Predation on giant flying squirrels (Petaurista philippensis) by black crested gibbons (Nomascus concolor jingdongensis) at Mt. Wuliang, Yunnan, China

Predation on vertebrates is infrequent in gibbons. In a 14-month field study of the central Yunnan black crested gibbon (Nomascus concolor jingdongensis) at Mt. Wuliang, Yunnan, China, we observed gibbons attacking, killing and eating giant flying squirrels (Petaurista philippensis). During 845 h of observation on one study group, the gibbons attacked giant flying squirrels 11 times, and succeeded in 4 cases. Although all members of the group attempted to attack the squirrels, all four successful attacks were made by the same adult female. The victims were infants in three cases and a juvenile or sub-adult in one case. Black crested gibbons also attacked adult giant flying squirrels by grabbing their long tails and throwing them from the canopy, but they failed to catch or kill the prey in three cases observed. Passive meat sharing occurred in three out of four successful cases. Besides hunting giant flying squirrels, the black crested gibbons also ate eggs or chicks in two birds’ nests and one lizard.     

Tests of hypotheses on predation as a factor maintaining polymorphic melanism in coastalplain fox squirrels (Sciurus niger L.)

Fox squirrels ( Sciurus niger ) in the south-eastern U.S. coastal plain differ from those in the rest of the species' range by having black heads with white nose and ears. Postcranially on the dorsum, they also show interindividual colour variation, ranging from all-light agouti to all-black non-agouti. I present results of experiments undertaken to test whether the evolution of these pigmentary features can be attributed to interactions with predators. Comparative static crypsis (when the squirrels are still) was tested by determining how well specimens of the squirrel morphs matched their backgrounds in terms of intensity (brightness) distributions and patch size. Comparative dynamic effects (when the squirrels are moving) were tested using captive red-tailed hawks ( Buteo jamaicensis ) and models of the fox squirrel morphs. Results indicated that morphs of coastal-plain fox squirrels with all-light backs are better static matches to unburned backgrounds than are the darker morphs with which they coexist. Against fire-blackened backgrounds, fox squirrel morphs with intermediate and all-black backs are better intensity matches than those with all-light backs, but the dark morphs are not better patch-length matches than light morphs. The superiority of dark morphs in intensity matching for a short time after a fire does not seem sufficient to account for their long-term maintenance. Hawks responded more slowly to moving fox squirrel models with intermediate amounts of black on the back than to all-light or all-dark morphs; this result suggests a possible factor that would favour retention of genes for dorsal blackness in the coastal-plain population. Patchy black and white heads appear to promote static crypsis of south-eastern fox squirrels, and hawks reacted more slowly to moving squirrel models with such colouration than to those with plain heads.     

Coevolution between crossbills and black pine: the importance of competitors,forest area and resource stability

Studies of predator‐prey interactions have found that geographically structured coevolution has played an important role in the adaptive diversification of crossbills (Loxia spp.). We extend those studies by considering common crossbills (L. curvirostra) in the Mediterranean where they rely on seeds in the cones of black pine (Pinus nigra). On the continent, where tree squirrels (Sciurus vulgaris) are present, enhanced defenses against crossbills were most evident in larger areas of pine forest. On islands in the absence of tree squirrels, crossbills and black pine have coevolved in a predator‐prey arms race on Cyprus but not Corsica. In contrast to other conifers that island endemic crossbills rely upon, black pine does not hold seeds in its cones year round. Consequently, key to the strong crossbill–pine interaction on Cyprus is likely the presence of an alternative conifer that provides seeds during early summer when black pine seeds are scarce.     

