DOI: 10.5061/dryad.dfn2z358p
title: Data from: revisiting niche divergence hypothesis in dimorphic birds: is diet overlap correlated with sexual size dimorphism?

description: The evolution of sexual size dimorphism (SSD) is a long-standing topic in
 evolutionary biology, but there is little agreement on the extent to which
 SSD is driven by the different selective forces. While sexual selection
 and fecundity selection have traditionally been proposed as the two
 leading hypotheses, SSD may also result from natural selection through
 mechanisms such as sexual niche divergence, which might have reduced
 resource competition between sexes. Here, we revisited the niche
 divergence hypothesis by testing the relationship between the sexual
 overlap in diet and SSD of 56 bird species using phylogenetic comparative
 analyses. We then assessed how SSD variation relates to the three main
 hypotheses: sexual selection, fecundity selection, and sexual niche
 divergence using phylogenetic generalized least squares (PGLS). Then, we
 compared sexual selection, fecundity selection, and niche divergence
 selection as SSD drivers through phylogenetic confirmatory path analyses
 to disentangle the possible causal evolutionary relationships between SSD
 and the three hypotheses. Phylogenetic generalized least squares showed
 that SSD was negatively correlated with diet overlap, i. e., the greater
 the difference in body size between males and females, the less diet
 overlap. As predicted by sexual selection theory, the difference in body
 size between sexes was higher in polygynous species. Confirmatory
 phylogenetic path analyses suggested that the most likely evolutionary
 path might include mating system as a main driver in SSD and niche
 divergence as a result of SSD. We found no evidence of a role of fecundity
 selection in the evolution of female-biased SSD. Our study provides
 evidence that sexual selection has likely been the main cause of SSD and
 that dietary divergence is likely an indirect effect of SSD.
description: The database of diet overlap was compiled through a literature
 survey of all major ornithological journals. The <em>ISI Web of
 Knowledge</em> was systematically searched for original case studies
 in which data on the diet composition of males and females were provided.
 A total of 289 references were examined, 62 of which provided data on the
 diet of both sexes for 58 species belonging to 32 families. We discarded
 studies based on prey types brought to the nest by adults (n=8) because
 food provisioning to chicks does not represent the actual nutritional
 requirements of males and females, or those based on isotope analyses
 (n=10), since both sexes might show overlapping isotopic niches, while
 having a different trophic niche, for instance, if both sexes feed on
 different prey with similar δ<sup>15</sup>N values (Bearhop et
 al., 2004). Diet composition was described using stomachs, esophageal
 contents, and regurgitations (80.3% of the studies), feces (13.1%), and
 direct observation (6.6%). The description of the
 mating system, male display type, and clutch size were obtained from the
 <em>Handbook of the birds of the world</em> (del Hoyo et al.,
 1992), Lislevand et al. (2007) and BoW (Billerman et al., 2022).
description: # Revisiting niche divergence hypothesis in sexually dimorphic birds: is
 diet overlap correlated with sexual size dimorphism?
 This study explores the
 relationship between Sexual Size Dimorphism (SSD) and ecological dynamics
 in bird species. The dataset includes information on the diet of 58 bird
 species, aiming to investigate the correlation between SSD and diet
 overlap, mating systems, sexual display behaviors, and clutch size.
 \**Dataset contents: ** We compiled data from a thorough literature
 survey, sifting through 289 references to focus on 58 bird species. The
 dataset includes details on diet overlapping between both males and
 females. Mating systems were categorized, incorporating polyandry,
 monogamy, and polygyny. Male sexual display behaviors were classified
 based on a five-point scale, ranging from ground displays to acrobatic
 aerial displays. Clutch size, representing fecundity, was also documented.
