Biodiversity Change group
Intertwined destinies, a new Art–Science project
The socio-ecological implications of glacier extinction
Welcome to Nora Khelidj, new PhD student in the group!
Qu’arrive-t-il à la biodiversité lorsque les glaciers disparaissent ? What happens to biodiversity when glaciers disappear?
Open PhD position in Environmental Sciences
Synergism between facilitation and mutualism
On one side, facilitation between plants promotes biodiversity and supports the structure of ecological networks; on the other, richness of plant and insect species increases ecosystem functions. However, we still don’t know the direct and indirect contribution of facilitation and biodiversity to ecosystem functioning and pollination networks.
We conducted a field experiment to show how facilitation by nurse plants and understorey diversity synergistically increase pollinator diversity and support mutualistic networks, revealing a novel mechanism underlying the consequences of biodiversity change.
Beyond competition: facilitation motifs and biodiversity maintenance
Previous studies exploring the mechanisms that promote biodiversity have tended to focus primarily on competition, so we know little about how positive and negative interactions may interact with one another and in turn shape biodiversity.
In this PNAS paper, we report not only that ecological network motifs involving the interplay of facilitation and competition are overrepresented within plant communities, but also that their prevalence consistently predicts biodiversity. By discovering a novel pattern of species coexistence based on competition between facilitated species and facilitation between inferior competitors, our study represents a key step forward in understanding the maintenance of Earth’s biodiversity. This means that competition alone does not explain the astonishing diversity of plants in alpine ecosystems, which is instead better understood when looking at how facilitation and competition combines, balancing each others. Surprisingly, we found that competition can lead to facilitation, likewise facilitation can create competition. This can happen when, for instance, one plant outcompetes two other plants that then facilitate each other, or when one plant facilitates two plants that begin competing with each other.
Many other natural and social systems involve both cooperative and antagonistic interactions among many interconnected members, these findings may prompt exploration of similar patterns and processes in fields beyond plant community ecology.
Glacier retreat and biodiversity change
The constructive role of ecosystem engineers and diversity
A cardinal notion in ecology is that the environment influences biological populations. Yet, organisms have the power to create and modify their surrounding environment, in turn influencing other populations and ecosystem processes. Using mountain plant communities and flower visitor networks as a case study, we developed an empirical approach to quantify changes in ecosystem functioning due to ecosystem engineers and associated biodiversity. The results of our synthesis paper show how facilitation and complementarity effects between plants increase ecosystem functioning across trophic levels. We found both positive and negative associational effects between plants depending on ecosystem engineer identity, indicating both pollination facilitation and interference. In both cases, patches supported by ecosystem engineers increased phylogenetic and functional diversity of flower visitors. Furthermore, complementarity effects between engineers and associated plants were positive for flower visitation rates. Our study reveals that plant facilitation can enhance the strength of biodiversity–ecosystem functioning relationships, with complementarity between plants for attracting more and diverse flower visitors being the likely driver.We also reveal a novel mechanism underlying the consequences of biodiversity change and the constructive impact of biological populations on their environment.
Unveiling trophic interactions and network structure with eDNA
The functioning of ecosystems is being impacted through the anthropogenic disassembly of community structure. Species interactions, the structural foundation, have evolved through millennia, however, are rapidly disappearing or reconnecting (rewiring) in novel ways. Creating a mechanism to capture not only biodiversity changes, but also to quantify species interactions is key to interpreting the cascading impacts of rewiring systems. Here, we develop molecular ecological network analyses (MENA) to capture both; and evaluate MENA as a comprehensive ecosystem assessment tool in a well-studied Californian reserve. Through the combination of rapidly advancing high-throughput sequencing techniques, which generates a high taxonomic resolution of DNA within the environment (eDNA), and network analyses to quantify and unveil the patterns of trophic interactions, we can estimate the future impacts of shifting community dynamics. Using fecal eDNA to identify the mammal and plant diets of mammalian carnivore, omnivore, and herbivore species, we assemble a real-world, multitrophic food-web network to assess the community. We demonstrate MENA’s ability to accurately capture the broader biodiversity of the area, key species, patterns of trophic interactions, and the structure within the community at an exceptional taxonomic resolution, thereby improving traditional food web analysis and providing a promising toolkit for biodiversity and ecosystem management.
