Dr Nadiah Kristensen

@nadiah.bsky.social

2412 Followers 1147 Following

modeller of ecology, evolution, and cooperation | she/her | 🤘 | 🐘 fediscience.org/@nadiah | nadiah.org

No one seriously doubted that the arguments underlying the computer calculations were correct; the objection instead hinged on the separation of proof from our old friend understanding, as in this reaction by British mathematician Frank Bonsall: “We cannot possibly achieve what I regard as the essential element of a proof—our own personal understanding—if part of the argument is hidden away in a box.”
A screenshot of a Claude chat from the phone app with most of the text greyed out. The text at the top indicates Opus 4.5 is being used. The first block of text has a link indicating the content was sourced from Wikipedia. The second block has a link indicating the content was sourced from Grokipedia.
Multi panel figure illustrating the following intuition for why group structures favoring altruism might be more common than those favoring spite. It considers the example scenarios with pairs of individuals. When the population is evenly split between 100 actors (altruistic or spiteful) and 100 non-actors, maximum positive assortment produces all same-type pairs (50 pairs actor+actor, 50 pairs actor+nonactor) and maximum negative assortment produces all opposite-type pairs (100 pairs actor+nonactor). Therefore, maximum assortativity produces equally group structures most favorable to altruism and group structures most favorable to spite. However, when actors outnumber non-actors (140 actors, 60 nonactors), positive and negative assortment have asymmetric effects on group structure. Maximum positive assortment still produces all same-type pairs (70 pairs actor+actor, 30 pairs actor+nonactor); however, maximum negative assortment cannot achieve all opposite-type pairs due to the surplus of actors – some same-type pairs (actor–actor) must remain (60 pairs actor+nonactor, 40 pairs actor+actor, ). Therefore, the maximum achievable positive assortment promotes altruism more effectively than the maximum negative assortment promotes spite. A similar asymmetry arises when non-actors outnumber actors (60 actors, 140 nonactors). Maximum positive assortment again produces all same-type pairs (30 pairs actor+actor, 70 pairs actor+nonactor), but maximum negative assortment cannot achieve all opposite-type pairs due to the surplus of non-actors – some same-type pairs (non-actor– non-actor) necessarily remain (60 pairs actor+nonactor, but 40 pairs nonactor+nonactor). Thus, once again, the maximum achievable positive assortment promotes altruism more effectively than the maximum negative assortment promotes spite.
A screen showing a movie. It’s an underwater shot of two Orcas.
Two equations, one after the other, contradicting each other. No variables are defined.
Just a really garbled figure
Screenshot of paragraph. It reads as follows:-- 3.2.1. Ecosystem services quantification Improving human well-being and fostering sustainable development are both made possible by ecosystem services (ESs). This is especially the case in places like the Longdong Loess Plateau, where issues like water scarcity, worries about food security, soil erosion, habitat loss, and the need to attain carbon neutrality are significant problems. To address these issues, this study zeroes in on five key indicators of ecosystem services critical to maintaining the region's ecological and socioeconomic stability. One measure of an ecosystem's ability to sustain life is its water yield (Schuldt et al., 2021). This resource is vital for farming and human consumption. Soil conservation is essential to sustaining agricultural production; it examines ecosystems' capacities to prevent soil erosion and degradation (Apostolopoulos et al., 2020). (Marschke and Rousseau, 2022) developed the Grain Provision indicator to measure environmental impacts on food production. This indicator focuses on grain, the primary food source in the region. An important step in mitigating climate change is evaluating ecosystems' capacity to sequester carbon. As a last consideration, Habitat Quality examines the availability and state of animal habitats, a crucial factor in protecting biodiversity. The estimations shown in Fig. 4 provide a comprehensive review of the area's ecological functions, highlighting their significance for the Longdong Loess Plateau's long-term development.
A flow diagram with some less egregious signs of AI generation.
A diagram titled "Ecological Network Optimisation" with attractive landscapes and networks and very clear AI-generation artifacts.
