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opencc-zeroJan 2020View details →

Long-term deepened snow cover alters litter layer turnover rate in temperate steppes

1. The turnover of litter layer is a biogeochemical process fundamental to carbon and nutrient cycling, influencing seed germination, species coexisting, and carbon storage. Winter snow depth is undergoing increasing trend in Northern China, which has been shown to alter litter decomposition rate of individual species. However, it remains unknown how changes in snow depth affect the turnover rate of the whole litter layer, and whether the responses vary between different steppes. Most current litter decomposition studies are site-based or short-term treated, limiting the exploration of the long-term response of litter layer turnover in regional pattern. 2. In this study, we selected six long-term (11-13 years) snow fence sites in Inner Mongolia, with three in the dry steppe and another three in the wet steppe, and investigated the responses of community-weighted litter residence time (LRT) to long-term increased snow treatment. 3. We found that LRT increased by 0.02 year for every 10 cm increase in snow depth in the wet steppe, but was not affected in the dry steppe. The lack of effect of deepened snow on LRT in the dry steppe was attributed to the offset between the positive effect of the increased plant community-weighted height possibly via inhibiting photodegradation and the enhanced litter recalcitrance by producing higher proportion of stem litter, and the negative effect of the increased soil moisture via accelerating microbial decomposition. The significantly positive effect of the increased snow depth on LRT in the wet steppe was mainly due to the positive effect of the increased grass biomass via decreasing litter quality. 4. Overall, our findings indicated that deepened snow changed plant community, which altered environmental conditions and enhanced litter recalcitrance, thereby increasing LRT in temperate steppes. However, this effect was diminished by enhancing microbial decomposition in the dry but not wet steppe, resulting in different overall responses of LRT to deep-snow in the two steppes. The slow litter turnover rate in the wet steppe might result in greater litter accumulation under future increased snow depth, which could be unfavorable for seed germination and alter plant diversity.

opencc-zeroDec 2017View details →

Data from: Challenges of NGS in conservation management: insights from long-term monitoring of corridor effects on the genetic diversity of mouse lemurs in a fragmented landscape

Long-term genetic monitoring of populations is essential for efforts aimed at preserving genetic diversity of endangered species. Here, we employ a framework of long-term genetic monitoring to evaluate the effects of fragmentation and the effectiveness of the establishment of corridors in restoring population connectivity and genetic diversity of mouse lemurs Micocebus ganzhorni. To this end, we supplement estimates of neutral genetic diversity with the assessment of adaptive genetic variability of the MHC. In addition, we address the challenges of long-term genetic monitoring of functional diversity by comparing the genotyping performance and estimates of MHC variability generated by SSCP/Sanger-sequencing with those obtained by high throughput sequencing (NGS, Illumina), an issue that is particularly relevant when previous work serves as a baseline for planning management strategies that aim to ensure the viability of a population. We report that SSCP greatly underestimates individual diversity and that discrepancies in estimates of MHC diversity attributable to the comparisons of traditional and NGS genotyping techniques can influence the conclusions drawn from conservation management scenarios. Evidence of migration among fragments in Mandena suggests that mouse lemurs are robust to the process of fragmentation and that the effect of corridors is masked by ongoing gene flow. Nonetheless, results based on a larger number of shared private alleles at neutral loci between fragment pairs found after the establishment of corridors in Mandena suggest that gene flow is augmented as a result of enhanced connectivity. Our data points out that despite low effective population size, M. ganzhorni maintains high individual heterozygosity at neutral loci and at MHC II DRB gene and that selection plays a predominant role in maintaining MHC diversity. These findings highlight the importance of long-term genetic monitoring in order to disentangle between the processes of drift and selection maintaining adaptive genetic diversity in small populations.

