Find research datasets worth reusing

Data from: Ice-cover is the principal driver of ecological change in High Arctic lakes and ponds

Recent climate change has been especially pronounced in the High Arctic, however, the responses of aquatic biota, such as diatoms, can be modified by site-specific environmental characteristics. To assess if climate-mediated ice cover changes affect the diatom response to climate, we used paleolimnological techniques to examine shifts in diatom assemblages from ten High Arctic lakes and ponds from Ellesmere Island and nearby Pim Island (Nunavut, Canada). The sites were divided a priori into four groups ("warm", "cool", "cold", and "oasis") based on local elevation and microclimatic differences that result in differing lengths of the ice-free season, as well as about three decades of personal observations. We characterized the species changes as a shift from Condition 1 (i.e. a generally low diversity, predominantly epipelic and epilithic diatom assemblage) to Condition 2 (i.e. a typically more diverse and ecologically complex assemblage with an increasing proportion of epiphytic species). This shift from Condition 1 to Condition 2 was a consistent pattern recorded across the sites that experienced a change in ice cover with warming. The "warm" sites are amongst the first to lose their ice covers in summer and recorded the earliest and highest magnitude changes. The "cool" sites also exhibited a shift from Condition 1 to Condition 2, but, as predicted, the timing of the response lagged the "warm" sites. Meanwhile some of the "cold" sites, which until recently still retained an ice raft in summer, only exhibited this shift in the upper-most sediments. The warmer "oasis" ponds likely supported aquatic vegetation throughout their records. Consequently, the diatoms of the "oasis" sites were characterized as high-diversity, Condition 2 assemblages throughout the record. Our results support the hypothesis that the length of the ice-free season is the principal driver of diatom assemblage responses to climate in the High Arctic, largely driven by the establishment of new aquatic habitats, resulting in increased diversity and the emergence of novel growth forms and epiphytic species.

Data from: Ecology of ontogenetic body-mass scaling of gill surface area in a freshwater crustacean

Several studies have documented ecological effects on intra- and interspecific body-size scaling of metabolic rate. However, little is known about how various ecological factors may affect the scaling of respiratory structures supporting oxygen uptake for metabolism. Our study is apparently the first to provide evidence for ecological effects on the scaling of a respiratory structure among conspecific populations of any animal. We compared the body-mass scaling of gill surface area (SA) among eight spring-dwelling populations of the amphipod crustacean Gammarus minus. Although gill SA scaling was not related to water temperature, conductivity or G. minus population density, it was significantly related to predation regime (and secondarily to pH). Body-mass scaling slopes for gill SA were significantly lower in four populations inhabiting springs with fish predators than for those in four springs without fish (based on comparing means of the population slopes, or slopes calculated from pooled raw data for each comparison group). As a result, gill SA was proportionately smaller in adult amphipods from fish vs. fishless springs. This scaling difference paralleled similar differences in the scaling exponents for the rates of growth and resting metabolic rate. We hypothesized that gill SA scaling is shallower in fish vs. fishless spring populations of G. minus because of effects of size-selective predation on size-specific growth and activity that in turn affect the scaling of oxygen demand and concomitantly the gill capacity (SA) for oxygen uptake. Although influential theory claims that metabolic scaling is constrained by internal body design, our study builds on previous work to show that the scaling of both metabolism and the respiratory structures supporting it may be ecologically sensitive and evolutionarily malleable.

