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Irreversible Processes in Ecological Evolution

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Category: Application Area

Date/Time: January 29, 2019 - January 31, 2019

Location: Santa Fe Institute (Noyce Conference Room) Upload a group photo

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Agenda/Schedule
Click each agenda item's title for more information.
Tuesday, January 29, 2019
8:15 am - 8:45 am Day 1 Continental Breakfast (outside SFI Noyce Conference Room)
8:45 am - 9:15 am Welcome & introduction around the room - Jacopo Grilli (ICTP), Dervis Can Vural (Univ. Notre Dame)
9:15 am - 9:30 am Working Group Context Framing - Jacopo Grilli (ICTP) Download Presentation
9:30 am - 10:00 am WG Context under Adaptation, Aging, Arrow of Time project - Amy P Chen (SFI), David Krakauer (SFI) Download Presentation
10:00 am - 11:00 am Pathogen diversity and negative frequency-dependent selection: consequences for intervention - Pamela Martinez (Harvard) Download Presentation
11:15 am - 12:15 pm Emergent structure and dynamics in stochastic, open, competitive communities - Annette Ostling (Univ. Michigan) Download Presentation (Encrypted)
12:15 pm - 12:45 pm Open discussion & reflection time I
12:45 pm - 1:30 pm Day 1 Lunch (outside SFI Noyce Conference Room)
1:30 pm - 2:30 pm Natural selection, population cycles, and climate change in forest insects - Greg Dwyer (Univ. Chicago) Download Presentation
2:30 pm - 3:30 pm Cooperative growth and cell-cell aggregation in marine bacteria - Otto Cordero (MIT)
3:30 pm - 3:45 pm Day 1 PM Break
3:45 pm - 4:45 pm Statistical mechanics of microbiomes - Robert Marsland (Boston Univ.) Download Presentation (Encrypted)
4:45 pm - 5:15 pm Open discussion & reflection time II
Wednesday, January 30, 2019
8:15 am - 8:45 am Day 2 Continental Breakfast (outside SFI Noyce Conference Room)
8:45 am - 9:45 am Phenotypic evolution in the Anthropocene - Priyanga Amarasekare (UCLA) Download Presentation
9:45 am - 10:45 am Irreversible processes in ecological networks - Fernanda Valdovinos (Univ. Michigan) Download Presentation
10:45 am - 11:00 am Day 2 AM Break
11:00 am - 12:00 pm Are changes in species interactions and their ecosystem consequences irreversible? - Samraat Pawar (Imperial College London) Download Presentation (Encrypted)
12:00 pm - 12:30 pm Open discussion & reflection time III
12:30 pm - 1:30 pm Day 2 Lunch (outside SFI Noyce Conference Room)
1:30 pm - 2:30 pm Higher-order interactions, stability across timescales, and macroecological patterns - Jacopo Grilli (ICTP) Download Presentation
2:30 pm - 3:30 pm Population genetics of low-probability transitions - Stephen Proulx (UCSB) Download Presentation
3:30 pm - 3:45 pm Day 2 PM Break
3:45 pm - 4:15 pm Day 2 Reflection time
4:15 pm - 5:15 pm Day 2 Open discussion
Thursday, January 31, 2019
8:15 am - 8:45 am Day 3 Continental Breakfast (outside SFI Noyce Conference Room)
8:45 am - 9:45 am Cooperation and specialization in dynamic fluids - Dervis Can Vural (Univ. Notre Dame) Download Presentation
9:45 am - 10:00 am Day 3 Reflection time
10:00 am - 10:15 am Day 3 AM Break
10:15 am - 10:45 am Collaborative Platform Work Time: references, reference note, presentation upload, additional reflection & commenting on each other’s reflection
10:45 am - 12:00 pm Day 3 Open discussion
12:00 pm - 1:00 pm Day 3 Lunch (outside SFI Noyce Conference Room); Adjourn

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Meeting Synopsis

An ink drop placed in water will dissolve and homogenize, never to return back to its original state. Many-body processes involving stochastic forces universally and irreversibly lead to entropy maximizing distributions. This working group aims to ask what the analog of ‘dissolving ink’ is in the context of ecological evolution. Specifically, this WG will explore irreversible changes in the ecological interaction structure and their consequences. Of particular interest are theoretical frameworks that incorporate dynamics as well as experimental approaches that can track irreversible transitions in strongly interacting populations. Key foci for this WG are the directionality of the coevolution of interspecific interactions and ecological transitions, and the synthetic control of such transitions.

