135 research outputs found
Modelling the impact of climate change on woody plant population dynamics in South African savanna
BACKGROUND: In Southern Africa savannas climate change has been proposed to alter rainfall, the most important environmental driver for woody plants. Woody plants are a major component of savanna vegetation determining rangeland condition and biodiversity. In this study we use a spatially explicit, stochastic computer model to assess the impact of climate change on the population dynamics of Grewia flava, a common, fleshy-fruited shrub species in the southern Kalahari. Understanding the population dynamics of Grewia flava is a crucial task, because it is widely involved in the shrub/bush encroachment process, a major concern for rangeland management due to its adverse effect on livestock carrying capacity and biodiversity. RESULTS: For our study we consider four climate change scenarios that have been proposed for the southern Kalahari for the coming decades: (1) an increase in annual precipitation by 30â40%, (2) a decrease by 5â15%, (3) an increase in variation of extreme rainfall years by 10â20%, (4) and increase in temporal auto-correlation, i.e. increasing length and variation of periodic rainfall oscillations related to El Niño/La Niña phenomena. We evaluate the slope z of the time-shrub density relationship to quantify the population trend. For each climate change scenario we then compared the departure of z from typical stable population dynamics under current climatic conditions. Based on the simulation experiments we observed a positive population trend for scenario (1) and a negative trend for scenario (2). In terms of the projected rates of precipitation change for scenario (3) and (4) population dynamics were found to be relatively stable. However, for a larger increase in inter-annual variation or in temporal auto-correlation of rainfall population trends were negative, because favorable rainfall years had a limited positive impact due to the limited shrub carrying capacity. CONCLUSIONS: We conclude that a possible increase in precipitation will strongly facilitate shrub encroachment threatening savanna rangeland conditions and regional biodiversity. Furthermore, the negative effects found for positive auto-correlated rainfall support current ecological theory stating that periodically fluctuating environments can reduce population viability because species suffer disproportionately from poor environmental conditions
The role of active movement in fungal ecology and community assembly
Movement ecology aims to provide common terminology and an integrative framework of movement research across all groups of organisms. Yet such work has focused on unitary organisms so far, and thus the important group of filamentous fungi has not been considered in this context. With the exception of spore dispersal, movement in filamentous fungi has not been integrated into the movement ecology field. At the same time, the field of fungal ecology has been advancing research on topics like informed growth, mycelial translocations, or fungal highways using its own terminology and frameworks, overlooking the theoretical developments within movement ecology. We provide a conceptual and terminological framework for interdisciplinary collaboration between these two disciplines, and show how both can benefit from closer links: We show how placing the knowledge from fungal biology and ecology into the framework of movement ecology can inspire both theoretical and empirical developments, eventually leading towards a better understanding of fungal ecology and community assembly. Conversely, by a greater focus on movement specificities of filamentous fungi, movement ecology stands to benefit from the challenge to evolve its concepts and terminology towards even greater universality. We show how our concept can be applied for other modular organisms (such as clonal plants and slime molds), and how this can lead towards comparative studies with the relationship between organismal movement and ecosystems in the focus
The influence of El NiñoâSouthern Oscillation regimes on eastern African vegetation and its future implications under the RCP8.5 warming scenario
Abstract. The El NiñoâSouthern Oscillation (ENSO) is the main driver of the
interannual variability in eastern African rainfall, with a significant impact
on vegetation and agriculture and dire consequences for food and social
security. In this study, we identify and quantify the ENSO contribution to the
eastern African rainfall variability to forecast future eastern African
vegetation response to rainfall variability related to a predicted intensified
ENSO. To differentiate the vegetation variability due to ENSO, we removed the
ENSO signal from the climate data using empirical orthogonal teleconnection
(EOT) analysis. Then, we simulated the ecosystem carbon and water fluxes under
the historical climate without components related to ENSO teleconnections. We
found ENSO-driven patterns in vegetation response and confirmed that EOT
analysis can successfully produce coupled tropical Pacific sea surface
