Observations and projections for mountain regions show a strong tendency towards upslope displacement of their biomes under future climate conditions. Because of their climatic and topographic ...heterogeneity, a more complex response is expected for biodiversity hotspots such as tropical mountain regions. This study analyzes potential changes in the distribution of biomes in the Tropical Andes and identifies target areas for conservation. Biome distribution models were developed using logistic regressions. These models were then coupled to an ensemble of 8 global climate models to project future distribution of the Andean biomes and their uncertainties. We analysed projected changes in extent and elevational range and identified regions most prone to change. Our results show a heterogeneous response to climate change. Although the wetter biomes exhibit an upslope displacement of both the upper and the lower boundaries as expected, most dry biomes tend to show downslope expansion. Despite important losses being projected for several biomes, projections suggest that between 74.8% and 83.1% of the current total Tropical Andes will remain stable, depending on the emission scenario and time horizon. Between 3.3% and 7.6% of the study area is projected to change, mostly towards an increase in vertical structure. For the remaining area (13.1%-17.4%), there is no agreement between model projections. These results challenge the common believe that climate change will lead to an upslope displacement of biome boundaries in mountain regions. Instead, our models project diverging responses, including downslope expansion and large areas projected to remain stable. Lastly, a significant part of the area expected to change is already affected by land use changes, which has important implications for management. This, and the inclusion of a comprehensive uncertainty analysis, will help to inform conservation strategies in the Tropical Andes, and to guide similar assessments for other tropical mountains.
•Flow-based weights are developed to formulate a climate ensemble strategy.•Our case study is the Hamilton Harbour watershed in Southern Ontario, Canada.•Climate change is projected to change the ...magnitude and timing of peak flow events.•Water cycle alterations are predicted along the urban-to-agriculture gradient.•Evapotranspiration rates will likely increase across the entire watershed.
Evaluation of hydrological response to future climate change is essential for water quality risk assessment and adaptive management implementation within a watershed context. In this study, we present a modeling framework that integrates a hydrological model with projections of General Circulation Models (GCMs). Temperature and precipitation projections of six GCMs with two downscaling methods are used to force the Soil and Water Assessment Tool (SWAT) model in the Hamilton Harbour watershed in Ontario, Canada. A flow-based weighting strategy was developed to integrate the projections of multiple GCMs based on their ability to recreate empirical flow frequency distributions in multiple monitoring sites. Our study renders support to the ability of the weighted model ensemble to draw meaningful hydrological forecasts. Nonetheless, we also note that the ensemble strategy understates the frequency and magnitude of flow extremes, and therefore the domain that is collectively delineated by individual GCMs can still provide complementary planning information. Climate change is projected to trigger a distinct increase in air temperature and precipitation during the late winter-early spring period, which in turn will likely result in an earlier snowmelt and changes in the magnitude and timing of peak flow events. Analysis of the water cycle shows that the sensitivity of the individual hydrological components to climate change may vary along the urban-to-agriculture gradient. The projected declining soil–water content in agricultural catchments highlights the likelihood of more intensified drought conditions in the croplands. Evapotranspiration rates will likely increase across the entire watershed, whereas surface runoff could be reduced but less so in urbanized locations. Overall, our findings suggest that any future planning exercise to ameliorate the prevailing water quality conditions will only be insightful if we consider the interplay between climate change and urbanization processes in the area.
Many hypotheses in ecology and evolution rely on indices measuring abstract phenomena, usually multifaceted or noisy (e.g., diversity indices may capture richness or evenness, and the data used can ...have large sampling error). Hence, different indices often provide uncorrelated values.Indices, experiments, and statistical methods all help to control for confounding factors, such as missing variables; still, this variety of approaches limits cross-study comparisons and may increase the odds of a researcher accepting hypotheses that fit their intuition.We propose guidelines to link hypotheses, study design, and index selection to help mitigate these challenges. Repositories of hypotheses and indices, building on existing collaborative tools and databases, could help researchers navigate and clarify complex and often obscure methodological decisions in hypothesis testing.
Hypothesis testing requires meaningful ways to quantify biological phenomena and account for alternative mechanisms that could explain the same pattern. Researchers combine experiments, statistics, and indices to account for these confounding mechanisms. Key concepts in ecology and evolution, such as niche breadth (NB) or fitness, can be represented by several indices, which often provide uncorrelated estimates. Is this because the indices use different types of noisy data or because the targeted phenomenon is complex and multidimensional? We discuss implications of these scenarios and propose five steps to aid researchers in identifying and combining indices, experiments, and statistics. Building on prior efforts to construct databases of hypotheses and indices and document assumptions, these steps help provide a formal strategy to reduce self-confirmatory bias.
