/ UiT Norges arktiske universitet
 

2013-11-15 10.54.08.jpg

Henden, John-André


Forsker
Arktisk og marin biologi


Telefon: 776 44769
Mobil jobb / Mobil privat: /
Epost : john-andre.henden@uit.no
Campus: Tromsø
Kontor/besøksadresse : NATURF 2410 / Naturfagbygget
Funksjon :

Stillingsbeskrivelse:

Temporary researcher

Forskningsinteresser

Population and Community Dynamics

Trophic Interactions (consumer-resource dynamics)

Quantitative Methods; statistical and mathematical modeling

Forskningsprosjekter

 

*** EcoFinn / Ecosystem Finnmark (Project homepage):

General framework: Applying food web theory to unravel management impacts on ecosystems

The functioning of ecosystems is ruled by trophic dynamics of food webs. Research on food web dynamics has two major conceptual frames: Trophic cascades and spatial subsidies (1). Trophic cascades consist of internal, top-down or bottom-up forcing by which predators or herbivores indirectly affect the abundance, diversity and functioning of species through chain-effects in the food web (2). The strength of trophic cascades becomes often accentuated when the forcing factors are removed or released due to anthropogenic actions. Spatial subsidies, on the other hand, represent influences on food webs in terms of external energy and nutrient inputs (3). Such subsidies may be due to a natural spatial coupling between adjacent food webs (i.e. marine and terrestrial) or they may be anthropogenically provided (i.e. changed land use). Spatial subsidies may have major impacts on ecosystem functioning, for instance, by paving the way for emergent trophic cascades.

The strength of trophic cascades in terrestrial ecosystems is variable (2,4). It is, however, evident that mismanagement of large ungulates can cause destructive trophic cascades in terms of loss of biodiversity and ecosystem functions (5). Ecologically, the problem is induced by ungulate overabundance (sensu Côté et al. [5]), a situation typically emerging from either extinction of apex predators, lack of harvesting and altered land use.

 

Specific framework: Trophic cascades and spatial subsidies due to reindeer overabundance 

Semi-domestic reindeer is the most abundant ungulate in North Norway. In Finnmark the present number of »170,000 reindeer conforms to the definition of ungulate overabundance in terms of strongly density-dependent production, increased vulnerability to climate variation and predation (6).

Nationally, mainly two issues connected to the problem of reindeer overabundance in Finnmark has been highlighted and subjected to recent research. One issue concerns the internal problems within the reindeer husbandry connected to low meat production, collapsing herds due to starvation and claimed losses to predators. Our own research has identified low harvesting rates as a major proximate driver of these internal problems (Fauchald et al. 2004, Tveraa et al. 2007). In an ongoing interdisciplinary research initiative to be concluded in 2008/2009 we are exploring the ultimate drivers of the overabundance/underharvesting problem within the realm governmental management regime and socio-economical factors (Hausner, Jernsletten et al. in progress). The other nationally highlighted issue, which is tightly intertwined with the first, is pasture degradation. In particular, much research devoted to the state of reindeer winter pastures and has demonstrated severe depletion of lichen forage (refs). Our own research, focusing on the state of summer pastures, has demonstrated an equivalent depletion of palatable vascular plant forage (Bråthen et al. 2007).

     Internationally, however, the current research emphasis on the widespread problem of ungulate overabundance extends beyond the deer abundance – range quality connection and embraces how ecosystem functioning and biodiversity is impacted (Cote, Danell et al. bok, Pringle et al. 2007. PNAS). This emphasis has recently also colored some statements and propositions about the consequences of reindeer husbandry in Finnmark. While some researchers have labeled the situation “an ecological disaster” (7), others have proposed specific trophic cascade scenarios leading to loss of ecosystem functions and biodiversity (8). However, as yet there are no studies that have devised adequate research designs based on the principles of food web theory (see §2.1.1 above) to quantitatively assess such claims about ecosystem level impacts of reindeer overabundance.

