An official website of the United States government
Black-throated blue warbler (Setophaga caerulescens) populations have been declining at the southern edge of the breeding range in North Carolina over the past two decades. Determining the causes of population declines in migratory species requires knowledge of the threats faced throughout the entire annual cycle, necessitating accurate information about the migratory routes and non-breeding areas used by birds. We used light-level geolocators to identify the fall migratory routes and non-breeding distributions of adults breeding at the southern edge of the range in North Carolina (n = 5), where populations are declining, and at the core of the range in New Hampshire (n = 8), where populations are stable. The strength of migratory connectivity was moderate (mean = 0.42). New Hampshire birds used non-breeding areas broadly distributed across the Caribbean, whereas North Carolina birds used a restricted non-breeding area largely in the Dominican Republic. Suitable forest cover declined at a higher rate from 2000 to 2019 in the Dominican Republic than in other Caribbean countries (8.4% vs. 2–4% loss), exposing birds from the trailing edge to significantly higher suitable habitat loss on the non-breeding grounds compared with range-core birds. Birds from the two study populations also exhibited differing migratory routes, with North Carolina birds migrating south through Florida and many New Hampshire birds performing an overwater flight from the Carolinas to the Caribbean. Our results suggest the possibility that, at least for this species, forest loss on the island of Hispaniola could be exacerbating population declines at the southern edge of the breeding range in North Carolina.
more »
« less
Factors Determining the Southern Range Limit of Hemigrapsus sanguineus in the Western Atlantic
ABSTRACT The southern range limit of the invasive Asian shore crab,Hemigrapsus sanguineus,along the United States East coast is further north than expected based on its native distribution. We investigated potential factors that may limit the southward spread of this species along the Mid‐Atlantic and South Atlantic bights from Virginia to South Carolina, including metabolic constraints, food availability, and habitat limitation. We searched sites identified as potential habitat forH. sanguineusto verify the presence/absence of the crab, measured the metabolic rates of crabs at their current southern range edge for comparison with previous measurements made further north on the New Hampshire coast, used digital images captured at each site to determine whether the availability of potential food decreases south of the current range limit, and used Google Earth to measure distances between suitable habitat patches north and south of the current range limit to determine whether habitat availability limits the range expansion toward the south. We encountered the species ~64 km further south than the documented range limit at Oregon Inlet, North Carolina. We found no difference in metabolism between crabs at the southern range edge compared to crabs from New Hampshire, and no consistent difference in the abundance of available food between sites north and south of the current range limit. However, we found greater distances between suitable hard‐substrate sites south of the current range limit than between sites found within the current range. We suggest that the availability of suitable habitat is the primary driver limiting the further southward range expansion ofH. sanguineus.
more »
« less
- Award ID(s):
- 2052246
- PAR ID:
- 10599187
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology and Evolution
- Volume:
- 15
- Issue:
- 6
- ISSN:
- 2045-7758
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Dopamine has been implicated in circadian timing underlying the food entrainable oscillator (FEO) circuitry and overexpression of the dopamine D2 receptor (D2R) in the striatum has been reported to reduce motivation to obtain food rewards in operant tasks. In the present study, we explored both of these mechanisms by examining food anticipatory activity (FAA) in dopamine D2 receptor‐overexpressing (D2R‐OE) mice under various durations of food availability. First, we noted that at baseline, there were no differences between D2R‐OEmice and their littermates in activity level, food intake, and body weight or in circadian activity. Under conditions of very restricted food availability (4 or 6 hr), both genotypes displayedFAA. In contrast, under 8‐hr food availability, control mice showedFAA, but D2R‐OEmice did not. Normalization of D2R by administration of doxycycline, a tetracycline analogue, rescuedFAAunder 8‐hr restricted food. We next tested for circadian regulation ofFAA. When given ad libitum access to food, neither D2R‐OEnor controls were active during the daytime. However, after an interval of food restriction, all mice showed elevated locomotor activity at the time of previous food availability in the day, indicating circadian timing of anticipatory activity. In summary, motivation is reduced in D2R‐OEmice but circadian timing behavior is not affected. We conclude that an increase in striatal D2R reducesFAAby modulating motivation and not by acting on a clock mechanism.more » « less
