Alternative Stable States Research Articles

Evolutionary gain and loss of a pathological immune response to parasitism.

Parasites impose fitness costs on their hosts. Biologists often assume that natural selection favors infection-resistant hosts. Yet, when the immune response itself is costly, theory suggests that selection may sometimes favor loss of resistance, which may result in alternative stable states where some populations are resistant and others are tolerant. Intraspecific variation in immune costs is rarely surveyed in a manner that tests evolutionary patterns, and there are few examples of adaptive loss of resistance. Here, we show that when marine threespine stickleback colonized freshwater lakes, they gained resistance to the freshwater-associated cestode Schistocephalus solidus. Extensive peritoneal fibrosis and inflammation are a commonly observed phenotype that contributes to suppression of cestode growth and viability but also imposes a substantial cost on fecundity. Combining genetic mapping and population genomics, we find that opposing selection generates immune system differences between tolerant and resistant populations, consistent with divergent optimization.

Characterizing Long Transients in Consumer–Resource Systems With Group Defense and Discrete Reproductive Pulses

During recent years, the study of long transients has been expanded in ecological theory to account for shifts in long-term behavior of ecological systems. These long transients may lead to regime shifts between alternative states that resemble the dynamics of alternative stable states for a prolonged period of time. One dynamic that potentially leads to long transients is the group defense of a resource in a consumer–resource interaction. Furthermore, time lags in the population caused by discrete reproductive pulses have the potential to produce long transients, either independently or in conjunction to the transients caused by the group defense. In this work, we analyze the potential for long transients in a model for a consumer–resource system in which the resource exhibits group defense and reproduces in discrete reproductive pulses. This system exhibits crawl-by transients near the extinction and carrying capacity states of resource, and a transcritical bifurcation, under which a ghost limit cycle appears. We estimate the transient time of our system from these transients using perturbation theory. This work advances an understanding of how systems shift between alternate states and their duration of staying in a given regime and what ecological dynamics may lead to long transients.

Interkingdom Plant–Soil Microbial Ecological Network Analysis under Different Anthropogenic Impacts in a Tropical Rainforest

Plants and their associated soil microorganisms interact with each other and form complex relationships. The effects of slash-and-burn agriculture and logging on aboveground plants and belowground microorganisms have been extensively studied, but research on plant–microbial interkingdom ecological networks is lacking. In this study, using old growth forest as a control, we used metagenomic data (ITS and 16S rRNA gene amplified sequences) and plant data to obtain interdomain species association patterns for three different soil disturbance types (slash-and-burn, clear cutting and selective cutting) in a tropical rainforest based on interdomain ecological network (IDEN) analysis. Results showed that the soil bacterial–fungal and plant–microbe ecological networks had different topological properties among the three forest disturbance types compared to old growth forest. More nodes, links, higher modularity and negative proportion were found in the selective cutting stand, indicating higher stability with increasing antagonistic relationships and niche differentiation. However, the area of slash-and-burn forest yield opposite results. Network module analysis indicated that different keystone species were found in the four forest types, suggesting alternative stable states among them. Different plant species had more preferential associations with specific fungal taxa than bacterial taxa at the genus level and plant–microbe associations lagged behind bacterial–fungal associations. Overall, compared with old growth forests, the bacterial–fungal and plant–microbe ecological networks in the slash-and-burn and clear cutting stands were simpler, while the network in the selective cutting stand was more complex. Understanding the relationships between aboveground plants and belowground microorganisms under differing disturbance patterns in natural ecosystems will help in better understanding the surrounding ecosystem functions of ecological networks.

Climatic legacy effects on the drought response of the Amazon rainforest.