The anatomy of a range expansion: changes in cranial morphology and rates of energy extraction for North American red squirrels from different latitudes

Species with expanding ranges provide unique opportunities to examine environmentally induced adaptations in ecological traits and anatomical characteristics. Since the late 1800s, the North American red squirrel (Tamiasciurus hudsonicus) has expanded its range into the central hardwoods of the United States in conjunction with increasing agricultural fragmentation. We examined whether red squirrels from the central hardwoods (west‐central Indiana, USA) displayed differences in foraging behaviors and morphology relative to red squirrels from conifer‐dominated environments (upper peninsula of Michigan, USA), a biome in which red squirrels evolved. Specifically, we measured rates of energy extraction, variation in cranial morphology, and diet preference between red squirrels from both regions. In addition, we compared foraging behaviors of red squirrels from the central hardwoods to those of a competitor that coevolved with nut‐producing trees, the gray squirrel (Sciurus carolinensis). Red squirrels from Indiana and Michigan differed significantly in the efficiency with which they used food items, with individuals from each region extracting calories at a more rapid rate for items that were common in their region. The enhanced efficiency of southern red squirrels feeding on black walnuts (Juglans nigra) was correlated with geographic differences in cranial morphology; skulls of southern squirrels were larger, with longer jaws and higher metrics associated with greater mandibular force than northern squirrels. Contrary to our expectations, red squirrels from Indiana and Michigan did not differ qualitatively in preferences for food items, suggesting that diet choice may be governed by perishability of food items rather than by rates of energy extraction. Gray squirrels were more efficient than Indiana red squirrels in using all food items, and differed only slightly from red squirrels with regard to preference for food items. Measures of efficiency of resource use, after accounting for species‐specific metabolic requirements, suggest that red squirrels are unlikely to compensate ecologically for declining gray squirrel populations in fragmented portions of the central hardwoods, with potentially adverse effects for forest regeneration and succession. Our results demonstrate that invading species can display significant flexibility in adapting to new environments, but they may not be flexible enough to exploit resources in a manner comparable to native species.     

Comparative evaluation of three sampling methods to estimate detection probability of American red squirrels (Tamiasciurus hudsonicus)

Measuring changes in species distribution and understanding factors influencing site occupancy are recurring goals in wildlife studies. Imperfect detection of species hinders such studies, resulting in the underestimation of the number of sites occupied by the species of interest. American red squirrels (Tamiasciurus hudsonicus) are sampled traditionally with live-traps that require substantial resources to deploy and monitor. Here, we assessed whether auditory methods yield similar detection probabilities. We compared the detection probability of American red squirrels in boreal forest using point counts, playback counts, and live-trapping. Over the summer of 2014, we conducted three trapping sessions in 60 sites within black spruce forests of northwestern Quebec, Canada. We also conducted 10 min point counts in the same sites, together with playback counts using recordings of American red squirrel alarm and territorial calls. Using dynamic occupancy models to analyse three primary periods, all composed of three secondary periods, we found that the detection probability of squirrels from point counts was as high as with live-trapping. Our results thus highlight the value of the point count method in measuring American red squirrel occupancy.     

Selection,caching, and consumption of hardwood seeds by forest rodents: implications for restoration of American chestnut

Recent field trials on blight‐resistant hybrids (BC₃F₃) of American chestnut (Castanea dentata) and Chinese chestnut (C. mollissima) have intensified planning for widespread restoration of Castanea to eastern U.S. forests. Restoration will likely rely on natural seed dispersal from sites planted with chestnut; however, we do not know how dispersal agents such as granivorous rodents will respond to hybrid chestnuts. At one extreme, excessive seed consumption may impede restoration. Alternatively, scatter‐hoarding rodents might facilitate the spread of chestnut by dispersal of seeds from restoration plantings. We conducted trials with five rodent species to quantify foraging preferences and to evaluate the potential role of granivores in chestnut restoration. Specifically, we presented seeds from American and hybrid chestnuts (BC₃F₂) with other common mast species and recorded the proportion of seeds removed and the fates of tagged seeds. Mice, chipmunks, and flying squirrels harvested both chestnut types preferentially over larger, tougher black walnut, hickory, and red oak seeds, but fox squirrels and eastern gray squirrels preferred larger seeds to chestnuts. All rodents consumed a greater proportion of the chestnuts than other seed types. American and hybrid chestnut also differed in important ways: except for fox squirrels, rodents preferentially removed American chestnuts over hybrid chestnuts, but we estimated that fox squirrels carried a greater proportion of hybrid chestnuts beyond our tag search area, suggesting that hybrids may be dispersed farther and cached more often than American chestnut. These differences indicate that hybrid chestnut may not be functionally equivalent to American chestnut with regard to seed–granivore interactions.     