Plant facilitation drives evolutionary trajectories
The notion that the environment influences evolution is well grounded in biology, greatly summarized by the popular expression of Hutchinson "The Ecological Theater and the Evolutionary Play". Yet, the fact that a specific component of the environment as the biotic space created by facilitation could influence evolution was not very well understood. Even less known was whether differences in DNA would emerge at the scale of plant facilitation processes, which is in the order of meters. By integrating field data with greenhouse experiments and genomic analysis, in this study we now unveil that facilitation by foundation species changes the evolutionary trajectories of associated plant species. Differences in DNA emerges at the community scale, between plants growing just few meters apart. We show that certain plants are locally adapted to the microhabitat conditions, while other plants undergo plastic adaptability (plasticity). Our results indicate that plant facilitation can affect both genotypic differentiation and phenotypic variation, providing a first evidence of the role of plant interaction actresses in the eco-evo dynamics.
Costs and benefits of ecosystem engineer facilitation
Studies exploring the mechanisms that promote stability of ecological communities focus mainly on one interaction type at the time. Recent results suggest that facilitative interactions between two species can involve both costs and benefits, while other indicate that facilitation is mainly costly for ‘facilitator’ species. However, little work to date has explored how costs and benefits of facilitative interactions may be mediated by a different trophic level, despite increasing evidence that a third species modifies the outcome of interactions between two species. We found that not only that direct costs of facilitation are accompanied by indirect benefits mediated by pollinators, but also that ‘facilitated’ plant species can be beneficial for ‘benefactor’ species via increasing pollinator attractiveness. Furthermore, the influence of ‘facilitated’ species and pollinator diversity on fitness components of ‘benefactor’ species suggests a mechanism that may promote the stability of facilitative interactions. By providing novel evidence about the evolutionary ecology of species interactions at the community level, this study represents a key step forward in understanding the features of biodiversity. [paper] [data & code]
Plant networks and the organisation of biodiversity
The biosphere is estimated to host about 450'000 plant species, but how many different species can coexist in a given community remains largely unknown. Plant communities are usually characterised by species composition and abundance. Yet, they underlie a multitude of complex interactions that we have only recently started unveiling and we are still far from understanding. In this Grubb Review, we synthesise recent methods and results of plant–plant networks, particularly focusing on the systemic mechanisms of plant–plant network assembly and their consequences for diversity patterns. We propose novel opportunities for advancing plant ecology by using ecological networks that encompass different ecological levels and spatio-temporal scales, and incorporate more biological information. Embracing networks of interactions among plants can shed new light on mechanisms driving evolution and ecosystem functioning, helping us to mitigate diversity loss. [paper]
Plant–plant facilitation expands the distribution of species
Understanding the processes that underlie patterns of species distribution is a cornerstone of ecology, which is increasingly relevant for predicting community assembly in a changing climate. Species distributions are driven by abiotic conditions that filter species with specific traits and physiological tolerances and match them with their suitable environment. Plant–plant interactions can constrict (through competition) or loosen (through facilitation) the strength of these environmental filters, which in turn inhibit or enhance establishment and recruitment of plant species at a finer spatial scale. We found that facilitation is important for loosening environmental filters (especially climatic filters such as temperature and precipitation), ultimately enhancing species occurrence beyond their physiological optimum. Our results highlight the importance of facilitation for alleviating physiological strain (in support of the strain hypothesis) and mediating regional species distributions, which has implications for understanding species movements and community assembly at larger-scales under hotter and drier climates. [paper]
The role of plant facilitation in pollination networks
Plants grow in communities where they interact with other plants and with other living organisms such as pollinators. On the one hand, studies of plant–plant interactions rarely consider how plants interact with other trophic levels such as pollinators. On the other, studies of plant–animal interactions rarely deal with interactions within trophic levels such as plant–plant competition and facilitation. Thus, to what degree plant interactions affect biodiversity and ecological networks across trophic levels is poorly understood. We manipulated plant communities driven by foundation species facilitation and sampled plant–pollinator networks at fine spatial scale in a field experiment in Sierra Nevada, Spain. We found that plant–plant facilitation shaped pollinator diversity and structured pollination networks. Nonadditive effects of plant interactions on pollinator diversity and interaction diversity were synergistic in one foundation species networks while they were additive in another foundation species. Nonadditive effects of plant interactions were due to rewiring of pollination interactions. In addition, plant facilitation had negative effects on the structure of pollination networks likely due to increase in plant competition for pollination. Our results empirically demonstrate how different network types are coupled, revealing pervasive consequences of interaction chains in diverse communities. [paper] [data & code]
