scholarly journals Persistent Clones and Local Seed Recruitment Contribute to the Resilience of Enhalus acoroides Populations Under Disturbance

2021 ◽  
Vol 12 ◽  
Author(s):  
Jasper Dierick ◽  
Thi Thuy Hang Phan ◽  
Quang Doc Luong ◽  
Ludwig Triest
Keyword(s):  
Land Use ◽  
Environmental Change ◽  
Seedling Recruitment ◽  
Spatial Scales ◽  
Alternative Stable States ◽  
Seagrass Species ◽  
Stable States ◽  
Seagrass Meadows ◽  
Enhalus Acoroides ◽  
South Central

Human-induced land use in coastal areas is one of the main threats for seagrass meadows globally causing eutrophication and sedimentation. These environmental stressors induce sudden ecosystem shifts toward new alternative stable states defined by lower seagrass richness and abundance. Enhalus acoroides, a large-sized tropical seagrass species, appears to be more resistant toward environmental change compared to coexisting seagrass species. We hypothesize that reproductive strategy and the extent of seedling recruitment of E. acoroides are altered under disturbance and contribute to the persistence and resilience of E. acoroides meadows. In this research, we studied eight populations of E. acoroides in four lagoons along the South Central Coast of Vietnam using 11 polymorphic microsatellite loci. We classified land use in 6 classes based on Sentinel-2 L2A images and determined the effect of human-induced land use at different spatial scales on clonal richness and structure, fine-scale genetic structure and genetic diversity. No evidence of population size reductions due to disturbance was found, however, lagoons were strongly differentiated and may act as barriers to gene flow. The proportion and size of clones were significantly higher in populations of surrounding catchments with larger areas of agriculture, urbanization and aquaculture. We postulate that large resistant genets contribute to the resilience of E. acoroides meadows under high levels of disturbance. Although the importance of clonal growth increases with disturbance, sexual reproduction and the subsequent recruitment of seedlings remains an essential strategy for the persistence of populations of E. acoroides and should be prioritized in conservation measures to ensure broad-scale and long-term resilience toward future environmental change.

scholarly journals Catastrophic Hydraulic Failure and Tipping Points in Plants

2021 ◽  
Author(s):  
Daniel Johnson ◽  
Gabriel G Katul ◽  
Jean-Christophe Domec
Keyword(s):  
Water Potential ◽  
Plant Biomass ◽  
Spatial Scales ◽  
Alternative Stable States ◽  
Soil Water Potential ◽  
Tipping Points ◽  
Stable States ◽  
Xylem Embolism ◽  
Plant Hydraulics ◽  
Hydraulic Failure

Water inside plants forms a continuous chain from water in soils to the water evaporating from leaf surfaces. Failures in this chain result in reduced transpiration and photosynthesis and these failures are caused by soil drying and/or cavitation-induced xylem embolism. Xylem embolism and plant hydraulic failure share a number of analogies to “catastrophe theory” in dynamical systems. These catastrophes are often represented in the physiological and ecological literature as tipping points or alternative stable states when control variables exogenous (e.g. soil water potential) or endogenous (e.g. leaf water potential) to the plant are allowed to slowly vary. Here, plant hydraulics viewed from the perspective of catastrophes at multiple spatial scales is considered with attention to bubble expansion (i.e. cavitation), organ-scale vulnerability to embolism, and whole-plant biomass as a proxy for transpiration and hydraulic function. The hydraulic safety-efficiency tradeoff, hydraulic segmentation and maximum plant transpiration are examined using this framework. Underlying mechanisms for hydraulic failure at very fine scales such as pit membranes, intermediate scales such as xylem network properties and at larger scales such as soil-tree hydraulic pathways are discussed. Lacunarity areas in plant hydraulics are also flagged where progress is urgently needed.

scholarly journals Microbiome of two predominant seagrass species of the Kenyan coast, Enhalus acoroides and Thalassodendron ciliatum

