Find research datasets worth reusing

Data from: Raccoon contact networks predict seasonal susceptibility to rabies outbreaks and limitations of vaccination

1. Infectious disease transmission often depends on the contact structure of host populations. Although it is often challenging to capture the contact structure in wild animals, new technology has enabled biologists to obtain detailed temporal information on wildlife social contacts. In this study, we investigated the effects of raccoon contact patterns on rabies spread using network modelling. 2. Raccoons (Procyon lotor) play an important role in the maintenance of rabies in the United States. It is crucial to understand how contact patterns influence the spread of rabies in raccoon populations in order to design effective control measures and to prevent transmission to human populations and other animals. 3. We constructed a dynamic system of contact networks based on empirical data from proximity logging collars on a wild suburban raccoon population and then simulated rabies spread across these networks. Our contact networks incorporated the number and duration of raccoon interactions. We included differences in contacts according to sex and season, and both short-term acquaintances and long-term associations. Raccoons may display different behaviours when infectious, including aggression (furious behaviour) and impaired mobility (dumb behaviour); the network model was used to assess the impact of potential behavioural changes in rabid raccoons. We also tested the effectiveness of different vaccination coverage levels. 4. Our results demonstrate that when rabies enters a suburban raccoon population, the likelihood of a disease outbreak affecting the majority of the population is high. Both the magnitude of rabies outbreaks and the speed of rabies spread depend strongly on the time of year that rabies is introduced into the population. When there is a combination of dumb and furious behaviours in the rabid raccoon population, there are similar outbreak sizes and speed of spread to when there are no behavioural changes due to rabies infection. 5. By incorporating detailed data describing the variation in raccoon contact rates into a network modelling approach, we were able to show that suburban raccoon populations are highly susceptible to rabies outbreaks, that the risk of large outbreaks varies seasonally and that current vaccination target levels may be inadequate to prevent the spread of rabies within these populations. Our findings provide new insights into rabies dynamics in raccoon populations and have important implications for disease control.

opencc-zeroDec 2016View details →

Data from: Exogenous kisspeptin enhances seasonal reproductive function in male Siberian hamsters

Animals living in temperate climates are faced with the challenge of reproducing only when environmental conditions are suitable for offspring survival. Environmental cues signalling current and future energy availability (e.g., food availability and photoperiod respectively) are used to appropriately time reproduction. The precise neuroendocrine mechanisms regulating reproduction in response to these cues are unknown. The goal of the present study was to investigate a functional role for kisspeptin, a neuropeptide that shows promise as a key regulator of seasonal reproduction, in integrating multiple environmental cues to regulate reproduction in the Siberian hamster (Phodopus sungorus). Siberian hamsters undergo robust gonadal regression and terminate reproduction in unsuitable environments [short winter-like day lengths (photoperiods), low food availability]. Adult male hamsters were housed in short-day or intermediate photoperiods, received either ad-libitum access to food or mild food restriction, and were treated with either kisspeptin or a vehicle for 6 weeks to determine the ability of kisspeptin to attenuate gonadal regression. Hamsters exhibited varying degrees of gonadal regression in response to inhibitory environments (short-day photoperiod, food restriction). Kisspeptin treatment successfully enhanced testis mass under these inhibitory conditions, but did not affect normal seasonal changes in body mass and food intake. Thus, kisspeptin specifically enhanced reproductive function without altering other, non-reproductive physiological responses to these environmental treatments. The inhibitory environmental conditions used in this study caused little if any decline in serum luteinizing hormone (LH) and testosterone over the course of the experiment. Kisspeptin treatment tended to exacerbate the decline in LH within individuals, but there were no significant effects of kisspeptin when comparing changes in the hormone levels amongst groups. The interesting outcome that kisspeptin enhanced testis mass, apparently independently of hypothalamic endocrine mechanisms, suggests the possibility of local kisspeptin action within the gonads. Overall, we show a functional role for kisspeptin in integrating complex environmental information to specifically support reproduction. Future work should focus on direct effects of kisspeptin at the gonadal level of the HPG axis as well as its interactions with the metabolic functions and other hormones involved in reproduction, e.g., gonadotropin-inhibitory hormone (GnIH).