 

*** The arctic fox project (Homepage):

Main objectives:

Perform an integrated management- and researchproject with the intention to:

  • Strengthen the potetial for a viable population of Arctic fox in Finnmark by reducing  the density and distribution of Red fox, in an aim to free potential Arctic fox habitats on the Varanger peninsula – probably the current core area of Arctic fox in Finnmark.
  • Evaluate the effectiveness and impact of Red fox dessimation.
  • Elucidate important aspects of the function of Red fox in the mountain ecosystem, including it's role as a potential competitor, for resources and habitat, for the Arctic fox.
  • Unveil the ecosystem conditions necessary for a viable Arctic fox population in Finnmark, especially with respect to access to food resources and competition with other species.
  • Establish a long-term strategy for the monitoring and conservation of Arctic fox in Finnmark.

 

*** Climate-ecological Observatory for Arctic Tundra (COAT):

COAT aims to be a fully ecosystem-based system for long-term adaptive monitoring based on a food web approach. A food web approach in context of adaptive monitoring confers several advantages. First, the system is strongly embedded in fundamental ecological theory. This allows the formulation of conceptual climate impact prediction models for tractable modules (compartments) of the food web which will act as a guide for defining adequate monitoring targets and state variables. Second, the comprehensive food web approach taken by COAT, with 7 modules and derived prediction models, accommodate the anticipated climate change impact on tundra ecosystems. Anticipated impacts include (1) “Arctic greening” due to encroachment of forest and tall shrubs and its resultant feedback to the ecosystem and climate system, (2) disrupted dynamics and changed abundance levels of arctic key-stone herbivores and the resultant trophic cascades likely to compromise main ecosystem functions and endemic arctic diversity, and (3) emergence of pest species outbreaks, zoonoses and invasive southern species and assessment of the consequent impacts. Third, the adopted food web approach of COAT should be sufficiently comprehensive to also accommodate early detection of unforeseen events that follow the development of new climates and ecosystems. COAT has a special focus on targets that provide important provisioning and cultural ecosystem services locally (e.g. game), as well as supporting services (e.g. for the climate system) and iconic value (e.g. endemic arctic species) globally. Finally, by embracing the novel paradigm of adaptive monitoring, COAT meets the dual requirements of scientific robustness and societal relevance. Consequently COAT includes routines for involving policy makers and  managers in order to provide a scientifically robust basis for decision making and  implementation of actions, and to ensure their feedback into COAT. According to the adaptive  protocol COAT will iteratively adjust prediction models and monitoring designs as new scientific  knowledge and new research and monitoring technologies become available.

