Linking Dynamic Habitat Selection with Wading Bird Foraging Distributions across Resource Gradients: SFC Model

The spatial foraging conditions (SFC) models grouped foraging observations over time at a fixed cell and integrated spatial patterns (e.g., topography) unaccounted for by the chosen set of hydrological predictors (i.e., spatial correlation; Beerens et al, in press). By accounting for patterns in the spatial variation of the landscape, the noise independent of the hydrologic parameters can be reduced to better capture the species-specific behavioral response to rapidly changing habitat conditions (Dormann 2007). In addition to depth, recession, and DSD, the SFC used dry-to-wet reversal, and hydroperiod, averaged over each instance of cell use. The dry-to-wet reversal variable estimated when a cell had gone dry and rewet (within a dry season), which results in highly depleted fish populations (Trexler et al. 2002). Hydroperiod was defined as the 10-year mean in the annual length of cell inundation, which influences wading bird distributions through long-term changes in microtopography and vegetation communities. Frequency of cell use was defined as the number of times over the study period that a species used a given cell. Output from the SFC averaged over the landscape can serve as a surrogate measure of the abundance of high-quality patches.

空间觅食条件（Spatial Foraging Conditions, SFC）模型将固定单元格内随时间序列获取的觅食观测数据进行归集，并纳入了所选水文预测因子（即空间自相关；Beerens等，待刊）未涵盖的空间格局（如地形特征）。通过纳入景观空间变异的格局特征，该模型可剔除与水文参数无关的噪声，从而更精准地捕捉物种对快速变化生境条件的特异性行为响应（Dormann，2007）。除水深、水位退落及DSD外，SFC模型还纳入了基于各单元格使用事件平均得到的干湿逆转与淹水时长变量。干湿逆转变量用于估算单元格在（旱季内）干涸后再次被淹没的时段，该过程会导致鱼类种群数量大幅下降（Trexler等，2002）。淹水时长被定义为单元格年淹水时长的10年均值，其通过长期改变微地形与植物群落结构，进而影响涉禽的分布格局。单元格使用频次被定义为研究周期内某一物种使用特定单元格的总次数。在整个景观尺度上平均得到的SFC模型输出结果，可作为高质量生境斑块丰度的替代评价指标。