Data from: Survival costs of within‐ and between‐season mate change in the European Blackbird (Turdus merula)

Many studies of socially monogamous birds discuss the adaptive role of between-season partner change, but only a handful of them refer to the benefits of pair fidelity in terms of increased survival. Moreover, there are no studies describing the benefits of within-season mate retention. Our data relating to an urban population of European Blackbirds (Turdus merula) enabled us to test the dependence of survival on pair faithfulness. Because Blackbirds divorce within and between seasons, we were able to test the influence of pair faithfulness on their within- and between-season survival and mate fidelity. For this purpose, we used a multievent capture-mark-recapture (MECMR) statistical model, which is based on recapture rates and different pair states (faithful to mate, paired with new partner, or dead). Our study indicated that between- and within-season survival depends on pair states: pair-bond duration increases survival to the next capture occasion in both sexes. We found that the pair-bond duration to the current partner increased the chances of being with the same partner during the next breeding occasion, although we failed to find any within-season pair-bond influence for females. Our results showed sex differences in mating at the end of the season: females had a much smaller chance of breeding with the current new partner in the next year. This study has demonstrated that within- and between-season survival is dependent on mate retention, and we discuss this in the context of how searching for a new partner could affect the birds' survival.

Data from: Seasonality of soil moisture mediates responses of ecosystem phenology to elevated CO2 and warming in a semi-arid grassland

Vegetation greenness, detected using digital photography, is useful for monitoring phenology of plant growth, carbon uptake, and water loss at the ecosystem level. Assessing ecosystem phenology by greenness is especially useful in spatially extensive, water-limited ecosystems such as the grasslands of the western United States, where productivity is moisture dependent and may become increasingly vulnerable to future climate change. We used repeat photography and a novel means of quantifying greenness in digital photographs to assess how the individual and combined effects of warming and elevated CO2 impact ecosystem phenology (greenness and plant cover) in a semi-arid grassland over an 8-year period. Climate variability within and among years was the proximate driver of ecosystem phenology. Individual and combined effects of warming and elevated CO2 were significant at times, but mediated by variation in both intra- and inter-annual precipitation. Specifically, warming generally enhanced plant cover and greenness early in the growing season but often had a negative effect during the middle of the summer, offsetting the early season positive effects. The individual effects of elevated CO2 on plant cover and greenness were generally neutral. Opposing seasonal variations in the effects of warming and less so elevated CO2 cancelled each other out over an entire growing season, leading to no net effect of treatments on annual accumulation of greenness. The main effect of elevated CO2 dampened quickly, but warming continued to affect plant cover and plot greenness throughout the experiment. The combination of warming and elevated CO2 had a generally positive effect on greenness, especially early in the growing season and in later years of the experiment, enhanced annual greenness accumulation. However, interannual precipitation variation had larger effect on greenness, with 2-3 times greater greenness in wet years than in dry years. Synthesis. Seasonal variation in timing and amount of precipitation governs grassland phenology, greenness, and the potential for carbon uptake. Our results indicate that concurrent changes in precipitation regimes mediate vegetation responses to warming and elevated atmospheric CO2 in semi-arid grasslands. Even small changes in vegetation phenology and greenness in response to warming and rising atmospheric CO2 concentrations, such as those we report here, can have large consequences for the future of grasslands.

Data from: Seasonal flooding, topography, and organic debris interact to influence the emergence and distribution of seedlings in a tropical grassland

In seasonally flooded wetlands, natural disturbances such as flooding and associated organic debris deposition followed by a drawdown period provide various opportunities for plant species regeneration, which can promote plant community diversity across space and time. Specifically, regeneration may be influenced by the direct effect of flooding on seed dispersal and seedling emergence as well as the indirect effect of organic debris on seed trapping and germination. Our objective was to examine the influence of seasonal flooding, topography, and cover of organic debris on seedling distribution in seasonally flooded grassland of the Pantanal. We measured species richness and abundance of seedlings for three years at three topographic levels with variable coverage of organic debris at the end of the flood season, and during the dry season when there was no debris deposition. A total of 43 species were recorded with no difference in species richness between immediate post-flood and dry seasons. However, the abundance of some species was higher post-flood than during the dry period. The distribution of seedlings differed between topographic levels post-flood with the greatest seedling abundance and richness occurring at the medium level, followed by the high and finally the low level, this was due to the higher concentration of organic debris in the low-level. Our results indicate that areas with predictable annual floods promote the individual species adaptation for successful regeneration.

