DOI: 10.5061/dryad.km044
title: Data from: Habitat niche breadth predicts invasiveness in solitary ascidians

description: A major focus of invasion biology is understanding the traits associated
 with introduction success. Most studies assess these traits in the invaded
 region, while only few compare non-indigenous species to the pool of
 potential invaders in their native region. We focused on the niche-breadth
 hypothesis, commonly evoked but seldom tested, which states that
 generalist species are more likely to become introduced since they are
 capable of thriving under a wide set of conditions. Based on the massive
 introduction of tropical species into the Mediterranean via the Suez Canal
 (Lessepsian migration), we defined ascidians in the Red Sea as the pool of
 potential invaders. We constructed unique settlement plates, each
 representing six different niches, to assess ascidian niche breadth, and
 deployed them in similar habitats in the native and invaded regions. For
 each species found on plates, we evaluated its abundance, relative
 abundance across successional stages and niche breadth, and then compared
 (1)species in the Red Sea known to have been introduced into the
 Mediterranean (Lessepsian species) and those not known from the
 Mediterranean (non-Lessepsian); and (2)non-indigenous and indigenous
 species in the Mediterranean. Lessepsian ascidians identified on plates in
 the Red Sea demonstrated wider niche breadth than non-Lessepsian
 ascidians, supporting the niche-breadth hypothesis within the native
 region. No differences were found between Lessepsian and non-Lessepsian
 species in species abundance and successional stages. In the
 Mediterranean, non-indigenous species numerically dominated the settlement
 plates. This precluded robust comparisons of niche breadth between
 non-indigenous and indigenous species in the invaded region. In
 conclusion, using Red Sea ascidians as the pool of potential invaders, we
 found clear evidence supporting the niche-breadth hypothesis in the native
 region. We suggest that such patterns may often be obscured when
 conducting trait-based studies in the invaded regions alone. Our findings
 indicate that quantifying the niche breadth of species in their native
 regions will improve estimates of invasiveness potential.
description: Solitary ascidians found
 on complex settlement plates in the Red Sea and the
 MediterraneanWe constructed unique
 settlement plates, each representing six different niches, to assess
 ascidian niche breadth, and deployed them in similar habitats in the Red
 Sea and the Mediterranean. Settlement plate design: To estimate and
 compare habitat niche breadth between species, we designed settlement
 plates each representing different niches, based on six substrate squares
 measures 10 x 10 cm as our basic units. The base of the plate was built
 from stainless steel, and the substrate squares were glued to the base. We
 used three substrate types within two current /light regimes to allocate
 six different "niches” to each settlement plate, with total
 measurement of 30 x 20 cm. The three substrate types were constructed from
 three materials: cement with sea shells, non-glazed ceramic and recycled
 plastic. Since substrate is a major factor for fouling species, we
 selected three materials that differ substantially from each other:
 plastic is smooth, the non-glazed ceramic is rough but homogenous, and the
 cement with sea shells is complex and heterogeneous. The two current and
 light regimes were achieved by placing the plates facing the pillars, and
 leaving the upper part of the plate open from three directions (from above
 and from either side) while the lower part remained open from the bottom
 only and was thus dark and with restricted water flow. We were interested
 in the relative patterns across species to these niche differences, and
 hence do not attempt to quantify the exact differences in light and flow
 between the upper and lower sections. Nevertheless, light measurements
 confirm the lower side was ~10 time darker than the upper side. We used
 all possible permutations (36 in total) of substrate type ordering within
 each current and light regime treatment in constructing the settlement
 plates. Study sites: The same experimental designs were used in the
 eastern Mediterranean Sea and northern Red Sea to facilitate direct
 comparisons. In the Mediterranean, the settlement plates were deployed on
 three pillars of the Israel Electric Company pier (32°28′ N 34°53 E), and
 in the Red Sea, on three pillars of the Israeli oil port (29°31′ N 34°56′
 E), with minimal distance of 10 meters between pillars. At both sites, the
 plates were deployed at about 15 meters depth, with the seabed at 20
 meters, in order to avoid any bottom effects such as sedimentation. The
 depth of 15 meters was chosen in order to minimize disturbance to the
 experiment by the strong winter storms, while still providing sufficient
 underwater work time when using scuba. As public entrance to both sites is
 prohibited, the experiment was subjected to minimal human disturbance.
 Pillars at both sites are located in the open sea (as opposed to closed
 harbors) and are &gt;30 years old, therefore the fauna found on them
 represent a climax community. Study design: The experiment lasted one
 year, from February 2014 to February 2015. For analyses, we combined two
 types of plates, seasonal and full-year. We deployed 15 full-year plates
 at each site and these remained undisturbed for the entire year of the
 experiment. In addition, 10 seasonal plates were replaced every three
 months, totaling 40 seasonal settlement plates at each site. At the end of
 each experiment, the settlement plates were removed and taken to the lab
 for taxonomic identification (using Nikon SMZ18 stereomicroscope and
 dissection tools). Solitary ascidians were counted and identified to
 species level where possible (649 out of 658 individuals). In addition, we
 took monthly underwater photos of all settlement plates. Plates were
 photographed from the exact same distance and angle using a custom-made
 tripod. These photos were used in order to identify individuals that were
 present on the plates during the experiment but did not survive to the
 point of plate removal, in order to increase sample size for the niche
 breadth calculations. Unfortunately, only four individuals were added
 using these photos. We categorized the species found in the Red Sea as
 Lessepsian (species that are known to establish populations in the
 Mediterranean) or non-Lessepsian species (species that have not yet been
 recorded in the Mediterranean, i.e., non-invaders). In the Mediterranean
 we categorized the species as non-indigenous or indigenous. We included
 Styela plicata with the indigenous species of the Mediterranean for
 analysis although it possibly invaded from the Atlantic Ocean (Pineda et
 al., 2011; Maltagliati et al., 2015) as it is clearly not of tropical
 origin, unlike the rest of the non-indigenous species, and has been found
 in the Mediterranean for at least a century (de Barros et al., 2009). Data
 file structure: plate – id for each settlement plate (reminder: the six
 different habitats described above are within each plate). site –
 Mediterranean or Red Sea species type – ‘Lessepsian’ and ‘non Lessepsian’
 for the species found on plates in the Red Sea site. ‘indigenous’ and
 ‘non-indigenous’ for species found on plates in the Mediterranean site.
 season – ‘spring’, ‘summer’, ‘autumn’, ‘winter’ for the seasonality
 plates. ‘long term’ for the long term (full year) plates. And ‘added by
 pictures’ for three records of P. nigra we added in order to increase its
 sample size for our niche breadth calculations. niche – ‘su’ for
 shells-up, ‘cu’ for ceramics-up, ‘pu’ for plastic-up, ‘sd’ for shells down
 etc… substrate – shells, ceramics or plastic light – up – upper part of
 the plate or down – the lower part of the plate. number of individuals –
 the actual data – number of individuals foundSolitaryAscdians_DryAdVersion.csv