Data from: Time-integrated habitat availability is a resource attribute that informs patterns of use in intertidal areas

In dynamic environments, resource availability may change by several orders of magnitude, over hours to months, but the duration of resource availability is not often included as a characteristic attribute of resources even though temporal resource dynamics might limit patterns of use. In our study of wading birds foraging in intertidal areas, tides cause large changes in the areal extent of shallow-water foraging habitat (i.e., the resource), but tides also constrain the duration of availability, which is often overlooked. We hypothesized that temporal constraints on habitat availability from tides would be reflected in patterns of habitat use by foraging birds. We estimated the time-integrated habitat availability and compared it to traditional habitat attributes (seagrass cover, substrate type, instantaneous water depth, and proximity to mangrove islands or deep water) that have strong evidential support for influencing patterns of use. To evaluate our hypotheses, we quantified habitat attributes at intertidal areas in the Florida Keys, U.S.A, where wading birds were observed foraging (Little Blue Heron, Egretta caerulea: N=183; Great White Heron, Ardea herodias occidentalis: N=162). We tested for non-random use by sampling habitat attributes at two spatial scales around the observed feeding locations and we analyzed the data using a conditional logistic regression model. There was no evidence that seagrass cover or substrate explained patterns of use. The proximity of foraging locations relative to mangroves and to deep water were important at both spatial scales but had lower effect sizes (odds-ratios) than time-integrated habitat availability and water depth, and the latter may only serve as a physical constraint on access. We found support that time-integrated habitat availability was a distinct resource attribute, had the greatest effect size (4-8-fold change in relative probability of use), and best explained patterns of habitat use at the largest spatial scale. In studies of resource use where changes in resource availability are non-linear or when strong constraints on access are imposed by behavior, incorporating time-integrated estimates of resource availability into analyses can improve insights into spatiotemporal patterns of resource use.

在动态环境中，资源可获得性（resource availability）可能在数小时至数月的尺度上发生数个数量级的变化，但尽管资源的时间动态可能会限制资源利用模式，资源可获得的持续时长却常未被纳入资源的特征属性范畴。在我们针对潮间带区域（intertidal areas）涉禽（wading birds）觅食行为的研究中，潮汐会大幅改变浅水觅食栖息地（shallow-water foraging habitat，即本次研究的资源）的面积范围，但潮汐同时也会限制该栖息地的可获得时长，这一点常被忽视。我们提出假说：潮汐带来的栖息地可获得性时间限制，会体现在涉禽的栖息地利用模式中。我们估算了时间整合式栖息地可获得性（time-integrated habitat availability），并将其与传统栖息地属性（海草覆盖度（seagrass cover）、底质类型（substrate type）、瞬时水深（instantaneous water depth）以及距红树林岛或深水区域的距离（proximity to mangrove islands or deep water））进行对比——这些传统属性已被大量证据证实会影响资源利用模式。为验证上述假说，我们在美国佛罗里达群岛（Florida Keys）的潮间带区域量化了栖息地属性，该区域内曾被观测到涉禽觅食行为：小蓝鹭（Egretta caerulea，样本量N=183）、大白鹭（Ardea herodias occidentalis，样本量N=162）。我们通过在观测到的觅食点位周边的两个空间尺度上采样栖息地属性，检验了栖息地利用是否为非随机模式，并采用条件逻辑回归模型（conditional logistic regression model）对数据进行分析。研究结果显示，并无证据表明海草覆盖度或底质类型能够解释栖息地利用模式。觅食点位距红树林及深水区域的距离在两个空间尺度上均具有显著影响，但其效应量（effect sizes）与优势比（odds-ratios）均低于时间整合式栖息地可获得性与水深；且水深仅可能作为一种物理可达性限制因素。我们的研究证实，时间整合式栖息地可获得性是一项独立的资源属性，其效应量最大（相对利用概率变化幅度达4~8倍），且在最大空间尺度上最能解释栖息地利用模式。在资源可获得性呈非线性变化，或行为会带来较强可达性限制的资源利用研究中，将时间整合式资源可获得性估算值纳入分析框架，能够提升我们对资源利用时空模式的认知水平。