Data from: Resource specialists lead local insect community turnover associated with temperature – analysis of an 18-year full-seasonal record of moths and beetles

Insect responses to recent climate change are well documented, but the role of resource specialization in determining species vulnerability remains poorly understood. Uncovering local ecological effects of temperature change with high-quality, standardized data provides an important first opportunity for predictions about responses of resource specialists, and long-term time series are essential in revealing these responses. Here, we investigate temperature-related changes in local insect communities, using a sampling site with more than a quarter-million records from two decades (1992–2009) of full-season, quantitative light trapping of 1543 species of moths and beetles. We investigated annual as well as long-term changes in fauna composition, abundance and phenology in a climate-related context using species temperature affinities and local temperature data. Finally, we explored these local changes in the context of dietary specialization. Across both moths and beetles, temperature affinity of specialists increased through net gain of hot-dwelling species and net loss of cold-dwelling species. The climate-related composition of generalists remained constant over time. We observed an increase in species richness of both groups. Furthermore, we observed divergent phenological responses between cold- and hot-dwelling species, advancing and delaying their relative abundance, respectively. Phenological advances were particularly pronounced in cold-adapted specialists. Our results suggest an important role of resource specialization in explaining the compositional and phenological responses of insect communities to local temperature increases. We propose that resource specialists in particular are affected by local temperature increase, leading to the distinct temperature-mediated turnover seen for this group. We suggest that the observed increase in species number could have been facilitated by dissimilar utilization of an expanded growing season by cold- and hot-adapted species, as indicated by their oppositely directed phenological responses. An especially pronounced advancement of cold-adapted specialists suggests that such phenological advances might help minimize further temperature-induced loss of resource specialists. Although limited to a single study site, our results suggest several local changes in the insect fauna in concordance with expected change of larger-scale temperature increases.

Data from: Timing is everything: fishing‐season placement may represent the most important angling‐induced evolutionary pressure on Atlantic salmon populations

Fisheries‐induced evolution can change the trajectory of wild fish populations by selectively targeting certain phenotypes. For important fish species like Atlantic salmon, this could have large implications for their conservation and management. Most salmon rivers are managed by specifying an angling season of predetermined length based on population demography, which is typically established from catch statistics. Given the circularity of using catch statistics to estimate demographic parameters, it may be difficult to quantify the selective nature of angling and its evolutionary impact. In the River Etne in Norway, a recently installed trap permits daily sampling of fish entering the river, some of which are subsequently captured by anglers upstream. Here, we used 31 microsatellites to establish an individual DNA profile for salmon entering the trap, and for many of those subsequently captured by anglers. These data permitted us to investigate time of rod capture relative to river entry, potential body size‐selective harvest, and environmental variables associated with river entry. Larger, older fish entered the river earlier than smaller, younger fish of both sexes, and larger, older females were more abundant than males and vice versa. There was good agreement between the sizes of fish harvested by angling, and the size distribution of the population sampled on the trap. These results demonstrate that at least in this river, and with the current timing of the season, the angling catch reflects the population's demographics and there is no evidence of size‐selective harvest. We also demonstrated that the probability of being caught by angling declines quickly after river entry. Collectively, these data indicate that that the timing of the fishing season, in relation to the upstream migration patterns of the different demographics of the population, likely represents the most significant directional evolutionary force imposed by angling.

Data from: Preen oil chemical composition encodes individuality, seasonal variation and kinship in black kites Milvus migrans

Evidence that bird odour can encode social information that can be used in chemical communication is growing, but is restricted to a few taxonomic groups. Among birds, diurnal raptors (i.e. birds from the Accipitriformes and Falconiformes order) have always been considered as mainly relying on their visual abilities. Although they seem to have a functional sense of smell, whether their odour can convey social information has yet to be determined. Combining gas-chromatography-mass-spectrometry (GCMS) and microsatellite data, we tested whether chemical compounds from preen gland secretions can encode sex, age, individuality, seasonal differences and genetic relatedness in the gregarious accipitriform black kite Milvus migrans. While no differences in preen oil composition were found between age classes, an individual signature was detected. While a seasonal variation was found in both sexes, compounds differ between sexes in the non-breeding season. Finally, a significant correlation between chemical proximity and genetic proximity was detected in male-male dyads and male-female dyads but not in female-female dyads. Our study provides the first evidence in raptors that preen secretion can convey information that may potentially be used in individual recognition, reproductive synchronization and inbreeding avoidance, and suggests that raptors may rely upon their olfactory abilities more than previously thought. This study opens promising avenues for further studies in raptor chemical communication.

