DOI: 10.5061/dryad.jwstqjqhw
title: Data from: Invertebrate diversity in groundwater filled lava caves is influenced by both neutral and niche-based processes

description: Aim: Understanding which factors shape and maintain biodiversity is
 essential to understand how ecosystems respond to crises. Biodiversity in
 ecological communities is a result of the interaction of various factors
 which can be classified as neutral or niche-based. The importance of these
 processes has been debated, but many scientists believe that both
 processes are important. Here we examined the importance of neutral vs.
 niche-based factors for shaping invertebrate communities. We hypothesized
 that if neutral processes are the main drivers of community structure we
 would not see any clear relationship between the structure of community
 and ecological factors. If niche-based processes are important we should
 see clear relationships between community structure and variation in
 ecological variables. Location: Groundwater-filled lava caves near Lake
 Mývatn, Iceland. Methods: We collected various ecological variables from
 these caves. Invertebrate communities were collected on the hard bottom
 using stone scrubbing and from epibenthic traps. Results: Both communities
 were species-poor, with low densities of invertebrates, showing the
 resource-limited and oligotrophic nature of these systems. Unusually for
 Icelandic freshwater ecosystems, the benthic communities were not
 dominated by Chironomidae (Diptera) larvae, but rather by crustaceans,
 mainly Cladocera. The epibenthic communities were not shaped by
 environmental variables, suggesting that they may be structured primarily
 by neutral processes. The benthic communities were shaped by the
 availability of energy, and to some extent pH, suggesting that niche-based
 processes were important drivers of community structure, although neutral
 processes may still be relevant.  Main conclusions: The results
 suggest that both processes are important for invertebrate communities in
 freshwater, and research should focus on understanding both of these
 processes. The ponds we studied are representative of a number of
 freshwater ecosystems that are extremely vulnerable to human disturbance,
 making it even more important to understand how their biodiversity is
 shaped and maintained.
description: The following environmental variables in the caves were measured
 in June and August from 2013 – 2019: temperature (°C), oxygen saturation
 (%), pH, and specific conductivity (µS/cm), using a multiprobe sonde
 (Hydrolab DS5 (46711) Water Quality Probes). From a digital map we
 estimated the minimal distance of each cave from the lake (in meters) and
 key physical characteristics of the caves, such as the combined vertical
 area of all openings and the size of the cave pond exposed to air (both in
 m<sup>2</sup>), in some caves the roof was overhanging, so the
 pond exposed to air value was negative. Based on this, we estimated the
 area available for photosynthesis by adding half the vertical area of
 openings to the size of the cave pond exposed to air. In each cave, we
 placed fall-in traps within 20 cm of the shore to collect external inputs
 into the pond. The main objective of the traps was to estimate food
 availability for Arctic charr for another study. The traps were built of
 clear buckets (Unipak model 5141, 2300 ml, 196 cm<sup>2</sup>
 surface area) placed in a bracket and tied fast with a zip-tag about 10 cm
 above the water surface. In each bucket, we mixed propylene glycol (30%)
 with water and a few drops of aroma free soap to reduce water tension. The
 number of traps differed among the caves, depending on the size of the
 cave and the number of cave openings, but the minimum number of fall-in
 traps per cave was two. However, not all traps survived the conditions
 during the winter, so on some occasions no trap data exist for a given
 sampling event. The traps were collected in June and August each year, by
 removing the old trap and replacing it with a new one. The content of the
 fall-in trap was sieved through a 125 µm sieve and preserved in 70%
 ethanol for at least 6 months. The fixed organic material of animal origin
 was then separated from obvious plant material, placed in a measuring cup,
 and allowed to sink for 15 – 30 min, and measured to the nearest mL. We
 thus obtained an estimation of gross volume of external organic animal
 material per cave. All invertebrate samples were
 collected in June 2014. Benthic invertebrates were collected from two to
 three stones along the shore of 16 caves, at a depth of 10 – 30 cm. Stones
 were carefully removed from the bottom and placed immediately in a 10L
 bucket containing water from the cave. They were then brushed, using a
 soft dishwasher brush. The stone was rinsed with clean filtered (125 µm
 sieve) water, placed as they were lying in the cave and photographed with
 a mm scale for size reference. This allowed us to estimate standardised
 densities (#/100 cm<sup>2</sup>) of invertebrates across
 stones and caves. The water and invertebrates retained in the bucket were
 sieved through a 125 µm sieve and stored in 70% ethanol until further
 analysis. Epibenthic invertebrates were collected from
 18 caves using crustacean traps modified from Örnólfsdóttir &
 Einarsson (2004). The traps were haphazardly laid within 2 m from the
 shore at the opening of each cave. The number of traps per cave varied
 from two to six depending on the size of the cave and the size and number
 of openings.  The traps were collected after 12 hours, and their content
 filtered through a 63 µm sieve and stored in 70% ethanol until further
 analysis.
description: # Cave invertebrates and environment - 2014
 [https://doi.org/10.5061/dryad.jwstqjqhw](https://doi.org/10.5061/dryad.jwstqjqhw) Here is data from research on freshwater invertebrates from benthic and epibenthic samples, and ecological measurements. These samples originate in freshwater ponds in lava caves around lake Mývatn SE Iceland. In total 18 caves were sampled, but the number differ though between the benthic and epibenthic samples ## Description of the data and file structure We have uploaded the following files: Env2. csv - Here is the environmental data across the different caves. Cave is the identifier of the cave. Area is the area the cave is located, there are two areas Haganes (H) and Vindbelgur (V). Temp, is temperature in °C, pH is a measure of pH, Cond, is a measure of conductivity in microsimens, Oxygen, is oxygen % of the water, Photosynthesis is an indicator of area available for photosynthesis, Distance, is the distance of the cave from Lake Mývatn, organic matter, is an estimation of the gross volume of external organic animal material falling in to the cave. Stonedensities_2014June.csv - This is the main datafile regarding the density of invertebrates from stone scrubbing. Sample indicates which stone the sample came from. Year, month and day are always the same, this is then followed by a list of taxa, Some of the names have been shortened - Chaet (Chaetogaster), Chiro (Choronomidae sp.), Ortho (Orthocladiinae), Tanyp (Tanypodinae), Tanyt (Tanytarsini), Clado (Cladocera sp), C.spha (*Chyodorus sphaericus*), Anana (*Alonella nana*), Aharp (*Acroperus harpae*), Mhirs (*Macrothrix hirsuticornis*), Isord (*Ilyocryptus sordidus*), Scryst (*Sida crystallina*), Cole (Coleoptera), Colle (Collembola), Cope (Copepoda), Nema (Nematoda), Ostra (Ostracoda), Oligo (Oligochaeta), Pleco (Plecoptera), Tardi (Tardigrada), Tricho (Trichoptera). Fly_traps.csv - The main datafile for the epibenthic traps. This follows the same structure as the stone dataset. Density.csv - Here are information on the density (Number/100 cm2) and the total number of taxa found on stones in the caves alpha_trap.csv - Here we have mean numbers for the number of invertebrates (mean_trap_innr), mean diversity (mean_trap_div) and the number of taxa Meannumber). ## Sharing/Access information At the moment the data is not for sharing, but only for review purpose. The data will be shared once published