Plant dispersal by Canada geese in Arctic Greenland RESEARCH NOTE Plant dispersal by Canada geese in Arctic Greenland Andy J. Green a, Ádám Lovas-Kiss b, Rachel A. Stroudc, Niall Tierneyc & Anthony D. Fox d aDepartment of Wetland Ecology, Estación Biológica de Doñana, CSIC, Sevilla, Spain; bDepartment of Botany, Faculty of Sciences and Technology, University of Debrecen, Debrecen, Hungary; cFaculty of Natural Resources and Environmental Sciences, Agricultural University of Iceland, Hvanneyri, Iceland; dDepartment of Bioscience, Aarhus University, Rønde, Denmark ABSTRACT Despite the abundance of migratory geese as herbivores in the Arctic, and ongoing changes in their populations and distributions, little is known about their role in seed dispersal. Climate change requires Arctic plants to adjust their distributions, and avian vectors may have an important role to play. We present the first study of endozoochory (internal trans- port) of Arctic plants by Canada geese. In central west Greenland, we collected 50 faecal samples, from which we extracted 2943 intact seeds from six species and four families, all but one of which (a non-native species) are extremely common and widespread in this part of Greenland. The majority (95%) of seeds were from Empetrum nigrum, but Carex nardina (3%) and Vaccinium uliginosum (2%) were also abundant. One seed of the non-native Persicaria lapathifolia was recorded. These results suggest migratory geese are likely to be vital vectors of Arctic plants. Although the sample size was small, there were indications that non- breeding geese may disperse more seeds than breeding geese, which stay closer to lakes to reduce the risk of predation, rarely accessing dwarf-scrub heath where non-breeders ingested seeds. Future research should address such possible links between reproductive status and seed dispersal in waterbirds. KEYWORDS Branta canadensis; Carex; Empetrum; endozoochory; faeces; seed dispersal Arctic plant species assemblages are highly struc- tured, on account of sequential Pleistocene glacia- tions and long-established physical barriers to dispersal and gene flow (such as mountain chains, glaciers and the oceans (Alsos et al. 2015; Eidesen et al. 2013) as well as biotic interactions such as herbivory (Post & Pedersen 2008). Vertebrate seed dispersers are important to maintain and enhance Arctic plant community richness (Bruun et al. 2008). This is especially significant in these times of climate change, which is reducing the extent of sea and terrestrial ice, and affecting seasonality, precipi- tation and wind patterns. Changing climate and resultant short-term changes in the Arctic environ- ment (for instance, in land ice cover) create new opportunities for colonization of novel plant species and genotypes, as well as imposing different tem- plates for patterns of activity, growth, reproduction and dispersal of existing plant life forms in these regions (Klein et al. 2008). Such vegetation dynamics are dependent on effective dispersal processes, including endozoochory (dispersal of seeds and other diaspores via gut passage) by migratory geese and other herbivores. Although the role of Arctic geese as herbivores and in nutrient cycling is well documented (e.g., Ruess et al. 1989; Jefferies et al. 1994), only a handful of studies worldwide show that geese can disperse a variety of plants both with and without a fleshy fruit (García-Álvarez et al. 2015; Green et al. 2016). As yet there is almost no informa- tion on the roles geese may play in maintaining and enhancing the diversity of Arctic plant communities. Here, we report on endozoochory by Canada geese (Branta canadensis interior) in a coastal area of central west Greenland, and consider their likely role as vec- tors in the local changes in cover of native and non- native plant species. Although apparently present in west Greenland since at least the 1860s, Canada geese have recently increased in abundance and range in west Greenland and have colonized this specific study area since the 1980s (Malecki et al. 2000; Fox & Glahder 2010; Fox et al. 2011; Fox et al. 2012). Study area, materials and methods The study area lies north and east of the town of Ilulissat (69° 13ʹN 51°6ʹW) in central west Greenland (Fig. 1). The area comprises a rocky plateau 100–400 m a.s.l. covered by dwarf-scrub heath vegetation. Dominant species are Cassiope tetragona, Empetrum nigrum and Vaccinium uliginosum microphyllum, with some grami- noids, and on the dry barrens Dryas octapetala, Salix arctica and graminoids such as Carex nardina and Kobresia myosuroides. Wetter sites and lake margins are dominated by Eriophorum scheuchzeri and Carex rariflora. Canada geese spending the summer in this CONTACT Anthony D. Fox tfo@bios.au.dk