How artificial light at night may rewire ecological networks: concepts and models

Abstract

Artificial light at night (ALAN) is eroding natural light cycles and thereby changing species distributions and activity patterns. Yet little is known about how ecological interaction networks respond to this global change driver. Here, we assess the scientific basis of the current understanding of community-wide ALAN impacts. Based on current knowledge, we conceptualize and review four major pathways by which ALAN may affect ecological interaction networks by (i) impacting primary production, (ii) acting as an environmental filter affecting species survival, (iii) driving the movement and distribution of species, and (iv) changing functional roles and niches by affecting activity patterns. Using an allometric-trophic network model, we then test how a shift in temporal activity patterns for diurnal, nocturnal and crepuscular species impacts food web stability. The results indicate that diel niche shifts can severely impact community persistence by altering the temporal overlap between species, which leads to changes in interaction strengths and rewiring of networks. ALAN can thereby lead to biodiversity loss through the homogenization of temporal niches. This integrative framework aims to advance a predictive understanding of community-level and ecological-network consequences of ALAN and their cascading effects on ecosystem functioning. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Keywords: activity patterns; ecological communities; human impact; light pollution; niche.

Figure 1.

Flow diagram showing the number of studies included in this review that investigate the impact of ALAN on ecological communities. The numbers show the type of community investigated (food web, plant–pollinator community or single trophic-level community, e.g. plants), the main pathways by which the ALAN impact is transmitted in the community (including two studies that report no impact) and the scientific approach used by the authors. The colours in the diagram indicate ALAN impact pathways. (Online version in colour.)

Figure 2.

A conceptual framework linking ALAN impact to changes in ecological interaction networks. ALAN impacts ecological-network assembly and species interactions via four different pathways. These have consequences for network structure, stability and the functions provided by the communities. (Online version in colour.)

Figure 3.

Concept of the food web modelling approach with the null model and four Scenarios (1–4). The effect of ALAN is modelled as a shift in the temporal niche of nocturnal, crepuscular and/or diurnal species, which affects their temporal niche overlap and therefore encounter probability. The change in total overlap indicates general niche separation or homogenization along the temporal dimension (Scenario 1: unaffected; Scenarios 2 and 3: niche separation and Scenario 4: niche homogenization). (Online version in colour.)

Figure 4.

Illustration of how the different Scenarios of temporal shifts in response to ALAN can affect food web structure and interaction strengths. For illustration purposes, we depicted a food web of only 13 animal and four basal species (simulations were always done with 20 plant and 40 animal species) with the maximum shift in temporal niches of 0.5. Dashed red links indicate newly established links and the thickness of links represents the interaction strength. Dotted grey links represent links to basal species that are not directly affected by ALAN in the model. (Online version in colour.)

Figure 5.

Impact of ALAN on the stability of modelled food webs. (a) Community persistence and (b–e) persistence of different groups (basal, crepuscular, nocturnal and diurnal species) in response to ALAN. The scenarios represent the different temporal niche shifts (figures 3 and 4). In Scenario 1, only crepuscular species shift (total niche overlap unaffected), in Scenario 2, only nocturnal species shift (total niche overlap decreased), in Scenario 3, nocturnal and crepuscular species shift (total niche overlap decreased) and in Scenario 4, diurnal and crepuscular species shift (total niche overlap increased). (Online version in colour.)