Extreme precipitation and drought events are predicted to become more intense and more frequent over the Amazon rainforest. Because changes in forest dynamics could prompt strong feedback loops to the global climate, it is of crucial importance to gain insight into the response of tropical forests to these recurring extreme climatic events. Here, we evaluated the Amazon forest stability (resistance and resilience) to drought in the context of past dry and wet climatic events using MODIS EVI satellite imagery and cumulative water deficit anomalies. We observed large spatial differences in the occurrence of extreme climatic events from 1980 to 2019, with an increase in drought frequency in the central and northern Amazon and drought intensity in the southern Amazon basin. An increasing trend in the occurrence of wet events was found in the western, southern, and eastern Amazon. Furthermore, we found significant legacy effects of previous climatic events on the forest drought response. An extreme drought closely preceding another drought decreased forest resilience, whereas the occurrence of a recent drier-than-usual event also decreased the forest resistance to later droughts. Both wetter-than-usual and extreme wet events preceding an extreme drought increased the resistance of the forest, and with similar effects sizes as dry events, indicating that wet and dry events have similarly sized legacy effects on the drought response of tropical forests. Our results indicate that the predicted increase in drought frequency and intensity can have negative consequences for the functioning of the Amazon forest. However, more frequent wet periods in combination with these droughts could counteract their negative impact. Finally, we also found that more stable forests according to the alternative stable states theory are also more resistant and resilient to individual droughts, showing a positive relationship between the equilibrium and non-equilibrium stability dynamics.

Prey–predator dynamics with adaptive protection mutualism

Prey can ease the burden of exploitation by attracting a third party that interferes with their predators. Such is the case for plant-ant or aphid-ant mutualisms, where the victim supplies food to the ants, while the ants attack or drive away the offenders. Since ants are adaptive foragers, defense services can be altered by alternative food sources (e.g., other plants, or human-supplied resource). This article explores the prey-predator-ant system, using a model that combines predator-prey population dynamics with ant optimal foraging, where ants consume prey-supplied resources or alternative resources. Feedbacks between prey-predator dynamics and adaptive ant foraging leads to complex dynamics. For a given ant colony size and supply rate of alternative resources, prey can coexist with predators at alternative stable states, or along alternative limit cycles. Limit cycles extend the scope of defensive mutualism beyond the point where ants would abandon prey in favor of alternative resources under equilibrium conditions. These results highlight the importance of trait-mediated indirect interactions for natural mutualistic–antagonistic systems, and potential outcomes of manipulating ant defense services using baits in the case of agriculture.

Sea‐surface temperature anomalies mediate changes in fish richness and abundance in Atlantic and Gulf of Mexico estuaries

AbstractAimAnthropogenic warming of marine systems has caused biological and physiological responses that are fundamentally altering ecosystem structure. Because estuaries exist at the land‐ocean interface, they are particularly vulnerable to the effects of ocean warming as they can undergo rapid biogeochemical and hydrological shifts due to climate and land‐use change. We explored how multiple components of estuarine fish diversity—turnover, richness, and abundance—have changed in the North Atlantic and Gulf of Mexico estuaries across space and time and the drivers of change.LocationNorth Atlantic and Gulf of Mexico.TaxaFish.MethodWe compiled long‐term (>30 years), continent‐wide fisheries independent trawl surveys conducted in estuaries—from the Gulf of Maine to the Gulf of Mexico (U.S. waters)—and combined these with climate and land‐use‐land‐cover data to examine trends and ecological drivers of fish richness, abundance and turnover using mixed‐effect models.ResultsSpecies richness, abundance and turnover have increased in North Atlantic and Gulf of Mexico estuaries in the last 30 years. These changes were mediated largely by sea‐surface temperature anomalies, especially in more northern estuaries where warming has been relatively pronounced.Main ConclusionThe increasing trajectory of turnover in many estuaries suggests that fish communities have changed fundamentally from the baselines. A fundamental change in community composition can lead to an irreversible trophic imbalance or alternative stable states among other outcomes. Thus, predicting how shifting community structures might influence food webs, ecosystem stability, and human resource use remain a pertinent task.