Online seminar: PopBio on the Dark Side Joe Wan National Taiwan University Thursday 31st July 1 pm AEST UTC+10 **A unified theory of community structure** Much of our theoretical understanding of biodiversity, including well-established tools such as coexistence theory, focuses on the identity and number of coexisting species. Yet even when species coexist, they may show stark differences in abundance. Though such differences in community structure determine ecosystem function, we lack general quantitative tools linking interactions to abundance patterns in complex communities. In this seminar, I will address this gap by proposing a theoretical framework uniting coexistence with community structure and function. Beginning with the classic niche–fitness framework and canonical models of small communities, I illustrate simple links between species' fitness (as measured by invasion growth rates) and abundance (or more generally, their contributions to total function). New quantitative tools generalize these relationships to non-additive competitive interactions and high species richness, providing a general way to predict the structure and function of complex communities. This extends foundational theories of coexistence to new questions of community structure and function: a functional coexistence theory which, as I show using plant and microbial case studies, provides tractable insight into both theoretical models and empirical systems. **Footer**: Add your email to the above google form to receive the zoom link and future seminar announcements!
An image resembling the text pop-up of an adventure game from the late 1990s. It reads: *Journal Entry Found* Dearest Dr Kristensen; At long last - and not without the eldritch whisper of unseen forces pressing at the frayed edges of my resolve - the Antarctic Documents have yielded to my labours and now lie assembled, murmuring with the strange energies of the austral post. They are ready. There is a sense, almost a tremor in the veil, as though by unearthing them we have disturbed something older than mere time. [Access the sealed archive] Yours at the threshold, Dr C. Hamalainen Scribe of the Forgotten Latitude
A screenshot of the downforeveryoneorjustme website saying biorxiv.org is down.
A snippet of code. It reads: # NOTE to future self - commented code is a more elegant way to find attractors and basins """ # find the attractors and their full basins of attraction # --- idx_2_attractor = {
Advert for the seminar with abstract: How ecosystems respond to environmental perturbations is a fundamental question in ecology, made especially challenging due to the strong coupling between species and their environment. Here, we introduce a theoretical framework for calculating the steady-state response of ecosystems to environmental perturbations in generalized consumer-resource. Our construction is applicable to a wide class of systems, including models with non-reciprocal interactions, cross-feeding, and non-linear growth/consumption rates. Within our framework, all ecological variables are embedded into four distinct vector spaces and ecological interactions are represented by geometric transformations between these spaces. We show that near a steady state, such geometric transformations directly map environmental perturbations - in resource availability and mortality rates - to shifts in niche structure. We illustrate these ideas in a variety of settings including a minimal model for pH-induced toxicity in bacterial denitrification. We end by discussing the biological implications of our framework. In particular, we show that it is extremely difficult to distinguish cooperative and competitive interactions by measuring species' responses to external perturbations.
A window with two columns. On the left-hand side is a scanned document. On the right-hand side is the text that was extract. It reads: --- INTRODUCTION The time is past now, when a yacht's arrival at an Antarctic base was the cause of marvel and admiration. That era, short though it was, is over - despite the still as yet un-cruised waters of most of Antarctica's coastline. Yachts and cruise ships, scientists and support personnel, all have contributed in these past few years to the opening up of Antarctica. We must be careful that this increasing familiarity with the Antarctic does not dull the emotions or lessen the respect that did so often transform the lives of earlier visitors, that enticed them back again and again, stimulating others to go, until visitors today must be numbered in their thousands every year. Because few visitors will be familiar with the Antarctic environment, or the way in which the various nations occupying bases here operate, these guidelines have been drawn up to help you and your crew during your season South. Above all, an understanding and appreciation of the Antarctic as a very special and fragile environment will go a long way to lessening the ... ---
A conference room with 7 people standing at the front hosting a Q&A. In the background is a screen that says "group break out sessions".
A net plot the dynamics between four strategies: Unconditional Cooperators, Liars, Unconditional Defectors, and Coordinating Cooperators. There are arrows showing the direction of evolution, and dots representing stable and unstable steady states. There’s a lot of info in there, but it’s more intended as decorative in this context.
