Editing IPCC:AR6/SROCC/Chapter-3 (section)

===== 3.4.3.2.2 Wildlife =====

Reindeer and caribou ( ''Rangifer tarandus'' ), through their numbers and ecological role as a large-bodied herbivores, are a key driver of Arctic ecology. The seasonal migrations that characterise ''Rangifer'' link the coastal tundra to the continental boreal forests for some herds, while others live year-round on the tundra. Population estimates and trends exist for most herds, and indicate that pan-Arctic migratory tundra ''Rangifer'' have declined from about 5 million in the 1990s to about 2 million in 2017 (Gunn, 2016 <sup>[[#fn:r1682|1682]]</sup> ; Fauchald et al., 2017a <sup>[[#fn:r1683|1683]]</sup> ) ( ''high confidence'' ). Numbers have recently increased for two Alaska herds and the Porcupine caribou herd straddling Yukon and Alaska is at a historic high.

There is ''low confidence'' in understanding the complex drivers of observed ''Rangifer'' changes. Hunting and predation (the latter exacerbated by modification of the landscape for exploration and resource extraction; Dabros et al., 2018 <sup>[[#fn:r1684|1684]]</sup> ) increase in importance as populations decline. Climate strongly influences productivity: extremes in heat, drought, winter icing and snow depth reduce ''Rangifer'' survival (Mallory and Boyce, 2017 <sup>[[#fn:r1685|1685]]</sup> ). Changes in the timing of sea ice formation have direct effects on risks during ''Rangifer'' migration via inter-island movement and connection to the mainland (Poole et al., 2010 <sup>[[#fn:r1686|1686]]</sup> ). Summer warming is changing the composition of tundra plant communities, modifying the relationship between climate, forage and ''Rangifer'' (Albon et al., 2017 <sup>[[#fn:r1687|1687]]</sup> ), which also impacts other Arctic species such as musk ox ( ''Ovibos moschatus)'' (Schmidt et al., 2015 <sup>[[#fn:r1688|1688]]</sup> ). As polar trophic systems are highly connected (Schmidt et al., 2017 <sup>[[#fn:r1689|1689]]</sup> ), changes will propagate through the ecosystem with effects on other herbivores such as geese and voles, as well as predators such as wolves (Hansen et al., 2013 <sup>[[#fn:r1690|1690]]</sup> ; Klaczek et al., 2016 <sup>[[#fn:r1691|1691]]</sup> ).

In northern Fennoscandia, there are approximately 600,000 semi-domesticated reindeer. Lichen rangelands are key to sustaining reindeer carrying capacity, with variable response to climate change: enhanced summer precipitation increases lichen biomass, while an increase in winter precipitation lowers it (Kumpula et al., 2014 <sup>[[#fn:r1692|1692]]</sup> ). Fire disturbance reduces the amount of pasture available for domestic reindeer and increases predation on herding lands (Lavrillier and Gabyshev, 2017 <sup>[[#fn:r1693|1693]]</sup> ). Later ice formation on waterbodies can impact herding activities (Turunen et al., 2016 <sup>[[#fn:r1694|1694]]</sup> ). Ice formation from rain-on-snow events is associated with population changes including cases of catastrophic mass starvation (Bartsch et al., 2010 <sup>[[#fn:r1695|1695]]</sup> ; Forbes et al., 2016 <sup>[[#fn:r1696|1696]]</sup> ), but there is no evidence of trends in rain-on-snow events (Cohen et al., 2015 <sup>[[#fn:r1697|1697]]</sup> ; Dolant et al., 2017 <sup>[[#fn:r1698|1698]]</sup> ).

Management of keystone species requires an understanding of pathogens and disease in the context of climate warming, but evidence of changing patterns across northern ecosystems (spanning terrestrial, aquatic, and marine environments) is hindered by an incomplete picture of pathogen diversity and distribution (Hoberg, 2013 <sup>[[#fn:r1699|1699]]</sup> ; Jenkins et al., 2013 <sup>[[#fn:r1700|1700]]</sup> ; Cook et al., 2017 <sup>[[#fn:r1701|1701]]</sup> ). Among ungulates, it is ''virtually certain'' that the emergence of disease attributed to nematode pathogens has accelerated since 2000 in the Canadian Arctic islands and Fennoscandia (Kutz et al., 2013 <sup>[[#fn:r1702|1702]]</sup> ; Hoberg and Brooks, 2015 <sup>[[#fn:r1703|1703]]</sup> ; Laaksonen et al., 2017 <sup>[[#fn:r1704|1704]]</sup> ; Kafle et al., 2018 <sup>[[#fn:r1705|1705]]</sup> ). Discovery of the pathogenic bacterium ''Erysipelothrix rhusiopathiae'' has been linked to massive and widespread mortality among muskoxen from the Canadian Arctic Archipelago; loss of &gt;50% of the population since 2010 may be attributable to disease interacting with extreme temperature events, although unequivocal links to climate have not been established (Kutz et al., 2015 <sup>[[#fn:r1706|1706]]</sup> ; Forde et al., 2016a <sup>[[#fn:r1707|1707]]</sup> ; Forde et al., 2016b <sup>[[#fn:r1708|1708]]</sup> ). Anthrax is projected to expand northward in response to warming, and resulted in substantial mortality events for reindeer on the Yamal Peninsula of Russia in 2016 with mobilisation of bacteria possibly from a frozen reindeer carcass or melting permafrost (Walsh et al., 2018 <sup>[[#fn:r1709|1709]]</sup> ). In concert with climate forcing, pathogens are ''very likely'' responsible for increasing mortality in Arctic ungulates (muskox, caribou/reindeer) and alteration of transmission patterns in marine food chains, broadly threatening sustainability of subsistence and commercial hunting and fishing and safety of traditional foods for northern cultures at high latitudes (Jenkins et al., 2013 <sup>[[#fn:r1710|1710]]</sup> ; Kutz et al., 2014 <sup>[[#fn:r1711|1711]]</sup> ; Hoberg et al., 2017 <sup>[[#fn:r1712|1712]]</sup> ).

<div id="section-3-4-3-2ecosystems-and-their-services-block-4"></div>

<span id="freshwater"></span>