Effects of parasites on the conservation of threatened predators

Kevin Lafferty, Per Arneberg, Andy Dobson, Peter Hudson, Bob Holt, Charles Mitchell (in no particular order, plus maybe Drew Harvel, Priyanga Amarasekare, Sonia Altizer, and others?)

The low popluation densities of threatened species, particularly predators, may prevent many potential parasite species from persisting within a host population. Two major categories of parasites may still have important effects on populations of threatened predators: (1) parasites with complex life cycles (either vector-transmitted or trophically-transmitted), and (2) directly transmitted parasites specific to prey of the threatened predator. We will examine the potential influences of these parasite categories on threatened predator species using model analyses accompanied by examples from the literature.

(1) Parasites with complex life cycles including the predator:

Perhaps as many as half of all parasite species employ complex life-cycles. Such life-cycles, due to their great variety, are difficult to model and to generalize from. In addressing the issue of how complex life-cycles may have unique implications for conservation biology, we found it useful to separate them into vector borne diseases and trophically transmitted diseases. Trematodes in molluscs are characteristic of a third category where a parasite moves from one host species to another using a free-living stage. One practical implication of complex life-cycles is that they provide more targets for intervention than direct life-cycle parasites. The impacts of Avian malaria in Hawaii, undersore the important possibility that vector transmitted diseases may be more generalist in vertebrate hosts, leading to a disproportionate impact on rare host species. Trophically transmitted parasites may be important for food webs, in terms of their indirect effects at multiple trophic levels as well as their plausible net benefit for final host top carnivores via the phenomenon of host manipulation of intermediate hosts. This sub-group proposes several topics to investigate. Per Arneberg will investigate a comparative study of the host range of directly and indirectly transmitted parasites. Andy Dobson will use models to determine how optimal intervention strategies vary when trying to control direct and complex lifecycle parasites. Andy Dobson and Kevin Lafferty will exlore data sets on tapeworm-moose-wolf and acanthocephalan-crab-bird/otter, to investigate related aspects of complex life-cycles and conservation.

(2) Parasites of prey, but not the predator:

We will consider both macro- and micro-parasites. Peter Hudson will lead work on the former, and Bob Holt work on the latter. For both models, the importance of several interactions between predator and prey parasite will be examined:

(1) The interactive effects of (a) differential predation on infected (or heavily infected in the case of macroparasites) prey and (b) predator removal on host population dynamics. If the predator is removed, and then reintroduced, does the success of this reintroduction depend on the prey-parasite interaction? In particular, if removing the predator changes the proportion of infected and susceptible (healthy) prey, this may prevent predator reintroduction if the prey class favored by the predator is the one that decreases.

(2) The addition of resources is predicted to destabilize predator-prey interactions, potentially causing the extinction of the predator. Does consideration of parasites infecting the prey alter this prediction?

(3) The effect of a parasite infecting the prey species on predator functional response