opencc-zeroDec 2017View details →

Data from: Approaches to integrating genetic data into ecological networks

As molecular tools for assessing trophic interactions become common, research is increasingly focused on the construction of interaction networks. Here we demonstrate three key methods for incorporating DNA data into network ecology and discuss analytical considerations using a model consisting of plants, insects, bats and their parasites from the Costa Rican dry forest. The simplest method involves the use of Sanger sequencing to acquire long sequences to validate or refine field identifications, for example of bats and their parasites, where one specimen yields one sequence and one identification. This method can be fully quantified and resolved and these data resemble traditional ecological networks. For more complex taxonomic identifications, we target multiple DNA loci e.g. from a seed or fruit pulp sample in faeces. These networks are also well resolved but gene targets vary in resolution and quantification is difficult. Finally for mixed templates such as faecal contents of insectivorous bats we use DNA metabarcoding targeting two sequence lengths (157bp, 407bp) of one gene region and a MOTU, BLAST and BIN association approach to resolve nodes. This network type is complex to generate and analyse and we discuss the implications of this type of resolution on network analysis. Using these data we construct the first molecular-based network of networks containing 3304 interactions between 762 nodes of 8 trophic functions and involving parasitic, mutualistic, and predatory interactions. We provide a comparison of the relative strengths and weaknesses of these data types in network ecology.

Data from: How are the phenologies of ripening and seed release affected by species' ecology and evolution?

The phenology of seed ripening and release are important for dispersal, reproductive success and survival of plants. Most phenological studies, however, consider early phenological phases. Here, we examined the ecological and evolutionary basis of ripening and seed release phenology. We monitored single flower phenology for 104 plant species from 30 families and three life forms from central Europe. Further, we undertook an associate monitoring study along an elevational gradient over two years. We calculated temperature demands (as growing degree days) for ripening and seed release and examined them with respect to the species' seed mass, life form, dispersal mode and phylogeny. We found a strong correlation between species' seed mass and temperature demands for ripening. For both variables seed mass and temperature demands for seed ripening, we found a strong effect of the species phylogeny. These phylogenetic signals strongly indicate that the evolutionary history of the species' lineage affects its seed mass and the temperature demands for seed ripening. Among the studied life forms, shrub species showed the most efficient ripening process. Anemochorous species showed lower relative humidity during seed release than epizoochorous species. For anemochorous species, the synchronisation of release timing with periods that show favourable environmental conditions for wind dispersal could be interpreted as a phenological adaptation to increase dispersal distances. According to the monitoring along the elevational gradient, individuals from higher altitudes showed lower temperature demands for ripening than individuals from lower altitudes. This might tentatively indicate physiological adaptations to lower temperature demands for locations with a shorter growing season. Our study provides basic insights into the ecological, environmental and evolutionary constraints that shape the ripening and seed release phenology of plants. We introduce data that can be used to advance existing models of ripening phenology, seed release and plant spread.

opencc-zeroDec 2012View details →

Data from: Ecological co-associations influence species' responses to past climatic change: an example from a Sonoran Desert bark beetle

Ecologically interacting species may have phylogeographic histories that are shaped both by features of their abiotic landscape, and by biotic constraints imposed by their co-association. The Baja California peninsula provides an excellent opportunity to examine the influence of abiotic vs. biotic factors on patterns of diversity in plant-insect species. This is because past climatic and geological changes impacted the genetic structure of plants quite differently to that of co-distributed free-living animals (e.g., herpetofauna and small mammals). Thus, 'plant-like' patterns should be discernible in host-specific insect herbivores. Here we investigate the population history of a monophagous bark beetle, Araptus attenuatus, and consider drivers of phylogeographic patterns in light of previous work on its host plant, Euphorbia lomelii. Based on mitochondrial and nuclear markers, we found that the evolutionary history of A. attenuatus exhibits similarities to host plant that are attributable to both biotic and abiotic processes. Southward range expansion and recent colonization of continental Sonora peninsula appear to be unique to this taxon pair, and likely reflect influences of the host plant. On the other hand, abiotic factors with landscape-level influences on suites of co-distributed taxa, such as Plio- and Pleistocene-aged marine incursions in the region, also left genetic signatures in beetle populations. Superimposed on these similarities, bark beetle-specific patterns and processes were also evident. Taken together, this work illustrates that the evolutionary history of species-specific insect herbivores may represent a mosaic of influences, including—but not limited to—those imposed by the host plant.