Toward a Beech-Dominated Alternative Stable State in Dinaric Mixed Montane Forests: A Long-Term Study of the Pecka Old-Growth Forest

In the last century, a synchronous beech expansion has been observed for many mixed mountain forests in southeastern Europe. This change is associated with the interaction of various disturbances. We analyzed structural changes in the Pecka old-growth forest in Slovenia during the last century, using several inventories of the tree layer, regeneration, and site factors. Throughout the observation period, the density of silver fir in the regeneration layer and in the overstory steadily decreased. In 1893, silver fir accounted for about 60% of the growing stock, whereas in 2013 it accounted for less than 13%. This is likely because of silver fir’s decline in the canopy layer due to air pollution, successive windthrows, and overbrowsing. However, climate change may also have played an important role, as silver fir also declined in southeastern European old-growth forests where air pollution was less pronounced and ungulate densities were low. A gradual decline of silver fir in the overstory resulted in a decrease of overall tree density to 231 trees ha–1, while growing stock remained relatively high at 712 m3 ha–1. Median diffuse light at 1.3 m was 3.7% and regeneration density was 19,954 ha–1. Beech was dominant (94%), followed by silver fir (4%), and sycamore maple (2%). No silver fir seedlings larger than 0.2 m were recorded. Silver fir, sycamore maple, and beech regeneration showed 87, 76, and 45% browsing damage, respectively. Regression models indicated some evidence of niche partitioning between silver fir and beech. However, many processes may be masked by the silver fir’s avoidance strategy. Given current red deer densities, climate change, and existing forest structure, the Pecka old-growth forest will likely reach an alternative stable state dominated by beech in a few decades. This calls for immediate reduction of ungulate populations. Despite the interaction of multiple disturbances, the Pecka old-growth forest has maintained a relatively high overall growing stock, a favorable microclimate, and succession pathway with shade-tolerant beech. This indicates the intrinsic resilience of natural forests. The mechanisms discussed here can be applied to the future governance of old-growth and managed montane mixed forests.

Advances in biophysical feedbacks and the resulting stable states in tidal flat systems

<p indent="0mm">As an integral part of the coastal wetland system, tidal flats play an important role in maintaining the health of coastal ecosystems, resisting natural coastal disasters, and blue carbon sequestration. Tidal flats can provide suitable habitats for a variety of organisms; simultaneously, such organisms mediate hydrodynamic and sediment processes, hence affecting the geomorphic evolution and stability of tidal flat systems. In recent years, tidal flat systems have faced the comprehensive impacts of rapid human activities, frequent storm surges, and reduced sediment availabilities, which have aggravated tidal flat erosion. Severe erosion is accompanied by a critical biomass loss, especially under complex biological-physical interactions. Tidal flat degradation is often amplified, threatening the stability of tidal flat systems. The ultimate goal of ecological protection and restoration of tidal flat systems is to establish a self-sustaining method with less artificial assistance. To date, only a few ecological restoration projects in China have considered the integration of biological and physical processes in tidal flats. The most important reason is the lack of understanding of the basic laws of natural construction and operation of the systems. Therefore, understanding and giving way to the self-organization process driven by the biophysical interactions in tidal flat systems have become an important scientific and technical necessity in the ecological protection and restoration of tidal flats. First, we summarized the biophysical effects of salt marsh vegetation and benthic microalgae on the hydrodynamic and sediment movement process of tidal flats. Salt marsh plants and benthic microalgae change the hydrodynamic and sediment processes through wave dissipation and sediment stabilization. Conversely, the changing physical conditions affect the growth and development of salt marsh and benthic microalgae. Second, we qualitatively analyzed the bistability and catastrophic shift of a tidal flat system driven by the salt marsh-sediment and benthic microalgae-sediment feedback, both containing some similarities and differences. Specifically, driven by biophysical feedbacks, both the salt marsh- and benthic microalgae-sediment systems have alternative stable states; with the increased bottom shear stress, both systems shift from a state characterized by high biomass and sediment deposition to that with low biomass and sediment deposition; the bistable range of the salt marsh-sediment system is wider, and the system has a greater hysteresis, indicating that once degraded, it is more difficult for the salt marsh system to be restored to its original state. Third, we discussed the self-organized bio-geomorphic characteristics. The scale-dependent feedback between organisms and physical environments results in spatial patterns. The self-organized patterns have been widely found in a tidal flat ecosystem, for example, circular salt marsh clusters, salt marsh cliffs, and patterned mudflats characterized by the microalgae-covered hummocks alternating with water-filled hollows. Self-organized patterns can improve the primary productivity and sediment deposition of tidal flats, thereby enhancing the stability of ecosystems, which is of great significance for the ecosystem function of tidal flats. Finally, this paper proposed the critical scientific problems that still need to be solved in the future, such as the continuous field observation at the system level, the regulation of biological interspecific interactions under physical conditions, and the quantitative simulation of catastrophic shift thresholds in the tidal flat bio-geomorphic system.