Hypothesis testing requires meaningful ways to quantify biological phenomena and account for alternative mechanisms that could explain the same pattern. Researchers combine experiments, statistics, and indices to account for these confounding mechanisms. Key concepts in ecology and evolution, such as niche breadth (NB) or fitness, can be represented by several indices, which often provide uncorrelated estimates. Is this because the indices use different types of noisy data or because the targeted phenomenon is complex and multidimensional? We discuss implications of these scenarios and propose five steps to aid researchers in identifying and combining indices, experiments, and statistics. Building on prior efforts to construct databases of hypotheses and indices and document assumptions, these steps help provide a formal strategy to reduce self-confirmatory bias.
•Spectral analysis is used to analyze water-level records in Lake Huron-Michigan.•Wavelet ridges elucidate the water-level evolution in the time–frequency domain.•1-, 8-, 12-, 36-year quasi-state ...periodicities were detected between 1860 and 2015.•Runoff and evaporation greatly affect the short-term water level fluctuations.
Understanding water level fluctuation patterns in the Great Lakes is one of the pillars for designing adaptive management practices that can mitigate the impacts of extreme water levels on shoreline infrastructure and associated economic activities. The present study uses continuous wavelet transformation to conduct a two-dimensional frequency-scale spectral analysis on monthly water levels in Lake Huron-Michigan. Consistent with past work, we detected 1-, 8-, 12-, and 36-year quasi-state periodicities in water level records during the 1860–2015 period. The wavelet analysis revealed diminishing, re-emergent, and/or intermodulation patterns in the long-term periodicities, but the 1-year cycle has persisted throughout the temporal domain studied. While the features of the dominant frequencies are consistent with previous findings, the consideration of wavelet ridges with the continuous wavelet transformation yielded a complete picture of evolution in time–frequency domain that is impossible to achieve with the same accuracy using conventional signal processing methods. Continuous wavelet transformation and analysis of wavelet coherence between hydrological and water level changes signified the role of runoff and evaporation as the primary drivers of water level fluctuations in Lake Huron-Michigan. Evaporation strongly influences the annual water level fluctuations, whereas runoff and precipitation covary with the water levels in both intraannual and interannual cycles. Specifically, analysis of phase differences indicated that runoff leads water level change by π/4 rad from 2-month up to 1.5-year cycles, then runoff starts to become nearly in-phase (with small intermittent lags) up to the 12-year cycle, two main recurring cycles of 0.5- and 1-year. Finally, we conducted a comprehensive assessment of 16,809 regression models, which highlighted the effects of runoff-minus-evaporation in modulating the extreme high or low water levels, which in turn could inundate the areas close to the shoreline or reduce the navigability in shallow parts of Lake Huron-Michigan.
Forecasts of increased frequency of meteorological extremes have received considerable attention due to their potential impact on the integrity of biotic communities, stability of terrestrial and ...aquatic environments, availability of ecosystem services, and broader societal prosperity. Canada is projected to experience greater warming rates than many other regions of the world and changes in meteorological extremes are predicted to be variable across the country. In this context, our goal is to evaluate the long-term trends of extreme meteorological variables (air and dew point temperature, relative humidity, wind speed, and precipitation) in southern and central Ontario (from 42°N to 50°N), while considering the role dynamics of large-scale atmospheric oscillations (El Niño–Southern Oscillation, North Atlantic Oscillation, Arctic Oscillation, and Pacific Decadal Oscillation). Air temperature minima increased year-round, while temperature maxima mainly increased during the cooler months of the year. Consistent with recent evidence from the literature, our study identified an increase in the amount of atmospheric water since the 1950s, as shown by the rising trends in dew point temperature maxima and minima during winter and mid-summer/early-autumn, respectively. Likewise, we found a weak decline in the relative humidity during the warm season, and a more discernible declining trend during the cooler part of the year, which could be in turn reflective of the moderate change of temperature maxima and rising minima, respectively. Consistent with the broader evidence of a global terrestrial stilling, our analysis showed a declining occurrence of high wind-speed events across the entire study domain, and more frequent slow-wind speeds during both warm and cold periods of the year. Interestingly, a closer examination of temporal trends in calm wind frequency provides evidence of a recent reversal in the latter trend with diminishing prevalence of very calm wind conditions. We generally found a weakly increasing temporal trend with maximum total daily precipitation, but without a coherent spatial pattern within the broader study area. Our analysis showed that large-scale phenomena have a discernible signature mostly on air temperature and humidity variables, but had little impact on low relative humidity, high and low wind-speed, and precipitation variability. Given the modest impact of teleconnections on long-term temporal trends, our study concludes that the meteorological extremes are more directly influenced by regional and local heat and humidity balance processes rather than global-scale atmospheric circulation. The observed trends of air temperature, humidity, and wind speed extremes suggest a profound impact on the phenology of aquatic and terrestrial ecosystems and human experience of weather.