Department of Bioscience, Aarhus University, Kalø, Grenåvej 14, Rønde DK-8410, Denmark POLAR RESEARCH 2018, VOL. 37, 1508268 https://doi.org/10.1080/17518369.2018.1508268 © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. http://orcid.org/0000-0002-1268-4951 http://orcid.org/0000-0002-8811-1623 http://orcid.org/0000-0001-8083-7633 http://www.tandfonline.com http://crossmark.crossref.org/dialog/?doi=10.1080/17518369.2018.1508268&domain=pdf area in July/early August comprise either moulting flocks of non-breeding (i.e., failed breeders or sub- adult individuals) or family groups of parents with goslings (too small to fly). All geese tend to resort to the open water of lakes and streams when threatened by predators such as Arctic fox (Vulpes lagopus), the only mammalian predator of this region, so tend to be con- strained to feed close to water, although they will forage away from shorelines on relatively profitable food. Fifty samples of fresh Canada goose droppings were collected from three sites near Ilulissat from 12 to 19 July 2016 within one to two hours of observing the birds feeding there (Fig. 1). Thirty-two faecal samples were obtained from a flock of 28 non-breeders moult- ing flight feathers on a lake at 69°19ʹ08.0”N 50° 48ʹ41.6”W on 19 July 2016, seven from nine non- breeding moulters at 69°15ʹ27.9”N 50°48ʹ05.6”W on 12 July 2016 and 11 from a family of two adults (five faecal pellets mean dry mass 3.74 g ± 0.82 S.E.) and four goslings (six faecal pellets mean dry mass 2.06 g ± 0.34 S.E., judged on clear size difference to adult faeces from young aged 25–30 days old and half grown) on 14 July 2016 at 69°14ʹ13.7”N 50°54ʹ34.0”W. Droppings from the non-breeder flock were 12–15 mm in diameter, adult droppings in the family groups were distinguishable in this way from the gosl- ing faeces, which were ca. 5–8 mm diameter. Although the very slightly smaller Greenland white-fronted goose (Anser albifrons flavirostris) is endemic to west Greenland, this species was not observed during pro- tracted exploration of the study area. This, together with our detailed observations of the Canada goose groups prior to faecal collection, gives us confidence that we sampled exclusively from this species. All samples were freshly collected and sun dried, placed in envelopes and transported in plastic bags to Hungary for further investigation. In Hungary, sam- ples were kept refrigerated at 4°C until analysis. Samples were then soaked in deionized water, sieved with a 100 µm sieve and deionized water, then inspected under a binocular microscope for plant dia- spores. Only intact, uncracked seeds were extracted and quantified. The seeds were identified based on shape, size, colour and seed coat pattern, in accordance with the recent literature (Aiken et al. 2007; Cappers et al. 2012; USDA, NRCS 2018). Viability tests were run for seeds on 1 August 2017, using the peroxidase test (Copeland & McDonald 1999). For those species for which we extracted more than 50 seeds, we randomly selected a subset of 50 (Table 2). As a consequence of their smaller size, some of the V. uliginosum seeds were accidentally destroyed during the testing process, so that final sample size was 25 (Table 2). Seeds were soaked for 12 h in deionized water, cut in half and inspected to confirm the pre- sence of an embryo. Half of each seed was immersed in 10% H2O2 solution, drained off and the seeds were rinsed in 90% ethyl alcohol followed by pH 8 phos- phate buffer. Finally, the seeds were soaked in benzi- dine diluted in 80% ethyl alcohol, which immediately turns viable seeds to a distinctive dark colour. Results From the 50 dried samples (mean dry mass = 3.536 g ± 2.39 g S.D.), we recovered a total of 2943 seeds, belonging to six species from four plant families (Table 1). Only one plant taxon was an aquatic emergent (Hippuris vulgaris); the remainder were terres- trial species. One family (Ericaceae) comprised two berry-bearing species; the others had no obvious adapta- tions for endozoochory. Overall, of all the faecal samples, 39 (78%) contained at least one seed (Table 1). We found one seed from the non-native Persicaria lapathifolia in one sample from the non-breeding flock, a plant species occurring outside its natural range, introduced to Greenland through human agency (Böcher et al. 1978). Faecal samples from non-breeding flocks were rich in seeds, and 95% of these samples contained at least one seed. In contrast, only 18% of samples from the goose family contained any seeds (Table 1). The peroxidase test confirmed viability for seeds of C. nardina, E. nigrum, V. uliginosum and P. lapathi- folia (Table 2). We also recorded fragments of mosses or lichens in four of our samples, which potentially were viable at the time of egestion. Discussion We showed that Canada geese are potentially impor- tant seed vectors in the Arctic biome, and that they disperse a range of flowering plant taxa by endo- zoochory. We focussed our study on large diaspores preserved after drying, but it is also possible that the Canada geese were vectors for the spores or viable fragments of the mosses and lichens, which were additional components of their diet (Wilkinson Figure 1. Study area in Greenland in relation to the town of Ilulissat. 