生物入侵对鸟类的生态影响

生物入侵是全球生物多样性面临的最主要威胁之一, 入侵种在改变入侵地环境的同时也使当地的生物受到极大影响。鸟类在生态系统中处于较高的营养级, 生态系统中任何一个环节的变化都可能对鸟类造成一定的影响。本文回顾了哺乳动物、鸟类、无脊椎动物和植物等不同生物类群的入侵对本地鸟类生态影响方面的研究进展。外来生物对鸟类的影响主要表现在以下几方面: (1)外来哺乳动物对成鸟、幼鸟或鸟卵的捕食作用; (2)外来鸟类与本地鸟类竞争栖息地和食物资源, 与当地的近缘种杂交而造成基因流失; (3)外来无脊椎动物改变本地鸟类的栖息环境和食物状况, 甚至直接捕食本地鸟类; (4)外来植物入侵改变入侵地的植物群落组成和结构, 造成本地鸟类的栖息地丧失或破碎化, 并通过改变入侵地生态系统的食物链结构而对高营养级的鸟类产生影响。最后, 作者还提出了该领域有待解决的问题和今后可能的研究方向。     

Ecosystem services provided by bromeliad plants: A systematic review

The unprecedented loss of biological diversity has negative impacts on ecosystems and the associated benefits which they provide to humans. Bromeliads have high diversity throughout the Neotropics, but they have been negatively affected by habitat loss and fragmentation, climate change, invasive species, and commercialization for ornamental purpose. These plants provide direct benefits to the human society, and they also form microecosystems in which accumulated water and nutrients support the communities of aquatic and terrestrial species, thus maintaining local diversity. We performed a systematic review of the contribution of bromeliads to ecosystem services across their native geographical distribution. We showed that bromeliads provide a range of ecosystem services such as maintenance of biodiversity, community structure, nutrient cycling, and the provisioning of food and water. Moreover, bromeliads can regulate the spread of diseases, and water and carbon cycling, and they have the potential to become important sources of chemical and pharmaceutical products. The majority of this research was performed in Brazil, but future research from other Neotropical countries with a high diversity of bromeliads would fill the current knowledge gaps and increase the generality of these findings. This systematic review identified that future research should focus on provisioning, regulating, and cultural services that have been currently overlooked. This would enhance our understanding of how bromeliad diversity contributes to human welfare, and the negative consequences that loss of bromeliad plants can have on communities of other species and the healthy functioning of the entire ecosystems.     

Food-web structure and ecosystem services: insights from the Serengeti

The central organizing theme of this paper is to discuss the dynamics of the Serengeti grassland ecosystem from the perspective of recent developments in food-web theory. The seasonal rainfall patterns that characterize the East African climate create an annually oscillating, large-scale, spatial mosaic of feeding opportunities for the larger ungulates in the Serengeti; this in turn creates a significant annual variation in the food available for their predators. At a smaller spatial scale, periodic fires during the dry season create patches of highly nutritious grazing that are eaten in preference to the surrounding older patches of less palatable vegetation. The species interactions between herbivores and plants, and carnivores and herbivores, are hierarchically nested in the Serengeti food web, with the largest bodied consumers on each trophic level having the broadest diets that include species from a large variety of different habitats in the ecosystem. The different major habitats of the Serengeti are also used in a nested fashion; the highly nutritious forage of the short grass plains is available only to the larger migratory species for a few months each year. The longer grass areas, the woodlands and kopjes (large partially wooded rocky islands in the surrounding mosaic of grassland) contain species that are resident throughout the year; these species often have smaller body size and more specialized diets than the migratory species. Only the larger herbivores and carnivores obtain their nutrition from all the different major habitat types in the ecosystem. The net effect of this is to create a nested hierarchy of subchains of energy flow within the larger Serengeti food web; these flows are seasonally forced by rainfall and operate at different rates in different major branches of the web. The nested structure that couples sequential trophic levels together interacts with annual seasonal variation in the fast and slow chains of nutrient flow in a way that is likely to be central to the stability of the whole web. If the Serengeti is to be successfully conserved as a fully functioning ecosystem, then it is essential that the full diversity of natural habitats be maintained within the greater Serengeti ecosystem. The best way to do this is by controlling the external forces that threaten the boundaries of the ecosystem and by balancing the economic services the park provides between local, national and international needs. I conclude by discussing how the ecosystem services provided by the Serengeti are driven by species on different trophic levels. Tourism provides the largest financial revenue to the national economy, but it could be better organized to provide more sustained revenue to the park. Ultimately, ecotourism needs to be developed in ways that take lessons from the structure of the Serengeti food webs, and in ways that provide tangible benefits to people living around the park while also improving the experience of all visitors.     