The relative roles of the parasol-like tail and burrow shuttling in thermoregulation of free-ranging Cape ground squirrels,Xerus inauris

As small arid-zone mammals, Cape ground squirrels (Xerus inauris) are unusual in being diurnally active. It is postulated that they remain active during the day by using their parasol-like tails to shade their bodies whilst foraging. However, no studies have continuously measured body temperature to determine the effect of using the tail as a parasol, relative to other thermoregulatory behaviours, such as burrow retreat. We caught four free-ranging Cape ground squirrels (673 ± 36 g) and surgically implanted miniature temperature-sensitive data loggers into their abdomens, to record body temperature every 5 min to an accuracy of 0.04 °C, before they were released back into their home range and observed for two weeks. Mean daily peak black globe temperature was 41 °C, and daily peak body temperature reached 40 °C. Ground squirrels raised their tails significantly more often at globe temperatures above 30 °C, but raising the tail did not decrease body temperature, nor prevent body temperature rising. Ground squirrels retreated to burrows, at 18 °C, significantly more often at high body temperatures and body temperature dropped 1–2 °C before re-emergence. We believe that the tail was raised to provide thermal comfort during high solar radiation exposure, and that burrow retreat was employed to dissipate a heat load and remain active diurnally.     

The Mechanism of Replacement of Red Squirrels by Grey Squirrels: A Test of the Interference Competition Hypothesis

Introduced American grey squirrels have replaced native red squirrels in most of the range currently occupied in Britain and northern Italy. The mechanisms of the replacement are not yet fully understood. We restated the commonly cited Interference Competition Hypothesis (ICH) that grey squirrels interfere with the behaviour of red squirrels in three possible ways: 1. by direct aggressive interactions; 2. by interrupting red squirrel mating-chases; or 3. by forcing red squirrels to actively avoid areas intensively used by grey squirrels. We compared the activity pattern, behaviour and reproductive performance of red squirrels in two study areas in northern Italy, one with only red squirrels (control area C1), the other with both species (experimental area E1). The following predictions were tested: 1. the total time spent in both intraspecific and interspecific interactions by red squirrels increases in the experimental area; 2. most interspecific interactions are aggressive, with grey squirrels being the dominant species; 3. the proportion of breeding female red squirrels that are unsuccessful at weaning offspring increases in area E1; 4. grey squirrels take part and interfere with red squirrel mating-chases, and thereby decrease the reproductive output of red squirrel females; 5. the activity pattern of red squirrels in the mixed-species area is shifted with respect to that in the control area to the hours of the day during which grey squirrels show little activity; and 6. red squirrels will shift their home range (or at least their core-area) when grey squirrel densities increase to avoid interspecific core-area overlap. Our results supported only the first prediction of the ICH: they failed to support all the other predictions. Moreover, the increase in the percentage of active time red squirrels spent interacting with other squirrels in the experimental study area was very small (only 1–2 min/day). Red squirrels did not avoid the woodland patches most intensively used by grey squirrels and the interspecific core-area overlap was similar to red squirrel intraspecific core-area overlap. This suggested that red squirrels avoided spatial overlap with grey squirrels in a similar manner as with conspecifics and that an increase in grey squirrel numbers will augment the intensity of resource competition. We therefore conclude that our results do not lend support to the Interference Competition Hypothesis and that interference competition by grey squirrels cannot explain the large-scale replacement of red by grey squirrels that has occurred in Britain and in Piedmont.     