Alternative stable states and hydrological regime shifts in a large intermittent river

Non-perennial rivers and streams make up over half the global river network and are becoming more widespread. Transitions from perennial to non-perennial flow are a threshold-type change that can lead to alternative stable states in aquatic ecosystems, but it is unknown whether streamflow itself is stable in either wet (flowing) or dry (no-flow) conditions. Here, we investigated drivers and feedbacks associated with regime shifts between wet and dry conditions in an intermittent reach of the Arkansas River (USA) over the past 23 years. Multiple lines of evidence suggested that these regimes represent alternative stable states, including (a) significant jumps in discharge time series that were not accompanied by jumps in flow drivers such as precipitation and groundwater pumping; (b) a multi-modal state distribution with 92% of months experiencing no-flow conditions for <10% or >90% of days, despite unimodal distributions of precipitation and pumping; and (c) a hysteretic relationship between climate and flow state. Groundwater levels appear to be the primary control over the hydrological regime, as groundwater levels in the alluvial aquifer were higher than the stream stage during wet regimes and lower than the streambed during dry regimes. Groundwater level variation, in turn, was driven by processes occurring at both the regional scale (surface water inflows from upstream, groundwater pumping) and the reach scale (stream–aquifer exchange, diffuse recharge through the soil column). Historical regime shifts were associated with diverse pressures including network disconnection caused by upstream water use, increased flow stability potentially associated with reservoir operations, and anomalous wet and dry climate conditions. In sum, stabilizing feedbacks among upstream inflows, stream–aquifer interactions, climate, vegetation, and pumping appear to create alternative wet and dry stable states at this site. These stabilizing feedbacks suggest that widespread observed shifts from perennial to non-perennial flow will be difficult to reverse.

How to evolve an alternative stable state

How to evolve an alternative stable state

Evidence for Alternate Stable States in an Ecuadorian Andean Cloud Forest

Tree diversity inventories were undertaken. The goal of this study was to understand changes in tree community dynamics that may result from common anthropogenic disturbances at the Reserva Los Cedros, a tropical montane cloud forest reserve in northern Andean Ecuador. The reserve shows extremely high alpha and beta tree diversity. We found that all primary forest sites, regardless of age of natural gaps, are quite ecologically resilient, appearing to return to a primary-forest-type community of trees following gap formation. In contrast, forests regenerating from anthropogenic disturbance appear to have multiple possible ecological states. Where anthropogenic disturbance was intense, novel tree communities appear to be assembling, with no indication of return to a primary forest state. Even in ancient primary forests, new forest types may be forming, as we found that seedling community composition did not resemble adult tree communities. We also suggest small watersheds as a useful basic spatial unit for understanding biodiversity patterns in the tropical Andes that confound more traditional Euclidean distance as a basic proxy of dissimilarity. Finally, we highlight the conservation value of Reserva Los Cedros, which has managed to reverse deforestation within its boundaries despite a general trend of extensive deforestation in the surrounding region, to protect a large, contiguous area of highly endangered Andean primary cloud forest.

Quantifying the impact of ecological memory on the dynamics of interacting communities.

