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. 2024 Apr 9;121(15):e2307525121.
doi: 10.1073/pnas.2307525121. Epub 2024 Apr 1.

Significant shifts in latitudinal optima of North American birds

Paulo Mateus Martins  1   2 , Marti J Anderson  1   2 , Winston L Sweatman  3 , Andrew J Punnett  2
Affiliations

Significant shifts in latitudinal optima of North American birds

Paulo Mateus Martins et al. Proc Natl Acad Sci U S A. .

Abstract

Changes in climate can alter environmental conditions faster than most species can adapt. A prediction under a warming climate is that species will shift their distributions poleward through time. While many studies focus on range shifts, latitudinal shifts in species' optima can occur without detectable changes in their range. We quantified shifts in latitudinal optima for 209 North American bird species over the last 55 y. The latitudinal optimum (m) for each species in each year was estimated using a bespoke flexible non-linear zero-inflated model of abundance vs. latitude, and the annual shift in m through time was quantified. One-third (70) of the bird species showed a significant shift in their optimum. Overall, mean peak abundances of North American birds have shifted northward, on average, at a rate of 1.5 km per year (±0.58 SE), corresponding to a total distance moved of 82.5 km (±31.9 SE) over the last 55 y. Stronger poleward shifts at the continental scale were linked to key species' traits, including thermal optimum, habitat specialization, and territoriality. Shifts in the western region were larger and less variable than in the eastern region, and they were linked to species' thermal optimum, habitat density preference, and habitat specialization. Individual species' latitudinal shifts were most strongly linked to their estimated thermal optimum, clearly indicating a climate-driven response. Displacement of species from their historically optimal realized niches can have dramatic ecological consequences. Effective conservation must consider within-range abundance shifts. Areas currently deemed "optimal" are unlikely to remain so.

Keywords: abundance shifts; climate change; non-linear species–environment models; species distributions.

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Conflict of interest statement

Competing interests statement:The authors declare no competing interest.

Figures

Fig. 1.
Fig. 1.
Model pathway for estimating the latitudinal optimum and temporal trends in the latitudinal optimum for bird species. (A) Obtain the raw abundance data for each combination of data subset (East, West, or Combined; Table 1), species, and year. As an example, we show the raw continental abundance data of Eastern Wood-Pewee (Contopus virens) for the year 2001. (B) Use the Modskurt modeling framework outlined in Appendices 1 and 2 to estimate the latitudinal optimum (modal position) (m) for each year. (C) Run generalized least squares (GLS) models to estimate the temporal trends in the latitudinal optimum (m) for each combination of species and data subset. In the example, we show the continental poleward trend of the Eastern Wood-Pewee. Image credit: Eastern Wood-Pewee by Andy Reago & Chrissy McClarren, licensed under CC BY 2.0 https://creativecommons.org/licenses/by/2.0, via Wikimedia Commons.
Fig. 2.
Fig. 2.
Meta-analysis plot of the estimated shift in latitudinal optimum per year (in decimal degrees) for each bird species (with 95% CI, ordered in increasing value from left to right), with colors indicating statistical significance toward either the north or south ( P < 0.05), and with three overall estimates shown at the far left of each panel: one for the subset of species shifting significantly northward (blue), one for the subset of species shifting significantly southward (orange) and one for all birds (black). Results are shown for each of three datasets (as outlined in Table 1): (A) the combined dataset (all of North America, n = 209 species), (B) the West ( n = 143 species), and (C) the East ( n = 119 species). Insets show the frequency distribution of P-values for the test of H0: no shift in latitudinal optimum, with the dotted line showing the expected (uniform) distribution of P-values under a true null hypothesis.
Fig. 3.
Fig. 3.
Significant relationships identified in the meta-regression analysis between the estimated annual shift in latitudinal optimum (in decimal degrees per year) and: (A) territoriality, (B) thermal optimum (in °C), and (C) the species specialization index (SSI), for n = 206 individual bird species across North America at the continental scale (combined dataset). Weights from the meta-analysis are shown using a color gradient in (B) and (C), with bird species having less variability in their estimated latitudinal optimum being weighted more heavily.
Fig. 4.
Fig. 4.
Significant relationships identified in the meta-regression analysis between the estimated annual shift in latitudinal optimum (in decimal degrees per year) and (A) habitat density, (B) thermal optimum (in °C), and (C) the SSI, for n = 140 individual bird species in the West (as per Table 1). Weights from the meta-analysis are shown using a color gradient in (B) and (C), with bird species having less variability in their estimated latitudinal optimum being weighted more heavily.
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References

    1. Bellard C., Bertelsmeier C., Leadley P., Thuiller W., Courchamp F., Impacts of climate change on the future of biodiversity: Biodiversity and climate change. Ecol. Lett. 15, 365–377 (2012). - PMC - PubMed
    1. IPCC, Climate Change 2022: Impacts, Adaptation and Vulnerability (IPCC, 2022).
    1. Grinnell J., The niche-relationships of the California thrasher. Auk 34, 427–433 (1917).
    1. Brown J. H., On the relationship between abundance and distribution of species. Am. Nat. 124, 255–279 (1984).
    1. Parmesan C., Ecological and evolutionary responses to recent climate change. Annu. Rev. Ecol. Evol. Syst. 37, 637–669 (2006).

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