| 1. |
- Chevalier, Mathieu, et al.
(författare)
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Changes in forest bird abundance, community structure and composition following a hurricane in Sweden
- 2019
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Ingår i: Ecography. - : Wiley. - 0906-7590 .- 1600-0587. ; 42:11, s. 1862-1873
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Tidskriftsartikel (refereegranskat)abstract
- The effect that extreme natural events have on biological diversity is relatively poorly known. We used a before–after control-impact (BACI) design to analyze changes in bird abundances and communities following Hurricane Gudrun, which struck southern Sweden in January 2005, felling 75 million m3 of forest and causing damage to 5% of forested areas (half a million hectares) in a few hours. We used recent measures of impact in combination with classical BACI contrasts to analyze bird count data from a monitoring program in Sweden. We investigated changes in the abundance of 17 species commonly found in forests, along with changes in species composition and functional structure of the bird community. In total, we considered 34 response variables and examined whether responses were immediate or long-term. There was no evidence of a strong effect of the hurricane on the abundances of six species. Estimates of the effects on five species were too uncertain to draw inferences. We detected positive and negative effects of the hurricane on the abundances of the remaining six species, but the magnitude of effects often was small. Generally, the effects were in the expected direction: negative on birds associated with mature forest and positive on birds associated with open land or young forest. We found evidence of an increase in the proportion of species that nest on the ground and a decrease in the proportion of species that nest in cavities and trees. In contrast, the hurricane had no discernible effect on functional measures of diversity (richness, evenness or divergence), or on communities’ reproductive or morphological characteristics. Our results suggest that the hurricane affected bird populations and communities, but the magnitude of effects was generally small.
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| 2. |
- Chevalier, Mathieu
(författare)
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Global assessment of early warning signs that temperature could undergo regime shifts
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Climate change metrics have been used to quantify the exposure of geographic areas to different facets of change and relate these facets to different threats and opportunities for biodiversity at a global scale. In parallel, a suite of indicators have been developed to detect approaching transitions between alternative stable states in ecological systems at a local scale. Here, we explore whether particular geographic areas over the world display evidence for upcoming critical transitions in the temperature regime using five Early Warning Indicators (EWIs) commonly used in the literature. Although all EWIs revealed strong spatial variations regarding the likelihood of approaching transitions we found differences regarding the strength and the distribution of trends across the world, suggesting either that different mechanisms might be at play or that EWIs differ in their ability to detect approaching transitions. Nonetheless, a composite EWI, constructed from individual EWIs, showed congruent trends in several areas and highlighted variations across latitudes, between marine and terrestrial systems and among ecoregions within systems. Although the underlying mechanisms are unclear, our results suggest that some areas over the world might change toward an alternative temperature regime in the future with potential implications for the organisms inhabiting these areas.
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| 3. |
- Chevalier, Mathieu
(författare)
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Interactions between species attributes explain population dynamics in stream fishes under changing climate
- 2018
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Ingår i: Ecosphere. - : Wiley. - 2150-8925. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Species responses to climate change have been shown to vary in both direction and magnitude. Understanding these idiosyncratic responses is crucial if we are to predict extinction risk and set up efficient conservation strategies. The variations observed across species have been related to several species attributes including intrinsic traits such as physiological tolerances or life-history strategies but also to niche characteristics (e.g., niche breadth [NB], niche position [NP]). However, although previous studies have successfully linked species attributes to population dynamics or range shifts, few have considered synergistic effects to explain responses to climate variations. Here, we assessed whether five species attributes (fecundity, thermal safety margin, trophic position [TP], NB, and NP) explained interspecific differences in four parameters influencing population dynamics of 35 stream fish species at the French scale. We used Bayesian N-mixture models to estimate posterior distributions of the growth rate, the strength of density dependence, and the influence of both mean temperature and temperature variability on populations for each species. We then used phylogenetic generalized least squares (PGLS) models to investigate the influence of species attributes and their interactions on interspecific differences in each of the four parameter driving population dynamics. The percentage of variance explained by the PGLS models was relatively high (around 40% on average), indicating that species attributes are good predictors of species population dynamics. Furthermore, we showed that the influence of these single attributes was mediated by other attributes, especially NP and TP. Importantly, we found that models including interaction terms had greater support over simple additive models in explaining interspecific differences in population dynamics. Taken together, these results point to the importance of considering the interplay between species attributes in unraveling the mechanisms involved in population dynamics and understanding the vulnerability of species to global change.
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| 4. |
- Chevalier, Mathieu, et al.