Abstracts by Presenters

Samraat Pawar (Imperial College London) - Are changes in species interactions and their ecosystem consequences irreversible?[edit source]

All interactions between individuals of the same or different species (populations) are metabolically-constrained. That is, the rate of an individual's energy use (metabolic rate) sets the rate of interactions with other individuals. In this talk, I will first describe the relationship between metabolic and species interaction rates as a function of the physical environment as well as the organism's mass, using ecological metabolic theory. I will then describe the effects of (metabolically-constrained) species interactions on the dynamics of ecosystems. Finally, I will consider whether changes in metabolically-constrained species interactions are irreversible.    

Dervis Can Vural (Univ. Notre Dame) - Cooperation and specialization in dynamic fluids[edit source]

Community ecology is built on the notion of interspecies interactions. The strengths of interactions are almost invariably taken as fixed parameters, which must either be measured or assumed. The few available models that do consider the formation and evolution of interactions, including some built by myself, are based on ad hoc definitions of fitness. In this talk I will present a first-principles approach to how interactions between and within species change. In this picture, the black box of "interspecies interactions" will be replaced with advection, diffusion, dispersal, chemical secretions and domain geometry. I will show that the fundamental laws of fluid dynamics and the physical parameters describing the fluid habitat determine whether species will be driven towards individualism, social cooperation, specialization, or extinction. I will end my talk by proposing ways to tailoring the interaction structure of a microbial community by manipulating flow patterns and domain geometry.    

Otto Cordero (MIT) - Cooperative growth and cell-cell aggregation in marine bacteria[edit source]

Bacterial cooperation, whereby cells secrete compounds that can facilitate the growth of neighboring cells, has been extensively studied through the lens of evolutionary biology. However, the environmental implications of cooperation and the ecological scenarios under which it takes place remain much less understood. In this talk I will discuss the conditions under which cooperative growth emerges in microbial populations that degrade complex organic materials in the ocean. I will show that organisms that are poor secretors of hydrolytic enzymes use chemotactic behavior to form cell-cell aggregates that enable individuals to increase local concentrations and efficiently uptake the solubilized organic matter. By contrast, when organisms secrete highly active enzymes dynamics turn competitive, cells avoid aggregation and the efficiency of carbon uptake drops. I will also discuss the theoretical limits of aggregation and how bacterial isolates from the ocean overcome these limits in the laboratory by developing multicellular behaviors. I will back up these results with theory, data from individual based models and experiments with natural isolates. Finally, I will discuss the potential role of social cheaters in the natural environment, based on a study with hundreds of micro-scale particle colonization experiments in natural seawater.

Annette Ostling (Univ. Michigan) - Emergent structure and dynamics in stochastic, open, competitive communities[edit source]

Here I describe recent theoretical work by my lab looking at the emergent patterning in models where niche differentiation acts in concert with drift and immigration, as well as empirical work looking for that patterning. The results of our study of “stochastic niche communities” provides further generalization of the recent theoretical developments suggesting that niche differentiation may actually lead to clusters of species similar in traits, in contrast with traditional expectations of even spacing or overdispersion. These traditional expectations are derived from models ignoring stochasticity and immigration as well as other factors. I will review both classical and more recent theoretical developments along the way. We also find niche differentiation plays a more complex role in species persistence in stochastic niche communities than classically expected, enhancing persistence of a select few species, and lessening the persistence of others. We have also demonstrated the occurrence of this pattern of clusters across an array of niche mechanisms, and groundtruthed metrics for its detection in field data. Finally, we have applied our metrics to trait and abundance data for tree species in the 50 ha plot on Barro Colorado Island, and find significant clusters in four traits linked to niche axes. I will discuss all of these developments and also highlight connections to the question of irreversibility in the ecological and evolutionary dynamics of competing species.