Data from: Biodiversity-ecosystem functioning relationships in long-term time series and palaeoecological records: deep sea as a test bed

The link between biodiversity and ecosystem functioning (BEF) over long temporal scales is poorly understood. Here, we investigate biological monitoring and palaeoecological records on decadal, centennial and millennial time scales from a BEF framework, by using deep-sea, soft-sediment environments as a test bed. Results generally show positive BEF relationships, in agreement with BEF studies based on present-day spatial analyses and short-term manipulative experiments. However, the deep-sea BEF relationship is much noisier across longer time scales compared with modern observational studies. We also demonstrate with palaeoecological time-series data that a larger species pool does not enhance ecosystem stability through time, whereas abundance, as an indicator of higher ecosystem functioning, may enhance ecosystem stability. These results suggest that BEF relationships are potentially timescale-dependent. Environmental impacts on biodiversity and ecosystem functioning may be much stronger than biodiversity impacts on ecosystem functioning at long, decadal–millennial, time scales. Longer time-scale perspectives, including palaeoecological and ecosystem monitoring data, are critical for predicting future BEF relationships on a rapidly changing planet.

Data from: No signs of inbreeding despite long-term isolation and habitat fragmentation in the critically endangered Montseny brook newt (Calotriton arnoldi)

Endemic species with restricted geographic ranges potentially suffer the highest risk of extinction. If these species are further fragmented into genetically isolated subpopulations, the risk of extinction is elevated. Habitat fragmentation is generally considered to have negative effects on species survival, despite some evidence for neutral or even positive effects. Typically, non-negative effects are ignored by conservation biology. The Montseny brook newt (Calotriton arnoldi) has one of the smallest distribution ranges of any European amphibian (8 km2) and is considered critically endangered by the International Union for Conservation of Nature. Here we apply molecular markers to analyze its population structure and find that habitat fragmentation owing to a natural barrier has resulted in strong genetic division of populations into two sectors, with no detectable migration between sites. Although effective population size estimates suggest low values for all populations, we found low levels of inbreeding and relatedness between individuals within populations. Moreover, C. arnoldi displays similar levels of genetic diversity to its sister species Calotriton asper, from which it separated around 1.5 million years ago and which has a much larger distribution range. Our extensive study shows that natural habitat fragmentation does not result in negative genetic effects, such as the loss of genetic diversity and inbreeding on an evolutionary timescale. We hypothesize that species in such conditions may evolve strategies (for example, special mating preferences) to mitigate the effects of small population sizes. However, it should be stressed that the influence of natural habitat fragmentation on an evolutionary timescale should not be conflated with anthropogenic habitat loss or degradation when considering conservation strategies.

Data from: Near-stasis in the long-term diversification of Mesozoic tetrapods

How did evolution generate the extraordinary diversity of vertebrates on land? Zero species are known prior to ~380 million years ago, and more than 30,000 are present today. An expansionist model suggests this was achieved by large and unbounded increases, leading to substantially greater diversity in the present than at any time in the geological past. This model contrasts starkly with empirical support for constrained diversification in marine animals, suggesting different macroevolutionary processes on land and in the sea. We quantify patterns of vertebrate standing diversity on land during the Mesozoic–early Paleogene interval, applying sample-standardization to a global fossil dataset containing 27,260 occurrences of 4,898 non-marine tetrapod species. Our results show a highly stable pattern of Mesozoic tetrapod diversity at regional and local levels, underpinned by a weakly positive, but near-zero, long-term net diversification rate over 190 million years. Species diversity of non-flying terrestrial tetrapods less than doubled over this interval, despite the origins of exceptionally diverse extant groups within mammals, squamates, amphibians, and dinosaurs. Therefore, although speciose groups of modern tetrapods have Mesozoic origins, rates of Mesozoic diversification inferred from the fossil record are slow compared to those inferred from molecular phylogenies. If high speciation rates did occur in the Mesozoic, then they seem to have been balanced by extinctions among older clades. An apparent 4-fold expansion of species richness after the Cretaceous/Paleogene (K/Pg) boundary deserves further examination in light of potential taxonomic biases, but is consistent with the hypothesis that global environmental disturbances such as mass extinction events can rapidly adjust limits to diversity by restructuring ecosystems, and suggests that the gradualistic evolutionary diversification of tetrapods was punctuated by brief but dramatic episodes of radiation.

opencc-zeroDec 2012View details →

Data from: Two decades of genetic profiling yields first evidence of natal philopatry and long-term fidelity to parturition sites in sharks

