The tropics contain the overwhelming majority of Earth's biodiversity: their terrestrial, freshwater and marine ecosystems hold more than three-quarters of all species, including almost all shallow-water corals and over 90% of terrestrial birds. However, tropical ecosystems are also subject to pervasive and interacting stressors, such as deforestation, overfishing and climate change, and they are set within a socio-economic context that includes growing pressure from an increasingly globalized world, larger and more affluent tropical populations, and weak governance and response capacities. Concerted local, national and international actions are urgently required to prevent a collapse of tropical biodiversity.

Understanding energy and material fluxes through ecosystems is central to many questions in global change biology and ecology. Ecosystem respiration is a critical component of the carbon cycle and might be important in regulating biosphere response to global climate change. Here we derive a general model of ecosystem respiration based on the kinetics of metabolic reactions and the scaling of resource use by individual organisms. The model predicts that fluxes of CO2 and energy are invariant of ecosystem biomass, but are strongly influenced by temperature, variation in cellular metabolism and rates of supply of limiting resources (water and/or nutrients). Variation in ecosystem respiration within sites, as calculated from a network of CO2 flux towers, provides robust support for the model's predictions. However, data indicate that variation in annual flux between sites is not strongly dependent on average site temperature or latitude. This presents an interesting paradox with regard to the expected temperature dependence. Nevertheless, our model provides a basis for quantitatively understanding energy and material flux between the atmosphere and biosphere.

Human-mediated transport beyond biogeographic barriers has led to the introduction and 73The transport of species across biogeographic barriers by humans is a key component of 74 global environmental change [1][2][3] . Some of the species introduced to new regions will establish 75 self-sustaining populations and, thus, become a persistent part of the local biota 95We expect regions with higher gross domestic product per capita (GDPpc) or with higher 96 population densities to receive more alien species introductions across taxa (i.e., to experience 97 higher colonisation pressure through trade and transport), resulting in higher EAS richness 7,8,10,21 . 98We also test whether EAS richness patterns follow the latitudinal gradients often observed for 99 native biota, with higher richness in regions with higher mean annual temperature and 100 precipitation 22,23 . We expect island regions to have higher EAS richness than mainland regions, 101as islands are thought to be more prone to the establishment of alien species 12,24,25 . In addition, 102we expect more isolated oceanic islands to have greater EAS richness, as they have been shown 103 to receive more introductions, at least for birds 9 . We also expect coastal regions (as points of human population density, with a weak trend of higher alien richness in wetter regions (Table 1). 125While we only have potential proxy data (GDPpc, population density) for colonisation pressure 126 here (i.e., the total numbers of species introduced) 26 , our results suggest that cumulative numbers 127 7 of EAS are driven to a greater extent by differences in area and the pressure of introductions 128 from human history and activity 1,3,5,12,21 than by climate. 129Island regions have on average higher cross-taxon EAS richness (mean ± 1 S.D. 130proportional cross-taxon richness = 0.17 ± 0.11) than mainland regions (mean ± 1 S.D. = 0.11 ± 131 0.07; Table 1). In addition, models explaining alien richness of island and mainland regions 132 separately reveal that EAS richness is more strongly related to area, GDPpc and population 133 density on islands than in mainland regions (Table 1) (Table 1). Among mainland regions, EAS richness is greater for coastal (mean ± 1 S.D. 139proportional cross-taxon richness = 0.13 ± 0.09) than for landlocked regions (mean ± 1 S.D. = 140 0.10 ± 0.04). Cross-taxon EAS richness on islands tends to be higher for those further from 141 continental landmasses (Table 1). 143 Taxonomic congruence 144The strongest correlations in alien richness between taxonomic groups exist for ants and 145 reptiles (r s = 0.62), followed by birds and mammals, and vascular plants and spiders (both r s = 146 0.55) ( Table 2). For ants and reptiles, EAS richness is high in the Hawaiian Islands, southern 147United States (especially Florida) and Madagascar and the Mascarene Islands (Fig. 1b, 1g). (Fig. 1f, 1h). In Europe, the United Kingdom has the highest established alien 154 plant richness, while Germany has the highest spider richness (Fig. 1h, 1h). Overa...

Our ability to predict the identity of future invasive alien species is largely based upon knowledge of prior invasion history. Emerging alien species-those never encountered as aliens before-therefore pose a significant challenge to biosecurity interventions worldwide. Understanding their temporal trends, origins, and the drivers of their spread is pivotal to improving prevention and risk assessment tools. Here, we use a database of 45,984 first records of 16,019 established alien species to investigate the temporal dynamics of occurrences of emerging alien species worldwide. Even after many centuries of invasions the rate of emergence of new alien species is still high: One-quarter of first records during 2000-2005 were of species that had not been previously recorded anywhere as alien, though with large variation across taxa. Model results show that the high proportion of emerging alien species cannot be solely explained by increases in well-known drivers such as the amount of imported commodities from historically important source regions. Instead, these dynamics reflect the incorporation of new regions into the pool of potential alien species, likely as a consequence of expanding trade networks and environmental change. This process compensates for the depletion of the historically important source species pool through successive invasions. We estimate that 1-16% of all species on Earth, depending on the taxonomic group, qualify as potential alien species. These results suggest that there remains a high proportion of emerging alien species we have yet to encounter, with future impacts that are difficult to predict.

Biogeographical, evolutionary and ecological processes interact to regulate patterns in metacommunities. However, as there are few quantitative methods for evaluating their joint effects, resolving this interaction is difficult. We develop a method that aims to evaluate the interaction between phylogenetic structure, historical biogeographic events and environmental filtering in driving species distributions in a large-scale metacommunity. Using freshwater zooplankton as a case study, we contrast the phylogenetic metacommunity structure of calanoid copepods and an ecologically similar but more vagile group, daphniids, in the northeastern US. We find that legacies of historical biogeographical events have strongly constrained calanoid distributions within this area, but that adaptation to different water chemistry and lake morphology drives the metacommunity structure of daphniids. Our findings show that biogeographic history and metacommunity processes jointly regulate community structure in these lakes and suggest that this also depends on factors that affect the colonization rate of different types of organisms.