Hjemmesider

http://scholar.google.com/citations?user=fDEkdsgAAAAJ&hl=no

Forskerprofil i Cristin

Klikk her

Arbeider i CRIStin

  • Barraquand, Frederic; Høye, Toke T.; Henden, John-André; Yoccoz, Nigel; Gilg, Olivier; Schmidt, Niels Martin; Sittler, Benoit; Ims, Rolf Anker. Demographic responses of a site-faithful and territorial predator to its fluctuating prey: Long-tailed skuas and arctic lemmings. (data) Journal of Animal Ecology 2014; Volum 83 (2). ISSN 0021-8790.s 375 - 387.s doi: 10.1111/1365-2656.12140.
  • Henden, John-André; Stien, Audun; Bårdsen, Bård-Jørgen; Yoccoz, Nigel Gilles; Ims, Rolf Anker. Community-wide mesocarnivore response to partial ungulate migration. (data) Journal of Applied Ecology 2014. ISSN 0021-8901.s doi: 10.1111/1365-2664.12328.
  • Hamel, Sandra; Killengreen, Siw Turid; Henden, John-André; Eide, Nina Elisabeth; Rød-Eriksen, Lars; Ims, Rolf Anker; Yoccoz, Nigel. Towards good practice guidance in using camera-traps in ecology: influence of sampling design on validity of ecological inferences. Methods in Ecology and Evolution 2013; Volum 4 (2). ISSN 2041-210X.s 105 - 113.s doi: 10.1111/j.2041-210x.2012.00262.x.
  • Henden, John-André; Yoccoz, Nigel; Ims, Rolf Anker; Langeland, Knut. How spatial variation in areal extent and configuration of labile vegetation states affect the riparian bird community in Arctic Tundra. (data) PLoS ONE 2013; Volum 8 (5). ISSN 1932-6203.s doi: 10.1371/journal.pone.0063312.
  • Ims, Rolf Anker; Henden, John-André; Thingnes, Anders Voss; Killengreen, Siw Turid. Indirect food web interactions mediated by rodent cycles: Relative roles of lemmings and voles. (data) Biology Letters 2013; Volum 9 (6). ISSN 1744-9561.s doi: 10.1098/rsbl.2013.0802.
  • Soininen, Eeva Marjatta; Zinger, Lucie; Gielly, Ludovic; Bellemain, Eva; Bråthen, Kari Anne; Brochmann, Christian; Epp, Laura; Gusarova, Galina; Hassel, Kristian; Henden, John-André; Killengreen, Siw Turid; Rämä, Teppo; Stenøien, Hans; Yoccoz, Nigel; Ims, Rolf Anker. Shedding new light on the diet of Norwegian lemmings: DNA metabarcoding of stomach content. Polar Biology 2013; Volum 36 (7). ISSN 0722-4060.s 1069 - 1076.s doi: 10.1007/s00300-013-1328-2.
  • Hamel, Sandra; Killengreen, Siw Turid; Henden, John-André; Yoccoz, Nigel; Ims, Rolf Anker. Disentangling the importance of interspecific competition, food availability, and habitat in species occupancy: Recolonization of the endangered Fennoscandian arctic fox. Biological Conservation 2013; Volum 160. ISSN 0006-3207.s 114 - 120.s doi: 10.1016/j.biocon.2013.01.011.
  • Ehrich, Dorothee; Henden, John-André; Ims, Rolf Anker; Doronina, Lilyia O; Killengreen, Siw Turid; Lecomte, Nicolas; Pokrovsky, Ivan; Skogstad, Gunhild; Sokolov, Alexander A.; Sokolov, Vasily A.; Yoccoz, Nigel. The importance of willow thickets for ptarmigan and hares in shrub tundra: the more the better?. Oecologia 2012; Volum 168 (1). ISSN 0029-8549.s 141 - 151.s doi: 10.1007/s00442-011-2059-0.
  • Menyushina, Irina; Ehrich, Dorothee; Henden, John-André; Ims, Rolf Anker; Ovsyanikov, N. The nature of lemming cycles on Wrangel: an island without small mustelids. Oecologia 2012; Volum 170 (2). ISSN 0029-8549.s 363 - 371.s doi: 10.1007/s00442-012-2319-7.
  • Ims, Rolf Anker; Henden, John-André. Collapse of an arctic bird community resulting from ungulate-induced loss of erect shrubs. Biological Conservation 2012; Volum 149 (1). ISSN 0006-3207.s 2 - 5.s doi: 10.1016/j.biocon.2012.02.008.
  • Henden, John-Andre; Ims, Rolf Anker; Yoccoz, Nigel; Sørensen, Raymond; Killengreen, Siw Turid. Population dynamics of tundra voles in relation to configuration of willow thickets in southern arctic tundra. Polar Biology 2011; Volum 34 (4). ISSN 0722-4060.s 533 - 540.s doi: 10.1007/s00300-010-0908-7.
