Completing Linnaeus’s inventory of the Swedish insect fauna: only 5,000 species left?

Abstract

Despite more than 250 years of taxonomic research, we still have only a vague idea about the true size and composition of the faunas and floras of the planet [1][2][3][4]. Many biodiversity inventories provide limited insight because they focus on a small taxonomic subsample or a tiny geographic area [5,6]. Here, we report on the size and composition of the Swedish insect fauna, representing roughly half the macroscopic diversity of one of the largest European countries, based on more than a decade of data from the Swedish Taxonomy Initiative and a massive inventory of the country's insect fauna [7,8]. The fauna is considered one of the best known in the world, but the inventory has nevertheless revealed a surprising amount of hidden diversity: more than 3,000 new species (301 new to science) have been documented so far. We show that three independent extrapolation methods converge on similar estimates of the true size and composition of the true fauna, suggesting that it comprises around 33,000 species. Of those, 8,600 (26%) were unknown at the start of the inventory and 5,500 (17%) still await discovery. Most of the new species belong to Hymenoptera and Diptera groups that are decomposers or parasitoids. Thus, current knowledge of the Swedish insect fauna is strongly biased taxonomically and ecologically, and we argue that this is likely true for most insect faunas. Addressing these biases is critical in understanding insect biomes and the ecosystem services they provide.Swedish fauna were analyzed from older sources using a less detailed classification [13,20], we split the listed species numbers based on the available literature from the time (see also Table S1). The analysis of the European data, and of taxa expected to occur in Sweden, was based on the Fauna Europaea taxonomy [21].Ecological composition. In the analysis of life-history traits, we focused on two traits that are conservative enough that they can be reasonably assumed, in most cases, to be homogeneous within the family-level groups we used: the main feeding niche and the main feeding (micro-)habitat. This is the niche and habitat of the immature stages (the main feeding stages), and may or may not be the same as the niche and habitat of more short-lived adult stages. Data were taken from standard works [20,[46][47][48][49][50] complemented with data from relevant taxonomic specialists and the primary literature. Specifically, we defined the feeding niches as follows:Parasite. This includes bloodsuckers, endoparasites (botflies) and exoparasites (lice).Phytophage (plant feeder). This includes both chewers and sap suckers, as well as stem borers, leaf miners, root feeders and gall inducers.Phytophage-parasitoid. This is restricted to all primary parasitoids of plant feeders.Predator. This is restricted to free-living predators, it does not include parasitoids. Predator-parasitoid. This includes both primary parasitoids of predators and all hyperparasitoids (parasitoids of parasitoids).Saprophage (decomposer). This includes scavengers, decomposer...

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“…The SMTP datasets are unique in that they contain a large proportion of data on previously poorly-known, but species-rich taxa in the Diptera and Hymenoptera . Due to this and the fact that the Swedish insect fauna was better known than most other insect fauna before the start of the inventory, the SMTP data offer biologists one of the best opportunities currently for detailed analysis of the size and composition of temperate insect fauna ( Ronquist et al 2020 ).…”

Detecting flying insects using mega-nets and meta-barcoding

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