High species turnover and low intraspecific trait variation in endemic and non-endemic plant species assemblages on an oceanic island

Questions Both species turnover and intraspecific trait variation can affect plant assemblage dynamics along environmental gradients. Here, we asked how community assemblage patterns in relation to species turnover and intraspecific variation differ between endemic and non-endemic species. We hypothesized that endemic species show lower intraspecific variation than non-endemic species because they tend to have high rates of in situ speciation, whereas non-endemic species are expected to have a larger gene pool and higher phenotypic plasticity. Location La Palma, Canary Islands. Methods We established 44 sampling sites along a directional gradient of precipitation, heat load, soil nitrogen, phosphorus and pH. Along this gradient, we estimated species abundances and measured three traits (plant height, leaf area and leaf thickness) on perennial endemic and non-endemic plant species. In total, we recorded traits for 1,223 plant individuals of 43 species. Subsequently, we calculated community-weighted mean traits to measure the relative contribution of species turnover, intraspecific variation and their covariation along the analysed gradient. Results The contribution of intraspecific variation to total variation was similar in endemic and non-endemic assemblages. For plant height, intraspecific variation explained roughly as much variation as species turnover. For leaf area and leaf thickness, intraspecific variation explained almost no variation. Species turnover effects mainly drove trait responses along the environmental gradient, but intraspecific variation was important for responses in leaf area to precipitation. Conclusions Despite their distinct evolutionary history, endemic and non-endemic plant assemblages show similar patterns in species turnover and intraspecific variation. Our results indicate that species turnover is the main component of trait variation in the underlying study system. However, intraspecific variation can increase individual species’ fitness in response to precipitation. Overall, our study challenges the theory that intraspecific trait variation is more important for the establishment of non-endemic species compared with endemic species.publishedVersio

High species turnover and low intraspecific trait variation in endemic and non-endemic plant species assemblages on an oceanic island

Questions: Both species turnover and intraspecific trait variation can affect plant assemblage dynamics along environmental gradients. Here, we asked how community assemblage patterns in relation to species turnover and intraspecific variation differ between endemic and non-endemic species. We hypothesized that endemic species show lower intraspecific variation than non-endemic species because they tend to have high rates of in situ speciation, whereas non-endemic species are expected to have a larger gene pool and higher phenotypic plasticity. Location: La Palma, Canary Islands. Methods: We established 44 sampling sites along a directional gradient of precipitation, heat load, soil nitrogen, phosphorus and pH. Along this gradient, we estimated species abundances and measured three traits (plant height, leaf area and leaf thickness) on perennial endemic and non-endemic plant species. In total, we recorded traits for 1,223 plant individuals of 43 species. Subsequently, we calculated community-weighted mean traits to measure the relative contribution of species turnover, intraspecific variation and their covariation along the analysed gradient. Results: The contribution of intraspecific variation to total variation was similar in endemic and non-endemic assemblages. For plant height, intraspecific variation explained roughly as much variation as species turnover. For leaf area and leaf thickness, intraspecific variation explained almost no variation. Species turnover effects mainly drove trait responses along the environmental gradient, but intraspecific variation was important for responses in leaf area to precipitation. Conclusions: Despite their distinct evolutionary history, endemic and non-endemic plant assemblages show similar patterns in species turnover and intraspecific variation. Our results indicate that species turnover is the main component of trait variation in the underlying study system. However, intraspecific variation can increase individual species’ fitness in response to precipitation. Overall, our study challenges the theory that intraspecific trait variation is more important for the establishment of non-endemic species compared with endemic species

Do image resolution and classifier choice impact island biogeographical parameters of terrestrial islands?

Island biogeography provides concepts for conservation management as fragmented habitats are comparable to ocean islands. Remote sensing can help to extract terrestrial habitat islands on the landscape scale. However, little is known about the effects of image resolution and classification algorithms on resulting island size and related parameters. We study the combined effect of three image resolutions (2, 10, and 30 m) and three classification algorithms (Artificial Neural Network, Random Forest, Support Vector Machine) by extracting quartz islands from WorldView‐2 imagery using image segmentation. We compared four island parameters (i.e., area, distance, shape index, and perimeter–area ratio between resolutions and classifiers). We found that in all cases, image resolution and classification algorithms had a strong effect. However, image resolution was more important for area and shape. Artificial Neural Network always provided the best performance as a classifier (OA: 0.880, kappa: 0.801, F1: 0.912). Hence, conservation strategies could lead to different results when different pattern extraction strategies are applied. Future studies which aim at extracting terrestrial habitat islands from image datasets should aim for the highest possible resolution and compare the outcomes of different classifiers to ensure the best possible results.Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165