 Morphometric traits, such as body mass, wing length, bill length, and
 tarsus length, offered a nuanced perspective on avian physical
 characteristics. ## Description of the data and file structure
 DATA-SPECIFIC INFORMATION FOR: Database_revisiting_niche_divergence.xlsx
 These are the data used to explore the relationship between Sexual Size
 Dimorphism (SSD) and ecological dynamics in bird species. The dataset
 includes information on the diet of 58 bird species, aiming to investigate
 the correlation between SSD and diet overlap, mating systems, sexual
 display behaviors, and clutch size. 1\. Number of variables: 25 2\. Number
 of cases/rows: 58 3\. Variable List: ***Species information***: * Order:
 Order of the specie * Family: Family of the species * Species: Scientific
 name of the species ***Biometric measures*** (BM_male, BM_female,
 Wing_male, Wing_female, Beak_male, Beak_female, Tarsus_male,
 Tarsus_female): Morphometric measurements were preferably obtained from
 the study from which the diet composition was taken. In case such
 biometric data were not available in that study, they were collected from
 other studies in the same area or from other published databases
 (Lislevand et al., 2007). * BM_male: Body mass of males (grams) *
 BM_female: Body mass of females (grams) * Wing_male: Wing length of males
 (mm) * Wing_female: Wing length of females (mm) * Beak_male: Beak length
 of males (mm) * Beak_female: Beak length of females (mm) * Tarsus_male:
 Tarsus length of males (mm)  * Tarsus_female: Tarsus length of females
 (mm) **Sexual size dimorphism data** (SSD_BM, SSD_wing, SSD_beak,
 SSD_tarsus): SSD was calculated as log10 (male size / female size), with
 values &lt; 0 indicating female-biased SSD and values &gt; 0 indicating
 male-biased SSD. We calculated SSD separately for four morphometric
 traits: body mass, wing length, bill length, and tarsus length. * SSD_BM:
 log10 (BM_male / BM_female) * SSD_wing: log10 (Wing_male / Wing_female) *
 SSD_beak: log10 (Beak_male / Beak_female) * SSD_tarsus: log10 (Tarsus_male
 / Tarsus_female) **Diet overlap data** (CD_total, CD_non-breeding,
 CD_breeding, CD_annual, CD_prey): The database of diet overlap was
 compiled through a literature survey of all major ornithological journals.
 The ISI Web of Knowledge was systematically searched for original case
 studies in which data on the diet composition of males and females were
 provided. Diet overlap calculated with the simplified Morisita index CD
 (Horn, 1966), using FSAmisc package (Ogle, 2015) of R version 4.0.5 (R
 Core Team, 2021). * CD_total: Diet overlap calculated with the simplified
 Morisita index (as described above) applied to the full dataset including
 species with breeding, non-breeding and annual overlap. * CD_non-breeding:
 Diet overlap calculated with the simplified Morisita index (as described
 above) applied to species with diet data corresponding to the non-breeding
 season. * CD_breeding: Diet overlap calculated with the simplified
 Morisita index (as described above) applied to species with diet data
 corresponding to the breeding season. * CD_annual: Diet overlap calculated
 with the simplified Morisita index (as described above) applied to species
 whose diet data is an average of different seasons. * CD_prey: Diet
 overlap calculated with the simplified Morisita index (as described above)
 applied to species whose diet data is the prey size. **Sexual selection
 and clutch size data** (Clutch_size, Mating_system, Sexual_display): *
 Clutch_size: Average clutch size of the species * Mating_system: (1)
 polyandry; (2) monogamy (&lt;5% polygyny); (3) mostly monogamy, but
 occasional polygyny (5–15% polygyny); (4) mostly polygyny (&gt; 15%
 polygyny) and (5) lek or promiscuous (Lislevand et al., 2007). *
 Sexual_display: (1) ground displays only, including displays on trees and
 bushes; (2) ground displays, but with occasional jumps/leaps into the air;
 (3) both ground and non-acrobatic flight displays; (4) mainly aerial
 displays, non-acrobatic; (5) mainly aerial displays, acrobatic (Lislevand
 et al., 2007). **Bibliography sources:** * Source_data_biometry:
 Bibliographic references of biometry data * Source_data_diet:
 Bibliographic references of diet data 4\. Missing data codes: NA (data not
 available)