  • Ravolainen, Virve; Bråthen, Kari Anne; Ims, Rolf Anker; Yoccoz, Nigel; Henden, John-André; Killengreen, Siw Turid. Rapid, landscape scale responses in riparian tundra vegetation to exclusion of small and large mammalian herbivores. Basic and Applied Ecology 2011; Volum 12 (8). ISSN 1439-1791.s 643 - 653.s doi: 10.1016/j.baae.2011.09.009.
  • Henden, John-André; Ims, Rolf Anker; Yoccoz, Nigel; Killengreen, Siw Turid. Declining willow ptarmigan populations: The role of habitat structure and community dynamics. Basic and Applied Ecology 2011; Volum 12 (5). ISSN 1439-1791.s 413 - 422.s doi: 10.1016/j.baae.2011.05.006.
  • Bårdsen, Bård-Jørgen; Henden, John-Andre; Fauchald, Per; Tveraa, Torkild; Stien, Audun. Plastic reproductive allocation as a buffer against environmental stochasticity - linking life history and population dynamics to climate. Oikos 2011; Volum 120 (2). ISSN 0030-1299.s 245 - 257.s doi: 10.1111/j.1600-0706.2010.18597.x.
  • Henden, John-Andre; Ims, Rolf Anker; Yoccoz, Nigel Gilles; Hellström, Peter; Angerbjörn, Anders. Strength of asymmetric competition between predators in food webs ruled by fluctuating prey: the case of foxes in tundra. Oikos 2010; Volum 119 (1). ISSN 0030-1299.s 27 - 34.s doi: 10.1111/j.1600-0706.2009.17604.x.
  • Henden, John-Andre; Ims, Rolf Anker; Yoccoz, Nigel Gilles. Nonstationary spatio-temporal small rodent dynamics: evidence from long-term Norwegian fox bounty data. Journal of Animal Ecology 2009; Volum 78 (3). ISSN 0021-8790.s 636 - 645.s doi: 10.1111/j.1365-2656.2008.01510.x.
  • Hanssen, Sveinn Are; Bustnes, Jan Ove; Tveraa, Torkild; Hasselquist, Dennis; Varpe, Øystein; Henden, John-Andre. Individual quality and reproductive effort mirrored in white wing plumage in both sexes of south polar skuas. Behavioral Ecology 2009; Volum 20 (5). ISSN 1045-2249.s 961 - 966.s doi: 10.1093/beheco/arp084.
  • Henden, John-Andre; Yoccoz, Nigel Gilles; Ims, Rolf Anker; Bårdsen, Bård-Jørgen; Angerbjörn, Anders. Phase-dependent effect of conservation efforts in cyclically fluctuating populations of arctic fox (Vulpes lagopus). Biological Conservation 2009; Volum 142 (11). ISSN 0006-3207.s 2586 - 2592.s doi: 10.1016/j.biocon.2009.06.005.
  • Ims, Rolf Anker; Henden, John-Andre; Killengreen, Siw turid. Collapsing population cycles. Trends in Ecology & Evolution 2008; Volum 23. ISSN 0169-5347.s 79 - 86.s doi: 10.1016/j.tree.2007.10.010.
  • Henden, John-Andre; Bardsen, BJ; Yoccoz, Nigel Gilles; Ims, Rolf Anker. Impacts of differential prey dynamics on the potential recovery of endangered arctic fox populations. Journal of Applied Ecology 2008; Volum 45. ISSN 0021-8901.s 1086 - 1093.s doi: 10.1111/j.1365-2664.2008.01515.x.
  • Killengreen, Siw turid; Ims, Rolf Anker; Yoccoz, Nigel Gilles; Bråthen, Kari Anne; Henden, John-Andre; Schott, Tino. Structural characteristics of a low Arctic tundra ecosystem and the retreat of the Arctic fox. Biological Conservation 2007; Volum 135 (4). ISSN 0006-3207.s 459 - 472.s doi: 10.1016/j.biocon.2006.10.039.
  • Bustnes, Jan Ove; Tveraa, Torkild; Varpe, Øystein; Henden, John-Andre; Skaare, Janneche Utne. Reproductive performance and organochlorine pollutants in an Antarctic marine top predator: The south polar skua. Environment International 2007; Volum 33. ISSN 0160-4120.s doi: 10.1016/j.envint.2007.04.010.
  • Bustnes, Jan Ove; Tveraa, Torkild; Henden, John-Andre; Varpe, Øystein; Janssen, Kirstin; Skaare, Janneche Utne. Organochlorines in Antarctic and Arctic Avian Top Predators: A Comparison between the South Polar Skua and Two Species of Northern Hemisphere Gulls. Environmental Science and Technology 2006; Volum 40 (8). ISSN 0013-936X.s 2826 - 2831.s doi: 10.1021/es051920q.
