The niche of a stress-tolerant specialist, Dinophysis acuminata, in a coastal upwelling system

Dinophysis acuminata, the main cause of shellfish harvesting bans in Europe, blooms in the Galician Rías (NW Spain) throughout the upwelling season (ca. March to September). Here we illustrate rapid changes in vertical and across ría-shelf distributions of diatoms and dinoflagellates (including D. acuminata vegetative and small cells) in Ría de Pontevedra (RP) and Ría de Vigo (RV) during transitions from spin-down to spin-up phases of upwelling cycles. A subniche approach based on a Within Outlying Mean Index (WitOMI) showed that under the transient environmental conditions met during the cruise, both vegetative and small cells of D. acuminata colonized the Ria and Mid-shelf subniches, exhibiting good tolerance and extremely high marginality, in particular the small cells. Bottom-up (abiotic) control overwhelmed biological constraints, and shelf waters became a more favourable environment than the Rías. Contrasting higher biotic constraints inside the Rías were found for the small cells, with a subniche possibly controlled by unsuitable physiological status (notwithstanding the higher density) of the vegetative cell population. Results here on behaviour (vertical positioning) and physiological traits (high tolerance but very specialized niche) of D. acuminata give new insights into the ability of this species to remain in the upwelling circulation system. Higher shelf-ría exchanges in the Ría (RP) with more dense and persistent D. acuminata blooms reveal the relevance of transient event-scales and species- and site-specific characteristics to the fate of these blooms. Earlier statements about simple linear relationships between average upwelling intensities and the recurrence of Harmful algae bloom (HAB) events in the Galician Rías Baixas are questioned.

Syntopic species interact with large boreal mammals' response to anthropogenic landscape change

Landscape change alters species' distributions, and understanding these changes is a key ecological and conservation goal. Species-habitat relationships are often modelled in the absence of syntopic species, but niche theory and emerging empirical research suggests heterospecifics should entrain (and statistically explain) variability in distribution, perhaps synergistically by interacting with landscape features. We examined the effects of syntopic species in boreal mammals' relationship to landscape change, using three years of camera-trap data in the western Nearctic boreal forest. Using an information-theoretic framework, we weighed evidence for additive and interactive variables measuring heterospecifics' co-occurrence in species distribution models built on natural and anthropogenic landscape features. We competed multiple hypotheses about the roles of natural features, anthropogenic features, predators, competitors, and species-habitat interaction terms in explaining relative abundance of carnivores, herbivores, and omnivores/scavengers. For most species, models including heterospecifics explained occurrence frequency better than landscape features alone. Dominant predator (wolf) occurrence was best explained by prey, while prey species were explained by apparent competitors and subdominant predators. Evidence for interactions between landscape features and heterospecifics was strong for coyotes and wolves but variable for other species. Boreal mammals' spatial distribution is a function of heterospecific co-occurrence as well as landscape features, with synergistic effects observed for most species. Understanding species' responses to anthropogenic landscape change thus requires a multi-taxa approach that incorporates interspecific relationships, enabling better inference into underlying processes from observed patterns.

Contrasting patterns from two invasion fronts suggest a niche shift of an invasive predator of native bees

Background

The accuracy of predictions of invasive species ranges is dependent on niche similarity between invasive and native populations and on our ability to identify the niche characteristics. With this work we aimed to compare the niche dynamics of two genetically related invasive populations of Vespa velutina (an effective predator of honeybees and wild pollinators), in two distinct climatic regions, one in central Europe and another one in the north-western Iberian Peninsula, and hence to identify uninvaded regions susceptible to invasion.

Methods

Niche dynamics and shifts of V. velutina were assessed by comparing the environmental niches of the native and of the two invasive populations, using climatic, topographic and land use variables. We also ran reciprocal distribution models using different algorithms and records from both native and invasive ranges to compare model predictions and estimate which regions are at a greater risk of being invaded.

