Mads C. Forchhammer

Greenland Institute of Natural Resources, Nuuk, Sermersooq, Greenland

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Publications (76)460.32 Total impact

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    ABSTRACT: As a response to current climate changes, individual species have changed various biological traits, illustrating an inherent phenotypic plasticity. However, as species are embedded in an ecological network characterised by multiple consumer–resource interactions, ecological mismatches are likely to arise when interacting species do not respond homogeneously. The approach of biological networks analysis calls for the use of structural equation modelling (SEM), a multidimensional analytical setup that has proven particularly useful for analysing multiple interactions across trophic levels. Here we apply SEM to a long-term dataset from a High-Arctic ecosystem to analyse how phenological responses across three trophic levels are coupled to snowmelt patterns and how changes may cascade through consumer–resource interactions. Specifically, the model included the effect of snowmelt on a High-Arctic tri-trophic system of flowers, insects and waders (Charadriiformes), with latent factors representing phenology (timing of life history events) and performance (abundance or reproduction success) for each trophic level. The effects derived from the model demonstrated that the time of snowmelt directly affected plant and arthropod phenology as well as the performance of all included trophic levels. Additionally, timing of snowmelt appeared to indirectly influence wader phenology as well as plant, arthropod and wader performance through effects on adjacent trophic levels and lagged effects. The results from the tri-trophic community presented here emphasise that effects of climate on species in consumer–resource systems may propagate through trophic levels.
    No preview · Article · Dec 2015 · Polar Biology
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    ABSTRACT: Although many studies have examined the phenological mismatches between interacting organisms, few have addressed the potential for mismatches between phenology and seasonal weather conditions. In the Arctic, rapid phenological changes in many taxa are occurring in association with earlier snowmelt. The timing of snowmelt is jointly affected by the size of the late winter snowpack and the temperature during the spring thaw. Increased winter snowpack results in delayed snowmelt, whereas higher air temperatures and faster snowmelt advance the timing of snowmelt. Where inter-annual variation in snowpack is substantial, changes in the timing of snowmelt can be largely uncoupled from changes in air temperature. Using detailed long-term data on the flowering phenology of four arctic plant species from Zackenberg, Greenland, we investigate whether there is a phenological component to the temperature conditions experienced prior to and during flowering. In particular, we assess the role of timing of flowering
    No preview · Article · Aug 2014 · Ecology
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    ABSTRACT: The high arctic is undergoing a faster change in climate than most other regions of the planet, with already observed ecological consequences. Combined with the characteristics of high-arctic ecosystems, such as low species redundancy, high seasonality and weather extremes, shifts in individual species performance and phenology may lead to altered interaction dynamics through trophic mismatch and cascades. An ecosystem approach is therefore desirable in the attempt to understand the multidimensional impacts of climate. Here, we present ecosystem-wide trend analyses of a long-term dataset on terrestrial and limnic biota with focus on the distribution of observed trends and associated variation across the eco-system. We used 114 time series drawn from 11 abiotic variables, 19 terrestrial and 7 limnic biotic species/taxa and compared temporal trends, changes and abrupt shifts in the variation within and across the two biota. A total of 36 % of the time series analysed showed a significant trend during the study period with a higher frequency of trends occurring within performance variables. Overall, the changes tended to be negative, indicating advances in phenology but reduced species performance. General sys-tem variance was also higher in the limnic biota than in the terrestrial biota, both exhibiting increasing variance up through the trophic system. Overall, our results suggest that multiple biotic responses to the climatic changes in this high-arctic ecosystem are not synchronised across trophic levels and may differ qualitatively and quantitatively between terrestrial and limnic biota.
    Full-text · Article · Aug 2014 · Polar Biology
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    ABSTRACT: Animals often alternate between searching for food locally and moving over larger distances depending on the amount of food they find. This ability to switch movement strategy can have large implications on the fate of individuals and populations, and a mechanism that allows animals to find the optimal balance between alternative movement strategies is therefore selectively advantageous. Recent theory suggests that animals are capable of switching movement mode depending on heterogeneities in the landscape, and that different modes may predominate at different temporal scales. Here we develop a conceptual model that enables animals to use either an area-concentrated food search behavior or undirected random movements. The model enables animals to increase their food intake by fine-tuning the relative contribution of the two types of behavior. In contrast to most models of optimal foraging, our model does not assume food to be distributed in large, well-defined patches, and our focus is on how animals should move rather than on which patch is most profitable. We demonstrate how the model, which builds on the animals’ ability to remember the profitability and location of previously visited areas, is capable of producing home ranges and of generating realistic movement patterns for the harbor porpoise, both at fine and intermediate temporal scales.
    Full-text · Article · Sep 2013 · Oikos
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    ABSTRACT: Advancing phenology in response to global warming has been reported across biomes, raising concerns about the temporal uncoupling of trophic interactions. Concurrently, widely reported flower visitor declines have been linked to resource limitations. Phenological responses in the Arctic have been shown to outpace responses from lower latitudes and recent studies suggest that differences between such responses for plants and their flower visitors could be particularly pronounced in the Arctic. The evidence for phenological uncoupling is scant because relevant data sets are lacking or not available at a relevant spatial scale. Here, we present evidence of a climate-associated shortening of the flowering season and a concomitant decline in flower visitor abundance based on a long-term, spatially replicated (1996-2009) data set from high-Arctic Greenland. A unique feature of the data set is the spatial and temporal overlap of independent observations of plant and insect phenology. The shortening of the flowering season arose through spatial variation in phenological responses to warming. The shorter flowering seasons may have played a role in the observed decline in flower visitor abundance. Our results demonstrate that the dramatic climatic changes currently taking place in the Arctic are strongly affecting individual species and ecological communities, with implications for trophic interactions.
