Rainbow Trout Predation, Essay Example

Abstract

Prior research has indicated the significance of predation on the size of the spines in Threespine Stickleback in Alaska. Trout are often times more successful at preying upon fish with pelvic reduction, supporting the notion that larger and full-bodied pelvic girdles are maintained in Stickleback populations because of the selection from their fish predators. This study examines the spine sizes in Stickleback throughout a number of lakes with high predation and low predation in the state of Alaska. Results of the study determine that Threespine Sticklebacks have larger spines than in lakes with fewer and/or smaller Trout and the Sticklebacks from high predation lakes have longer spines than the Stickleback from low predation lakes.

Introduction

Threespine Stickleback contain locking pelvic and dorsal spines that perform as means of defense against predators by increasing effective diameter and repelling compression of the predator’s jaws. Oceanic Stickleback have large pelvic girdles containing a complete structure of anterior process, ascending branch, posterior process, and pelvic spine on either side of the body. Selective freshwater populations, though, have evolved over the years and contain smaller and reduced pelvic girdles. Nonetheless, Stickleback breeds with smaller pelvic girdles are relatively rare. Many freshwater populations of Stickleback actually contain complete pelvic structures. The decrease in pelvic size tends to draw a parallel to a lack of predators. This study provides further evidence on Rainbow Trout predation and how it does in fact act as a significant selective force on the size of the spines in Threespine Stickleback in Alaska. As noted throughout the research and this particular study, in lakes with many, large Trout, the Threespine Sticklebacks have larger spines than in lakes with fewer and/or smaller Trout. The Sticklebacks from high predation lakes have longer spines than the Stickleback from low predation lakes.

Methods

The selection of lakes for this experiment was chosen from a table of information on Rainbow Trout populations in 20 Alaskan lakes also containing Threespine Stickleback. The eight lakes for this particular experiment included Big Lake, Ohmer Lake, Scout Lake, Neklason Lake, Claw Lake, Lorraine Lake, Frog Lake and Lalen Lake. Four of these lakes surveyed are considered high pressure lakes and four of them are considered low predation pressure lakes. In each of these eight lakes, fifteen Sticklebacks were chosen as sample.

Furthermore, all of the fifteen Sticklebacks were measured by their two pelvic spines, dorsal spins and body length. After collecting the data of spine and body length for each fish, p-values were then calculated. T-tests were performed in order to calculate p-values.

Results

Graph1: The spine size measurement for different lakes in Alaska.

Graph2: The spine size compare between high predation pressure and low predation pressure.

Both Graph1 and Graph2 support the hypothesis: that the Threespine Sticklebacks have larger spines than in lakes with fewer and/or smaller Trout and the Sticklebacks from high predation lakes have longer spines than the Stickleback from low predation lakes. In Graph2, spine size in high predation pressure was much larger than that in low predation level. Graph1 shows two high predation level lakes and two low predation level lakes, and further supports the result from Graph2. The result from p-value is accept the two graphs. Because results are significant between Stickleback’s spine size in lakes with high predation pressure and low predation pressure due to p-value is less than 0.05.

Discussion

Both of the graphs support the general hypothesis. However, the results do not support the hypothesis because the p-value is 0.047. The sample value is clearly not large enough to make a significant difference in this experiment. Further research would need to be conducted, under the same conditions with a much larger sample size.

Kenyon (2011) demonstrates that the Stickleback that come from high predation pressure lakes have larger spine size when compared to the Stickleback that come from low predation pressure lakes. This matches the results from this experiment and the graphs represented in this experiment.

Prior research as well as this particular experiment point toward the fact that in lakes with many, large Trout, the Threespine Sticklebacks have larger spines than in lakes with fewer and/or smaller Trout. The Sticklebacks from high predation lakes have longer spines than the Stickleback from low predation lakes. However, future research should use a much larger sample size to solidify and confirm the results from this experiment. A larger sample would add to the validity of this research; making a more accurate and larger sample size could help achieve a statistically significant difference in results.

Literature Cited

Hoogland, R., D. Morris, and N. Tinbergen. “The spines of sticklebacks (Gasterosteus and Pygosteus) as means of defence against predators (Perca and Esox).” Behaviour (1956): 205-236.

Reimchen, Thomas E. “Predators and morphological evolution in threespine stickleback.” The evolutionary biology of the threespine stickleback (1994): 240-276.

Kenyon, Mobley, et al. “Morphological and genetic divergence in Swedish postglacial stickleback (Pungitius pungitius) populations.” (2011).