Global change re-structures alpine plant communities under 15 years of warming, nitrogen, and snow addition: disentangling density independent and dependent effects

Global change is altering patterns of community assembly, with net outcomes dependent on species’ responses to the environment, both directly and mediated through biotic interactions. Here, we assess alpine plant community responses in a 15-year factorial nitrogen addition, warming and snow manipulation experiment. We used a dynamic competition model to estimate the density-dependent and independent processes underlying changes in species-group abundances over time. Density-dependent shifts in competitive interactions drove long-term changes in abundance of species-groups under global change. Density-independent processes were important when counteracting environmental drivers limited the growth response of the dominant species. Furthermore, competitive interactions shifted with environmental change, primarily with nitrogen, and drove non-linear abundance responses across environmental gradients. Our results highlight that global change can either reshuffle species hierarchies or further favor already dominant species; predicting which outcome will occur requires incorporating both density-dependent and independent mechanisms and how they interact across multiple global change factors.

A Single Intranasal Dose of Bacterial Therapeutics to Calves Confers Longitudinal Modulation of the Nasopharyngeal Microbiota

To address the emergence of antimicrobial-resistant pathogens in livestock, microbiome-based strategies are increasingly being sought to reduce antimicrobial use. Here, we describe the intranasal application of bacterial therapeutics (BTs) for mitigating bovine respiratory disease (BRD) and used structural equation modeling to investigate the causal networks after BT application. Beef cattle received i) an intranasal cocktail of previously characterized BT strains, ii) an injection of metaphylactic antibiotic tulathromycin or iii) intranasal saline. Despite being transient colonizers, inoculated BT strains induced longitudinal modulation of the nasopharyngeal bacterial microbiota while showing no adverse effect on animal health. The BT-mediated changes in bacteria included reduced diversity and richness and strengthened cooperative and competitive interactions. In contrast, tulathromycin increased bacterial diversity and antibiotic resistance, and disrupted bacterial interactions. Overall, a single intranasal dose of BTs can modulate the bovine respiratory microbiota, highlighting that microbiome-based strategies have the potential in being utilized to mitigate BRD in feedlot cattle.

Behavioural Competition in the Intertidal Shore Crab, Petrolisthes elongatus

<p>Competition is a well-documented ecological interaction that underpins community structures and much of population ecology. Physical characteristics such as size, age, sex and weaponry all have an important part to play in how an organism competes, and for many animals, competition is mediated by behavioural patterns. Outcomes of these competitive interactions are not only driven by these characteristics, but by the environmental conditions and external pressures that influence them. The focal species of my study is Petrolisthes elongatus (H. Milne Edwards, 1837), a porcellanid crab that aggregates in high densities among cobblestone beaches along the intertidal shores of New Zealand and Tasmania. They utilize rocks and crevices as shelter spaces to protect themselves from environmental and predation pressures, displaying variation in physical characteristics, such as sexual dimorphism and autotomy, as well as high levels of behavioural complexity. I used laboratory experiments with crabs collected from the field and placed them in shelter-limited tanks under the following comparisons; 1) adult and juvenile males, 2) males and females, 3) ovigerous and non-ovigerous females, and 4) autotomized and non-autotomized males. For each of these experiments I used three different environmental conditions; 1) a control high tide, 2) a low tide treatment (where water was drained from the experimental tank), and 3) with the presence of a predator, a juvenile spiny rock lobster (Jasus edwarsii). Each experiment was recorded for 8 hours, where time spent under shelter and shoving interactions among individuals were counted. In the adult vs. juvenile and male vs. female experiments, smaller individuals spent a significantly more time under shelter than larger conspecifics, but increasing size resulted in more time spent under shelter in the autotomized vs. non-autotomized experiment. In all experiments, smaller individuals initiated the least amount of competitive interactions, and each size class was more likely to displace a smaller individual from a shelter, than a larger one. There was no significant difference in the time spent under shelter between males and females, but ovigerous females and autotomized males spent significantly more time under shelter than their respective competitors. Males also engaged in more shoving interactions than females, with smaller classes of males displacing larger classes of females from shelter spaces. Ovigerous females also outcompeted non-ovigerous conspecifics in the large majority of competitive interactions, and autotomized individuals engaged in significantly more contests than non-autotomized conspecifics. In all experiments, the presence of a predator had no effect on the number of shoving interactions and only resulted in an increase in time spent under shelter for individuals in the male vs. female and ovigerous vs. non-ovigerous experiments. A field survey on body to cheliped size ratios, autotomy and claw punctures counts was also conducted in support of the shelter-competition experiments. Crabs were collected over a one-month period in November 2018, brought back to the lab to be sexed, measured (Carapace Width, BW; and Cheliped Length, CL) and then surveyed for autotomy and claw puncture wounds. Juveniles of both sex (BW =</p>