    Full-text · Article · Aug 2013 · Nature Climate Change
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    ABSTRACT: Predicting which species will occur together in the future, and where, remains one of the greatest challenges in ecology, and requires a sound understanding of how the abiotic and biotic environments interact with dispersal processes and history across scales. Biotic interactions and their dynamics influence species' relationships to climate, and this also has important implications for predicting future distributions of species. It is already well accepted that biotic interactions shape species' spatial distributions at local spatial extents, but the role of these interactions beyond local extents (e.g. 10 km(2) to global extents) are usually dismissed as unimportant. In this review we consolidate evidence for how biotic interactions shape species distributions beyond local extents and review methods for integrating biotic interactions into species distribution modelling tools. Drawing upon evidence from contemporary and palaeoecological studies of individual species ranges, functional groups, and species richness patterns, we show that biotic interactions have clearly left their mark on species distributions and realised assemblages of species across all spatial extents. We demonstrate this with examples from within and across trophic groups. A range of species distribution modelling tools is available to quantify species environmental relationships and predict species occurrence, such as: (i) integrating pairwise dependencies, (ii) using integrative predictors, and (iii) hybridising species distribution models (SDMs) with dynamic models. These methods have typically only been applied to interacting pairs of species at a single time, require a priori ecological knowledge about which species interact, and due to data paucity must assume that biotic interactions are constant in space and time. To better inform the future development of these models across spatial scales, we call for accelerated collection of spatially and temporally explicit species data. Ideally, these data should be sampled to reflect variation in the underlying environment across large spatial extents, and at fine spatial resolution. Simplified ecosystems where there are relatively few interacting species and sometimes a wealth of existing ecosystem monitoring data (e.g. arctic, alpine or island habitats) offer settings where the development of modelling tools that account for biotic interactions may be less difficult than elsewhere.
    Full-text · Article · Feb 2013 · Biological Reviews
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    ABSTRACT: Alpine and arctic lemming populations appear to be highly sensitive to climate change, and when faced with warmer and shorter winters, their well-known high-amplitude population cycles may collapse. Being keystone species in tundra ecosystems, changed lemming dynamics may convey significant knock-on effects on trophically linked species. Here, we analyse long-term (1988-2010), community-wide monitoring data from two sites in high-arctic Greenland and document how a collapse in collared lemming cyclicity affects the population dynamics of the predator guild. Dramatic changes were observed in two highly specialized lemming predators: snowy owl and stoat. Following the lemming cycle collapse, snowy owl fledgling production declined by 98 per cent, and there was indication of a severe population decline of stoats at one site. The less specialized long-tailed skua and the generalist arctic fox were more loosely coupled to the lemming dynamics. Still, the lemming collapse had noticeable effects on their reproductive performance. Predator responses differed somewhat between sites in all species and could arise from site-specific differences in lemming dynamics, intra-guild interactions or subsidies from other resources. Nevertheless, population extinctions and community restructuring of this arctic endemic predator guild are likely if the lemming dynamics are maintained at the current non-cyclic, low-density state.
    Full-text · Article · Sep 2012 · Proceedings of the Royal Society B: Biological Sciences
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    ABSTRACT: Snow cover plays a major role in the climate, hydrological and ecological systems of the Arctic and other regions through its influence on the surface energy balance (e.g. reflectivity), water balance (e.g. water storage and release), thermal regimes (e.g. insulation), vegetation and trace gas fluxes. Feedbacks to the climate system have global consequences. The livelihoods and well-being of Arctic residents and many services for the wider population depend on snow conditions so changes have important consequences. Already, changing snow conditions, particularly reduced summer soil moisture, winter thaw events and rain-on-snow conditions have negatively affected commercial forestry, reindeer herding, some wild animal populations and vegetation. Reductions in snow cover are also adversely impacting indigenous peoples’ access to traditional foods with negative impacts on human health and well-being. However, there are likely to be some benefits from a changing Arctic snow regime such as more even run-off from melting snow that favours hydropower operations. KeywordsSnow–Arctic–Climate–Albedo–Hydrology–Ecology–Biogeochemical cycling–Geochemical processes–Forestry–Infrastructure–Tourism–Indigenous cultures–Human health
    Full-text · Article · Dec 2011 · AMBIO A Journal of the Human Environment
  • E. Post · P. Boving · S. M. Cahoon · J. Kerby · T. Hoye · M. Forchhammer · P. Sullivan · J. M. Welker
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    ABSTRACT: The study of phenology is a unifying discipline in ecology. Although studied most commonly as a response to environmental variation such as climate change, phenology is a conceptually powerful integrator of ecological dynamics across levels of biological organization. Here, we will present data from two long-term study sites in Greenland, where spring is advancing rapidly due to recent warming. Our results highlight important features of phenology as an integrator of ecological dynamics in the Arctic, from variation at the plant species level in time and space, to species interactions across trophic levels between plants and herbivores, to the importance of phenology in ecosystem carbon exchange. Beyond its role as a response variable and integrator of ecological dynamics, we suggest phenology is an important driver of ecological response to climate change.
    No preview · Article · Dec 2011
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    Full-text · Chapter · Nov 2011
