Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
171
result(s) for
"Bertness, Mark D."
Sort by:
Extreme stresses, niches, and positive species interactions along stress gradients
Since proposed two decades ago, the stress-gradient hypothesis (SGH), suggesting that species interactions shift from competition to facilitation with stress, has been widely examined. Despite broad support across species and ecosystems, ecologists debate whether the SGH applies to extreme environments, arguing that species interactions switch to competition or collapse under extreme stress. We show that facilitation often expands distributions on species borders. SGH exceptions occur when weak stress gradients or stresses outside of species' niches are examined, multiple stresses co-occur canceling out their effects, temporally dependent effects are involved, or results are improperly analyzed. We suggest that ecologists resolve debates by standardizing key SGH terms, such as fundamental and realized niche, stress gradients vs. environmental gradients, by quantitatively defining extreme stress, and by critically evaluating the functionality of stress gradients. We also suggest that new research examine the breadth and relevance of the SGH. More rigor needs to be applied to SGH tests to identify actual exceptions rather than those due to failures to meet its underlying assumptions, so that the general principles of the SGH and its exceptions can be incorporated into ecological theory, conservation strategies, and environmental change predictions.
Journal Article
موجز التاريخ الطبيعي للحضارة : لماذا التوازن بين التعاون والمنافسة حتمي للبشرية /
يحدثنا الكتاب عن أن أقدم معركة على وجه الأرض دارت في الواقع بين المنافسة والتعاون، ويؤكد أن التعاون هو الحل الوحيد للأزمة البيئية الحالية في العالم ؛ كان المؤرخون وعلماء البيئة والبيولوچيا التطورية يركزون عادة على التفاعلات التنافسية السلبية والعلاقات بين الفريسة والمفترس، وفاتهم بشكل عام الدور المهم الذي لعبه التعاون في نشوء الإنسان وتطور الحضارة ؛ يتناول الكتاب أيضا التطور المشترك بين الكائنات، سباق التسلح التطوري بين الفريسة والمفترس، ويوضح الفرق بين تفاعلات التطور المشترك المباشرة وغير المباشرة، ويعطينا مثلا بالتعاملات المتبادلة المعقدة لنا مع الميكروبات، والتي تحفظ صحتنا وتحافظ على حياتنا، بينما تبادلاتنا مع النباتات والحيوانات أدت إلى استئناس الحيوانات، والثورة الزراعية ؛ كما أن تطوير النباتات لدفاعها الكيميائي في سياق سباق التسلح التطوري بينها وبين مستهلكيها أمدتنا بشكل غير مباشر بالمستحضرات الدوائية والاتجاهات الروحانية.
Book
Shorebirds-driven trophic cascade helps restore coastal wetland multifunctionality
Ecosystem restoration has traditionally focused on re-establishing vegetation and other foundation species at basal trophic levels, with mixed outcomes. Here, we show that threatened shorebirds could be important to restoring coastal wetland multifunctionality. We carried out surveys and manipulative field experiments in a region along the Yellow Sea affected by the invasive cordgrass
Spartina alterniflora
. We found that planting native plants alone failed to restore wetland multifunctionality in a field restoration experiment. Shorebird exclusion weakened wetland multifunctionality, whereas mimicking higher predation before shorebird population declines by excluding their key prey – crab grazers – enhanced wetland multifunctionality. The mechanism underlying these effects is a simple trophic cascade, whereby shorebirds control crab grazers that otherwise suppress native vegetation recovery and destabilize sediments (via bioturbation). Our findings suggest that harnessing the top-down effects of shorebirds – through habitat conservation, rewilding, or temporary simulation of consumptive or non-consumptive effects – should be explored as a nature-based solution to restoring the multifunctionality of degraded coastal wetlands.
Ecological restoration success may depend on interactions between multiple trophic levels. Here, the authors show that top-down control of crab grazers by shorebirds could help rebuild wetland multifunctionality after invasive cordgrass eradication.
