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Island mammals have influenced ecological and evolutionary theory since Darwin, and many of them provide textbook examples of the dramatic morphological evolution that often occurs in island communities. However, patterns of evolution in the climatic niches of island mammals have yet to be fully explored. Several hypotheses explaining niche divergence in island species have been introduced, linking niche evolution to increased competition among closely related or sympatric species, and as a by‐product of morphological evolution or geographical patterns. Here, we evaluate these hypotheses using closely related species pairs (sister taxa). We characterized the climatic niches of island endemic species and their closest relatives and calculated two metrics of niche divergence between the species (niche overlap and centroid distance). We compared these metrics between island endemics that have island‐dwelling sister taxa and those that have mainland‐dwelling sister taxa. We then related the degree of niche divergence to phylogenetic relatedness between the sister taxa, sympatry, morphological trait differences and island characteristics (isolation, size, age). Overall, despite significant niche divergence across species pairs, we found little evidence that competition or biotic interactions drive large‐scale climatic niche evolution in island mammals. Niche divergence in island‐endemic mammals is not driven by sympatry with their closest relatives, nor is it linked to phylogenetic relatedness. Furthermore, the phenotypic evolution of island‐endemic species does not lead to corresponding evolution in climatic niches. Instead, abiotic, geographical patterns appear to drive niche divergence in these species. Sister taxa that were more geographically isolated from each other had significantly lower niche overlaps. Island‐endemic mammals that live in montane regions likewise diverged from their closest relatives. These results suggest that competition between related species on islands may lead to niche partitioning only on local scales and that niche evolution in island‐endemic mammals may occur primarily in response to geographical patterns.
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This content will become publicly available on June 7, 2026
Niche Dynamics in Complex Online Community Ecosystems
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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- PAR ID:
- 10610986
- Publisher / Repository:
- AAAI
- Date Published:
- Journal Name:
- Proceedings of the International AAAI Conference on Web and Social Media
- Volume:
- 19
- ISSN:
- 2162-3449
- Page Range / eLocation ID:
- 1880 to 1892
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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