Results

An apparent niche shift was detected in the population of the NW of Iberian Peninsula, where the species is living under environmental conditions different from the native niche. In central Europe, large suitable areas remain unoccupied. The fact that both invasive populations are well established, despite occupying environmentally distinct regions indicates that V. velutina has a high ability to successfully invade different environmental envelopes from those existing in its native range. For example, in north-western Iberian Peninsula the species is now thriving out of its native niche limits. Moreover, the large extent of still unoccupied environmental space with similar conditions to those used by the species in its native range suggests that there is still a large area of central and eastern Europe that can be potentially invaded by the species.

Niche differentiation of Dinophysis acuta and D. acuminata in a stratified fjord

Dinophysis acuta and D. acuminata are associated with lipophilic toxins in Southern Chile. Blooms of the two species coincided during summer 2019 in a highly stratified fjord system (Puyuhuapi, Chilean Patagonia). High vertical resolution measurements of physical parameters were carried out during 48 h sampling to i) explore physiological status (e.g., division rates, toxin content) and ii) illustrate the fine scale distribution of D. acuta and D. acuminata populations with a focus on water column structure and co-occurring plastid-bearing ciliates. The species-specific resources and regulators defining the realized niches (sensu Hutchinson) of the two species were identified. Differences in vertical distribution, daily vertical migration and in situ division rates (with record values, 0.76 d^-1, in D. acuta), in response to the environmental conditions and potential prey availability, revealed their niche differences. The Outlying Mean Index (OMI) analysis showed that the realized niche of D. acuta (cell maximum 7 × 10³ cells L^-1 within the pycnocline) was characterized by sub-surface estuarine waters (salinity 23 - 25), lower values of turbulence and PAR, and a narrow niche breath. In contrast, the realized niche of D. acuminata (cell maximum 6.8 × 10³ cells L^-1 just above the pycnocline) was characterized by fresher (salinity 17 - 20) outflowing surface waters, with higher turbulence and light intensity and a wider niche breadth. Results from OMI and PERMANOVA analyses of co-occurring microplanktonic ciliates were compatible with the hypothesis of species such as those from genera Pseudotontonia and Strombidium constituting an alternative ciliate prey to Mesodinium. The D. acuta cell maximum was associated with DSP (OA and DTX-1) toxins and pectenotoxins; that of D. acuminata only with pectenotoxins. Results presented here contribute to a better understanding of the environmental drivers of species-specific blooms of Dinophysis and management of their distinct effects in Southern Chile.

Naming the untouchable - environmental sequences and niche partitioning as taxonomical evidence in fungi

Due to their submerged and cryptic lifestyle, the vast majority of fungal species are difficult to observe and describe morphologically, and many remain known to science only from sequences detected in environmental samples. The lack of practices to delimit and name most fungal species is a staggering limitation to communication and interpretation of ecology and evolution in kingdom Fungi. Here, we use environmental sequence data as taxonomical evidence and combine phylogenetic and ecological data to generate and test species hypotheses in the class Archaeorhizomycetes (Taphrinomycotina, Ascomycota). Based on environmental amplicon sequencing from a well-studied Swedish pine forest podzol soil, we generate 68 distinct species hypotheses of Archaeorhizomycetes, of which two correspond to the only described species in the class. Nine of the species hypotheses represent 78% of the sequenced Archaeorhizomycetes community, and are supported by long read data that form the backbone for delimiting species hypothesis based on phylogenetic branch lengths.

Soil fungal communities are shaped by environmental filtering and competitive exclusion so that closely related species are less likely to co-occur in a niche if adaptive traits are evolutionarily conserved. In soil profiles, distinct vertical horizons represent a testable niche dimension, and we found significantly differential distribution across samples for a well-supported pair of sister species hypotheses. Based on the combination of phylogenetic and ecological evidence, we identify two novel species for which we provide molecular diagnostics and propose names. While environmental sequences cannot be automatically translated to species, they can be used to generate phylogenetically distinct species hypotheses that can be further tested using sequences as ecological evidence. We conclude that in the case of abundantly and frequently observed species, environmental sequences can support species recognition in the absences of physical specimens, while rare taxa remain uncaptured at our sampling and sequencing intensity.