Journal Article
Multiple stressors and the potential for synergistic loss of New England salt marshes
Climate change and other anthropogenic stressors are converging on coastal ecosystems worldwide. Understanding how these stressors interact to affect ecosystem structure and function has immediate implications for coastal planning, however few studies quantify stressor interactions. We examined past and potential future interactions between two leading stressors on New England salt marshes: sea-level rise and marsh crab (Sesarma reticulatum) grazing driven low marsh die-off. Geospatial analyses reveal that crab-driven die-off has led to an order of magnitude more marsh loss than sea-level rise between 2005 and 2013. However, field transplant experimental results suggest that sea-level rise will facilitate crab expansion into higher elevation marsh platforms by inundating and gradually softening now-tough high marsh peat, exposing large areas to crab-driven die-off. Taking interactive effects of marsh softening and concomitant overgrazing into account, we estimate that even modest levels of sea-level rise will lead to levels of salt marsh habitat loss that are 3x greater than the additive effects of sea-level rise and crab-driven die-off would predict. These findings highlight the importance of multiple stressor studies in enhancing mechanistic understanding of ecosystem vulnerabilities to future stress scenarios and encourage managers to focus on ameliorating local stressors to break detrimental synergisms, reduce future ecosystem loss, and enhance ecosystem resilience to global change.
Journal Article
Indirect Human Impacts Reverse Centuries of Carbon Sequestration and Salt Marsh Accretion
Direct and indirect human impacts on coastal ecosystems have increased over the last several centuries, leading to unprecedented degradation of coastal habitats and loss of ecological services. Here we document a two-century temporal disparity between salt marsh accretion and subsequent loss to indirect human impacts. Field surveys, manipulative experiments and GIS analyses reveal that crab burrowing weakens the marsh peat base and facilitates further burrowing, leading to bank calving, disruption of marsh accretion, and a loss of over two centuries of sequestered carbon from the marsh edge in only three decades. Analogous temporal disparities exist in other systems and are a largely unrecognized obstacle in attaining sustainable ecosystem services in an increasingly human impacted world. In light of the growing threat of indirect impacts worldwide and despite uncertainties in the fate of lost carbon, we suggest that estimates of carbon emissions based only on direct human impacts may significantly underestimate total anthropogenic carbon emissions.
Journal Article
Role of Crab Herbivory in Die-Off of New England Salt Marshes
Die-offs of cordgrass are pervasive throughout western Atlantic salt marshes, yet understanding of the mechanisms precipitating these events is limited. We tested whether herbivory by the native crab, Sesarma reticulatum, is generating die-offs of cordgrass that are currently occurring on Cape Cod, Massachusetts (U.S.A.), by manipulating crab access to cordgrass transplanted into die-off areas and healthy vegetation. We surveyed 12 Cape Cod marshes to investigate whether the extent of cordgrass die-off on creek banks, where die-offs are concentrated, was related to local Sesarma grazing intensity and crab density. We then used archived aerial images to examine whether creek bank die-off areas have expanded over the past 2 decades and tested the hypothesis that release from predation, leading to elevated Sesarma densities, is triggering cordgrass die-offs by tethering crabs where die-offs are pervasive and where die-offs have not yet been reported. Intensity of crab grazing on transplanted cordgrass was an order of magnitude higher in die-off areas than in adjacent vegetation. Surveys revealed that Sesarma herbivory has denuded nearly half the creek banks in Cape Cod marshes, and differences in crab-grazing intensity among marshes explained >80% of variation in the extent of the die-offs. Moreover, the rate of die-off expansion and area of marsh affected have more than doubled since 2000. Crab-tethering experiments suggest that release from predation has triggered elevated crab densities that are driving these die-offs, indicating that disruption of predator-prey interactions may be generating the collapse of marsh ecosystems previously thought to be exclusively under bottom-up control.