temperatureâeastern African rainfall teleconnection from observed datasets. We
further simulated eastern African vegetation response under future climate
change as it is projected by climate models and under future climate change
combined with a predicted increased ENSO intensity. Our EOT analysis
highlights that climate simulations are still not good at capturing rainfall
variability due to ENSO, and as we show here the future vegetation would be
different from what is simulated under these climate model outputs lacking
accurate ENSO contribution. We simulated considerable differences in eastern
African vegetation growth under the influence of an intensified ENSO regime
which will bring further environmental stress to a region with a reduced
capacity to adapt effects of global climate change and food security
Current models broadly neglect specific needs of biodiversity conservation in protected areas under climate change
<p>Abstract</p> <p>Background</p> <p>Protected areas are the most common and important instrument for the conservation of biological diversity and are called for under the United Nations' <it>Convention on Biological Diversity</it>. Growing human population densities, intensified land-use, invasive species and increasing habitat fragmentation threaten ecosystems worldwide and protected areas are often the only refuge for endangered species. Climate change is posing an additional threat that may also impact ecosystems currently under protection. Therefore, it is of crucial importance to include the potential impact of climate change when designing future nature conservation strategies and implementing protected area management. This approach would go beyond reactive crisis management and, by necessity, would include anticipatory risk assessments. One avenue for doing so is being provided by simulation models that take advantage of the increase in computing capacity and performance that has occurred over the last two decades.</p> <p>Here we review the literature to determine the state-of-the-art in modeling terrestrial protected areas under climate change, with the aim of evaluating and detecting trends and gaps in the current approaches being employed, as well as to provide a useful overview and guidelines for future research.</p> <p>Results</p> <p>Most studies apply statistical, bioclimatic envelope models and focus primarily on plant species as compared to other taxa. Very few studies utilize a mechanistic, process-based approach and none examine biotic interactions like predation and competition. Important factors like land-use, habitat fragmentation, invasion and dispersal are rarely incorporated, restricting the informative value of the resulting predictions considerably.</p> <p>Conclusion</p> <p>The general impression that emerges is that biodiversity conservation in protected areas could benefit from the application of modern modeling approaches to a greater extent than is currently reflected in the scientific literature. It is particularly true that existing models have been underutilized in testing different management options under climate change. Based on these findings we suggest a strategic framework for more effectively incorporating the impact of climate change in models exploring the effectiveness of protected areas.</p
Smallâscale heterogeneity shapes grassland diversity in lowâtoâintermediate resource environments
Questions
Soil resource heterogeneity influences the outcome of plantâplant interactions and, consequently, species co-existence and diversity patterns. The magnitude and direction of heterogeneity effects vary widely, and the processes underlying such variations are not fully understood. In this study, we explored how and under what resource conditions small-scale heterogeneity modulates grassland plant diversity.
Location
OderhÀnge Mallnow, Potsdam, Brandenburg, Germany.
Methods
We expanded the individual-based plant community model (IBC-grass) to incorporate dynamic below-ground resource maps, simulating spatial heterogeneity of resource availability. Empirical centimeter-scale data of soil C/N ratio were integrated into the model, accounting for both configurational and compositional heterogeneity. We then analyzed the interplay between small-scale heterogeneity and resource availability on the interaction and co-existence of plant species and overall diversity.
Results
Our results showed significant differences between the low- and high-resource scenarios, with both configurational and compositional heterogeneity having a positive effect on species richness and Simpson's diversity, but only under low-resource conditions. As compositional heterogeneity in the fine-scale C/N ratio increased, we observed a positive shift in Simpson's diversity and species richness, with the highest effects at the highest level of variability tested. We observed little to no effect in nutrient-rich scenarios, and a shift to negative effects at the intermediate resource level. The study demonstrates that site-specific resource levels underpin how fine-scale heterogeneity influences plant diversity and species co-existence, and partly explains the divergent effects recorded in different empirical studies.
