1 3 Oecologia DOI 10.1007/s00442-017-3817-4 PLANT-MICROBE-ANIMAL INTERACTIONS - ORIGINAL RESEARCH Asymmetric competition for nectar between a large nectar thief and a small pollinator: an energetic point of view Eliška Padyšáková 1,2,3 · Jan Okrouhlík 2 · Mark Brown 4 · Michael Bartoš 3,5 · Šte ˇpán Janec ˇek 3,5 Received: 8 June 2016 / Accepted: 11 January 2017 © Springer-Verlag Berlin Heidelberg 2017 Hypoestes aristata (Acanthaceae) in Bamenda Highlands, Cameroon. For comparative purpose, we established a sim- plistic model of daily energy expenditure and daily energy intake by both visitor species assuming that they spend all available daytime feeding on H. aristata. We revealed the energetic gain–expenditure balance of the studied visi- tor species in relation to diurnal changes in nectar quality and quantity. In general, smaller energy requirements and related ability to utilise smaller resources made the main pollinator X. caffra competitively superior to the larger nec- tar thief C. reichenowi. Nevertheless, sunbirds are endowed with several mechanisms to reduce asymmetry in exploita- tive competition, such as the use of nectar resources in times of the day when rivals are inactive, aggressive attacks on carpenter bees while defending the nectar plants, and higher speed of nectar consumption. Keywords Africa · Carpenter bee · Cinnyris · Hypoestes · Sunbird · Xylocopa Introduction Nectar is an important resource of energy and nutrients for a large spectrum of flower visitors including bacteria, yeasts, mites, and diverse orders of insects, birds, reptiles and mammals. Nectar might, however, be temporally and spatially limited and in consequence interspecific com- petition will occur whenever the foraging of two or more organisms overlap in time and/or space (Brown et al. 1981; Galen and Geib 2007; Ramalho et al. 1991; Tiple et al. 2009). Such interactions are common in nature and play an important role in the organisation of guilds of nectar-feed- ing animals and the co-evolution of plant–pollinator rela- tionships (Ferriere et al. 2007). Abstract There are two alternative hypotheses related to body size and competition for restricted food sources. The first one supposes that larger animals are superior competi- tors because of their increased feeding abilities, whereas the second one assumes superiority of smaller animals because of their lower food requirements. We examined the relationship between two unrelated species of different size, drinking technique, energy requirements and roles in plant pollination system, to reveal the features of their competi- tive interaction and mechanisms enabling their co-existence while utilising the same nectar source. We observed diur- nal feeding behaviour of the main pollinator, the carpenter bee Xylocopa caffra and a nectar thief, the northern dou- ble-collared sunbird Cinnyris reichenowi on 19 clumps of Communicated by Nina Farwig. Electronic supplementary material The online version of this article (doi:10.1007/s00442-017-3817-4) contains supplementary material, which is available to authorized users. * Eliška Padyšáková paddysek@gmail.com 1 Biology Centre, Institute of Entomology, Academy of Sciences of the Czech Republic, Branišovská 31, 370 05 Ceske Budejovice, Czech Republic 2 Department of Zoology, Faculty of Science, University of South Bohemia, Branišovská 31, 370 05 Ceske Budejovice, Czech Republic 3 Department of Ecology, Faculty of Science, Charles University in Prague, Vinic ˇná 7, 128 44 Prague 2, Czech Republic 4 School of Life Sciences, University of KwaZulu-Natal, Durban, South Africa 5 Institute of Botany, Academy of Sciences of the Czech Republic, Dukelská 135, 379 82 Trˇebon ˇ, Czech Republic