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Henden, John-André

Arktisk og marin biologi


Temporary researcher


Population and Community Dynamics

Trophic Interactions (consumer-resource dynamics)

Quantitative Methods; statistical and mathematical modeling


*** SUSTAIN -  Sustainable management of renewable resources in a changing environment:
an integrated approach across ecosystems

Overall objective: Develop a framework for sustainable ecosystem based management of harvested ecosystems under a changing environment, promoting ecosystem resilience to climatic changes as well as other stressors and their interactions.
Secondary goals: i) develop foodweb models incorporating demographic structure to improve understanding of ecosystem resilience and develop better demographic harvest strategies, ii) develop improved multispecies harvesting models including environmental stochasticity, iii) increase our knowledge of ecosystem resilience to develop better harvesting strategies in spatially and seasonally structured environments, iv) investigate how climate change in combination with harvesting affects foodweb interactions and ecosystem functions, and v) implement the knowledge in a strategic foresight protocol, in close collaboration with user panels of managers.

*** 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.

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BIO-3013 Nordlige næringsnetts økologi. Tar utgangspunkt i rammeverket for næringsnett for å forstå økosystemers struktur og funksjon. Tar utgangspunkt i veletablert økologisk teori for trofiske interaksjoner (produsent-forbruker relasjoner) mellom planter, plantespisere og kjøttetere.

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