Screenshot of a Zoom meeting of an online talk. The title is "A unified theory of niche assembly and dispersal assembly in community ecology". At the top of the right-hand panel is Courtney Taylor's video stream. She organised the seminar.
A photo of a whiteboard with some maths scribbled on it. It's very messy and doesn't mean very much to me anymore in this moment. In the reflection, you can see Hisashi and me. We're both wearing COVID masks, and I'm holding up a phone to take the photograph.
Hisashi, Ryan, and me standing in front of a sign reading "Department of Biolog[y]".
Screenshot of an abstract. Title: Many-strategy games in groups with relatives and the evolution of coordinated cooperation Authors: Nadiah P. Kristensen, Ryan A. Chisholm, Hisashi Ohtsuki Text: Humans often cooperate in groups with friends and family members with varying degrees of genetic relatedness. Past kin selection can also be relevant to interactions between strangers, explaining how the cooperation first arose in the ancestral population. However, modelling the effects of relatedness is difficult when the benefits of cooperation scale nonlinearly with the number of cooperators (e.g., economies of scale). Here, we present a direct fitness method for rigorously accounting for kin selection in $n$-player interactions with $m$ discrete strategies, where a genetically homophilic group-formation model is used to calculate the necessary higher-order relatedness coefficients. Our approach allows us to properly account for non-additive fitness effects between relatives (synergy). Analytical expressions for dynamics are obtained, and they can be solved numerically for modestly sized groups and numbers of strategies. We illustrate with an example where group members can verbally agree (cheap talk) to contribute to a public good with a sigmoidal benefit function, and we find that such coordinated cooperation is favoured by kin selection. As interactions switched from family to strangers, in order for coordinated cooperation to persist and for the population to resist invasion by liars, either some level of homophily must be maintained or following through on the agreement must be in the self-interests of contributors. Our approach is useful for scenarios where fitness effects are non-additive and the strategies are best modelled in a discrete way, such as behaviours that require a cognitive `leap' of insight into the situation (e.g., shared intentionality, punishment).
Early evidence In 1966, Lerner and his colleagues began a series of experiments that used shock paradigms to investigate observer responses to victimization. In the first of these experiments conducted at the University of Kansas, 72 female participants watched what appeared to be a confederate receiving electrical shocks for her errors during a learning task (learning pairs of nonsense syllables). Initially, these observing participants were upset by the victim's apparent suffering. But as the suffering continued and observers remained unable to intervene, the observers began to reject and devalue the victim. Rejection and devaluation of the victim was greater when the observed suffering was greater. But when participants were told the victim would receive compensation for her suffering, the participants did not derogate the victim.[6] Lerner and colleagues replicated these findings in subsequent studies, as did other researchers.[8] Theory To explain these studies' findings, it was theorized that there was a prevalent belief in a just world. A just world is one in which actions and conditions have predictable, appropriate consequences. These actions and conditions are typically individuals' behaviors or attributes. The specific conditions that correspond to certain consequences are socially determined by a society's norms and ideologies. Lerner presents the belief in a just world as functional: it maintains the idea that one can influence the world in a predictable way. Belief in a just world functions as a sort of "contract" with the world regarding the consequences of behavior. This allows people to plan for the future and engage in effective, goal-driven behavior. Lerner summarized his findings and his theoretical work in his 1980 monograph The Belief in a Just World: A Fundamental Delusion.[7] Lerner hypothesized that the belief in a just world is crucially important for people to maintain for their own well-being. But people are confronted daily with evide…
In 1966, Lerner and his colleagues began a series of experiments that used shock paradigms to investigate observer responses to victimization. In the first of these experiments conducted at the University of Kansas, 72 female participants watched what appeared to be a confederate receiving electrical shocks for her errors during a learning task (learning pairs of nonsense syllables). Initially, these observing participants were upset by the victim's apparent suffering. But as the suffering continued and observers remained unable to intervene, the observers began to reject and devalue the victim. Rejection and devaluation of the victim was greater when the observed suffering was greater. But when participants were told the victim would receive compensation for her suffering, the participants did not derogate the victim.[6] Lerner and colleagues replicated these findings in subsequent studies, as did other researchers.[8] Theory To explain these studies' findings, it was theorized that there was a prevalent belief in a just world. A just world is one in which actions and conditions have predictable, appropriate consequences. These actions and conditions are typically individuals' behaviors or attributes. The specific conditions that correspond to certain consequences are socially determined by a society's norms and ideologies. Lerner presents the belief in a just world as functional: it maintains the idea that one can influence the world in a predictable way. Belief in a just world functions as a sort of "contract" with the world regarding the consequences of behavior. This allows people to plan for the future and engage in effective, goal-driven behavior. Lerner summarized his findings and his theoretical work in his 1980 monograph The Belief in a Just World: A Fundamental Delusion.[7]
Speaker list: Toby Sumpter, Jay B., and Gabriel Rench.
