# Tropical bees and nectar choice

These data are from a PhD project regarding amino acids and floral nectar. Tropical stingless bees (*Trigona hockingsii*) were presented with a choice of nectar:

- Sugar – plain sugar water (a mix of carbohydrates).
- Amino – added amino acids. A sugar solution with additional amino acids to mimic “natural” nectar.

The number of bees feeding at each type was recorded at intervals, over a period of 9 days. The bee hive was located at James Cook University, Townsville, Queensland, Australia.

Table 1. Bee visits to different feed types. Values are daily totals.

Date | Amino | Sugar |

20/11/2000 | 96 | 135 |

21/11/2000 | 97 | 136 |

22/11/2000 | 115 | 78 |

23/11/2000 | 129 | 100 |

24/11/2000 | 137 | 121 |

25/11/2000 | 79 | 120 |

27/11/2000 | 93 | 117 |

28/11/2000 | 183 | 109 |

29/11/2000 | 134 | 201 |

The table shows the daily totals. The full dataset is also available, which gives the counts at each time interval (400 observations for each feed type).

## Download

You can download the dataset as a CSV file using this link: <Trigona-pairs.csv>. Alternatively, you might copy the table to the clipboard and paste into a spreadsheet. The full dataset, which includes the counts at each time interval is available using this link: <Trigona-indiv.csv>.

## Usage

You can use these data to practice/illustrate various topics:

- Using a Pivot Table.
- Simple summary statistics.
- Graphical summary.
- Paired differences test.

## Keywords

Invertebrate, pollinator, bee, paired test, differences, graphics, Pivot Table, scatter plot, isocline.

## Examples

The following examples will give you a few ideas about how you might explore these data.

### Pivot Table

The dataset Trigona-indiv.csv contains the complete set of observations. This dataset could be summarized and explored using a Pivot Table. The column headings are:

*Day*– a simple integer giving the day of observation.*Obs*– an integer value as an index, the observation number.*Count*– the number of bees observed.*Feed*– a categorical variable giving the feed type (A = amino, S = sugar).

You might also use the Pivot Table to make a Pivot Chart. A bar chart showing the sum of counts compared by day might be useful for example.

### Summary statistics

These datasets can be summarized in various ways, including:

- Averages – mean, median.
- Dispersion – standard deviation, inter-quartile ranges.
- Shape – parametric or not (e.g. Histogram or Shapiro-Wilk test).

The “shape” is important, as it will inform you which kind of differences test is most appropriate.

### Paired test

Since the observations for the two samples are matched, we can use a matched-pair version of the t-test or U-test to compare differences between feed types. The choice of test will depend on the distribution of the data.

The Trigona-pairs.csv data are normally distributed so you could use a paired t-test. A paired U-test can also be conducted:

- T-test: t = -0.38589, df = 8, p-value = 0.7096.
- U-test: V = 17, p-value = 0.5533.

The individual data,* Trigona-indiv.csv* are definitely not normally distributed so a paired U-test would be the best option:

- U-test: V = 7492.5, p-value = 0.2915

### Graphics

Paired tests can be problematic to display visually. A “traditional” bar chart or box-whisker plot would compare the overall mean or median values. However, in a paired test we are more interested in the pair by pair comparisons.

In the scatter plot, each datum is a paired observation with the daily sum of visits to the Amino feed plotted against the Sugar feed. The line is an isocline, drawn with a slope of 1 and an intercept of 0.

If all the points lay to one side of the line it would be a strong indication that one feed-type was more visited than the other. In this case we see more or less equal spread.

## References

Gardener, M. C., Rowe, R. J. & Gillman, M. P. 2003. Tropical bees (*Trigona hockingsi*) show no preference for nectar with amino acids. *Biotropica*, **35**, 119-125. [PDF].

## Links

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