Vascular flora of the Outer Banks, North Carolina, U.S.A.

A complete catalogue of the vascular flora of the North Carolina Outer Banks is presented. Rarity, habitat, distribution within the Outer Banks, and earliest and latest specimens are given for each taxon. The flora contains 1020 species and infraspecific taxa, plus an additional 80 taxa that lack voucher specimens. Some 770 taxa are considered native; 250 non-native. Fifty-one taxa reach their northern range limit on the Outer Banks; 11 their southern limit. Fifty-five taxa are listed as rare in North Carolina; one of them also listed Threatened by the U.S. Fish and Wildlife Service. Twenty-four natural communities are described and assessed for vulnerabil-ity to sea level rise. Prior botanical research is listed chronologically.

Breeding behaviour of ectotherms at high latitudes: the case of the natterjack toad Epidalea calamita at its northern range limit

We explored the breeding behaviour of a threatened amphibian, the natterjack toad, at its northern range limit in Estonia, to determine the extent to which reproduction is affected by harsh and unstable climatic conditions. Using photo identification of specimens, we found that in optimal weather conditions males formed three breeding cohorts, while in adverse conditions only a single cohort occurred and under extreme conditions reproduction was skipped entirely. During the extended breeding season, larger males participated in reproduction throughout the breeding period, while smaller males appeared in later cohorts. Breeding success was related to the calling effort of a male, where larger males had greater mating success than smaller ones. We found that the natterjack toad males exhibit significant plasticity in reproductive behaviour at the northern range limit, which, given the energetic cost of reproduction and the increased risk of predation, allows them to increase their fitness at high latitudes.

Balsam Fir and American Beech Influence Soil Respiration Rates in Opposite Directions in a Sugar Maple Forest Near Its Northern Range Limit

Conifers and deciduous trees greatly differ in regard to their phylogenetics and physiology as well as their influence on soil microclimate and chemical properties. Soil respiration (Rs) in forests can therefore differ depending on tree species composition, and assessments of the variation in Rs in various forest types will lead to a more thorough understanding of the carbon cycle and more robust long-term simulations of soil carbon. We measured Rs in 2019 and 2020 in stands of various species composition in a sugar maple forest near the northern range limit of temperate deciduous forests in Quebec, Canada. Seasonal variations in soil temperature had the largest influence on Rs, but conditions created by the stands also exerted a significant effect. Relative to the typical sugar maple-yellow birch forest (hardwoods), Rs in stands with >20% of basal area from balsam fir (mixedwoods) was increased by 21%. Whilst, when American beech contributed >20% of litterfall mass (hardwood-beech stands), Rs was decreased by 11 and 36% relative to hardwoods and mixedwoods, respectively. As a whole, Rs was significantly higher in mixedwoods than in other forest types, and Rs was significantly higher in hardwoods than in hardwood-beech stands. Sugar maple and American beech at the study site are near their northern range limit, whereas balsam fir is near its southern limit. Rs in mixedwoods was therefore higher than in hardwoods and hardwood-beech stands due to high root activity in the presence of fir, despite colder and drier soils. We estimated that root respiration in mixedwoods was more than threefold that in hardwoods and hardwood-beech stands. The lower Rs in hardwood-beech stands compared to hardwoods points to the lower soil temperature as well as the poor quality of beech litter (low decomposability) as indicated by a generally lower heterotrophic respiration. Other than soil temperature, regression models identified mixedwoods, soil water potential and Mg2+ activity in the soil solution as important predictor variables of Rs with about 90% of its variation explained. Our study shows the benefits of combining forest-specific properties to climatic data for more robust predictions of Rs.

Is a species distribution model output reliable to test niche limitation at the northern range limit of a Pacific coastal dune plant?

Jacqueline Grubel* and Christopher G. Eckert (Faculty Supporter) It is widely thought that the size, shape and location of a species’ geographical distribution are a spatial expression of its realized niche, and this assumption is central to evolutionary biology, biogeography and conservation. Yet, the hypothesis that geographical range limits are niche limits is not well supported by experimental translocations of species beyond their range limits. Beyond range populations often exhibit fitness high enough for self-replacement. In contrast, environmental niche models based on bioclimatic data often suggest a decline in habitat suitability beyond range limits, thereby supporting niche limitation. However very few studies have evaluated whether species distribution models (SDMs) accurately predict the viability of populations in nature, and scant results to date are not supportive. Long-term transplant with the short-lived, Pacific costal dune endemic plant Camissoniopsis cheiranthifolia (Onagraceae) suggest that populations are viable beyond the northern range limit over multiple generations. We constructed an SDM based on a large range-wide database of species records plus standard bioclimatic variables and substrate type. We also included sea surface temperature, which greatly modifies the climate of dune habitat. Preliminary results suggest that our SDM reliably predicts the fitness of experimental populations. However, both approaches indicate that something other than niche limitation enforces the northern range limit of this species. Results from this well-studied dune plant suggest that range limitation via constraints on dispersal may play an important role in limiting northern range expansion.

Living on the edge: spatial response of coyotes (Canis latrans) to wolves (Canis lupus) in the subarctic

Understanding how mesopredators manage the risks associated with apex predators is key to explaining impacts of apex predators on mesopredator populations and patterns of mesopredator space use. Here we examine the spatial response of coyotes (Canis latrans Say, 1823) to risk posed by wolves (Canis lupus Linnaeus, 1758) using data from sympatric individuals fitted with GPS collars in subarctic Alaska, near the northern range limit for coyotes. We show that coyotes do not universally avoid wolves, but instead demonstrate season-specific responses to both wolf proximity and long-term use of the landscape by wolves. Specifically, coyotes switched from avoiding wolves in summer to preferring areas with wolves in winter, and this selection was consistent across short and longer-term temporal scales. In the summer, coyotes responded less strongly to risk of wolves when in open areas than when in closed vegetation. We also demonstrate that coyotes maintain extremely large territories averaging 291 km2, and experience low annual survival (0.50) with large carnivores being the largest source of mortality. This combination of attraction and avoidance predicated on season and landcover suggests that mesopredators use complex behavioral strategies to mediate the effects of apex predators.