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Data from: Spatially heterogeneous selection in nature favors phenotypic plasticity in anuran larvae

Theory holds that adaptive phenotypic plasticity evolves under spatial or temporal variation in natural selection. I tested this prediction in a classic system of predator-induced plasticity: frog tadpoles (Rana temporaria) reacting to predaceous aquatic insects. An outdoor mesocosm experiment manipulating exposure to Aeshna dragonfly larvae revealed plasticity in most characters: growth, development, behavior, and external morphology. I measured selection by placing 1927 tadpoles into enclosures within natural ponds; photographs permitted identification of the survivors 6–9 days later. Fitness was defined as a linear combination of growth, development, and survival that correlates with survival to age 2 in another anuran species. In enclosures with many predators, selection favored character values similar to those induced by exposure to Aeshna in mesocosms. The shift in selection along the predation gradient was strongest for characters that exhibited high predator-induced plasticity. A field survey of 50 ponds revealed that predator density changes over a spatial scale relevant for movement of individual adults and larvae: 17% of variation in predation risk was among ponds separated by tens to thousands of meters and 81% was among sites ≤10m apart within ponds. These results on heterogeneity in the selection regime confirm a key tenant of the standard model for the evolution of plasticity.

Data from: Heterogeneous distributional responses to climate warming: evidence from rodents along a subtropical elevational gradient

Background: Understanding whether species' elevational range is shifting in response to directional changes in climate and whether there is a predictable pattern in that response is one of the major challenges in ecology. However, so far very little is known about the distributional responses of subtropical species to climate change, especially for small mammals. In this study, we examined the elevational range shifts at three range points (upper and lower range limits and abundance-weighted range centre) of rodents over a 30-year period (1986 to 2014-2015), in a subtropical forest of Southwest China. We also examined the influences of four ecological traits (body mass, habitat breadth, diet and daily activity pattern) on the upslope shifts in species' abundance-weighted range centres. Results: Despite the warming trend between 1986 and 2015, the eleven rodent species in analysis displayed heterogeneous dynamics at each of the three range points. Species which have larger body sizes and narrower habitat breadths, show both diurnal and nocturnal activities and more specialized dietary requirements, are more likely to exhibit upslope shifts in abundance-weighted range centres. Conclusions: Species' distributional responses can be heterogeneous even though there are directional changes in climate. Our study indicates that climate-induced alleviation of competition and lag in response may potentially drive species' range shift, which may not conform to the expectation from climate change. Difference in traits can lead to different range dynamics. Our study also illustrates the merit of multi-faceted assessment in studying elevational range shifts.

opencc-zeroDec 2018View details →

Data from: Local and landscape-scale heterogeneity shape spotted wing drosophila (Drosophila suzukii) activity and natural enemy abundance: implications for trophic interactions

Like natural enemies, invasive polyphagous pests may respond positively to local and landscape-scale diversity, making them more serious challenges to sustainable management than specialists. Yet the current view of landscape effects on pests rarely considers perennial systems or polyphagous pests. We investigated Drosophila suzukii (SWD) and natural enemy distributions and trophic interactions in blueberry systems of the southeast US in relation to local management and landscape structure. Fields were nested in 1-km landscapes along gradients of crop and forest heterogeneity (landscape compositional diversity) and field border and crop border lengths (landscape configurational diversity). Yeast-sugar bait traps were used to collect SWD and canopy suction sampling for natural enemies. Management practices at the local scale did not influence SWD abundance, but natural enemy abundance was higher in organic systems and fields with vegetation present between rows. Landscape configurational diversity and greater proportion of non-cropping habitat promoted higher SWD populations. Natural enemy communities were composed of highly generalized species, and contrary to our predictions, we observed lower abundances in landscapes with higher proportion of non-cropping area. Few predators were detected to have fed on SWD, and communities were dominated by predators with low specialization on prey in blueberry. Our results indicate that local and landscape features in blueberry landscapes have differential effects on a polyphagous pest and generalist natural enemies. Our initial analysis of predator diets, using a metabarcoding approach, suggests spatial structure in specialization on prey with high diversity of prey in predators collected in forested margins.

