Range edges of North American marine species are tracking temperature over decades
SHORT RUNNING TITLE (45 character limit): Thermal niche tracking of species range edges
AUTHORS:
Alexa Fredston1,2*, fredston@rutgers.edu; Malin Pinsky2, malin.pinsky@rutgers.edu; Rebecca L. Selden3, bselden@wellesley.edu; Cody Szuwalski4, cody.szuwalski@noaa.gov; James T. Thorson4, james.thorson@noaa.gov; Steven D. Gaines1, gaines@bren.ucsb.edu; and Benjamin S. Halpern1,5, halpern@nceas.ucsb.edu
1 Bren School of Environmental Science & Management, University of California, Santa Barbara, Santa Barbara, CA, United States
2 Department of Ecology, Evolution, and Natural Resources, Rutgers, The State University of New Jersey, New Brunswick, NJ, United States
3 Department of Biological Sciences, Wellesley College, Science Center, Wellesley, MA, United States
4 Alaska Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Seattle, WA, United States
5 National Center for Ecological Analysis and Synthesis, University of California, Santa Barbara, Santa Barbara, CA, United States
* Corresponding author: 14 College Farm Road, New Brunswick, NJ 08901. Phone: (848) 932-9631. Fax: (732) 932-2587.
AUTHORSHIP STATEMENT: AF conducted the analysis, prepared the figures, and drafted the manuscript. JTT was responsible for the development of software used in the analysis. All authors contributed to the design of the project, to interpretation and visualization of the results, and to editing the manuscript.
DATA ACCESSIBILITY STATEMENT: If this manuscript is accepted, the data supporting our analysis will be archived in a public repository and the DOI will be included in the article.
ARTICLE TYPE: Letters
KEYWORDS (up to 10): biogeography, climate change, global warming, thermal tolerance, range limit, range margin, thermal niche
NUMBER OF WORDS IN ABSTRACT AND MAIN TEXT: abstract 150, main text 4761
NUMBER OF REFERENCES: 69
NUMBER OF TABLES, FIGURES, AND TEXT BOXES: 0 tables, 3 figures, 0 text boxes
ABSTRACT
Understanding range edges is key to addressing fundamental biogeographic questions about abiotic and biotic drivers of species distributions. Range edges are where colonization and extirpation happen, so their dynamics are also important for natural resource management and conservation. We quantified positions for 153 range edges of marine fishes and invertebrates from three US continental shelf regions using decades of survey data and a spatiotemporal model to account for changes in survey design. We analyzed whether range edges maintained their edge thermal niches—temperature extremes at the range edge—over time. Most range edges (86%) maintained either cold or warm temperature extremes; 73% maintained both. However, the substantial fraction of range edges that altered their thermal niche underscore the multiplicity of relevant drivers. This study suggests that temperate marine species largely maintained their edge thermal niches during rapid change and provides a blueprint for testing temperature tracking of species range edges.
INTRODUCTION
Human-caused global climate change now affects, directly or indirectly, all biomes and levels of biological organization (Scheffers et al. 2016). One of the most profound effects has been changes in the spatial distributions of species that align with shifting climates—up mountains, deeper in the oceans, and generally toward the poles(Parmesan and Yohe 2003, Pecl et al. 2017). A strong correlation between regional climate change and shifting species ranges has been documented in many taxa (Chen et al. 2011, Pinsky et al. 2013). However, individualistic responses and “ecological surprises” are also common (Poloczanska et al. 2011, Zhu et al. 2012, La Sorte and Jetz 2012), underscoring the need to consider the interplay of climatic constraints and non-climate processes in determining the edges of species ranges (Sexton et al. 2009, Urban et al. 2016).
Range edges often arise where biotic or abiotic conditions prevent persistence of a species. We use the definition of the fundamental niche as the range of environments in which a species could theoretically persist in the absence of biotic interactions, and the realized niche as the range of environments in which the species is actually found (Godsoe et al. 2017). Changing environments provide an opportunity to test whether niches are conserved through time. If a species is shifting its geographic range to track temperature, for example, it will occur at the same temperature over time and the realized thermal niche will be conserved. Conversely, if a species does not shift in concert with temperature change, the geographic range may remain stable but the realized thermal niche will change (La Sorte and Jetz 2012). In addition, temperature extremes are more likely to be range-limiting than means (Sunday et al. 2019), but either poleward or equatorward range edges can theoretically be limited by either cold or warm temperature extremes; e.g., a poleward range edge might occur where it becomes too cold in winter for adults to survive, or where summers are not warm enough for reproduction and/or juvenile survival (Hutchins 1947). We define the edge thermal niche as the thermal extremes found at a species’ range edge. Testing which temperature extreme is important for which range edges has rarely been examined across full assemblages of species (Ma et al. 2015, Urban et al. 2016). In this study, we test whether range edges of marine species in three continental shelf regions in the United States have conserved their edge thermal niches over decades of environmental change.
Marine continental shelf species are ideal for studying these biogeographical questions: they are shifting rapidly, experience relatively few barriers to dispersal, and large-scale, long-term datasets of their historical distributions and abundances exist (Pinsky et al. 2020). Some studies on range edges and climate have predicted that marine species should track temperature readily throughout their range, because marine range edges occur on average at the limits of species’ thermal tolerances (Sunday et al. 2012, Stuart-Smith et al. 2017). Other theory—primarily developed in terrestrial systems but supported by a recent test using marine data (Fredston‐Hermann et al. 2020)—suggests that one or both range edges are driven by other processes like species interactions and will not shift as much in response to temperature change (Connell 1961, MacArthur 1972, Sax and Gaines 2003, Poloczanska et al. 2011, Cahill et al. 2014, Louthan et al. 2015).
The extension of these tests to more regions and taxa is partially limited by data availability, because quantifying range edge dynamics requires large-scale and long-term biodiversity surveys (Parmesan et al. 2005). To date, very few studies have measured range edge dynamics at high temporal resolution—a necessary prerequisite to understanding the relationship between range edges and temperature change, particularly because using too few time points can create misleading trends (La Sorte and Jetz 2012, Brown et al. 2016, Fredston‐Hermann et al. 2020). Biodiversity survey programs also often use different sampling methods and schedules, further complicating cross-regional comparative biogeography. To address both of these constraints, we used large-scale biodiversity survey data from the National Oceanic and Atmospheric Administration (NOAA) beginning as early as 1968. We then fitted spatiotemporal models to estimate biomass density and then range edge positions through time, which allowed us to estimate range edge uncertainty and to more clearly compare results across species and regions.
Overall, we quantified conservatism of species’ edge thermal niches over time, drawing on repeated large-scale biodiversity surveys in three North American marine regions to describe shifts in poleward and equatorward range edges across 153 fish and invertebrate species. The three study regions have divergent climatic histories that allowed us to test for edge thermal niche conservatism in different temperature change regimes: the Northeast US has warmed rapidly and almost continuously, the Eastern Bering Sea has warmed episodically, and the US West Coast has not warmed overall but periodically experiences dramatic temperature fluctuations among years.
MATERIALS AND METHODS