Sharks are a globally threatened group of marine fishes that often breed in their natal region of origin. There has even been speculation that female sharks return to their exact birthplace to breed ("natal philopatry"), which would have important conservation implications. Genetic profiling of lemon sharks (Negaprion brevirostris) from 20 consecutive cohorts (1993-2012) at Bimini, Bahamas showed that certain females faithfully gave birth at this site for nearly two decades. At least six females born in the 1993-1997 cohorts returned to give birth 14-17 years later, providing the first direct evidence of natal philopatry in the chondrichthyans. Long-term fidelity to specific nursery sites coupled with natal philopatry highlights the merits of emerging spatial and local conservation efforts for these threatened predators.

opencc-zeroDec 2012View details →

Data from: The symmetry of children's knees is linked to their adult sprinting speed and their willingness to sprint in a long-term Jamaican study

Jamaican athletes are prominent in sprint running but the reasons for their success are not clear. Here we consider the possibility that symmetry, particularly symmetry of the legs, in Jamaican children is linked to high sprinting speed in adults. Our study population was a cohort of 288 rural children, mean age 8.2 (±1 SD = 1.7) years in 1996. Symmetry was measured in 1996 and 2006 from the fluctuating asymmetry (FA) of three lower-body traits and we constructed a lower body composite FA trait (Comp lb-FA). In 2010 we measured sprinting speed (for 90 m and 180 m races) in participants recruited from our original cohort. There were 163 untrained adults in our sample. We found: (i) high Comp lb and knee symmetry in 1996 and 2006 were linked to fast sprinting times in our 2010 runners and (ii) our sample of sprinters appears to have self-selected for greater symmetry. We conclude that high knee symmetry in childhood is linked to an ability to sprint fast in adult Jamaicans as well as a readiness to sprint.

Data from: Ectomycorrhizal and saprotrophic fungi respond differently to long-term experimentally increased snow depth in the High Arctic

Changing climate is expected to alter precipitation patterns in the Arctic, with consequences for subsurface temperature and moisture conditions, community structure, and nutrient mobilization through microbial belowground processes. Here, we address the effect of increased snow depth on the variation in species richness and community structure of ectomycorrhizal (ECM) and saprotrophic fungi. Soil samples were collected weekly from mid-July to mid-September in both control and deep snow plots. Richness of ECM fungi was lower, while saprotrophic fungi was higher in increased snow depth plots relative to controls. [Correction added on 23 September 2016 after first online publication: In the preceding sentence, the richness of ECM and saprotrophic fungi were wrongly interchanged and have been fixed in this current version.] ECM fungal richness was related to soil NO3-N, NH4-N, and K; and saprotrophic fungi to NO3-N and pH. Small but significant changes in the composition of saprotrophic fungi could be attributed to snow treatment and sampling time, but not so for the ECM fungi. Delayed snow melt did not influence the temporal variation in fungal communities between the treatments. Results suggest that some fungal species are favored, while others are disfavored resulting in their local extinction due to long-term changes in snow amount. Shifts in species composition of fungal functional groups are likely to affect nutrient cycling, ecosystem respiration, and stored permafrost carbon.

Data from: Trophic interactions of fish communities at midwater depths enhance long-term carbon storage and benthic production on continental slopes

Biological transfer of nutrients and materials between linked ecosystems influences global carbon budgets and ecosystem structure and function. Identifying the organisms or functional groups that are responsible for nutrient transfer, and quantifying their influence on ecosystem structure and carbon capture is an essential step for informed management of ecosystems in physically distant, but ecologically linked areas. Here, we combine natural abundance stable isotope tracers and survey data to show that mid-water and bentho-pelagic-feeding demersal fishes play an important role in the ocean carbon cycle, bypassing the detrital particle flux and transferring carbon to deep long-term storage. Global peaks in biomass and diversity of fishes at mid-slope depths are explained by competitive release of the demersal fish predators of mid-water organisms, which in turn support benthic fish production. Over 50% of the biomass of the demersal fish community at depths between 500 and 1800 m is supported by biological rather than detrital nutrient flux processes, and we estimate that bentho-pelagic fishes from the UK–Irish continental slope capture and store a volume of carbon equivalent to over 1 million tonnes of CO2 every year.

