Influence of the yellow-legged gull on soil, composition and organisation of plant communities on some small Islands of Algeria

Impacts of the yellow-legged Gull on soil chemistry, composition and organization of island plant communities in Algeria were hitherto unknown. Statistical correlations (linear regression, partial Mantel test, general linear model mixed and Canonical correspondence analysis) among island flora, physiographic variables and edaphic parameters including densities of the yellow-legged Gull were tested. Floristic similarity was evaluated by the Sørensen index. The linear regressions revealed that densities of the yellow-legged Gull affected soil nitrogen and that floristic diversity was dependent on the surface area of individual islands. To verify floristic similarities among the islands by accounting for spatial autocorrelation we used the partial Mantel test. Analysis of the island flora response to environmental disturbances using a GLMM showed that the floristic composition was dependent on the density of the yellow-legged Gulls, the nitrogen content of the soil and the distance from the sea. In addition, four distinct plant groups were identified by CCA that accorded with low, intermediate and high levels of disturbance leading to our conclusion that this provided a bioindicative value of the state of the island environments in this study.