互利关系和植物多样性对节肢动物群落不同营养级的影响路径和强度

食物网中的上行效应和下行效应对于群落的动态和生态系统功能有十分重要的影响,旨在探讨互利关系和植物多样性对节肢动物群落中食物网不同营养级之间的影响。通过随机裂区试验方法,分别设置了3种蚂蚁-紫胶虫互利关系处理(有互利关系、无互利关系和自然对照)以及3种植物多样性处理(单一种植、2树种混植和3树种混植),于2016年8月和9月分两次用手捡法、网扫法和震落法采集试验地寄主植物上所有的节肢动物,并按照不同营养级将其分类。利用结构方程模型分析方法对不同营养级之间的相互作用的路径和强度进行了比较,结果显示:1)互利关系对捕食者和消费者均有显著的下行作用,有互利关系处理下蚂蚁对捕食者的路径强度要强于自然对照组,互利关系对捕食者的影响要强于对消费者的影响。2)植物多样性会通过影响植物的生物量而对消费者和捕食者产生显著的上行效应影响,这种影响会随着营养级的升高而显著减小。3)消费者主要受植物多样性的上行效应影响,而捕食者主要受互利关系的下行效应影响。有互利关系的食物网结构更加复杂,营养级之间的相互作用更为显著。探讨了以蚂蚁-紫胶虫互利关系为核心作用的紫胶林生态系统中互利关系和植物多样性对节肢动物食物网中各营养级的影响,揭示了上行效应和下行效应对各营养级的作用途径和强度,其结果有一定的理论参考价值。     

Ecosystem Functions across Trophic Levels Are Linked to Functional and Phylogenetic Diversity

In experimental systems, it has been shown that biodiversity indices based on traits or phylogeny can outperform species richness as predictors of plant ecosystem function. However, it is unclear whether this pattern extends to the function of food webs in natural ecosystems. Here we tested whether zooplankton functional and phylogenetic diversity explains the functioning of 23 natural pond communities. We used two measures of ecosystem function: (1) zooplankton community biomass and (2) phytoplankton abundance (Chl a). We tested for diversity-ecosystem function relationships within and across trophic levels. We found a strong correlation between zooplankton diversity and ecosystem function, whereas local environmental conditions were less important. Further, the positive diversity-ecosystem function relationships were more pronounced for measures of functional and phylogenetic diversity than for species richness. Zooplankton and phytoplankton biomass were best predicted by different indices, suggesting that the two functions are dependent upon different aspects of diversity. Zooplankton community biomass was best predicted by zooplankton trait-based functional richness, while phytoplankton abundance was best predicted by zooplankton phylogenetic diversity. Our results suggest that the positive relationship between diversity and ecosystem function can extend across trophic levels in natural environments, and that greater insight into variation in ecosystem function can be gained by combining functional and phylogenetic diversity measures.     