2 A. J. GREEN ET AL. et al. 2017; Lovas-Kiss et al. 2018). Our conservative viability test, conducted a year after faeces were col- lected, confirmed viability of > 10% of seeds. Our findings are consistent with previous studies sug- gestingthatthisgoosespecies isanimportantplantvector in other biomes. Morton & Hogg (1989) germinated seeds of three species from Canada geese faeces collected on an island in Georgian Bay, Great Lakes, including V. angustifolium, which did not grow on the island and was thought to be dispersed several kilometres from the lake shore. Neff & Baldwin (2005) germinated six taxa from faeces in a freshwater marsh in Washington D.C. Best and Arcese (2009) germinated five taxa from faeces from islands near Vancouver. In the only previous study of endozoochory by Arctic geese we are aware of, Bruun et al. (2008) recorded viable seeds of 12 taxa (including C. nardina, K. myosuroides and V. uliginosum) in faeces of barnacle geese B. leucopsis in coastal north-east Greenland. Canada geese have recently increased in abundance in west Greenland and can assist in the dispersal of native plant species that are shifting their distribution, as well as potentially with new additions to the Greenland flora, especially under a scenario of rapid climate change (Klein et al. 2008). They are also thought to be the vectors of local dispersal for Daphnia that rapidly colonize new ponds and lakes formed as ice retreats in western Greenland (Haileselasie et al. 2016). The appearance of a single seed of P. lapathifolia suggests geese have a role in the spread of non-native species in Greenland. This plant is also non-native in the Canadian Arctic (USDA, NRCS 2018), and to date in west Greenland it is relatively restricted to the vicinity of human settlements along the coast. Geese and other waterbirds are known to disperse many non-native plants (Green 2016), and P. lapathifolia has been recorded as dispersed by European dabbling ducks (Green et al. 2016). On islands near Vancouver, Canada geese have been shown to play a key role in the spread of non-native grasses through both endozoochory and grazing (Best & Arcese 2009). Larger seeds are thought more likely destroyed during passage through the avian gut, so it is noteworthy that all the seeds we recorded were > 1 mm and < 3 mm long (in contrast to studies of endozoochory by European ducks (Soons et al. 2016; Lovas-Kiss et al. 2018). Two of the three most abundant angiosperms in our samples have a fleshy fruit characteristic of an endozoochory syndrome (Table 1). In contrast, half of the species we recorded are usually assumed to rely on gravity (barochory) or water (hydrochory) for their dispersal (Table 1). Although we sampled the geese at a time when they would probably deposit seeds only tens or hundreds of metres away from the mother plants, this is likely to be further than the seeds could disperse by other means such as water or wind (Bullock et al. 2017). This may therefore represent a vital process enabling changes in vegetation in response to climate change (Gonzalez-Varo et al. 2017). Furthermore, it is very possible that the geese can dis- perse these same plant species over hundreds of kilo- metres during their long-distance migrations in a similar manner to migratory ducks, since the longest seed reten- tion times in the guts of geese exceed the time required for migration (Viana et al. 2013; García-Álvarez et al. 2015). Geese have not been shown to empty their diges- tive tract before migrations, and flight activity is likely to increase seed survival (Kleyheeg et al. 2015). A role for geese as long-distance vectors in Arctic environments is strongly consistent with genetic and floristic analyses (Alsos et al. 2015). All the plant species we recorded are widely distributed in Canada and the coastal USA (USDA, NRCS 2018), suggesting that Canada geese may have contributed as vectors to their broad distributions and to contemporary long-distance gene flow. Table 1. Plant diaspores recovered from Canada goose droppings in Greenland. Total number of intact seeds (TS), number of samples with seeds (NS) and maximum number of seeds in any given sample (Max). Plants Non-breeding (n = 39) Breeding (n = 11) Family Species Length (mm)a Dispersal syndromeb TS NS Max TS NS Max Cyperaceae Carex nardina 2.22 NDc 82 16 22 – – – Kobresia myosuroides 2.63 barochory 8 6 3 – – – Ericaceae Empetrum nigrum 1.85 endozoochory 2780 32 494 2 1 2 Vaccinium uliginosum 1.3 endozoochory 69 11 25 – – – Plantaginaceae Hippuris vulgaris 1.85 hydrochory – – – 1 1 1 Polygonaceae Persicaria lapathifoliad 2.88 barochory 1 1 1 – – – Total 2940 37 494 3 2 2 aLength data were derived from the LEDA database (Kleyer et al. 2008) and our own measurements. bDispersal syndromes were taken from Baseflor (Julve 1998): barochory implies self-dispersal via gravity, hydrozoochory implies water dispersal, endozoochory implies dispersal via frugivory. cNo data because this species is not listed in Baseflor. Wind dispersal has been proposed elsewhere for C. nardina (Flora of Svalbard 2018). dSpecies not native to Greenland according to Böcher et al. (1978). Table 2. Viability of seeds recovered from Canada goose droppings in Greenland. Results of the peroxidase test for a subset of seeds, showing numbers of tested seeds (TS), seeds with an embryo (SE), and viable seeds (VS). Family Species TS SE VS Cyperaceae Carex nardina 50 7 4 Kobresia myosuroides 8 0 0 Ericaceae Empetrum nigrum 50 10 3 Vaccinium uliginosum 25 12 6 Plantaginaceae Hippuris vulgaris 1 0 0 Polygonaceae Persicaria lapathifolia 1 1 1 Total 135 30 14 POLAR RESEARCH 3 In spite of the small sample size, our results also suggest that endozoochorous seed dispersal by Arctic geese can be affected by microhabitat use, which could potentially be related to social status. Different groups from within a given goose population that feed within the same landscape, but differ in social status, can show radically different diets. Our results are consistent with our direct field observations of Canada goose behaviour during the moult period. Non-breeding Canada geese tend to aggregate into relatively large flocks during the ca. three weeks they are flightless. During this time, they resort to the safety of open water bodies to avoid preda- tion, largely from Arctic fox, but may feed out on dwarf- scrub heath where their diet may be predominantly the berries of E. nigrum and V. uliginosum, which frequently form the dominant vegetation cover in areas of deeper soil. Empetrum berries provide relatively little metaboliz- able biomass for geese, but may provide critical antiox- idants and fatty acids, which may be important for completion of moult and for successful autumn migra- tion (e.g., Hupp et al. 2013). The larger flock size of non- breeders enhances predator detection, enabling them to forage at greater distances from the water’s edge than smaller groups of breeding pairs with their broods. Breeding groups tend to graze the aboveground growth of graminoids such as C. rariflora along lake shores, especially when goslings are very young, rarely leaving the safety of peripheral lake wetland habitats to ensure an escape route to open water. Hence, they do not tend to feed where the berries and dry habitat graminoids such as C. nardina occur. Given that we only collected faeces from breeding birds at a single site, however, we remain prudent about inferring much from the differences between these and the more abundant samples from non-breeders at two sites. More detailed studies are required to fully investi- gate the role of Arctic geese as plant vectors at dif- ferent spatial scales. This should include the influence of social status on microhabitat use and the quantity and quality (sensu Schupp et al. 2010) of seed dis- persal, a research topic not yet addressed in water- birds (Green et al. 2016). Acknowledgements This study was supported by Spanish Ministerio de Economía, Industria y Competitividad project CGL2016-76067-P (AEI/ FEDER, EU) to AJG. ALK was supported by the New National Excellence Program ÚNKP-17-3-I-DE-385. We greatly appreciate the help of Csaba Máthé, Márta Mikóné Hamvas and Tamás Garda in undertaking the viability tests. We thank Juan P. González-Vero and two anonymous refer- ees for comments and suggestions that improved the article. Disclosure statement No potential conflict of interest was reported by the authors. Funding This work was supported by the New National Excellence Program (ÚNKP-17-3-I-DE-385) and the Spanish Economy Ministry (CGL2016-76067-P). ORCID Andy J. Green http://orcid.org/0000-0002-1268-4951 Ádám Lovas-Kiss http://orcid.org/0000-0002-8811-1623 Anthony D. 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POLAR RESEARCH 5 http://perso.wanadoo.fr/philippe.julve/catminat.htm http://perso.wanadoo.fr/philippe.julve/catminat.htm http://plants.usda.gov Abstract Study area, materials and methods Results Discussion Acknowledgements Disclosure statement Funding References