Michener’s group-size paradox in cooperatively breeding birds

According to Michener's Paradox, most altruistic groups in nature should be small, and large groups should not exist. This is because per capita productivity is thought to decrease as groups get larger, meaning that the share of indirect fitness available to each group member declines, which favours dispersal. The empirical evidence for a decrease in per capita productivity is contradictory, however, and limited to the social Hymenoptera. I report that per capita reproductive success decreased with increasing group size across 26 cooperatively breeding bird species. Small groups comprising two or three individuals were the most common (79% of 16,101 groups) and these had the highest per capita reproductive success. This close fit between per capita reproductive success and the distribution of group sizes in nature suggests that it may indeed be difficult for large groups to evolve through indirect fitness benefits alone., , , # Michener's group-size paradox in cooperatively breeding birds

Author: Philip A. Downing

Contact: [[e-mail]](mailto:[e-mail])

Number of supplementary items: seven

1\. MP_R_Code.R

2\. MP_Table_S1.csv

3\. MP_Table_S2.csv

4\. MP_Table_S3.csv

5\. MP_Data_Extraction.txt

6\. Cooperative_bird_literature.pdf

7\. MP_Supp_Methods_Figures.pdf

### File name: MP\_R\_Code.R

This R script contains all the code needed to replicate the analyses (including packages and functions).

Models cited in the manuscript are located in this code.

The lettering in the code matches the lettering used in the methods section of the manuscript.

\- Data manipulation (lines 25 to 100)

\- Part A. Per capita and total reproductive success across group sizes (lines 106 to 256)

\- Part B. Per capita and total reproductive success and the frequency of group sizes (lines 262 to 434)

\- Part C. Study effort (lines 440 to 627)

Note that the code includes two-stage models fit using ...