Ecological memory refers to the influence of past events on the response of an ecosystem to exogenous or endogenous changes. Memory has been widely recognized as a key contributor to the dynamics of ecosystems and other complex systems, yet quantitative community models often ignore memory and its implications. Recent modeling studies have shown how interactions between community members can lead to the emergence of resilience and multistability under environmental perturbations. We demonstrate how memory can be introduced in such models using the framework of fractional calculus. We study how the dynamics of a well-characterized interaction model is affected by gradual increases in ecological memory under varying initial conditions, perturbations, and stochasticity. Our results highlight the implications of memory on several key aspects of community dynamics. In general, memory introduces inertia into the dynamics. This favors species coexistence under perturbation, enhances system resistance to state shifts, mitigates hysteresis, and can affect system resilience both ways depending on the time scale considered. Memory also promotes long transient dynamics, such as long-standing oscillations and delayed regime shifts, and contributes to the emergence and persistence of alternative stable states. Our study highlights the fundamental role of memory in communities, and provides quantitative tools to introduce it in ecological models and analyse its impact under varying conditions.

The absence of alternative stable states in vegetation cover of northeastern India.

Globally, forests and savannah are shown to be alternative stable states for intermediate rainfall regimes. This has implications for how these ecosystems respond to changing rainfall conditions. However, we know little about the occurrence of alternative stable states in forest ecosystems in India. In this study, we investigate the possibility of alternative stable states in the vegetation cover of northeastern India, which is a part of the Eastern Himalaya and the Indo-Burma biodiversity hotspots. To do so, we construct the so-called state diagram, by plotting frequency distributions of vegetation cover as a function of mean annual precipitation (MAP). We use remotely sensed satellite data of the enhanced vegetation index (EVI) as a proxy for vegetation cover (at 1 km resolution). We find that EVI exhibits unimodal distribution across a wide range of MAP. Specifically, EVI increases monotonically in the range 1000–2000 mm of MAP, after which it plateaus. This range of MAP corresponds to the vegetation transitional zone (1200–3700 m), whereas MAP greater than 2000 mm covers the larger extent of the tropical forest (less than or equal to 1200 m) of northeast India. In other words, we find no evidence for alternative stable states in vegetation cover or forest states at coarser scales in northeast India.

Vegetation recovery rates provide insight into reburn severity in southwestern Oregon, USA

Like much of western North America, The Klamath-Siskiyou Ecoregion of southwest Oregon and northern California is experiencing a departure from its historical fire regime, with greater proportions of high severity fire and less low to moderate severity fire compared to historical norms. Reburn events (i.e. when wildfires burn through areas that have recently burned) can exacerbate this departure when high reburn severity contributes to a conversion from mixed-conifer forests to an alternative stable state dominated by pyrogenic shrubs. Spatially explicit understanding of the predictors of reburn severity is necessary to identify areas where the risk of high reburn severity should be mitigated and areas where low to moderate severity fire can be encouraged to promote resilience to future wildfires. Previous research concerning drivers of reburn severity has considered the severity of the initial fire, topography, and fuel and weather conditions immediately preceding the reburning fire, but has not evaluated the potential effects of vegetation dynamics after a fire on reburn severity. We investigated whether remotely sensed rates of vegetation recovery following an initial fire, measured by change in Normalized Burn Ratio (NBR) over 2, 5, and 10 years, are important predictors of reburn severity, once other known drivers of fire severity have been accounted for. Though a Random Forests analysis revealed that other variables (notably pre-reburn vegetation cover, average fire season PDSI, and initial fire severity) were more important predictors of reburn severity, vegetation recovery rates after an initial fire were found to be moderately important predictors of reburn severity, with comparable importance to fire weather variables and higher importance than some topographical variables. Short-term (2-year and 5-year) vegetation responses to wildfire representing either delayed mortality or elevated vegetation recovery were both associated with higher reburn severity, as were higher 10-year rates of annual vegetation accumulation. The results indicate that along with previously identified drivers of reburn severity, remotely sensed metrics of vegetation recovery relatively soon after a fire may provide important insight that can support post-fire management decisions and wildfire response planning for future reburn events.

