Studies that have evaluated potential determinants of network structure

Interaction type	Explanatory variable	Predicted network attribute	No. of networks	Result	Reference
Plant–pollinator	Abundance	Nestedness	1	Abundance partly predicts nestedness	Ollerton et al. (2003)
Plant–pollinator	Abundance	Nestedness	1	Abundance partly predicts degree	Dupont et al. (2003)
Plant–seed disperser	Abundance	Pairwise interactions	1	Abundance explains 83 % of variation of interactions	Burns (2006)
Plant–ant, plant–pollinator	Abundance	Strength asymmetry	1	Abundance partly predicts strength asymmetry	Vázquez et al. (2007)
Plant–pollinator	Abundance and trait matching (complementarity and barriers)	Connectance–richness and nested–richness correlations	40	Abundance and complementarity (but not barriers) separately partly predict these correlations	Santamaría and Rodríguez-Gironés (2007)
Plant–pollinator	Abundance and trait matching (complementarity and barriers)	Size-specific interaction patterns	1	Abundance, complementarity and barriers predict interactions among size classes of plants and flower visitors	Stang et al. (2009)
Plant–pollinator	Abundance and trait matching (exploitation barriers)	Interaction asymmetry, nestedness	1	Abundance and exploitation barriers predict number of interaction partners and degree asymmetry	Stang et al. (2007)
Theoretical	Abundance and trait matching (complementarity)	Nestedness	2	Abundance explains most variation in nestedness, but trait complementarity also contributes	Krishna et al. (2008)
Plant–pollinator	Abundance and trait matching (exploitation barriers)	Plant degree	1	Abundance and exploitation barriers explain 71 % of variation in plant degree	Stang et al. (2006)
Plant–pollinator	Abundance and spatio-temporal distribution	Connectance, nestedness, interaction evenness, strength asymmetry, overall network structure	1	Abundance and spatio-temporal distribution predict aggregate properties, but only partially overall structure	Vázquez et al. (2009)
Plant–seed disperser	Abundance, geographic range, phenological spread and phylogenetic structure	Degree	2	Abundance, geographic range, phenological spread and phylogenetic structure partly predict degree	Jordano and Bascompte unpubl. (cited in Bascompte and Jordano, 2007)
Plant–ant	Body size	Degree	8	Body size partly predicts degree (R2 = [0·05, 0·20])	Chamberlain and Holland (2009)
Simulation	Evenness of species observation records	Connectance, nestedness, degree distribution, strength asymmetry, interaction evenness, generality, standardized diversity (H2′)	0	Evenness in species observation records influences network statistics	Blüthgen et al. (2008)
Anemone–anemonefish	Geographic range	Nestedness	1	Geographic range partly predicts nestedness	Ollerton et al. (2007)
Plant–pollinator, plant–seed disperser	Interaction frequency	Shape of degree distribution	12 (p–p), 5 (p–sd)	Interaction frequency predicts degree distribution	Vázquez (2005)
Plant–ant	Interaction intimacy	Nestedness and compartmentalization	19	Interaction intimacy explains both nestedness and compartmentalization	Guimarães et al. (2007)
Plant–hemiptera–ant	Interaction type	Network specialization (H2′)	1	H2′ higher for plant–hemiptera than ant–hemiptera and ant–plant associations	Blüthgen et al. (2006a)
Plant–ant, plant–pollinator, plant–seed disperser	Interaction type, species richness, total frequency, network asymmetry	Network specialization (H2'), species-level specialization (d')	51	Interaction type influences specialization after correcting for the effect of total frequency	Blüthgen et al. (2007)
Plant–pollinator	Latitude, sampling effort	Degree		Sampling effort partly predicts degree	Ollerton and Cramer (2002)
Simulation	Trait matching and phylogenetic relatedness	Nestedness	1	Trait complementarity and phylogenetic relationships can result in observed network patterns	Rezende et al. (2007a)
Plant–seed disperser	Phylogenetic structure	Degree, species strength and ecological–phylogenetic distance correlation	36 (p–p), 37 (p–sd)	There is a detectable phylogenetic signal in some of the networks analysed	Rezende et al. (2007b)
