Macroecological Analyses Research Articles

The global ecology of bird migration: patterns and processes

Nearly 20% of bird species are migratory, their seasonal movements causing a redistribution of bird diversity that radically changes avian community composition worldwide. And yet, bird migration has been largely ignored in studies of global avian biodiversity. My thesis is the first global macroecological analysis of bird migration. Using a dataset on the geographical distributions of the world’s birds, I mapped global patterns of migratory bird diversity, revealing strong spatial features. I then used these patterns to test hypotheses exploring the ecological processes driving bird distributions in space and time. From these results, I developed the first mechanistic, process-based model of bird migration at the global scale. From first principles – converting key ecological processes into a common currency of energy – this model successfully explains the global patterns previously described. My research provides a better understanding of why birds migrate and opens new research avenues on this remarkable phenomenon.

Global associations between birds and vane-dwelling feather mites.

Understanding host-symbiont networks is a major question in evolutionary ecology. Birds host a great diversity of endo- and ectosymbiotic organisms, with feather mites (Arachnida: Acariformes: Analgoidea, Pterolichoidea) being among the most diverse of avian symbionts. A global approach to the ecology and evolution of bird-feather-mite associations has been hampered because of the absence of a centralized data repository. Here we present the most extensive data set of associations between feather mites and birds. Data include 12 036 records of 1887 feather mite species located on the flight feathers of 2234 bird species from 147 countries. Feather mites typically located inside quills, on the skin, or on downy body feathers are not included. Data were extracted from 493 published sources dating from 1882 to 2015. Data exploration shows that although most continents and bird families are represented, most bird species remain unexplored for feather mites. Nevertheless, this is the most comprehensive data set available for enabling global macroecological analyses of feather mites and their hosts, such as ecological network analyses. This metadata file outlines the structure of these data and provides primary references for all records used.

Comparing macroecological patterns across continents: evolution of climatic niche breadth in varanid lizards

Macroecological analyses often test hypotheses at the global scale, or among more closely related species in a single region (e.g. continent). Here, we test several hypotheses about climatic niche widths among relatively closely related species that occur across multiple continents, and compare patterns within and across continents to see if they differ. We focus on the lizard genus Varanus (monitor lizards), which occurs in diverse environments in Africa, Asia, and Australia. We address three main questions. 1) How do climatic niche breadths of species on a given niche axis change based on the position of species along that niche axis? (E.g. are species that occur in more extreme environments more narrowly specialized for those conditions?) 2) Are there trade‐offs in niche breadths on temperature and precipitation axes among species, or are niche widths on different axes positively related? 3) Is variation in niche breadths among species explained primarily by within‐locality seasonal variation, or by differences in climatic conditions among localities across the species range? We generate a new time‐calibrated phylogeny for Varanus and test these hypotheses within and between continents using climatic data and phylogenetic methods. Our results show that patterns on each continent often parallel each other and global patterns. However, in many other cases, the strength of relationships can change dramatically among closely related species on different continents. Overall, we found that: 1) species in warmer environments have narrower temperature niche breadths, but there is no relationship between precipitation niche breadth and niche position; 2) temperature and precipitation niche breadths tend to be positively related among species, rather than showing trade‐offs; and 3) within‐locality seasonal variation explains most variation in climatic niche breadths. Some of these results are concordant with previous studies (in amphibians and North American lizards), and might represent general macroecological patterns.

Distribution patterns of arbuscular mycorrhizal and non-mycorrhizal plant species in Germany

