The influence of spatial sampling scales on ant-plant interaction network architecture

1.Despite great interest in metrics to quantify the structure of ecological networks, the effects of sampling and scale remain poorly understood. In fact, one of the most challenging issues in ecology is how to define suitable scales (i.e., temporal or spatial) to accurately describe and understand ecological systems.

2.Here, we sampled a series of ant‐plant interaction networks in the southern Brazilian Amazon rainforest in order to determine whether the spatial sampling scale, from local to regional, affects our understanding of the structure of these networks.

3.To this end, we recorded ant‐plant interactions in adjacent 25 x 30 m subplots (local sampling scale) nested within twelve 250 x 30 m plots (regional sampling scale). Moreover, we combined adjacent or random subplots and plots in order to increase the spatial sampling scales at the local and regional levels. We then calculated commonly used binary and quantitative network‐level metrics for both sampling scales (i.e., number of species and interactions, nestedness, specialization, and modularity), all of which encompass a wide array of structural patterns in interaction networks.

4.We observed increasing species and interactions across sampling scales, and while most network descriptors remained relatively constant at the local level, there was more variation at the regional scale. Among all metrics, specialization was most constant across different spatial sampling scales. Furthermore, we observed that adjacent assembly did not generate more variation in network descriptor values compared to random assembly. This finding indicates that the spatially aggregated distribution of species/individuals and abiotic conditions does not affect the organization of these interacting assemblages.

5.Our results have a direct impact on our empirical and theoretical understanding of the ecological dynamics of species interactions by demonstrating that small spatial sampling scales should suffice to record some patterns commonly found in ant‐plant interaction networks in a highly diverse tropical rainforest.

1. 尽管学界对量化生态网络结构的度量指标抱有极高关注，但采样与尺度效应对网络结构的影响仍未得到充分解析。事实上，生态学领域最具挑战性的议题之一，便是如何定义适宜的尺度（即时间或空间尺度），以精准描述并理解生态系统的运作规律。
2. 本研究于巴西南部亚马逊雨林中采集了一系列蚁植互作网络（ant‐plant interaction networks）样本，旨在探究从局域到区域的空间采样尺度，是否会影响我们对这类网络结构的认知。
3. 为此，我们在12个250×30 m的样地（区域采样尺度）内嵌套设置相邻的25×30 m亚样地（局域采样尺度），并记录其中的蚁植互作关系。此外，我们通过合并相邻或随机选取的亚样地与样地，分别提升局域与区域层面的空间采样尺度。随后，我们针对两类采样尺度计算了常用的二元与定量网络水平度量指标，包括物种数、互作关系数、嵌套性（nestedness）、特化度（specialization）与模块化（modularity），上述指标均可覆盖互作网络中多样的结构模式。
4. 研究结果显示，随着采样尺度扩大，样地内的物种数与互作关系数均呈上升趋势；多数网络描述指标在局域尺度下相对稳定，但在区域尺度下的变异程度更高。在所有度量指标中，特化度在不同空间采样尺度下的稳定性最强。此外，相较于随机合并方式，相邻合并并未使网络描述指标的数值产生更大变异。这一发现表明，物种/个体的空间聚集分布与非生物环境条件，并不会影响这类互作群落的组织模式。
5. 本研究证实，在物种高度丰富的热带雨林中，仅需采用较小的空间采样尺度，即可记录到蚁植互作网络中常见的部分结构模式；这一结果将直接推动学界对物种互作生态动力学的实证与理论认知。