Seagrasses evolved from terrestrial plants into marine foundation species around 100 million years ago. Their ecological success, however, remains a mystery because natural organic matter ...accumulation within the beds should result in toxic sediment sulfide levels. Using a meta-analysis, a field study, and a laboratory experiment, we reveal how an ancient three-stage symbiosis between seagrass, lucinid bivalves, and their sulfide-oxidizing gill bacteria reduces sulfide stress for seagrasses. We found that the bivalve-sulfide-oxidizer symbiosis reduced sulfide levels and enhanced seagrass production as measured in biomass. In turn, the bivalves and their endosymbionts profit from organic matter accumulation and radial oxygen release from the seagrass roots. These findings elucidate the long-term success of seagrasses in warm waters and offer new prospects for seagrass ecosystem conservation.
Positive Interactions in the Coral Macro and Microbiome Ainsworth, Tracy D.; Renzi, Julianna J.; Silliman, Brian R.
Trends in microbiology (Regular ed.),
August 2020, 2020-08-00, 20200801, Letnik:
28, Številka:
8
Journal Article
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Researchers now recognize the importance of the coral microbiome, but they often overlook other species that live on corals and influence coral–microbe interactions. These ‘interstitial associates’ ...should be incorporated into the metaorganism concept for insights into how facilitations between associates, corals, and their microbiomes can be leveraged in ecology and restoration.
Ecological interactions may vary geographically as a function of diversity, density, or per capita interaction strengths, but we know little about the relative importance of these three mechanisms. ...We examined variation in species richness, abundance, and interactions among leaf-chewing herbivores and the dominant salt-marsh plant Spartina alterniflora along the Atlantic Coast of the United States. High-latitude S. alterniflora plants are more palatable to herbivores than are low-latitude plants. Within this range of latitude, diversity and density of the dominant leaf-chewing consumers, snails and grasshoppers, in Spartina-dominated portions of the marsh varied little. Low-latitude plants, however, experienced much greater levels of leaf damage from consumers than did high-latitude plants. Per capita feeding rates of low-latitude snails (Littoraria irrorata) and grasshoppers (Orchelimum fidicinum) in the laboratory were greater than feeding rates of high-latitude snails (Melampus bidentatus) and grasshoppers (Conocephalus spartinae). In field experiments, low-latitude snails strongly suppressed S. alterniflora growth, but high-latitude snails had no effect on primary production. Thus, latitudinal differences in the effect of herbivores on plants (i.e., interaction strength), driven by differences in per capita effects among species, rather than differences in diversity or density, may contribute to selection for latitudinal differences in plant palatability. Because geographical differences in interaction strength can occur in the absence of differences in diversity or density, linking biogeography with community ecology will require experimental studies that explicitly measure interaction strength at multiple geographic locations.
Fungal farming in a snail Silliman, B.R; Newell, S.Y
Proceedings of the National Academy of Sciences - PNAS,
12/2003, Letnik:
100, Številka:
26
Journal Article
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Mutualisms between fungi and fungus-growing animals are model systems for studying coevolution and complex interactions between species. Fungal growing behavior has enabled cultivating animals to ...rise to major ecological importance, but evolution of farming symbioses is thought to be restricted to three terrestrial insect lineages. Surveys along 2,000 km of North America's Atlantic coast documented that the marine snail Littoraria irrorata grazes fungus-infected wounds on live marsh grass throughout its range. Field experiments demonstrate a facultative, farming mutualism between Littoraria and intertidal fungi. Snails graze live grass primarily not to feed but to prepare substrate for fungal growth and consume invasive fungi. Fungal removal experiments show that snails and fungi act synergistically to suppress marsh grass production. These results provide a case of fungus farming in the marine environment and outside the class Insecta and reveal a previously undemonstrated ecological mechanism (i.e., facilitation of fungal invasion) by which grazers can exert top-down control of marine plant production.
A major challenge in ecology is to understand broadscale trends in the impact of environmental change. We provide the first integrative analysis of the effects of eutrophication on plants, ...herbivores, and their interactions in coastal wetlands across latitudes. We show that fertilisation strongly increases herbivory in salt marshes, but not in mangroves, and that this effect increases with increasing latitude in salt marshes. We further show that stronger nutrient effects on plant nitrogen concentration at higher latitudes is the mechanism likely underlying this pattern. This biogeographic variation in nutrient effects on plant–herbivore interactions has consequences for vegetation, with those at higher latitudes being more vulnerable to consumer pressure fuelled by eutrophication. Our work provides a novel, mechanistic understanding of how eutrophication affects plant–herbivore systems predictably across broad latitudinal gradients, and highlights the power of incorporating biogeography into understanding large‐scale variability in the impacts of environmental change.
Although salinity in many ecosystems such as salt marshes can be extremely high, an asymmetry in salinity range between experimental studies (relatively narrow) and field conditions (potentially ...broad) has strongly affected current understanding of plant salinity tolerance. To improve understanding, it is thus important to examine plant tolerances over a broad range of salinities and identify potential tolerance thresholds. We examine tolerances of two widely distributed marsh plants, Suaeda salsa and Salicornia europaea, to salinities ranging from 0 to 100 g/kg, and determine survival, above‐ and belowground biomass after 8 weeks of salinity treatment. Both species, Sa. europaea in particular, have much broader salinity tolerances than other plants previously examined, (2) plant survival, above‐ and belowground biomass have remarkably different responses to salinity, and (3) there is a nonlinear, threshold response of S. salsa to salinity, above which S. salsa survivorship drastically decreases. These results provide multiple important insights. Our study suggests that the potential for using these halophytes to revegetate and restore salt‐affected land may be greater than previously thought, and highlights the importance of studying multiple plant responses. Importantly, our study calls for a better integration of thresholds into understanding plant salinity tolerances and their applications.