Trait-based assembly of plant networks
Plant ecology has always focused on interactions among species within communities. Ecological research has targeted the importance of negative interactions such as competition among plants for resources. But in the last years there is increasing interest in understanding how plants can cooperate with each other. This is particularly the case in harsh ecosystems like the alpine where some stress-tolerant plants contribute to ameliorate growing conditions for their neighbours. In our study, we analysed the spatial distribution of plants and modelled their associations to test how plant networks are formed and maintained in alpine vegetation. We collected data about the spatial location and the phenotype of thousands individual plants and analysed them with state-of-the-art computational model. We found that plant species were highly connected through many positive interactions. Dominant, stress-tolerant species were the most important plants for supporting the plant community network. The plant community network was more cohesive than expected by chance. This study reveals a new class of mechanisms underlying the formation of plant communities and has important implications for understanding the biodiversity of alpine vegetation. [paper] [data + code] [blog post]
The power of flowers for predicting pollination networks over time
Both plant and insect communities undergo phenological changes across the season, leading to seasonal changes in species diversity and interactions. Network theory offers important tools for understanding how groups of flowering plants and insects interact. However, most studies of plant–pollinator networks aggregate samples over time, masking phenological changes in the network over the growing season. Furthermore, estimates of biodiversity are derived from network observations, meaning that the ecological community is not assessed independently from the structure of the network. Understanding how biodiversity influences network structure over time is important for predicting how global change will affect the ecological processes shaping networks. In this study, we sampled the flower community, insect community, and the pollination network of a high Arctic dwarf-shrub ecosystem over the course of an entire growing season. We found that the flower community was a stronger predictor of network complexity and interaction diversity than the insect community. We suggest that studying networks at scales relevant to both plants and pollinators can provide insight into the mechanisms underlying network formation. This improved knowledge could help to better understand and predict the ongoing phenological changes in Arctic and alpine ecosystems. [paper]
The role of life history stage and ontogeny in the assembly of plant multilayer networks
As every child knows, plants grow from seeds and became adult through their lifetime. But when studying at ecological networks involving plants, we ecologists often look only at adult plants, hence overlooking a fundamental aspect of plants life such as seeds. We therefore do not know how ecological networks are organised over the course of an organism’s lifetime. This understanding is crucial for predicting the dynamics of interacting populations and communities across temporal scales. In this study we explored how life history stages such as seeds and adult plants contribute to the development and stability of plant multilayer networks. Our results show that life history and ontogeny affect the development of plant networks. Assembly of the seed community is stochastic while adult plants establishment is deterministic. With this study we also highlight the importance of mature plant communities for maintaining rare species populations and supporting the stability of ecological communities through time. [paper] [data & code] [blog post]
Plant interaction networks. Spatial dynamics, robustness and scaling up to pollinators
My PhD research in Ecology at the University of Zurich focused on integrating the ecology of plant–plant interactions with network theory. My thesis—“Plant interaction networks. Spatial dynamics, robustness and scaling up to pollinators”— addressed the challenge of applying a network-based approach to understand the effects of interactions among plant species such as competition and ecological facilitation on biodiversity. Initially, I focused on analysing networks on the basis of observational, spatial data and found that facilitation supported biodiversity and network development, while competition lead to network breakdown. I then developed a novel, biology-informed framework based on functional traits to analyse the resistance of plant facilitation networks to different environmental change scenarios. My next goal was to move towards an integration of species interactions occurring both within and across trophic-levels. Toward this end, I designed a field experiment to quantify the effects of plant–plant facilitation on plant–pollinator interactions. The results revealed that higher-order effects of plant facilitation can affect biodiversity and shape ecological networks. My thesis highlights the complexity and interdependence of ecological systems and the role positive plant interactions play in supporting the stability of communities. [thesis]