We analysed the spatial distribution patterns of plant species’ arbuscular mycorrhizal status across an intermediate geographical scale (i.e. the country of Germany) and related these distributions to environmental drivers. Three levels of arbuscular mycorrhizal status of plant species could be defined: (1) obligate arbuscular mycorrhizal species that are always colonised by mycorrhizal fungi, (2) facultative arbuscular mycorrhizal species that are colonised under some conditions but not colonised under others and (3) non-mycorrhizal species that are never found to be colonised by mycorrhizal fungi. We aimed to investigate whether plant species assemblages at the studied grid cell scale are composed of different proportions of species regarding their arbuscular mycorrhizal status, and whether the variation of these proportions can be linked to the geographical variation of ecological and environmental factors. We fitted a vector generalised additive model (VGAM) for log-ratios of proportions of plant species’ arbuscular mycorrhizal status per grid cell (2859 grid cells, each c. 130km2). The spatially explicit plant arbuscular mycorrhizal status distribution model was based on environmental predictors related to climate, geology and land use. The spatial distribution of plant arbuscular mycorrhizal status can be explained as a function of nine environmental predictors (D2=0.54). Proportion of obligate arbuscular mycorrhizal plant species per grid cell increased with increasing temperature range, mean annual temperature, urban area and area of lime as geological parent material and decreased with increasing area of mixed forest and coniferous forest. Annual temperature range was by far the most important predictor. These results extend the comparative context of former studies that established relationships between mycorrhizal status and other plant characteristics at species level, including those describing species ecological requirements, to a context at the level of assemblages and species distributions. We encourage integrating plant mycorrhizal status as a functional trait in future macroecological analyses.

Towards a more reproducible ecology

Towards a more reproducible ecology

Metabolic heat production and thermal conductance are mass-independent adaptations to thermal environment in birds and mammals

The extent to which different kinds of organisms have adapted to environmental temperature regimes is central to understanding how they respond to climate change. The Scholander-Irving (S-I) model of heat transfer lays the foundation for explaining how endothermic birds and mammals maintain their high, relatively constant body temperatures in the face of wide variation in environmental temperature. The S-I model shows how body temperature is regulated by balancing the rates of heat production and heat loss. Both rates scale with body size, suggesting that larger animals should be better adapted to cold environments than smaller animals, and vice versa. However, the global distributions of ∼9,000 species of terrestrial birds and mammals show that the entire range of body sizes occurs in nearly all climatic regimes. Using physiological and environmental temperature data for 211 bird and 178 mammal species, we test for mass-independent adaptive changes in two key parameters of the S-I model: basal metabolic rate (BMR) and thermal conductance. We derive an axis of thermal adaptation that is independent of body size, extends the S-I model, and highlights interactions among physiological and morphological traits that allow endotherms to persist in a wide range of temperatures. Our macrophysiological and macroecological analyses support our predictions that shifts in BMR and thermal conductance confer important adaptations to environmental temperature in both birds and mammals.

A high-resolution model of bat diversity and endemism for continental Africa

Bats are the second-most species-rich mammal group numbering more than 1270 species globally. Our knowledge of their geographic distributions and diversity patterns however is very limited – possibly the poorest among mammals – mainly due to their nocturnal and volant life history, and challenging fieldwork conditions in the tropics where most bat species occur. This knowledge gap obscures the geographic extent of ecosystem services provided by bats (i.e. pollination, seed dispersal and insect control), translates into inefficient conservation policies, and restricts macroecological analyses to coarse spatial resolutions. In contrast to the currently prevailing method of estimating species distributions using expert-drawn range maps, correlative species distribution models (SDMs) can provide estimates at very fine spatial grains and largely account for widespread sample bias as well as the prevalent Wallacean shortfall in species occurrence data. Very few such studies have hitherto been published that cover a large and complete taxonomic group with fine resolution at continental extent. Using an unparalleled amount of occurrence data, the MaxEnt algorithm and tailored solutions to specific modelling challenges, we created SDMs for nearly all 250 African bat species to explore emerging diversity patterns at a resolution of 1km2. Predicted species richness generally increases towards the equator conforming to expectations. Within the tropical area of elevated richness, several pronounced richness peaks and lows stand out, hinting at a complex interplay of determining factors. Richness gradients are often steep, decreasing strongly away from streams, and especially so in savanna biomes. Species richness also seems positively associated with rugged terrain, in particular at lower elevations. Centres of endemism are found primarily at low latitudes near major elevational ranges. Overlap with hotspots of species richness is rather low, and confined to five or six topodiverse, relatively low lying areas between western Guinea and the East African coast. Several poorly sampled regions are identified that may represent rewarding future survey targets. Our results demonstrate the value of stacking SDMs to infer plausible continent-wide diversity gradients at a spatial resolution fine enough to directly inform conservation policies and to open up new avenues in macroecological research.

Macroecological analysis of the fish fauna inhabiting Cymodocea nodosa seagrass meadows.