Data from: Functional responses in animal movement explain spatial heterogeneity in animal-habitat relationships

1. Understanding why heterogeneity exists in animal-habitat spatial relationships is critical for identifying the drivers of animal distributions. Functional responses in habitat selection – whereby animals adjust their habitat selection depending on habitat availability – are useful for describing animal-habitat spatial heterogeneity. However, they could be yielded by different movement tactics, involving contrasting inter-specific interactions. 2. Identifying functional responses in animal movement, rather than in emergent spatial patterns like habitat selection, could disentangle the effects of different movement behaviours on spatial heterogeneity in animal-habitat relationships. This would clarify how functional responses in habitat selection emerge and provide a general tool for understanding the mechanistic drivers of animal distributions. 3. We tested this approach using data from GPS-collared woodland caribou (Rangifer tarandus), a prey species under top-down control. We tested how caribou selected and moved with respect to a key resource (lichen-conifer stands) as a function of the availability of surrounding refuge land-cover (closed-conifer stands), using step selection functions. 4. Caribou selected resource patches more strongly in areas richer in refuge land-cover – a functional response in habitat selection. However, adjustments in multiple movement behaviours could have generated this pattern: stronger directed movement towards resources patches and/or longer residency within resource patches, in areas richer in refuges. Different contributions of these behaviours would produce contrasting forager spatial dynamics. 5. We identified functional responses in both movement behaviours: caribou were more likely to move towards resource patches in areas richer in refuge land-cover, and to remain in these patches during movement steps. This tactic enables caribou to spend longer foraging in safer areas where they could rapidly seek refuge in dense cover when predators are detected. 6. Our study shows that functional responses in movement can expose the context-dependent movement decisions that generate heterogeneity in animal-habitat spatial relationships. We used these functional responses to characterise anti-predator movement tactics employed by a large herbivore, but they could be applied in many different scenarios. The movement rules from functional responses in movement are well-suited to integration in spatial explicit individual-based models for forecasting animal distributions in landscapes undergoing environmental change.

Data from: Spatial genetic and morphologic structure of wolves and coyotes in relation to environmental heterogeneity in a Canis hybrid zone

Eastern wolves have hybridized extensively with coyotes and gray wolves and are listed as a 'species of special concern' in Canada. However, a distinct population of eastern wolves has been identified in Algonquin Provincial Park (APP) in Ontario. Previous Canis studies have not linked genetic analysis with field data to investigate genotype-specific morphology or determine how resident animals of different ancestry are distributed across the landscape in relation to heterogeneous environmental conditions. Accordingly, we studied resident wolves and coyotes in and adjacent to APP to identify distinct Canis types, clarify the occurrence of eastern wolves adjacent to APP, and investigate spatial genetic structure and landscape-genotype associations in the hybrid zone. We documented 3 genetically distinct Canis types that also differed morphologically, corresponding to putative gray wolves, eastern wolves, and coyotes. We also documented a substantial number of hybrid individuals (36%). Breeding eastern wolves were less common outside of APP, but occurred in some unprotected areas. We identified a steep cline extending west from APP where the dominant genotype shifted abruptly from eastern wolves to coyotes and hybrids. The genotypic pattern to the south and northwest was a more complex mosaic of alternating genotypes. We modeled genetic ancestry in response to prey availability and human disturbance and found positive and negative associations between wolf ancestry and 1) moose density and 2) road densities, respectively. Our results clarify the structure of the Canis hybrid zone adjacent to APP and provide unique insight into environmental conditions influencing hybridization dynamics between wolves and coyotes.

opencc-zeroDec 2014View details →

Data from: Configurational landscape heterogeneity shapes functional community composition of grassland butterflies

