Cascading effects of a disease outbreak in a remote protected area

Abstract

Disease outbreaks induced by humans increasingly threaten wildlife communities worldwide. Like predators, pathogens can be key top-down forces in ecosystems, initiating trophic cascades that may alter food webs. An outbreak of mange in a remote Andean protected area caused a dramatic population decline in a mammalian herbivore (the vicuña), creating conditions to test the cascading effects of disease on the ecological community. By comparing a suite of ecological measurements to pre-disease baseline records, we demonstrate that mange restructured tightly linked trophic interactions previously driven by a mammalian predator (the puma). Following the mange outbreak, scavenger (Andean condor) occurrence in the ecosystem declined sharply and plant biomass and cover increased dramatically in predation refuges where herbivory was historically concentrated. The evidence shows that a disease-induced trophic cascade, mediated by vicuña density, could supplant the predator-induced trophic cascade, mediated by vicuña behaviour, thereby transforming the Andean ecosystem.

Novel pathogen introduction rapidly alters evolved movement strategies, restructuring animal societies

“…Ecological models expect even isolated pathogen outbreaks, such as that of swine fever in wild boar, to last over a decade due to interacting effects of host movement and landscape structure (Scherer et al, 2020). These outbreaks are expected to have substantial cascading effects for landscape and community ecology (Monk et al, 2022). Our model shows that rapid, disease-dominated ecological cascades — individuals have less intake, exerting less top-down pressure on their resource — can occur even without mortality effects, due to evolutionary shifts in movement alone.…”

“…Furthermore, our results suggest that selection against sociality (usually held constant in ecological models) could bring infection outbreaks under control more swiftly than predicted, as the population shifts from gregarious to solitary. Nonetheless, the altered ecological state (here, less resource consumption, as in Monk et al 2022) may be maintained long after — and indeed because — a population has adapted to be less social in the presence of a pathogen. Our network epidemiological models suggest that the spread of pathogens and parasites that are better transmitted by actual social contact (e.g.…”

“…Movement is therefore an important mechanism linking landscape spatial structure and individual distributions with the emergent structure of animal societies. Together, they influence the dynamics of disease outbreaks in animal populations (White et al, 2018 b ; Romano et al, 2020, 2021), and outbreaks may in turn cause cascading effects on landscape and community ecology (Monk et al, 2022).…”

“…Multiple animal taxa — from mammals (Blehert et al 2009; Fereidouni et al 2019; Kuchipudi et al 2022), to birds (Wille and Barr 2022) and amphibians (Scheele et al 2019)—currently face novel pathogen outbreaks; such scenarios will likely become more common due to climate change (Sanderson and Alexander 2020; Carlson et al 2022). Wildlife pathogen outbreaks are primarily studied for their immediate ecological (Monk et al 2022) and potential medical implications (especially for human societies: Kuchipudi et al 2022; Wille and Barr 2022), with host evolutionary dynamics mostly ignored — presumably because the evolution of pathogen hosts is expected to be slow, and not immediately relevant.…”

“…Incorporating an evolutionary component to movement-disease models could allow predictions on important feedbacks between the ecological outcomes of infectious disease and the consequences for the evolution of host behaviour (Cantor et al 2021). This could include the emergence of tradeoffs in the costs and benefits of sociability (Gartland et al 2021), with cascading ecological and social effects (Tanner and Jackson 2012; Spiegel et al 2017; Monk et al 2022; Webber et al 2022). The range of animal taxa at risk from a wide array of pathogens and parasites (Sanderson and Alexander 2020; Carlson et al 2022) makes it important to conceive of models that can capture the key features of the diversity of host-pathogen interactions, and offer broad conceptual insights (White et al 2018 a , b ).…”