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    ABSTRACT: The use of stable isotopes in diet analysis usually relies on the different photosynthetic pathways of C3 and C4 plants, and the resulting difference in carbon isotope signature. In the Arctic, however, plant species are exclusively C3, and carbon isotopes alone are therefore not suitable for studying arctic herbivore diets. In this study, we examined the potential of both stable carbon and nitrogen isotopes to reconstruct the diet of an arctic herbivore, here the muskox (Ovibos moschatus (Zimmermann, 1780)), in northeast Greenland. The isotope composition of plant communities and functional plant groups was compared with those of muskox faeces and shed wool, as this is a noninvasive approach to obtain dietary information on different temporal scales. Plants with different root mycorrhizal status were found to have different δ15N values, whereas differences in δ13C, as expected, were less distinct. As a result, our examination mainly relied on stable nitrogen isotopes. The interpretation of stable isotopes from faeces was difficult because of the large uncertainty in diet–faeces fractionation, whereas isotope signatures from wool suggested that the muskox summer diet consists of around 80% graminoids and up to 20% willows. In conclusion, the diet composition of an arctic herbivore can indeed be inferred from stable isotopes in arctic areas, despite the lack of C4 plants.
    Full-text · Article · Sep 2011 · Canadian Journal of Zoology
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    ABSTRACT: Dendroclimatological reconstructions may be influenced by intraspecific variation in radial growth caused by plant gender and ecotypic differentiation. We examined the growth response of the High Arctic Salix arctica to interannual variation in snow precipitation in Zackenberg, NE Greenland. Tree ring examinations revealed a consistent response of annual radial growth in this dwarf shrub to variation in the amount of snow precipitation across gender and across three distinct vegetation types. Annual growth, however, differed between vegetation types. These results are discussed with respect to an improved understanding of the factors limiting the growth of S. arctica, which can be used for future reconstructions of climatic conditions, especially in remote High Arctic regions.
    Full-text · Article · Nov 2010 · Arctic Antarctic and Alpine Research
  • Jacob Nabe-Nielsen · Richard M Sibly · Mads C Forchhammer · Valery E Forbes
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    ABSTRACT: Background / Purpose: The shape, distribution and size of habitat patches affects the long-term dynamics of populations. This can only be studied using simulation modelling.Landscape fragmentation causes reduced equilibrium population sizes and slower return from disturbances, particularly in short-dispersing species. Main conclusion: The spatial configurations of landscapes influence the long-term conservation of species, and has the largest effect on short-dispersing species and species that depend on resources in multiple patch types.
    No preview · Conference Paper · Jul 2010
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    Dataset: Appendix S1
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    ABSTRACT: Relationship between return time and return rate. (0.15 MB PDF)
    Preview · Dataset · Jan 2010
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    Dataset: Figure S2
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    ABSTRACT: Monthly population sizes for vole. Population sizes during the first 44 years of a 181-year simulation (example). The first 11 y were used as a burn-in period and only data from the last 170 years were analyzed. Only population sizes from 1 January were used for fitting logistic growth curves. The illustrated populations were perturbed by 95% every 17 y (dashed vertical lines). Different colors indicate landscapes of different complexities. (0.81 MB TIF)
    Preview · Dataset · Jan 2010
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    Dataset: Figure S1
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    ABSTRACT: Land cover in the 10×10-km Bjerringbro landscape. Size class distribution for selected patch types for (A) landscapes A–C and (B) landscape D in Figs. 1 and 3. Patches were divided in classes of size Log10(x)/4 where x is patch size in m2. Areas of circles are proportional to the number of patches in a size class. Buildings, lakes, streams, roads and railways (red circles) were left untouched by all patch randomizations. Numbers in right hand side of the figure give mean patch size in hectares (ha). (1.46 MB TIF)
    Preview · Dataset · Jan 2010
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    ABSTRACT: The effects of landscape modifications on the long-term persistence of wild animal populations is of crucial importance to wildlife managers and conservation biologists, but obtaining experimental evidence using real landscapes is usually impossible. To circumvent this problem we used individual-based models (IBMs) of interacting animals in experimental modifications of a real Danish landscape. The models incorporate as much as possible of the behaviour and ecology of four species with contrasting life-history characteristics: skylark (Alauda arvensis), vole (Microtus agrestis), a ground beetle (Bembidion lampros) and a linyphiid spider (Erigone atra). This allows us to quantify the population implications of experimental modifications of landscape configuration and composition.
    Full-text · Article · Jan 2010 · PLoS ONE
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    Dataset: Figure S3
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    ABSTRACT: Variations in K and ϕ among replicate landscapes. For each of the landscape types B–D we generated 10 landscapes; each of these were used in a single 181-year simulation for the studied species. The grey circles show K and ϕ for each landscape (calculated as in Figs 2–3), and error bars show the 95% confidence intervals corresponding to these. Variations in K and ϕ result from differences among landscapes and stochastic variations among simulations. Results are only shown for vole and skylark, which were relatively strongly influenced by differences among landscapes. (2.58 MB TIF)
    Preview · Dataset · Jan 2010
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    ABSTRACT: The climate effects research program in Zackenberg in high arctic Greenland got a counterpart in Nuuk in low arctic West Greenland in 2007. The programme NuukBasic is described and, for the first time, results will presented from several of the monitoring components (Table 1). In particular, we focus on changes in plant phenology, vegetation greenness, graded effects of UVB radiation and lake ecology. Results are compared and contrasted concurrent changes at the high arctic site Zackenberg in Northeast Greenland.Biological Monitoring elements in NuukBasis
    No preview · Article · Dec 2009
  • M. C. Forchhammer · T. V. Callaghan · E. Post
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    ABSTRACT: It is well established that climate affects organisms in a wide range of different ways, including their distributions and, indeed, their performance (i.e. changes in growth, survival and reproduction). However, establishing whether species respond to changes in climate is not necessarily equal to establishing whether species performance is also affected. This argument also applies when climate effects are considered across trophic levels, such as consumer-resources interactions. For example, a phenological response of a plant may have no effect on its performance but may indeed have significant effects on herbivores. Here we emphasize and exemplify how the choice of a ``biological currency'' of climate change effects may be highly informative in one aspect but apparently useless in another. We do this by using the comprehensive data collected on plant species, large herbivore and their interactions at Zackenberg and Kangerlussuaq in Greenland.
    No preview · Article · Dec 2009