(författare)
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New measures for evaluation of environmental perturbations using Before-After-Control-Impact analyses
- 2019
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Ingår i: Ecological Applications. - : Wiley. - 1051-0761 .- 1939-5582. ; 29
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Tidskriftsartikel (refereegranskat)abstract
- Before-After-Control-Impact (BACI) designs are powerful tools to derive inferences about environmental perturbations (e.g., hurricanes, restoration programs) when controlled experimental designs are unfeasible. Applications of BACI designs mostly rely on testing for a significant interaction between periods and treatments (so-called BACI contrast) to demonstrate the effects of the perturbation. However, significant interactions can emerge for several reasons, including when changes are larger in control sites, such that additional diagnostics must be performed to determine the full complexity of system changes. We propose two measures that detail the nature of change implied by BACI contrasts, along with its uncertainty. CI-divergence (Control-Impact divergence) quantifies to what extent control and impact sites have diverged between the after and the before period, whereas CI-contribution (Control-Impact contribution) quantifies to what extent the change between periods is stronger in impact sites relative to control sites. To illustrate how these two CI measures can be combined with BACI contrast to gain insights about effects of environmental perturbations, we used count data from the Swedish Breeding Bird Survey to investigate how hurricane Gudrun affected the long-term abundances of four bird species in forested areas of southern Sweden. Before-After-Control-Impact contrasts suggested the hurricane affected all four species. However, the values of the two CI measures strongly differed, even among species showing similar BACI contrasts. Those differences highlight qualitatively distinct population trajectories between periods and treatments requiring different ecological explanations. Overall, we show that BACI contrasts do not provide the full story in assessing the effects of environmental perturbations. The two CI measures can be used to assist ecological interpretations, or to specify detailed hypotheses about effects of restoration actions to allow stronger confirmatory inference about their outcomes. By providing a framework to develop more detailed explanations and hypotheses about ecological changes, the two CI measures can improve conclusions and strengthen evidence of effects of conservation actions and impact assessments under BACI designs.
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| 5. |
- Chevalier, Mathieu
(författare)
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Planktonic diatom community dynamics in a tropical flood-pulse lake: the Tonle Sap (Cambodia)
- 2019
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Ingår i: Diatom Research. - 0269-249X .- 2159-8347. ; 34, s. 1-22
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Tidskriftsartikel (refereegranskat)abstract
- It has been proposed that, within flood-pulse systems, seasonally dynamic conditions promote extremely high levels of biodiversity. In this paper, we aim to understand how variation in environmental conditions and habitat availability, across space and time, influences the structure and composition of plankton diatom communities within the Tonle-Sap Lake (Cambodia) during two flood-pulse cycles. We hypothesize that (i) communities vary considerably across space and time, (ii) environmental filtering accounts for a substantial portion of the variation in community composition, and (iii) shifts in meta-community structure occur seasonally, due to variation in both environmental conditions and habitat availability. A principal component analysis and a permutational multivariate analysis of variance were used to characterize spatio-temporal variations in environmental conditions, community structure and composition. Determinants of community variations across space were identified by redundancy analyses and variation partitioning, while seasonal changes in meta-community structure were assessed by investigating temporal changes in beta-diversity. Our results indicate that (i) spatial variations in community structure and composition are largely influenced by the seasonal flood-pulse, (ii) environmental filtering is the most likely process driving the compositional changes, and (iii) changes in diatom life-form community provide insights into the hydrological functioning of the Tonle Sap. We conclude that the survey of diatom communities may constitute a relevant sensor of hydrological change in the system and could be used to derive regionally specific hypotheses about how global climate change is impacting the lake's functioning.
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| 6. |
- Chevalier, Mathieu
(författare)
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Seasonal variations in diet composition, diet breadth and dietary overlap between three commercially important fish species within a flood-pulse system: The Tonle Sap Lake (Cambodia)
- 2018
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Tropical lakes and their associated floodplain habitats are dynamic habitat mosaics strongly influenced by seasonal variations in hydrologic conditions. In flood-pulse systems, water level oscillations directly influence the connectivity to floodplain habitats for fish. Here, we aimed to investigate whether seasonal changes in the water level of a flood-pulse system (the Tonle Sap Lake, Cambodia) differentially affect diet breadth and dietary overlap of three common and commercially important fish species (Anabas testudineus, Boesemania microplepis and Notopterus notopterus) presenting important differences in their life-cycle (e.g. seasonal migration). For this purpose, the three fish species were sampled at four locations spread over the lake and their stomach contents extracted for analyses. Dietary differences were investigated across seasons regarding the diet composition and diet breadth of each species as well as the amount of dietary overlap between species. We found that the proportion of empty stomachs changed similarly across seasons for the three species, thus suggesting that ecological differences between species are not sufficient to outweigh the effect of seasonal variations in resource abundance. In contrast, changes in diet composition were species-specific and can be explained by ecological and behavioral differences between species. Diet breadth differed between species in all seasons, except during the wet season, and tended to be higher during the dry season when dietary overlap was the lowest. These variations likely result from changes in the diversity and amount of resources and may lead to habitat use shifts with potential implications for competitive interactions. In particular, increasing connectivity to floodplain habitats may reduce the competitive pressure during the wet season, while resource scarcity during the dry season may constrain individuals to diversify their diet to avoid competition. Overall, our results suggest a considerable plasticity in the feeding behavior of the three species as demonstrated by seasonal variation in both diet breadth and dietary overlap. Such variations can be explained by a number of factors and processes, including changes in resource availability or competitive interactions between individuals for resources, whose relative influence might vary depending on the magnitude and the timing of the flood-pulse driving the connectivity to floodplain habitats. Gaining knowledge on the seasonal evolution of fish's diet is relevant for fisheries management and conservation and our result could be used to guide aquaculture development in Cambodia.