In this study, patterns in the taxonomic richness and composition of the fish fauna inhabiting Cymodocea nodosa seagrass meadows were described across their entire distribution range in the Mediterranean Sea and adjacent Atlantic Ocean. Specifically, the study tested whether there are differences in the composition of fish assemblages between those ecoregions encompassed by the distribution range of C. nodosa, and whether these differences in composition are connected with differences in bioclimatic affinities of the fish faunas. A literature review resulted in a total of 19 studies, containing 22 fish assemblages at 18 locations. The ichthyofauna associated with C. nodosa seagrass meadows comprises 59 families and 188 species. The western Mediterranean (WM) Sea has the highest species richness (87 species). Fish assemblages from the Macaronesia-Canary Islands, the Sahelian Upwelling, South European Atlantic Shelf and the WM differ, in terms of assemblage composition, relative to other ecoregions. In contrast, the composition of the fish fauna from the central and eastern Mediterranean overlaps. There is a significant serial correlation in fish assemblage composition between adjacent ecoregions along the distribution range of C. nodosa. Dissimilarities in assemblage composition are connected with the geographical separation between locations, and the mean minimum annual seawater temperature is the environmental factor that explains most variation in fish assemblage composition.

Historic and prehistoric human-driven extinctions have reshaped global mammal diversity patterns

Aim To assess the extent to which humans have reshaped Earth's biodiversity, by estimating natural ranges of all late Quaternary mammalian species, and to compare diversity patterns based on these with diversity patterns based on current distributions. Location Globally. Methods We estimated species, functional and phylogenetic diversity patterns based on natural ranges of all mammalian species (n = 5747 species) as they could have been today in the complete absence of human influence through time. Following this, we compared macroecological analyses of current and natural diversity patterns to assess whether human-induced range changes bias evolutionary and ecological analyses based on current diversity patterns. Results We find that current diversity patterns have been drastically modified by humans, mostly due to global extinctions and regional to local extirpations. Current and natural diversities exhibit marked deviations virtually everywhere outside sub-Saharan Africa. These differences are strongest for terrestrial megafauna, but also important for all mammals combined. The human-induced changes led to biases in estimates of environmental diversity drivers, especially for terrestrial megafauna, but also for all mammals combined. Main conclusions Our results show that fundamental diversity patterns have been reshaped by human-driven extinctions and extirpations, highlighting humans as a major force in the Earth system. We thereby emphasize that estimating natural distributions and diversities is important to improve our understanding of the evolutionary and ecological drivers of diversity as well as for providing a benchmark for conservation.

Trends and stability of inland fishery resources in Japanese lakes: introduction of exotic piscivores as a driver.

Although many studies have focused on marine resources, few studies have considered the resources of inland fisheries. Inland fishery resources are typically either monitored on the basis of catch data alone or are not assessed quantitatively at all, despite their social, economic, and ecological importance. Because freshwater ecosystems have been severely degraded by human activities, evaluating the trends and current status of fishery resources and assessing their drivers are urgent tasks. We compiled long-term data on the annual catch, fishing effort, and fishing power of 23 Japanese lakes, using two sets of government statistics that date back to the 1950s, which were previously neglected because of the large number of missing values. Using Bayesian state-space models, we examined the trajectories of the catch per unit effort (CPUE) of entire communities, considering changes in fishing effort and fishing power, and quantified both changes in the CPUE over the 10-, 20-, and 30-year periods preceding 2008 and the temporal detrended stability of the CPUE over the three periods. We also investigated the relationships among the CPUE changes and stability, anthropogenic drivers, and lake morphometric characteristics. The CPUE declined in 17, 19, and 15 of the 23 lakes over the past 10-, 20-, and 30-year periods, respectively. Our macroecological analyses demonstrate that the functional group richness of exotic piscivores was the most important predictor of changes in the CPUE among the drivers we considered. The stability of the CPUE was positively related to lake area; larger lakes have more stable CPUE. The functional group richness of exotic piscivores also negatively affected the stability of the CPUE. The effect of overfishing was considered to be small because both fishing effort and power declined in almost all of the lakes. Thus, our findings suggest that increasing exotic piscivore species may diminish the resources and their stability, particularly in Japanese lakes where native piscivores are rare. This might lead to a substantial decline in ecosystem services. Our study highlights the importance of assessing inland fishery resources in a comprehensive manner and the need for restoration strategies to mitigate the effects of exotic piscivores.

