Co-extinction in a host-parasite network: identifying key hosts for network stability

Abstract

Parasites comprise a substantial portion of total biodiversity. Ultimately, this means that host extinction could result in many secondary extinctions of obligate parasites and potentially alter host-parasite network structure. Here, we examined a highly resolved fish-parasite network to determine key hosts responsible for maintaining parasite diversity and network structure (quantified here as nestedness and modularity). We evaluated four possible host extinction orders and compared the resulting co-extinction dynamics to random extinction simulations; including host removal based on estimated extinction risk, parasite species richness and host level contributions to nestedness and modularity. We found that all extinction orders, except the one based on realistic extinction risk, resulted in faster declines in parasite diversity and network structure relative to random biodiversity loss. Further, we determined species-level contributions to network structure were best predicted by parasite species richness and host family. Taken together, we demonstrate that a small proportion of hosts contribute substantially to network structure and that removal of these hosts results in rapid declines in parasite diversity and network structure. As network stability can potentially be inferred through measures of network structure, our findings may provide insight into species traits that confer stability.

Australian spiny mountain crayfish and their temnocephalan ectosymbionts: an ancient association on the edge of coextinction?

“…Therefore, these species are likely to represent key hosts for the conservation of temnocephalan biodiversity [52]. This is a region of high biodiversity, the MacPherson-Macleay overlap (MMO) zone, where temperate and tropical Australian biota overlap [55,56].…”

“…This is to be expected, because the ED distributions are positively skewed (because most species have comparatively low ED and a few have high ED). However, when simulated host extinction probabilities are weighted more realistically [52], according to the IUCN assessment, the average ED for surviving Temnosewellia species declines progressively as host species go extinct (electronic supplementary material, figure S21). In contrast, ED values for the smaller Temnohaswellia dataset are more similar for equal and weighted extinction probabilities, although slightly lower ED values were also observed with weighted host extinction (electronic supplementary material, figure S23).…”

Host traits associated with species roles in parasite sharing networks

“…For example, treating host-parasite interactions as a bipartite network, in which host and parasite species represent nodes of two different classes that interact through parasitism, has provided connections between graph theoretic measures (e.g. nestedness, modularity) and pathogen transmission and diversity (Guegan and Hugueny 1994, Fortuna et al 2010, Poulin 2010, Dallas and Cornelius 2015. Topological measures of host-parasite networks allow for the comparison of networks across space and time (Poisot et al 2012, Morris et al 2014, and thus enable testing of biogeographical and macroecological hypotheses at the level of entire networks.…”

Linking community assembly and structure across scales in a wild mouse parasite community

“…To assess the connection between community assembly and structure, we need empirical systems at which processes at distinct scales can be quantified, and for which a large number of replicates can be sampled. Within-host-parasite communities have recently been suggested to have potential for developing our understanding of the processes underlying community assembly and structure (Blackwell, Martin, Kaplan, & Gurven, 2013;Cobey & Lipsitch, 2013;Costello, Stagaman, Dethlefsen, Bohannan, & Relman, 2012;Dallas & Cornelius, 2015;Dallas, Park, & Drake, 2016). While host-parasite systems carry some important differences to free-living systems, such as habitat patches being mobile (in the case of animal hosts) and the host being an evolving habitat and food resource (Johnson, De Roode, & Fenton, 2015;Poulin & Valtonen, 2001;Seabloom et al, 2015;Ulrich, Almeida, & Gotelli, 2009), the typically large number of communities (infected hosts) and relative ease of longitudinal study of successive infections within individual hosts provides a great opportunity to study the assembly of multiple replicate communities in an easily observable timespan.…”