opencc-zeroDec 2014View details →

Data from: Phylogenetic measures of plant communities show long-term change and impacts of fire management in tallgrass prairie remnants

1. Phylogenies are increasingly incorporated into ecological studies on the basis that evolutionary relatedness broadly correlates with trait similarity. However, phylogenetic approaches have rarely been applied to monitoring long-term community change or guiding management. 2. We analysed a 25-year resampling data set (1976–2001) of 41 tallgrass prairie remnants (Illinois, USA) to test for phylogenetic signals of plant community structure, change, environmental associations, fire management and functional traits. A community phylogeny was constructed using GenBank sequences and trait data were acquired from the TRY consortium. Phylogenetic measures of alpha and beta diversity were compared with taxonomic and functional measures. 3. From 1976–2001, communities became more phylogenetically clustered relative to null model expectations, i.e. increasingly restricted to subsets of species more closely related than expected by chance. Phylogeny was a sensitive indicator of environmental gradients and fire management. There were strong relationships between phylogeny and traits: key traits were phylogenetically non-random and phylogenetic diversity was a necessary complement to species richness for explaining variation in trait diversity. 4. Phylogeny revealed a shift in community structure over time, with sites having been phylogenetically random in 1976 but becoming differentiated from each other by 2001. In contrast, measures of taxonomic and functional diversity showed differentiation at both time points. Phylogenetic patterns likely reflected changes in species' abundances mediated by the influence of environmental conditions and fire frequency. 5. Synthesis and applications. Phylogenetic analyses can elucidate factors central to sound monitoring and management of plant communities. In this system, phylogeny was not a proxy for other indicators, but provided information complementing taxonomic-based and trait-based approaches for understanding vegetation structure, change and response to fire management. Phylogenetic approaches to ecological analysis are increasingly accessible, but fuller understanding of phylogeny–trait relationships and further development of user-friendly analytical tools are needed for phylogenetics to widely inform restoration and management. In some systems, targeting phylogenetic diversity may be an effective means for restoring functionally diverse plant communities.

Data from: Parental and hybrid Daphnia from the D. longispina complex: long-term dynamics in genetic structure and significance of overwintering modes

In recent decades, hybridization has become a focus of attention because of its role in evolutionary processes. However, little is known about changes in genetic structure within and between parental species and hybrids over time. Here, we studied processes of genetic change in parental species and hybrids from the Daphnia longispina complex (Crustacea, Cladocera) over a period of six years across ten habitats. These cyclical parthenogens respond to fluctuating environments by switching from asexual to sexual reproduction. Importantly, sexually produced diapausing eggs, which resist extreme conditions such as low temperatures and serve as dispersal stages, are produced to a lower extent by hybrids. Long-term microsatellite data revealed clear differences between hybrids and parental species. In hybrids, clonal diversity values were lower, whereas heterozygosity and linkage disequilibrium values were higher compared to parental species. Clonal diversity of hybrids responded to the strength of the winter, with cold winters resulting in few genotypes in the following spring. In time windows when only asexual hybrid females survive, priority effects will favour the establishment of the hybrid offspring before hatchlings from parental diapause eggs can enter the community. The constant high levels of heterozygosity maintained by clonal reproduction in hybrids might lead to their successful establishment over time, when they are able to escape competition from both parental species. Although we found evidence that hybrids diversity depends on fluctuating environments, a direct link between hybrid abundance and the strength of winter was missing. Because of reduced adaptability in clonally reproducing hybrids, multiple factors must contribute to promoting their long-term success in fluctuating environments.

