The species composition, primary productivity and relative
abundance of the plankton organisms in Marion Lake, British Columbia
were recorded at biweekly intervals for two months following artificial
enrichment with nitrate or phosphate or both, of six large wooden
enclosures within the lake in four seasons during the year.
Enrichment resulted initially in a decrease in diversity and
an increase in the productivity of the phytoplankton and standing
crop of the entire plankton community. These events were collectively
termed a "regressive succession" because their "direction" of change
was the reverse of that normally encountered in primary and secondary
successions. The regressive succession terminated following algal
bloom formation, and diversity began to increase slowly while the
primary productivity and standing crop of the plankton dropped. This
was indicative of the beginning of a secondary succession in which one
group of dominant species was replaced by another and then others in
turn replaced these.
This successional pattern occurred regardless of season, prevailing
physical, chemical, or climatological factors. Thus, such a pattern
appeared to be a very general one and was disrupted only by the physical
removal of the majority of the planktonic species from the lake resulting
from persistent and heavy rains which "flushed" the lake.
A statistical analysis of each of the 167 euplankton species
observed in the lake was performed using the data from each of the
four enrichment series to determine which species responded significantly
to artificial enrichment. The individual response patterns were nearly
as diverse as the species themselves, however, one of the most common
responses was made by very rare species which "bloomed" two to three
weeks after nutrient addition. Few primary producers responded to
more than one type of nutrient enrichment in any one season which
emphasized the importance of Liebig’s Law of the Minimum. The higher
trophic levels, on the other hand, responded more to the increase in
standing crop in the different enclosures than to any one particular
type of nutrient enrichment.
The Shannon-Weaver formula, H =nP, log P, was modified by
changing the definition of Pi, that is, the individuals in the ith
species divided by the total number in the sample. This index was
insensitive to changes in the relative abundance of the planktonic
species from the higher trophic levels. Pi was redefined so that it
was less sensitive to number and more sensitive to both relative biomass
and relative productivity. This new index of diversity (Hp ) did not
act selectively on the different trophic levels represented in the
plankton samples.
An understanding of the principles governing community organization
and biotic succession should be based on the life history of the
individual species comprising the community and not on assumptions
about supposed trophic changes. This study indicated that pertinent
information about the changes in the structure of a planktonic community
could be gained from an analysis of the changes in the relative abundance
of each of the species without artificially isolating and culturing these
species and without lumping all the organisms into vague trophic
categories. / Science, Faculty of / Zoology, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/42425 |
| Date | January 1968 |
| Creators | Dickman, Michael David |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
Page generated in 0.0015 seconds