Jacopo Grilli (ICTP) - Higher-order interactions, stability across timescales, and macroecological patterns[edit source]

The difficulty of reconciling the staggering biodiversity found in tropical rainforests with classical theories of resource partitioning has led ecologists to explore neutral theories of coexistence, in which all species are assumed to have the same physiological parameters, and variations in species abundance arise from stochastic fluctuations. Here we propose a theory of coexistence in which all species have different physiological rates, and interact with each other through a network of competitive interactions. We show that our models produce robust coexistence of many species even when parameters are drawn at random. Importantly, the dynamical stability of our models is due to higher-order interactions — interactions involving more than two species at a time. Moving from deterministic to stochastic models, we find that the presence of higher-order interactions, which make equilibrium points attractive, dramatically increases the time to extinction in isolated systems, allowing for the prolonged coexistence of species. When we let the system evolve, we recover many empirically observed macroecological patterns.

Fernanda Valdovinos (Univ. Michigan) - Irreversible processes in ecological networks[edit source]

Inspired by the exciting topic of this workshop, my talk will present research by my group that have found irreversible processes in the ecological and evolutionary dynamics of species-interaction networks. The first work I will present evaluates the interplay between the structure and dynamics of plant-pollinator networks when population and behavioral dynamics are incorporated in more mechanistic models of those networks. I will focus on the irreversible dynamics caused by adaptive foraging that may explain why we only observe moderately connected plant-pollinator networks in nature even when pollinator would benefit from fully connected networks. The second work I will present predicts the invasion success of pollinators in plant-pollinator networks and their subsequent impacts on natives. I will focus on the impacts that can and cannot be reversed by restoration practices seeking to remove the invasive species. The third work I will present evaluates the interplay between economic and ecological dynamics governing fishing effort in harvested food webs. I will focus on the irreversible transients that cause a fisheries industry to either thrive or collapse, the harvested species to either go extinct or persist, and food webs to suffer either dramatic cascade extinctions or sustainable harvest. Finally, I will present our work on the evolution of food webs integrating population, speciation and invasion dynamics over evolutionary timescale. I will focus on the irreversible extinctions patterns and whether the specialization tendency found can be reversed by increasing the frequency of perturbations. In my presentation of each of those four projects I will share with you what I still do not understand to hopefully ignite insightful discussion on the specific subjects.

Greg Dwyer (Univ. Chicago) - Natural selection, population cycles, and climate change in forest insects[edit source]

Cyclic outbreaks of forest insects devastate forests, leading to widespread defoliation and tree death. Outbreaks would be far worse if not for epidemics of fatal virus diseases, which decimate outbreaking insect populations. The selection pressure imposed by these diseases suggests that natural selection may affect outbreaks, but understanding such effects is impossible with data alone. My lab has therefore used a combination of field experiments and models to test for effects of selection on outbreaks. Our work shows that both heritable host resistance and variation in viral virulence strongly affect outbreaks of the the gypsy moth, Lymantria dispar, an introduced pest of eastern hardwood forests in North America. Over the last few decades, however, an introduced fungal pathogen has competitively displaced the virus. The fungus provides better control, but its survival is much higher when the weather is cool and wet, whereas climate change is likely to cause weather conditions in the range of the gypsy moth to become increasingly hot and dry. By again combining models and data, we have shown that climate change will have a strong negative effect on the gypsy moth fungus, which may lead to the devastation of hardwood forests in North America. A key question is therefore, can the virus make a comeback? Our answers to this question are as yet incomplete, but provide initial chapters in an interesting story about the ecological effects of climate change.    