Behavioural Competition in the Intertidal Shore Crab, Petrolisthes elongatus

<p>Competition is a well-documented ecological interaction that underpins community structures and much of population ecology. Physical characteristics such as size, age, sex and weaponry all have an important part to play in how an organism competes, and for many animals, competition is mediated by behavioural patterns. Outcomes of these competitive interactions are not only driven by these characteristics, but by the environmental conditions and external pressures that influence them. The focal species of my study is Petrolisthes elongatus (H. Milne Edwards, 1837), a porcellanid crab that aggregates in high densities among cobblestone beaches along the intertidal shores of New Zealand and Tasmania. They utilize rocks and crevices as shelter spaces to protect themselves from environmental and predation pressures, displaying variation in physical characteristics, such as sexual dimorphism and autotomy, as well as high levels of behavioural complexity. I used laboratory experiments with crabs collected from the field and placed them in shelter-limited tanks under the following comparisons; 1) adult and juvenile males, 2) males and females, 3) ovigerous and non-ovigerous females, and 4) autotomized and non-autotomized males. For each of these experiments I used three different environmental conditions; 1) a control high tide, 2) a low tide treatment (where water was drained from the experimental tank), and 3) with the presence of a predator, a juvenile spiny rock lobster (Jasus edwarsii). Each experiment was recorded for 8 hours, where time spent under shelter and shoving interactions among individuals were counted. In the adult vs. juvenile and male vs. female experiments, smaller individuals spent a significantly more time under shelter than larger conspecifics, but increasing size resulted in more time spent under shelter in the autotomized vs. non-autotomized experiment. In all experiments, smaller individuals initiated the least amount of competitive interactions, and each size class was more likely to displace a smaller individual from a shelter, than a larger one. There was no significant difference in the time spent under shelter between males and females, but ovigerous females and autotomized males spent significantly more time under shelter than their respective competitors. Males also engaged in more shoving interactions than females, with smaller classes of males displacing larger classes of females from shelter spaces. Ovigerous females also outcompeted non-ovigerous conspecifics in the large majority of competitive interactions, and autotomized individuals engaged in significantly more contests than non-autotomized conspecifics. In all experiments, the presence of a predator had no effect on the number of shoving interactions and only resulted in an increase in time spent under shelter for individuals in the male vs. female and ovigerous vs. non-ovigerous experiments. A field survey on body to cheliped size ratios, autotomy and claw punctures counts was also conducted in support of the shelter-competition experiments. Crabs were collected over a one-month period in November 2018, brought back to the lab to be sexed, measured (Carapace Width, BW; and Cheliped Length, CL) and then surveyed for autotomy and claw puncture wounds. Juveniles of both sex (BW =</p>

Trophic niche overlap between coyotes and gray foxes in a temperate forest in Durango, Mexico

Resource partitioning, and especially dietary partitioning, is a mechanism that has been studied for several canid species as a means to understand competitive relationships and the ability of these species to coexist. Coyotes (Canis latrans) and gray foxes (Urocyon cinereoargenteus) are two canid species that are widely distributed, in Mexico, and they are sympatric throughout most of their distribution range. However, trophic dynamic and overlap between them have not been thoroughly studied. In order to better understand their ecological relationship and potential competitive interactions, we studied the trophic niche overlap between both canids in a temperate forest of Durango, Mexico. The results are based on the analysis of 540 coyote and 307 gray fox feces collected in 2018. Both species consumed a similar range of food items, but the coyote consumed large species while the gray fox did not. For both species, the most frequently consumed food categories throughout the year and seasonally were fruit and wild mammals (mainly rodents and lagomorphs). Coyotes had higher trophic diversity in their annual diet (H’ = 2.33) than gray foxes (H’ = 1.80). When analyzing diets by season, trophic diversity of both species was higher in winter and spring and tended to decrease in summer and autumn. When comparing between species, this parameter differed significantly during all seasons except for summer. Trophic overlap throughout the year was high (R0 = 0.934), with seasonal variation between R0 = 0.821 (autumn) and R0 = 0.945 (spring). Both species based their diet on the most available food items throughout each season of the year, having high dietary overlap which likely can lead to intense exploitative competition processes. However, differences in trophic diversity caused by differential prey use can mitigate competitive interactions, allowing these different sized canid species to coexist in the study area.