An asymmetry in salinity range between experimental studies (relatively narrow) and field conditions (potentially broad) has strongly affected understanding plant salinity tolerance. Using two widely distributed marsh plants, Suaeda salsa and Salicornia europaea, as our test species, our study shows potential plant tolerance thresholds along broad salinity gradients, and calls for better integration of thresholds into understanding plant salinity tolerances and their applications.
Marine protected areas (MPAs) are key tools for combatting the global overexploitation of endangered species. The prevailing paradigm is that MPAs are beneficial in helping to restore ecosystems to ...more ‘natural’ conditions. However, MPAs may have unintended negative effects when increasing densities of protected species exert destructive effects on their habitat. Here, we report on severe seagrass degradation in a decade-old MPA where hyper-abundant green turtles adopted a previously undescribed below-ground foraging strategy. By digging for and consuming rhizomes and roots, turtles create abundant bare gaps, thereby enhancing erosion and reducing seagrass regrowth. A fully parametrized model reveals that the ecosystem is approaching a tipping point, where consumption overwhelms regrowth, which could potentially lead to complete collapse of the seagrass habitat. Seagrass recovery will not ensue unless turtle density is reduced to nearly zero, eliminating the MPA's value as a turtle reserve. Our results reveal an unrecognized, yet imminent threat to MPAs, as sea turtle densities are increasing at major nesting sites and the decline of seagrass habitat forces turtles to concentrate on the remaining meadows inside reserves. This emphasizes the need for policy and management approaches that consider the interactions of protected species with their habitat.
Prolonged droughts exacerbated by climate change have been widely documented to interact with consumers to decimate vegetation in many ecosystems. Although climate change is increasing within-year ...variation in precipitation and temperature, how weather fluctuations affect the impact of consumers on vegetation processes remains poorly understood. In a salt marsh that has recently experienced drought-associated vegetation die-off, we investigated how top-down control of plant recovery by a prominent salt marsh grazer varies with weather. Our results showed that grazing-driven plant mortality varied strongly with weather in spring, with intense grazing occurring during cool, wet days immediately following rain. Intense grazing on cool, wet days across the generally dry spring season had a strong impact that eliminated plant seedlings that could otherwise have become tolerant of grazing in the following summer, thereby restricting vegetation recovery and contributing to the persistence of an unvegetated salt barren state. Thus, weather fluctuations can modulate the impact of consumers on vegetation recovery, a fundamental process underlying the fate of ecosystems after disturbances. A multi-timescale perspective on top-down control that combines the impact of short-term fluctuations in weather and that of long-term variation in mean climate can not only help understand ecosystem dynamics in an increasingly variable climate, but may also inform conservation strategies or recovery plans for ecosystems that are already lost to climate change.
Understanding the factors that generate and maintain biodiversity is a central goal in ecology. While positive species interactions (i.e., facilitation) have historically been underemphasized in ...ecological research, they are increasingly recognized as playing important roles in the evolution and maintenance of biodiversity. Dominant habitat-forming species (foundation species) buffer environmental conditions and can therefore facilitate myriad associated species. Theory predicts that facilitation will be the dominant community-structuring force under harsh environmental conditions, where organisms depend on shelter for survival and predation is diminished. Wind-swept, arid Patagonian rocky shores are one of the most desiccating intertidal rocky shores ever studied, providing an opportunity to test this theory and elucidate the context-dependency of facilitation.
Surveys across 2100 km of southern Argentinean coastline and experimental manipulations both supported theoretical predictions, with 43 out of 46 species in the animal assemblage obligated to living within the matrices of mussels for protection from potentially lethal desiccation stress and predators having no detectable impact on diversity.
These results provide the first experimental support of long-standing theoretical predictions and reveal that in extreme climates, maintenance of whole-community diversity can be maintained by positive interactions that ameliorate physical stress. These findings have important conservation implications and emphasize that preserving foundation species should be a priority in remediating the biodiversity consequences of global climate change.
Invertebrate diversity can be a key driver of ecosystem functioning, yet understanding what factors influence local biodiversity remains uncertain. In many marine and terrestrial systems, ...facilitation cascades where primary foundation and/or autogenic ecosystem engineering species promote the settlement and survival of a secondary foundation/engineering species have been shown to enhance local biodiversity and ecosystem functioning. We experimentally tested if a facilitation cascade occurs among eelgrass (Zostera marina), pen clams (Atrina rigida), and community diversity in temperate seagrass beds in North Carolina, U.S.A., and if this sequence of direct positive interactions created feedbacks that affected various metrics of seagrass ecosystem function and structure. Using a combination of surveys and transplant experiments, we found that pen clam density and survivorship was significantly greater in seagrass beds, indicating that eelgrass facilitates pen clams. Pen clams in turn enhanced local diversity and increased both the abundance and species richness of organisms (specifically, macroalgae and fouling invertebrate fauna)—the effect of which scaled with increasing clam density. However, we failed to detect an impact of pen clams on other seagrass functions and hypothesize that functioning may more likely be enhanced in scenarios where secondary foundation species specifically increase the diversity of key functional groups such as epiphyte grazers and/or when bivalves are infaunal rather than epifaunal. Our findings add to the growing amount of literature that demonstrates that secondary foundation species are important drivers of local biodiversity in marine ecosystems. Further experimentation is needed that directly examines (i) the role of functional versus overall diversity on seagrass functions and (ii) the relative importance of life-history strategy in determining when and where engineering bivalves increase biodiversity and/or functioning of seagrass beds.
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