Scale-Dependence in Elk Habitat Selection for a Reintroduced Population in Wisconsin, USA.

Habitat selection is a critical aspect of a species’ ecology requiring
complex decision-making that is both hierarchical and scale-dependent,
since factors that influence selection may be nested or unequal across
scales. Elk (Cervus canadensis) ranged widely across diverse habitats in
North America prior to European settlement and subsequent eastern
extirpation. Most habitat studies have occurred within their contemporary
western range, even after eastern elk reintroductions began. As habitat
selection can vary by geographic location, available cover, season, and
diel period, it is important to understand how a non-migratory,
reintroduced population in northern Wisconsin, USA is limited by the lack
of variation in topography, elevation, and vegetation. We tested
scale-dependent habitat selection on 79 adult elk from 2017–2020. We used
resource selection functions across both temporal and spatial scales to
understand differences in selection of topographic and environmental
features. We found that selection varied both spatially and temporally and
elk selected areas with the greatest potential to influence fitness at
larger scales (i.e., landscape scale), meaning elk selected areas closer
to escape cover and further from “risky” features (e.g., wolf territory
centers, county roads and highways). We found stronger avoidance to wolf
territory centers during spring, suggesting elk were selecting safer
habitats during calving season. We found elk selected habitats with less
canopy cover across both spatial scales and all seasons, suggesting that
elk selected these areas for better access to forage as forest stands in
early seral stages have greater nutritional value and forage biomass than
closed-canopy forests and direct solar radiation to provide warmth in the
cooler seasons. This study highlights how processes at different spatial
and temporal scales influence species’ decision-making. It provides
insight into the complexity of making informed decisions in which an
individual is responding to their immediate environment while
simultaneously making decisions in the context of the larger landscape.
Scale-dependent behavior is crucial to understand within specific
geographic regions as these decisions scale up to influence population
dynamics.

生境选择（Habitat selection）是物种生态学中的关键环节，其需要兼具层级性与尺度依赖性的复杂决策过程，因为影响生境选择的因素可能在不同尺度上呈嵌套分布或权重不均。在欧洲殖民北美之前，美洲马鹿（Cervus canadensis）广泛分布于该大陆多样的生境中，但后续的殖民活动导致其东部种群遭遇局部灭绝。多数生境选择研究均聚焦于其当代分布的西部范围，即便在东部美洲马鹿重新引入项目启动后亦是如此。由于生境选择会随地理位置、可获取遮蔽物、季节以及昼夜时段发生变化，因此理解美国威斯康星州北部一处非迁徙性的重新引入种群如何受限于地形、海拔与植被缺乏变化的现状，具有重要研究意义。
本研究以2017至2020年间的79头成年美洲马鹿为研究对象，开展尺度依赖的生境选择分析。我们通过时空尺度上的资源选择函数（resource selection functions），探究马鹿对地形与环境特征的选择差异。研究发现，生境选择同时存在空间与时间维度的变异；美洲马鹿在更大尺度（即景观尺度）上选择最有可能提升适合度的区域，具体表现为更靠近逃逸遮蔽物、远离“高风险”特征（如狼领地核心、县道与高速公路）的区域。
我们还发现，春季时马鹿对狼领地核心的回避行为更强，这表明美洲马鹿在产仔季会选择更安全的生境。此外，无论在何种空间尺度与季节下，美洲马鹿均会选择冠层覆盖度更低的生境，这可能是因为早期演替阶段的林分相较于郁闭林分，拥有更高的营养价值与饲草生物量，且能提供直射日光以在寒冷季节帮助个体维持体温，因此此类生境更便于马鹿获取饲草。
本研究阐明了不同时空尺度下的过程如何影响物种的决策行为，为理解个体如何在响应即时环境的同时，结合更大尺度的景观背景做出决策提供了洞见。尺度依赖的行为模式在特定地理区域内的研究至关重要，因为此类决策最终会累积影响种群动态。