Comparative myology of the forelimb of squirrels (Sciuridae)

The musculature of the shoulder, arm, and forearm was studied in 19 genera of squirrels, representing the Pteromyinae (flying squirrels) and all 7 tribes of the Sciurinae (tree and ground squirrels). The objective was to locate derived anatomical features of functional or phylogenetic significance and to determine how much morphological variation underlies the diverse locomotor behavior of squirrels, which includes terrestrial and arboreal bounding, climbing, digging, and gliding. The fossil evidence suggests that arboreality is primitive for squirrels, and in fact tree squirrels appear to represent the primitive sciurid morphology. Ground squirrels are less uniform and exhibit a few derived features, including a clavobrachialis muscle not seen in other squirrels. Pygmy tree squirrels, which have evolved independently in three tribes, exhibit convergence of forelimb anatomy, including the loss or reduction of several muscles in the shoulder and forearm. The forelimb anatomy of flying squirrels is the most derived and differs from that of tree squirrels in details of shoulder, arm, and forearm musculature. Some of these muscular differences among squirrels have phylogenetic significance, being shared by closely related genera, but none has significance above the tribal level. Many of the differences suggest a variety of changes in function that are amenable to further study. J. Morphol. 234:155–182, 1997. © 1997 Wiley-Liss, Inc.     

Diabetes mellitus in the 13-lined ground squirrel (Citellus tridecemlineatus).

Spontaneous diabetes mellitus was diagnosed in six of 126, 13-lined ground squirrels, Citellus tridecemlineatus. Serum glucose values were significantly higher in the diabetic ground squirrels than in the non-diabetic ground squirrels, while serum insulin values of fasted diabetic squirrels were significantly lower than fasted nondiabetic ground squirrels. In addition, the classic diabetic signs of poly-dipsia, polyuria, glycosuria, ketonuria, polyphasia, and weight loss were present. The proportion of islet tissue to total pancreatic area in diabetic ground squirrels was less than 25% of that in the nondiabetic ground squirrels. Both the number and size of the islets of Langerhans in diabetic ground squirrels were less than those in nondiabetic ground squirrels.     

Contrasting stress response of male arctic ground squirrels and red squirrels

A hormonal-challenge protocol was used to compare the stress response of males of Arctic ground squirrels and red squirrels during the breeding season (May). These squirrels live in the same boreal forest of the Yukon, but have very different life histories and utilize the forest in markedly different ways. Red squirrels had levels of total cortisol, maximum corticosteroid-binding capacity, and free cortisol that were 5, 7, and 2 times, respectively, those of Arctic ground squirrels. Red squirrels were resistant to suppression by an artificial glucocorticoid, dexamethasone (DEX); Arctic ground squirrels were not. Cortisol levels in red squirrels responded slowly but continuously to the ACTH injection; Arctic ground squirrels responded rapidly and then stabilized. Testosterone levels in red squirrels were extremely sensitive to the challenge, being suppressed by both DEX and ACTH; levels in Arctic ground squirrels were resistant to the challenge, being modestly suppressed by DEX and stimulated by ACTH. Energy mobilization, as measured by glucose and free fatty acid responses, was not affected. Red squirrels had four times the levels of white blood cells and higher proportions of lymphocytes and lower proportions of eosinophils than Arctic ground squirrels, indicating that the latter were in worse condition immunologically. Our evidence suggests that the functions associated with the hypothalamic-pituitary-adrenal axis are compromised in breeding male Arctic ground squirrels, but not in red squirrels. We propose that in male red squirrels this axis has evolved in the context of a stable social system based on long-lived animals with individual territories which are needed to deal with unpredictable winter food supplies. In contrast, Arctic ground squirrels escape the rigors of winter by hibernation and this hormonal axis has evolved in short-lived males in the context of intense intra-sexual competition in a social system based on female kin groups and regular male dispersal to avoid inbreeding. J. Exp. Zool. 286:390-404, 2000.     

