COLONY SIZE AS A BUFFER AGAINST SEASONALITY - BERGMANNS RULE IN SOCIAL INSECTS

In eusocial species, the size of the superorganism is the summed sizes of its component individuals. Bergmann's rule, the dine of decreasing size with decreasing latitude, applies to colony size in ants. Using data from the literature and our own collections, we show that colony sizes of tropical ant species are about one-tenth the average size of temperate species. This pattern holds when species or genera are sampl e units. Further, this trend is shown in 17 of 19 genera and five of s ix subfamilies. Bergmann's rule may arise if seasonal famine favors la rger organisms, given their increased energy reserves, We constructed three colony sizes of the ant Solenopsis invicta. We deprived these co lonies of food, or food and water. Queens, when surrounded by 10(2) wo rkers or 10(4) workers, survived longer than solitary queens. When dep rived only of food, days of queen survival had an allometry of M(0.21) (where M is mass), not significantly different from the predicted M(0 .25) for unitary organisms, We propose that shorter growing seasons in the temperate latitudes cull small-colony species through overwinteri ng starvation, which contributes to Bergmann's rule in social insects.