1. Landscape heterogeneity represents two aspects of landscape simplification: (i) compositional heterogeneity (diversity of habitat types) and (ii) configurational heterogeneity (number, size and arrangement of habitat patches); both with different ecological implications for community composition. 2. We examined how independent gradients of compositional and configurational landscape heterogeneity, at eight spatial scales, shape taxonomic and functional composition of butterfly communities in 91 managed grasslands across Germany. We used landscape metrics that were calculated from functional maps based on habitat preferences of individual species during different life stages. The relative effects of compositional and configurational landscape heterogeneity were compared with those of local land use intensity on butterfly taxonomic diversity, community composition and functional diversity of traits related to body size, feeding breadth and migratory tendency. 3. As expected, compositional heterogeneity had strong positive effects on taxonomic diversity while configurational heterogeneity had strong positive effects on trait dominance within the community. When landscapes had smaller mean patch size and greater boundary area, communities were dominated by species with more specialized larval feeding, decreased forewing length and limited migratory tendency. 4. The positive effects of increased configurational landscape heterogeneity outweighed the negative effects of local land use intensity on larval feeding specialization, at all spatial scales, highlighting its importance for specialists of all dispersal capabilities. 5. Synthesis and applications. We show that landscapes with high compositional heterogeneity support communities with greater taxonomic diversity, while landscapes with high configurational heterogeneity support communities that include vulnerable species (feeding specialists with larger body size, sedentary nature and more negatively affected by local management intensity). A decline in functional community composition can lead to functional homogenization, affecting the viability of the ecosystems by decreasing the variability in their responses to disturbance and altering their functioning. A landscape management for grasslands that promotes the maintenance of small patch sizes and a diversity of land-uses in the surrounding landscape (within 250–1000 m) is recommended for the conservation of diverse butterfly communities. These strategies could also benefit Government programs such as the EU 2020 Biodiversity Strategy in their efforts to reduce the loss of biodiversity in agricultural landscapes.

opencc-zeroDec 2018View details →

Data from: Accounting for heterogeneity when estimating stopover duration, timing and population size of red knots along the Luannan Coast of Bohai Bay, China

1. To successfully perform their long-distance migrations, migratory birds require sites along their migratory routes to rest and refuel. Monitoring the use of so-called stopover and staging sites provides insights into (1) the timing of migration and (2) the importance of a site for migratory bird populations. A recently developed Bayesian superpopulation model that integrates mark-recapture data and ring density data enabled the estimation of stopover timing, duration and population size. Yet, this model did not account for heterogeneity in encounter (p) and staying (ϕ) probabilities. 2. Here we extended the integrated superpopulation model by implementing finite mixtures to account for heterogeneity in p and ϕ. We used simulations and real data on red knots Calidris canutus staging in Bohai Bay, China, during spring migration to (1) show the importance of accounting for heterogeneity in encounter and staying probabilities to get unbiased estimates of stopover timing, duration and numbers of migratory birds at staging sites and (2) get accurate stopover parameter estimates for a migratory bird species at a key staging site that is threatened by habitat destruction. 3. Our simulations confirmed that heterogeneity in p affected stopover parameter estimates more than heterogeneity in ϕ. Bias was particularly severe when most birds had both low ϕ and p. Bias was largest for population size, intermediate for stopover duration and negligible for stopover timing. 4. 50,000-100,000 red knots were estimated to annually stop for 5-9 days in Bohai Bay between 10 and 30 May. This shows the key importance of this staging site for this declining species. There were no clear changes in stopover parameters over time. 5. Our study shows the importance of accounting for heterogeneity in both encounter and staying probabilities for accurately estimating stopover duration and population size and provides an appropriate modelling framework.

opencc-zeroDec 2017View details →

Data from: Heterogeneity of ecological patterns, processes and funding of marine manipulative field experiments conducted in Southeastern Pacific coastal ecosystems

