Table 3. Association of colony size and fitness in ants.
Evidence supporting and refuting fitness-enhancing contributions of long-lived workers to increased colony size. Research has concentrated on species in the Subfamilies Myrmicinae and Formicinae.
| Factor | Species | Effect of colony size | Notes | Reference |
|---|---|---|---|---|
| Colony growth and reproduction | Solenopsis invicta | None | Positive effect of number of 4th instar larvae on queen laying rate | Tschinkel 1988 |
| Positive | For immature colonies | Tschinkel 1993 | ||
| Mixed | No effect: mature colonies; Positive: when immature colonies included; effect appears to be driven by immature and adolescent colonies | Cassill 2002 | ||
| None | Effects of worker size class on brood production/survival | Porter and Tschinkel 1985 | ||
| Positive | Reduction of workforce size in mature colonies led to a reduction in production of sexuals and an increase in worker production | Vargo 1988 | ||
| Camponotus impressus | Mixed | Positive: alate males and females; in large colonies positively with number of majors Negative: in large colonies with number of minors |
Walker and Stamps 1986 | |
| Meta-analysis of 15–65 spp. | Mixed | Negative: larger colonies had proportionately fewer alates per worker Neutral: biomass scaled isometrically |
Shik 2008 | |
| Temnothorax crassispinus, T. longispinosus, T. nylanderi, Leptothorax acervorum, L. muscorum, Myrmica punctiventris, Protomognathus americanus, Harpagoxenus sublaevis | Mixed | Negative: Per capita productivity declined in 6 of 8 species Mixed: some populations differed in the direction of the effect within species Production was pooled across all castes |
Kramer et al. 2014 | |
| Resource acquisition | Pogonomyrmex spp. | Neutral | Intraspecific comparison between species with different colony sizes; larger numbers of foragers no better at harvesting clumped food; but larger colonies given larger territories | Flanagan et al. 2012 |
| Eciton hamatum | Mixed | Neutral: effect on average or peak raid intake Positive: peak colony intake |
Powell 2011 | |
| Temnothorax rugatulus | Mixed | Higher density colonies had higher foraging rates; field density relatively constant among colonies | Cao 2013 | |
| Global division of labor | Pogonomyrmex californicus | Positive | During ontogeny and with age-matched colonies | Holbrook et al. 2011 |
| Neutral | Experiment only conducted over ~ 3 days | Holbrook et al. 2013 | ||
| Temnothorax albipennis | Neutral | In small colonies, a smaller proportion of workers did most of the work | Dornhaus et al. 2009 | |
| Rhytidoponera metallica | Positive | Greater task specialization in larger colonies; older workers spent more time foraging in larger colonies but no effect of age in small colonies | Thomas and Elgar 2003 | |
| 140 spp. | Positive | Not phylogenetically controlled, based on number of morphological castes | Bonner 1993 | |
| Group decision-making | Temnothorax sp. | Mixed | Neutral: no difference in ability to select nests Positive: larger colonies found good nests faster |
Franks et al. 2006 |
| Defense | Oecophylla longinoda | Positive | Colonies with highest density of majors win intraspecific contests | Hölldobler and Wilson 1978 |
| Solenopsis invicta | Positive | Experimental removal of workers | Adams 2003 | |
| Formica rufa | Mixed | Negative: workers in smaller groups fight more aggressively Positive: larger groups have higher levels of total aggression |
Batchelor and Briffa 2011 | |
| Formica xerophila | Positive | Workers housed in larger and denser subcolonies prior to fighting were more aggressive (fighting groups held at equal sizes) | Tanner 2006 | |
| Immunocompetence | Attine species | Positive | Larger colony sizes necessitated a switch to behavioral and chemical defense | Fernández-Marín et al. 2009 |
| Acromyrmex echinatior | Positive | Isolated ants had compromised immune function | Hughes et al. 2002 | |
| Temnothorax nylanderi | Positive | Cestode-infected colonies were larger than unifected colonies; no effect of infection on per worker productivity | Scharf et al. 2012 | |
| Nursing | Solenopsis invicta | Neutral | Required minimum number of workers but otherwise no effect | Cassill and Tschinkel 1999 |
| Formica selysi | Mixed | Non-linear; intermediate ratios and sizes had highest rate of brood eclosion; confounds of group size and worker:brood ratio | Purcell et al. 2011 |