Critique of:

Werner, E., Mittelbach, D., Gilliam, J., 1983. Experimental Tests of Optimal Habitat Use In Fish; The Role of Relative Habitat Profitability. Ecological Society of America, pp. 1525-1539.

This paper deals with optimal habitats for fish and relative habitat profitability. The authors started with three different sizes of the bluegill sunfish. With laboratory results in hand they desired to test their theoretical models with actual numbers. They compared the three sizes of bluegill in three separate habitats: these being the open water, bottom sediments and side vegetation of the pond. As time went by, diets were checked and compared to both the model and the laboratory. All the while with the results being carefully recorded. For this type of work, it is indeed necessary to write all the variables down and compare them against their own calculations.

The parameters sounded simple enough at first. With continued reading, much finer variables started appearing.

Smaller fish preyed on larger than expected prey and the question of active size selection arose. Hypothesis were ran against formulated models and the results ran against model numbers. For the sediment habitat, the ideal diet was not even realized or represented. Model errors occurred when it came to actual life conditions. Larvae midges, thought to only burrow within 2.5 cm. of the sediment surface, were found at between 5 - 25 cm. in the medium. This depth was too far for the fish to access so this information was fudged accordingly. On the edge of the pond was the final habitat. This area fared better. Differences were within 4% of the optimal diet and the prey (with more diversity) was in line with prior estimates.

Time at the different habitats and their relationships with each other were scrutinized next. It was noted that only the smaller fish went back to open water after feeding with their larger brethren. They preyed on smaller zooplankton which was not profitable to the larger fish because of their size.

In estimating food variance, a shadow appeared. One food source was barely noticeable while in abundance and the noticeable was present when not as plentiful. The fish seemed to be sampling their resources and changing habitats when profitabilities of food rose and fell.

Overall, other factors slowly figure in. These include differences in metabolic rates, body size, and the habitat. Large fish couldnt justify feeding on smaller prey when they had to burn more energy in order to catch them. On the other hand, smaller fish could get into the smaller areas where the larger fish couldnt.

The importance of this paper lies in its methodology. If other species can be explored in a like manner, doesnt it make sense that similar results would abound?

This was kind of hard reading but I thought that it would be interesting to see what kind of quirks would be involved. It would have been better reading if the authors could have given a visual representation of their research. Just having a picture (even a stick fish) would have been helpful. With all the little charts showing up they should have represented them on top of each other to contrast or correlate them. The formulas representing the foraging model and relative frequency of prey size would have been more meaningful if numbers were involved and pictographs of fish relative to size included. With all the variables, it was kind of hard to keep a mental picture. After reading it through a couple of times I found it not as interesting as I thought it would be.