# Sampling networks of ecological interactions

## TL;DR

This paper discusses the challenges of sampling ecological interactions and proposes a framework to better understand and monitor these interactions in ecological networks.

## Contribution

The paper introduces a conceptual framework for sampling ecological interactions, analogous to biodiversity sampling methods.

## Key findings

- Sampling ecological interactions is challenging due to spatial and temporal uncoupling and low encounter probabilities.
- Interaction networks are typically sparse with low connectance due to forbidden links.
- A robust characterization of interaction networks requires explicit sampling protocols and natural history knowledge.

## Abstract

Sampling ecological interactions presents similar challenges, problems, potential biases, and constraints as sampling individuals and species in biodiversity inventories. Interactions are just pairwise relationships among individuals of two unrelated species, such as those among plants and their seed dispersers in frugivory interactions or those among plants and their pollinators. Sampling interactions is a fundamental step to build robustly estimated interaction networks, yet few analyses have attempted a formal approach to their sampling protocols.

Robust estimates of the actual number of interactions (links) within diversified ecological networks require adequate sampling effort that needs to be explicitly gauged. Yet we still lack a sampling theory explicitly focusing on ecological interactions.

While the complete inventory of interactions is likely impossible, a robust characterization of its main patterns and metrics is probably realistic. We must acknowledge that a sizable fraction of the maximum number of interactions Imax among, say, A animal species and P plant species (i.e., Imax = AP) is impossible to record due to forbidden links, the restrictions imposed by the organisms life-histories. Thus, the number of observed interactions I in robustly sampled networks is typically I << Imax, resulting in extremely sparse interaction matrices with low connectance.

Reasons for forbidden links are multiple but mainly stem from spatial and temporal uncoupling of partner species encounters and from intrinsically low probabilities of interspecific encounter for many of the potential pairwise interactions. Adequately assessing the completeness of a network of ecological interactions thus needs a deep knowledge of the natural history details embedded, so that forbidden links can be “discounted” when addressing sampling effort.

Here I provide a review and outline a conceptual framework for interaction sampling by building an explicit analogue to individuals and species sampling, thus extending diversity-monitoring approaches to the characterization of complex networks of ecological interactions. This is crucial to assess the fast-paced and devastating effects of defaunation-driven loss of key ecological interactions and the services they provide.