Trophic interactions and the relationship between species diversity and ecosystem stability

Several theoretical studies propose that biodiversity buffers ecosystem functioning against environmental fluctuations, but virtually all of these studies concern a single trophic level, the primary producers. Changes in biodiversity also affect ecosystem processes through trophic interactions. Therefore, it is important to understand how trophic interactions affect the relationship between biodiversity and the stability of ecosystem processes. Here we present two models to investigate this issue in ecosystems with two trophic levels. The first is an analytically tractable symmetrical plant-herbivore model under random environmental fluctuations, while the second is a mechanistic ecosystem model under periodic environmental fluctuations. Our analysis shows that when diversity affects net species interaction strength, species interactions--both competition among plants and plant-herbivore interactions--have a strong impact on the relationships between diversity and the temporal variability of total biomass of the various trophic levels. More intense plant competition leads to a stronger decrease or a lower increase in variability of total plant biomass, but plant-herbivore interactions always have a destabilizing effect on total plant biomass. Despite the complexity generated by trophic interactions, biodiversity should still act as biological insurance for ecosystem processes, except when mean trophic interaction strength increases strongly with diversity.     

Restoration for variability: emergence of the habitat diversity paradigm in terrestrial ecosystem restoration

Ecosystem restoration implies focusing on multiple trophic levels and ecosystem functioning, yet higher trophic levels, that is, animals, are less frequently targeted by restoration than plants. Habitat diversity, the spatial heterogeneity between and within habitat patches in a landscape, is a well‐known driver of species diversity, and offers possible ways to increase species diversity at multiple trophic levels. We argue that habitat diversity is central in whole‐ecosystem restoration as we review its importance, provide a practical definition for its components, and propose ways to target it in restoration. Restoration targeting habitat diversity is used commonly in aquatic ecosystems, mostly to increase the physical diversity of habitats, meant to provide more niches available to a higher number of animal species. To facilitate the uptake of habitat diversity in terrestrial ecosystem restoration, we distinguish between compositional and structural habitat diversity, because different animal groups will respond to different aspects of habitat diversity. We also propose four methods to increase habitat diversity: varying the starting conditions to obtain divergent successional pathways, emulating natural disturbances, establishing keystone structures, and applying ecosystem engineer species. We provide two case studies to illustrate how these components and methods can be incorporated in restoration. We conclude that targeting habitat diversity is a promising way to restore habitats for a multitude of species of animals and plants, and that it should become mainstream in restoration ecology and practice. We encourage the restoration community to consider compositional and structural habitat diversity and to specifically target habitat diversity in ecosystem restoration.     

互花米草入侵对鸟类的生态影响

生物入侵威胁本地物种生存,破坏生态系统的结构和功能,是导致全球生物多样性丧失的重要原因之一。外来植物是入侵生物中的重要一类,可以显著改变本地植被群落,并影响其他生物类群。鸟类作为生态系统中的较高营养级,对由入侵植物引起的栖息地变化十分敏感。互花米草自引入中国沿海以来,其分布区域不断扩散,多数研究认为互花米草入侵造成本地生物多样性降低和生态系统退化。系统梳理了互花米草入侵对鸟类栖息地、食物资源、繁殖、群落等方面的生态影响。主要负面影响有:(1)植被群落结构不利于鸟类栖息、筑巢、觅食;(2)鸟类食物资源丰度和多样性下降;(3)本地鸟类种群数量和物种多样性显著下降。在我国东部沿海湿地,互花米草入侵已经显著改变了植被与鸟类分布格局。但随着入侵历史的增长,少数小型雀形目鸟类却可以逐渐适应互花米草生境。互花米草入侵为某些非本地鸟类提供了空白生态位,在一定程度上丰富了本地物种多样性,对互花米草的快速清除反而可能不利于已适应并依赖互花米草生境的鸟类。综上,认为互花米草入侵对鸟类群落甚至整个生态系统的影响可能需要更多研究进行综合评价,应开展长期、大尺度、多因子的监测研究和多物种比较研究,建立生态评价模型并制定科学有效的互花米草管理对策。     

Species richness and trophic diversity increase decomposition in a co-evolved food web