Data from: Immigrant reproductive dysfunction facilitates ecological speciation

The distributions of species are not only determined by where they can survive – they must also be able to reproduce. Although immigrant inviability is a well-established concept, the fact that immigrants also need to be able to effectively reproduce in foreign environments has not been fully appreciated in the study of adaptive divergence and speciation. Fertilization and reproduction are sensitive life history stages that could be detrimentally affected for immigrants in non-native habitats. We propose that 'immigrant reproductive dysfunction' is a hitherto overlooked aspect of reproductive isolation caused by natural selection on immigrants. This idea is supported by results from experiments on an externally fertilizing fish (sand goby, Pomatoschistus minutus). Growth and condition of adults were not affected by non-native salinity whereas males spawning as immigrants had lower sperm motility and hatching success than residents. We interpret these results as evidence for local adaptation or acclimation of sperm, and possibly also components of paternal care. The resulting loss in fitness, which we call 'immigrant reproductive dysfunction', has the potential to reduce gene flow between populations with locally adapted reproduction, and it may play a role in species distributions and speciation.

opencc-zeroDec 2014View details →

Data from: The evolution of life cycle complexity in aphids: ecological optimization, or historical constraint?

For decades, biologists have debated why many parasites have obligate multi-host life cycles. Here, we use comparative phylogenetic analyses of aphids to evaluate the roles of ecological optimization and historical constraint in the evolution of life cycle complexity. If life cycle complexity is adaptive, it should be evolutionarily labile, i.e., change in response to selection. We provide evidence that this is true in some aphids (aphidines), but not others (non-aphidines) – groups that differ in the intensity of their relationships with primary hosts. Next, we test specific mechanisms by which life cycle complexity could be adaptive or a constraint. We find that among aphidines there is a strong association between complex life cycles and polyphagy but only a weak correlation between life cycle complexity and reproductive mode. In contrast, among non-aphidines the relationship between life cycle complexity and host breadth is weak but the association between complex life cycles and sexual reproduction is strong. Thus, although the adaptiveness of life cycle complexity appears to be lineage specific, across aphids, life cycle evolution appears to be tightly linked with the evolution of other important natural history traits.

opencc-zeroDec 2014View details →

Data from: Correlation between genetic diversity and environmental suitability: taking uncertainty from ecological niche models into account

The hindcast of shifts in the geographical ranges of species as estimated by ecological niche modelling (ENM) has been coupled with phylogeographical patterns, allowing the inference of past processes that drove population differentiation and genetic variability. However, more recently, some studies have suggested that maps of environmental suitability estimated by ENM may be correlated to species' abundance, raising the possibility of using environmental suitability to infer processes related to population demographic dynamics and genetic variability. In both cases, one of the main problems is that there is a wide variation in ENM development methods and climatic models. In this study, we analyse the relationship between heterozygosity (He) and environmental suitability from multiple ENMs for 25 population estimates for Dipteryx alata, a widely distributed, endemic tree species of the Cerrado region of central Brazil. We propose a new approach for generating a statistical distribution of correlations under randomly generated ENM. The confidence intervals from these distributions indicate how model selection with different properties affects the ability to detect a correlation of interest (e.g. the correlation between He and suitability). Additionally, our approach allows us to explore which particular ensemble of ENMs produces the better result for finding an association between environmental suitability and He. Caution is necessary when choosing a method or a climatic data set for modelling geographical distributions, but the new approach proposed here provides a conservative way to evaluate the ability of ensembles to detect patterns of interest.

opencc-zeroDec 2014View details →

Data from: Photosynthetic pathways in Bromeliaceae: phylogenetic and ecological significance of CAM and C3 based on carbon isotope ratios for 1893 species