LetsR: a new R package for data handling and analysis in macroecology

Summary The current availability of large ecological data sets and the computational capacity to handle them have fostered the testing and development of theory at broad spatial and temporal scales. Macroecology has particularly benefited from this era of big data, but tools are still required to help transforming this data into information and knowledge. Here, we present ‘letsR’, a package for the R statistical computing environment, designed to handle and analyse macroecological data such as species’ geographic distributions (polygons in shapefile format and point occurrences) and environmental variables (in raster format). The package also includes functions to obtain data on species’ habitat use, description year and current as well as temporal trends in conservation status as provided by the IUCN RedList online data base. ‘letsR’ main functionalities are based on the presence–absence matrices that can be created with the package's functions and from which other functions can be applied to generate, for example species richness rasters, geographic mid‐points of species and species‐ and site‐based attributes. We exemplify the package's functionality by describing and evaluating the geographic pattern of species’ description year in tailless amphibians. All data preparation and most analyses were made using the ‘letsR’ functions. Our example illustrates the package's capability for conducting macroecological analyses under a single computer platform, potentially helping researchers to save time and effort in this endeavour.

A review of the Polystira clade--the Neotropic's largest marine gastropod radiation (Neogastropoda: Conoidea: Turridae sensu stricto).

The Polystira clade (here comprising Polystira and Pleuroliria) is a poorly known but hyper-diverse clade within the neogastropod family Turridae (sensu stricto). It has extensively radiated within the tropics and subtropics of the Americas, to which it is endemic. In this paper we present a synthetic overview of existing information on this radiation together with new information on estimated species diversity, systematic relationships, a species-level molecular phylogenetic analysis and preliminary macroecological and diversification analyses, to serve as a platform for further study. We currently estimate that about 300 species (122 extant) are known from its 36 million year history but this number will undoubtedly increase as we extend our studies. We discuss the relationships of Polystira to other Neotropical Turridae (s.s.) and examine the taxonomy and systematics of the geologically oldest described members of the clade. To aid taxonomic description of shells we introduce a new notation for homologous major spiral cords. Focusing on key publications, we discuss in detail the changing historical understanding of the taxonomy of the clade and the relationships of its component genus-level taxa: Polystira Woodring, 1928, Pleuroliria de Gregorio, 1890, Josephina Gardner, 1945 and Oxytropa Glibert, 1955. We designate a neotype for Pleurotoma (Pleuroliria) supramirifica de Gregorio, 1890, to stabilize our understanding of this, the type species of Pleuroliria. Application of the name Oxytropa is restricted to the type species. The genus Polystira is conchologically re-described and for the first time we synthesize available information on the anatomy, feeding and toxinology, reproduction and life history, larval modes and life habits, and geographic and bathymetric ranges of its species. We give an updated list of the 19 formally described living species and present the pitfalls of the currently poor species-level taxonomy of Polystira using case examples. We present a molecular phylogenetic analysis of 22 extant species using three mitochondrial gene fragments (COI, 12S rRNA and 16S rRNA). This reveals undescribed species and indicates that Recent genetic clades ('biospecies') are consistent with finely divided conchological 'morphospecies'. Historically, there has been a slow realisation of the high species diversity of the Polystira clade and we consider that this may be due to inadequate precision of morphological description of shells and a lack of clear homology statements. We suggest how these both might be improved. Finally, using a data compilation based on museum specimens we examine species range-size distributions and species abundance distributions for 85 of the 112 extant western Atlantic species that we have delimited to date. Our results indicate that the majority of species are rare and have short geographic ranges; only a few are wide-ranging and abundant. This has important implications for surveys of biodiversity.

The hidden side of plant invasions: the role of genome size.

