Are patterns of sampling effort and completeness of inventories congruent? A test using databases for five insect taxa in the Iberian Peninsula

Evaluating data quality and inventory completeness must be a preliminary step in any biodiversity research, particularly in the case of insects and high biodiversity areas. Yet, this step is often neglected or, at best, assessed only for one insect group, and the degree of congruence of sampling effort ffor different insect groups remains unexplored. We assess the congruence in the spatial distribution of sampling effort for five insect groups (butterflies, caddisflies, dung beetles, moths, and aquatic beetles) in the Iberian Peninsula. We identify well-surveyed areas for each taxonomic group and examine the degree to which the patterns of sampling effort can be explained by a set of variables related to environmental conditions and accessibility. Irrespective of the general lack of reliable inventories, we found a general but low congruence in the completeness patterns of the different taxa. This suggests that there is not a common geographical pattern in survey effort and that idiosyncratic and contingent factors (mainly the proximity to the workplaces of entomologists) are differentially affecting each group. After many decades of taxonomic and faunistic work, distributional databases of Iberian insects are still in a very preliminary stage, thus limiting our capacity to obtain reliable answers to basic and applied questions. We recommend carrying out long-term, standardised and well-designed entomological surveys able to generate a reliable image of the distribution of different insect groups. This will allow us to estimate accurately insect trends and better understand the full extent of global biodiversity loss.