Data from: Hatching late in the season requires flexibility in the timing of song learning

Most songbirds learn their songs from adult tutors, who can be their father or other male conspecifics. However, the variables that control song learning in a natural social context are largely unknown. We investigated whether the time of hatching of male domesticated canaries has an impact on their song development and on the neuroendocrine parameters of the song control system. Average age difference between early- and late-hatched males was 50 days with a maximum of 90 days. Song activity of adult tutor males decreased significantly during the breeding season. While early-hatched males were exposed to tutor songs for on average the first 99 days, late-hatched peers heard adult song only during the first 48 days of life. Remarkably, although hatching late in the season negatively affected body condition, no differences between both groups of males were found in song characteristics either in autumn or in the following spring. Similarly, hatching date had no effect on song nucleus size and circulating testosterone levels. Our data suggest that late-hatched males must have undergone accelerated song development. Furthermore, the limited tutor song exposure did not affect adult song organization and song performance.

opencc-zeroDec 2016View details →

Data from: Seawater environmental DNA reflects seasonality of a coastal fish community

Coastal marine fish populations are in decline due to overfishing, habitat destruction, climate change and invasive species. Seasonal monitoring is important for detecting temporal changes in the composition of fish communities, but current monitoring is often non-existent or limited to annual or semi-annual surveys. In the present study, we investigate the potential of using environmental DNA (eDNA) metabarcoding of seawater samples to detect the seasonal changes in a coastal marine fish community. Water sampling and snorkelling visual census were performed over 1 year (from 23rd of August 2013 to 11th of August 2014) at a temperate coastal habitat in Denmark (55°45′39″N, 12°35′59″E) and compared to long-term data collected over a 7-year period. We used Illumina sequencing of PCR products to demonstrate that seawater eDNA showed compositional changes in accordance with seasonal changes in the fish community. The vast majority of fish diversity observed in the study area by snorkelling was recovered from sequencing, although the overlap between methods varied widely among sampling events. In total, 24 taxa were detected by both methods, while five taxa were only detected using eDNA and three taxa were only detected by snorkelling. A limitation of the applied primers was the lack of resolution to species level in a few diverse families, and varying sequencing depth between samples represents a potential bias. However, our study demonstrates the utility of eDNA for recovering seasonal variation in marine fish communities, knowledge of which is essential for standardised long-term monitoring of marine biodiversity.

opencc-zeroDec 2012View details →

Data from: One phase of the dormancy developmental pathway is critical for the evolution of insect seasonality

Evolutionary change in the timing of dormancy enables animals and plants to adapt to changing seasonal environments and can result in ecological speciation. Despite its clear biological importance, the mechanisms underlying the evolution of dormancy timing in animals remain poorly understood because of a lack of anatomical landmarks to discern which phase of dormancy an individual is experiencing. Taking advantage of the nearly universal characteristic of metabolic suppression during insect dormancy (diapause), we use patterns of respiratory metabolism to document physiological landmarks of dormancy and test which of the distinct phases of the dormancy developmental pathway contribute to a month-long shift in diapause timing between a pair of incipient moth species. Here, we show that divergence in life cycle between the earlier-emerging E-strain and the later-emerging Z-strain of European corn borer (ECB) is clearly explained by a delay in the timing of the developmental transition from the diapause maintenance phase to the termination phase. Along with recent findings indicating that life-cycle differences between ECB strains stem from allelic variation at a single sex-linked locus, our results demonstrate how dramatic shifts in animal seasonality can result from simple developmental and genetic changes. Although characterizing the multiple phases of the diapause developmental programme in other locally adapted populations and species will undoubtedly yield surprises about the nature of animal dormancy, results in the ECB moth suggest that focusing on genetic variation in the timing of the dormancy termination phase may help explain how (or whether) organisms rapidly respond to global climate change, expand their ranges after accidental or managed introductions, undergo seasonal adaptation, or evolve into distinct species through allochronic isolation.