Album cover: Archspire Bleed the Future
The Jurassic Park kitchen scene, but instead of raptors, it’s Jesus.
An email to Hisashi letting him know about the post above. Subject line is “Your paper is pop culture now” with the following text: Hi Hisashi, I thought you might get a kick out of this. I was scrolling BlueSky on the train yesterday (the new alternative to Twitter/X), and someone wrote a humorous post referencing your ‘leading 8’ paper. Screenshot attached. Cheers, Nadiah
Water colour of two lizards on a branch. One says to the other “Rock-paper-scissors isn’t really the best way to settle territorial disputes…”
A mysterious item has been placed on my desk?
A three panel figure depicting a sequential-sampling algorithm. There are many urns and bunch of red and blue balls and arrows between them. Honestly, for the purposes of this thread, it's just decorative.
A two-panel figure with a connectionist model on the left and the activation of nodes over time on the right
A photo of a robot ... [spoiler alert] ... the robot from I Am Mother.
Promotional photo for 1985 horror movie "Re-Animator". Actor Jeffrey Combs poses as Herbert West, holding up a syringe filled with glowing goo and looking determinedly at the camera.
Screenshot from Twitter. Original post from Libs of Tiktok has a video of the UK riots captioned "Wtf is going on in the UK. Total madness". User Ashley St. Clair quote Tweets with the reply, "The effects of mass migration and open borders is what's going on." Elon Musk, owner of Twitter, replies "Civil war is inevitable".
A certificate that reads "WILEY Top Cited Article 2022-2023 Congratulations to: Nadiah Kristensen" etc. It is inexplicably decorated with a picture of a surfer in the water at sunset.
Some example sea-stack plots and an illustration of the sea stacks they're named after
Screenshot of an Introduction of a paper. First line reads “Certainly, here is a possible introduction for your topic: Lithium-metal batteries are promising candidates for…”
A woman (me!) gestures at a whiteboard at the front of a class.
A figure from the Estrela paper showing how a model with implicit environmental interaction can map onto different model structures when the environment is made explicit. Sometimes there is only one environmentally explicit model, sometimes 2, and sometimes we need two types of environment to capture the implicit model.
Screen shot of a Nature headline. Reads “Surge in number of ‘extremely productive’ authors concerns scientists”.
Screen shot of the bio with the line "I watch worms die to learn how to live" highlighted
Interval estimates for the proportion of species that went extinct in each taxonomic group (mammals, birds, reptiles, fished, butterflies, bees, phasmids, dec. crustaceans, plants).
A 4-panel cartoon featuring two squirrels searching the ground. Panel 1: Squirrel 1 says, "everyone thinks that we accidentally pla nt trees because we forget where we buried our acorns". Panel 2: Squirrel 1 continues, "nobody assumes that we're intentionally pla nting trees for future generations". Panel 3: Squirrel 2 replies, "you forgot where you buried your actors again, didn't you?". Pa nel 4: Squirrel 1 replies, "for the future".