The impact of competition on global-change induced range shifts in birds


Many species of birds are currently undergoing rapid range shifts in response to human-induced changes. As their ranges change, species encounter new species with which they hadn’t before coexisted. These novel interactions could markedly impact the future distribution of biodiversity [1]. This PhD project will fill crucial gaps in our understanding of the consequences of such range dynamics, addressing questions such as:
(1) How do novel species interactions impact the outcome of range expansions? As species’ ranges change, novel species assemblages emerge, and competition between species may influence the dynamics of range expansion events. For instance, competitive exclusion can prevent species from colonizing areas where species occupying similar niches already exist [2]. In addition, territorial aggression with other species and reproductive interference may also limit coexistence and range expansion [3-6]. Yet, the impact of species interactions on contemporary range expansions remain largely unknown.
(2) What is the relative importance of exploitative competition (i.e., competition for access to limiting resources) and interference competition (e.g., territorial aggression between species) in structuring novel assemblages? Although some research has focused on predicting how species will respond to competition for resources as ranges change, less is known about how social behaviours might influence range dynamics. Studies demonstrate that territorial species are likely to be aggressive toward closely related species as their ranges expand, which may slow range expansion [5-6]. Similarly, theory predicts that reproductive interference—wasteful reproductive interactions between species—should prevent hybridizing species from coexisting, so reproductive interactions between species may also slow range expansions. Yet, the relative impact of these different forms of species interactions remains unknown.
(3) How do abiotic factors such as climate change and land use interact with interspecific competition during range expansions? While it is clear that changes in climate and land use impact bird populations and range dynamics [1], it is less clear which factors play the largest role in determining the relative success and failure of range shifts.

Despite broad appreciation for the importance of biotic interactions in shaping species’ ranges, studies that identify a role for species interactions in influencing the rates or outcomes of range expansion are surprisingly rare. Therefore, this project is likely to yield several high impact publications.

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Image Captions

Figure 1. Interspecific aggression between a red-winged blackbird (Agelaius phoeniceus) and a yellow-headed blackbird (Xanthocephalus xanthocephalus). Photo credit: Feng Yu / Alamy Stock Photo.

Figure 2. Map citizen scientist observations of chipping sparrows (Spizella passerina) on eBird (, where recent observations (in red) reveal putative regions of recent northerly range shifts. Inset photo by Kenneth C. Schneider, CC BY-ND 2.0).


To address these questions, the PhD student will use data from several decades-long standardised surveying efforts, such as the Breeding Bird Survey from North America [7] and the PanEuropean Common Bird Monitoring Scheme [8], as well as data collected at fine spatial scales by citizen scientists via (Fig. 2). To better understand the underlying data, the PhD student will join in the field as UK BBS monitors conduct surveys in their first year. In addition to collating existing datasets, the student will take part in the finalisation and management of a database (already under development) documenting published accounts of territorial behaviour and hybridisation. Combining these various sources of data, the student will explore factors underling the rate, magnitude, and outcome of recent range shifts.

Project Timeline

Year 1

Complete species-level database of published accounts of territorial behaviour and hybridisation; develop indices for quantifying historical shifts in species’ ranges and dynamics of assemblages from monitoring and citizen science datasets. Complete field observation of survey methodology.

Year 2

Complete the development of the computational tools for analysing species range dynamics, begin write-up of manuscript describing trends apparent with different indices of range expansion and assemblage turnover.

Year 3

Submit first manuscript. Using methods developed in years 1 and 2, conduct empirical analyses of the impact of competition on different aspects of range dynamics.

Year 3.5

Complete and submit thesis, begin submitting remaining manuscripts for publication

& Skills

The student will receive training in (1) computational techniques and coding in R, (2) data management and (3) analyses of spatial datasets.

References & further reading

[1] Stewart, P., Voskamp, A., Biber, M.F., Hof, C., Willis, S.G. and View Tobias, J.A. (2020) Global impacts of climate change on avian functional diversity. BioRiv:

[2] Pigot, A.L., Jetz, W., Sheard, C. and Tobias, J.A., 2018. The macroecological dynamics of species coexistence in birds. Nature ecology & evolution, 2(7), pp.1112-1119.

[3] Drury, J., Cowen, M., & Grether, G. 2020. Competition and hybridization drive interspecific territoriality in birds. PNAS. doi: 10.1073/pnas.1921380117

[4] Cowen, M., Drury, J., & Grether, G. 2020. Multiple routes to interspecific territoriality in sister species of North American perching birds. Evolution. doi: 10.1111/evo.14068

[5] Freeman, B.G., Tobias, J.A. and Schluter, D., 2019. Behavior influences range limits and patterns of coexistence across an elevational gradient in tropical birds. Ecography, 42(11), pp.1832-1840.

[6] Grether, G.F., Peiman, K.S., Tobias, J.A. and Robinson, B.W., 2017. Causes and consequences of behavioral interference between species. Trends in Ecology & Evolution, 32(10), pp.760-772.

[7] Sauer, J.R., Link, W.A., Fallon, J.E., Pardieck, K.L. and Ziolkowski Jr, D.J., 2013. The North American breeding bird survey 1966–2011: summary analysis and species accounts. North American Fauna, 79(79), pp.1-32.

[8] Klvanova, A.L.E.N.A., Vorisek, P., Gregory, R., Van Strien, A.R.C.O. and Meyling, A.G., 2009. Wild birds as indicators in Europe: latest results from the Pan-European Common Bird Monitoring Scheme (PECBMS). Avocetta, 33, pp.7-12.

Further Information

For further information, contact Jonathan Drury (

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