Among the most widely used information underpinning conservation is the concept of Red-Listing species according to criteria developed by the IUCN. The Red List designates species extinction risk based on geographic range, population size, or declines in either. However, it has frequently been questioned whether Red List criteria are appropriate for terrestrial arthropods, which comprise the bulk of animal diversity. Due to their small size, difficulty in identification, and inherent rarity, many invertebrates are hard to study, making Red List criteria hard to apply. We assess this criticism using empirical evidence from one of the largest terrestrial arthropod surveys to date, documenting the abundance and distribution of over 13,000 species in Sweden. Of these taxa, 13% have been found at a single site, and 11% of species are found only in a single weekly sample. Using these data we demonstrate that estimates of trends based on low sample sizes are associated with major uncertainty and a major risk of misclassification under IUCN criteria. We argue that even the most ambitious monitoring efforts are unlikely to produce enough observations to reliably estimate population sizes and ranges for more than a fraction of species. Thus, there is likely to be substantial uncertainty in classifying most species according to current criteria. In response, we discuss the adaptation of IUCN criteria to more accurately capture the conservation needs of invertebrates, and to adequately assess the future of the majority of global animal diversity.

Species traits and environmental conditions determine the existence and strength of trophic interactions, but how they do so is poorly understood. To enable the informed inclusion of such driving factors in dynamic trophic-interaction models, we revisit and expand the functional and numerical response functions using a modular approach which is readily integrated into existing models. We divide the trophic interaction between predator and prey into eight steps: (1) search, (2) prey detection, (3) attack decision, (4) pursuit, (5) subjugation, (6) ingestion, (7) digestion, and (8) nutrient allocation. Formulating this as a modular functional-response function, we build a general dynamical model where trophic interactions can be explicitly parameterized for multiple traits and environmental factors. We then concretize this approach by outlining how a specific community can be modeled by selecting key modules (steps) and parameterizing them for relevant factors. This we exemplify for a community of terrestrial arthropods using empirical data on body size and temperature responses. With species interactions at the core of community dynamics, our modular approach allows for quantification and comparisons of the importance of different steps, traits, and abiotic factors across ecosystems and trophic interaction types, and provides a powerful tool for trait-based prediction of food-web structure and dynamics.

The exchange of material and individuals between neighbouring food webs is ubiquitous, but theory remains scarce for how such spatial flows affect ecosystem functioning. Here, we combine dynamic food web models with models for nutrient recycling to explore how animal foraging movement, between habitats of contrasting fertility and plant diversity, affects species persistence as well as the stocks and fluxes of biomass, detritus, and nutrients. We found that the net flow of consumers went from the habitat of higher fertility or diversity to the habitat with lower fertility or diversity, boosting ecosystem functioning in the receiving habitat. By explicitly modelling stocks and interconnecting fluxes we could replicate empirically observed effects of spatial subsidies, such as biomass distribution shifts and effect attenuation, and elucidate the underlying mechanisms. Our results demonstrate how foraging movement can drastically alter local functioning. Overall, our approach offers a start toward understanding ecosystem function in human-dominated landscapes.

To associate specimens identified by molecular characters to other biological knowledge, we need reference sequences annotated by Linnaean taxonomy. In this paper, we 1) report the creation of a comprehensive reference library of DNA barcodes for the arthropods of an entire country (Finland), 2) publish this library, and 3) deliver a new identification tool based on this resource. The reference library contains mtDNA COI barcodes for 11,275 (43%) of 26,437 arthropod species known from Finland, including 10,811 (45%) of 23,956 insect species. To quantify the improvement in identification accuracy enabled by the current reference library, we ran 1,000 Finnish insect and spider species through the Barcode of Life Data system (BOLD) identification engine. Of these, 91% were correctly assigned to a unique species when compared to the new reference library alone, 85% were correctly identified when compared to BOLD with the new material included, and 75% with the new material excluded. To capitalize on this resource, we used the new reference material to train a probabilistic taxonomic assignment tool, FinPROTAX, scoring high success. For the full-length barcode region, the accuracy of taxonomic assignments at the level of classes, orders, families, subfamilies, tribes, genera, and species reached 99.9%, 99.9%, 99.8%, 99.7%, 99.4%, 96.8%, and 88.5%, respectively. The FinBOL arthropod reference library and FinPROTAX are available through the Finnish Biodiversity Information Facility (www.laji.fi). Overall, the FinBOL investment represents a massive capacity-transfer from the taxonomic community of Finland to all sectors of society.

Current climate change is disrupting biotic interactions and eroding biodiversity worldwide. However, species sensitive to drought, high temperatures and climate variability might persist in microclimatic refuges, such as leaf shelters built by arthropods. We conducted a distributed experiment across an 11,790 km latitudinal gradient to explore how the importance of leaf shelters for terrestrial arthropods changes with latitude, elevation and underlying climate. Our analyses revealed leaf shelters to be key facilitative elements for the diversity of arthropods. Predator diversity and overall biomass within shelters increased with local drought and temperature variability, regardless of latitude and elevation. In contrast, shelter usage by herbivores increased with abundance of predators on those same plants and in wetter climates. Projected increase in climatic variability and drought in certain geographic regions is therefore likely to enhance the importance of biotic refuges, especially for predators, in mitigating the impact of climate change on species persistence.