Five decades of misunderstanding in the social Hymenoptera: a review and meta-analysis of Michener's paradox

In a much-cited 1964 paper entitled "Reproductive efficiency in relation to colony size in hymenopterous societies," Charles Michener investigated the correlation between a colony's size and its reproductive efficiency - the ability of its adult females to produce reproductives, measured as per-capita output. Based on his analysis of published data from destructively sampled colonies in 18 species, he reported that in most of these species efficiency decreased with increasing colony size. His conclusion that efficiency is higher in smaller groups has since gained widespread acceptance. But it created a seeming paradox: how can natural selection maintain social behaviour when a female apparently enjoys her highest per-capita output by working alone? Here we treat Michener's pattern as a hypothesis and perform the first large-scale test of its prediction across the eusocial Hymenoptera. Because data on actual output of reproductives were not available for most species, Michener used various proxies, such as nest size, numbers of brood, or amounts of stored food. We show that for each of Michener's data sets the reported decline in per-capita productivity can be explained by factors other than decreasing efficiency, calling into question his conclusion that declining efficiency is the cause of the pattern. The most prominent cause of bias is the failure of the proxy to capture all forms of output in which the colony invests during the course of its ontogeny. Other biasing factors include seasonal effects and a variety of methodological flaws in the data sets he used. We then summarize the results of 215 data sets drawn from post-1964 studies of 80 species in 33 genera that better control for these factors. Of these, 163 data sets are included in two meta-analyses that statistically synthesize the available data on the relationship between colony size and efficiency, accounting for variable sample sizes and non-independence among the data sets. The overall effect, and those for most taxonomic subgroups, indicates no loss of efficiency with increasing colony size. Two exceptional taxa, the halictid bees and independent-founding paper wasps, show negative trends consistent with the Michener hypothesis in some species. We conclude that in most species, particularly those with large colony sizes, the hypothesis of decreasing efficiency with increasing colony size is not supported. Finally, we explore potential mechanisms through which the level of efficiency can decrease, be maintained, or even increase, as colonies increase in size.

Comparison of activities of daily living (ADLs) in two different one arm drive wheelchairs: a study of individuals/participants with hemiplegia

AIMS

This pilot study measured activities of daily living performance in individuals/participants with hemiplegia propelling both a standard dual handrim Action 3 wheelchair and a standard Action 3 wheelchair with a Neater Uni-Wheelchair kit attachment. The kit consists of a steerable front.

RESEARCH QUESTIONS

Does the use of the NUW affect the performance quality of activities of daily living in individuals/participants with hemiplegia. Is there a difference in the motor and process skills during activities of daily living performance, and in the time taken to complete the activities.

METHODS

Four individuals/participants with hemiplegia were used in a cross over, repeated measures trial. Assessment of Motor and Process Skills of users undertaking making a bed and laying a table "Swedish style", tasks were measured and time taken to complete each task were recorded.

RESULTS

Bed making completion time was quicker in the Neater Uni-wheelchair (p < 0.03). Motor skills were significantly higher than the process ability skills (p < 0.05).

CONCLUSION

Activities of daily living tasks in the Neater Uni-wheelchair were completed more efficiently with no loss in quality of motor and process skills performance. This suggests that the Neater Uni-wheelchair is a viable alternative to current one arm drive provision. Implications for Rehabilitation Inappropriate wheelchair provision can result in capacity limitation and poorer quality of ADL motor skill as well-lowered process performance skill. AMPS can help to explain motor and process skill differences in complex activities.