Transcript Keller - York College of Pennsylvania

The Effect of Oddity in Prey Selection of Largemouth Bass
(Micropterus salmoides)
Nathan Keller
Department of Biology
York College of Pennsylvania
Introduction
Materials and Methods
Results cont’d
•
• Largemouth bass were purchased from a local hatchery.
• A single “odd” fish is at a significant disadvantage
when placed into a school of “normal” fish (Landeau
& Terborgh 1986).
• Significantly more normal fish were eaten on
day 1 of part 1 and part 2 when a paired t-test
was run (P < 0.0001-part 1; P = 0.0493-part 2).
• Pilot studies were run to determine how many fish would be eaten per
day and if the largemouth bass would consume both types of fish.
The effect of oddity in predation is a very important
factor when it comes to prey selection.
• The introduction of an “odd” fish may also make the
“normal” fish more susceptible to predation.
•Schooling of prey, to avoid predation, causes the
confusion effect in the predator, because they cannot
single out one individual to pursue until capture
(Landeau & Terborgh 1986, Pitcher & Parrish 1993).
Objective
•
To discover if largemouth bass show a
significant preference for an introduced “odd”
phenotype when accustomed to consuming the
“normal” phenotype.
• Fathead minnows (Pimphales promelas) and rosie reds (Pimphales
promelas) were purchased from a local sporting goods store.
• All bass not being tested were kept in a 568 L holding tank until
testing began
• When tested each bass was placed into a 95 L tank and given two
days to become acclimated.
• Schools of eight minnows were used at a 1:1 ratio of fathead minnows
and rosie reds.
• Each day the number of each type of eaten fish was recorded and the
appropriate number of minnows was added to bring the school back to
eight minnows at a 1:1 ratio
• Minnows were introduced into the tank using two clear two-liter soda
bottles connected at the center with clear packaging tape, with rubber
tubing attached to the top as seen in diagrams 1 and 2 (Jadlocki 2002).
• The experiment consisted of two parts
•Part 1 (n=22)– Fathead minnows (normal), Rosie reds (odd)
•Part 2 (n=20)– Fathead minnows (odd), Rosie reds (normal)
• Largemouth bass accustomed to feeding on
the “normal” fish will show a preference for the
“odd” phenotype when introduced.
Diagram 1
Diagram 2
• Largemouth bass, on several occasions, ate all
four “normal” fish. However, none of them ate
all four “odd” fish.
• Largemouth bass actually preferred the “normal”
phenotype on day one of both parts of the study.
Results
Figure 1. Paired t-tests were run on the
mean number of fish eaten each day to
see if the means differed for part 1. Only
day one differed significantly (P <
0.0001). Day two and three were not
significantly different (day 2 P = 0.9999,
day 3 P = 0.3161).
Figure 2. Paired t-tests were run on the
mean number of fish eaten each day to
see if the means differed for part 2. Day
one showed a significant difference (P =
0.0493). Days 2 and 3 showed no
significant difference (day 2 P = 0.1189,
day 3 P = 0.0528)
Part 1
• Mean differences in some cases leveled out over the
three day testing period suggesting that the bass may
prefer the “odd” phenotype if the testing period is
extended (5 days, 10 days, etc.)
Part 2
Literature Cited
Table 1. Total number of fish eaten each day and difference between each phenotype, with respective Standard Deviation.
Part 2
• A one-way ANOVA test was run on the total
number of fish eaten each day for part 1 and 2.
No significant differences were found in part 1,
however, day one was significantly different in
part 2 (P = 0.0002).
• Largemouth bass did not prefer the “odd” phenotype
over the “normal” phenotype.
- Bass were fed fathead minnows while not being tested.
Part 1
• The mean difference of fish eaten each day
was not significantly different for part 2 (P =
0.7576, one-way ANOVA).
Conclusion
- Bass were fed fathead minnows while not being tested.
Hypothesis
• The mean difference of fish eaten each day
was only significantly different on day 1 of part 1
which was determined using a one-way ANOVA
test (P = 0.0037).
Total Eaten
Difference a
Mean
Difference b
Standard
Deviation
nc
Day 1
65
35
1.59
1.47
22
Day 2
54
0
0.00
1.31
22
Day 3
71
9
0.41
1.87
22
Day 1
40
14
0.70
1.49
20
Day 2
76
8
0.40
1.10
20
Day 3
65
11
0.55
1.19
20
a
red numbers indicate more rosie reds were eaten, and black indicated more fatheads were eaten
b
mean difference of fish eaten each day
c
sample size used
Landeau, L. and Terborgh, J. 1986. Oddity and the ‘confusion’ in predation.
Animal Behaviour 34:1372-1380.
Pitcher, T. J. and Parrish, J. K. 1993. Functions of shoaling behaviour in teleosts. Behaviour of Teleost
Fishes (ed. T. J. Pitcher), pp 363 – 439. London: Chapman &
Hall.
Jadlocki, J.A. 2002. Predators and the strength of preferences for familiar schools in the fathead minnow,
Pimephales promelas. MENTOR: Rehnberg
Acknowledgments
•I would like to thank God for giving me the patience to complete this project.
•I would like to thank Dr. Rehnberg for helping me throughout my entire experiment.