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Aim: To investigate the species-area relationship (SAR) of plants on very small islands, to examine the effect of other factors on species richness, and to check for a possible Small Island Effect (SIE). Location: The study used data on the floral composition of 86 very small islands (all < 0.050 km 2) of the Aegean archipelago (Greece). Methods: We used standard techniques for linear and nonlinear regression in order to check several models of the SAR, and stepwise multiple regression to check for the effects of factors other than area on species richness ('habitat diversity', elevation, and distance from nearest large island), as well as the performance of the Choros model. We also checked for the SAR of certain taxonomic and ecological plant groups that are of special importance in eastern Mediterranean islands, such as halophytes, therophytes, Leguminosae and Gramineae. We used one-way anova to check for differences in richness between grazed and non-grazed islands, and we explored possible effects of nesting seabirds on the islands' flora. Results: Area explained a small percentage of total species richness variance in all cases. The linearized power model of the SAR provided the best fit for the total species list and several subgroups of species, while the semi-log model provided better fits for grazed islands, grasses and therophytes. None of the nonlinear models explained more variance. The slope of the SAR was very high, mainly due to the contribution of non-grazed islands. No significant SIE could be detected. The Choros model explained more variance than all SARs, although a large amount of variance of species richness still remained unexplained. Elevation was found to be the only important factor, other than area, to influence species richness. Habitat diversity did not seem important, although there were serious methodological problems in properly defining it, especially for plants. Grazing was an important factor influencing the flora of small islands. Grazed islands were richer than non-grazed, but the response of their species richness to area was particularly low, indicating decreased floral heterogeneity among islands. We did not detect any important effects of the presence of nesting seabird colonies. Main conclusions: Species richness on small islands may behave idiosyncratically, but this does not always lead to a typical SIE. Plants of Aegean islets conform to the classical Arrhenius model of the SAR, a result mainly due to the contribution of non-grazed islands. At the same time, the factors examined explain a small portion of total variance in species richness, indicating the possible contribution of other, non-standard factors, or even of stochastic effects. The proper definition of habitat diversity as pertaining to the taxon examined in each case is a recurrent problem in such studies. Nevertheless, the combined effect of area and a proxy for environmental heterogeneity is once again superior to area alone in explaining species richness. © 2006 The Authors. 33 1223 1234 Cited By :58

Aim To investigate how plant diversity of whole islands ('gamma') is related to alpha and beta diversity patterns among sampling plots within each island, thus exploring aspects of diversity patterns across scales. Location Nineteen islands of the Aegean Sea, Greece. Methods Plant species were recorded at both the whole-island scale and in small 100m 2 plots on each island. Mean plot species richness was considered as a measure of alpha diversity, and six indices of the 'variation'-type beta diversity were also applied. In addition, we partitioned beta diversity into a 'nestedness' and a 'replacement' component, using the total species richness recorded in all plots of each island as a measure of 'gamma' diversity. We also applied 10 species-area models to predict the total observed richness of each island from accumulated plot species richness. Results Mean alpha diversity was not significantly correlated with the overall island species richness or island area. The range of plot species richness for each island was significantly correlated with both overall species richness and area. Alpha diversity was not correlated with most indices of beta diversity. The majority of beta diversity indices were correlated with whole-island species richness, and this was also true for the 'replacement' component of beta diversity. The rational function model provided the best prediction of observed island species richness, with Monod's and the exponential models following closely. Inaccuracy of predictions was positively correlated with the number of plots and with most indices of beta diversity. Main conclusions Diversity at the broader scale (whole islands) is shaped mainly by variation among small local samples (beta diversity), while local alpha diversity is not a good predictor of species diversity at broader scales. In this system, all results support the crucial role of habitat diversity in determining the species-area relationship. © 2011 Blackwell Publishing Ltd. 39 750 759 Cited By :9

The native flora and a number of environmental factors were recorded for twenty islands in the eastern Aegean archipelago (Greece) in order to study the patterns of native and endemic plant species diversity as well as the effects of environmental factors in shaping these patterns at different levels of endemism. Stepwise regressions were used to test the effects of these factors on species richness of native and especially of endemic plants, at local scales. The performance of the Choros model was also compared with the separate effects of area and habitat diversity using simple linear regressions. The residuals from the species-area functions of native and endemic species were used as indices of relative island richness. Out of the 2238 species and subspecies recorded in total, 302 taxa (13.4%) are endemics (either single island endemics or endemic at a broader scale, namely Aegean, Greek-Aegean, or Anatolian-Aegean). All native, all endemic and Aegean endemic species similarities among islands were assessed and the three matrices were compared with the matrices of among-island geographical distances and island similarities based on components of habitat diversity using Mantel test. Among the factors tested, habitat diversity, of which elevation is another dimension, is the main factor affecting floral richness on east Aegean islands. The patterns exhibited by local endemics, though, are of a more idiosyncratic nature since this factor is the major predictor of species richness of most of the endemics levels (including single island endemics) except the Aegean endemics which are better predicted by elevation. The Choros model does not provide a better prediction of richness than habitat diversity alone. There is a positive correlation between native species similarities and geographical distances among islands, but no correlation between environmental and floral similarities. © 2010 Elsevier Masson SAS. 36 431 437 Cited By :18

Aim: To estimate species turnover of plants on 32 small islands within a 20-year period and to assess possible changes in community composition and properties, such as species richness and factors affecting it, nestedness, species co-occurrence and overall community similarity. Additionally, to assess the possible effects of grazing, gull colonies and fire on turnover values. Location: Thirty-two islets in the eastern Aegean Sea (Greece). Methods: Complete sampling of plants was performed in 1974 and in 1990-94 (mostly in 1994, which was used as the reference year). Species turnover rates were estimated using both per island and per species approaches. Multiple regression was used to evaluate factors affecting species richness. Chi-square tests were applied to compare community composition among sampling periods. The effects of various factors on turnover rates and species richness were examined using one-way anova and ancova. Mann-Whitney tests were applied in order to check for differences between frequencies of occurrence of extinct, immigrant and persisting species. Community nestedness was calculated using bitmatnest and the C-score index for co-occurrence was estimated using EcoSim7. Species similarities among islands in each of the 1974 and 1994 data sets were assessed using Jaccard's index and the two similarity matrices were compared using a Mantel test. Results: Of 391 species recorded on the islets, 334 were present in 1974, 301 in 1994 and 244 were common to both these periods. Species richness in the 1974 and 1994 data sets was significantly correlated with elevation and area, but not with distance from the nearest large island. Richness was positively affected by grazing, but not by fire or gull colonies. The slopes of species-area and species-elevation regressions were almost identical in 1974 and 1994. Mean relative turnover was 2.06 (species per islet) and 3.26 (islets per species). Turnover was not correlated with area, elevation or distance from the nearest large island. Nestedness and co-occurrence levels were very similar. Tables of islet by islet floral similarity (Jaccard's index) did not differ between the 1974 and 1994 data sets. Main conclusions: The turnover rates found are among the highest recorded for plants at the same time the islet communities exhibit notable stability in overall properties. Our results provide evidence for rapid shifts in species number that may nonetheless be considered as equilibrial dynamics, as these islets are able to respond rapidly to environmental change and disturbance. Human activities, notably the application of grazing, have a significant complicating effect on community dynamics, enhancing observed turnover rates. © 2007 The Authors. 35 1049 1061 Cited By :19