Assessing the direct and indirect effects of food provisioning and nutrient enrichment on wildlife infectious disease dynamics

Abstract

Anthropogenic resource supplementation can shape wildlife disease directly by altering the traits and densities of hosts and parasites or indirectly by stimulating prey, competitor or predator species. We first assess the direct epidemiological consequences of supplementation, highlighting the similarities and differences between food provisioning and two widespread forms of nutrient input: agricultural fertilization and aquatic nutrient enrichment. We then review an aquatic disease system and a general model to assess whether predator and competitor species can enhance or overturn the direct effects of enrichment. All forms of supplementation can directly affect epidemics by increasing host population size or altering parasite production within hosts, but food provisioning is most likely to aggregate hosts and increase parasite transmission. However, if predators or competitors increase in response to supplementation, they could alter resource-fuelled outbreaks in focal hosts. We recommend identifying the traits of hosts, parasites or interacting species that best predict epidemiological responses to supplementation and evaluating the relative importance of these direct and indirect mechanisms. Theory and experiments should examine the timing of behavioural, physiological and demographic changes for realistic, variable scenarios of supplementation. A more integrative view of resource supplementation and wildlife disease could yield broadly applicable disease management strategies.This article is part of the theme issue 'Anthropogenic resource subsidies and host-parasite dynamics in wildlife'.

Elucidating mechanisms of invasion success: Effects of parasite removal on growth and survival rates of invasive and native frogs

“…Anthelmintic treatments increased 2‐week survival rates by 1.4% (Figure 1d; Table ), which compounds to a maximum of 2.4% after 2 months, and did not affect growth rates (Tables 1 and2; Figures 3 and 4). These small effects of parasitic worms on hosts were unexpected, given the potential costs of parasitic infections on hosts as host resources are consumed directly by parasites and additional energy is lost to immune defences and repair of tissues damaged by feeding, attachment and migration (Bonneaud et al., 2003; Civitello, Allman, Morozumi, & Rohr, 2018; Civitello, Fatima, Johnson, Nisbet, & Rohr, 2018; Cressler, Nelson, Day, & McCauley, 2014; Medzhitov, Schneider, & Soares, 2012). Frogs may have been able to compensate for energy lost to worms by increasing their food intake, as has been shown experimentally in captive Cuban treefrogs that were parasitized by A. hamatospicula (Knutie et al., 2017).…”

Emerging human infectious diseases and the links to global food production

“…Agricultural development can yield direct improvements to nutrition, and through several mechanisms, nutrition can be a critical determinant of infectious disease susceptibility and progression 4,32 (Figs. 1 and 2).…”

Anthropogenic resource subsidies and host–parasite dynamics in wildlife

“…Civitello et al [46] expand the breadth of work included in this theme issue by reviewing the similarities and differences in the epidemiological impacts of widespread forms of nutrient input from human activities: agricultural fertilization and aquatic nutrient enrichment. They further develop mathematical models to assess whether including trophic complexity affects the relationship between resource enrichment and host-pathogen interactions.…”