The ecological role of genome size in plant biology, biogeography, and morphology has garnered increasing attention as the methods and technology associated with measuring cytological characteristics have become more reliable and accessible. However, how plant genome size influences plant invasions and at what stage in the invasion this influence occurs have been little explored. Several large-scale analyses of published data have yielded valuable interspecific comparisons, but experimental studies that manipulate environmental factors are needed, particularly below the species level, to fully understand the role that genome size plays in plant invasion. In this review, we summarize the available knowledge, discuss the integration of genome size data into invasion research, and suggest how it can be applied to detect and manage invasive species. We also explore how global climate change could exert selective pressures on plant populations with varying genome sizes, thereby increasing the distribution range and invasiveness of some populations while decreasing others. Finally, we outline avenues for future research, including considerations of large-scale studies of intraspecific variation in genome size of invasive populations, testing the interaction of genome size with other factors in macroecological analyses of invasions, as well as the role this trait may play in plant-enemy interactions.

A long-term macroecological analysis of the recovery of a waterbird metacommunity after site protection.

We used the so called “land-bridge island” or “nested-subsets” theory to test the resilience of a highly fragmented and perturbated waterbird metacommunity, after legal protection of 18 wetlands in the western Mediterranean. Sites were monitored during 28 years and two seasons per year. The metacommunity was composed by 44 species during breeding and 67 species during wintering, including shorebirds, ducks, herons, gulls and divers (Podicipedidae). We identified a strong nested pattern. Consistent with the fact that the study system was to a large extent a spatial biogeographical continuous for thousands of years, fragmented only during the last centuries due to human activities. Non-random selective extinction was the most likely historical process creating the nested pattern, operated by the differential carrying capacity (surface-area) of the remaining sites. We also found a positive temporal trend in nestedness and a decreasing trend in species turnover among sites (β-diversity), indicating that sites are increasingly more alike to each other (i.e. increased biotic homogenization). This decreasing trend in β-diversity was explained by an increasing trend in local (α) diversity by range expansion of half the study species. Regional (γ) diversity also increased over time, indicating that colonization from outside the study system also occurred. Overall our results suggest that the study metacommunity is recovering from historical anthropogenic perturbations, showing a high long-term resilience, as expected for highly vagile waterbirds. However, not all waterbird groups contributed equally to the recovery, with most breeding shorebird species and most wintering duck species showing no geographical expansion.

Population-level perspectives on global change: genetic and demographic analyses indicate various scales, timing, and causes of scyphozoan jellyfish blooms

Whether a perceived increase in the abundance of jellyfishes is related to changing marine environments has been considered primarily using large-scale analyses of multi-species assemblages. Yet jellyfish blooms—rapid increases in the biomass of pelagic coelenterate species—are single-species demographic events. Using published and new genetic analyses and population surveys, we investigate whether there may be a critical knowledge gap between the scales of recent analyses and the scales of natural phenomena. We find that scyphomedusae may show population genetic structure over scales of tens to hundreds of kilometers, that environments vary regionally and locally, and that populations of medusae can display uncorrelated dynamics on these scales. These findings suggest genetic differences between populations and/or environmental differences between sites are important determinants of population dynamics in these jellyfishes. Moreover, the local abundance of medusae may be most strongly correlated with preceding rather than current local environmental conditions, indicating there is a cumulative time-course to the formation of ‘blooms’. Broad-scale macro-ecological analyses will need to build from coordinated, long-term, fine-grained studies to synthesize, rather than mask, population-level phenomena in larger-scale analyses.

