Parasite‐Mediated Competition in Deer and Moose: How Strong is the Effect of Meningeal Worm on Moose?

• Published in: Ecological Applications
• Main Authors: Schmitz, Oswald J., Nudds, Thomas D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1994
• Subjects: Alces alces
• Online Access: http://dx.doi.org/10.2307/1942118; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.2307%2F1942118; https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.2307/1942118

It is widely acknowledged (1) that meningeal helminths (Parelaphostrongylus tenuis) carried by white—tailed deer (Odocoileus virginianus) but fatal to moose (Alces alces) and other cervids, have caused widespread population declines where deer have invaded the ranges of other cervids, (2) that meningeal worms can alter the outcome of interspecific competition between cervid hosts, and (3) that moose populations persist on enzootic range in habitat refuges not frequented by deer. Further, some attempts to reintroduce other cervids to range now occupied by deer have failed. However, moose have been observed to persist on range sympatric with deer, there is evidence that at least one moose population introduced to range with deer is growing, and other events (such as habitat change) are confounded with the presumed effects of meningeal worms. Thus, it is still not clear whether the mortality of individual cervids attributed to meningeal worms necessarily has the effects on population dynamics ascribed to it. Using conventional host—macroparasite models, we describe the population dynamics of deer, moose, intermediate gastropod hosts, and the parasite to determine conditions under which the meningeal worm might be implicated in widespread declines of moose populations. The analysis resulted in three general scenarios depending on (1) the magnitude of parameters that affect transmission rates between different phases of the parasite life cycle, (2) the parasite—induced mortality rate of moose, and (3) the difference in comptitive ability between deer and moose. First, when larval transmission to intermediate hosts, consumption of intermediate hosts by definitive hosts, and parasite—induced mortality of moose were all small, and the competitive difference between definitive hosts was large, moose excluded deer. Second, moose and deer could coexist at either a stable or unstable equilibrium. Stable coexistence occurred when transmission rates, mortality rates, and competitive differences were all large; then deer ...