Area-restricted search by the plains pocket gopher (Geomys bursarius) in tallgrass prairie habitat

Because pocket gophers have the high energetic cost of excavatingburrows and an inability to detect distant food items throughthe soil, I hypothesized that individuals within establishedburrow systems would use area-restricted search as a foragingstrategy. To examine this hypothesis I compared gopher foragingeffort over a 10-month period between areas in which overallplant densities were experimentally varied. Gophers expendedapproximately 50% of their foraging effort in areas with thehighest plant density, even though these made up only 33% ofthe available area in experimental plots. In large, griddedareas sampled for an entire season as well as in small areasin which gophers foraged for less than 1 week, gopher foragingeffort was related to the density of a single leguminous plantspecies, Psoralea argophylla. In small plots where this plantspecies was at high density, gophers created more tunnel branches,thereby intensifying their search effort. Thus, area-restrictedsearch appears to increase the rate of encounter with the patchilydistributed Psoralea plants.     

Temporal patterns in seedling establishment on pocket gopher disturbances

Disturbances often facilitate seedling establishment, and can change the species composition of a community by increasing recruitment of disturbance-adapted species. To understand the effects of pocket gopher disturbances on alpine seedling dynamics, we examined the gopher disturbances effects on seedling emergence and survival on gopher disturbances 0 to 5 years old. In contrast to results from most other ecosystems, these recently created gopher mounds had lower seedling emergence and survival rates than undisturbed areas. A lack of correlation between species abundances on gopher mounds and undisturbed sites in one of the two communities studied suggested that a suite of disturbance-adapted species recruited onto the mounds. To explain low seedling emergence on recent gopher mounds, we quantified gopher mound seed banks and studied recruitment in a site with mounds that ranged from 0 to >20 years old. Seed numbers in first-year gopher mound soils were extremely low relative to undisturbed soils, and this pattern was mirrored in seedling establishment patterns over the long term. Gopher disturbance depressed seedling emergence density for the first 5 years. Subsequently, emergence density increased until at least 20 years following the disturbance. Emergence on disturbances more than 20 years old was higher than on undisturbed sites. Therefore, gopher disturbances probably facilitate seedling establishment in alpine dry and moist meadow; however, this process takes place over decades.     

Arthropod and helminth parasites from the Plains Pocket Gopher, Geomys bursarius bursarius from the hosts' northern boundary range in Minnesota

As part of a continuing and more general study of the diversity of parasites from subterranean mammals in central North America, individuals of the Plains Pocket Gopher, Geomys bursarius bursarius, were collected from 7 localities in northwestern Minnesota from September 1991 through October 1996. Arthropods collected included the fleas, Opisocrostis bruneri (4 of 124, 3.2%), Foxella ignota ignota (85 of 124, 68.5%); the chewing louse, Geomydoecus geomydis geomydis from 98 of 124 (79%), and larvae of the tick, Dermacentor variabilis (1 of 124, 0.8%). Nematodes found included Physaloptera limbata (2 of 118 gophers, 1.7%), Capillaria americana (4 of 118, 3.4%), and Ransomus rodentorum (31 of 118, 26.3%). Cestodes recovered included Anoplocephaloides infrequens (12 of 136 gophers, 8.8%), Anoplocephaloides variabilis (19 of 136, 14%), Andrya macrocephala (20 of 136, 14.7%), and Hymenolepis weldensis from 12 of 136, 8.8%. The acanthocephalan, Moniliformis clarki was found in 1 of 118 gophers (0.8%). No parasites were found in the cheek pouches, thoracic, or peritoneal cavities.     

Karyotypic variation following an elevational gradient in the pocket gopher,Thomomys bottae grahamensis Goldman

A system of non-Robertsonian chromosomal polymorphism is described for populations of the pocket gopher, Thomomys bottae grahamensis Goldman, from the Graham Mountains of southeastern Arizona. The polymorphism occurs in three of the four populations sampled, but the range of chromosomal variation within each population is less than for the whole sample. The diversity varies clinally with elevation and is strongly correlated with both habitat and moisture gradients. Each population is considered to be at an adaptive norm with respect to the occupied habitat, and the karyotypic changes are presumed to have played a role in this adaptability. Maintenance of the polymorphic conditions in each population is considered to be due to karyotypic stability (either frequency equilibrium or population monotypy) coupled with gene flow from adjacent populations.     

