The Northern Flying Squirrel (Glaucomys sabrinus): a Conservation Challenge

Anthropogenically-induced range expansion as an invasion front in native species: An example in North American flying squirrels

Biological invasions are typically framed as non-native species impacting the populations of native species or ecosystems. However, in a changing world, taxonomically similar native species that were previously parapatric or allopatric may become increasingly sympatric over short time periods (<100 years). In the context of climate change in the Northern Hemisphere, this may have a negative impact on northern species whose ranges are being invaded by southern species. To highlight factors that may influence invasion fronts in native species, I use two species of North American flying squirrels, small-bodied nocturnal arboreal Sciurids, as an example. I discuss what factors may enable or limit the expansion of southern flying squirrels (SFS; Glaucomys fuscus) into northern flying squirrel (NFS; Glaucomys sabrinus) habitat and potential impacts that anthropogenically-induced factors have on range shift dynamics. The range expansion of SFS may impact NFS via resource competition, hybridization, and parasite-mediation. Factors potentially enabling the expansion of SFS into NFS habitat include anthropogenic habitat disturbance and climate change, wherein historical land-use (i.e., logging) alters forest composition increasing habitat suitability for SFS and a warming climate allows SFS to expanded their ranges northward into colder regions. Shifts in forest species composition from historical logging may interact with a warming climate to enable SFS to quickly expand their range. Factors limiting SFS expansion include thermoregulation limitations and absence of potential food and denning resources. The factors influencing the dynamics between these two species may be applicable to the shifting ranges of other taxonomically and functionally similar native species in the context of a rapidly changing world in the Anthropocene.

Mammalian mycophagy: A global review of ecosystem interactions between mammals and fungi

The consumption of fungi by animals is a significant trophic interaction in most terrestrial ecosystems, yet the role mammals play in these associations has been incompletely studied. In this review, we compile 1 154 references published over the last 146 years and provide the first comprehensive global review of mammal species known to eat fungi (508 species in 15 orders). We review experimental studies that found viable fungal inoculum in the scats of at least 40 mammal species, including spores from at least 58 mycorrhizal fungal species that remained viable after ingestion by mammals. We provide a summary of mammal behaviours relating to the consumption of fungi, the nutritional importance of fungi for mammals, and the role of mammals in fungal spore dispersal. We also provide evidence to suggest that the morphological evolution of sequestrate fungal sporocarps (fruiting bodies) has likely been driven in part by the dispersal advantages provided by mammals. Finally, we demonstrate how these interconnected associations are widespread globally and have far-reaching ecological implications for mammals, fungi and associated plants in most terrestrial ecosystems. Citation: Elliott TF, Truong C, Jackson S, Zúñiga CL, Trappe JM, Vernes K (2022). Mammalian mycophagy: a global review of ecosystem interactions between mammals and fungi. Fungal Systematics and Evolution 9: 99-159. doi: 10.3114/fuse.2022.09.07.

Testing the parasite-mediated competition hypothesis between sympatric northern and southern flying squirrels

Competition is a driving factor in shaping ecological communities and may act directly or indirectly through apparent competition. We examined a classic example of parasite-mediated competition between northern (Glaucomys sabrinus) and southern flying squirrels (G. volans) via the intestinal nematode, Strongyloides robustus, and tested whether it could act as a species barrier in a flying squirrel hybrid zone. We live-trapped flying squirrels (G. sabrinus and G. volans), grey squirrels (Sciurus carolinensis), red squirrels (Tamiasciurus hudsonicus), and chipmunks (Tamias striatus) from June–September 2019 at 30 woodlots in Ontario, Canada. Fecal samples from squirrels were collected and analyzed for the presence of endoparasite eggs. For each individual, we calculated Scaled Mass Index (SMI) as a measure of body condition to assess the effect of S. robustus on squirrels. We found eggs of S. robustus in all species except chipmunks. Infection with S. robustus did not appear to affect body condition of southern flying squirrels and grey squirrels, but we did find a weak negative effect on northern flying squirrels and red squirrels. Despite a weak asymmetric effect of S. robustus on flying squirrels, we did not find any evidence that parasite-mediated competition could lead to competitive exclusion from woodlots. Furthermore, S. robustus eggs were common in feces of the red squirrel, a species largely sympatric with northern flying squirrel.

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Strongyloides robustus was detected in 4 squirrel species.

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The highest prevalence of S. robustus was found in red squirrels and northern flying squirrels.

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Body condition was lowest in red squirrels and northern flying squirrels infected with S. robustus.

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No evidence of parasite-mediated competition between sympatric flying squirrels leading to competitive exclusion.

