Parasite biodiversity faces extinction and redistribution in a changing climate

Abstract

Climate change is a well-documented driver of both wildlife extinction and disease emergence, but the negative impacts of climate change on parasite diversity are undocumented. We compiled the most comprehensive spatially explicit data set available for parasites, projected range shifts in a changing climate, and estimated extinction rates for eight major parasite clades. On the basis of 53,133 occurrences capturing the geographic ranges of 457 parasite species, conservative model projections suggest that 5 to 10% of these species are committed to extinction by 2070 from climate-driven habitat loss alone. We find no evidence that parasites with zoonotic potential have a significantly higher potential to gain range in a changing climate, but we do find that ectoparasites (especially ticks) fare disproportionately worse than endoparasites. Accounting for host-driven coextinctions, models predict that up to 30% of parasitic worms are committed to extinction, driven by a combination of direct and indirect pressures. Despite high local extinction rates, parasite richness could still increase by an order of magnitude in some places, because species successfully tracking climate change invade temperate ecosystems and replace native species with unpredictable ecological consequences.

Fig. 1. Gradients of species richness and predicted turnover through extinction and redistribution.

(A) Current distribution of parasite species richness (S) in our data set is calculated by stacking binary outputs of species distribution models (see point distributions in fig. S5). (B) Turnover (in species units) is measured by following the same procedure from 18 combinations of GCMs and RCPs for the year 2070 and taking the average difference (ΔS) from 2016. (C) Proportional change (ΔS/S) is most severe in low-diversity areas where parasite richness is predicted to increase as a consequence of latitudinal shifts.

Fig. 2. Comparative IUCN “Red List” breakdowns by clade.

(A) Breakdowns are given by habitat loss categories from now to 2070: 0 to 25%, least concern; 25 to 50%, vulnerable; 50 to 80%, endangered; 80 to 100%, critically endangered. (B to I) Conservation classifiers are broken down for eight major clades: (B) Acanthocephala (n = 14 spp.), (C) Astigmata (n = 18), (D) Cestoda (n = 25), (E) Ixodida (n = 141), (F) Nematoda (n = 147), (G) Phthiraptera (n = 5), (H) Siphonaptera (n = 67), and (I) Trematoda (n = 40).

Fig. 3. Primary, secondary, and compounded extinction rates (%) for major helminth clades.

Error bars represent lower and upper bounds to estimation based on the Thomas et al. method and errors in the Dobson method, and means between the two interval ends are shown in bars for (left to right) acanthocephalans, cestodes, nematodes, and trematodes. Cause of extinction is broken down into primary extinction (direct impacts of climate change, no dispersal), secondary extinction (coextinction with hosts, calculated in text S1), and a combined risk (total). Scenarios are presented for (A) no dispersal and (B) full dispersal capacity for parasites. Most helminths face high risk when accounting for coextinction, although acanthocephalans consistently appear much less threatened.