2018 ◽  
Author(s):  
Davies Kiambi Kaimenyi ◽  
Etienne P De Villiers ◽  
Joyce Ngoi ◽  
James B Ndiso ◽  
Santie M De Villiers
Keyword(s):  
Microbial Communities ◽  
Water Samples ◽  
Bacterial Communities ◽  
Anthropogenic Activities ◽  
Seagrass Beds ◽  
Seagrass Species ◽  
Microbial Composition ◽  
Seagrass Meadows ◽  
Enhalus Acoroides ◽  
Kenyan Coast

Background. Metagenomics studies have reported on the complexity of microbiomes associated with seagrass and can provide critical insights into the sustainable use and conservation of seagrasses. Recent conservation activities in Kenya focused mainly on coral reefs and mangrove forests with little direct action taken to conserve seagrass meadows. Pollution, over-exploitation of marine resources and minimal efforts towards enforcement of conservation laws of marine environments, have caused degradation and defoliation of seagrass habitats. Little is known about the microbes associated with seagrass species in Kenya and this study aimed to characterize the genetic diversity of the microbiomes of two prominent seagrass species, Enhalus acoroides and Thallasodendron ciliatum, which are the most commonly occurring species. Methods. Replicate microbiome samples were collected from leaves, roots, sediment and water columns associated with the two seagrass species from two sites on the Kenyan coast. The microbial communities of the samples were characterized and compared using 16S ribosomal RNA gene PCR and sequencing. Microbiome features including diversity and taxonomic composition were used to compare within and between sample types and sites. Results. Leaf samples from both E. acoroides and T. ciliatum had significantly different microbial communities comparted to root and sediment samples, revealing a diversity gradient with lowest diversity in water samples and highest in sediment. There were no significant variation in seagrass microbial composition associated with leaf and rhizosphere microbiomes of either E. acoroides or T. ciliatum. However, we did see a difference between water samples associated with each seagrass species. Discussion. This study of the microbiomes associated with the sediments, roots, leaves and surrounding water of E. acoroides and T. ciliatum, included a limited number of samples from a small geographic area, providing a valuable first assessment of the microbial diversity of seagrass beds on the Kenyan coast. We found no significant differences between the plant-associated bacterial communities of the two-seagrass species investigated. Significant differences however, were observed amongst leaf-, root-, sediment- and water-associated bacterial communities. This work will contribute to understanding the dynamic environment of seagrass beds and will contribute to helping conserving and re-establishing seagrass beds degraded by due to anthropogenic activities.

scholarly journals At what spatial scales are alternative stable states relevant in highly interconnected ecosystems?

2019 ◽  
Author(s):  
Vadim A. Karatayev ◽  
Marissa L. Baskett
Keyword(s):  
Spatial Scales ◽  
Alternative Stable States ◽  
Stable State ◽  
Environmental Stochasticity ◽  
Rocky Reef ◽  
Alternative States ◽  
Stable States ◽  
Long Distance ◽  
Rocky Reefs ◽  
Model Predictions

AbstractWhether ecosystems recover from disturbance depends on the presence of alternative stable states, which are theoretically possible in simple models of many systems. However, definitive empirical evidence for this phenomenon remains limited to demographically closed ecosystems such as lakes. In more interconnected systems such as temperate rocky reefs, the local relevance of alternative stable states might erode as immigration overwhelms local feedbacks and produces a single stable state. At larger spatial scales, dispersal might counter localized disturbance and feedbacks to synchronize states throughout a region. Here, we quantify how interconnectedness affects the relevance of alternative stable states using dynamical models of California rocky reef communities that incorporate observed environmental stochasticity and feedback loops in kelp-urchin-predator interactions. Our models demonstrate the potential for localized alternative states despite high interconnectedness likely due to feedbacks affecting dispersers as they settle into local communities. Regionally, such feedbacks affecting settlement can produce a mosaic of alternative stable states that span local (10-20km) scales despite the synchronizing effect of long-distance dispersal. The specific spatial scale and duration of each state predominantly depend on the scales of environmental variation and on local dynamics (here, fishing). Model predictions reflect observed scales of community states in California rocky reefs and suggest how alternative states co-occur in the wide array of marine and terrestrial systems with settlement feedbacks.