Hibernation confers resistance to intestinal ischemia-reperfusion injury

The damaging effects of intestinal ischemia-reperfusion (I/R) on the gut and remote organs can be attenuated by subjecting the intestine to a prior, less severe I/R insult, a process known as preconditioning. Because intestines of hibernating ground squirrels experience repeated cycles of hypoperfusion and reperfusion, we examined whether hibernation serves as a model for natural preconditioning against I/R-induced injury. We induced intestinal I/R in either the entire gut or in isolated intestinal loops using rats, summer ground squirrels, and hibernating squirrels during natural interbout arousals (IBA; body temperature 37-39 degrees C). In both models, I/R induced less mucosal damage in IBA squirrels than in summer squirrels or rats. Superior mesenteric artery I/R increased MPO activity in the gut mucosa and lung of rats and summer squirrels and the liver of rats but had no effect in IBA squirrels. I/R in isolated loops increased luminal albumin levels, suggesting increased gut permeability in rats and summer squirrels but not IBA squirrels. The results suggest that the hibernation phenotype is associated with natural protection against intestinal I/R injury.     

Direct vs. Indirect Benefits of Caching by Gray Squirrels (Sciurus carolinensis)

Individuals of many species cache food to gain direct benefits from consuming their own caches, but individuals of a few species also gain indirect benefits by sharing caches with kin. We investigated whether gray squirrels cache primarily to gain direct benefits or if they also gain indirect benefits by sharing caches with kin. If squirrels share caches with kin, then genetically related squirrels should live near one another and cache near one another to facilitate cache sharing. In contrast, if squirrels cache primarily for direct benefits, then they should clump their caches near the center of their ranges to facilitate cache defense. This study was conducted with 140 squirrels in a 10 ha forest. DNA was extracted from blood samples taken from squirrels, and genetic similarity scores from randomly amplified polymorphic DNA (RAPD) loci were used to measure relatedness. Squirrels were given piles of pecans for caching at six sites and observed from a blind. We recorded the direction squirrels took nuts from piles and at one site determined the location of caches. For male–female comparisons, related squirrels lived significantly closer to one another than unrelated squirrels, but this was not the case for female–female and male–male comparisons. The genetic similarity of neighboring squirrels did not influence the location of caches or the direction that squirrels took nuts from piles. Squirrels clumped their own caches and moved nuts toward their own home range centers. These results suggest that gray squirrels cache primarily to gain direct benefits rather than indirect benefits.     

Ectoparasites of gray squirrels in two different habitats and screening of selected ectoparasites for bartonellae

Gray squirrels, Sciurus carolinensis, were livetrapped in 2 different habitat types, woodland (67 squirrels) and parkland (53 squirrels), in southeastern Georgia. Ectoparasites were recovered from anesthetized squirrels and compared between hosts from the 2 habitats. Because of the absence of low vegetation in parkland habitats, it was hypothesized that the ectoparasite fauna, especially ticks and chiggers, would be more diverse on woodland squirrels. The results were generally in agreement with this hypothesis. Seventeen species of ectoparasites were recovered from woodland squirrels, compared with 6 species from parkland squirrels. Five species of ticks and 3 species of chiggers parasitized the woodland squirrels compared with no ticks or chiggers on the parkland squirrels. Significantly higher infestation prevalences were recorded on woodland compared with parkland squirrels for the flea Orchopeas howardi, the tick Amblyomma americanum, and the mesostigmatid mite Androlaelaps fahrenholzi. The mean intensity for O. howardi also was significantly higher on woodland than on parkland squirrels. Because a new strain of Bartonella sp. was isolated recently from S. carolinensis in Georgia, selected ectoparasites from this study were screened for bartonellae by polymerase chain reaction (PCR). Some of the fleas and lice, but none of the mites tested, were PCR positive, suggesting that fleas, or lice, or both, might be vectors of bartonellae between squirrels. Six distinct strains of Bartonella sp. were detected, 2 in fleas and 4 in lice.     