Mountain goat survival and mortality during a period of increased puma abundance in the Black Hills, South Dakota

We investigated survival and cause-specific mortality for a mountain goat (Oreamnos americanus) population during a period when the puma (Puma concolor) population was growing in the Black Hills, South Dakota, 2006–2018. We obtained survival data from 47 adult goats (n = 33 females, n = 14 males). Annual survival varied from 0.538 (95% CI [0.285–0.773]) to 1.00 (95% CI [1.00–1.00]) and puma predation was the primary cause-specific mortality factor over a 12-year period. Cumulative hectares of mountain pine beetle (Dendroctonus ponderosae) disturbance was a covariate of importance (w_i = 0.972; β = 0.580, 95% CI [0.302–0.859]) influencing survival. To our knowledge, this is the first account of puma being the primary mortality factor of mountain goats over a long-term study. The Black Hills system is unique because we could examine the expanded realized niche of puma in the absence of other large carnivores and their influence on mountain goats. We hypothesize that puma were being sustained at higher densities due to alternate prey sources (e.g., white-tailed deer; Odocoileous virginianus) and this small population of mountain goats was susceptible to predation by one or several specialized puma in the Black Hills. However, we also hypothesize a changing landscape with increased tree mortality due to insect infestation provided conditions for better predator detection by goats and increased survival. Alternatively, open canopy conditions may have increased understory forage production potentially increasing mountain goat survival but we did not evaluate this relationship. Survival and mortality rates of mountain goats should continue to be monitored as this small population may be highly susceptible to population declines due to slow growth rates.

Fundamental niche unfilling and potential invasion risk of the slider turtle Trachemys scripta

Background

How species colonize new environments is still a fundamental question in ecology and evolution, assessable by evaluating range characteristics of invasive species. Here we propose a model approach to evaluate environmental conditions and species features to predict niche changes in non-equilibrium contexts. It incorporates potentially range-limiting processes (fundamental niche), hence allowing for better predictions of range shifts, differentiation of analog and non-analog conditions between the native and non-native (invaded) ranges, and identification of environmental conditions not currently available but likely in the future. We apply our approach with the worldwide invasive slider-turtle Trachemys scripta.

Methods

We estimated the native and non-native realized niches of T. scripta and built its fundamental niche based on key features of the turtle’s temperature physiological tolerance limits and survival-associated factors. We next estimated response functions adjusted to the physiological predictor variables and estimated habitat suitability values, followed by a comprehensive set of analyses and simulations to compare the environmental conditions occupied by T. scripta (at its native and non-native ranges).

Results

Climatic space analysis showed that the T. scripta’s non-native realized niche is 28.6% greater than the native one. Response curves showed that it does not use its entire range of temperature tolerances (density curves for native: 5.3–23.7 °C and non-native: 1.7–28.4 °C ranges). Whether considering the mean temperature of the warmest or the coldest quarter, it occupies a wider range of temperatures along its non-native distribution. Results of the response curves for worldwide (global) and across Mexico (regional) comparisons showed it occupies analog and non-analog conditions between its native and invaded ranges, exhibiting also unoccupied suitable climatic conditions.

Discussion

We demonstrate that T. scripta occupies a wider subset of its fundamental niche along its non-native range (within its physiological tolerances), revealing that the species observed niche shift corresponds to a different subset of its fundamental niche (niche unfilling). We also identified suitable environmental conditions, globally and regionally, where the slider turtle could potentially invade. Our approach allows to accurately predict niche changes in novel or non-equilibrium contexts, which can improve our understanding about ecological aspects and geographic range boundaries in current and potential invasions.