GlUV: a global UV‐B radiation data set for macroecological studies

Summary Macroecology has prospered in recent years due in part to the wide array of climatic data, such as those provided by the WorldClim and CliMond data sets, which has become available for research. However, important environmental variables have still been missing, including spatial data sets on UV‐B radiation, an increasingly recognized driver of ecological processes. We developed a set of global UV‐B surfaces (glUV) suitable to match common spatial scales in macroecology. Our data set is based on remotely sensed records from NASA's Ozone Monitoring Instrument (Aura‐OMI). Following a similar approach as for the WorldClim and CliMond data sets, we processed daily UV‐B measurements acquired over a period of eight years into monthly mean UV‐B data and six ecologically meaningful UV‐B variables with a 15‐arc minute resolution. These bioclimatic variables represent Annual Mean UV‐B, UV‐B Seasonality, Mean UV‐B of Highest Month, Mean UV‐B of Lowest Month, Sum of Monthly Mean UV‐B during Highest Quarter and Sum of Monthly Mean UV‐B during Lowest Quarter. We correlated our data sets with selected variables of existing bioclimatic surfaces for land and with Terra–MODIS Sea Surface Temperature for ocean regions to test for relations to known gradients and patterns. UV‐B surfaces showed a distinct seasonal variance at a global scale, while the intensity of UV‐B radiation decreased towards higher latitudes and was modified by topographic and climatic heterogeneity. UV‐B surfaces were correlated with global mean temperature and annual mean radiation data, but exhibited variable spatial associations across the globe. UV‐B surfaces were otherwise widely independent of existing bioclimatic surfaces. Our data set provides new climatological information relevant for macroecological analyses. As UV‐B is a known driver of numerous biological patterns and processes, our data set offers the potential to generate a better understanding of these dynamics in macroecology, biogeography, global change research and beyond. The glUV data set containing monthly mean UV‐B data and six derived UV‐B surfaces is freely available for download at: http://www.ufz.de/gluv.

Where next for macroecology: citizen macroecology?

ISSN 1948-6596 news and update symposium summary Where next for macroecology: citizen macroecology? 2 nd annual symposium of the British Ecological Society’s Macroecology Special Interest Group – Sheffield, UK, 10 th –11 th July 2013 Introduction Following the success of the first meeting of the British Ecological Society’s (BES) Macroecology Special Interest Group in 2012 (see Keith et al. 2012), the second annual meeting of the group took place at the University of Sheffield in July The main themes were the ‘big data’ ap- proach to testing general theory in macroecology, the role of citizen science, and the drafting of a ‘manifesto for macroecology’. There was an overt focus on the current limitations of macroecology, centred on a set of five ‘provocations’ that were put forward early on and returned to repeatedly. These were statements (designed to provoke): (1) that macroecology is now limited by theory, not data availability; (2) that we cannot study natural systems without consideration of human influ- ences; (3) that meaningful predictions of ecosys- tem-level responses to climate change cannot be generated through modelling, because we can never model every interaction; (4) that functional groups, rather than species, are the meaningful units for macroecological analysis; and (5) that macroecology needs a ‘flagship project’. The meeting’s keynote speaker was Ethan White (Utah State University, USA), who focused on one poten- tial flagship: the pursuit of a unifying theory. The other talks were a mix of 5-minute presentations by delegates interspersed with a few longer con- tributions on topics related to collecting and ana- lysing large datasets. The main point emerging from the discus- sions and presentations was that, contrary to the first provocation, macroecology is still strongly limited by data availability, especially data with fine-scale coverage over large spatial extents and, ideally, through time. Citizen science frequently arose as a possible avenue for resolving the data deficit. Indeed, macroecology and citizen science inherently have much in common. Citizen macroecology Citizen science—the contribution to scientific re- search by non-specialists—has the potential to enable fine-grained data collection over large spa- tial extents and through time, beyond what would be feasible by scientists alone, given our limited time and resources (Devictor et al. 2010, Tulloch et al. 2013). We consider much of the ecological and biogeographical research undertaken as 'citizen science' to be macroecology, and argue that macroecology should harness its potential more. Done well, citizen science promotes public interest in, and awareness of, science. In turn, ac- tive public engagement can strengthen the impact of the research (Dickinson et al. 2012). The discus- sions in Sheffield identified a need for greater public engagement with macroecological re- search, suggesting that macroecologists would do well to engage with citizen science sooner rather than later. Below we outline, and then discuss in the wider context, three areas of citizen science rep- resenting a selection of the research presented at the Sheffield meeting: (i) developing citizen sci- ence projects and engaging the public; (ii) the op- portunities and challenges surrounding the use of volunteer-collected data; and (iii) digitising mu- seum collections for macroecology. Developing Citizen Science Projects Heather Sugden (University of Newcastle, UK) de- scribed a very successful ongoing citizen science project. The Big Sea Survey 1 is a project in which volunteers in the North East of England have filled a large data gap for intertidal species’ occurrences along a 150 km stretch of the local coastline. The success of this project stems in part from the flexi- 1 http://www.bigseasurvey.co.uk/, last accessed 21/01/2014 frontiers of biogeography 6.1, 2014 — © 2014 the authors; journal compilation © 2014 The International Biogeography Society

