Data from: Giant mice on small islands: Biogeographic and ecological differences contribute to gigantism in island populations

Island populations of small land vertebrates frequently exhibit insular
gigantism, presenting with larger body sizes compared to their mainland
counterparts. While insular gigantism has been observed globally, the
effects of biogeographic and ecological factors on body size in island
systems are not well understood. Here we examine the biogeographic and
ecological associations of insular gigantism. Deer Mice (Peromyscus
maniculatus) were live-trapped, and body mass was measured on six of the
Gulf Islands and the mainland of British Columbia, Canada. In
addition to field sampling, body mass measurements were also recovered
from museum specimens from the Gulf Islands area via the VertNet database.
Biogeographic measures of land area and island distance from the mainland
were estimated using ArcMap. The ecological measure of predator species
richness was estimated from iNaturalist observations. These data were used
in piecewise structural equation modeling to identify associations with
insular gigantism. We found evidence of insular gigantism in the Gulf
Islands system, with island mice having a larger mean body mass than
mainland populations. Land area was positively associated with predator
species richness, and predator species richness had a strong negative
effect on Deer Mouse body mass, resulting in the observed pattern of
insular gigantism. The concurrent analysis of biogeographic and ecological
factors contributes to a better understanding of the evolution of insular
gigantism in small vertebrates and its juxtaposition to the phenomenon of
insular dwarfism of large vertebrates.

小型陆生脊椎动物的岛屿种群常表现出岛屿巨型化（insular gigantism）现象，即相较于大陆同种种群，其体型更大。尽管岛屿巨型化已在全球范围内被观测到，但生物地理与生态因子对岛屿种群体型的影响机制仍未被充分阐明。本研究针对岛屿巨型化与生物地理、生态因子之间的关联展开探讨。研究对象为鹿鼠（Deer Mouse，Peromyscus maniculatus）：研究团队在加拿大不列颠哥伦比亚省的6座海湾群岛（Gulf Islands）及该省大陆区域布设活捕笼进行野外采样，并测定其体质量；此外还通过VertNet数据库获取了海湾群岛区域博物馆馆藏标本的体质量测定数据。研究利用ArcMap软件估算了岛屿面积、岛屿与大陆的距离等生物地理因子参数，捕食者物种丰富度这一生态因子参数则通过iNaturalist平台的观测数据进行估算。研究采用分段结构方程模型（piecewise structural equation modeling）对上述数据进行分析，以探明其与岛屿巨型化的关联机制。分析结果证实海湾群岛区域存在岛屿巨型化现象：岛屿鹿鼠的平均体质量显著高于大陆种群。岛屿面积与捕食者物种丰富度呈显著正相关，而捕食者物种丰富度对鹿鼠体质量具有极强的负向影响，这一关系最终造就了本次观测到的岛屿巨型化格局。本研究同时整合生物地理与生态因子进行分析，有助于深化对小型脊椎动物岛屿巨型化演化机制的认知，并为理解大型脊椎动物的岛屿侏儒化（insular dwarfism）现象提供了参照。