scholarly journals Temporal variability of a protected multispecific tropical seagrass meadow in response to environmental change

2019 ◽  
Vol 191 (12) ◽  
Author(s):  
E. Alonso Aller ◽  
J. S. Eklöf ◽  
M. Gullström ◽  
U. Kloiber ◽  
H. W. Linderholm ◽  
...  
Keyword(s):  
Species Composition ◽  
Environmental Change ◽  
Low Income ◽  
Environmental Variables ◽  
Seagrass Meadow ◽  
Spatial Scales ◽  
Temporal Changes ◽  
Climate Impacts ◽  
Seagrass Meadows ◽  
Seagrass Cover

AbstractIn a changing environment, there is an increasing interest to monitor ecosystems to understand their responses to environmental change. Seagrass meadows are highly important ecosystems that are under constant pressure from human activities and climate impacts, with marked declines observed worldwide. Despite increasing efforts, monitoring of multispecific tropical seagrass meadows is scarce, particularly in low-income regions. Based on data from a monitoring programme in a marine protected area in Zanzibar (Tanzania), we assessed temporal changes in seagrass cover and species composition during a 10-year period in relation to local variability in environmental variables. We observed a strong, gradual decline in seagrass cover and changes in species composition, followed by a period of recovery. However, the timing and length of these temporal patterns varied in space (between transects). Multiple environmental variables—cloud cover, temperature, storm occurrence, sunspot activity, and tidal amplitude and height—influenced seagrass cover, although only to a minor extent, suggesting that the monitored seagrass meadow may be influenced by other unmeasured factors (e.g. water currents and sediment movement). Our results show that seagrass meadows can be highly dynamic at small (10–50 m) spatial scales, even in the absence of major local anthropogenic impacts. Our findings suggest that high-resolution monitoring programmes can be highly valuable for the detection of temporal changes in multispecific seagrass meadows; however, to understand the causes of change, there is a need of long-term (> 10 years) data series that include direct measurements of environmental variables and extreme events.

scholarly journals Microbiome of two predominant seagrass species of the Kenyan coast, Enhalus acoroides and Thalassodendron ciliatum

2018 ◽  
Author(s):  
Davies Kiambi Kaimenyi ◽  
Etienne P De Villiers ◽  
Joyce Ngoi ◽  
James B Ndiso ◽  
Santie M De Villiers
Keyword(s):  
Microbial Communities ◽  
Water Samples ◽  
Bacterial Communities ◽  
Anthropogenic Activities ◽  
Seagrass Beds ◽  
Seagrass Species ◽  
Microbial Composition ◽  
Seagrass Meadows ◽  
Enhalus Acoroides ◽  
Kenyan Coast