  • Weimerskirch, Henri; Chastel, Olivier; Cherel, Yves; Henden, John-Andre; Tveraa, Torkild. Nest attendance and foraging movements of northern fulmars rearing chicks at Bjørnøya Barents Sea. Polar Biology 2001; Volum 24 (2). ISSN 0722-4060.s 83 - 88.
  • Henden, John-André. Status of Norwegian Arctic Tundra. How will COAT contribute to improve our understanding of current and projected anthropogenic threats?. Tundra Conservation Network 2014-02-10 - 2014-02-13 2014.
  • Henden, John-André; Ims, Rolf Anker; Yoccoz, Nigel; Stien, Audun; Bårdsen, Bård-Jørgen. EcoFinn: Betydningen av reinsdyr abundans for tilstedeværelse og rikhet av predatorsamfunnet på fjellet. Fjellrev i Finnmark, Referansemøte 2013-01-23 - 2013-01-24 2013.
  • Stien, Audun; Bråthen, Kari Anne; Cooper, Elisabeth J.; Ehrich, Dorothee; Hausner, Vera Helene; Henden, John-André; Ims, Rolf Anker; Jensvoll, Ingrid; Killengreen, Siw Turid; Ravolainen, Virve; Yoccoz, Nigel Gilles; Biuw, Martin; Fauchald, Per; Jepsen, Jane Uhd; Tombre, Ingunn; Tveraa, Torkild; Fuglei, Eva; Kohler, Jack; Pedersen, Åshild Ø.; Coulson, Steve; Eidesen, Pernille Bronken; Müller, Eike; Tveito, Ole Einar; Madsen, Jesper. COAT - Climate- ecological Observatory for Arctic Tundra. Biodiversity and ecosystem services in a changing environment : Challenges for science and conservation 2013-03-14 - 2013-03-14 2013.
  • Killengreen, Siw Turid; Hamel, Sandra; Henden, John-André; Ehrich, Dorothee; Yoccoz, Nigel Gilles; Ims, Rolf Anker. An ecosystem approach for monitoring and management of the arctic fox. The 4th International Conference on Arctic Fox 2013-10-10 - 2013-10-13 2013.
  • Ims, Rolf Anker; Killengreen, Siw Turid; Jensvoll, Ingrid; Yoccoz, Nigel Gilles; Henden, John-André; Arriola, Aline; Mørk, Torill; Sarre, Arne Petter; Ørjebu, Alfred; Kristoffersen, Bjørn Hugo; Bye, Åshild. Fjellrev i Finnmark:Årsrapport 2013. 2013.
  • Killengreen, Siw Turid; Ims, Rolf Anker; Henden, John-André; Yoccoz, Nigel Gilles; Ehrich, Dorothee. Prosjekt “Fjellrev i Finnmark” Rapport for 2008-2012. 2013.
  • Henden, John-André. New monitoring of Lemming winter dynamics by use of fecal pellet counts in snowbeds.. Lemming Snow 2013-12-05 - 2013-12-06 2013.
  • Henden, John-André. KOAT - Økosystembasert, adaptiv overvåkning av Norsk Arktisk Tundra. Nasjonalt Rypeforvaltningsseminar 2013-05-29 - 2013-05-30 2013.
  • Hamel, Sandra; Killengreen, Siw Turid; Henden, John-André; Yoccoz, Nigel; Ims, Rolf Anker. Camera-traps, sampling design, and the recolonization of the arctic fox in northern Norway. Norwegian Ecological Society Conference 2013-03-13 - 2013-03-15 2013.
  • Henden, John-André. Effects of Increased Reindeer Abundance in Finnmark: An Ecosystem Approach. APECS-FRAM webinar 2013-03-07 - 2013-03-07 2013.
  • Henden, John-André. COAT - Long-term adaptive monitoring of Ptarmigan in Norwegian Arctic Tundra. Grouse Monitoring/Management Network 2013-03-26 - 2013-03-28 2013.
  • Henden, John-André. COAT - Climate ecological Observatory for Arctic Tundra. Grouse Monitoring/Management Network 2013-03-26 - 2013-03-28 2013.
  • Hamel, Sandra; Killengreen, Siw Turid; Henden, John-André; Yoccoz, Nigel; Ims, Rolf Anker. Evaluering av rekolonisering av den truede fennoskandiske fjellreven ved bruk av fotobokser. Fjellrev i Finnmark prosjekt 2013-01-23 - 2013-01-24 2013.