Data from: Seasonal characteristics of phosphorus sorption by sediments from plain lakes with different trophic statuses

Phosphorus (P) sorption in sediments plays a significant role in trophic status of a lake. This study investigated the characteristics of P sorption in sediments from three lakes with different trophic statuses (moderately eutrophic, lightly eutrophic, and moderately trophic) through kinetic, batch equilibrium, and thermodynamic experiments. Results show that pseudo-second-order kinetics best describe P sorption in sediments from the three lakes. Fitting by modified Langmuir and Freundlich isotherms indicate that the moderately trophic lake sediments has higher sorption capacity (maximum of 0.848 mg g-1 at 35 °C) than the sediments of the other two lakes at different temperatures (5, 15, 25, and 35 °C). Thermodynamic results indicate that the process of P sorption of the three sediments are spontaneous, entropy-driven, and endothermic reactions. The risk of P release in sediments was analyzed according to the calculated results of isotherms combined with the change in P fraction. Sediments from the moderately eutrophic lake act as a source in summer. The lightly eutrophic and moderately trophic lakes act as sources in spring and winter, and a pool in summer and autumn, respectively. Furthermore, the amounts of reductant-soluble P (RS-P), calcium bound P (Ca-P), and iron bound P (Fe-P) are significantly related to the sorption capacity of sediments from the three lakes (p<0.05). The different sediments have the different P release risk, and P fraction in sediment is one of the significant factors of P sorption.

Data from: Seasonal changes in the altitudinal distribution of nocturnally migrating birds during autumn migration

Wind plays a significant role in the flight altitudes selected by nocturnally migrating birds. At mid-latitudes in the Northern Hemisphere, atmospheric conditions are dictated by the polar-front jet stream, whose amplitude increases in the autumn. One consequence for migratory birds is that the region's prevailing westerly winds become progressively stronger at higher migration altitudes. We expect this seasonality in wind speed to result in migrants occupying progressively lower flight altitudes, which we test using density estimates of nocturnal migrants at 100 m altitudinal intervals from 12 weather surveillance radar stations located in the northeastern USA. Contrary to our expectations, median migration altitudes deviated little across the season, and the variance was lower during the middle of the season and higher during the beginning and especially the end of the season. Early-season migrants included small- to intermediate-sized long-distance migrants in the orders Charadriiformes and Passeriformes, and late-season migrants included large-bodied and intermediate-distance migrants in the order Anseriformes. Therefore, seasonality in the composition of migratory species, and related variation in migration strategies and behaviours, resulted in a convex–concave bounded distribution of migration altitudes. Our results provide a basis for assessing the implications for migratory bird populations of changes in mid-latitude atmospheric conditions probably occurring under global climate change.

Data from: Synchronized shift of oral, fecal and urinary microbiotas in bats and natural infection dynamics during seasonal reproduction

Seasonal reproduction is a period of extreme physiological and behavioral changes, yet we know little about how it may affect host microbial communities (i.e. microbiota) and pathogen transmission. Here, we investigated shifts of the bacterial microbiota in saliva, urine and faeces during the seasonal reproduction of bats in South Africa, and test for an interaction in shedding patterns of both bacterial (Leptospira) and viral (adeno- and herpes-viruses) agents. Based on a comparative approach in two cave-dwelling bat species and high-throughput sequencing of the 16S rRNA gene, we demonstrated a clear signature in microbiota changes over the reproduction season, consistent across the multiple body habitats investigated, and associated with sex, age and reproductive condition of bats. We observed in parallel highly dynamic shedding patterns for both bacteria and viruses, but did not find a significant association between viral shedding and bacterial microbiota composition. Indeed, only Leptospira shedding was associated with alterations in both the diversity and composition of the urinary microbiota. These results illustrate how seasonal reproduction in bats substantially affects microbiota composition and infection dynamics, and have broad implications for the understanding of disease ecology in important reservoir hosts, such as bats.