Ecological communities show great variation in species richness, composition and food web structure across similar and diverse ecosystems. Knowledge of how this biodiversity relates to ecosystem functioning is important for understanding the maintenance of diversity and the potential effects of species losses and gains on ecosystems. While research often focuses on how variation in species richness influences ecosystem processes, assessing species richness in a food web context can provide further insight into the relationship between diversity and ecosystem functioning and elucidate potential mechanisms underpinning this relationship. Here, we assessed how species richness and trophic diversity affect decomposition rates in a complete aquatic food web: the five trophic level web that occurs within water-filled leaves of the northern pitcher plant, Sarracenia purpurea. We identified a trophic cascade in which top-predators--larvae of the pitcher-plant mosquito--indirectly increased bacterial decomposition by preying on bactivorous protozoa. Our data also revealed a facultative relationship in which larvae of the pitcher-plant midge increased bacterial decomposition by shredding detritus. These important interactions occur only in food webs with high trophic diversity, which in turn only occur in food webs with high species richness. We show that species richness and trophic diversity underlie strong linkages between food web structure and dynamics that influence ecosystem functioning. The importance of trophic diversity and species interactions in determining how biodiversity relates to ecosystem functioning suggests that simply focusing on species richness does not give a complete picture as to how ecosystems may change with the loss or gain of species.     

Relationships between species richness of vascular plants and terrestrial vertebrates in China: analyses based on data of nature reserves

The relationship between plant diversity and animal diversity on a broadscale and its mechanisms are uncertain. In this study, we explored this relationship and its possible mechanisms using data from 186 nature reserves across China on species richness of vascular plants and terrestrial vertebrates, and climatic and topographical variables. We found significant positive correlations between species richness in almost all taxa of vascular plants and terrestrial vertebrates. Multiple regression analyses indicated that plant richness was a significant predictor of richness patterns for terrestrial vertebrates (except birds), suggesting that a causal association may exist between plant diversity and vertebrate diversity in China. The mechanisms for the relationships between species richness of plants and animals are probably dependent on vertebrate groups. For mammals (endothermic vertebrates), this relationship probably represents the integrated effects of plants on animals through trophic links (i.e. providing foods) and non-trophic interactions (i.e. supplying habitats), whereas for amphibians and reptiles (ectothermic vertebrates), this may be a result of the non-trophic links, such as the effects of plants on the resources that amphibians and reptiles require.     

Bird and bat predation services in tropical forests and agroforestry landscapes

Understanding distribution patterns and multitrophic interactions is critical for managing bat‐ and bird‐mediated ecosystem services such as the suppression of pest and non‐pest arthropods. Despite the ecological and economic importance of bats and birds in tropical forests, agroforestry systems, and agricultural systems mixed with natural forest, a systematic review of their impact is still missing. A growing number of bird and bat exclosure experiments has improved our knowledge allowing new conclusions regarding their roles in food webs and associated ecosystem services. Here, we review the distribution patterns of insectivorous birds and bats, their local and landscape drivers, and their effects on trophic cascades in tropical ecosystems. We report that for birds but not bats community composition and relative importance of functional groups changes conspicuously from forests to habitats including both agricultural areas and forests, here termed ‘forest‐agri’ habitats, with reduced representation of insectivores in the latter. In contrast to previous theory regarding trophic cascade strength, we find that birds and bats reduce the density and biomass of arthropods in the tropics with effect sizes similar to those in temperate and boreal communities. The relative importance of birds versus bats in regulating pest abundances varies with season, geography and management. Birds and bats may even suppress tropical arthropod outbreaks, although positive effects on plant growth are not always reported. As both bats and birds are major agents of pest suppression, a better understanding of the local and landscape factors driving the variability of their impact is needed.     