Publication Stats

4k Citations
460.32 Total Impact Points

Institutions

  • 2011-2014
    • Greenland Institute of Natural Resources
      Nuuk, Sermersooq, Greenland
  • 1993-2014
    • Aarhus University
      • • Center for Informatics Research on Complexity in Ecology "CIRCE"
      • • Department of Bioscience
      • • Department of Ecology and Genetics
      Aarhus, Central Jutland, Denmark
  • 2013
    • University of Veterinary Medicine Hannover
      Hanover, Lower Saxony, Germany
  • 2008-2010
    • Roskilde University
      • • Department of Environmental, Social and Spatial Change (ENSPAC)
      • • Centre for Integrated Population Ecology (CIPE)
      Roskilde, Zealand, Denmark
  • 2006-2009
    • Marine Environmental Research Institute
      Blue Hills, Connecticut, United States
  • 2002-2008
    • Pennsylvania State University
      • Department of Biology
      University Park, MD, United States
  • 2001-2008
    • IT University of Copenhagen
      København, Capital Region, Denmark
  • 1999-2002
    • University of Cambridge
      • Department of Zoology
      Cambridge, England, United Kingdom
  • 1997-2002
    • University of Oslo
      • • Centre for Ecological and Evolutionary Synthesis
      • • Department of Biosciences
      Kristiania (historical), Oslo, Norway
  • 2000
    • National Environmental Engineering Research Institute
      Ajni, Maharashtra, India

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