Spatiotemporal dynamics in vital rates of Humboldt’s flying squirrels and Townsend’s chipmunks in a late-successional forest

Knowledge of the spatiotemporal variability of abundance and vital rates is essential to the conservation of wildlife populations. In Pacific Northwest forests, previous small mammal research has focused on estimating abundance; few studies have focused on vital rates. We used robust design temporal symmetry models and live-trapping data collected 2011–2016 at nine sites to estimate apparent annual survival, population growth rate, and recruitment of Humboldt’s flying squirrels (Glaucomys oregonensis) and Townsend’s chipmunks (Neotamias townsendii) in a late-successional forest of the Cascade Mountains of Oregon, United States. We also estimated the proportional contribution of apparent annual survival and recruitment to population growth rate. Covariates previously associated with abundance were also associated with vital rates for Townsend’s chipmunks, but less so for Humboldt’s flying squirrels. Apparent annual survival was nearly constant (range = 0.47 to 0.51) among years and sites for Humboldt’s flying squirrels but was consistently lower and more variable among years for Townsend’s chipmunks (range = 0.13 to 0.31). Recruitment was variable among years for both species. Apparent annual survival generally contributed more than recruitment to the population growth rate of Humboldt’s flying squirrels. For Townsend’s chipmunks, recruitment consistently contributed more than apparent annual survival to population growth rate. These findings suggest that life history strategies differed for these co-occurring species. This study demonstrates substantial temporal variation in vital rates and some differences in abundance and vital rate habitat associations, suggesting that habitat suitability inferences based on short time series or variation in abundance could be misleading.

An examination of endoparasites and fecal testosterone levels in flying squirrels (Glaucomys spp.) using high performance liquid chromatography-ultra-violet (HPLC-UV)

The immuno-competence hypothesis proposes that higher levels of testosterone increases the susceptibility to parasitism. Here we examined the testosterone levels in two species of flying squirrels (Glaucomys): one known to regularly host a nematode species (Strongyloides robustus) without ill effects (G. volans) and a closely related species that is considered negatively affected by the parasite. We quantified fecal testosterone levels in northern and southern flying squirrels (G. sabrinus, G. volans) with high-performance liquid chromatography-ultraviolet spectroscopy (HPLC-UV), and compared levels to endoparasites detected in individual squirrels. Qualitatively, we found highest levels of testosterone in male northern flying squirrels infected with Strongyloides robustus. This analytical approach represents an alternative and equally reliable method to using enzyme-linked immunosorbent assay (ELISA), for detecting and quantifying fecal testosterone levels.

Home range, den selection and habitat use of Carolina northern flying squirrels (Glaucomys sabrinus coloratus)

Context Understanding habitat selection is important for determining conservation and management strategies for endangered species. The Carolina northern flying squirrel (CNFS; Glaucomys sabrinus coloratus) is an endangered subspecies found in the high-elevation montane forests of the southern Appalachians, USA. The primary use of nest boxes to monitor CNFS has provided biased information on habitat use for this subspecies, as nest boxes are typically placed in suitable denning habitat. Aims We conducted a radio-telemetry study on CNFS to determine home range, den site selection and habitat use at multiple spatial scales. Methods We radio-collared 21 CNFS in 2012 and 2014–15. We tracked squirrels to diurnal den sites and during night-time activity. Key results The MCP (minimum convex polygon) home range at 95% for males was 5.2±1.2ha and for females was 4.0±0.7. The BRB (biased random bridge) home range at 95% for males was 10.8±3.8ha and for females was 8.3±2.1. Den site (n=81) selection occurred more frequently in montane conifer dominate forests (81.4%) vs northern hardwood forests or conifer–northern hardwood forests (9.9% and 8.7%, respectively). We assessed habitat selection using Euclidean distance-based analysis at the 2nd order and 3rd order scale. We found that squirrels were non-randomly selecting for habitat at both 2nd and 3rd order scales. Conclusions At both spatial scales, CNFS preferentially selected for montane conifer forests more than expected based on availability on the landscape. Squirrels selected neither for nor against northern hardwood forests, regardless of availability on the landscape. Additionally, CNFS denned in montane conifer forests more than other habitat types. Implications Our results highlight the importance of montane conifer to CNFS in the southern Appalachians. Management and restoration activities that increase the quality, connectivity and extent of this naturally rare forest type may be important for long-term conservation of this subspecies, especially with the impending threat of anthropogenic climate change.

Biodiversity threats from outside to inside: effects of alien grey squirrel (Sciurus carolinensis) on helminth community of native red squirrel (Sciurus vulgaris)

Biological invasions are among the major causes of biodiversity loss worldwide, and parasites carried or acquired by invaders may represent an added threat to native species. We compared gastrointestinal helminth communities of native Eurasian red squirrels (Sciurus vulgaris) in the presence and absence of introduced Eastern grey squirrels (Sciurus carolinensis) to detect alterations induced by the alien species. In particular, we investigated whether spillover of a North American nematode Strongyloides robustus occurs and whether prevalence of a local parasite Trypanoxyuris sciuri in red squirrels is affected by grey squirrel presence. The probability of being infected by both parasites was significantly higher in areas co-inhabited by the alien species, where 61 % of examined red squirrels (n = 49) were infected by S. robustus and 90 % by T. sciuri. Conversely, in red-only areas, the two parasites infected only 5 and 70 % of individuals (n = 60). Overall, our findings support the hypothesis that red squirrels acquire S. robustus via spillover from the alien congener and suggest that invaders' presence may also indirectly affect infection by local parasites through mechanisms diverse than spill-back and linked to the increased competitive pressure to which red squirrels are subjected. These results indicate that the impact of grey squirrel on red squirrels may have been underestimated and highlight the importance of investigating variation in macroparasite communities of native species threatened by alien competitors.