Aim: Latitudinal clines in dietary specialisation and range size are used to explain biodiversity distributions at large spatial scale, such as the latitudinal diversity gradient. The aim of this study was to test whether diet breadth (as a dimension of niche breadth) and range size decrease towards lower latitudes in a species-rich clade of herbivorous insects as predicted by the latitude – niche breadth hypothesis and Rapoport’s rule, respectively. We further aimed at studying if these species characteristics are positively linked with each other as stated by the niche breadth – range size hypothesis.

Location: Europe (35°N – 71°N)

Time period: Present-day

Major Taxa: Geometrid moths (Lepidoptera, Geometridae)

Methods: For every species, we compiled information on latitudinal distribution and host-plant use based on available literature and online sources. We estimated each species’ level of fundamental dietary specialisation while accounting for phylogenetic relationships among utilised host plants. We further reconstructed a phylogeny including all studied moth taxa in order to control for phylogenetic dependence in species characteristics. Phylogenetic least squares (PGLS) analyses were used to test each of our hypotheses.

Results: We analysed 631 species of geometrids (85.2% of taxa within the biogeographical region), and found strong support for the latitude – niche breadth hypothesis as well as for Rapoport’s rule. Fundamental diet breadth was further found to be positively related to latitudinal range size, which supports the niche breadth – range size hypothesis. These results were retained when the subfamilies Ennominae and Larentiinae were analysed separately.

Main conclusions: Our findings indicate that latitudinal clines in range size and fundamental diet breadth covary in European geometrid moths and are likely drivers of increased species richness towards lower latitudes. This supports the idea that both characteristics should be studied simultaneously in order to unveil mechanisms structuring biodiversity patterns at macroecological scale.

1. We created a dataset inlcuding information on moth body size, larval host plants and distribution based on available literature and online sources.

2. Published barcode sequences and nuclear sequences were otbained from BOLD and GenBank in order to create a phylogney of geometrid moths.

3. Phylogenetic comparative methods (PGLS analyses) and correlation tests were applied in order to analyse the data.

The subfamily Sterrhinae is excluded.

Geometrid species without available sequence data and/or reliable host plant information are not included.