Alternance of alternative stable states influence the functional diversity of microcrustaceans in a shallow subtropical lake

AbstractShallow lakes in subtropical climate regions may have a clear water state with a predominance of submerged or floating macrophytes and a turbid water state with a predominance of phytoplankton. The relationship between microcrustaceans and these changes in alternative states is still incipient in the literature. And to better understand these relationships, the functional approach is an excellent tool. Thus, the present work seeks to test the hypothesis that changes in alternative stable states over time reflect the variability of composition and functional diversity of microcrustaceans. For this, samples of microcrustaceans collected in a subtropical shallow lake, which underwent alternate state changes in the period to 2000–2014, were used. Our results demonstrate a variation in composition and functional diversity among alternative states, thus supporting our hypothesis. In periods of clear water with a predominance of floating macrophytes, we found a greater functional diversity and richness of genera. This result may be associated with several factors such as greater habitat heterogeneity and lower predation pressure. The lowest values of functional diversity found in periods of turbid waters with predominance of phytoplankton and periods of clear waters with submerged macrophytes are related to the dominance of functional traits, such as scraper feeding type, herbivorous/omnivorous trophic group, littoral habitat and asexual reproduction. These traits are functional features of most Ostracoda genera, a taxonomic group abundant in these two alternative states. The predominance of this group may be related to the environmental characteristics of these periods, such as the high vegetation cover and the availability of niches unoccupied by more sensitive species, since most Ostracoda have high environmental tolerance. We conclude that the functional traits approach combined with taxonomic groups respond to temporal variations of alternative stable states and are important tools to detect environmental changes.

A stylized model of stochastic ecosystems with alternative stable states

AbstractWe construct a generic ecosystem model that features the basic mechanisms of alternative stable states as well as two different stochastic influences. In particular, we use a mean‐reverting jump‐diffusion process to model the evolution of the ecosystem state over time. We review key concepts of multistability theory and the simple heuristics commonly employed to illustrate them. We then provide mathematical definitions for these concepts in the model context. Our contribution to the literature is twofold: we improve the representation of stochasticity in, and clarify key concepts of, multistability theory. The simplicity of the model enables a number of applications, such as finding economically optimal management strategies, identifying criteria for sustainable ecosystem management in a stochastic viability framework, deriving the probability of a regime shift, or empirically identifying the factors which have caused a specific regime shift.

Effects of fecal stream deprivation on human intestinal barrier after loop ileostomy.

Background and AimIntestinal homeostasis is closely associated with the normal intestinal luminal physiological environment. Temporary loop ileostomy changes the intestinal structure and diverts the fecal stream, thereby disturbing the intestinal environment. This study aimed to clarify the changing situation of the human intestinal mucosa barrier in the absence of a fecal stream after loop ileostomy.MethodsWe obtained paired samples from the fed (fecal stream maintained) and unfed (no fecal stream) portions of the loop ileostomy and subjected these samples to RNA sequencing. We also determined transepithelial electrical resistance. The mucus layer thickness and content of MUC2, tight junction proteins, and common antimicrobial peptides in ileum mucosa were studied.ResultsTranscriptome data revealed that genes associated with enhancing the intestinal barrier function of the unfed ileum were significantly decreased and genes associated with immune defense response were significantly increased. The transepithelial electrical resistance was lower and the mucus layer thickness was thinner in the unfed ileal mucosa than in the fed ileum. The MUC2, Occludin, and zonula occludens 1 content was lower in the unfed ileum than in the fed ileum. α‐Defensin 5, α‐defensin 6, and lysozyme content was higher in the unfed ileum than in the enterally fed ileum.ConclusionIntestinal barrier function is weakened after long‐term fecal diversion, but antimicrobiota defense function is strengthened. Thus, the intestinal mucosa barrier adopts an alternative stable state during fecal diversion, which may explain the clinical paucity of cases of enterogenic infection caused by loop ileostomy.

Evolution of Plant Niche Construction Traits in Biogeomorphic Landscapes.