Assessing the influence of geography, land cover and host species on the local abundance of a generalist brood parasite, the brown‐headed cowbird

AbstractAimThe brown‐headed cowbird is an obligate brood parasite known to exploit a large number of host species and use a variety of habitats. Much attention has been directed towards uncovering the fundamental factors that affect cowbird abundance; however, no study has evaluated these factors in the context of a biogeographic‐scale analysis that takes into account spatial autocorrelation. Our primary objective was to compare the relative influence of geography, land cover and host species on the local abundance of cowbirds.LocationGreat Plains region of the USA.MethodsWe used data from the North American Breeding Bird Survey and the National Land Cover Database to examine the relationships between cowbird abundance and host species, land cover composition and geographic location of a survey route. Multiple regression models were developed for various combinations of these factors. To control for spatial autocorrelation, we used SAM 4.0 (Spatial Analysis in Macroecology) software to implement simultaneous autoregressive modelling of the error term. We then used a model comparison approach to identify the factors that most influence cowbird abundance.ResultsAmong all models examined, host species richness was the single most strong predictor and the sole statistically significant predictor. Cowbird abundance increased with host species richness but did not change in any significant way with non‐host passerine richness or abundance of host species. Models with land cover variables tended to have the poorest fit to the cowbird abundance data.Main conclusionsOur results suggest that cowbirds may be attracted to areas with greater host richness and/or recruit better in such areas, although our data did not allow direct examination of either process. In a greater context, our study demonstrates the utility of a spatially based and geographically extensive analysis in finding range‐wide factors that affect the local abundance of a species.

The igapó of the Negro River in central Amazonia: Linking late-successional inundation forest with fluvial geomorphology

Despite important progress on Amazonian floodplain research, the flooded forest of the Negro River “igapó” has been little investigated. In particular, no study has previously focused the linkage between fluvial geomorphology and the floristic variation across the course of the river. In this paper we describe and interpret relations between igapó forest, fluvial geomorphology and the spatial evolution of the igapó forest through the Holocene. Therefore, we investigate the effect of geomorphological units of the floodplain and channel patterns on tree diversity, composition and structural parameters of the late-successional igapó forest. Our results show that sites sharing almost identical flooding regime, exhibit variable tree assemblages, species richness and structural parameters such as basal area, tree density and tree heights, indicating a trend in which the geomorphologic styles seem to partially control the organization of igapó's tree communities. This can be also explained by the high variability of well-developed geomorphologic units in short distances and concentrated in small areas. In this dynamic the inputs from the species pool of tributary rivers play a crucial role, but also the depositional and erosional processes associated with the evolution of the floodplain during the Holocene may control floristic and structural components of the igapó forests. These results suggest that a comprehensive approach integrating floristic and geomorphologic methods is needed to understand the distribution of the complex vegetation patterns in complex floodplains such as the igapó of the Negro River. This combination of approaches may introduce a better comprehension of the temporal and spatial evolutionary analysis and a logic rationale to understand the vegetation distribution and variability in function of major landforms, soil distributions and hydrology. Thus, by integrating the past into macroecological analyses will sharpen our understanding of the underlying forces for contemporary floristic patterns along the inundation forests of the Negro River.

Enhancing conservation of large‐river biodiversity by accounting for tributaries

Alteration of rivers for human use has resulted in substantial biodiversity declines, particularly for species restricted to the largest rivers. Conservation and restoration efforts on large rivers often focus on the mainstem, but societal reliance on benefits derived from these alterations generally prevents complete restoration of the river. We propose that certain tributaries, by virtue of their lower degree of alteration, offer underappreciated opportunities for conserving large‐river biota. Using the distribution patterns of large‐river specialist fishes from the Mississippi River Basin, we identify a threshold discharge (166 cubic meters per second) beyond which tributaries support all or most of these species. We merge our macroecological analysis of assemblage structure with data on dam locations to identify tributaries where restoration efforts offer the highest potential conservation gains for 60 of the 68 large‐river specialist fish species that are of state, federal, or international conservation concern. Given the highly altered state of many mainstem rivers, this analytical approach could be used to select tributaries that will aid in the conservation of large‐river species worldwide.