Complexity of multitrophic interactions in a grassland ecosystem depends on plant species diversity

1.?We studied the theoretical prediction that a loss of plant species richness has a strong impact on community interactions among all trophic levels and tested whether decreased plant species diversity results in a less complex structure and reduced interactions in ecological networks. 2.?Using plant species-specific biomass and arthropod abundance data from experimental grassland plots (Jena Experiment), we constructed multitrophic functional group interaction webs to compare communities based on 4 and 16 plant species. 427 insect and spider species were classified into 13 functional groups. These functional groups represent the nodes of ecological networks. Direct and indirect interactions among them were assessed using partial Mantel tests. Interaction web complexity was quantified using three measures of network structure: connectance, interaction diversity and interaction strength. 3.?Compared with high plant diversity plots, interaction webs based on low plant diversity plots showed reduced complexity in terms of total connectance, interaction diversity and mean interaction strength. Plant diversity effects obviously cascade up the food web and modify interactions across all trophic levels. The strongest effects occurred in interactions between adjacent trophic levels (i.e. predominantly trophic interactions), while significant interactions among plant and carnivore functional groups, as well as horizontal interactions (i.e. interactions between functional groups of the same trophic level), showed rather inconsistent responses and were generally rarer. 4.?Reduced interaction diversity has the potential to decrease and destabilize ecosystem processes. Therefore, we conclude that the loss of basal producer species leads to more simple structured, less and more loosely connected species assemblages, which in turn are very likely to decrease ecosystem functioning, community robustness and tolerance to disturbance. Our results suggest that the functioning of the entire ecological community is critically linked to the diversity of its component plants species.     

The relationship between biodiversity and ecosystem functioning in food webs

Recent theoretical and experimental work provides clear evidence that biodiversity loss can have profound impacts on functioning of natural and managed ecosystems and the ability of ecosystems to deliver ecological services to human societies. Work on simplified ecosystems in which the diversity of a single trophic level is manipulated shows that diversity can enhance ecosystem processes such as primary productivity and nutrient retention. Theory also strongly suggests that biodiversity can act as biological insurance against potential disruptions caused by environmental changes. However, these studies generally concern a single trophic level, primary producers for the most part. Changes in biodiversity also affect ecosystem functioning through trophic interactions. Here we review, through the analysis of a simple ecosystem model, several key aspects inherent in multitrophic systems that may strongly affect the relationship between diversity and ecosystem processes. Our analysis shows that trophic interactions have a strong impact on the relationships between diversity and ecosystem functioning, whether the ecosystem property considered is total biomass or temporal variability of biomass at the various trophic levels. In both cases, food-web structure and trade-offs that affect interaction strength have major effects on these relationships. Multitrophic interactions are expected to make biodiversity–ecosystem functioning relationships more complex and non-linear, in contrast to the monotonic changes predicted for simplified systems with a single trophic level.     

Influence of habitat complexity and landscape configuration on pollination and seed-dispersal interactions of wild cherry trees

Land-use intensification is a major cause for the decline in species diversity in human-modified landscapes. The loss of functionally important species can reduce a variety of ecosystem functions, such as pollination and seed dispersal, but the intricate relationships between land-use intensity, biodiversity and ecosystem functioning are still contentious. Along a gradient from forest to intensively used farmland, we quantified bee species richness, visitation rates of bees and pollination success of wild cherry trees (Prunus avium). We analysed the effects of structural habitat diversity at a local scale and of the proportion of suitable habitat around each tree at a landscape scale. We compared these findings with those from previous studies of seed-dispersing birds and mammals in the same model system and along the same land-use gradient. Bee species richness and visitation rates were found to be highest in structurally simple habitats, whereas bird species richness—but not their visitation rates—were highest in structurally complex habitats. Mammal visitation rates were only influenced at the landscape scale. These results show that different functional groups of animals respond idiosyncratically to gradients in habitat and landscape structure. Despite strong effects on bees and birds, pollination success and bird seed removal did not differ along the land-use gradient at both spatial scales. These results suggest that mobile organisms, such as bees and birds, move over long distances in intensively used landscapes and thereby buffer pollination and seed-dispersal interactions. We conclude that measures of species richness and interaction frequencies are not sufficient on their own to understand the ultimate consequences of land-use intensification on ecosystem functioning.     