•Meteorological extremes cause extensive infrastructural damages in Canada.•Air temperature minima display an increase year-round.•Rising trends in dew point temperature suggest an increase in atmospheric water.•Declining occurrence of high wind speeds suggests a global terrestrial stilling.•Teleconnections have a discernible signature on air temperature/humidity variables.
We examine the ability of a SPARROW-based model (SPAtially Referenced Regression On Watershed attributes) to assess regional P export coefficients that can assist with evaluation of nutrient ...mitigation projects and support adaptive watershed management. Limitations in number of tributary monitoring stations were overcome by assembling multi-agency water quality data from provincial, municipal, citizen science, and academic programs. We introduced a Bayesian hierarchical framework designed to guide parameter estimation from tributary nutrient loading in southern Georgian Bay drainage basin during contrasting flow regimes, such as dry and wet years. Agriculture was identified as a major non-point P source representing between 30 and 48% of delivered P loading. Our source apportionment predicted TP loss rates from croplands that exceeded those from forested areas by 320% during dry years and by 360% during wet years, while low intensity agricultural areas (hay and pasture) exceeded P export from forests by a mere 20% and 30%, respectively. Our study identified urban runoff as another significant non-point nutrient source displaying the highest variability between dry and wet years. In particular, owing to the extensive urbanization in the Lake Simcoe watershed, urban runoff contributed nearly half of delivered P loading from tributaries into the lake. The nutrient loading management plan for Lake Simcoe calls for a reduction in P loading by ∼40% from a long-term average of 72 t P y−1 in 2002–2007 to 44 t P y−1 by 2045. Our analysis emphasizes the importance of mitigating urban non-point sources together with efforts to control agricultural runoff.
The Bay of Quinte watershed, located on the northeastern shore of Lake Ontario, Canada. Special focus is placed on the Napanee River and Wilton Creek catchments, where the presence of a subterranean ...network of conduits that facilitate groundwater-surface water interactions is conducive to an increase in the delivery of nutrients during storm events and can exacerbate the risk of eutrophication.
Development of a rigorous modelling framework that can advance our understanding of past and present trends of streamflow and tributary phosphorus (P) concentration and loads. We also analyze future streamflow rates and P export trends in order to guide the long-term watershed management in the area. Our analysis is carried out through a comprehensive combination of data-driven and process-based models.
Retrospective analysis provides evidence of a recent increase in the impact of nonpoint-source P pollution. General Circulation Models suggest a future increase in both temperature minima and maxima relative to present conditions (2002–2018). Precipitation projections are indicative of increased frequency of occurrence of high extreme precipitation events during the summer and mid-fall, when the Bay of Quinte is more susceptible to undesirable ecological shifts. Our study predicts a seasonality shift in the streamflow, with the spring freshet occurring earlier in the year accompanied by higher flow rates in the local creeks for the winter and early spring. We also examined the relationship between precipitation and streamflow across varying levels of flow regulation. Our analysis indicates that our predictive capacity declines with increased flow regulation as well as when streamflow rates are predicted by contemporaneous precipitation values.
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•A unique ensemble of models is employed in the eutrophic Bay of Quinte.•Retrospective analysis of riverine P signifies the success in mitigating point-source loading.•GCMs predict that the area will experience an increase in both temperature minima and maxima.•Frequency of summer and mid-fall extreme precipitation events is projected to increase.•Spring freshet will occur earlier, but may not be conducive to stimulating the primary productivity.
Declines in grassland diversity in response to nutrient addition are a general consequence of global change. This decline in species richness may be driven by multiple underlying processes operating ...at different time‐scales. Nutrient addition can reduce diversity by enhancing the rate of local extinction via competitive exclusion, or by reducing the rate of colonization by constraining the pool of species able to colonize under new conditions. Partitioning net change into extinction and colonization rates will better delineate the long‐term effect of global change in grasslands.
We synthesized changes in richness in response to experimental fertilization with nitrogen, phosphorus and potassium with micronutrients across 30 grasslands. We quantified changes in local richness, colonization, and extinction over 8–10 years of nutrient addition, and compared these rates against control conditions to isolate the effect of nutrient addition from background dynamics.