Grazing weakens competitive interactions between active methanotrophs and nitrifiers modulating greenhouse-gas emissions in grassland soils

Grassland soils serve as a biological sink and source of the potent greenhouse gases (GHG) methane (CH4) and nitrous oxide (N2O). The underlying mechanisms responsible for those GHG emissions, specifically, the relationships between methane- and ammonia-oxidizing microorganisms in grazed grassland soils are still poorly understood. Here, we characterized the effects of grazing on in situ GHG emissions and elucidated the putative relations between the active microbes involving in methane oxidation and nitrification activity in grassland soils. Grazing significantly decreases CH4 emissions while it increases N2O emissions basing on 14-month in situ measurement. DNA-based stable isotope probing (SIP) incubation experiment shows that grazing decreases both methane oxidation and nitrification processes and decreases the diversity of active methanotrophs and nitrifiers, and subsequently weakens the putative competition between active methanotrophs and nitrifiers in grassland soils. These results constitute a major advance in our understanding of putative relationships between methane- and ammonia-oxidizing microorganisms and subsequent effects on nitrification and methane oxidation, which contribute to a better prediction and modeling of future balance of GHG emissions and active microbial communities in grazed grassland ecosystems.

Intraspecific antagonism through viral toxin encoded by chronic Sulfolobus spindle-shaped virus

Virus–host interactions evolve along a symbiosis continuum from antagonism to mutualism. Long-term associations between virus and host, such as those in chronic infection, will select for traits that drive the interaction towards mutualism, especially when susceptible hosts are rare in the population. Virus–host mutualism has been demonstrated in thermophilic archaeal populations where Sulfolobus spindle-shaped viruses (SSVs) provide a competitive advantage to their host Sulfolobus islandicus by producing a toxin that kills uninfected strains. Here, we determine the genetic basis of this killing phenotype by identifying highly transcribed genes in cells that are chronically infected with a diversity of SSVs. We demonstrate that these genes alone confer growth inhibition by being expressed in uninfected cells via a Sulfolobus expression plasmid. Challenge of chronically infected strains with vector-expressed toxins revealed a nested network of cross-toxicity among divergent SSVs, with both broad and specific toxin efficacies. This suggests that competition between viruses and/or their hosts could maintain toxin diversity. We propose that competitive interactions among chronic viruses to promote their host fitness form the basis of virus–host mutualism. This article is part of the theme issue ‘The secret lives of microbial mobile genetic elements’.

Ecological theory of mutualism: Robust patterns of stability and thresholds in two-species population models

Mutualisms are ubiquitous in nature, provide important ecosystem services, and involve many species of interest for conservation. Theoretical progress on the population dynamics of mutualistic interactions, however, comparatively lagged behind that of trophic and competitive interactions, leading to the impression that ecologists still lack a generalized framework to investigate the population dynamics of mutualisms. Yet, over the last 90 years, abundant theoretical work has accumulated, ranging from abstract to detailed. Here, we review and synthesize historical models of two-species mutualisms. We find that population dynamics of mutualisms are qualitatively robust across derivations, including levels of detail, types of benefit, and inspiring systems. Specifically, mutualisms tend to exhibit stable coexistence at high density and destabilizing thresholds at low density. These dynamics emerge when benefits of mutualism saturate, whether due to intrinsic or extrinsic density-dependence in intraspecific processes, interspecific processes, or both. We distinguish between thresholds resulting from Allee effects, low partner density, and high partner density, and their mathematical and conceptual causes. Our synthesis suggests that there exists a robust population dynamic theory of mutualism that can make general predictions.