Fine-scale structure and cross-taxon congruence of bird and beetle assemblages in an old-growth boreal forest mosaic

Authors

  • Ermias T. Azeria,

    Corresponding author
    1. NSERC–Université Laval Industrial Research Chair in Silviculture and Wildlife, Département de Biologie, Université Laval, Pavillon Alexandre-Vachon, Québec (Québec), G1K 7P4, Canada,
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  • Daniel Fortin,

    1. NSERC–Université Laval Industrial Research Chair in Silviculture and Wildlife, Département de Biologie, Université Laval, Pavillon Alexandre-Vachon, Québec (Québec), G1K 7P4, Canada,
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  • Jérôme Lemaître,

    1. NSERC–Université Laval Industrial Research Chair in Silviculture and Wildlife, Département de Biologie, Université Laval, Pavillon Alexandre-Vachon, Québec (Québec), G1K 7P4, Canada,
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  • Philippe Janssen,

    1. NSERC–Université Laval Industrial Research Chair in Silviculture and Wildlife, Département de Biologie, Université Laval, Pavillon Alexandre-Vachon, Québec (Québec), G1K 7P4, Canada,
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  • Christian Hébert,

    1. Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, 1055 du P.E.P.S., PO Box 3800, Sainte-Foy, Québec, G1V 4C7, Canada,
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  • Marcel Darveau,

    1. NSERC–Université Laval Industrial Research Chair in Silviculture and Wildlife, Département de Biologie, Université Laval, Pavillon Alexandre-Vachon, Québec (Québec), G1K 7P4, Canada,
    2. Ducks Unlimited Canada, Québec (Québec), Canada, and
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  • Steven G. Cumming

    1. University Laval, Department of Forestry, Pavillon Abitibi-Price, Québec (Québec), G1V 0A6, Canada
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*Correspondence: Ermias Azeria, University Laval, Department of Biology, Pavillon Alexandre-Vachon, Québec, Québec, G1K 7P4, Canada.
E-mail: Ermias.azeria.1@ulaval.ca (Ermias.azeria@ekol.slu.se)

ABSTRACT

Aim  Nestedness occurs when species present in depauperate sites are subsets of those found in species-rich sites. The degree of congruence of site nestedness among different assemblages can inform commonalities of mechanisms structuring the assemblages. Well-nested assemblages may still contain idiosyncratic species and sites that notably depart from the typical assemblage pattern. Idiosyncrasy can arise from multiple processes, including interspecific interactions and habitat preferences, which entail different consequences for species co-occurrences. We investigate the influence of fine-scale habitat variation on nestedness and idiosyncrasy patterns of beetle and bird assemblages. We examine community-level and pairwise species co-occurrence patterns, and highlight the potential influence of interspecific interactions for assemblage structure.

Location  Côte-Nord region of Québec, Canada.

Methods  We sampled occurrences of ground-dwelling beetles, flying beetles and birds at sites within old-growth boreal forest. We examined the nestedness and idiosyncrasy of sites and sought relationships to habitat attributes. We analysed non-random species co-occurrence patterns at pairwise and community levels, using null model analysis and five ‘association’ indices.

Results  All three assemblages were significantly nested. There was limited congruence only between birds and flying beetles whose nestedness was related to canopy openness. For ground-dwelling beetles, nestedness was related to high stand heterogeneity and sapling density, whereas site idiosyncrasy was inversely related to structural heterogeneity. For birds, site idiosyncrasy increased with canopy cover, and most idiosyncratic species were closed-canopy specialists. In all assemblages, species idiosyncrasy was positively correlated with the frequency of negative pairwise associations. Species co-occurrence patterns were non-random, and for flying beetles and birds positive species pairwise associations dominated. Community-level co-occurrence summaries may not, however, always reflect these patterns.

Main conclusions  Nestedness patterns of different assemblages may not correlate, even when sampled at common locations, because of different responses to local habitat attributes. We found idiosyncrasy patterns indicating opposing habitat preferences, consistent with antagonistic interactions among species within assemblages. Analysis of such patterns can thus suggest the mechanisms generating assemblage structures, with implications for biodiversity conservation.

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