Worldwide effects of non-native species on species-area relationships.

Non-native species have invaded most parts of the world, and the invasion process is expected to continue and accelerate. Because many invading non-native species are likely to become permanent inhabitants, future consideration of species-area relationships (SARs) should account for non-native species, either separately or jointly with native species. If non-native species occupy unused niches and space in invaded areas and extinction rate of native species remains low (especially for plants), the resultant SARs (with both native and non-native species) will likely be stronger. We used published and newly compiled data (35 data sets worldwide) to examine how species invasions affect SARs across selected taxonomic groups and diverse ecosystems around the world. We first examined the SARs for native, non-native, and all species. We then investigated with linear regression analyses and paired or unpaired t tests how degree of invasion (proportion of non-native species) affected postinvasion SARs. Postinvasion SARs for all species (native plus non-native) became significantly stronger as degree of invasion increased (r2 = 0.31, p = 0.0006), thus, reshaping SARs worldwide. Overall, native species still showed stronger and less variable SARs. Also, slopes for native species were steeper than for non-native species (0.298 vs. 0.153). There were some differences among non-native taxonomic groups in filling new niches (especially for birds) and between islands and mainland ecosystems. We also found evidence that invasions may increase equilibrial diversity. Study of such changing species-area curves may help determine the probability of future invasions and have practical implications for conservation.

Efectos Globales de las Especies No Nativas sobre las Relaciones Especie-Área Resumen Las especies no nativas han invadido la mayor parte del mundo y se espera que el proceso de invasión continúe y se acelere. Ya que muchas especies invasoras no nativas probablemente se conviertan en habitantes permanentes, la consideración a futuro de las relaciones especie-área (REA) debería considerar a las especies no nativas, ya sea por separado o en conjunto con las especies nativas. Si las especies no nativas ocupan nichos sin usar y el espacio en las áreas invadidas y la tasa de extinción de las especies nativas permanecen bajas (especialmente para las plantas), las REA resultantes (tanto con las especies nativas como las no nativas) probablemente sean más fuertes. Usamos datos publicados y recientemente compilados (35 conjuntos de datos mundiales) para examinar cómo las invasiones de especies afectan a las REA en grupos taxonómicos selectos y en diversos ecosistemas en todo el mundo. Primero examinamos las REA para todas las especies, así como para las nativas y las no nativas. Después investigamos con análisis de regresión lineal y pruebas t emparejadas o no emparejadas cómo afectó el grado de invasión (proporción de la especie no nativa) a las REA post-invasión. Las REA post-invasión para todas las especies (nativas más no nativas) se volvieron significativamente más fuertes conforme incrementó el grado de invasión (r2 = 0.31, p = 0.0006), remodelando así las REA en todo el mundo. En general, las especies nativas todavía mostraron REA más fuertes y menos variables. De igual manera, las pendientes de las especies nativas fueron más pronunciadas para las especies no nativas (0.298 vs. 0.153). Hubo algunas diferencias entre los grupos taxonómicos no nativos al llenar nichos nuevos (especialmente para las aves) y entre las islas y los ecosistemas de tierra firme. También encontramos evidencias de que las invasiones pueden incrementar la diversidad equilibrada. El estudio de dichas curvas cambiantes de relación especie-área podría ayudar a determinar la probabilidad de las futuras invasiones y tener implicaciones prácticas para la conservación.

Changes in taxonomic and phylogenetic diversity in the Anthropocene.