Pamela Martinez (Harvard) - Pathogen diversity and negative frequency-dependent selection: consequences for intervention[edit source]

Understanding how populations respond to selective pressures is an active area of research, of particular relevance for pathogens, which often adapt after the implementation of epidemic control strategies. Yet attempts to anticipate how and when these populations will evolve, are challenging. By looking at population diversity of rotavirus and Streptococcus pneumoniae, we have explored the impact of negative-frequency dependent selection, which tends to confer an advantage to the rare and a disadvantage to the common, in the response to intervention. Our results emphasize the resilience to control measures, and thus low vaccine effectiveness, in pathogens for which frequency-dependent selection is a key driving force.

Priyanga Amarasekare (UCLA) - Phenotypic evolution in the Anthropocene[edit source]

Phenotypic traits constitute the interface between the organism and the environment. Adaptive evolution occurs when trait responses to the  environment maximize fitness subject to constraints. These constraints can be morphological, biochemical or genetic.  On the one hand, evidence of rapid evolution in response to environmental perturbations (e.g., pollution, habitat degradation, climate warming) suggests that evolution in response to these novel selection pressures can proceed unconstrained. On the other hand, evidence of extinctions and disruptions of species interactions suggests that constraints can impede evolution in response to novel selective regimes.  There is much we do not understand about the interplay between selection and constraints, particularly in light of anthropogenically-induced selection regimes.  I am particularly interested in the role of biochemical constraints in reaction norm evolution.  This interest is fueled by my work on temperature effects on ectotherm life history, population dynamics and species interactions.  I want to gain a mechanistic understanding of biochemical constraints all the way from protein folding to enzyme kinetics so that I can incorporate these mechanisms into models of reaction norm evolution.  There is a great deal I do not understand about these processes themselves and how they translate into the mathematics of population dynamics.  I do, however, entertain some speculations about the role of how biochemical constraints in irreversible outcomes in phenotypic evolution.    

Stephen Proulx (UCSB) - Population genetics of low-probability transitions[edit source]

I will discuss several examples from population genetics and adaptive dynamics where the probability for a transition between “equilibrium” states is very low. These situations can occur when stochastic environmental conditions create scenarios with alternate stable states that can only be invaded by mutations of large effect, for instance in scenarios with overlapping generations and lottery competition. In a similar vein, when mutations of small effect cause intermediate phenotypes with low fitness, transitions can be rare. Another type of transition involves feedback between the environment and the distribution of population phenotypes, for example in terms of the evolution of mating preferences in combination with the evolution of ecological specialization. Yet another scenario occurs when multiple independent mutations are required to cross an “adaptive valley”. This has parallels in ecological theory, for example with the invasion of novel habitats (e.g. zoonotic diseases). I will encourage discussion of how these different concepts and modes of analysis may be extended to situations with eco-evo feedbacks.

Robert Marsland (Boston Univ.) - Statistical mechanics of microbiomes[edit source]

In a seminal paper in 1972, Robert May studied complex ecosystems using Random Matrix Theory. Nearly fifty years later, the rise of quantitative microbial ecology makes it possible to test and refine this approach. Random matrix models successfully capture a wide range of large-scale patterns observed in real microbial communities, including functional and family-level reproducibility, compositional clustering by environment, enterotypes, dissimilarity-overlap correlations, decreased diversity in harsh environments, compositional nestedness, succession dynamics and modularity. After describing the computational model we have developed to reproduce all these patterns, I will present a set of analytic results that explain why this works in the real world. Adding even a small amount of noise to a sufficiently diverse community induces a phase transition to a “typical” phase, where community-level properties such as diversity and rank-abundance curves are indistinguishable from those of a completely random ecosystem. I will explain how the properties of this phase are governed by “susceptibilities” describing the linear response of the ecosystem to small changes in population sizes or resource concentrations. These susceptibilities can be obtained from Random Matrix Theory, in the spirit of May’s paper, and can also be measured by subjecting a community to controlled perturbations.

Post-meeting Reflection by Presenter
Post-meeting Reflection by Non-presenting Attendees

Reference Materials by Presenting Attendees[edit source]

Reference Materials by Non-presenting Attendees


General Meeting Reference Material[edit source]