Geographic genetic architecture of pocket gopher (Thomomys bottae) populations in Baja California, Mexico

Phylogenetic analyses of complete mitochondrial cytochrome b sequences support the monophyly of pocket gopher (Thomomys bottae) populations from the 1000 km length of the Baja California peninsula of Mexico, relative to other geographical segments of the species range in western North America. The Baja California peninsula is an area that encompasses considerable ecomorphological and infraspecific diversity within this pocket gopher species. However, detailed population analyses encompassing 35 localities distributed over the southern half of the peninsula reveal only trivial phylogeographical structure. Rather, most of the 72 unique 500-base pair haplotypes examined from 142 individuals is restricted to single populations, although a few haplotypes are shared broadly across geography. Individual populations are typically comprised of haplotype sets from different branches in a network of relationships. Analysis of molecular variance (amova) indicates that approximately half of the total pool of variation is contained among individuals within local populations, and that only about 25% can be explained by the regional subdivisions of current subspecies distributions or physiographic realms. A hypothesized historical vicariant event that has been causally linked to the phylogeographical structure of other, codistributed species has had little influence on these pocket gopher populations, explaining only 13% of the total variation. The temporal depth, estimated by coalescence parameters, of the haplotype lineage in Baja California is relatively recent, approximately 300,000 generations; both the mismatch distribution of pairwise comparisons and a significantly positive exponential growth estimate support a recent history of expanding populations; but current, or recent past, migration estimates have remained small, are largely unidirectional from north to south, and weak isolation by distance is present. All data suggest that pocket gophers have relatively recently invaded the southern half of peninsular Baja California, with the genetic signature of expansion still evident but with sufficient time having lapsed to result in a weak isolation by distance pattern. The geographical assemblage of sampled populations thus appears as a meta-population, with limited gene flow contrasting with random haplotype loss due to drift in small, localized populations.     

The relationship between genetic variability and growth rate among populations of the pocket gopher, Thomomys bottae

Perhaps the oldest unresolved debate inconservation genetics is whether geneticvariability matters – in other words, whetherrelatively low average genetic variationcontributes to deficits in individual andpopulation level vigor and fitness. Using astatistically powerful paired sampling designin which each of three pairs of populationsconsisted of one high genetic variability andone low genetic variability population from aparticular subspecies of the pocket gopher,Thomomys bottae, we tested the hypothesisthat individuals from populations with lowergenetic variability have lower growth rates (acommonly used surrogate for fitness) than thosefrom populations with higher variability. Wemeasured genetic variability using averageallozyme heterozygosity and two measures of DNAfingerprint band sharing (Jeffreys 33.15 andMS1 probes). The population rankings of thelevels of genetic variability among the threemeasures were concordant. The least squaresmean growth rate (controlling for sex,subspecies and initial mass) of gophers fromlow variability populations (0.41 ± 0.06g/day, n = 48) was less than half that ofgophers from high variability populations (1.04± 0.07 g/day, n = 45). This result lendscredence to the premise that differences inpopulation level genetic variability havesignificant fitness consequences andunderscores the importance of maintaininggenetic variability in managed populations.     

Pocket gophers (Geomys bursarius), vegetation,and soil nitrogen along a successional sere in east central Minnesota

Summary Insect size tactics or developmental strategies are discussed in relation to decisions individuals make about when to mature. Such decisions carry with them costs and benefits in terms of that individual's reproductive success. Whenever size affects fitness, selection should act such that individuals evaluate the costs and benefits due to changes in size and should mature when the ratio of benefit to cost is maximized.Predictions about seasonal changes in adult sizes within a population are tested on two species of mole cricket, Scapteriscus acletus and vicinus. Specifically, individuals maturing in the fall should be larger than average because there is no cost associated with delayed reproduction since reproduction occurs only during spring months. Smaller than average individuals should remain in juvenile stages and get larger before reproducing. Also it is predicted that as the spring reproductive season progresses a greater proportion of smaller individuals should mature because the costs due to delaying reproduction increase. The changes in seasonal distribution of adult sizes of mole crickets support the predictions and suggest that individuals make decisions about when to mature based on costs and benefits associated with changes in size.     

