DOI: 10.5061/dryad.cnp5hqcb6
title: Ancient human colonization explains dung beetle species richness in the Mediterranean and Macaronesian islands

description: Aim: Different hypothesis have been proposed to explain differences in
 species richness among islands. However, few studies have attempted to
 compare the explanatory power of multiple hypotheses using a large data
 set. Here we analyse how different types of predictors
 (energetic/climatic, environmental heterogeneity, island biogeography and
 anthropogenic) affect variation in dung beetle species richness on
 Mediterranean and Macaronesian islands. Location: Mediterranean and
 Macaronesian islands. Taxon: Dung beetles. Methods: Using a large dataset
 of islands (n = 147), we extracted the species richness of dung beetles on
 each island using 362 bibliographic reference sources. We performed GLMs
 to analyse the relationship between the species richness of dung beetles
 and eleven explanatory variables (temperature, evapotranspiration,
 aridity, area, maximum elevation, connection to continent during LGM,
 geological origin, distance from continent, nearest continent, years since
 first human colonization and human density) representing four types of
 causal hypotheses. We also included as a covariate the number of published
 papers studying dung beetles as a surrogate of the survey/study effort
 carried out in each island. Results: GLMs suggest that the years since
 first human colonization, the number of published papers, and island area
 were the predictors with a higher explanatory capacity. The volcanic
 character of the islands and the distance from the mainland had some
 relevance in the case of Scarabaeinae and Geotrupinae, and maximum
 elevation appeared relevant in the species richness of Scarabaeinae and
 Aphodiidae. The anthropogenic and island biogeography hypotheses on the
 variation in species richness were the ones that have the strongest
 explanatory capacity, regardless of the inclusion of the surrogate of
 survey effort as a covariate in the models. Main conclusions: The long
 history of human movements and agricultural activities has facilitated the
 colonization of dung beetles and provided trophic resources for their
 persistence, leading to increased species richness. Thus, the importance
 of anthropogenic factors in shaping the biodiversity patterns of island
 biogeography cannot be ignored. These human-induced influences may play a
 fundamental role in altering the biogeographic patterns of islands, even
 overriding the importance of other variables. Consequently, our findings
 underline the profound impact of historical human actions on islands
 biodiversity.
description: The study focused on the
 islands of the Mediterranean and Macaronesian regions, totalling 147
 islands. Islands were included in this study when they had faunistic
 studies or published records of dung beetle species. The great variability
 in the environmental features of all these islands maximize the capacity
 of finding geographical species richness patterns able to be explained by
 the used explanatory variables and factors.
 The dung beetle species
 considered were those belonging to the superfamily Scarabaeoidea, which
 mainly feed on mammal faeces at any stage of their development. In other
 words, dung beetles strictly belong to the subfamilies Geotrupinae,
 Scarabaeinae, and Aphodiinae. However, in our analysis we used data of
 dung beetles <em>sensu lato</em> because we added data of all
 the family Aphodiidae, which also includes the subfamilies Psammodiinae,
 Aegialiinae, and Eremazinae, which have a saprophagous feeding behaviour.
 Thus, we studied here the geographical variation in the species richness
 of dung beetle species belonging to Geotrupinae, Scarabaeinae, and
 Aphodiidae. All available published manuscripts concerning
 dung beetles in the Mediterranean and Macaronesian regions were compiled,
 such as atlases, books, peer-reviewed papers, and grey literature. Most of
 these references come from the authors’ exhaustive library. A total of 362
 bibliographic reference sources published from 1838 to 2019 were used to
 extract dung beetle occurrence data in islands (see Supplementary Material
 S1 for more details). All these data were checked, and the nomenclature
 was standardized following an up-to-date taxonomical criterion avoiding
 subspecies, recent species splitting, and doubtful citations. All dung
 beetles species finally listed (n = 220) are considered native to the
 biogeographic region in which the islands studied are
 located.
description: The primary data used are provided in excel format.