Total richness at steady state in the control plots was the sum of equal, relatively high rates of local colonization and extinction. On aggregate, 30%–35% of initial species were lost and the same proportion of new species were gained at least once over a decade. Absolute turnover increased with site‐level richness but was proportionately greater at lower‐richness sites relative to starting richness. Loss of total richness with nutrient addition, especially N in combination with P or K, was driven by enhanced rates of extinction with a smaller contribution from reduced colonization. Enhanced extinction and reduced colonization were disproportionately among native species, perennials, and forbs. Reduced colonization plateaued after the first few (<5) years after nutrient addition, while enhanced extinction continued throughout the first decade.
Synthesis. Our results indicate a high rate of colonizations and extinctions underlying the richness of ambient communities and that nutrient enhancement drives overall declines in diversity primarily by exclusion of previously established species. Moreover, enhanced extinction continues over long time‐scales, suggesting continuous, long‐term community responses and a need for long‐term study to fully realize the extinction impact of increased nutrients on grassland composition.
High rates of colonizations and extinctions underly the richness of grassland communities. Nutrient enhancement drives declines in richness by disrupting this approximate equilibrium primarily by continuous, long‐term exclusion of previously established, more resource‐conservative and native species. Fewer new colonizations also contribute to declines in richness with nutrient addition, but to a much smaller degree and at shorter time‐scales.
Biotic and abiotic factors interact with dominant plants—the locally most frequent or with the largest coverage—and nondominant plants differently, partially because dominant plants modify the ...environment where nondominant plants grow. For instance, if dominant plants compete strongly, they will deplete most resources, forcing nondominant plants into a narrower niche space. Conversely, if dominant plants are constrained by the environment, they might not exhaust available resources but instead may ameliorate environmental stressors that usually limit nondominants. Hence, the nature of interactions among nondominant species could be modified by dominant species. Furthermore, these differences could translate into a disparity in the phylogenetic relatedness among dominants compared to the relatedness among nondominants. By estimating phylogenetic dispersion in 78 grasslands across five continents, we found that dominant species were clustered (e.g., co‐dominant grasses), suggesting dominant species are likely organized by environmental filtering, and that nondominant species were either randomly assembled or overdispersed. Traits showed similar trends for those sites (<50%) with sufficient trait data. Furthermore, several lineages scattered in the phylogeny had more nondominant species than expected at random, suggesting that traits common in nondominants are phylogenetically conserved and have evolved multiple times. We also explored environmental drivers of the dominant/nondominant disparity. We found different assembly patterns for dominants and nondominants, consistent with asymmetries in assembly mechanisms. Among the different postulated mechanisms, our results suggest two complementary hypotheses seldom explored: (1) Nondominant species include lineages adapted to thrive in the environment generated by dominant species. (2) Even when dominant species reduce resources to nondominant ones, dominant species could have a stronger positive effect on some nondominants by ameliorating environmental stressors affecting them, than by depleting resources and increasing the environmental stress to those nondominants. These results show that the dominant/nondominant asymmetry has ecological and evolutionary consequences fundamental to understand plant communities.
We found a prevalent disparity between the dominant and nondominant species (measured as the standardized effect size of the mean nearest taxonomic distance), with the former more clustered than the latter, suggesting a disparity in the mechanisms organizing both groups. We also found several clades more likely to have nondominant species than dominant species, measured as the probability of finding a species of a given clade among the third less abundant species in the sites where that clade occurred. Unexpectedly, many nondominant clades have a large number of species, mainly were comprised of nonwoody species, and often appeared in the phylogeny. Together, these findings suggest dominance and nondominance are conserved and that their differences have ecological consequences.
Understanding why communities appear deterministically dominated by relatively few species is an age‐old debate in ecology. We hypothesised that the dominant and non‐dominant species in a community ...are governed by different assembly mechanisms where environmental conditions influence dominant species more than non‐dominant species. Further, dominant plants moderate the environment where non‐dominant species thrive, diminishing the influence of environmental filtering and increasing the influence of limiting similarity for non‐dominant species. We tested these hypotheses by removing two dominant species in five temperate meadows. We found that the composition of the non‐dominants diverged while the new dominants converged over time. Phylogenetic analyses suggested that habitat filtering and limiting similarity drove the new dominant species simultaneously. Conversely, non‐dominant community assembly appeared more unpredictable. These suggest that dominant species converged towards a predictable environmentally driven optimum, while non‐dominant species thrive in a moderated habitat, which probably reduced non‐dominant species predictability.
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