difficult to perceive how the
community is changing as a whole. For
this purpose, I am using Multi-Dimensional Scaling, or MDS…
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