Ecological manipulative experiments conducted in marine coastal ecosystems have substantially improved ecological theory during the last decades, and have provided useful knowledge for the management and conservation of coastal ecosystems. Although different studies report global trends in ecological patterns worldwide, Southeastern Pacific coastal ecosystems have been poorly considered. Given that the SE Pacific coast encompasses diverse coastal ecosystems, consideration of studies conducted along this range can shed light on the heterogeneity of processes regulating coastal communities. We reviewed the biotic interactions and habitat type considered, as well as the complexity in terms of spatial and temporal extent of manipulative field experimental studies conducted along the SE Pacific coast from 0°S to 56° S (Ecuador to Chile). We test the effect of funding reported by different studies as a main factor limiting experimental complexity. From field ecological studies published from 1970 to 2016, we found that 81 studies were truly manipulative, in which one or multiple factors were "manipulated". Around 77% of these studies were located between 21°S to 40°S, and conducted in intertidal rocky habitats. An increase in experimental studies was observed between 2010 and 2015, especially focused on herbivore-alga interactions, although we found that both the temporal and spatial extent of these studies have shown a decrease in recent decades. Funding grant amount reported had a positive effect on elapsed time of field experiments, but no effect was observed on spatial extent or in the biotic interactions considered. Elapsed time of experiments was different among the main biotic interactions considered i.e. herbivory, predation, and competition. We suggest that to further progress in applied ecological knowledge, it will be necessary to consider pollution and urbanization processes explicitly using a field experimental framework. This information could improve our understanding of how ecosystems present along the SE Pacific coast respond to climate change and increased levels of human interventions.

opencc-zeroDec 2018View details →

Data from: Next-generation phylogeography of the cockle Cerastoderma glaucum: highly heterogeneous genetic differentiation in a lagoon species

Aim. Coastal lagoons form an intriguing example of fragmented marine habitats. Restricted gene flow among isolated populations of lagoon species may promote their genetic divergence, and may thus provide a first step towards speciation. In the present study, the population genetic structure of the lagoon cockle Cerastoderma glaucum has been investigated to clarify the complex phylogeographic pattern found in previous studies, to localize major genetic breaks and to discuss their origin and maintenance. Location. The Atlantic and Mediterranean coasts, including the Baltic, North Sea and Black Sea. Methods. 204 C. glaucum individuals from 14 populations were genotyped using restriction-site associated DNA-sequencing (RADseq). The genetic diversity, divergence and structure were analyzed using genome-wide Single Nucleotide Polymorphisms (SNPs). Phylogenetic relationships were inferred under a coalescent model using SVDquartets. Results. The RADseq approach allowed inferring phylogeogeaphic relationships with an unprecedented resolution. Three deeply divergent lineages were identified within C. glaucum that are separated by many genetic barriers: one lineage in the Aegean-Black Sea region, one in the Ionian Sea, and the last one widely distributed from the Western Mediterranean to the Baltic Sea. The nested branching pattern displayed on the species tree largely agrees with the likely scenario of C. glaucum post-glacial expansion from the Mediterranean to the Baltic Sea. Main conclusion. The genetic differentiations between geographically separated lagoons proved to be strong, highlighting the evolutionary influence of these naturally fragmented habitats. The post-glacial expansion created complex patterns of spatial segregation of genetic diversity with allele frequency gradients in many outlier loci, but also discrepancies between the nuclear and mitochondrial genetic markers that probably arose from genetic surfing of mitochondrial variation.

Data from: Whether larval amphibians school does not affect the parasite aggregation rule: testing the effects of host spatial heterogeneity in field and experimental studies

Almost all macroparasites show over-dispersed infections within natural host populations such that most parasites are distributed among a few heavily-infected individuals. Despite the importance of parasite aggregation for understanding system stability, the potential for population regulation, and super-spreading events, many questions persist about its underlying drivers. Theoretically, aggregation results from heterogeneity in host exposure, resistance, and tolerance. However, few studies have examined how host spatial arrangement – which likely affects both parasite encounter and density-dependent interactions – influences infection and dispersion, representing a critical gap in our current knowledge regarding the possible drivers of parasite aggregation. Using field data from over 165 ponds and 8,000 hosts, we evaluated how the spatial clustering of amphibian larvae within ponds 1) varied among different amphibian species, and 2), affected the distribution of parasites within the host population using Taylor's Power Law. A complementary mesocosm experiment used field-guided manipulations of the spatial arrangement of larval amphibians to create a gradient in host clustering while controlling host density, thereby testing for spatial effects on both infection success and aggregation by three different trematode species. Our field data indicated that larval amphibians exhibited significant spatial clustering that was well captured by Taylor's Power Law (R2 0.92 to 0.97 for different host species), but the residual variation only weakly correlated with observed patterns of trematode parasite over-dispersion. Correspondingly, experimental manipulation of host clustering had no effects on parasite infection success or the degree of parasite aggregation among cages or mesocosms. Given the importance of parasite over-dispersion for host populations and disease dynamics, we advocate for further investigations of host and parasite spatial aggregation, particularly studies that incorporate and/or control for heterogeneity in exposure and susceptibility.