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| 7. |
- Josefsson, Jonas, et al.
(författare)
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Improving scientific rigour in conservation evaluations and a plea deal for transparency on potential biases
- 2020
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Ingår i: Conservation Letters. - : Wiley. - 1755-263X. ; 13:5
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Forskningsöversikt (refereegranskat)abstract
- The delivery of rigorous and unbiased evidence on the effects of interventions lay at the heart of the scientific method. Here we examine scientific papers evaluating agri-environment schemes, the principal instrument to mitigate farmland biodiversity declines worldwide. Despite previous warnings about rudimentary study designs in this field, we found that the majority of studies published between 2008 and 2017 still lack robust study designs to strictly evaluate intervention effects. Potential sources of bias that arise from the correlative nature are rarely mentioned, and results are still promoted by using a causal language. This lack of robust study designs likely results from poor integration of research and policy, while the erroneous use of causal language and an unwillingness to discuss bias may stem from publication pressures. We conclude that scientific reporting and discussion of study limitations in intervention research must improve and propose some practices toward this goal.
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| 8. |
- Knape, Jonas, et al.
(författare)
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Sensitivity of binomial N-mixture models to overdispersion: The importance of assessing model fit
- 2018
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Ingår i: Methods in Ecology and Evolution. - 2041-210X. ; 9, s. 2102-2114
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Tidskriftsartikel (refereegranskat)abstract
- 1. Binomial N-mixture models are commonly applied to analyse population survey data. By estimating detection probabilities, N-mixture models aim at extracting information about abundances in terms of absolute and not just relative numbers. This separation of detection probability and abundance relies on parametric assumptions about the distribution of individuals among sites and of detections of individuals among repeat visits to sites. Current methods for checking assumptions are limited, and their computational complexity has hindered evaluations of their performance.2. We use simulations and a case study to assess the sensitivity of binomial N-mixture models to overdispersion in abundance and in detection, develop computationally efficient graphical goodness of fit checks to detect it, and evaluate the ability of the checks to identify overdispersion.3. The simulations show that if the parametric assumptions are not exact the bias in estimated abundances can be severe: underestimation if there is overdispersion in abundance relative to the fitted model and overestimation if there is overdispersion in detection. Our goodness-of-fit checks performed well in detecting lack of fit when the abundance distribution was overdispersed, but struggled to detect lack of fit when detections were overdispersed. We show that the inability to detect lack of fit due to overdispersed detection is caused by a fundamental similarity between N-mixture models with beta-binomial detections and N-mixture models with negative binomial abundances.4. The strong biases that can occur in the binomial N-mixture model when the distribution of individuals among sites, or the detection model, is mis-specified implies that checking goodness of fit is essential for sound inference about abundance. To check the assumptions we provide computationally efficient goodness of fit checks that are available in an R-package nmixgof. However, even when a binomial N-mixture model appears to fit the data well, estimates are not robust in the presence of overdispersion. We show that problems can occur even when estimated detection probabilities are high, and that previously reported problems with negative binomial models cannot always be diagnosed by checking the sensitivity of abundance estimates to numerical cutoff values used in likelihood computations.
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| 9. |
- Petroff, E., et al.
(författare)
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A polarized fast radio burst at low Galactic latitude
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford Academic. - 0035-8711 .- 1365-2966. ; 469:4, s. 4465-4482
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Tidskriftsartikel (refereegranskat)abstract
- We report on the discovery of a new fast radio burst (FRB), FRB 150215, with the Parkes radio telescope on 2015 February 15. The burst was detected in real time with a dispersion measure (DM) of 1105.6 +/- 0.8 pc cm(-3), a pulse duration of 2.8(-0.5)(+1.2) ms, and a measured peak flux density assuming that the burst was at beam centre of 0.7(-0.1)(+0.2) Jy. The FRB originated at a Galactic longitude and latitude of 24.66 degrees, 5.28 degrees and 25 degrees away from the Galactic Center. The burst was found to be 43 +/- 5 per cent linearly polarized with a rotation measure (RM) in the range -9 < RM < 12 rad m(-2) (95 per cent confidence level), consistent with zero. The burst was followed up with 11 telescopes to search for radio, optical, X-ray, gamma-ray and neutrino emission. Neither transient nor variable emission was found to be associated with the burst and no repeat pulses have been observed in 17.25 h of observing. The sightline to the burst is close to the Galactic plane and the observed physical properties of FRB 150215 demonstrate the existence of sight lines of anomalously low RM for a given electron column density. The Galactic RM foreground may approach a null value due to magnetic field reversals along the line of sight, a decreased total electron column density from the Milky Way, or some combination of these effects. A lower Galactic DM contribution might explain why this burst was detectable whereas previous searches at low latitude have had lower detection rates than those out of the plane.
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