A mechanistic, stigmergy model of territory formation in solitary animals: Territorial behavior can dampen disease prevalence but increase persistence

Abstract

Although movement ecology has leveraged models of home range formation to explore the effects of spatial heterogeneity and social cues on movement behavior, disease ecology has yet to integrate these potential drivers and mechanisms of contact behavior into a generalizable disease modeling framework. Here we ask how dynamic territory formation and maintenance might contribute to disease dynamics in a territorial, solitary predator for an indirectly transmitted pathogen. We developed a mechanistic individual-based model where stigmergy-the deposition of signals into the environment (e.g., scent marking, scraping)dictates local movement choices and long-term territory formation, but also the risk of pathogen transmission. Based on a variable importance analysis, the length of the infectious period was the single most important variable in predicting outbreak success, maximum prevalence, and outbreak duration. Host density and rate of pathogen decay were also key predictors. We found that territoriality best reduced maximum prevalence in conditions where we would otherwise expect outbreaks to be most successful: slower recovery rates (i.e., longer infectious periods) and higher conspecific densities. However, for slower pathogen decay rates, stigmergy-driven movement increased outbreak durations relative to random movement simulations. Our findings therefore support a limited version of the "territoriality benefits" hypothesis-where reduced home range overlap leads to reduced opportunities for pathogen transmission, but with the caveat that reduction in outbreak severity may increase the likelihood of pathogen persistence. For longer infectious periods and higher host densities, key trade-offs emerged between the strength of pathogen load, the strength of the stigmergy cue, and the rate at which those two quantities decayed; this finding raises interesting questions about the evolutionary nature of these competing processes and the role of possible feedbacks between parasitism and territoriality. This work also highlights the importance of considering social cues as part of the movement landscape in order to better understand the consequences of individual behaviors on population level outcomes.

How territoriality reduces disease transmission among social insect colonies

“…Many other group-living animals may also benefit from territoriality reducing opportunities for transmission between groups (e.g., Loehle 1995 ; Craft et al 2011 ; Rozins et al 2018 ), which may make aspects of our findings relevant beyond eusocial animals. Our findings also complement those of a recent computational model, which showed that increased territoriality (through stigmergy) in a solitary species resulted in less severe outbreaks but could promote the persistence of infection within the population as a whole (White et al 2020 ). In that study, territoriality had the greatest impact when individuals recovered more slowly from infection and the population density of hosts was higher (White et al 2020 ).…”

Domestic Dogs and Wild Foxes Interactions in a Wildlife-Domestic Interface of North-Central Chile: Implications for Multi-Host Pathogen Transmission

“…Second, due to our sampling design was composed by passive single-camera stations monitoring restricted areas during delimited periods, it prevented us from better describing social signaling behaviors potentially involved in disease transmission, such as sniffing, rolling, defecating, urinating. According to previous studies, cross-species scent marking could potentially promote the persistence and spread of pathogens released into feces and urine of dogs and foxes interacting at the wildlife-domestic interface [e.g., ( 24 , 43 , 90 , 91 )], which may be mediated by the interplay between prolonged shedding (e.g., CDV) and extended environmental resistance (e.g., CPV) characterizing several multi-host pathogens ( 92 ). Third, because random camera sampling could only record indirect interactions derived from animal movement through the landscape, perhaps the simultaneous monitoring of aggregation points (i.e., known canid paths) by camera trapping, and individual tracking with GPS telemetry or proximity loggers may be alternative approaches to account for more precise dog-fox interaction frequencies and their related temporal patterns ( 93 ).…”

Transmission of one predicts another: Apathogenic proxies for transmission dynamics of a fatal virus

“…In order to determine if certain transmission parameters were particularly important for feasible performance, we performed post hoc random forest analyses using the R package randomForest (63,64) for each of the four model types (see supplementary results). While random forests typically showed poor balanced accuracy and area under the curve (AUC) results, the parameter shaping transmission from regressively infected individuals (C), showed support for weak to moderate transmission from regressives (i.e., C = 0.1 or 0.5; Figure S10).…”

“…To determine if certain transmission parameters were important for feasible outcomes, we performed post hoc random forest variable importance analyses for each of the four model types with "feasible" as the binary response variable (using the R package randomForest [56,57]; see supplementary results).…”