opencc-zeroMay 2019View details →

Data from: Ecosystem services and disservices by birds, bats and monkeys change with macadamia landscape heterogeneity

1.The relative importance of ecosystem services and disservices can change with landscape structure in a poorly understood way. 2.We compare the impact of biocontrol, provided by bats and birds, with that of crop raiding by vervet monkeys on yield in South African macadamia orchards. Insectivorous bats and birds are known to feed on macadamia pest insect species, like the macadamia nut borer or the green vegetable bug. Vervet monkeys move into the orchards during the day to feed on premature macadamia nuts. Bats, birds and monkeys benefit from patches of natural vegetation adjacent to orchards. 3.With exclusion experiments (four treatments: day, night, day & night, control) we quantified the relative importance of biocontrol and crop raiding on yield, comparing two different landscape settings of the orchards, a natural and a human‐modified. 4.Crop raiding occurred only close to natural vegetation and caused yield losses of about 26%. Biocontrol by bats and birds was higher near natural vegetation, but still significant in human‐modified landscapes, at up to 530m distance to forest patches. Prevented biocontrol through the exclusion of bats and birds resulted in yield losses of up to 60%. 5.Effects of biocontrol by bats and birds (USD ~5000/ha/yr) were economically more important than the losses of crop raiding (USD ~1600/ha/yr). As both are linked to the vicinity of forest patches, the removal of natural vegetation to limit monkey abundances would also limit biocontrol service provision. 6.Synthesis and applications. This study highlights the high economic benefits of biocontrol by bats and birds, which outweighed negative impacts through yield losses caused by crop‐raiding monkeys. Management practices to prevent crop damage, such as guarding, excluding vertebrates or removal of adjacent natural vegetation, would also limit access for bats and birds and the great economic benefits provided by their biocontrol. Ecosystem services by bats and birds can be promoted by the exposure of artificial roost and nest sites, but research into species‐specific preferences is needed. The education of farmers is crucial, as many are unaware of the benefits from birds and bats and the fact that these benefits can outweigh the disadvantages of the monkeys' crop‐raiding.

Data from: Heterogeneity in genetic diversity among non-coding loci fails to fit neutral coalescent models of population history

Inferring aspects of the population histories of species using coalescent analyses of non-coding nuclear DNA has grown in popularity. These inferences, such as divergence, gene flow, and changes in population size, assume that genetic data reflect simple population histories and neutral evolutionary processes. However, violating model assumptions can result in a poor fit between empirical data and the models. We sampled 22 nuclear intron sequences from at least 19 different chromosomes (a genomic transect) to test for deviations from selective neutrality in the gadwall (Anas strepera), a Holarctic duck. Nucleotide diversity among these loci varied by nearly two orders of magnitude (from 0.0004 to 0.029), and this heterogeneity could not be explained by differences in substitution rates. Using two different coalescent methods to infer models of population history and then simulating neutral genetic diversity under these models, we found that the among-locus heterogeneity in nucleotide diversity was significantly higher than expected for these simple models. Defining more complex models of population history demonstrated that a pre-divergence bottleneck was also unlikely to explain this heterogeneity. However, both selection and interspecific hybridization could account for the heterogeneity observed among loci. Regardless of the cause of the deviation, our results illustrate that violating key assumptions of coalescent models can mislead inferences of population history.