An epizootic of fibromatosis in gray squirrels (Sciurus carolinensis) in Florida

Beginning in the fall of 1998 and extending into the spring and early summer of 1999 there was a large epizootic of squirrel fibromatosis in squirrels in seven counties in peninsular Florida. Hundreds of gray squirrels (Sciurus carolinensis) with multiple cutaneous tumors were submitted or reported to biologists, veterinary hospitals, and private wildlife rehabilitators. Most squirrels died or were euthanized soon after submission. Twenty squirrels were submitted for necropsy. The majority of the squirrels examined were adults (12/20) and male (15/20). The number and location of tumors varied widely among the affected squirrels; however, a consistent finding was involvement of the eyelids (20/20). Histopathology revealed a proliferative population of mesenchymal cells within the dermis and marked ballooning degeneration of keratinocytes in the overlying epidermis. Intracytoplasmic viral inclusions were present in the neoplastic mesenchymal cell population and the degenerating keratinocytes. Ulceration and necrosis of the surface of the tumors or associated tissues was present in 14 of the 20 squirrels. Virions consistent with poxvirus were observed via electron microscopy in samples collected from a representative tumor. Death of the squirrels was attributed to emaciation, tissue damage, and severe negative energy balance associated with poxvirus infection and massive tumor growth. The underlying cause of this unusual epizootic of fibromatosis in gray squirrels remains unknown.     

THE IMPACT OF TREE SQUIRRELS (TAMIASCIURUS) ON LIMBER PINE SEED DISPERSAL ADAPTATIONS

Tree squirrels (Tamiasciurus) are important selective agents on conifer reproductive strategies (Smith 1970, 1975). Although this is well established for wind-dispersed pines, the impact of tree squirrels on bird-dispersed pines has been largely ignored. I assessed the impact of tree squirrels on the allocation of reproductive energy in the bird-dispersed limber pine (Pinus flexilis) by comparing its cone and seed traits from three sites in the Rocky Mountains where tree squirrels (Tamiasciurus) are present to those from three mountain ranges in the Great Basin where tree squirrels are absent. As predicted, differences between the two regions in individual cone and seed traits are consistent with the hypothesis that tree squirrels are important selective agents on these traits. In the absence of tree squirrels, limber pine allocates more than twice as much energy to kernel compared with that invested in putative seed defenses (cone, resin, and seed coat) as does limber pine where tree squirrels are present. Such a large difference is particularly striking, because tree squirrels may have become extinct in the Great Basin in only the last 12,000 yr. Although many factors influence the allocation of energy to cones and seeds, no single factor other than the presence of tree squirrels is compatible with the large and consistent differences between limber pine in the Rocky Mountains and Great Basin. These results show that tree squirrels are an important constraint on the evolution of cone and seed traits that promote the dispersal of seeds by birds.     

Epizootiology and pathologic findings associated with a newly described adenovirus in the red squirrel, Sciurus vulgaris

An infectious disease caused by Squirrelpox virus has contributed to the decline of red squirrels, Sciurus vulgaris, in the British Isles. Because of the heightened disease surveillance activity in red squirrels, adenovirus infection with associated mortality has been detected. Adenoviral disease is described in other rodent species usually associated with stressors. Here we 1) describe the pathologic findings in red squirrels found dead with adenoviral infection and gastrointestinal disease, and 2) investigate the epizootiology of the disease through pathologic investigation, scanning surveillance, and virologic studies. Ten red squirrels involved in conservation studies were diagnosed with adenoviral infection by electron microscopy or PCR. All squirrels exhibited diarrhea and small intestinal inflammation or hemorrhage was evident in seven cases. Lesions indicative of splenic lymphocytolysis were observed in one squirrel and leukocytic hepatitis in another. No adenovirus was detected in grey squirrels, Sciurus carolinensis, inhabiting the same forest area, but previous serologic studies showed that grey squirrels cannot be discounted as a reservoir of the virus. Scanning surveillance showed that 12% of 493 red squirrels had diarrheal disease and two of 13 free-living red squirrels with diarrheal disease had adenovirus infection. Adenoviral disease in declining free-living wild red squirrel populations in the British Isles occurs at a detectable frequency and its impact on the conservation of this species deserves further attention.     

