Determinants of cyanobacterial species composition in the splash zone of two Croatian islands

<p>Cyanobacterial communities of the splash zone of two Croatian islands, Veruda and Ugljan, were surveyed. At each island, we studied eight localities with different aspects. From all 336 samples, a total of 42 cyanobacterial species, one green alga, and one red alga were found. In both islands <i>Hyella</i> spp. and <i>Gloeocapsopsis crepidinum</i> dominated and <i>Entophysalis deusta, Solentia</i> spp., <i>Kyrtuthrix dalmatica</i> and <i>Mastigocoleus testarum</i> were found frequently. Multivariate statistical analysis of species composition shows that the vertical gradient is the strongest determinant of species composition and that there are statistically significant but not very pronounced differences in species composition between the two islands. Species composition among individual sites within islands differed slightly, and between localities decreased rather slowly with the distance of individual samples (i.e. the similarity distance decay was very slow), showing that even close samples can have quite different species composition. The species accumulation curves do not reach their asymptote, indicating that many samples are needed to reasonably cover the species richness of a site. This study highlights the importance of in-depth species counts and high density sampling along vertical gradients for satisfactory cyanobacterial community assessments in marine coastal splash zones.</p

Sample-based rarefaction curves of the number of ant species in trees.

<p>Ant species richness (a) in 0.32 ha plot of primary and (b) in 0.32 ha plot of secondary rainforest. The curves for the numbers of species observed are shown separately for ant nests, foraging ant species and for both groups combined respectively. Overall diversity of ants in each forest plot is estimated using Chao 2 (mean ± SD).</p

Cumulative probability of distances to the nearest nest of tree-foraging species.

<p>Curves based on observed nest data (F-N species records) for primary and secondary forest plots are compared to the area given by minimal and maximal values of 100 curves randomly generated by the permutations of the presence-absence matrix of nests in trees (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117853#sec002" target="_blank">Methods</a> for details and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117853#pone.0117853.s007" target="_blank">S3 Table</a> for the data). Cumulative probability of distances between all trees in each forest plot is indicated by dashed lines.</p

Characteristics of vegetation in 0.32 ha plots of primary and secondary rainforest (all trees with DBH ≥ 5 cm).

<p>Characteristics of vegetation in 0.32 ha plots of primary and secondary rainforest (all trees with DBH ≥ 5 cm).</p

Number of ant species per tree in primary and secondary forest plot.

<p>Box-plots show median and mean values per a tree (black line and dot respectively) with 25–75% quartiles and whiskers represent 1.5 interquartile ranges for all species combined (All records), foraging species (F), nesting ant species (N) and species that foraged but did not nest on tree (F-N). Average species richness per tree is significantly higher for F than for N ants in both habitat types (paired t-test, log-transformed data, <i>P</i> < 0.001). See also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117853#pone.0117853.t002" target="_blank">Table 2</a> for the mean and SE values.</p

Abundance of tree-foraging and nesting ant species in each forest plot.

<p>Total individual abundance in % of number of foraging individuals (left column) and of arboreal nests (right column) collected in trees in primary (a) and secondary (b) forest plot. Different color patterns express the proportions of the five most abundant species and of the rest of the species respectively. Invasive species are cross-hatched (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117853#pone.0117853.s005" target="_blank">S1 Table</a> for full species names and their individual abundances).</p

Multivariate analyses of the effect of forest plot (primary and secondary) and tree size traits (DBH, tree height, trunk height, crown height, crown width, total leaves weight; log-transformed data) on ant species composition.

<p>Canonical analysis (CA) and canonical correspondence analysis (CCA) was performed on ant presence-absence data (i.e. number of occupied trees by species) for i) all ant occurrences combined, ii) foraging ant occurrences and iii) arboreal-nesting occurrences. Results are shown for all canonical axes (i.e. all variables) combined and then for each variable tested separately in order of its significance in forward selection (only significant results up to fourth canonical axis shown).</p><p>^aRank of canonical axis and significant variable in forward selection.</p><p>^bCanonical eigenvalue for all axes (total value) and for each axis and corresponding variable separately.</p><p>^cThe per cent variance in species data explained by respective CA and CCA canonical axes.</p><p>^dSignificances of canonical axes assessed via Monte-Carlo permutation (F-ratio value, P < 0.05, 999 runs per analysis).</p><p>^eThe per cent variance in species data explained by variables across all and by individual CA axes.</p><p>Multivariate analyses of the effect of forest plot (primary and secondary) and tree size traits (DBH, tree height, trunk height, crown height, crown width, total leaves weight; log-transformed data) on ant species composition.</p

Probability of nesting of tree-foraging species in surrounding trees.

<p>Mean nesting probability of ant foragers (F-N species records) is calculated with increasing maximum distance from tree where they forage (but not nest) in the primary and secondary forest plot. Means are shown for observed data and 100 random permutations of the presence-absence matrix of nests, including 95% confidence interval envelopes (2.5% to 97.5 quantile range) of the model (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117853#sec002" target="_blank">Methods</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117853#pone.0117853.s009" target="_blank">S1 Text</a> for details on calculation).</p

Characteristics of arboreal ant communities in 0.32 ha plots of primary and secondary rainforest (in trees with DBH ≥ 5 cm).

<p>Different capital letters within each column indicate a significant difference between primary and secondary forest plots (mean ± SE, ANOVA on log-transformed data, <i>P</i> < 0.05). F-N indicates values for arboricolous ant species that foraged and did not nest on tree (species with ≥ 1 nest per plot included).</p><p>Characteristics of arboreal ant communities in 0.32 ha plots of primary and secondary rainforest (in trees with DBH ≥ 5 cm).</p

Ordination diagram of ant species composition in studied trees.

<p>Ordination based on CCA analysis (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117853#pone.0117853.t003" target="_blank">Table 3</a> for the significance and % of variance related to the ordination canonical axes). Variation of ant community composition (all presence—absence records of ant species in trees) is related to the explanatory variables Forest plot on the first axis (primary and secondary rainforest) and Tree size on the second axis (DBH after logarithmic transformation). Solid symbols indicate tree-nesting species and empty symbols the species found only foraging in trees (in green: occurrence of the species in primary forest, in blue: secondary forest, in black: both forests). The enlarged symbols with species abbreviations refer to the most common ant species (i.e. present in > 20 trees, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117853#pone.0117853.s005" target="_blank">S1 Table</a> for their full names).</p