Background. Metagenomics studies have reported on the complexity of microbiomes associated with seagrass and can provide critical insights into the sustainable use and conservation of seagrasses. Recent conservation activities in Kenya focused mainly on coral reefs and mangrove forests with little direct action taken to conserve seagrass meadows. Pollution, over-exploitation of marine resources and minimal efforts towards enforcement of conservation laws of marine environments, have caused degradation and defoliation of seagrass habitats. Little is known about the microbes associated with seagrass species in Kenya and this study aimed to characterize the genetic diversity of the microbiomes of two prominent seagrass species, Enhalus acoroides and Thallasodendron ciliatum, which are the most commonly occurring species. Methods. Replicate microbiome samples were collected from leaves, roots, sediment and water columns associated with the two seagrass species from two sites on the Kenyan coast. The microbial communities of the samples were characterized and compared using 16S ribosomal RNA gene PCR and sequencing. Microbiome features including diversity and taxonomic composition were used to compare within and between sample types and sites. Results. Leaf samples from both E. acoroides and T. ciliatum had significantly different microbial communities comparted to root and sediment samples, revealing a diversity gradient with lowest diversity in water samples and highest in sediment. There were no significant variation in seagrass microbial composition associated with leaf and rhizosphere microbiomes of either E. acoroides or T. ciliatum. However, we did see a difference between water samples associated with each seagrass species. Discussion. This study of the microbiomes associated with the sediments, roots, leaves and surrounding water of E. acoroides and T. ciliatum, included a limited number of samples from a small geographic area, providing a valuable first assessment of the microbial diversity of seagrass beds on the Kenyan coast. We found no significant differences between the plant-associated bacterial communities of the two-seagrass species investigated. Significant differences however, were observed amongst leaf-, root-, sediment- and water-associated bacterial communities. This work will contribute to understanding the dynamic environment of seagrass beds and will contribute to helping conserving and re-establishing seagrass beds degraded by due to anthropogenic activities.

Evolutionary rescue can prevent rate-induced tipping in predator-prey systems

2021 ◽  
Author(s):  
Ulrike Feudel ◽  
Anna Vanselow ◽  
Lukas Halekotte
Keyword(s):  
Environmental Change ◽  
Time Scale ◽  
Alternative Stable States ◽  
Rapid Evolution ◽  
Regime Shifts ◽  
Rate Of Change ◽  
Stable States ◽  
Critical Rate ◽  
Predator Prey ◽  
Evolutionary Rescue

<p>Nowadays, populations are faced with unprecedented rates of global climate change, habitat fragmentation and destruction causing an accelerating conversion of their living conditions. Critical transitions in ecosystems, often called regime shifts, lead to sudden shifts in the dominance of species or even to species’ extinction and decline of biodiversity. Many regime shifts are explained as transitions between alternative stable states caused by (i) certain bifurcations when certain parameters or external forcing cross critical thresholds, (ii) fluctuations or (iii) extreme events. We address a fourth mechanism which does not require alternative states but instead, the system performs a large excursion away from its usual behaviour when environmental  conditions change too fast. During this excursion, the system can embrace dangerously, unexpected states. We demonstrate that predator-prey systems can exhibit a population collapse if the rate of environmental change crosses a certain critical rate. In reference to this critical rate of change which has to be surpassed, this transition is called rate-induced tipping (R-tipping). A further difference to the other three tipping mechanisms is that R-tipping mainly manifests during the transient dynamics – the dynamics before the long-term dynamics are reached.  Whether a system will track its usual state or will tip with the consequence of a possible extinction of a species depends crucially on the time scale relations between the ecological timescale and the time scale of environmental change as well as the initial condition. However, populations have the ability to respond to environmental change due to rapid evolution. Employing an eco-evolutionary model we show how such kind of adaptation can prevent rate-induced tipping in predator-prey systems. The corresponding mechanism, called evolutionary rescue, introduces a third timescale which needs to be taken into account. Only a large genetic variation within a population reflecting rapid evolution would be able to successfully counteract an overcritically fast environmental change.</p><p> </p>

Fire Feedbacks with Vegetation and Alternative Stable States

2009 ◽  
Vol 18 (1) ◽  
pp. 159-173 ◽  
Author(s):  
Brian Beckage ◽  
Chris Ellingwood ◽  
Keyword(s):  
Alternative Stable States ◽  
Stable States ◽  
Fire Feedbacks

Are systems with strong underlying abiotic regimes more likely to exhibit alternative stable states?

Oikos ◽  
2005 ◽  
Vol 110 (2) ◽  
pp. 409-416 ◽  
Author(s):  
Raphael K. Didham ◽  
Corinne H. Watts ◽  
David A. Norton
Keyword(s):  
Alternative Stable States ◽  
Stable States
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