Data from: Short- and long-term effects of litter size manipulation in a small wild-derived rodent

Iteroparous organisms maximise their overall fitness by optimising their reproductive effort over multiple reproductive events. Hence, changes in reproductive effort are expected to have both short- and long-term consequences on parents and their offspring. In laboratory rodents, manipulation of reproductive efforts during lactation have however revealed little short-term reproductive adjustments, suggesting that female laboratory rodents might express maximal rather than optimal levels of reproductive investments as observed in semelparous organisms. Using a litter size manipulation (LSM) experiment in a small wild-derived rodent (the common vole; Microtus arvalis), we show that females altered their reproductive efforts in response to LSM, with females having higher metabolic rates and showing alternative body mass dynamics when rearing an enlarged rather than reduced litter. Those differences in female reproductive effort were nonetheless insufficient to fully match their pups' energy demand, pups being lighter at weaning in enlarged litters. Interestingly, female reproductive effort changes had long-term consequences, with females that had previously reared an enlarged litter being lighter at birth of their subsequent litter and producing lower quality pups. We discuss the significance of using wild-derived animals in studies of reproductive effort optimisation.

opencc-zeroDec 2011View details →

Data from: Density dependence and population regulation in marine fish: a large-scale, long-term field manipulation

Do small-scale experiments showing spatial density dependence in marine fishes scale-up to temporal density dependence and regulation of relatively large local populations? If so, what are the causative mechanisms and their implications? We conducted an 8-year multi-generation study of population dynamics of bicolor damselfish (Stegastes partitus) inhabiting four large coral reefs in the Bahamas. After a 4-year baseline period, it was clear that two populations naturally received very few settlement-stage larvae, so recruitment of recently settled fish was artificially enhanced at one low-settlement reef and reduced at one high-settlement reef to ensure a broad range of population sizes over which to test for regulation. Over all 8 years, populations on the two naturally high-settlement reefs experienced temporal density dependence in multiple per capita demographic rates mortality, survival to adulthood, and fecundity. These local populations also displayed components of regulation persistence, boundedness, and return tendency. Reefs supporting regulated populations were structurally complex, providing sufficient prey refuges that ensured high survival at low densities. In contrast, populations at low-settlement reefs experienced either density-independent or slightly inversely density-dependent demographic rates, even though recruitment was artificially augmented to high levels at one reef. There was no evidence of regulation at these reefs, and indeed, one local population suffered temporary extirpation. Here, habitat complexity was relatively low, increasing the risk of predation, especially at low population densities when fish would have to travel longer distances when finding mates or home sites inhabited by conspecifics. Among all demographic parameters, density dependence in individual growth (an indicator of within-species competition for food) was least correlated with the presence or absence of local population regulation. We conclude that, for systems like these, the environmental context of a local population -- especially predation risk and the distribution and abundance of spatial refuges -- is more important than the magnitude of larval supply alone in determining the existence of regulating density dependence. At the broader metapopulation scale, density dependence in both survival and fecundity exogenously caused by predation may provide regulation for the entire stock, even when endogenous within-species competition (assumed to be important in most fisheries models) is weak.

opencc-zeroDec 2016View details →

Data from: Long-term changes in the seasonal timing of landbird migration on the Pacific Flyway

The seasonal phenology of latitudinal movements is one of the key life-history traits of migratory birds. We used quantile regression to examine long-term changes in the timing of spring and autumn migration in 5 species of migratory passerine birds captured at a banding station in northern California, USA, over a 22 yr period from 1987 to 2008. Our 5 study species included 3 short-distance migrants, Pacific-slope Flycatcher (Empidonax difficilis), Orange-crowned Warbler (Oreothlypis celata), and Wilson's Warbler (Cardellina pusilla); and 2 long-distance migrants, Swainson's Thrush (Catharus ustulatus) and Yellow Warbler (Setophaga petechia). Median timing of migration advanced in spring for 2 of the 5 species (−2.5 days decade−1) but was delayed during autumn migration for 3 of the species (+2.9 days decade−1). The duration of the migration period also became compressed in some species but more protracted in others. We tested whether annual variation in migration timing was related to 3 indices of regional climatic conditions: the Pacific–North American index, multivariate El Niño–Southern Oscillation index, and North Atlantic Oscillation index. Climate indices explained relatively little of the variation in migration timing (r2 < 0.35), but advances in spring migration and delays in autumn migration were associated with warm, wet conditions during positive phases of the climate indices. The strongest effects of climatic conditions on migration timing were found among short-distance migrants, with the largest changes in timing due to variation in the El Niño–Southern Oscillation and Pacific–North American indices. Linkages between the timing of movements and climatic conditions indicate that passerine birds on the Pacific coast exhibit phenotypic plasticity in their migration timing, but future studies based on experimental methods are needed to test alternative ecological mechanisms.

