Translocation experiment reveals capacity for mountain pine beetle persistence under climate warming

Abstract

Predicting species response to climate change is a central challenge in ecology, particularly for species that inhabit large geographic areas. The mountain pine beetle (MPB) is a significant tree mortality agent in western North America with a distribution limited by climate. Recent warming has caused large‐scale MPB population outbreaks within its historical distribution, in addition to migration northward in western Canada. The relative roles of genetic and environmental sources of variation governing MPB capacity to persist in place in a changing climate, and the migratory potential at its southern range edge in the United States, have not been investigated. We reciprocally translocated MPB populations taken from the core and southern edge of their range, and simultaneously translocated both populations to a warmer, low‐elevation site near the southern range boundary where MPB activity has historically been absent despite suitable hosts. We found genetic variability and extensive plasticity in multiple fitness traits that would allow both populations to persist in a warming climate that resembles the thermal regime of our low‐elevation site. We demonstrate, for the first time, that supercooling points in MPBs are influenced both by genetic and environmental factors. Both populations reproduced with seasonally appropriate univoltine generation times at all translocated sites, and bivoltinism was not observed. The highest reproductive success occurred at the warmest, out‐of‐range low‐elevation site, suggesting that southward migration may not be temperature limited.

Field Translocation of Mountain Pine Beetles Suggests Phoretic Mite Communities Are Locally Adapted, and Mite Populations Respond Variably to Climate Warming

“…To determine the overall temperature profiles of the three field sites, we collected air and internal log temperature using CR1000 measurement and data loggers (Campbell Scientific, Logan, UT, USA) which recorded data hourly for the duration of the experiment, specific details of which are available in a previously published study [ 26 ]. We used these data to calculate daily maximum and minimum temperatures for the beetle log environment in all three field sites to make inferences on environmental temperature effects.…”

“…The novel warm environment (CF) had the warmest temperatures on average with the highest average maximum temperature, although minimum temperatures were similar to those of LM, and served as the novel warming environment for both populations ( Table 1 ). Internal log temperatures did not vary within sites [ 26 ].…”

“…Detailed beetle emergence patterns (synchrony, development rate, genetic differences in populations) have already been published [ 26 ]. Here, we present successful beetle emergence per site estimated based on the number of beetles per site and the number of successful galleries ( Figure S1 ) per site to provide information about mite abundances relative to beetle emergence across sites and populations.…”

“…Dendroctonus ponderosae , whose range spans most of western North America, is considered a keystone species with the potential to influence forests on a landscape level [ 19 , 25 ]. These beetles exhibit resilience to short-term changes in climate regimes [ 26 ], distinct genetic differences across populations [ 27 ], and trait phenotypic plasticity [ 9 ]. They are also directly associated with an array of symbiotic organisms (symbiota), forming a biodiverse community comprising multiple interactions that directly and indirectly influence their (beetle) performance [ 28 , 29 , 30 ].…”

“…We additionally measure effects of warming temperatures on mite communities with a novel field translocation treatment outside the beetle’s historic distribution range to simulate “climate warming” in its native range. Dendroctonus ponderosae populations from Utah and Arizona, though distinctly different populations [ 9 , 26 ], have nested mite communities [ 37 ]; therefore, we asked whether shifts in mite community composition could be explained by differences in their local environment and climate warming. We hypothesized that the mite community compositions on D. ponderosae (based on the presence and absence of species and their abundances) are significantly affected by changes in their local climate.…”