Nucleotide polymorphism at the alcohol dehydrogenase locus of pocket gophers, genus Geomys

Using the strictly neutral model as a null hypothesis, we tested for deviations from expected levels of nucleotide polymorphism at the alcohol dehydrogenase locus (Adh-1) within and among four species of pocket gophers (Geomys bursarius major, G. knoxjonesi, G. texensis llanensis, and G. attwateri). The complete protein-encoding region was examined, and 10 unique alleles, representing both electromorphic and cryptic alleles, were used to test hypotheses (e.g., the neutral model) concerning the maintenance of genetic variation. Nineteen variable sites were identified among the 10 alleles examined, including 9 segregating sites occurring in synonymous positions and 10 that were nonsynonymous. Several statistical methods, including those that test for within-species variation as well as those that examine variation within and among species, failed to reject the null hypothesis that variation (both within and between species of Geomys) at the Adh locus is consistent with the neutral theory. However, there was significant heterogeneity in the ratio of polymorphism to divergence across the gene, with polymorphisms clustered in the first half of the coding region and fixed differences clustered in the second half of the gene. Two alternative hypotheses are discussed as possible explanations for this heterogeneity: an old balanced polymorphism in the first half of the gene or a recent selective sweep in the second half of the gene.      

Influence of pocket gopher mounds on a Texas coastal prairie

Summary Effects of pocket gopher (Geomys attwateri) mound-building activity on plant community composition and soil nutrient concentrations were investigated in south Texas on both burned and unburned coastal prairie sites. Pocket gophers deposited large amounts of soil which were lower in nutrient content than randomly-collected samples. Above-ground plant biomass was greater around mounds than in random samples mainly because of increased dicots around mounds on the burned area when compared with random samples on the same area. Pocket gophers may have concentrated their activities (and therefore, mounds) in areas with higher dicot biomass on the burned area since they prefer perennial dicots as food, or the presence of mounds may have ameliorated the apparent negative effect of fire on dicots.     

Morphology, genetics, and ecology of pocket gophers (genus Geomys) in a narrow hybrid zone

A population of hybrid pocket gophers ( Geomys bursarius × G. lutescens ) exists 1–2 km west of Oakdale, Antelope County, Nebraska, U.S.A. The hybrids occur in soil that has characteristics intermediate between that occupied by G. lutescens (sand) and by G. bursarius (silt loam); the vegetation associations on the different soils are Sandhills Prairie and Tall-grass Prairie, respectively, with mixed prairie on the intermediate soils. Hybrids are identifiable on the basis of both qualitative and quantitative morphological characteristics, allozymes and karyology. Concordance between morphological, allozymic, karyotypic and ecological data sets is very high. Hybrids appear to reproduce normally and survive well; i.e. they suffer no obvious loss of fitness. Backcrossing to either parental type is apparently rare. The parental species each support obligate parasitic lice ( Geomydoecus : Trichodectidae) of different species; these species are not sister species. We suggest that hybrid zones resulting from primary and secondary contact may be distinguished by (1) concordance of clines in different character sets, (2) fossil and biogeographic data, and (3) parasite data. We conclude that this zone resulted from secondary contact, and that the zone is maintained either by selection against hybrids (less likely) or by hybrid superiority (more likely).     

The impact of attractants on pocket gopher trapping

Pocket gophers （Geomyidae） have an extensive impact on both natural and agricultural systems. Trapping is a tech- nique often used to sample and manage these populations. The identification of an attractant that increases capture rates of pocket gophers would greatly assist researchers and pest management professionals alike. Therefore, we tested the attractiveness of four attractants （peanut butter, anise, grapefruit attractant, and carrot） plus a control （no attractant） using uncovered and covered trap sets to determine what impact they have on visitation and capture rates of pocket gophers. We also determined how the impact of cover status and attractants differ across varying weights and gender of pocket gophers. We found no direct effect of any attracrant on visitation and capture rates of pocket gophers, nor on the gender of captured individuals. However, when no attractant was used, the mtmber of pocket gophers captured per 100 trap nights was greater when trap sets were uncovered vs. when covered, and capture rates were generally high and consistent when using peanut butter as an attractant. Additionally, we noted that covered trap sets that were baited with peanut butter yielded heavier pocket gopher captures than uncovered trap sets using this same attractant. This is key, given the difficulty associated with capturing older, more experienced individuals. Combined with data from a previous investigation, this suggests that there is no advantage to using any attractant when utilizing uncovered trap sets, but there is likely some benefit to using peanut butter in covered trap sets [Current Zoology 60 （4）： 472-478, 2014].