-
ABSTRACT The Indo‐Pacific lionfish,Pterois volitans,is an invasive species in the western Atlantic. Since its introduction to Florida in the early 1980s, populations have surged with lionfish now found from North Carolina to Venezuela. As their range expands, these generalist predators threaten native fauna, and while they are primarily a marine species, their tolerance for low salinity conditions may allow them to expand into sensitive estuarine habitats undetected. Traditional approaches for tracking invasive species such as direct observation or trapping are impractical over large spatial scales, making environmental DNA (eDNA) an attractive alternative. Molecular assays, such as those employing quantitative polymerase chain reaction (qPCR), amplify low copy number DNA fragments in environmental samples and are increasingly employed as a complement to traditional methods for the detection of invasive species. Currently, there is one published PCR assay for the detection of lionfish eDNA. However, the specificity of this assay is unverified, and the critical performance parameters limit of detection (LOD) and limit of quantification (LOQ) have not been established. Here we evaluate the efficacy of this assay and show that it is likely to result in false negatives in the western Atlantic. As an alternative, we developed a new TaqMan probe‐based qPCR assay that is species‐specific forP. volitansand highly sensitive with a LOD of 12 copies per reaction and a LOQ of 598 copies per reaction. While our assay does not amplify the closely relatedP. miles, which was also introduced in the western Atlantic, the low prevalence of this species in the invasive population means our assay is effective for most monitoring purposes. We conclude that our assay is a robust method for the detection of lionfish and can be employed in any habitat, offering new opportunities for controlling the spread of invasive lionfish.more » « less
-
ABSTRACT In integrative distributional, demographic and coalescent (iDDC) modelling, a critical component is the statistical relationship between habitat suitability and local population sizes. This study explores this relationship in twoEnyaliuslizard species from the Brazilian Atlantic Forest: the high‐elevationE. iheringiiand low‐elevationE. catenatusand how this transformation affects spatiotemporal demographic inference. Most previous iDDC studies assumed a linear relationship, but this study hypothesises that the relationship may be nonlinear, especially for high‐elevation species with broader environmental tolerances. We test two key hypotheses: (1) The habitat suitability to population size relationship is nonlinear forE. iheringii(high‐elevation) and linear forE. catenatus(low‐elevation); and (2)E. iheringiiexhibits higher effective migration across populations thanE. catenatus. Our findings provide clear support for hypothesis (2), but mixed support for hypothesis (1), with strong model support for a nonlinear transformation in the high‐elevationE. iheringiiand some (albeit weak) support for a nonlinear transformation also inE. catenatus. The iDDC models allow us to generate landscape‐wide maps of predicted genetic diversity for both species, revealing that genetic diversity predictions for the high‐elevationE. iheringiialign with estimated patterns of historical range stability, whereas predictions for low‐elevationE. catenatusare distinct from range‐wide stability predictions. This research highlights the importance of accurately modelling the habitat suitability to population size relationship in iDDC studies, contributing to our understanding of species' demographic responses to environmental changes.more » « less
-
ABSTRACT Mycobacterium ulceranspseudoshottsiiis a mycolactone‐producing bacterium previously isolated from Striped Bass (Morone saxatilis(Walbaum)) from Chesapeake Bay and adjacent waters of the Atlantic Coast of North America. We report the first molecular detection of this pathogen in the native Gulf strain ofMorone saxatiliscollected from the Pearl River, Mississippi (USA). Molecular identification was conducted using a novel PCR assay targeting the parA‐625 intergenic spacer of the virulence‐associated pMUM plasmid. The isolate was unambiguously assigned toM. u. pseudoshottsiibased on diagnostic single nucleotide polymorphisms (SNPs) and phylogenetic analysis. This report expands the known range ofM. u. pseudoshottsiito include Gulf Coast watersheds and highlights the need for enhanced surveillance in wild and aquacultured fish populations of the southern United States.more » « less