opencc-zeroDec 2014View details →

Data from: Environmental heterogeneity has a weak effect on diversity during community assembly in tallgrass prairie

Understanding what constrains the persistence of species in communities is at the heart of community assembly theory and its application to conserving and enhancing biodiversity. The "environmental heterogeneity hypothesis" predicts greater species coexistence in habitats with greater resource variability. In the context of community assembly, environmental heterogeneity may influence the variety and strength of abiotic conditions and competitive interactions (environmental filters) to affect the relative abundance of species and biodiversity. We manipulated key resources that influence plant diversity in tallgrass prairie (i.e., soil depth and nitrogen availability) to increase environmental heterogeneity prior to sowing native prairie species into a former agricultural field. We compared variability in nutrient availability, aboveground annual net primary productivity (ANPP), and the composition of species between replicate plots containing soil heterogeneity manipulations and plots with no resource manipulations (n = 4 per treatment) during the first 15 yr of community assembly as a test of the "environmental heterogeneity hypothesis." The manipulations increased environmental heterogeneity, measured as the coefficient of variation in NO3-N availability and ANPP. Plant diversity, however, was similar and decayed exponentially and indiscriminately over time between the heterogeneity treatments. Species richness declined linearly over time in both heterogeneity treatments, but richness was higher in the more heterogeneous soil 2 yr following a second propagule addition 8 yr after the initial sowing. As a result, there was a lower rate of species loss over time in the more heterogeneous soil (0.60 species yr−1) relative to the control soil (0.96 species yr−1). Communities in each treatment exhibited strong convergence over time resulting from a shift in dominant species across all treatments and a gradual increase in the clonal C4 grass, Andropogon gerardii. We attribute the weak effect of heterogeneity on diversity to increasing dominance of a clonal species, which decreased the scale of soil treatments relative to plant size, dispersal limitation, and absence of a key driver (grazing) known to increase plant diversity under a frequent fire regime. Thus, steering community assembly to attain high biodiversity may depend more on manipulating processes that reduce dominance and facilitate the arrival of new species than promoting environmental heterogeneity.

Data from: Biomass responses to elevated CO2, soil heterogeneity and diversity: an experimental assessment with grassland assemblages

While it is well-established that the spatial distribution of soil nutrients (soil heterogeneity) influences the competitive ability and survival of individual plants, as well as the productivity of plant communities, there is a paucity of data on how soil heterogeneity and global change drivers interact to affect plant performance and ecosystem functioning. To evaluate the effects of elevated CO2, soil heterogeneity and diversity (species richness and composition) on productivity, patterns of biomass allocation and root foraging precision, we conducted an experiment with grassland assemblages formed by monocultures, two- and three-species mixtures of Lolium perenne, Plantago lanceolata and Holcus lanatus. The experiment lasted for 90 days, and was conducted on microcosms built out of PVC pipe (length 38 cm, internal diameter 10 cm). When nutrients were heterogeneously supplied (in discrete patches), assemblages exhibited precise root foraging patterns, and had higher total, above- and belowground biomass. Greater aboveground biomass was observed under elevated CO2. Species composition affected the below:aboveground biomass ratio and interacted with nutrient heterogeneity to determine belowground and total biomass. Species richness had no significant effects, and did not interact with either CO2 or nutrient heterogeneity. Under elevated CO2 conditions, the two- and three-species mixtures showed a clear trend towards underyielding. Our results show that differences among composition levels were dependent on soil heterogeneity, highlighting its potential role in modulating diversity–productivity relationships.