A comprehensive analysis of photosynthetic pathways in relation to phylogeny and elevational distribution was conducted in Bromeliaceae, an ecologically diverse Neotropical family containing large numbers of both terrestrial and epiphytic species. Tissue carbon isotope ratio (δ13C) was used to determine the occurrence of crassulacean acid metabolism (CAM) and C3 photosynthesis in 1893 species, representing 57% of species and all 56 genera in the family. The frequency of δ13C values showed a strongly bimodal distribution: 1074 species (57%) had values more negative than −20‰ (mode = −26.7‰), typical of predominantly daytime carbon fixation via the C3 pathway, whereas 819 species (43%) possessed values less negative than −20‰ (mode = −13.3‰), indicative of predominantly nocturnal fixation of carbon via the CAM pathway. Amongst the six almost exclusively terrestrial subfamilies in Bromeliaceae, Brocchinioideae, Lindmanioideae and Navioideae consisted entirely of C3 species, with CAM species being restricted to Hechtioideae (all species of Hechtia tested), Pitcairnioideae (all species belonging to a xeric clade comprising Deuterocohnia, Dyckia and Encholirium) and Puyoideae (21% of Puya spp.). Of the other two subfamilies, in the overwhelmingly epiphytic (plus lithophytic) Tillandsioideae, 28% of species possessed CAM photosynthesis, all restricted to the derived genus Tillandsia and tending towards the more extreme epiphytic 'atmospheric' life-form. In Bromelioideae, with comparable numbers of terrestrial and epiphytic species, 90% of taxa showed CAM; included in these are the first records of CAM photosynthesis in Androlepis, Canistropsis, Deinacanthon, Disteganthus, Edmundoa, Eduandrea, Hohenbergiopsis, Lymania, Pseudananas, Ronnbergia and Ursulaea. With respect to elevational gradients, the greatest number of C3 bromeliad species were found at mid-elevations between 500 and 1500 m, whereas the frequency of CAM species declined monotonically with increasing elevation. However, in Puya, at least ten CAM species have been recorded at elevations > 3000 m, showing that CAM photosynthesis is not necessarily incompatible with low temperatures. This survey identifies five major origins of CAM photosynthesis at a higher taxonomic level in Bromeliaceae, but future phylogenetic work is likely to reveal a more fine-scale pattern of gains and losses of this trait, especially in ecologically diverse and widely distributed genera such as Tillandsia and Puya

Data from: At least some meiofaunal species are not everywhere. Indication of geographic, ecological and geological barriers affecting the dispersion of species of Ototyphlonemertes (Nemertea, Hoplonemertea)

Most meiofaunal species are known to have a broad distribution with no apparent barriers to their dispersion. However, different morphological and/or molecular methods supported patterns of diversity and distribution that may be different among taxa while also conflicting within the same group. We accurately assessed the patterns of geographic distribution in actual genetic species of a marine meiofaunal animal model: Ototyphlonemertes. Specimens were collected from several sites around Europe, Northern and Central America, Southern America, Pacific Islands and Asia. We sequenced regions of two mitochondrial and two nuclear genes. Using single-gene, a concatenated data set, multilocus approaches and different DNA taxonomy methods, we disentangled the actual diversity and the spatial structures of haplotypes and tested the possible correlation between genetic diversity and geographic distance. The results show (i) the importance of using several genes to uncover both diversity and highlight phylogeographic relationships among species and that (ii) independent genetic evolutionary entities have a narrower distribution than morphological species. Moreover, (iii) a Mantel test supported a positive correlation between genetic and geographical distance. By sampling from the two sides of Isthmus of Panama, we were additionally able to identify lineage divergence times that are concordant with vicariance mechanisms caused by the geological closure of the seaway across the Isthmus. We therefore propose that in addition to distance, other geological and ecological conditions are also barriers to the dispersion of and gene flow in marine meiofaunal organisms.

