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1. Niche Dynamics in Complex Online Community Ecosystems

   https://doi.org/10.1609/icwsm.v19i1.35907  

   TeBlunthuis, Nathan (June 2025, Proceedings of the International AAAI Conference on Web and Social Media)

   Online communities are important organizational forms where members socialize and share information. Curiously, different online communities often overlap considerably in topic and membership. Recent research has investigated competition and mutualism among overlapping online communities through the lens of organizational ecology; however, it has not accounted for how the nonlinear dynamics of online attention may lead to episodic competition and mutualism. Neither has it explored the origins of competition and mutualism in the processes by which online communities select or adapt to their niches. This paper presents a large-scale study of 8,806 Reddit communities belonging to 1,919 clusters of high user overlap over a 5-year period. The method uses nonlinear time series methods to infer bursty, often short-lived ecological dynamics. Results reveal that mutualism episodes are longer lived and slightly more frequent than competition episodes. Next, it tests whether online communities find their niches by specializing to avoid competition using panel regression models. It finds that competitive ecological interactions lead to decreasing topic and user overlaps; however, changes that decrease such niche overlaps do not lead to mutualism. The discussion considers future designs for online community ecosystem management. 

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2. Word length, proportion of overlap, and phonological competition in spoken word recognition

   Simmons, E. S.; Magnuson, J. S. (July 2018, Proceedings of the Cognitive Science Society)

   We examined how phonological competition effects in spoken word recognition change with word length. Cohort effects (competition between words that overlap at onset) are strong and easily replicated. Rhyme effects (competition between words that mismatch at onset) are weaker, emerge later in the time course of spoken word recognition, and are more difficult to replicate. We conducted a simple experiment to examine cohort and rhyme competition using monosyllabic vs. bisyllabic words. Degree of competition was predicted by proportion of phonological overlap. Longer rhymes, with greater overlap in both number and proportion of shared phonemes, compete more strongly (e.g., kettle-medal [0.8 overlap] vs. cat-mat [0.67 overlap]). In contrast, long and short cohort pairs constrained to have constant (2-phoneme) overlap vary in proportion of overlap. Longer cohort pairs (e.g., camera-candle) have lower proportion of overlap (in this example, 0.33) than shorter cohorts (e.g., cat-can, with 0.67 overlap) and compete more weakly. This finding has methodological implications (rhyme effects are less likely to be observed with shorter words, while cohort effects are diminished for longer words), but also theoretical implications: degree of competition is not a simple function of overlapping phonemes; degree of competition is conditioned on proportion of overlap. Simulations with TRACE help explicate how this result might emerge. 

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3. ASSESSING MOOSE HUNTER DISTRIBUTION TO EXPLORE HUNTER COMPETITION

   Hasbrouck, T.R. (August 2020, Alces)

   null (Ed.)

   Traditional values, motivations, and expectations of seclusion by moose (Alces alces) hunters, more specifically their distributional overlap and encounters in the field, may exacerbate perceptions of competition among hunters. However, few studies have quantitatively addressed overlap in hunting activity where hunters express concern about competition. To assess spatial and temporal characteristics of competition, our objectives were to: 1) quantify temporal harvest patterns in regions with low (roadless rural) and high (roaded urban) accessibility, and 2) quantify overlap in harvest patterns of two hunter groups (local, non-local) in rural regions. We used moose harvest data (2000–2016) in Alaska to quantify and compare hunting patterns across time and space between the two hunter groups in different moose management areas. We created a relative hunter overlap index that accounted for the extent of overlap between local and non-local harvest. The timing of peak harvest was different (P < 0.01) in urban and rural regions, occurring in the beginning and middle of the hunting season, respectively. In the rural region, hunter overlap scores revealed a concentration in 20% of the area on 16–20 September, with 50% of local harvest on 33% of the area and 54% of non-local harvest on 18% of the area. We recommend specific management strategies, such as lifting the air transportation ban into inaccessible areas, to redistribute hunters and reduce overlap and concerns of competition in high-use areas. We also encourage dissemination of information about known hotspots of hunter overlap to modify hunter expectations and subsequent behavior. Our hunter overlap index should prove useful in regions where similar concerns about hunter competition, hunter satisfaction, and related management dilemmas occur. 

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4. Mixed‐species groups of Serengeti grazers: a test of the stress gradient hypothesis

   https://doi.org/10.1002/ecy.3163  

   Beaudrot, Lydia; Palmer, Meredith S.; Anderson, T. Michael; Packer, Craig (August 2020, Ecology)

   Understanding the role of species interactions within communities is a central focus of ecology. A key challenge is to understand variation in species interactions along environmental gradients. The stress gradient hypothesis posits that positive interactions increase and competitive interactions decrease with increasing consumer pressure or environmental stress. This hypothesis has received extensive attention in plant community ecology, but only a handful of tests in animals. Furthermore, few empirical studies have examined multiple co‐occurring stressors. Here we test predictions of the stress gradient hypothesis using the occurrence of mixed‐species groups in six common grazing ungulate species within the Serengeti‐Mara ecosystem. We use mixed‐species groups as a proxy for potential positive interactions because they may enhance protection from predators or increase access to high‐quality forage. Alternatively, competition for resources may limit the formation of mixed‐species groups. Using more than 115,000 camera trap observations collected over 5 yr, we found that mixed‐species groups were more likely to occur in risky areas (i.e., areas closer to lion vantage points and in woodland habitat where lions hunt preferentially) and during time periods when resource levels were high. These results are consistent with the interpretation that stress from high predation risk may contribute to the formation of mixed‐species groups, but that competition for resources may prevent their formation when food availability is low. Our results are consistent with support for the stress gradient hypothesis in animals along a consumer pressure gradient while identifying the potential influence of a co‐occurring stressor, thus providing a link between research in plant community ecology on the stress gradient hypothesis, and research in animal ecology on trade‐offs between foraging and risk in landscapes of fear. 

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5. Ecological Interactions and Macroevolution: A New Field with Old Roots

   https://doi.org/10.1146/annurev-ecolsys-011720-121505  

   Hembry, David H.; Weber, Marjorie G. (November 2020, Annual Review of Ecology, Evolution, and Systematics)

   null (Ed.)

   Linking interspecific interactions (e.g., mutualism, competition, predation, parasitism) to macroevolution (evolutionary change on deep timescales) is a key goal in biology. The role of species interactions in shaping macroevolutionary trajectories has been studied for centuries and remains a cutting-edge topic of current research. However, despite its deep historical roots, classic and current approaches to this topic are highly diverse. Here, we combine historical and contemporary perspectives on the study of ecological interactions in macroevolution, synthesizing ideas across eras to build a zoomed-out picture of the big questions at the nexus of ecology and macroevolution. We discuss the trajectory of this important and challenging field, dividing research into work done before the 1970s, research between 1970 and 2005, and work done since 2005. We argue that in response to long-standing questions in paleobiology, evidence accumulated to date has demonstrated that biotic interactions (including mutualism) can influence lineage diversification and trait evolution over macroevolutionary timescales, and we outline major open questions for future research in the field. 

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