Conclusions
This study provides mechanistic insights into the complex relationship between resource heterogeneity and diversity patterns. It highlights the context-dependent effects of small-scale heterogeneity, which can be positive under low-resource, neutral under high-resource, and negative under intermediate-resource conditions. These findings provide a foundation for future investigations into small-scale heterogeneityâdiversity relationships, contributing to a deeper understanding of the processes that promote species co-existence in plant communities
While shoot herbivores reduce, root herbivores increase nutrient enrichmentâs impact on diversity in a grassland model
Nutrient enrichment is widespread throughout grassland systems and expected to increase during the Anthropocene. Trophic interactions, like aboveground herbivory, have been shown to mitigate its effect on plant diversity. Belowground herbivory may also impact these habitatsâ response to nutrient enrichment, but its influence is much less understood, and likely to depend on factors such as the herbivoresâ preference for dominant species and the symmetry of belowground competition. If preferential toward the dominant, fastest growing species, root herbivores may reduce these speciesâ relative fitness and support diversity during nutrient enrichment. However, as plant competition belowground is commonly considered to be symmetric, root herbivores may be less impactful than shoot herbivores because they do not reduce any competitive asymmetry between the dominant and subordinate plants. To better understand this system, we used an established, two-layer, grassland community model to run a full-factorially designed simulation experiment, crossing the complete removal of aboveground herbivores and belowground herbivores with nutrient enrichment. After 100 yr of simulation, we analyzed communities' diversity, competition on the individual level, as well as their resistance and recovery. The model reproduced both observed general effects of nutrient enrichment in grasslands and the short-term trends of specific experiments. We found that belowground herbivores exacerbate the negative influence of nutrient enrichment on Shannon diversity within our model grasslands, while aboveground herbivores mitigate its effect. Indeed, data on individualsâ above- and belowground resource uptake reveals that root herbivory reduces resource limitation belowground. As with nutrient enrichment, this shifts competition aboveground. Since shoot competition is asymmetric, with larger, taller individuals gathering disproportionate resources compared to their smaller, shorter counterparts, this shift promotes the exclusion of the smallest species. While increasing the root herbivoresâ preferences toward dominant species lessens their negative impact, at best they are only mildly advantageous, and they do very little reduce the negative consequences of nutrient enrichment. Because our modelâs belowground competition is symmetric, we hypothesize that root herbivores may be beneficial when root competition is asymmetric. Future research into belowground herbivory should account for the nature of competition belowground to better understand the herbivoresâ true influence
Time-lagged response of siberian treeline forests revealed by individual-based modelling
Global warming allows arctic vegetation, which is mainly limited by temperatures, to move north. A change from tundra to taiga will cause a decrease of albedo which further fuels the warming through positive feedback mechanisms. This raises several questions of which we want to address here: (1) Will trees move northwards and thereby change vast treeless tundra areas to taiga? (2) And if so, how long does this response lags behind the temperature changes? To answer these questions we built an individual-based and spatially-explicit vegetation simulator model for larches in Siberia (LAVESI). We present the parameterization and validation of the model's incorporated processes which describe the full life-cycle of the simulated larch species Larix gmelinii. Furthermore, we share results of the first regional-scale simulations testing the model's performance at the Taymyr Peninsula, Russia, ranging from 64-80° N and 92-120° E. In a second experiment, we tested the influence of up to 6 °C warmer and cooler climates on simulated populations. Our results show that already the recent temperature rise will allow forests to expand farther north by roughly one degree, when no seed limitation hinders populations to migrate. Furthermore, climate warming caused populations to densify but with a time-lag of decades. We conclude that in the near future expanding taiga after its first establishment in the former tundra will rapidly form dense tree stands, thus ultimatively fueling the feedback loop of global warming. We show that simulation results of the newly-build vegetation model were reliable, and hence the model can be used as a tool to improve our knowledge about individual-based processes that are important to understand past and future treeline migration
Integrating movement ecology with biodiversity research - exploring new avenues to address spatiotemporal biodiversity dynamics
Movement of organisms is one of the key mechanisms shaping biodiversity, e.g. the distribution of genes, individuals and species in space and time. Recent technological and conceptual advances have improved our ability to assess the causes and consequences of individual movement, and led to the emergence of the new field of âmovement ecologyâ. Here, we outline how movement ecology can contribute to the broad field of biodiversity research, i.e. the study of processes and patterns of life among and across different scales, from genes to ecosystems, and we propose a conceptual framework linking these hitherto largely separated fields of research. Our framework builds on the concept of movement ecology for individuals, and demonstrates its importance for linking individual organismal movement with biodiversity. First, organismal movements can provide âmobile linksâ between habitats or ecosystems, thereby connecting resources, genes, and processes among otherwise separate locations. Understanding these mobile links and their impact on biodiversity will be facilitated by movement ecology, because mobile links can be created by different modes of movement (i.e., foraging, dispersal, migration) that relate to different spatiotemporal scales and have differential effects on biodiversity. Second, organismal movements can also mediate coexistence in communities, through âequalizingâ and âstabilizingâ mechanisms. This novel integrated framework provides a conceptual starting point for a better understanding of biodiversity dynamics in light of individual movement and space-use behavior across spatiotemporal scales. By illustrating this framework with examples, we argue that the integration of movement ecology and biodiversity research will also enhance our ability to conserve diversity at the genetic, species, and ecosystem levels
Defining ecological buffer mechanisms should consider diverse approaches
In their response letter, Gascoigne et al. propose a relevant approach to characterizing ecological buffer mechanisms, akin to the study of buffer mechanisms in chemistry [1]. Their chemistry-inspired viewpoint enables them to pinpoint opportunities for further advances in the population buffering framework. We welcome the authors' response and concur with their belief that ecology stands to gain significantly from increased crosstalk with chemistry and other more mechanistic, first-principles-driven fields of natural sciences.acceptedVersio
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