Linking behavior,life history and food supply with the population dynamics of white-footed mice(Peromyscus leucopus)

In this paper we review and integrate key aspects of behavioral and life history traits, food supply and populationdynamics of the white-footed mouse (Peromyscus leucopus), a species that is abundant and widely distributedacross much of eastern North America. Results are based largely on a 33-year mark-and-recapture study in a forestfragment in northwest Ohio, USA. Behavioral plasticity in such reproductive traits as mating system and parentalcare allows this species to adjust quickly to changing environments. The species has a relatively “fast” life history,with rapid attainment of sexual maturity and high fecundity in the face of high mortality rates. Maximal reproductiveeffort early in life enables a rapid population response. Food supply, in the form of mast, determines thesize of the reproducing population in early spring, which, in turn, influences the size of the late summer peak population.The peak population size is also affected by short-term weather events possibly acting via the food supply.The effects of weather and food on population growth are in part mediated through competition, including defenseof space and suppression of reproduction. The inelasticity of female territories appears to set an upper limit topopulation density.

Testing the effectiveness of conservation management within biosphere reserves:the case of the Mexican deer mouse(Peromyscus mexicanus)as a bioindicator

Biosphere reserves are protected areas whose purpose is to combine conservation and sustainable development.However,their effectiveness has not been tested sufficiently,especially from an ecological and genetic ap­proach.In this sense,the Peromyscus genus represents an excellent bioindicator to address these questions,due to its short life and high evolutionary rate and fecundity.For conservation managers,genetic structure can in­crease the rate of loss of genetic diversity because alleles exclusive of a subpopulation are more likely to disap­pear as a consequence of genetic drift in comparison with a panmictic population.Here we analyzed the abun­dance,movement distances,morphology/morphometry and genetic structure of 3 populations of Mexican deer mouse(Peromyscus mexicanus)located in different protected zones of La Tigra National Park(Honduras).Our results are consistent among the 3 approaches and showed the highest values of abundance,morphometry and genetic diversity in the population located at the core zone,whereas non-statistically significant differenc­es were found between buffer and transition zone populations,suggesting suitable effectiveness of conservation management in the core zone but a lack of ecological buffering function of the other zones.In addition,the low movement distances and high genetic structure among the studied populations provide evidence of poor con­servation management in the buffer and transition zone.Thus,we discuss the utility of the novel methodology used in this work,combining morphometry,abundance and genetics,in testing the effectiveness of conservation strategies in biosphere reserves,and the value of the Peromyscus genus as a bioindicator.

Polychlorinated Biphenyls in Whole-Body Field Mice Collected Upgradient and Downgradient of a Sediment Retention Structure in Los Alamos Canyon, Los Alamos National Laboratory, New Mexico, USA

Polychlorinated biphenyl (PCBs) congeners were measured in (unwashed) whole-body field (deer) mice (Peromyscus maniculaltus) collected directly upgradient from a sediment retention structure (weir) within Los Alamos Canyon (LAC), Los Alamos National Laboratory (LANL), New Mexico, USA, from 2007 through 2013. Samples were also collected approximately 8 km downgradient of the retention structure in 2009 and 2013. LAC, a major drainage that crosses LANL lands, contains legacy waste, including PCBs, and occasionally discharges storm water and snowmelt flows to the Rio Grande approximately 8.8 km away from the weir. The Rio Grande is the major waterway that flows southward across the state. The weir was constructed across the channel on the northeastern boundary of LANL in late 2000 to help contain sediments mobilized by floodwaters as a result of a large wildfire in early 2000 that burned forest lands west and adjacent to LANL. Total PCBs in field mice directly upgradient of the sediment retention structure from 2007 through 2012 were significantly greater (p 0.05) than in field mice collected from background locations but decreased in concentration over time;by 2013 the levels were statistically similar (p > 0.05) to background. The highest mean total PCB concentration in field mice was below the levels that may negatively impact field mice population attributes. Total PCBs in field mice collected 8 km below the sediment retention structure in 2009 were lower than field mice collected from behind the weir and decreased over time;also by 2013, the amount of PCBs in field mice 8 km below the sediment retention structure were not significantly different (p > 0.05) from background. The rank order of concentrations of ICES 7 PCB congeners in upgradient and downgradient field mice were: No. 153 > 180 > 138 > 118 > 28 > 101 > 52 and No. 153 > 180 > 138 > 52 > 101 > 118 > 28, respectively. Based on the PCB homolog distribution, the major formulation detected in field mice was Aroclor-1260. Overall, the reduction of PCBs in whole-body field mice from both sites over time was attributed, in part, to sediment control practices.

