Human land use causes major changes in species abundance and composition, yet native and exotic species can exhibit different responses to land use change. Native populations generally decline in human-impacted habitats while exotic species often benefit. In this study, we assessed the effects of human land use on exotic and native reptile diversity, including functional diversity, which relates to the range of habitat use strategies in biotic communities. We surveyed 114 reptile communities from localities that varied in habitat structure and human impact level on two Caribbean islands, and calculated species richness, overall abundance, and evenness for every plot. Functional diversity indices were calculated using published trait data, which enabled us to detect signs of trait filtering associated with impacted habitats. Our results show that environmental variation among sampling plots was explained by two Principal Component Analysis (PCA) ordination axes related to habitat structure (i.e., forest or nonforest) and human impact level (i.e., addition of man-made constructions such as roads and buildings). Several diversity indices were significantly correlated with the two PCA axes, but exotic and native species showed opposing responses. Native species reached the highest abundance in forests, while exotic species were absent in this habitat. Human impact was associated with an increase in exotic abundance and species richness, while native species showed no significant associations. Functional diversity was highest in nonforested environments on both islands, and further increased on St. Martin with the establishment of functionally unique exotic species in nonforested habitat. Habitat structure, rather than human impact, proved to be an important agent for environmental filtering of traits, causing divergent functional trait values across forested and nonforested environments. Our results illustrate the importance of considering various elements of land use when studying its impact on species diversity and the establishment and spread of exotic species.

Aim: Island biogeography theory states that species richness increases with habitat diversity and decreases with isolation from source pools. However, ecological theory must incorporate effects of human activity to explain contemporary patterns of biodiversity. We contemporized island biogeography theory by conceptualizing island trajectories of how species richness changes over time with accelerating land development and economic trade, which increase extinction and immigration rates, respectively. With this contemporized theory, we then articulate and empirically assess expected relationships of native, introduced and total species richness with natural and anthropogenic metrics of habitat diversity and isolation from source pools. Location: Greater Caribbean region.Time period: Database finalized in 2020. Methods:We built a database of 1,042 native and introduced reptiles and amphibians (herps) for 840 Caribbean islands. For each island, we calculated natural and anthropogenic metrics of island habitat diversity and isolation from source pools and used linear model averaging to assess the expected relationships under the contemporized theory for 15 major herp clades.

Classic ecological theory must explain effects of humans on biodiversity to be more applicable today. We contemporized island biogeographic theory providing native, introduced, and total species richness relationship expectations with natural and anthropogenic metrics of habitat diversity (geographic and economic area) and isolation from source pools (geographic and economic isolation). We assessed these expectations across Caribbean island herpetofauna clades. As expected by the contemporized theory, natural habitat diversity metrics exhibited positive relationships with native and introduced richness, strengthening positive total richness-area relationships. Geographic isolation exhibited negative relationships with native and positive relationships with introduced richness, weakening total richness-isolation relationships. Economic area and isolation exhibited negative and positive relationships, respectively, with native richness but positive and negative relationships, respectively, with introduced richness. Total richness relationships with economic area and isolation were strongest in clades with many introductions. As more species spread globally, these contemporary expectations will increasingly predict Anthropocene island biogeography.

Urban development and species invasion are two major global threats to biodiversity.These threats often co-occur, as developed areas are more prone to species invasion. However, few empirical studies have tested if both factors affect biodiversity in similar ways. Here we study the individual and combined effects of urban development and plant invasion on the composition of arthropod communities. We assessed 36 paired invaded and non-invaded sample plots, invaded by the plant Antigonon leptopus, with half of these pairs located in natural and the other half in developed land-use types on the Caribbean island of St. Eustatius. We used several taxonomic and functional variables to describe community composition and diversity. Our results show that both urban development and A. leptopus invasion affected community composition, albeit in different ways. Development significantly increased species richness and exponential Shannon diversity, while invasion had no effect on these variables. However, invasion significantly increased arthropod abundance and caused biotic homogenization. Specifically, uninvaded arthropod communities were distinctly different in species composition between developed and natural sites, while they became undistinguishable after A. leptopus invasion. Moreover, functional variables were significantly affected by species invasion, but not by urban development. Invaded communities had higher community-weighted mean body size and the feeding guild composition of invaded arthropod communities was characterized by the exceptional numbers of nectarivores, herbivores, and detritivores. With the exception of species richness and exponential Shannon diversity, invasion influenced four out of six response variables to a greater degree than urban development did.Hence, we can conclude that species invasion is not just a passenger of urban development but also a driver of change.

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The Anthropocene is marked by unprecedented changes to species ranges worldwide. Introduced species expand their native range into new geographic regions while extinction-prone species experience severe native range contraction. Introductions and extinctions are both caused by how species respond to human influence within their native ranges. The question arises if the opposite response in distributional change is due to introduced and extinction-prone species falling at opposite ends of geographic, evolutionary and ecological trait continua. Here, we assess the factors that explain the introduction and extinction-prone status for 3111 squamate reptile species native to the western hemisphere, of which 142 species have been introduced elsewhere and 483 species are threatened with extinction. We first asked what geographic regions contained the most introduced and extinction-prone species and if these species are evolutionarily related. We then tested the opposite ends hypothesis for several species characteristics. Our results show that the native ranges of introduced and extinction-prone reptiles are skewed towards island regions and that significant phylogenetic signal exists for these two groups, indicating they are not a random selection of the reptiles that have evolved in the western hemisphere. Species whose native ranges were more insular and were more influenced by humans were more likely to be introduced or extinction-prone. Evolutionary factors did not explain species status, but multiple geographic and ecological factors supported the opposite ends hypothesis. Introduced species were positively associated with herbivory and omnivory and had large and complex ranges, whereas extinction-prone species were generally carnivorous with small and simple ranges. In addition, introduced species produced larger clutches and extinction-prone species had relatively small body sizes. In the Anthropocene, the naive ranges of introduced and extinction-prone species are situated in the same human-impacted regions, but species range characteristics and functional traits determine whether species ranges expand or contract in the continuing face of global change.

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Human activity has greatly accelerated in the past century impacting biodiversity across the globe. To accurately explain contemporary patterns of biodiversity, classic ecological theory must be updated to incorporate the effects of this Great Acceleration on biodiversity. We contemporized island biogeographic theory (IBT) and its extension, the general dynamic model (GDM), to incorporate these effects. At their core, IBT and GDM predict positive relationships between island species richness and habitat diversity, and negative relationships between island species richness and isolation from source pools of species. Through the Great Acceleration, land development on islands has altered habitat diversity and the introduction of species through global trade has reduced island isolation. We contemporize IBT and GDM by conceptualizing trajectories of how species richness on islands will change given accelerations to land development and trade. Considering these contemporary trajectories, we provide expectations for the relationships of native, introduced, and total species richness with natural and anthropogenic metrics of habitat diversity (geographic and economic area, respectively) and isolation from source pools (geographic and economic isolation, respectively). We assessed the expectations across reptile and amphibian clades of the Caribbean islands. As expected by the contemporized theory, natural habitat diversity metrics exhibited positive relationships with both native and introduced species richness, strengthening total species richness-area relationships. Geographic isolation exhibited negative relationships with native and positive relationships with introduced species richness, weakening total species richness-isolation relationships. Economic area and isolation both exhibited negative relationships with native richness, but positive and negative relationships, respectively, with introduced richness. Total species richness relationships with economic area and isolation were also strongest in clades with many introduced species. As more species spread globally, the contemporary expectations we articulate here will increasingly predict island biogeography of the Anthropocene.