Dispersion Patterns in Fiddler Crab Populations on Ward Island

Introduction

Purpose: The purpose of this study was to observe and identify dispersion patterns among populations of fiddler crabs on Ward Island. Background: Dispersion is the distance between organisms in an ecosystem population and is categorized in three ways: random, uniform, and clumping. Random dispersion is the unorganized grouping of a population, uniform dispersion is the organized spacing of individuals, and clumping is groups of organisms spaced close together but not uniformly. These patterns of dispersion are important to study in order to understand the ecology of an ecosystem and each organism’s place in it.

A dispersion pattern among a population can reflect what resources are available for that population, which environment it needs, and if it suffers from predation or not.

Hypothesis: Fiddler crabs burrows fall into random dispersion based on knowledge of marine organisms and the Ward Island area.

Null hypothesis: The distribution pattern of fiddler crabs won’t be able to be determined from the sampling methods.

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Methods

For data collection, quadrat sampling was used in groups of 3-4 to measure fiddler crab burrows on Ward Island. Each quadrat of 0.25 m2 were used for each section to measure the spacing, as well as individual divisions of yarn measured at 10cm2. The number of fiddler crab burrows was then recorded in each section.

Table 1: Distribution of Fiddler Crab Burrows

Id=n*(Sum Burrows^2*frequency)-N/N(N-1)

Id=1371*(89725785-1203)/1203(1203-1)

Id=85070

Based on the data collected in the table, X was found from multiplying the number of burrows in the plot wit the amount of plots present.

X2 was the amount of X squared, and the number of Burrows2 * Frequency was calculated by squaring the number of borrows and multiplying by the amount of plots.

The first calculation made was Morisita’s Index of Dispersion.

The next calculation is the X2 Statistic test.

X^2=(n*Sum X^2)/(N)-N

X^2=(1371*314501)/(1203)-1203

X^2=357218

The final test is the Chi Squared Test.

X^2 a= v((1-(2/9v)+(c√2/9v))^3 v=1371-1=1370

X^2 a= 1370 ((1-2/9(1370)+(1.64485√2/9(1370))^3 c=1.64485

X^2 a=1370 ((1-1.62*10^-4)+(1.64485+0.0127))^3

X^2 a= 1370((1-1.62*10^-4)+0.0209))^3

X^2 a= 1370((1.021))^3

X^2 a= 1370(1.06)

X^2 a= 1457

Discussion

The dispersion pattern of fiddler crabs shows clumped distribution among the population on Ward Island. These results could indicate predation patterns or food resource patterns for these particular fiddler crabs. While this sample is helpful in determining the specific details of why fiddler crabs are distributed this way, further studies of fiddler crabs will reveal more information.

Conclusion

The study successfully identified a clumped dispersion pattern within the fiddler crab populations on Ward Island, challenging the initial hypothesis of random dispersion. These findings underscore the complexity of ecological interactions and the importance of detailed spatial analysis in understanding ecosystem dynamics. Further studies are recommended to explore the factors contributing to this clumped distribution, including food resource availability, predation pressure, and habitat suitability.