Interspecific information on predation risk affects nest site choice in a passerine bird

Background

Breeding site choice constitutes an important part of the species niche. Nest predation affects breeding site choice, and has been suggested to drive niche segregation and local coexistence of species. Interspecific social information use may, in turn, result in copying or rejection of heterospecific niche characteristics and thus affect realized niche overlap between species. We tested experimentally whether a migratory bird, the pied flycatcher Ficedula hypoleuca, collects information about nest predation risk from indirect cues of predators visiting nests of heterospecific birds. Furthermore, we investigated whether the migratory birds can associate such information with a specific nest site characteristic and generalize the information to their own nest site choice.

Results

Our results demonstrate that flycatchers can use the fate of heterospecific nesting attempts in their own nest site choice, but do so selectively. Young flycatcher females, when making the decision quickly, associated the fate of an artificial nest with nest-site characteristics and avoided the characteristic associated with higher nest predation risk.

Conclusions

Copying nest site choices of successful heterospecifics, and avoiding choices which led to failed attempts, may amplify or counter effects of nest predation on niche overlap, with important consequences for between-species niche divergence-convergence dynamics, species coexistence and predator-prey interactions.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1301-3) contains supplementary material, which is available to authorized users.

Recolonizing wolves influence the realized niche of resident cougars

BACKGROUND

Niche differentiation may betray current, ongoing competition between two sympatric species or reflect evolutionary responses to historic competition that drove species apart. The best opportunity to test whether ongoing competition contributes to niche differentiation is to test for behavioral shifts by the subordinate competitor in controlled experiments in which the abundance of the dominant competitor is manipulated. Because these circumstances are difficult to coordinate in natural settings for wide-ranging species, researchers seize opportunities presented by species reintroductions. We tested for new competition between reintroduced wolves and resident cougars in the Southern Yellowstone Ecosystem to assess whether wolves might be impacting the realized niche of sympatric cougars.

RESULTS

Between2002 and 2012, a period during which wolves increased from 15 to as high as 91 in the study area, cougars significantly increased the percentage of deer and decreased the percentage of elk in their diet in summer. Our top models explaining these changes identified elk availability, defined as the number of elk per wolf each year, as the strongest predictor of changing cougar prey selection. Both elk and deer were simultaneously declining in the system, though deer more quickly than elk, and wolf numbers increased exponentially during the same time frame. Therefore,we concluded that prey availability did not explain prey switching and that competition with wolves at least partially explained cougar prey switching from elk to deer. We also recorded 5 marked cougar kittens killed by wolves and 2 more that were killed by an undetermined predator. In addition, between 2005 and 2012, 9 adult cougars and 10 cougar kittens died of starvation, which may also be in part explained by competition with wolves.

CONCLUSIONS

Direct interspecific predation and shifting cougar prey selection as wolves increased in the system provided evidence for competition between recolonizing wolves and resident cougars. Through competition, recolonizing wolves have impacted the realized niche of resident cougars in the Southern Yellowstone Ecosystem (SYE), and current resident cougars may now exhibit a realized niche more reflective of an era when these species were previously sympatric in the Yellowstone Ecosystem.

The contribution of a niche-based approach to ecological risk assessment: using macroinvertebrate species under multiple stressors

We propose that a niche-based experimental approach at population level could be used to solve some uncertainties in traditional approaches in ecotoxicology. We tested this approach in the context of multiple stressors (i.e. chemical and physical) in a selection of six run-of-river reservoirs with different levels of sediment contamination and associated upstream and downstream river sites. A niche-based approach was tested using three functional traits (habitat, food preferences and body size) and discrepancy between the realized and theoretical niches. We first identified three groups of taxa and then recorded differences along the disturbance gradients, such as an increase in competition, a narrowing of spatial and trophic niche breadth (e.g. of Leuctra major and Gammarus pulex), a widening of spatial niche breadth (e.g. of Ephemerella ignita), a greater proportion of small individuals (e.g. of G. pulex) and a decreasing or an increasing (e.g. L. major) discrepancy between realized and theoretical niches.