Plant–pollinator	Sampling effort	Degree–frequency correlation	1	Sampling effort does not drive this correlation	Vázquez and Aizen (2006)
Plant–pollinator	Sampling effort, species richness and number of links	Nestedness	4	Nestedness is more influenced by sampling than by species richness and number of links	Nielsen and Bascompte (2007)
Plant–pollinator	Sampling effort, species richness, richness ratio, precipitation	Connectance, number of links	8	Sampling effort, species richness and richness ratio influence connectance and number of links	Devoto et al. (2005)
Simulation	Spatial aggregation and scale of animal movement	Connectance, nestedness, strength asymmetry, interaction evenness, CV of rare interactions	0	Spatial aggregation and animal movement influence network properties	Morales and Vázquez (2008)
Plant–seed disperser	Spatial distribution and trait matching	Occurrence of pairwise interactions	1	Spatio-temporal segregation and trait matching partly explain absence of interactions	Jordano et al. (2006)
Plant–pollinator	Species richness	Connectance	24	Connectance decreases with increasing richness	Thébault and Fontaine (2008)
Plant–pollinator	Species richness	Connectance and other metrics		Species richness predicts network attributes	Olesen et al. (2006)
Plant–pollinator, plant–seed disperser	Species richness	Connectance, number of links	33 (p–p), 19 (p–sd)	Connectance decreases and number of links increases with increasing richness	Jordano (1987)
Plant–pollinator	Species richness	Degree asymmetry	18	Asymmetric specialization increasing with increasing richness	Vázquez and Aizen (2004)
Theoretical, plant–pollinator	Species richness	Degree distribution, nestedness	5	Truncation of degree distribution and nestedness depend on network size	Medan et al. (2007)
Plant–pollinator	Species richness	Modularity, nestedness	51	Networks >150 plants always modular, <50 never; most networks nested	Olesen et al. (2007)
Plant–ant	Species richness	Nestedness	4	Nestedness increases with increasing richness	Guimarães et al. (2006)
Plant–pollinator, plant–seed disperser	Species richness	Nestedness	25 (p–p), 27 (p–sd)	Nestedness increases with increasing richness	Bascompte et al. (2003)
Plant–pollinator	Species richness	Proportion of species with only one link (extreme specialists)	23	Proportion of species with one link increases with network size	Vázquez and Stevens (2004)
Simulation	Species richness of network core	Shape of degree distribution	0	Truncation increases with increasing network core	Guimarães et al. (2005)
Plant–pollinator	Species richness, latitude	Connectance	29	Connectance decreases with increasing richness	Olesen and Jordano (2002)
Plant–pollinator, plant–seed disperser	Species richness, richness ratio	Shape of degree distribution	29 (p–p), 24 (p–sd)	Species richness and richness ratio may determine truncation of degree distribution	Guimarães et al. (2007)
Plant–pollinator	Temporal variation (between years)	Between-year similarity, matrix size, connectance, degree centralization, clustering, nestedness, average distance, network diameter	1	Aggregate network properties temporally invariant, but identity of interactions highly variable	Petanidou et al. (2008)
Plant–pollinator	Temporal variation (between years)	Between-year similarity, matrix size, connectance, degree distribution, nestedness	1	Aggregate network properties temporally invariant, but identity of interactions highly variable	Chacoff and Vázquez (unpubl.)
Plant–pollinator	Temporal variation (between years)	Number of unique links, comparison of entire matrix composition, nestedness, centrality scores	1	Invariant nestedness, high variation in identity of generalized core and composition of reciprocally specialized groups	Alarcón et al. (2008)
Plant–pollinator	Temporal variation (within and between years)	Similarity, matrix size, connectance, linkage level, shape of degree distribution	1	Aggregate properties temporally invariant, but identity of interactions highly variable	Olesen et al. (2008)
Plant–pollinator	Temporal variation (within year)	Matrix size, connectance, assemblage similarity, shape of degree distribution	1	Month-to-month fluctuation in partners' identity, matrix size and connectance	Basilio et al. (2006)