Data from: Hybridization associated with cycles of ecological succession in a passerine bird

Identifying the diversity of contexts that can lead to hybridization is important for understanding its prevalence and dynamics in natural populations. Despite the potential of ecological succession to dramatically alter species co-occurrence and abundances, it is unknown whether it directly promotes hybridization and, if so, has long-lasting consequences. Here, we summarize 30 years of survey data across 10 populations to show that in western and mountain bluebirds, heterospecific pairing occurs during repeatable and transient colonization events at the early stages of species turnover. Despite mixed pairing occurring only during early succession, genetic data showed presence of hybrids at both early and late successional stages. Moreover, hybrids showed novel patterns of variation in morphology and behavior, emphasizing that even ephemeral contexts for hybridization can have important evolutionary consequences. Our results suggest that because ecological succession often brings together closely related competitors in disparate numbers but lasts for only a brief period of time, it may be a widespread but underappreciated context for hybridization.

opencc-zeroDec 2017View details →

Data from: Diversification rates of the "Old Endemic" murine rodents of Luzon Island, Philippines are inconsistent with incumbency effects and ecological opportunity

Diversity-dependent cladogenesis occurs when a colonizing lineage exhibits increasing interspecific competition as it ecologically diversifies. Repeated colonization of a region by closely related taxa may cause similar effects as species within each lineage compete with one another. This may be particularly relevant for secondary colonists, which could experience limited diversification due to competition with earlier, incumbent colonists over evolutionary time. We tested the hypothesis that an incumbent lineage may diminish the diversification of secondary colonists in two speciose clades of Philippine "Old Endemic" murine rodents—Phloeomyini and Chrotomyini—on the relatively old oceanic island of Luzon. Although phylogenetic analyses confirm the independent, non-contemporaneous colonization of Luzon by the ancestors of these two clades, we found no support for arrested diversification in either. Rather, it appears that diversification of both clades resulted from constant-rate processes that were either uniform or favored the secondary colonists (Chrotomyini), depending on the method used. Our results suggest that ecological incumbency has not played an important role in determining lineage diversification among Luzon murines, despite sympatric occurrence by constituent species within each lineage, and a substantial head start for the primary colonists.

opencc-zeroDec 2018View details →

Data from: Resolving the paradox of environmental quality and sociality: the ecological causes and consequences of cooperative breeding in two lineages of birds

Cooperatively breeding animals occur in virtually every ecosystem on earth. Comparative and biogeographic studies suggest that that both benign and harsh, as well as stable and fluctuating, environments can favor the evolution of cooperative breeding behavior. The fact that cooperative societies occur in environments of such contrasting quality creates a paradox of environmental quality and sociality. The dual-benefits framework—which leads to the prediction that the ecological consequences of sociality (e.g. range size) vary depending on the benefits that individuals of each species receive by forming social groups—offers a potential resolution to this paradox. Here, we use a case study of two avian lineages, starlings (Sturnidae) and hornbills (Bucerotidae), in which environmental unpredictability appears to have opposite effects on the evolution of cooperation to test the dual-benefits framework. Consistent with previous work, harsh and unpredictable environments promote cooperative breeding behavior in starlings, which in turn leads to larger geographic ranges. However, cooperatively breeding hornbills occur in benign and stable environments, but sociality does not influence range size. Our study suggests that the paradox of environmental quality and sociality arises largely because cooperative breeding is an umbrella term, encompassing social species that form groups for different reasons. Differentiating between these reasons that social groups form is crucial for developing a predictive framework for understanding the evolution of cooperative breeding behavior.

Data from: Resource availability and roosting ecology shape reproductive phenology of rain forest insectivorous bats