Habitat structure, trophic structure and ecosystem function: interactive effects in a bromeliad–insect community

Although previous studies have shown that ecosystem functions are affected by either trophic structure or habitat structure, there has been little consideration of their combined effects. Such interactions may be particularly important in systems where habitat and trophic structure covary. I use the aquatic insects in bromeliads to examine the combined effects of trophic structure and habitat structure on a key ecosystem function: detrital processing. In Costa Rican bromeliads, trophic structure naturally covaries with both habitat complexity and habitat size, precluding any observational analysis of interactions between factors. I therefore designed mesocosms that allowed each factor to be manipulated separately. Increases in mesocosm complexity reduced predator (damselfly larva) efficiency, resulting in high detritivore abundances, indirectly increasing detrital processing rates. However, increased complexity also directly reduced the per capita foraging efficiency of the detritivores. Over short time periods, these trends effectively cancelled each other out in terms of detrital processing. Over longer time periods, more complex patterns emerged. Increases in mesocosm size also reduced both predator efficiency and detritivore efficiency, leading to no net effect on detrital processing. In many systems, ecosystem functions may be impacted by strong interactions between trophic structure and habitat structure, cautioning against examining either effect in isolation.     

Rainfall and hydrological stability alter the impact of top predators on food web structure and function

Climate change will alter the distribution of rainfall, with potential consequences for the hydrological dynamics of aquatic habitats. Hydrological stability can be an important determinant of diversity in temporary aquatic habitats, affecting species persistence and the importance of predation on community dynamics. As such, prey are not only affected by drought‐induced mortality but also the risk of predation [a non‐consumptive effect (NCE)] and actual consumption by predators [a consumptive effect (CE)]. Climate‐induced changes in rainfall may directly, or via altered hydrological stability, affect predator–prey interactions and their cascading effects on the food web, but this has rarely been explored, especially in natural food webs. To address this question, we performed a field experiment using tank bromeliads and their aquatic food web, composed of predatory damselfly larvae, macroinvertebrate prey and bacteria. We manipulated the presence and consumption ability of damselfly larvae under three rainfall scenarios (ambient, few large rainfall events and several small rainfall events), recorded the hydrological dynamics within bromeliads and examined the effects on macroinvertebrate colonization, nutrient cycling and bacterial biomass and turnover. Despite our large perturbations of rainfall, rainfall scenario had no effect on the hydrological dynamics of bromeliads. As a result, macroinvertebrate colonization and nutrient cycling depended on the hydrological stability of bromeliads, with no direct effect of rainfall or predation. In contrast, rainfall scenario determined the direction of the indirect effects of predators on bacteria, driven by both predator CEs and NCEs. These results suggest that rainfall and the hydrological stability of bromeliads had indirect effects on the food web through changes in the CEs and NCEs of predators. We suggest that future studies should consider the importance of the variability in hydrological dynamics among habitats as well as the biological mechanisms underlying the ecological responses to climate change.     

Diversity of Neotropical migratory landbird species assemblages in forest fragments and man-made vegetation in Los Tuxtlas,Mexico

We investigated the presence of Neotropical migratory landbirds in a 90-km² landscape in the region of Los Tuxtlas, Veracruz, Mexico. Using the fixed-radius count point procedure, migratory landbirds were surveyed in 21 forest fragments and in four replicates of shaded (coffee, cacao and mixed) and unshaded (citrus and allspice) plantations, live fences, non-arboreal crops (corn and jalapeño chili pepper) and pastures. The surveys resulted in the count of 4732 birds representing 72 species. While forest fragments accounted for 65% of the total species count, 73% of the birds were counted in the arboreal man-made habitats. Pastures contributed to 10% of the species and to 1% of the individuals counted. Live fences were particularly rich in individuals, accounting for 28% of the birds counted. Rarefaction analysis showed that forest fragments were the sites richest in species, followed by shaded and unshaded plantations and by live fences. Pastures were the habitats poorest in species, followed by non-arboreal crops. Species richness of Neotropical migratory landbirds was associated to vertical and horizontal diversity of vegetation in the habitats investigated. Shaded and unshaded plantations as well as live fences were more similar to forest fragments in species assemblages than non-arboreal crops and pastures. We discuss the conservation value of arboreal agricultural habitat and of live fences in conjunction with forest fragments as temporary habitats for Neotropical migratory landbirds that stop over or winter in Los Tuxtlas.     