Data from: Early hatching enhances survival despite beneficial phenotypic effects of late-season developmental environments

Seasonal shifts in environmental conditions provide predictable cues to which organisms can respond in adaptive ways. For example, seasonal changes in temperature can induce phenotypes at different times of the year that have season-specific fitness benefits. Here, we tested the hypothesis that embryo responses to seasonal changes in thermal environments are adaptively matched to the timing of reproduction (environmental-matching hypothesis). We collected eggs of the brown anole lizard (Anolis sagrei) from early and late seasons and exposed them to early and late thermal regimes that mimic nest temperatures. After measuring offspring morphology and performance, we quantified their survival in the field. Females had higher fecundity, but produced smaller eggs, early in the season compared to late in the season. Late-season eggs exposed to late thermal regimes had relatively high survival, but early-season eggs exposed to early thermal regimes had similar survival rates to those exposed to mismatched conditions. Late-season nest temperatures and late-season eggs produced offspring that were relatively large and fast runners. However, despite phenotypic benefits of late-season conditions, early-season hatchlings had greater survival in the field. Our results do not fully support the environmental-matching hypothesis but suggest that selection favors seasonal shifts in reproductive investment of mothers (high early-season fecundity) over plastic responses of embryos to seasonal environmental changes.

opencc-zeroDec 2019View details →

Heat dissipation behaviour of birds in seasonally hot, arid-zones: are there global patterns?

<p>Quantifying organismal sensitivity to heat stress provides one means for predicting vulnerability to climate change. Birds are ideal for investigating this approach, as they display quantifiable fitness consequences associated with behavioural and physiological responses to heat stress. We used a recently developed method that examines correlations between readily-observable behaviours and air temperature (Tair) to investigate interspecific variation in avian responses to heat stress in seasonally hot, arid regions on three continents: the southwestern United States, the Kalahari Desert of southern Africa and the Gascoyne region of Western Australia. We found substantial interspecific variation in heat dissipation behaviours (wing-drooping, panting, activity-reduction, shade-seeking) across all three regions. However, pooling the data revealed that little of this interspecific variation was systematically explained by organismal traits (foraging guild, diet, drinking dependency, body mass, or activity levels) at the scale we tested. After accounting for phylogeny, we found that larger birds engaged in wing-drooping behaviour at lower Tair and had lower activity levels at high Tair compared to smaller birds, indicating an effect of body mass on heat dissipation behaviour (HDB). In the Kalahari, reliance on drinking was correlated with significantly lower Tair at which panting commenced, suggesting a key role of water acquisition in HDB in that region. Birds also tended to retreat to shade at relatively lower Tair when more active, suggesting a behavioural trade-off between activity, heat load, and microsite selection. Our results imply that the causes underlying interspecific variation in heat dissipation behaviours are complex. While the variation we observed was not systematically explained by the broad scale organismal traits we considered, we predict that the indices themselves will still reflect vulnerability to potential fitness costs of high air temperatures. Further research is needed on a species-specific basis to establish the functional significance of these indices.</p>

opencc-zeroDec 2018View details →

Data from: Seasonal climate effects on the survival of a hibernating mammal

Global climate change and associated regional climate variability is impacting the phenology of many species, ultimately altering individual fitness and population dynamics. Yet, few studies have considered the effects of pertinent seasonal climate variability on phenology and fitness. Hibernators may be particularly susceptible to changes in seasonal climate since they have a relatively short active season in which to reproduce and gain enough mass to survive the following winter. To understand whether and how seasonal climate variability may be affecting hibernator fitness, we estimated survival from historical (1964-1968) and contemporary (2014-2017) mark-recapture data collected from the same population of Uinta ground squirrels (UGS, Urocitellus armatus), a hibernator endemic to the western United States. Despite a locally warming climate, the phenology of UGS did not change over time, yet season-specific climatic variables were important in regulating survival rates. Specifically, older age classes experienced lower survival when winters or the following spring were warm, while juveniles benefited from warmer winter temperatures. Although metabolic costs decrease with decreasing temperature in the hibernacula, arousal costs increase with decreasing temperature. Our results suggest that this trade-off is experienced differently by immature and mature individuals. We also observed an increase in population density during that time period, suggesting resources are less limited today than they used to be. Cheatgrass is now dominating the study site and may provide a better food source to UGS than native plants did historically.

opencc-zeroDec 2018View details →

Data from: The effect of drought and season on root life span in temperate arbuscular mycorrhizal and ectomycorrhizal tree species

