Host density drives macroparasite abundance across populations of a critically endangered megaherbivore

Abstract

What determines the abundance of parasites is a central question within epidemiology. Epidemiological models predict that density-dependent transmission has a principal influence on parasite abundance. However, this mechanism is seldom tested in macroparasites, perhaps because multiple, comparable populations of the same host-parasite relationship are rare. We test the influence of a range of factors on parasite abundance across 18 populations of black rhinoceros (Diceros bicornis) in South Africa. Here we show that host density strongly predicts parasite abundance at the population level for both directly and indirectly transmitted parasites. All other models were not supported. The surprising influence of a single key factor, host density, within a complex ecological system demonstrates the validity of simple epidemiological models. Establishing this previously assumed relationship between host density and parasite abundance has major implications for disease control and parasite ecology. For instance, it is central to the idea of population density thresholds for parasitism, below which a parasite would become extinct. Density-dependent transmission is also essential for calculations of the basic reproductive number, and the hypothesis that parasites may regulate host population size.

Ecological and evolutionary legacy of megafauna extinctions

“…There are two reasons for this expectation. First, parasite co-extinctions are predicted to precede host extinctions when parasites require a minimum host density threshold for successful transmission (Anderson & May, 1978), and second, host density strongly predicts parasite abundance at the population level (Stringer & Linklater, 2015).…”

Parasite vulnerability to climate change: an evidence-based functional trait approach

“…If too few parasites migrate with their hosts, parasite density in the new habitat may be too low to maintain occupancy [ 81 ]; indeed, an increasing body of literature suggests that parasite range shifts may lag behind host range shifts [ 82 ], though this phenomenon is not limited to host–parasite interactions [ 83 ]. For example, Hopper et al.…”

How invasive oysters can affect parasite infection patterns in native mussels on a large spatial scale

“…While such effects have been studied experimentally (e.g., Kopp and Jokela 2007;Thieltges et al 2009, Goedknegt et al 2015, surprisingly few studies have attempted to study the effects of invasive species on infection patterns in native hosts in the field (but see Paterson et al 2011Paterson et al , 2013 who used a combined approach). Parasite infection levels in native hosts are not only potentially affected by invasive species but also influenced by many other factors which have been shown to underlie the generally high spatial heterogeneities in infection levels observed in the field (Thieltges and Reise 2007;Byers et al 2008;Wilson et al 2011;Galaktionov et al 2015;Stringer and Linklater 2015). For example, the population density of native hosts often affects infection patterns across many parasite and host taxa (Arneberg 1998;Galaktionov et al 2015;Stringer and Linklater 2015;Searle et al 2016).…”

“…Parasite infection levels in native hosts are not only potentially affected by invasive species but also influenced by many other factors which have been shown to underlie the generally high spatial heterogeneities in infection levels observed in the field (Thieltges and Reise 2007;Byers et al 2008;Wilson et al 2011;Galaktionov et al 2015;Stringer and Linklater 2015). For example, the population density of native hosts often affects infection patterns across many parasite and host taxa (Arneberg 1998;Galaktionov et al 2015;Stringer and Linklater 2015;Searle et al 2016). Other factors known to affect infection patterns include host size (Mouritsen et al 2003;Thieltges and Reise 2007), the supply of free-living infective stages (often approximated via preceding intermediate host densities for parasites with complex life cycles; Byers et al 2008;Wilson et al 2011;Galaktionov et al 2015) and environmental variables such as temperature, pH and salinity (Pietrock and Marcogliese 2003;Poulin 2006).…”