Anatomy of the squirrel wrist: bones, ligaments, and muscles

Anatomical differences among squirrels are usually most evident in the comparison of flying squirrels and nongliding squirrels. This is true of wrist anatomy, probably reflecting the specializations of flying squirrels for the extension of the wing tip and control of it during gliding. In the proximal row of carpals of most squirrels, the pisiform articulates only with the triquetrum, but in flying squirrels there is also a prominent articulation between the pisiform and the scapholunate, providing a more stable base for the styliform cartilage, which supports the wing tip. In the proximal wrist joint, between these carpals and the radius and ulna, differences in curvature of articular surfaces and in the location of ligaments also correlate with differences in degree and kind of movement occurring at this joint, principally reflecting the extreme dorsal flexion and radial deviation of the wrist in flying squirrels when gliding. The distal wrist joint, between the proximal and distal rows of carpals, also shows most variation among flying squirrels, principally in the articulations of the centrale with the other carpal bones, probably causing the distal row of carpal bones to function more like a single unit in some animals. There is little variation in wrist musculature, suggesting only minor evolutionary modification since the tribal radiation of squirrels, probably in the early Oligocene. Variation in the carpal bones, particularly the articulation of the pisiform with the triquetrum and the scapholunate, suggests a different suprageneric grouping of flying squirrels than previously proposed by McKenna (1962) and Mein (1970). J. Morphol. 246:85-102, 2000. Published 2000 Wiley-Liss, Inc.     

EVOLUTIONARY RELATIONSHIPS AMONG COLONIES OF COLUMBIAN GROUND SQUIRRELS AS SHOWN BY MITOCHONDRIAL DNA

Mitochondrial DNA (mtDNA) from 71 Columbian ground squirrels (Spermophilus columbianus) collected in 12 locations in western Canada were assayed for restriction-site variation with 10 endonucleases. Five of these endonucleases revealed variant patterns, and the composite genotypes were used to develop a linear transformation series among the mtDNA genotypes. Two of the four clones had a wide distribution, while the remaining two clones were geographically restricted. The mtDNA of Columbian ground squirrels was also compared to two other species of Sciuridae: Richardson's ground squirrels (S. richardsonii) and Arctic ground squirrels (S. parryii). Calculation of divergences from fragment length and restriction-site data indicated that Arctic ground squirrels and Richardson's ground squirrels were more closely related to each other than either was to Columbian ground squirrels. The transformation series among clones within the Columbian ground squirrels was rooted using Richardson's and Arctic ground squirrels as out-groups. From these data, we conclude that the colonization by female founders of Columbian ground squirrel populations occurred after deglaciation along the eastern ranges of the Rocky Mountains, while colonies on the western ranges may have been present before extensive deglaciation occurred, having existed in refugia in northwestern Alberta.     

Space invaders: effects of invasive alien Pallas’s squirrel on home range and body mass of native red squirrel

Alien species can affect native species through several ecological processes such as competition. Here we tested the hypothesis of interspecific competition for space and food resources between the native Eurasian red squirrel and the invasive Pallas’s squirrel introduced in Italy. We used an experimental study design comparing space and habitat use and body condition parameters of red squirrels between areas of co-occurrence with the Pallas’s squirrel and areas without it. There were no differences in mean home range size of red squirrels between red-only areas and red-Pallas. However, when Pallas’s squirrels were removed, the red squirrels increased their home ranges. Moreover, in the area of syntopy, red squirrels had a higher degree of intraspecific home range overlap than in the red-only area. We also found indirect evidence for competition for food with red squirrels having a poorer body condition when co-occurring with the alien species. We analyzed the body mass and size of red squirrels in the two areas and our results showed that red squirrels had a reduced body mass and size when in syntopy, confirming that the interspecific competition does not allow red squirrels to reach the optimum body condition that they would have if the competitor was not present. Moreover, tree-species niche overlap was very high and both species fed primarily on the same tree seeds. Differences in vegetation cover between areas are discussed. This is the first study that confirms the invasiveness of the Pallas’s squirrel also in terms of capability to compete with native species.