Data from: Pine afforestation decreases the long-term performance of understory shrubs in a semiarid Mediterranean ecosystem: a stable isotope approach.

1. Plant–plant interactions shape the structure and composition of plant communities, but shifts in interaction outcomes might occur in the face of ongoing climate change. 2. We assessed the influence of Pinus halepensis plantations on the long-term ecophysiological performance of understorey vegetation, by conducting a retrospective comparison (1989–2007) of growth-ring widths, δ13C and δ18O between Rhamnus lycioides shrubs from two contrasting vegetation types: P. halepensis plantations vs. open woodlands. We also measured the leaf δ13C, δ18O, δ15N, and nutrient concentrations of understorey R. lycioides shrubs growing at varying distances from planted trees within pine plantations. 3. Dendroecological and stable isotope data revealed strong competitive effects of planted P. halepensis trees on R. lyciodies. Shrubs in pine plantations showed lower radial growth and higher growth ring δ13C and δ18O than those in open woodlands, indicating lower stomatal conductance and photosynthesis in the former. The strong competitive effects of P. halepensis on understorey R. lycioides were most evident in wet, productive years. Conversely, in very dry years, there were indications of a facilitative effect of planted P. halepensis canopies on understorey shrubs. 4. Within pine plantations, understorey R. lycioides shrubs growing at shorter distances from planted trees were forced to rely on more superficial and ephemeral soil water sources, which reduced their stomatal conductance (higher leaf δ18O) and interfered with nutrient uptake (lower leaf N and P concentrations and more negative δ15N). 5. The intrinsic water use efficiency of R. lycioides shrubs growing in open woodlands has increased during recent decades as a result of their ability to adjust their stomatal conductance in response to increasing temperature and atmospheric CO2. However, this adaptive response was much weaker or absent in the severely drought-stressed shrubs from pine plantations. 6. Pine afforestation strongly reduces water and nutrient availability for understorey shrubs in drylands, with potential long-term consequences for ecosystem biodiversity, structure and functioning. Competition by P. halepensis on R. lycioides clearly outweighed facilitation in the long-term, thus compromising the ability of understorey shrubs in semi-arid pine plantations to cope with climate change.

opencc-zeroOct 2019View details →

Data from: Long-term isolation at a low effective population size greatly reduced genetic diversity in Gulf of California fin whales

The Gulf of California, Mexico is home to many cetacean species, including a presumed resident population of fin whales, Balaenoptera physalus. Past studies reported very low levels of genetic diversity among Gulf of California fin whales and a significant level of genetic differentiation from con-specifics in the eastern North Pacific. The aim of the present study was to assess the degree and timing of the isolation of Gulf of California fin whales in a population genetic analysis of 18 nuclear microsatellite genotypes from 402 samples and 565 mitochondrial control region DNA sequences (including mitochondrial sequences retrieved from NCBI). The analyses revealed that the Gulf of California fin whale population was founded ~2.3 thousand years ago and has since remained at a low effective population size (~360) and isolated from the eastern North Pacific (Nem between 0.89–1.4). The low effective population size and high degree of isolation implied that Gulf of California fin whales are vulnerable to the negative effects of genetic drift, human-caused mortality and habitat change.

opencc-zeroDec 2010View details →

Data from: Kinship of long-term associates in the highly social sperm whale

The evolution of stable social groups can be promoted by both indirect and direct fitness benefits. Sperm whales (Physeter macrocephalus) are highly social, with a hierarchical social structure based around core groups of adult females and sub-adults, a rare level of complexity among mammals. We combined long-term satellite tracking (ranging from 11 to 607 days) of 51 individual sperm whales with genetic kinship analysis to assess the pattern of kin associations within and among coherent social units. Unlike findings for other species with similar social structure, we find no consistent correlation between kinship and association apart from close associations between two pairs of first-order relatives. A third pair of first order relatives did not associate, and overall the mean relatedness was the same within as among social groups. However, social behaviour can also be promoted by ecological factors such as resource dispersion. We assessed putative foraging behaviour during travel from the satellite tracking data, which suggested that prey resources were dispersed and unpredictable; a condition that could promote living in groups.