1. Fine roots play a key role in carbon (C) and nutrient cycling, since fine root lifespan drives soil organic C input and, thus, N availability. The two principal fungal symbioses found in temperate forest trees, ectomycorrhizae (ECM) and arbuscular mycorrhizae (AM), induce different root morphological changes upon infection, but the consequences for root lifespan are not clear. 2. We explored differences in fine root lifespan between four AM and four ECM tree species using mini-rhizotrons in a factorial drought experiment in large mesocosms. 3. Median root lifespan of young AM and ECM trees differed fundamentally in its response to soil moisture and season of root birth: ECM root lifespan was reduced from 176 to 81 d in dry soil compared to moist soil, independent of season. By contrast, AM root lifespan was less responsive to drought, but decreased from 185 to 127 d when comparing roots produced early in the growing season vs. mid-season. In both mycorrhizal types, root lifespan was positively related to root diameter and negatively to the portion of lower-order roots. 4. Synthesis. While our results indicate morphological and architectural traits that predict root lifespan across tree species, they also indicate principal differences in the environmental response of root lifespan in young AM and ECM trees. This knowledge helps to improve global predictions of root lifespan.

opencc-zeroDec 2018View details →

Data from: Comparing diel activity patterns of wildlife across latitudes and seasons: time transformations using day length

(1) Camera trapping allows scientists to study activity patterns of animals under natural conditions. However, comparisons of activity patterns across seasons or latitudes can be biased, because activity is often attuned to sunrise and sunset, the timing of which varies with latitude and season. Existing transformation methods to solve this problem have limitations. (2) Here, we explore whether and how activity patterns can be transformed more accurately using two alternative 'double anchoring' transformations – equinoctial and average anchoring – that anchor activity time to two chosen anchor points during the study period. (3) Using simulated noisy datasets mimicking species with either crepuscular, diurnal or cathemeral activity patterns, we compared the ability of different transformation methods to extract the latent pattern and activity levels under different study conditions. We found that average anchoring best retrieved the original diel activity pattern and yielded accurate estimates of activity level. Two alternative transformation methods – single anchoring and equinoctial anchoring – performed less well. Bias in estimates from using untransformed clock times was most marked (up to 2.5-fold over-estimation) for longer studies covering 4-5 months either side of an equinox at high latitude, and focusing on crepuscular species. (4) We applied the average anchoring method to 9 months of data on Red deer (Cervus elaphus), Wild boar (Sus scrofa) and Mouflon (Ovis amon musimon) activity as captured by camera traps in National Park Hoge Veluwe, the Netherlands. Average anchoring revealed more pronounced peaks of activity after sunset than was apparent from untransformed data in red deer and wild boar, but not for mouflon, a cathemeral species. Similarly, activity level was lower when calculated using average-anchored time for red deer and wild boar, but no difference was observed for mouflon. (5) We conclude that transformation of time might not be necessary at latitudes below 20°, or in studies with a duration of less than a month (below 40° latitude). For longer study periods and/or higher latitudes, average-anchoring resolves the problem of variable day length. Code is provided. The transformation functions are incorporated in the R-package 'activity'.

Data from: Faster spring migration in northern wheatears is not explained by an endogenous seasonal difference in refueling rates

A widespread phenomenon in migrant birds is that they travel faster in spring than in autumn. During migration birds spend most time at stopover sites and, correspondingly, the faster spring migration is mainly explained by shorter stopovers in spring than autumn. Because a main purpose of stopovers is to replenish the fuel used in flight, a higher rate of fuel deposition (FDR) in spring is thought to explain the shorter stopovers and hence shorter total duration of migration in spring. Critical migratory processes, including the onset and extent of pre-migratory fueling, are endogenously regulated. It is therefore not unlikely that refueling at stopover sites is, at least partly, also under endogenous control. We here tested whether there is an endogenous seasonal difference in food intake and FDR, which could contribute to shorter stopovers and hence faster migration in spring. We measured daily food intake and daily FDR in two subspecies of the northern wheatear Oenanthe oenanthe, temporarily confined at stopover under identical constant indoor conditions in spring and autumn. The two wheatear subspecies differed markedly in absolute food intake and FDR. Within subspecies, however, food intake and FDR did not differ between spring and autumn, indicating that faster spring migration in northern wheatears is not explained by an endogenously controlled seasonal difference in birds' motivation to refuel. To further substantiate this claim, similar measurements should be taken at other locations along northern wheatears' migration routes. Comparable experiments in other species could test the generality of our results.