Effects of nitrogen deposition on soil microbial communities in forest ecosystems
Increasing nitrogen deposition has aroused large concerns because of its potential negative effects on forest ecosystems. Although microorganisms play a vital role in ecosystem carbon and nutrient cycling, the effect of N deposition on soil microbiota still remains unclear. We investigated the responses of microbial biomass and and microbial community composition to N deposition in forest ecosystems. In subtropical forests, N addition showed a significant negative effect on microbial biomass, community composition and arbuscular mycorrhizal fungi, while the effect of N addition was not significant in the temperate forests. Our findings suggest that N deposition may have negative influence on soil microorganisms and potentially alter carbon and nutrient cycling in subtropical forests. [paper]
Robustness of plant networks against species extinction following environmental change
In Mediterranean alpine ecosystems, plants cooperate with neighbouring plants to survive in such harsh environments. However, it is still unclear how environmental change affects networks of plant–plant interactions. We developed a novel framework to explore the resistance of plant interaction networks to drivers of environmental change. We combined field data including species traits and computer simulation and quantified the probabilities of environmental change causing species extinctions. We found that the response of plant interaction networks depended on the type of environmental change. The examined plant communities were more resistant to drought and temperature increase rather than nitrogen deposition. This study suggests that the fate of species and communities with the on-going global environmental change will depend on the main driver of environmental change and how this might affect the network of interacting species. Consequently, knowledge about species interaction networks in natural communities could improve our understanding of how ecosystems will respond to global change, which in turn may help to improve current conservation and restoration practices. [paper] [data] [code] [Blog post]
Life in harsh environments: Insect trait diversity changes with glacier recession
The richness and composition of arthropod communities vary with increasing glacier recession. However, patterns of functional traits are little explored. Characterising the functional trait diversity is crucial to understand the colonisation and survival of insect in such harsh environment. We found that the diversity of functional traits of insects increased with increasing glacier recession. There was no trait turnover but rather addition of new traits. The distribution of arthropods was driven by dispersal ability and foraging strategy. Our functional approach improves knowledge of the adaptive strategies of ground-dwelling arthropods colonising glacier surfaces and recently deglaciated terrains, which represent landforms quickly changing due to global warming. [paper]
The response of plant interaction networks to environmental change
What are the consequences of the adverse effects of climate warming on plants? In this issue of the PSC newsletter, I contribute with an example of my research activity as well as with the cover picture. Understanding the role of plant interactions, for instance in reducing species extinctions, for mediating the impact of environmental change on ecosystems is critical and urgent.
Feedbacks between plant and insect communities along a glacier-recession gradient
The composition of plant and insect communities changes in response to glacier recession. Nonetheless, mechanisms underlying plant–insect interactions change are poorly understood. We were interested in understanding how changes in plant and insect communities affected each other's development and their consequences for plant reproduction. We found that plant cover and diversity affected the structure of insect communities. In turn, pollinators regulated the variation of plant reproduction. We emphasise that plant–insect interactions are driven by feedbacks. This study indicates how the impact of glacier recession on the dynamic of alpine plant and insect communities is mediated by biotic interactions. [paper]
Consequences of glacier recession for the structure and dynamic of plant–insect networks
We just published my first paper arising from my master thesis. In this study, we examined how glacier recession affected the assembly of plant–insect networks and its functional implications for ecosystem stability. We found that the structure of ecological networks changed along the glacier-recession gradient. Interactions shifted from pollination networks to functionally diversified food webs. This study provides new insight into the initial steps of formation of plant–insect networks and sheds light on the consequences of environmental change for the structure and dynamic of ecological networks. [paper]