Data from: Long-term expansion of juniper populations in managed landscapes: patterns in space and time

1. Forest cover has increased world-wide over the last decade despite continuous forest fragmentation. However, a lack of long-term demographic data hinders our understanding of the spatial dynamics of colonization in remnant populations inhabiting recently protected areas or set-aside rural lands. 2. We investigated the population expansion of the Phoenician juniper (Juniperus phoenicea subsp. turbinata), which is an endozoochorous Mediterranean tree species inhabiting landscapes that have been managed for many centuries. By combining the photointerpretation of aerial photos that have been taken over the last 50 years with in situ sampling and spatial analyses of replicated plots, we estimated the population growth over the chronosequence; identified hotspots, coldspots and outliers of regeneration; and assessed the roles of key environmental factors in driving demographic expansion patterns, including elevation, initial density and distance to remnant forests. 3. Ecological factors leading to seed limitation, such as initial plant density, are expected to drive colonization patterns at the early stages. Factors mediating the competition for limiting resources, such as water availability, would prevail at later stages of expansion. We further expect that nucleated colonization patterns emerge driven by vertebrate seed dispersal. 4. The photointerpretation of aerial images in combination with in situ measurements has yielded reliable density data. Overall, our results show a marked demographic expansion during the first decade followed by a period of steady and heterogeneous population growth with signs of local population decline. We found evidence of nucleated establishment patterns as expected for an endozoochorous species. Hotspots and outliers of regeneration emerged throughout the study chronosequence, whereas coldspots of regeneration only appeared at advanced colonization stages. Factors influencing dispersal limitation had contrasting effects at different colonization stages, and the initial density influenced population growth at various spatial scales. 5. Synthesis. The photointerpretation of aerial images shows that the influence of dispersal limitation versus factors mediating competitive responses changes throughout colonization stages. Whereas dispersal limitation is the main factor influencing colonization at early stages, competition for local resources controls population growth at later stages. Therefore, long-term studies are required to capture the overall combined influence of key ecological factors in shaping long-term spatial demographic trends.

opencc-zeroDec 2018View details →

Data from: Long-term sound and movement recording tags to study natural behaviour and reaction to ship noise of seals

The impact of anthropogenic noise on marine fauna is of increasing conservation concern with vessel noise being one of the major contributors. Animals that rely on shallow coastal habitats may be especially vulnerable to this form of pollution. Very limited information is available on how much noise from ship traffic individual animals experience, and how they may react to it due to a lack of suitable methods. To address this, we developed long‐duration audio and 3D‐movement tags (DTAGs) and deployed them on three harbor seals and two gray seals in the North Sea during 2015–2016. These tags recorded sound, accelerometry, magnetometry, and pressure continuously for up to 21 days. GPS positions were also sampled for one seal continuously throughout the recording period. A separate tag, combining a camera and an accelerometer logger, was deployed on two harbor seals to visualize specific behaviors that helped interpret accelerometer signals in the DTAG data. Combining data from depth, accelerometer, and audio sensors, we found that animals spent 6.6%–42.3% of the time hauled out (either on land or partly submerged), and 5.3%–12.4% of their at‐sea time resting at the sea bottom, while the remaining time was used for traveling, resting at surface, and foraging. Animals were exposed to audible vessel noise 2.2%–20.5% of their time when in water, and we demonstrate that interruption of functional behaviors (e.g., resting) in some cases coincides with high‐level vessel noise. Two‐thirds of the ship noise events were traceable by the AIS vessel tracking system, while one‐third comprised vessels without AIS. This preliminary study demonstrates how concomitant long‐term continuous broadband on‐animal sound and movement recordings may be an important tool in future quantification of disturbance effects of anthropogenic activities at sea and assessment of long‐term population impacts on pinnipeds.