Abstract
We synthesize observations from 1979 to 2016 of a contact zone involving two subspecies of pocket gophers (Thomomys bottae connectens and T. b. opulentus) and their respective chewing lice (Geomydoecus aurei and G. centralis) along the Río Grande Valley in New Mexico, U.S.A., to test predictions about the dynamics of the zone. Historically, the natural flood cycle of the Rio Grande prevented contact between the two subspecies of pocket gophers. Flood control measures completed in the 1930s permitted contact, thus establishing the hybrid zone between the pocket gophers and the contact zone between their lice (without hybridization). Since that time, the pocket gopher hybrid zone has stabilized, whereas the northern chewing louse species has replaced the southern louse species at a consistent rate of ~150 m/year. The 0.2–0.8 width of the replacement zone has remained constant, reflecting the constant rate of chewing louse species turnover on a single gopher and within a local pocket gopher population. In contrast, the full width of the replacement zone (northernmost G. centralis to southernmost G. aurei) has increased annually. By employing a variety of metrics of the species replacement zone, we are better able to understand the dynamics of interactions between and among the chewing lice and their pocket gopher hosts. This research provides an opportunity to observe active species replacement and resulting distributional shifts in a parasitic organism in its natural setting.
Highlights
Most studies of species contact are restricted to two taxa at a sin‐ gle point in time, despite theoretical studies indicating the value of considering interactions among multiple species (Svenning et al, 2014) over long time periods (Buggs, 2007)
We identified samples of chewing lice from 377 pocket gophers from the study area (San Acacia to south of Lemitar, Figures 2c and 3) as pure G. aurei, mixed‐species samples, or pure G. centralis
The dispersal rate of chewing lice across the landscape is dependent on a complicated set of nonindependent factors in‐ cluding pocket gopher density, rate of pocket gopher dispersal, fre‐ quency of physical contact among pocket gophers, rate of successful colonization of new host individuals by chewing lice, and rate of spe‐ cies replacement on a newly colonized pocket gopher
Summary
Most studies of species contact are restricted to two taxa at a sin‐ gle point in time, despite theoretical studies indicating the value of considering interactions among multiple species (Svenning et al, 2014) over long time periods (Buggs, 2007). From five time periods (1979–1980, 1989–1991, 1996, 2001, and 2016), have enabled a more complete description of the rate and dynamics of the moving chewing louse replacement zone, while leading to a more precise explanation for the recent contacts between the two pocket gopher subspecies and their chewing lice. By employing these additional zone metrics, we are able to better understand the dynamics of interactions between and among the chewing lice and their pocket gopher hosts
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