Bats in temperate and subtropical regions typically synchronize birth of a single young with peaks in resource availability driven by local climate patterns. In tropical rain forest, insects are available throughout the year, potentially allowing departures from seasonal monoestry. However, reproductive energy budgets may be constrained by the cost of commuting to foraging grounds from distant roosts. To test these hypotheses, we simultaneously tracked female reproductive activity of 11 insectivorous bat species, insect biomass, and local weather variables for 20 months in a Malaysian rain forest. Five species roost in forest structures and hence have low commuting costs, whereas six species depend on caves, which are limited in the landscape, and are presumed to incur higher commuting costs to foraging sites. Monthly insect biomass was positively correlated with monthly rainfall, and there was a significant relationship between insect biomass and lactation in cave-roosting but not forest-roosting species. Cave-roosting species were seasonally monoestrus, with parturition confined to a two-month period, whereas in forest-roosting species, pregnancy and lactation were recorded throughout the year. Our results suggest that the energetic costs of commuting from roosts to foraging grounds shape annual reproductive patterns in tropical rain forest insectivorous bats. Ongoing changes in forest landscapes are likely to increase these costs for cave-roosting bats, further restricting reproductive opportunities. Climate change is projected to influence the timing of rainfall events in many tropical habitats, which may disrupt relationships between rainfall, insect biomass, and bat reproductive timing, further compromising reproductive success.

opencc-zeroDec 2011View details →

Data from: The robustness and restoration of a network of ecological networks

Understanding species' interactions and the robustness of interaction networks to species loss is essential to understand the effects of species' declines and extinctions. In most studies, different types of networks (such as food webs, parasitoid webs, seed dispersal networks, and pollination networks) have been studied separately. We sampled such multiple networks simultaneously in an agroecosystem. We show that the networks varied in their robustness; networks including pollinators appeared to be particularly fragile. We show that, overall, networks did not strongly covary in their robustness, which suggests that ecological restoration (for example, through agri-environment schemes) benefitting one functional group will not inevitably benefit others. Some individual plant species were disproportionately well linked to many other species. This type of information can be used in restoration management, because it identifies the plant taxa that can potentially lead to disproportionate gains in biodiversity.

Data from: Genetic signatures of ecological diversity along an urbanization gradient

Despite decades of work in environmental science and ecology, estimating human influences on ecosystems remains challenging. This is partly due to complex chains of causation among ecosystem elements, exacerbated by the difficulty of collecting biological data at sufficient spatial, temporal, and taxonomic scales. Here, we demonstrate the utility of environmental DNA (eDNA) for quantifying associations between human land use and changes in an adjacent ecosystem. We analyze metazoan eDNA sequences from water sampled in nearshore marine eelgrass communities and assess the relationship between these ecological communities and the degree of urbanization in the surrounding watershed. Counter to conventional wisdom, we find strongly increasing richness and decreasing beta diversity with greater urbanization, and similar trends in the diversity of life histories with urbanization. We also find evidence that urbanization influences nearshore communities at local (hundreds of meters) rather than regional (tens of km) scales. Given that different survey methods sample different components of an ecosystem, we then discuss the advantages of eDNA—which we use here to detect hundreds of taxa simultaneously—as a complement to traditional ecological sampling, particularly in the context of broad ecological assessments where exhaustive manual sampling is impractical. Genetic data are a powerful means of uncovering human-ecosystem interactions that might otherwise remain hidden; nevertheless, no sampling method reveals the whole of a biological community.

opencc-zeroDec 2018View details →

Data from: Ecology of the growth of Anolis nebulosus (Squamata: Dactyloidae) in a seasonal tropical environment in the Chamela region, Jalisco, Mexico

Juvenile growth rates are thought to be restricted by available food resources. In animals that grow throughout the year, such as tropical lizards, growth is therefore predicted to be faster during the rainy season. We test this prediction using a population of Anolis nebulosus by describing the growth trajectories of both sexes using nonlinear regression models, and we then correlate the growth rates of individuals with food available in the environment, precipitation and temperature. The Von Bertalanffy model fit the growth rates of the females better, while the logistic-by-length model fit the males better. According to both models, the males grew faster than females, reaching slightly smaller sizes at adulthood. Males reached sexual maturity when 35 mm long, at an age of seven months, and females matured at 37 mm (SVL), taking nine months to reach this size. In 1989, juvenile males and females grew more in both seasons (rainy and dry) than adults; for 1990 there were no differences by season or between age classes. These results are interesting since in the 1989 and 1990 rainy seasons, practically the same orders of prey and the greatest abundance of prey available in the environment were registered. A possible explanation could be that predation was more intense in 1990 than in 1989. The influence of food, temperature and humidity in A. nebulosus shows little evidence to support our working hypothesis, mainly due to the low growth variation observed in 1990, so, we believe that the growth pattern of this species can be a complex combination of ecological and genetic factors.

