Variation In Probability Of Occurrence Research Articles

Increased landscape disturbance and streamflow variability threaten fish biodiversity in the Red River catchment, USA

AbstractAimStream fish distributions are hypothesized to be strongly associated with landscape characteristics at multiple scales. Variation in flow regimes and intensity of landscape disturbance are associated with stream fish distributions; however, relationships are poorly understood in many high‐diversity regions. Our objective was to identify occurrence relationships between fish distributions and streamflow and landscape characteristics in the south‐central United States.LocationOur study area was the central Red River catchment in Oklahoma, Texas and Arkansas, USA.MethodsWe used existing fish surveys to model the occurrence of a diverse, warmwater assemblage among hydraulic response units (HRUs). We used multispecies occupancy modelling to identify variation in occurrence probability among 111 stream fishes in relation to landscape disturbance and flow regime characteristics.ResultsWe found occurrence relationships with landscape disturbance and 11 metrics comprising all flow‐regime components. The relationships varied within both major species groups and some genera. Frequency and duration were the most common metrics underlying flow regime relationships. More common stream fishes tended to be positively associated with higher levels of landscape disturbance and flow regime metrics representing variability; conversely, narrow‐ranged fishes tended to be negatively associated. Occurrence relationships with flow metrics representing high‐flow events were predominately negative. As expected, many species were strongly associated with ecoregion with landscape disturbance and flow relationships held constant.Main conclusionsOur study informs land use and water management decisions and stream fish conservation at multiple spatial scales. Collectively, the findings suggest potential homogenization of the Red River fish assemblage with increased landscape disturbance and streamflow variability. A reduction in landscape disturbance and maintenance of natural flow patterns at coarser scales may benefit endemic and narrow‐ranged fishes. Our findings also help guide finer‐scale land use and water management decisions by identifying stream network areas with a high occurrence probability of less tolerant fishes.

Unraveling a century of global change impacts on winter bird distributions in the eastern United States.

One of the most pressing questions in ecology and conservation centers on disentangling the relative impacts of concurrent global change drivers, climate and land-use/land-cover (LULC), on biodiversity. Yet studies that evaluate the effects of both drivers on species' winter distributions remain scarce, hampering our ability to develop full-annual-cycle conservation strategies. Additionally, understanding how groups of species differentially respond to climate versus LULC change is vital for efforts to enhance bird community resilience to future environmental change. We analyzed long-term changes in winter occurrence of 89species across nine bird groups over a 90-year period within the eastern United States using Audubon Christmas Bird Count (CBC) data. We estimated variation in occurrence probability of each group as a function of spatial and temporal variation in winter climate (minimum temperature, cumulative precipitation) and LULC (proportion of group-specific and anthropogenic habitats within CBC circle). We reveal that spatial variation in bird occurrence probability was consistently explained by climate across all nine species groups. Conversely, LULC change explained more than twice the temporal variation (i.e., decadal changes) in bird occurrence probability than climate change on average across groups. This pattern was largely driven by habitat-constrained species (e.g., grassland birds, waterbirds), whereas decadal changes in occurrence probabilities of habitat-unconstrained species (e.g., forest passerines, mixed habitat birds) were equally explained by both climate and LULC changes over the last century. We conclude that climate has generally governed the winter occurrence of avifauna in space and time, while LULC change has played a pivotal role in driving distributional dynamics of species with limited and declining habitat availability. Effective land management will be critical for improving species' resilience to climate change, especially during a season of relative resource scarcity and critical energetic trade-offs.

A field‐validated species distribution model to support management of the critically endangered Poweshiek skipperling (Oarisma poweshiek) butterfly in Canada

AbstractThe Poweshiek skipperling (Oarisma poweshiek) is a critically endangered grassland butterfly with six populations remaining in the United States and Canada. The single Canadian population, with the largest remaining contiguous habitat, includes less than ~50 observed individuals and extirpation is potentially imminent. Captive breeding is underway and there is a need to locate suitable sites for reintroduction and habitat management. Species distribution models (SDMs) predict habitat quality and guide management decisions. Most SDMs rely on statistical validation as a surrogate metric for accuracy, with presence‐only SDMs usually reporting area under the curve (AUC). Although experts have long cautioned against relying on statistical validation alone, accuracy is rarely field‐validated. We developed a presence‐only SDM using the maximum entropy (Maxent) method to predict probability of occurrence for the Poweshiek skipperling and determine environmental covariates associated with high probability of occurrence. We collected two independent datasets to (a) calibrate our model to predict categories of habitat quality (using factor analysis) and (b) compare expected and observed habitat quality to calculate model accuracy. Statistical validation showed that we predicted presence‐absence of training data with high accuracy (AUC = 0.98). Covariates responsible for most of the variation in probability of occurrence included soil drainage, habitat patch size, and land use type. Only 0.4% of the study area was expected to represent good‐excellent habitat with the remaining 99.6% medium‐poor. Our model predicted novel habitat quality with 81% accuracy (better than chance). Poor‐medium habitat was predicted more accurately (92%) than good‐excellent habitat (54%). Our model showed better accuracy than most other field‐validated SDMs reviewed. We reiterate calls for greater field‐validation of SDMs: if we had relied on statistical validation alone, perceived accuracy of our model would be inflated. Finally, managers can use our results to reliably exclude predicted poor‐medium habitats as candidates for Poweshiek skipperling habitat management or reintroduction.