To better understand how ecosystems are changing, a multifaceted approach to measuring biodiversity that considers species richness (SR) and evolutionary history across spatial scales is needed. Here, we compiled 162 datasets for fish, bird and plant assemblages across the globe and measured how taxonomic and phylogenetic diversity changed at different spatial scales (within site α diversity and between sites spatial ß diversity). Biodiversity change is measured from these datasets in three ways: across land use gradients, from species lists, and through sampling of the same locations across two time periods. We found that local SR and phylogenetic α diversity (Faith's PD (phylogenetic diversity)) increased for all taxonomic groups. However, when measured with a metric that is independent of SR (phylogenetic species variation, PSV), phylogenetic α diversity declined for all taxonomic groups. Land use datasets showed declines in SR, Faith's PD and PSV. For all taxonomic groups and data types, spatial taxonomic and phylogenetic ß diversity decreased when measured with Sorensen dissimilarity and phylogenetic Sorensen dissimilarity, respectively, providing strong evidence of global biotic homogenization. The decoupling of α and ß diversity, as well as taxonomic and phylogenetic diversity, highlights the need for a broader perspective on contemporary biodiversity changes. Conservation and environmental policy decisions thus need to consider biodiversity beyond local SR to protect biodiversity and ecosystem services.

Pattern and process of biotic homogenization in the New Pangaea.

Human activities have reorganized the earth's biota resulting in spatially disparate locales becoming more or less similar in species composition over time through the processes of biotic homogenization and biotic differentiation, respectively. Despite mounting evidence suggesting that this process may be widespread in both aquatic and terrestrial systems, past studies have predominantly focused on single taxonomic groups at a single spatial scale. Furthermore, change in pairwise similarity is itself dependent on two distinct processes, spatial turnover in species composition and changes in gradients of species richness. Most past research has failed to disentangle the effect of these two mechanisms on homogenization patterns. Here, we use recent statistical advances and collate a global database of homogenization studies (20 studies, 50 datasets) to provide the first global investigation of the homogenization process across major faunal and floral groups and elucidate the relative role of changes in species richness and turnover. We found evidence of homogenization (change in similarity ranging from -0.02 to 0.09) across nearly all taxonomic groups, spatial extent and grain sizes. Partitioning of change in pairwise similarity shows that overall change in community similarity is driven by changes in species richness. Our results show that biotic homogenization is truly a global phenomenon and put into question many of the ecological mechanisms invoked in previous studies to explain patterns of homogenization.

Land snail dispersal, abundance and diversity on green roofs.

We present the first major systematic study of land snail diversity on green roofs. We surveyed 27 green roofs and the adjacent ground habitat in six major cities in the southeastern United States. We found a total of 18 species of land snails, with three considered to be non-native or invasive species. The majority of land snails encountered in surveys are widespread, generalist species, typically adapted to open habitats. Twelve of the land snails encountered are "greenhouse" species that are very commonly transported via the horticultural trade. Therefore, we infer that at least some land snail species are introduced to green roofs via initial green roof installation and associated landscaping. The major determinants of snail species richness and abundance are the size of each roof and the quality of green roof maintenance regime.

The botanist effect revisited: plant species richness, county area, and human population size in the United States.

The "botanist effect" is thought to be the reason for higher plant species richness in areas where botanists are disproportionately present as an artefactual consequence of a more thorough sampling. We examined whether this was the case for U.S. counties. We collated the number of species of vascular plants, human population size, and the area of U.S. counties. Controlling for spatial autocorrelation and county area, plant species richness increased with human population size and density in counties with and without universities and/or botanical gardens, with no significant differences in the relation between the two subsets. This is consistent with previous findings and further evidence of a broad-scale positive correlation between species richness and human population presence, which has important consequences for the experience of nature by inhabitants of densely populated regions. Combined with the many reports of a negative correlation between the two variables at a local scale, the positive relation between plant species richness in U.S. counties and human population presence stresses the need for the conservation of seminatural areas in urbanized ecosystems and for the containment of urban and suburban sprawl.

TITANOTHERE ALLOMETRY, HETEROCHRONY, AND BIOMECHANICS: REVISING AN EVOLUTIONARY CLASSIC.

A reanalysis of Osborn's titanothere data indicates that extrapolative growth of a constant allometric relationship alone ("hypermorphosis") does not account for the trend toward body and horn size increase. Empirically, we also observe possible positive changes in the y-intercept ("predisplacement" or early onset of development), and possibly, changes in the slope ("acceleration/neoteny" or changes in growth rate) between the Oligocene and Eocene groups. Theoretically, these may be responses to more massive body shapes, perforce accompanying size increase, which increase the amount of force to which the horns were subjected.