The food web in a subterranean ecosystem is driven by intraguild predation

Behavioural drivers of ecotone exploitation: activity of groundwater animals in spring

Abstract

Border habitats such as interfaces and ecotones are promising research targets being likely areas of high species richness and genetic and phenotypic diversity. Springs are intriguing habitats exploited by both subterranean and surface species. For subterranean species, springs can provide higher trophic resources but can be risky in terms of predation and UV radiation, while for surface species, springs can be safer but less productive environments. We coupled field surveys and laboratory experiments to understand how predation risk and physical constraints, like light occurrence, affect spring exploitation by both a subterranean (Niphargus thuringius) and a surface crustacean amphipod species (Echinogammarus stammeri). From March to May 2021, we surveyed multiple springs and evaluated the activity (both during day and night) of the amphipods and of their predators. Furthermore, in a subterranean laboratory, we reared 80 N. thuringius and 80 E. stammeri under safe and risky conditions with both constant darkness and diel light variation assessing their activity and survival. Risky conditions were represented by the occurrence of meso-predators alone or coupled with the presence of a top predator. In the field, N. thuringius activity was negatively related to the density of predators, while laboratory experiments revealed a main role played by light treatments and night period. E. stammeri activity in the field was higher close to surface while in laboratory conditions decreased during time. In laboratory conditions, predation risk negatively affected survival of both amphipods. Our findings reveal that physical constraints play a key role in affecting the exploitation of ecotones and can mediate antipredator responses, thus providing selective pressures for the exploitation of border environments.

Significance statement

Understanding environmental pressures acting on ecotones is a key point to verify if new adaptations may occur at the border between two distinct habitats. Using both field and laboratory approaches, we show that, in springs, the behaviour of subterranean invertebrates is affected by surface physical constraints which can mediate the effects of predation risk. Behavioural strategies to avoid predation, such as nocturnal activity, may promote spring ecotone exploitation by groundwater animals, such as amphipod crustaceans.

Species conservation profiles of the endemic spiders Troglohyphantes (Araneae, Linyphiidae) from the Alps and the north-western Dinarides

Background

The genus Troglohyphantes Joseph, 1882 (Araneae, Linyphiidae) includes 131 species, mainly distributed across the main European mountain ranges. The Alps and the north-western Dinarides account for 66 species, most of them showing narrow or even point-like distributions. The majority of Troglohyphantes spiders dwell in subterranean habitats including caves, mines, soil litter, rocky debris and other moist and shaded retreats. Despite being intensively studied from taxonomic, ecological and biogeographic standpoints, knowledge on the status of conservation and on the potential risk of extinction of these spiders is lagging. To date, only three species have been included in the global IUCN Red List, but their status has not been updated ever since their last assessment in 1996. The aim of this contribution is to assess the Alpine and north-western Dinaric species of the genus Troglohyphantes and to re-assess the species previously evaluated, according to the last version of the IUCN Red List Categories and Criteria.

New information

Amongst the 66 species here considered, 62 had sufficient data to allow the quantification of their Extent Of Occurrence (EOO) and Area Of Occupancy (AOO). Most of the species have a narrow distribution range, with an estimated EOO < 20,000 km² and AOO < 2,000 km², meeting the thresholds for the inclusion in the threatened categories. Five species have a more widespread distribution (EOO > 20,000 km²), extending across multiple countries. The quality of the data on distribution of four species was not sufficient to provide a reliable estimation of the distribution range.A continuing decline in EOO, AOO and habitat quality was inferred for 30 species. The majority of them were subterranean specialised species, with a reduced thermal tolerance and a low dispersal ability. Accordingly, changes in subterranean microclimatic conditions due to climate change represent a major threat for these species. Land-use change and habitat alteration were identified as additional relevant threats for several species.A considerable proportion of the species here assessed was found in protected areas and in sites of the Natura 2000 network. In addition, 14 species are formally protected by national and sub-national legislation. At present, 25 species are listed in the regional Red Lists.Long-term monitoring programmes, management plans for both the species and their habitats, expansion of the extant protected areas and designation of new ones, should be considered as the most effective approaches to species conservation.