Journal Article
A Trophic Cascade Regulates Salt Marsh Primary Production
Nutrient supply is widely thought to regulate primary production of many ecosystems including salt marshes. However, experimental manipulation of the dominant marsh grazer (the periwinkle, Littoraria irrorata) and its consumers (e.g., blue crabs, Callinectes sapidus, terrapins, Malaclemys terrapin) demonstrates plant biomass and production are largely controlled by grazers and their predators. Periwinkle grazing can convert one of the most productive grasslands in the world into a barren mudflat within 8 months. Marine predators regulate the abundance of this plant-grazing snail. Thus, top-down control of grazer density is a key regulatory determinant of marsh grass growth. The discovery of this simple trophic cascade implies that over-harvesting of snail predators (e.g., blue crabs) may be an important factor contributing to the massive die-off (tens of km2) of salt marshes across the southeastern United States. In addition, our results contribute to a growing body of evidence indicating widespread, predator regulation of marine macrophyte production via trophic cascades (kelps, seagrasses, intertidal algae).
Journal Article
Plant zonation in low-latitude salt marshes: disentangling the roles of flooding, salinity and competition
1 We investigated the factors producing zonation patterns of the dominant plants in south-eastern USA salt marshes where Juncus roemerianus dominates the high marsh, and Spartina alterniflora the middle and low marsh. 2 Juncus did not occur naturally in the Spartina zone and performed poorly when transplanted there, irrespective of whether neighbours were present or removed, indicating that its lower limit was set by physical stress. 3 In contrast, although Spartina occurred naturally at low densities in the Juncus zone, it performed well if transplanted there only if neighbours were removed, indicating that its upper limit was set by competition. 4 Parallel laboratory and field manipulations of flooding, salinity and competition indicated that the lower limit of Juncus was mediated by both flooding and salinity, but not by competition. 5 The general mechanisms producing zonation patterns of vegetation in coastal salt marshes may be universal, as suggested by previous studies, but the importance of particular factors is likely to vary geographically. In particular, salinity stress probably plays a much more important role in mediating plant zonation patterns at lower latitudes. 6 Our results suggest that the nature of ecological interactions is likely to vary geographically because of variation in the physical environment, and this variation must be taken into account in order to successfully generalize the results of field studies across geographical scales.
Journal Article
Shoreline Development Drives Invasion of Phragmites australis and the Loss of Plant Diversity on New England Salt Marshes
The reed Phragmites australis Cav. is aggressively invading salt marshes along the Atlantic Coast of North America. We examined the interactive role of habitat alteration (i.e., shoreline development) in driving this invasion and its consequences for plant richness in New England salt marshes. We surveyed 22 salt marshes in Narragansett Bay Rhode Island, and quantified shoreline development, Phragmites cover, soil salinity, and nitrogen availability. Shoreline development, operationally defined as removal of the woody vegetation bordering marshes, explained >90% of intermarsh variation in Phragmites cover. Shoreline development was also significantly correlated with reduced soil salinities and increased nitrogen availability, suggesting that removing woody vegetation bordering marshes increases nitrogen availability and decreases soil salinities, thus facilitating Phragmites invasion. Soil salinity (64%) and nitrogen availability (56%) alone explained a large proportion of variation in Phragmites cover, but together they explained 80% of the variation in Phragmites invasion success. Both univariate and aggregate (multidimensional scaling) analyses of plant community composition revealed that Phragmites dominance in developed salt marshes resulted in an almost three-fold decrease in plant species richness. Our findings illustrate the importance of maintaining integrity of habitat borders in conserving natural communities and provide an example of the critical role that local conservation can play in preserving these systems. In addition, our findings provide ecologists and natural resource managers with a mechanistic understanding of how human habitat alteration in one vegetation community can interact with species introductions in adjacent communities (i.e., flow-on or adjacency effects) to hasten ecosystem degradation.
Journal Article