Turbulence statistics of flow through degraded channel bed of sand–gravel mixture

This paper describes the results of an experimental study on the turbulence characteristics of flow through bed profile of a laboratory channel that was degraded by detachment of its bed material consisting of sand–gravel mixture. The measurements of velocity and turbulence characteristics over the degraded bed profile were made at three locations along the degraded bed profile using an ADV. The maximum value of turbulence intensity and the Reynolds shear stress were found to occur at the level of bed surface existing before the detachment and these values decreased towards the flow surface. The magnitude of turbulence intensities and Reynolds shear stress are observed to reduce, as one moves towards the downstream along the degraded bed profile which signifies that vortex structure weakened by bed profile degradation. Quadrant analysis was performed which demonstrated the importance of ejection and sweep phases in sediment detachment and transport. Highest occurrence probabilities are found for sweep and ejection event. The other two events i.e. outward and inward interactions are found to have very small occurrence on the probabilities. Variation of occurrence probability with hole size (H) is also discussed.

Trait-dependent occupancy dynamics of birds in temperate forest landscapes: fine-scale observations in a hierarchical multi-species framework

Silvicultural practices lead to changes in forest composition and structure and may impact species diversity from the overall regional species pool to stand-level species occurrence. We explored to what extent fine-scale occupancy patterns in differently managed forest stands are driven by environment and ecological traits in three regions in Germany using a multi-species hierarchical model. We tested for the possible impact of environmental variables and ecological traits on occupancy dynamics in a joint modelling exercise while taking possible variation in coefficient estimates over years and plots into account. Bird species richness differed across regions and years, and trends in species richness across years were different in the three regions. On the species level, forest management affected occupancy of species in all regions, but only 3–5% of the total assemblage-level variation in occurrence probability was explained by either forest type and successional stage and < 1% by forest edge. On the assemblage level, bird occurrence decreased with body mass in all regions. Species with smaller breeding ranges had lower occurrence probabilities in one region, while later spring arrival decreased occurrence probabilities in the two other regions. Spatial variation in the effect size of trait covariates such as species phylogeny and breeding strata showed that variation in patch occupancy due to fine-scale differences in forest management is, to some extent, predictable from ecological traits. Our results show that environmental factors and ecological traits jointly predict variation in bird occupancy patterns and their response to forest management. Observations at the fine scale of forest stands, at which conservation efforts can be arranged along with forest management practices in heterogeneous environments, have been shown to provide meaningful insights despite the difficulties involved in monitoring mobile organisms such as birds at the plot level.

Spread F, GPS phase fluctuations, and plasma bubbles near the crest of equatorial ionization anomaly during solar maximum

This work is the first attempt to concurrently study the occurrence probabilities of spread F, GPS phase fluctuations, and plasma bubbles near the crest of equatorial ionization anomaly (EIA). The data were observed by an ionosonde, a GPS receiver, and ROCSAT‐1 during 2000, the solar maximum year. Results show that the occurrences of the range spread F (RSF) differ from those of the frequency spread F (FSF). For the seasonal variation, the RSF occurrence has the maximum values in March and September, while the FSF occurrence peaks at June. For the nighttime variation, RSF and FSF peak at 2300 and 0300 LT, respectively. Regarding the GPS phase fluctuations, an index Fp is applied to characterize the irregularity strength. The similarity between the 50 &lt; Fp ≤ 200 and RSF occurrences demonstrates that the characteristics of F region irregularities forming 50 &lt; Fp ≤ 200 are mainly related to RSF. The occurrence of 200 &lt; Fp is almost absent. The rare event is also found in the observation of plasma bubbles by ROCSAT‐1. Furthermore, the seasonal variations in GPS phase fluctuations at the EIA crest and the dip equator have similar trends. This indicates that the F region irregularities of RSF and 50 &lt; Fp ≤ 200 at the EIA crest are originated from the equatorial ionosphere. On the other hand, the seasonal variation in occurrence probability of FSF at the EIA crest is close to that of spread F at midlatitudes. This suggests that the generation mechanisms of FSF and midlatitude spread F might be same, but the further study is required.

Subjective Criticality Importance of the Fundamental Events to the Top Event in Fault Tree

A procedure is proposed which can subjectively estimate the relative occurrence probability of each fundamental event in fault tree by applying a pairwise comparison method. The proposed procedure could be applied to calculate the subjective criticality importance for the fundamental event. Consequently, it is possible to estimate the effect of the variation in the occurrence probability of each fundamental event on the variation in occurrence probability of top event, even if some of probability data for fundamental event should be lacking.

Return period relationships

The samples available in hydrology are often so small that it is desirable to take their size into account when estimating parameters. By using a simple classical model the relationship between various estimates of return periods derived from hydrologic time series has been obtained. Results for the ‘annual’ and ‘base stage’ series are compared with values given previously for a ‘complete’ series and also with empirical values used by the U. S. Weather Bureau. Effects of departures from the model assumed, caused by seasonal variation in probability of occurrence, or by correlation in magnitude, are reconciled with observed results.