Horseshoe Crabs

Introduction

“Horseshoe crabs arrive on the beach in pairs and spawn … during … high tides. Unattached males also come to the beach, crowd around the nesting couples and compete with attached males for fertilizations. Satellite males form large groups around some couples while ignoring others, resulting in a nonrandom distribution that cannot be explained by local environmental conditions or habitat selection.” (Brockmann, H. J. (1996) Satellite Male Groups in Horseshoe Crabs, Limulus polyphemus, Ethology, 102, 1–21.)

Data

We have a data set about 173 mating female crabs. Data collected included whether or not a male satellite was present (and how many if present) and the shade, spine condition, weight, and carapace width of the female crab.

Numeric Summaries

We’ll consider three categorical variables from the data set: female shade, spine condition, and whether or not a satellite was present.

Full Table

Below is a table showing the frequency of spine conditions according to the shade of the female horseshoe crab.
Color and Spine Condition Information
Both Good Both Worn/Broken One Worn/Broken
Dark 3 37 4
Darker 1 20 1
Light 24 63 8
Lighter 9 1 2

Table by Satellite Indicator

The tables below show the frequency of spine conditions based on the shade of the female and the presence of male satellites.
For Female Crabs With At Least One Satellite
Both Good Both Worn/Broken One Worn/Broken
Dark 3 21 2
Darker 0 7 0
Light 16 50 3
Lighter 7 0 2
For Female Crabs With No Satellite
Both Good Both Worn/Broken One Worn/Broken
Dark 0 16 2
Darker 1 13 1
Light 8 13 5
Lighter 2 1 0

Visuals

One Variable

The charts below show the frequency of female crab shades, female crab spine conditions, and the presence of male satellites.

Two Variables

The following charts compare two different aspects of the data to one another. The first chart compares color to the presence of a satellite, the second compares spine condition to the presence of a satellite, and the third compares spine condition to color.

Three Variables

The following chart compares all three aspects (color, spine condition, and the presence of satellites) to one another.