AbstractBy virtue of their niche construction traits, plants play a significant role in shaping landscapes. The resultant outcome could change the selective environment, which then influences the evolution of these same plants. To date, almost all biogeomorphic models have assumed that niche construction traits are invariant in time. Conversely, niche construction studies often assume that independent abiotic changes either are nonexistent or are simply linear. Here, I consider the concomitant evolution of plant niche construction traits during complex landscape development. I construct a geo-evolutionary model that couples a population genetic module with a landscape development module. Allowing plants to evolve always results in landforms different from those that appear when evolution is not included. The topographic difference between cases with and without evolution ranges from a small difference in steady-state elevation (topography) to pronounced differences in landforms. Furthermore, evolution of niche construction traits could introduce alternative stable states and hysteresis, modifying the responses of landscapes to environmental stress. Allowing the landscape to develop while evolution occurs alters evolutionary trajectories for niche construction traits. The system can even develop into states that suppress natural selection. Model results support the need to integrate niche construction theory and biogeomorphology to better understand both.

Grazing and Recovery of Kelp Gametophytes Under Ocean Warming

Kelp forests are economically important ecosystems that support a wealth of biodiversity but are declining globally. They are often replaced by biologically depauperate alternate stable states dominated by turfing algae. Hysteresis maintains algal turfs by inhibiting kelp recruitment, preventing the reestablishment of kelp forests. The mechanisms inhibiting kelp recruitment remain poorly understood as microscopic stages of kelp are difficult to study in situ. A potential mechanism contributing to the suppression of recruitment may be turf-facilitated grazing of kelp gametophytes, the haploid free-living reproductive life stage. Here we assess the resilience of kelp gametophytes to grazing pressure from a gastropod micrograzer commonly present in turf under current and future ocean warming scenarios. Gametophyte coverage and abundance were significantly reduced following grazing under all temperatures, however there was no significant effect of temperature on grazing rates. Once grazing pressure was removed, gametophyte abundance recovered to control levels, but the total coverage and length of gametophytes continued to decline in all treatments. Gametophytes were found to survive micrograzer ingestion and continued to grow in aggregations in the gastropod’s mucus trail and faeces, even producing sporophytes. Gametophyte survival post-ingestion may positively contribute to dispersal and sporophyte recruitment, however the lack of gametophyte recovery at elevated temperatures may counteract this effect under future ocean warming. Taken together, this study demonstrates complex interactions that take place in the turf micro-habitat of kelp gametophytes and highlights biotic factors influencing transitions between kelp forests and algal turfs.

Fast growth can counteract antibiotic susceptibility in shaping microbial community resilience to antibiotics

Microbial communities often face external perturbations that can induce lasting changes in their composition and functions. Our understanding of how multispecies communities respond to perturbations such as antibiotics is limited, with susceptibility assays performed on individual, isolated species our primary guide in predicting community transitions. Here, we studied how bacterial growth dynamics can overcome differences in antibiotic susceptibility in determining community resilience: the recovery of the original community state following antibiotic exposure. We used an experimental community containing Corynebacterium ammoniagenes and Lactobacillus plantarum that displays two alternative stable states as a result of mutual inhibition. Although C. ammoniagenes was more susceptible to chloramphenicol in monocultures, we found that chloramphenicol exposure nonetheless led to a transition from the L. plantarum-dominated to the C. ammoniagenes-dominated community state. Combining theory and experiments, we demonstrated that growth rate differences between the two species made the L. plantarum-dominated community less resilient to several antibiotics with different mechanisms of action. Taking advantage of an observed cooperativity—a dependence on population abundance—in the growth of C. ammoniagenes, we next analyzed in silico scenarios that could compromise the high resilience of the C. ammoniagenes-dominated state. The model predicted that lowering the dispersal rate, through interacting with the growth at low population densities, could make the C. ammoniagenes state fragile against virtually any kind of antibiotic, a prediction that we confirmed experimentally. Our results highlight that species susceptibility to antibiotics is often uninformative of community resilience, as growth dynamics in the wake of antibiotic exposure can play a dominant role.