Data from: Individual heterogeneity determines sex differences in mortality in a monogamous bird with reversed sexual dimorphism

Sex differences in mortality are pervasive in vertebrates, and usually result in shorter life spans in the larger sex, although the underlying mechanisms are still unclear. On the other hand, differences in frailty among individuals (i.e. individual heterogeneity), can play a major role in shaping demographic trajectories in wild populations. The link between these two processes has seldom been explored. We used Bayesian survival trajectory analysis to study age-specific mortality trajectories in the Eurasian sparrowhawk (Accipiter nisus), a monogamous raptor with reversed sexual size dimorphism. We tested the effect of individual heterogeneity on age-specific mortality, and the extent by which this heterogeneity was determined by average reproductive output and wing length as measures of an individual's frailty. We found that sex differences in age-specific mortality were primarily driven by the differences in individual heterogeneity between the two sexes. Females were more heterogeneous than males in their level of frailty. Thus, a larger number of females with low frailty are able to survive to older ages than males, with life expectancy for the least frail adult females reaching up to 4·23 years, while for the least frail adult males it was of 2·68 years. We found that 50% of this heterogeneity was determined by average reproductive output and wing length in both sexes. For both, individuals with high average reproductive output had also higher chances to survive. However, the effect of wing length was different between the two sexes. While larger females had higher survival, larger males had lower chances to survive. Our results contribute a novel perspective to the ongoing debate about the mechanisms that drive sex differences in vital rates in vertebrates. Although we found that variables that relate to the cost of reproduction and sexual dimorphism are at least partially involved in determining these sex differences, it is through their effect on the level of frailty that they affect age patterns of mortality. Therefore, our results raise the possibility that observed differences in age-specific demographic rates may in fact be driven by differences in individual heterogeneity.

Data from: Comparative landscape genetics of pond-breeding amphibians in Mediterranean temporal wetlands: the positive role of structural heterogeneity in promoting gene flow

Comparative landscape genetics studies can provide key information to implement cost-effective conservation measures favoring a broad set of taxa. These studies are scarce, particularly in Mediterranean areas, which include diverse but threatened biological communities. Here we focus on Mediterranean wetlands in central Iberia and perform a multi-level, comparative study of two endemic pond-breeding amphibians, a salamander (Pleurodeles waltl) and a toad (Pelobates cultripes). We genotyped 411 salamanders from 20 populations and 306 toads from 16 populations at 18 and 16 microsatellite loci, respectively, and identified major factors associated with population connectivity through the analysis of three sets of variables potentially affecting gene flow at increasingly finer levels of spatial resolution. Topographic, land use/cover, and remotely sensed vegetation/moisture indices were used to derive optimized resistance surfaces for the two species. We found contrasting patterns of genetic structure, with stronger, finer-scale genetic differentiation in Pleurodeles waltl, and notable differences in the role of fine-scale patterns of heterogeneity in vegetation cover and water content in shaping patterns of regional genetic structure in the two species. Overall, our results suggest a positive role of structural heterogeneity in population connectivity in pond-breeding amphibians, with habitat patches of Mediterranean scrubland and open oak woodlands ("dehesas") facilitating gene flow. Our study highlights the usefulness of remotely sensed continuous variables of land cover, vegetation and water content (e.g., NDVI, NDMI) in conservation-oriented studies aimed at identifying major drivers of population connectivity.

opencc-zeroDec 2017View details →

Data from: Genet dynamics of a regenerating dwarf bamboo population across heterogeneous light environments in a temperate forest understorey

Despite the advantage of plant clonality in patchy environments, studies focusing on genet demography in relation to spatially heterogeneous environments remain scarce. Regeneration of bamboos in forest understoreys after synchronous die-off provides an opportunity for assessing how they come to proliferate across heterogeneous light environments. In a Japanese forest, we examined genet demography of a population of Sasa kurilensis over a 7-year period starting 10 years after die-off, shortly after which some genets began spreading horizontally by rhizomes. The aboveground biomass was estimated and genets were discriminated in 9-m2 plots placed under both canopy gaps and closed canopies. Overall, the results suggest that the survival and spread of more productive genets and the spatial expansion of genets into closed canopies underlie the proliferation of S. kurilensis. Compared to canopy gaps, the recovery rate of biomass was much slower under closed canopies for the first 10 years after the die-off, but became accelerated during the next seven years. Genet survival was greater for more productive genets (with greater initial number of culms), and the spaces occupied by genets that died were often colonized afterward by clonal growth of surviving genets. The number of genets decreased under canopy gaps due to greater mortality, but increased under closed canopies where greater number of genets colonized clonally from outside the plots than genets died. The colonizing genets were more productive (having larger culms) than those originally germinated within the plots, and the contribution of colonizing genets to the biomass was greater under closed canopies. Our study emphasizes the importance of investigating genet dynamics over relevant spatio-temporal scales to reveal processes underlying the success of clonal plants in heterogeneous habitats.