Towards a mechanistic understanding of temperature and enrichment effects on species interaction strength,omnivory and food‐web structure

Revealing the links between species functional traits, interaction strength and food‐web structure is of paramount importance for understanding and predicting the relationships between food‐web diversity and stability in a rapidly changing world. However, little is known about the interactive effects of environmental perturbations on individual species, trophic interactions and ecosystem functioning. Here, we combined modelling and laboratory experiments to investigate the effects of warming and enrichment on a terrestrial tritrophic system. We found that the food‐web structure is highly variable and switches between exploitative competition and omnivory depending on the effects of temperature and enrichment on foraging behaviour and species interaction strength. Our model contributes to identifying the mechanisms that explain how environmental effects cascade through the food web and influence its topology. We conclude that considering environmental factors and flexible food‐web structure is crucial to improve our ability to predict the impacts of global changes on ecosystem diversity and stability.     

Urbanization alters interactions between Darwin's finches and Tribulus cistoides on the Galápagos Islands

Emerging evidence suggests that humans shape the ecology and evolution of species interactions. Islands are particularly susceptible to anthropogenic disturbance due to the fragility of their ecosystems; however, we know little about the susceptibility of species interactions to urbanization on islands. To address this gap, we studied how the earliest stages of urban development affect interactions between Darwin''s finches and its key food resource, Tribulus cistoides, in three towns on the Galápagos Islands. We measured variation in mericarp predation rates, mericarp morphology, and finch community composition using population surveys, experimental manipulations, and finch observations conducted in habitats within and outside of each town. We found that both seed and mericarp removal rates were higher in towns than natural habitats. We also found that selection on mericarp size and defense differed between habitats in the survey and experimental populations and that towns supported smaller and less diverse finch communities than natural habitats. Together, our results suggest that even moderate levels of urbanization can alter ecological interactions between Darwin''s finches and T. cistoides, leading to modified natural selection on T. cistoides populations. Our study demonstrates that trophic interactions on islands may be susceptible to the anthropogenic disturbance associated with urbanization. Despite containing the highest diversity in the world, studies of urbanization are lacking from the tropics. Our study identified signatures of urbanization on species interactions in a tropical island ecosystem and suggests that changes to the ecology of species interactions has the potential to alter evolution in urban environments.     

Environmental metabarcoding reveals heterogeneous drivers of microbial eukaryote diversity in contrasting estuarine ecosystems

Assessing how natural environmental drivers affect biodiversity underpins our understanding of the relationships between complex biotic and ecological factors in natural ecosystems. Of all ecosystems, anthropogenically important estuaries represent a ‘melting pot'' of environmental stressors, typified by extreme salinity variations and associated biological complexity. Although existing models attempt to predict macroorganismal diversity over estuarine salinity gradients, attempts to model microbial biodiversity are limited for eukaryotes. Although diatoms commonly feature as bioindicator species, additional microbial eukaryotes represent a huge resource for assessing ecosystem health. Of these, meiofaunal communities may represent the optimal compromise between functional diversity that can be assessed using morphology and phenotype–environment interactions as compared with smaller life fractions. Here, using 454 Roche sequencing of the 18S nSSU barcode we investigate which of the local natural drivers are most strongly associated with microbial metazoan and sampled protist diversity across the full salinity gradient of the estuarine ecosystem. In order to investigate potential variation at the ecosystem scale, we compare two geographically proximate estuaries (Thames and Mersey, UK) with contrasting histories of anthropogenic stress. The data show that although community turnover is likely to be predictable, taxa are likely to respond to different environmental drivers and, in particular, hydrodynamics, salinity range and granulometry, according to varied life-history characteristics. At the ecosystem level, communities exhibited patterns of estuary-specific similarity within different salinity range habitats, highlighting the environmental sequencing biomonitoring potential of meiofauna, dispersal effects or both.