  • Bråthen, Kari Anne; Ims, Rolf Anker; Yoccoz, Nigel; Ravolainen, Virve; Henden, John-André; Killengreen, Siw Turid; Stien, Audun. Reindeer husbandry’s effects on biodiversity. Reindeer husbandry as a resource for the society Present contribution and future possibilities 2012-12-03 - 2012-12-04 2012.
  • Ravolainen, Virve; Bråthen, Kari Anne; Soininen, Eeva Marjatta; Kollstrøm, Julie; Stien, Audun; Killengreen, Siw Turid; Henden, John-André; Yoccoz, Nigel; Ims, Rolf Anker. Tall shrub tundra vegetation and drivers of change. Arctic Net Annual scientific meeting 2012 2012-12-10 - 2012-12-14 2012.
  • Hamel, Sandra; Killengreen, Siw Turid; Henden, John-André; Yoccoz, Nigel; Ims, Rolf Anker. Disentangling the importance of interspecific competition and food availability in species occupancy: recolonization of the endangered Fennoscandian arctic fox. Fagdag, AMB, UiT 2012-11-21 - 2012.
  • Henden, John-André. Ecosystem effects of increased reindeer abundance in Finnmark. Fagdagen 2012 2012-11-21 - 2012-11-21 2012.
  • Henden, John-André; Yoccoz, Nigel; Ims, Rolf Anker. Understanding long term changes in tundra food webs: the challenge of integrating study designs and models.. Tundra Change Conferance 2012-11-05 - 2012-11-07 2012.
  • Henden, John-André. KOAT - Modul for overvåkning og forvaltning av rype på fastlandet. Rypeseminar 2012-06-04 - 2012-06-06 2012.
  • Henden, John-André. KOAT - bakgrunn og visjoner. Rypeseminar 2012-06-04 - 2012-06-06 2012.
  • Henden, John-André. Klima-økologisk Observatorie for Arktisk Tundra - Modul for overvåkning og forvaltning av rype på fastlandet. FEFO-møte 2012-05-15 - 2012.
  • Ims, Rolf Anker; Killengreen, Siw Turid; Jensvoll, Ingrid; Henden, John-André; Hamel, Sandra; Mørk, Torill; Sarre, Arne Petter; Ørjebu, Alfred; Bye, Åshild; Knutsen, Kjartan. Fjellrev i Finnmark: Årsrapport 2011. 2011.
  • Henden, John-Andre. Hva kan studier av nordlige økosystemer si oss om mulige effekter av klimaforandringen. Forskningsdagene 2010, Forskermaraton 2010-09-24 - 2010.
  • Ims, Rolf Anker; Killengreen, Siw Turid; Jensvoll, Ingrid; Yoccoz, Nigel; Henden, John-André; Mørk, Torill; Sarre, Arne Petter; Ørjebu, Alfred; Bye, Åshild. Fjellrev i Finnmark: Årsrapport 2010. 2010.
  • Lecomte, Nicolas; Ehrich, Dorothee; Yoccoz, Nigel; Ims, Rolf Anker; Fuglei, Eva; Steen, Harald; Killengreen, Siw Turid; Henden, John-Andre. Metamorphosis of the arctic terrestrial food webs: between collapse of native species and explosion of exotic predators?. Oslo Science Conference 2010-06-07 - 2010-06-13 2010.
  • Henden, John-Andre. Phase-dependent effect of conservation efforts on populations of Arctic fox (Vulpes lagopus), a modeling approach. Arctic fox conference 2009-02-16 - 2009-02-19 2009.
  • Ims, Rolf Anker; Killengreen, Siw Turid; Jensvoll, Ingrid; Yoccoz, Nigel Gilles; Henden, John-Andre; Mørk, Torill; Sarre, Arne Petter; Ørjebu, Alfred; Knutsen, Kjartan. Fjellrev i Finnmark: Årsrapport 2009. 2009.
  • Ims, Rolf Anker; Killengreen, Siw Turid; Yoccoz, Nigel Gilles; Henden, John-Andre; Mørk, Torill; Sarre, Arne Petter; Ørjebu, Alfred; Knutsen, Kjartan. Fjellrev i Finnmark: Årsrapport for 2008. 2008.
  • Ims, Rolf Anker; Killengreen, Siw Turid; Henden, John-Andre; Yoccoz, Nigel Gilles. Prosjekt "Fjellrev i Finnmark" Rapport for perioden 2004-2007. 2007.
  • Ims, Rolf Anker; Killengreen, Siw Turid; Henden, John-Andre; Ravolainen, Virve; Mørk, Torill; Langeland, Knut; Knutsen, Kjartan. Fjellrev i Finnmark: Forskning og tiltak 2006. 2006.
  • Ims, Rolf Anker; Killengreen, Siw Turid; Yoccoz, Nigel Gilles; Henden, John-Andre; Ravolainen, Virve; Skog, Elin; Scheie, Jon Ove; Mørk, Torill; Langeland, Knut. Fjellrev i Finnmark: Forskning og tiltak 2005. 2005.
  • Medlem i forskningsgrupper:

    Northern Populations and Ecosystems