opencc-zeroDec 2017View details →

Data from: Ecological change alters the evolutionary response to harvest in a freshwater fish

Harvesting can induce rapid evolution in animal populations, yet the role of ecological change in buffering or enhancing that response is poorly understood. Here, we developed an eco-genetic model to examine how ecological changes brought about by two notorious invasive species – zebra and quagga mussels– influence harvest-induced evolution and resilience in a freshwater fish. Our study focused on lake whitefish (Coregonus clupeaformis) in the Laurentian Great Lakes, where the species supports valuable commercial and subsistence fisheries, and where the invasion of dreissenid (zebra and quagga) mussels caused drastic shifts in ecosystem productivity. Using our model system, we predicted faster rates of evolution of maturation reaction norms in lake whitefish under pre-invasion ecosystem conditions when growth and recruitment of young to the population were high. Slower growth rates that occurred under post-invasion conditions delayed when fish became vulnerable to the fishery, thus decreasing selection pressure and lessening the evolutionary response to harvest. Fishing with gill nets and traps nets generally selected for early maturation at small sizes, except when fishing at low levels with small mesh gill nets under pre-invasion conditions; in this latter case, evolution of delayed maturation was predicted. Overall, the invasion of dreissenid mussels lessened the evolutionary response to harvest, while also reducing the productivity and commercial yield potential of the stock. These results demonstrate how ecological conditions shape evolutionary outcomes and how invasive species can have a direct effect on evolutionary responses to harvest and sustainability.

opencc-zeroDec 2013View details →

Data from: Evidence for ecological divergence across a mosaic of soil types in an Amazonian tropical tree: Protium subserratum (Burseraceae)

Soil gradients are known to be an important driver of divergent natural selection in plant populations. Neotropical trees have the highest diversity on earth and it is not uncommon to find soil specialist congeners distributed parapatrically. Nevertheless very little is known about the role that edaphic heterogeneity plays in the origin and maintenance of tropical tree diversity. We predict that the mosaic of different soils in the lowland Amazon rainforest play a major role in generating and maintaining genetic variation in tropical tree populations through ecological divergence. This study examines genetic and morphological differentiation in the tropical tree Protium subserratum populations growing on the mosaic of white-sand, brown-sand and clay soil types distributed parapatrically throughout the western Amazon basin. We use nuclear microsatellites and vegetative characters to answer four major questions: (1) Are populations phenotypically and genetically differentiated across all three habitat types? (2) Can we detect a signature of natural selection over drift divergence among populations on different soil types? (3) What is the extent of hybridization and introgression across habitat types? (4) What is the relative importance of spatial distance and soil type in structuring P. subserratum tree populations and influencing migration rates among populations? We found significant morphological variation in populations across the three soil types. Higher levels of genetic differentiation and lower levels of gene flow were observed between adjacent populations found on different soil types than between geographically distant populations on the same soil type. Comparisons of phenotypic and neutral genetic variation among soil specialist populations suggest a role for natural selection in population divergence and a small number of hybrid individuals were detected between soil ecotypes showing that gene flow among populations may be occurring at a low frequency. Our results suggest that edaphic specialization in P. subserratum populations has occurred across multiple soil boundaries. While we cannot discern which factors caused initial divergence our results do suggest that natural selection is plays an important role in maintaining the integrity of populations across ecological boundaries and that edaphic specialization may be a general mechanism that promotes and maintains Amazonian tree diversity.