A trait database and updated checklist for European subterranean spiders

Species traits are an essential currency in ecology, evolution, biogeography, and conservation biology. However, trait databases are unavailable for most organisms, especially those living in difficult-to-access habitats such as caves and other subterranean ecosystems. We compiled an expert-curated trait database for subterranean spiders in Europe using both literature data (including grey literature published in many different languages) and direct morphological measurements whenever specimens were available to us. We started by updating the checklist of European subterranean spiders, now including 512 species across 20 families, of which at least 192 have been found uniquely in subterranean habitats. For each of these species, we compiled 64 traits. The trait database encompasses morphological measures, including several traits related to subterranean adaptation, and ecological traits referring to habitat preference, dispersal, and feeding strategies. By making these data freely available, we open up opportunities for exploring different research questions, from the quantification of functional dimensions of subterranean adaptation to the study of spatial patterns in functional diversity across European caves.

Measurement(s)	morphological trait • ecological trait
Technology Type(s)	literature extraction • observation
Sample Characteristic - Organism	Agelenidae • Amaurobiidae • Anapidae • Cybaeidae • Dysderidae • Hahniidae • Leptonetidae • Linyphiidae • Liocranidae • Mysmenidae • Nesticidae • Pholcidae • Pimoidae • Segestriidae • Sicariidae • Sparassidae • Symphytognathidae • Telemidae • Tetragnathidae • Theridiidae
Sample Characteristic - Environment	caves • subterranean habitats
Sample Characteristic - Location	Europe

Observations on the habitat and feeding behaviour of the hypogean genus Eukoenenia (Palpigradi, Eukoeneniidae) in the Western Italian Alps

The order Palpigradi includes species characterized by millimetric size and a characteristic flagellum with bristles at the end of the opisthosoma. They represent one of the less well-known and obscure arachnid orders. In this paper, observations were made on the ecology and feeding behavior of species belonging to the genus Eukoenenia Börner, 1901, from the Western Italian Alps. Direct observations and photographic documentation of 141 individuals in their cave habitat, allowed the recording of data on the physical and trophic conditions such as the presence/absence of trophic resources, temperature and relative humidity, of the underground environment in which they were found. Results showed that the species of this taxon are not as rare as previously reported and that their presence is mainly influenced by temperature, relative humidity, trophic resources and the presence of two speleothems: rimstone dams and rafts. The combination of our observations as well as data previously published highlights that the taxon can have predatory and saprophagous feeding behavior depending on the availability of the food resources. This work represents the starting point for a further investigation of the taxon.

Inferring predator-prey interaction in the subterranean environment: a case study from Dinaric caves

Predator–prey interactions are among the most important biotic interactions shaping ecological communities and driving the evolution of defensive traits. These interactions and their effects on species received little attention in extreme and remote environments, where possibilities for direct observations and experimental manipulation of the animals are limited. In this paper, we study such type of environment, namely caves of the Dinarides (Europe), combining spatial and phylogenetic methods. We focused on several species of Niphargus amphipods living in phreatic lakes, as some of them use the dorsal spines as putative morphological defensive traits. We predicted that these spines represent a defense strategy against the olm (Proteus anguinus), a top predator species in the subterranean waters. We tested for spatial overlap of the olm and Niphargus species and showed that spined species live in closer proximity to and co-occur more frequently with the olm than non-spined species. Modeling of the evolution of the spines onto Niphargus phylogeny implies coevolution of this trait in the presence of olm. We conclude that these spines likely evolved as defensive traits in a predator–prey arms race. Combining multiple analyses, we provide an example for a methodological framework to assess predator–prey interactions when in-situ or laboratory observations are not possible.