Pilfering of western juniper seed caches by scatter-hoarding rodents varies by microsite and canopy type

Scatter-hoarding rodents store seeds throughout their home ranges in superficially buried caches which,unlike seeds larder-hoarded in burrows,are difficult to defend.Cached seeds are often pilfered by other scatter-hoarders and either re-cached,eaten or larder-hoarded.Such seed movements can influence seedling recruitment,because only seeds remaining in caches are likely to germinate.Although the importance of scatter-hoarding rodents in the dispersal of western juniper seeds has recently been revealed,the level of pilfering that occurs after initial burial is unknown.Seed traits,soil moisture,and substrate can influence pilfering processes,but less is known about how pilfering varies among caches placed in open versus canopy microsites,or how cache discovery and removal varies among different canopy-types,tree versus shrub.We compared the removal of artificial caches between open and canopy microsites and between tree and shrub canopies at two sites in northeastern California during late spring and fall.We also used trail cameras at one site to monitor artificial cache removal,identify potential pilferers,and illuminate microsite use by scatter-hoarders.Removal of artificial caches was faster in open microsites at both sites during both seasons,and more caches were removed from shrub than tree canopies.California kangaroo rats were the species observed most on cameras,foraging most often in open microsites,which could explain the observed pilfering patterns.This is the first study to document pilfering of western juniper seeds,providing further evidence of the importance of scatter-hoarding rodent foraging behavior in understanding seedling recruitment processes in juniper woodlands.

Ecology and management of rodents in no-till agriculture in Washington, USA

No-till farming is an important approach to sustainable agriculture because it can conserve soil and water resources.Unfortunately, rodent populations can thrive under no-till conditions because burrow systems are not disrupted byannual plowing and plant residues build-up on the surface, providing cover and insulation. This can result in substantialcrop damage. We assessed rodent populations, habitat use, food habits, and crop damage in a no-till croppingsystem in Washington, USA. We also conducted preliminary trials of methods to reduce rodent populationsand crop damage. In the fall, many more rodents were captured in fields with unharvested crops than in fieldscontaining only plant stubble, suggesting that rodents leave fields after crop harvest, providing that suitable habitatsare nearby, even when adequate cover is still available in harvested crop fields. By spring, the number of volescaptured was much lower relative to fall. Despite this, capture rates were much higher in surrounding permanentgrass areas than in crop (barley, wheat, pea) fields, suggesting that these grassy areas serve as refugia for rodents.Furthermore, the permanent grass cover type was the landscape variable most associated with rodent capture rates.In three winter pea fields, rodents removed 5–15% of the pea plants over winter. Examination of stomach contentsrevealed that voles mainly fed on grain plants in spring, but that their diet was more diversified in fall. Deer micefed heavily on grain plants in both spring and fall, but also used insects as food. Metal barrier exclosures (9 m × 9m), extending above and below ground, did not prevent access by rodents. Rodent populations in areas treated withzinc phosphide on grain were comparable to untreated areas 1 year after application of the rodenticide, perhaps becauseof immigration and recruitment, suggesting that baiting does not provide a long-term solution to rodent damagein no-till agricultural fields.