opencc-zeroDec 2014View details →

Data from: Ground ice melt in the high Arctic leads to greater ecological heterogeneity

1. The polar desert biome of the Canadian high Arctic Archipelago is currently experiencing some of the greatest mean annual air temperature increases on the planet, threatening the stability of ecosystems residing above temperature-sensitive permafrost. 2. Ice wedges are the most widespread form of ground ice, occurring in up to 25% of the world's terrestrial near-surface, and their melting (thermokarst) may catalyze a suite of biotic and ecological changes, facilitating major ecosystem shifts. 3. These unknown ecosystem shifts raise serious questions as to how permafrost stability, vegetation diversity, and edaphic conditions will change with a warming high Arctic. Ecosystem and thermokarst processes tend to be examined independently, limiting our understanding of a coupled system whereby the effect of climate change on one will affect the outcome of the other. 4. Using in-depth, comprehensive field observations and a space-for-time approach, we investigate the highly structured landscape that has emerged due to the thermokarst-induced partitioning of microhabitats. We examine differences in vegetation diversity, community composition, and soil conditions on the Fosheim Peninsula, Ellesmere Island, Nunavut. We hypothesize that: (i) greater ice wedge subsidence results in increased vegetation cover due to elevated soil moisture, thereby decreasing the seasonal depth of thaw and restricting groundwater outflow; (ii) thermokarst processes result in altered vegetation richness, turnover, and dispersion, with greater microhabitat diversity at the landscape scale; (iii) shifts in hydrology and plant community structure alter soil chemistry. 5. We found that the disturbance caused by melting ice wedges catalyzes a suite of environmental and biotic effects: topographical changes, a new hydrological balance, significant species richness and turnover changes, and distinct soil chemistries. Thermokarst areas favour a subset of species unique from the polar desert and are characterized by greater species turnover (β-diversity) across the landscape. 6. Synthesis. Our findings suggest that projected increases of thermokarst in the polar desert will lead to the increased partitioning of microhabitats, creating a more heterogeneous high arctic landscape through diverging vegetation communities and edaphic conditions, resulting in a wetland-like biome in the high Arctic that could replace much of the ice-rich polar desert.

Data from: Spatial heterogeneity in soil nutrient supply modulates nutrient and biomass responses to multiple global change drivers in model grassland communities

Changes in the atmospheric concentration of carbon dioxide ([CO2]), nutrient availability and biotic diversity are three major drivers of the ongoing global change impacting terrestrial ecosystems worldwide. While it is well established that soil nutrient heterogeneity exerts a strong influence on the development of plant individuals and communities, it is virtually unknown how nutrient heterogeneity and global change drivers interact to affect plant performance and ecosystem functioning. We conducted a microcosm experiment to evaluate the effect of simultaneous changes in [CO2], nutrient heterogeneity (NH), nutrient availability (NA) and species evenness on the biomass and nutrient uptake patterns of assemblages formed by Lolium perenne, Plantago lanceolata and Holcus lanatus. When the nutrients were heterogeneously supplied,assemblages exhibited precise root foraging patterns, and had higher above- and belowground biomass (average increases of 32% and 29% for above- and belowground biomass, respectively). Nutrient heterogeneity also modulated the effects of NA on biomass production, complementarity in nitrogen uptake and below: aboveground ratio, as well as those of [CO2] on the nutrient use efficiency at the assemblage level. Our results show that nutrient heterogeneity has the potential to influence the response of plant assemblages to simultaneous changes in [CO2], nutrient availability and biotic diversity, and suggest that it is an important environmental factor to interpret and assess plant assemblage responses to global change.